@article{KarLipowskyKnecht2011, author = {Kar, Parimal and Lipowsky, Reinhard and Knecht, Volker}, title = {Importance of polar solvation for cross-reactivity of antibody and its variants with steroids}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {115}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp201538t}, pages = {7661 -- 7669}, year = {2011}, abstract = {Understanding the factors determining the binding of ligands to receptors in detail is essential for rational drug design. Here, the free energies of binding of the steroids progesterone (PRG) and 5 beta-androstane-3,17-dione (SAD) to the Diels-Alderase antibody 1E9, as well as the Leu(H47)Trp/Arg(H100)Trp 1E9 double mutant (1E9dm) and the corresponding single mutants, have been estimated and decomposed using the molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) method. Also the difference in binding free energies between the PRG-1E9dm complex and the complex of PRG with the antiprogesterone antibody DB3 have been evaluated and decomposed. The steroids bind less strongly to 1E9 than to DB3, but the mutations tend to improve the steroid affinity, in quantitative agreement with experimental data. Although the complexes formed by PRG or SAD with 1E9dm and by PRG with DB3 have similar affinity, the binding mechanisms are different. Reduced Waals for SAD-1E9dm versus PRG-1E9dm or for PRG-1E9dm versus PRG-DB3 are energetically compensated by an increased solvation of polar groups, partly contrasting previous conclusions based on structural inspection. Our study illustrates that deducing binding mechanisms from structural models alone can be misleading. Therefore, taking into account solvation effects as in MM-PBSA calculations is essential to elucidate molecular recognition.}, language = {en} } @article{KappelAbelGerhard2011, author = {Kappel, Marcel and Abel, Markus and Gerhard, Reimund}, title = {Characterization and calibration of piezoelectric polymers in situ measurements of body vibrations}, series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, volume = {82}, journal = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, number = {7}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.3607435}, pages = {6}, year = {2011}, abstract = {Piezoelectric polymers are known for their flexibility in applications, mainly due to their bending ability, robustness, and variable sensor geometry. It is an optimal material for minimal-invasive investigations in vibrational systems, e.g., for wood, where acoustical impedance matches particularly well. Many applications may be imagined, e. g., monitoring of buildings, vehicles, machinery, alarm systems, such that our investigations may have a large impact on technology. Longitudinal piezoelectricity converts mechanical vibrations normal to the polymer-film plane into an electrical signal, and the respective piezoelectric coefficient needs to be carefully determined in dependence on the relevant material parameters. In order to evaluate efficiency and durability for piezopolymers, we use polyvinylidene fluoride and measure the piezoelectric coefficient with respect to static pressure, amplitude of the dynamically applied force, and long-term stability. A known problem is the slow relaxation of the material towards equilibrium, if the external pressure changes; here, we demonstrate how to counter this problem with careful calibration. Since our focus is on acoustical measurements, we determine accurately the frequency response curve - for acoustics probably the most important characteristic. Eventually, we show that our piezopolymer transducers can be used as a calibrated acoustical sensors for body vibration measurements on a wooden musical instrument, where it is important to perform minimal-invasive measurements. A comparison with the simultaneously recorded airborne sound yields important insight of the mechanism of sound radiation in comparison with the sound propagating in the material. This is especially important for transient signals, where not only the long-living eigenmodes contribute to the sound radiation. Our analyses support that piezopolymer sensors can be employed as a general tool for the determination of the internal dynamics of vibrating systems.}, language = {en} } @phdthesis{Kalbitz2011, author = {Kalbitz, Ren{\´e}}, title = {Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57276}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Organic thin film transistors (TFT) are an attractive option for low cost electronic applications and may be used for active matrix displays and for RFID applications. To extend the range of applications there is a need to develop and optimise the performance of non-volatile memory devices that are compatible with the solution-processing fabrication procedures used in plastic electronics. A possible candidate is an organic TFT incorporating the ferroelectric co-polymer poly(vinylidenefluoride-trifluoroethylene)(P(VDF-TrFE)) as the gate insulator. Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) as the gate insu-lator. The capacitance spectra of MIS devices, were measured under different biases, showing the effect of charge accumulation and depletion on the Maxwell-Wagner peak. The position and height of this peak clearly indicates the lack of stable depletion behavior and the decrease of mobility when increasing the depletion zone width, i.e. upon moving into the P3HT bulk. The lack of stable depletion was further investigated with capacitance-voltage (C-V) measurements. When the structure was driven into depletion, C-V plots showed a positive flat-band voltage shift, arising from the change in polarization state of the ferroelectric insulator. When biased into accumulation, the polarization was reversed. It is shown that the two polarization states are stable i.e. no depolarization occurs below the coercive field. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flat-band voltage expected during the sweep to accumulation voltages. The measured output characteristics of the studied ferroelectric-field-effect transistors confirmed the results of the C-V plots. Furthermore, the results indicated a trapping of electrons at the positively charged surfaces of the ferroelectrically polarized P(VDF-TrFE) crystallites near the insulator/semiconductor in-terface during the first poling cycles. The study of the MIS structure by means of thermally stimulated current (TSC) revealed further evidence for the stability of the polarization under depletion voltages. It was shown, that the lack of stable depletion behavior is caused by the compensation of the orientational polarization by fixed electrons at the interface and not by the depolarization of the insulator, as proposed in several publications. The above results suggest a performance improvement of non-volatile memory devices by the optimization of the interface.}, language = {en} } @article{KalbitzFruebingGerhardetal.2011, author = {Kalbitz, Rene and Fr{\"u}bing, Peter and Gerhard, Reimund and Taylor, D. M.}, title = {Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures}, series = {Applied physics letters}, volume = {98}, journal = {Applied physics letters}, number = {3}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3543632}, pages = {3}, year = {2011}, abstract = {Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) as the gate insulator. It is shown that the polarization states remain stable after poling with accumulation and depletion voltage. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flatband voltage expected during the sweep to accumulation voltages.}, language = {en} } @article{JordanMcCarthySchleppleetal.2011, author = {Jordan, Grace and McCarthy, Denis N. and Schlepple, N. and Krissler, Jan and Schroeder, H. and Kofod, Guggi}, title = {Actuated micro-optical submount using a dielectric elastomer actuator}, series = {IEEE ASME transactions on mechatronics}, volume = {16}, journal = {IEEE ASME transactions on mechatronics}, number = {1}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1083-4435}, doi = {10.1109/TMECH.2010.2089991}, pages = {98 -- 102}, year = {2011}, abstract = {Analysis of the operating characteristics of a dielectric elastomer actuator (DEA) submount for the high-precision positioning of optical components in one dimension is presented. Precise alignment of a single-mode fiber is demonstrated and variation of the sensitivity of the submount motion by changing the bias voltage is confirmed. A comparison of the performance of the DEA submount with a piezoelectric alignment stage is made, which demonstrates that DEAs could present a very attractive, low-cost alternative to currently used manual technologies in overcoming the hurdle of expensive packaging of single-mode optical components.}, language = {en} } @article{JewittWeaverMutchleretal.2011, author = {Jewitt, David and Weaver, Harold and Mutchler, Max and Larson, Stephen and Agarwal, Jessica}, title = {Hubble space telescope observations of main-belt comet (596) scheila}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {733}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.1088/2041-8205/733/1/L4}, pages = {5}, year = {2011}, abstract = {We present Hubble Space Telescope Observations of (596) Scheila during its recent dust outburst. The nucleus remained point-like with absolute magnitude H(V) = 8.85 +/- 0.02 in our data, equal to the pre-outburst value, with no secondary fragments of diameter >= 100m (for assumed albedos 0.04). We find a coma having a peak scattering cross section similar to 2.2x10(4) km(2), corresponding to a mass in micron-sized particles of similar to 4x10(7) kg. The particles are deflected by solar radiation pressure on projected spatial scales similar to 2x10(4) km, in the sunward direction, and swept from the vicinity of the nucleus on timescales of weeks. The coma fades by similar to 30\% between observations on UT 2010 December 27 and 2011 January 4. The observed mass loss is inconsistent with an origin either by rotational instability of the nucleus or by electrostatic ejection of regolith charged by sunlight. Dust ejection could be caused by the sudden but unexplained exposure of buried ice. However, the data are most simply explained by the impact, at similar to 5 km s(-1), of a previously unknown asteroid similar to 35m in diameter.}, language = {en} } @article{JanottaGogolinBarrettetal.2011, author = {Janotta, Peter and Gogolin, Christian and Barrett, Jonathan and Brunner, Nicolas}, title = {Limits on nonlocal correlations from the structure of the local state space}, series = {New journal of physics : the open-access journal for physics}, volume = {13}, journal = {New journal of physics : the open-access journal for physics}, number = {23}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/13/6/063024}, pages = {24}, year = {2011}, abstract = {The outcomes of measurements on entangled quantum systems can be nonlocally correlated. However, while it is easy to write down toy theories allowing arbitrary nonlocal correlations, those allowed in quantum mechanics are limited. Quantum correlations cannot, for example, violate a principle known as macroscopic locality, which implies that they cannot violate Tsirelson's bound. This paper shows that there is a connection between the strength of nonlocal correlations in a physical theory and the structure of the state spaces of individual systems. This is illustrated by a family of models in which local state spaces are regular polygons, where a natural analogue of a maximally entangled state of two systems exists. We characterize the nonlocal correlations obtainable from such states. The family allows us to study the transition between classical, quantum and super-quantum correlations by varying only the local state space. We show that the strength of nonlocal correlations-in particular whether the maximally entangled state violates Tsirelson's bound or not-depends crucially on a simple geometric property of the local state space, known as strong self-duality. This result is seen to be a special case of a general theorem, which states that a broad class of entangled states in probabilistic theories-including, by extension, all bipartite classical and quantum states-cannot violate macroscopic locality. Finally, our results show that models exist that are locally almost indistinguishable from quantum mechanics, but can nevertheless generate maximally nonlocal correlations.}, language = {en} } @article{IlnytskyiNeherSaphiannikova2011, author = {Ilnytskyi, Jaroslav M. and Neher, Dieter and Saphiannikova, Marina}, title = {Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture molecular dynamics study}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {135}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.3614499}, pages = {12}, year = {2011}, abstract = {Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases.}, language = {en} } @article{HuebenerKruszynskaHartmannetal.2011, author = {H{\"u}bener, Robert and Kruszynska, Caroline and Hartmann, Lorenz and Duer, Wolfgang and Plenio, Martin B. and Eisert, Jens}, title = {Tensor network methods with graph enhancement}, series = {Physical review : B, Condensed matter and materials physics}, volume = {84}, journal = {Physical review : B, Condensed matter and materials physics}, number = {12}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.84.125103}, pages = {24}, year = {2011}, abstract = {We present applications of the renormalization algorithm with graph enhancement (RAGE). This analysis extends the algorithms and applications given for approaches based on matrix product states introduced in [Phys. Rev. A 79, 022317 (2009)] to other tensor-network states such as the tensor tree states (TTS) and projected entangled pair states. We investigate the suitability of the bare TTS to describe ground states, showing that the description of certain graph states and condensed-matter models improves. We investigate graph-enhanced tensor-network states, demonstrating that in some cases (disturbed graph states and for certain quantum circuits) the combination of weighted graph states with TTS can greatly improve the accuracy of the description of ground states and time-evolved states. We comment on delineating the boundary of the classically efficiently simulatable states of quantum many-body systems.}, language = {en} } @phdthesis{Husemann2011, author = {Husemann, Bernd}, title = {The AGN-host galaxy connection : new insights from the extended ionised gas}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-55556}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Active Galactic Nuclei (AGN) are powered by gas accretion onto supermassive Black Holes (BH). The luminosity of AGN can exceed the integrated luminosity of their host galaxies by orders of magnitude, which are then classified as Quasi-Stellar Objects (QSOs). Some mechanisms are needed to trigger the nuclear activity in galaxies and to feed the nuclei with gas. Among several possibilities, such as gravitational interactions, bar instabilities, and smooth gas accretion from the environment, the dominant process has yet to be identified. Feedback from AGN may be important an important ingredient of the evolution of galaxies. However, the details of this coupling between AGN and their host galaxies remain unclear. In this work we aim to investigate the connection between the AGN and their host galaxies by studying the properties of the extendend ionised gas around AGN. Our study is based on observations of ~50 luminous, low-redshift (z<0.3) QSOs using the novel technique of integral field spectroscopy that combines imaging and spectroscopy. After spatially separating the emission of AGN-ionised gas from HII regions, ionised solely by recently formed massive stars, we demonstrate that the specific star formation rates in several disc-dominated AGN hosts are consistent with those of normal star forming galaxies, while others display no detectable star formation activity. Whether the star formation has been actively suppressed in those particular host galaxies by the AGN, or their gas content is intrinsically low, remains an open question. By studying the kinematics of the ionised gas, we find evidence for non-gravitational motions and outflows on kpc scales only in a few objects. The gas kinematics in the majority of objects however indicate a gravitational origin. It suggests that the importance of AGN feedback may have been overrated in theoretical works, at least at low redshifts. The [OIII] line is the strongest optical emission line for AGN-ionised gas, which can be extended over several kpc scales, usually called the Narrow-Line Region (NLR). We perform a systematic investigation of the NLR size and determine a NLR size-luminosity relation that is consistent with the scenario of a constant ionisation parameter throughout the NLR. We show that previous narrow-band imaging with the Hubble Space Telescope underestimated the NLR size by a factor of >2 and that the continuum AGN luminosity is better correlated with the NLR size than the [OIII] luminosity. These affects may account for the different NLR size-luminosity relations reported in previous studies. On the other hand, we do not detect extended NLRs around all QSOs, and demonstrate that the detection of extended NLRs goes along with radio emission. We employ emission line ratios as a diagnostic for the abundance of heavy elements in the gas, i.e. its metallicity, and find that the radial metallicity gradients are always flatter than in inactive disc-dominated galaxies. This can be interpreted as evidence for radial gas flows from the outskirts of these galaxies to the nucleus. Recent or ongoing galaxy interactions are likely responsible for this effect and may turn out to be a common prerequisite for QSO activity. The metallicity of bulge-dominated hosts are systematically lower than their disc-dominated counterparts, which we interpret as evidence for minor mergers, supported by our detailed study of the bulge-dominated host of the luminous QSO HE 1029-1401, or smooth gas accretion from the environment. In this line another new discovery is that HE 2158-0107 at z=0.218 is the most metal poor luminous QSO ever observed. Together with a large (30kpc) extended structure of low metallicity ionised gas, we propose smooth cold gas accretion as the most likely scenario. Theoretical studies suggested that this process is much more important at earlier epochs of the universe, so that HE 2158-0107 might be an ideal laboratory to study this mechanism of galaxy and BH growth at low redshift more detailed in the furture.}, language = {en} } @article{HundertmarkDimovaLengefeldetal.2011, author = {Hundertmark, Michaela and Dimova, Rumiana and Lengefeld, Jan and Seckler, Robert and Hincha, Dirk K.}, title = {The intrinsically disordered late embryogenesis abundant protein LEA18 from Arabidopsis thaliana modulates membrane stability through binding and folding}, series = {Biochimica et biophysica acta : Biomembranes}, volume = {1808}, journal = {Biochimica et biophysica acta : Biomembranes}, number = {1}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0005-2736}, doi = {10.1016/j.bbamem.2010.09.010}, pages = {446 -- 453}, year = {2011}, abstract = {Intrinsically disordered proteins (IDPs) constitute a substantial part of cellular proteomes. late embryogenesis abundant (LEA) proteins are mostly predicted to be IDPs associated with dehydration tolerance in many plant, animal and bacterial species. Their functions, however, are largely unexplored and also their structure and interactions with potential target molecules have only recently been experimentally investigated in a small number of proteins. Here, we report on the structure and interactions with membranes of the Pfam LEA_1 protein LEA18 from the higher plant Arabidopsis thaliana. This functionally uncharacterized positively charged protein specifically aggregated and destabilized negatively charged liposomes. Isothermal titration calorimetry showed binding of the protein to both charged and uncharged membranes. LEA18 alone was largely unstructured in solution. While uncharged membranes had no influence on the secondary structure of LEA18, the protein partially folded into beta-sheet structure in the presence of negatively charged liposomes. These data suggest that LEA18 does not function as a membrane stabilizing protein, as suggested for other LEA proteins. Instead, a possible function of LEA18 could be the composition-dependent modulation of membrane stability, e.g., during signaling or vesicle-mediated transport.}, language = {en} } @article{HubrigOskinovaSchoeller2011, author = {Hubrig, Swetlana and Oskinova, Lida and Schoeller, M.}, title = {First detection of a magnetic field in the fast rotating runaway Oe star zeta Ophiuchi}, series = {Astronomische Nachrichten = Astronomical notes}, volume = {332}, journal = {Astronomische Nachrichten = Astronomical notes}, number = {2}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0004-6337}, doi = {10.1002/asna.201111516}, pages = {147 -- 152}, year = {2011}, abstract = {The star zeta Ophiuchi is one of the brightest massive stars in the northern hemisphere and was intensively studied in various wavelength domains. The currently available observational material suggests that certain observed phenomena are related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Oph with FORS 1 mounted on the 8-m Kueyen telescope of the VLT to investigate if a magnetic field is indeed present in this star. Using all available absorption lines, we detect a mean longitudinal magnetic field < B(z)>(all) = 141 +/- 45 G, confirming the magnetic nature of this star. We review the X-ray properties of zeta Oph with the aim to understand whether the X-ray emission of zeta Oph is dominated by magnetic or by wind instability processes.}, language = {en} } @article{HuangChenKurths2011, author = {Huang, Tingwen and Chen, Guanrong and Kurths, J{\"u}rgen}, title = {Synchronization of chaotic of chaotic systems with time-varying coup{\"o}ing delays}, series = {Discrete and continuous dynamical systems : a journal bridging mathematics and sciences ; Series B, Mathematical modelling, analysis and computations}, volume = {16}, journal = {Discrete and continuous dynamical systems : a journal bridging mathematics and sciences ; Series B, Mathematical modelling, analysis and computations}, number = {4}, publisher = {American Institute of Mathematical Sciences}, address = {Springfield}, issn = {1531-3492}, doi = {10.3934/dcdsb.2011.16.1071}, pages = {1071 -- 1082}, year = {2011}, abstract = {In this paper, we study the complete synchronization of a class of time-varying delayed coupled chaotic systems using feedback control. In terms of Linear Matrix Inequalities, a sufficient condition is obtained through using a Lyapunov-Krasovskii functional and differential equation in equalities. The conditions can be easily verified and implemented. We present two simulation examples to illustrate the effectiveness of the proposed method.}, language = {en} } @article{HoffmannDietzelSchulzetal.2011, author = {Hoffmann, Katrin and Dietzel, Birgit and Schulz, Burkhard and Reck, Guenter and Hoffmann, Angelika and Orgzall, Ingo and Resch-Genger, Ute and Emmerling, Franziska}, title = {Combined structural and fluorescence studies of methyl-substituted 2,5-diphenyl-1,3,4-oxadiazoles - Relation between electronic properties and packing motifs}, series = {Journal of molecular structure}, volume = {988}, journal = {Journal of molecular structure}, number = {1-3}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2010.11.071}, pages = {35 -- 46}, year = {2011}, abstract = {Prerequisite for the rational design of functional organic materials with tailor-made electronic properties is the knowledge of the structure-property relationship for the specific class of molecules under consideration. This encouraged us to systematically study the influence of the molecular structure and substitution pattern of aromatically substituted 1,3,4-oxadiazoles on the electronic properties and packing motifs of these molecules and on the interplay of these factors. For this purpose, seven diphenyl-oxadiazoles equipped with methyl substituents in the ortho- and meta-position(s) were synthesized and characterized. Absorption and fluorescence spectra in solution served here as tools to monitor substitution-induced changes in the electronic properties of the individual molecules whereas X-ray and optical measurements in the solid state provided information on the interplay of electronic and packing effects. In solution, the spectral position of the absorption maximum, the size of Stokes shift, and the fluorescence quantum yield are considerably affected by ortho-substitution in three or four ortho-positions. This results in blue shifted absorption bands, increased Stokes shifts, and reduced fluorescence quantum yields whereas the spectral position and vibrational structure of the emission bands remain more or less unaffected. In the crystalline state, however, the spectral position and shape of the emission bands display a strong dependence on the molecular structure and/or packing motifs that seem to control the amount of dye-dye-interactions. These observations reveal the limited value of commonly reported absorption and fluorescence measurements in solution for a straightforward comparison of spectroscopic results with single X-ray crystallography. This underlines the importance of solid state spectroscopic studies for a better understanding of the interplay of electronic effects and molecular order.}, language = {en} } @phdthesis{Hoffmann2011, author = {Hoffmann, Anne}, title = {Comparative aerosol studies based on multi-wavelength Raman LIDAR at Ny-{\AA}lesund, Spitsbergen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52426}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The Arctic is a particularly sensitive area with respect to climate change due to the high surface albedo of snow and ice and the extreme radiative conditions. Clouds and aerosols as parts of the Arctic atmosphere play an important role in the radiation budget, which is, as yet, poorly quantified and understood. The LIDAR (Light Detection And Ranging) measurements presented in this PhD thesis contribute with continuous altitude resolved aerosol profiles to the understanding of occurrence and characteristics of aerosol layers above Ny-{\AA}lesund, Spitsbergen. The attention was turned to the analysis of periods with high aerosol load. As the Arctic spring troposphere exhibits maximum aerosol optical depths (AODs) each year, March and April of both the years 2007 and 2009 were analyzed. Furthermore, stratospheric aerosol layers of volcanic origin were analyzed for several months, subsequently to the eruptions of the Kasatochi and Sarychev volcanoes in summer 2008 and 2009, respectively. The Koldewey Aerosol Raman LIDAR (KARL) is an instrument for the active remote sensing of atmospheric parameters using pulsed laser radiation. It is operated at the AWIPEV research base and was fundamentally upgraded within the framework of this PhD project. It is now equipped with a new telescope mirror and new detection optics, which facilitate atmospheric profiling from 450m above sea level up to the mid-stratosphere. KARL provides highly resolved profiles of the scattering characteristics of aerosol and cloud particles (backscattering, extinction and depolarization) as well as water vapor profiles within the lower troposphere. Combination of KARL data with data from other instruments on site, namely radiosondes, sun photometer, Micro Pulse LIDAR, and tethersonde system, resulted in a comprehensive data set of scattering phenomena in the Arctic atmosphere. The two spring periods March and April 2007 and 2009 were at first analyzed based on meteorological parameters, like local temperature and relative humidity profiles as well as large scale pressure patterns and air mass origin regions. Here, it was not possible to find a clear correlation between enhanced AOD and air mass origin. However, in a comparison of two cloud free periods in March 2007 and April 2009, large AOD values in 2009 coincided with air mass transport through the central Arctic. This suggests the occurrence of aerosol transformation processes during the aerosol transport to Ny-{\AA}lesund. Measurements on 4 April 2009 revealed maximum AOD values of up to 0.12 and aerosol size distributions changing with altitude. This and other performed case studies suggest the differentiation between three aerosol event types and their origin: Vertically limited aerosol layers in dry air, highly variable hygroscopic boundary layer aerosols and enhanced aerosol load across wide portions of the troposphere. For the spring period 2007, the available KARL data were statistically analyzed using a characterization scheme, which is based on optical characteristics of the scattering particles. The scheme was validated using several case studies. Volcanic eruptions in the northern hemisphere in August 2008 and June 2009 arose the opportunity to analyze volcanic aerosol layers within the stratosphere. The rate of stratospheric AOD change was similar within both years with maximum values above 0.1 about three to five weeks after the respective eruption. In both years, the stratospheric AOD persisted at higher rates than usual until the measurements were stopped in late September due to technical reasons. In 2008, up to three aerosol layers were detected, the layer structure in 2009 was characterized by up to six distinct and thin layers which smeared out to one broad layer after about two months. The lowermost aerosol layer was continuously detected at the tropopause altitude. Three case studies were performed, all revealed rather large indices of refraction of m = (1.53-1.55) - 0.02i, suggesting the presence of an absorbing carbonaceous component. The particle radius, derived with inversion calculations, was also similar in both years with values ranging from 0.16 to 0.19 μm. However, in 2009, a second mode in the size distribution was detected at about 0.5 μm. The long term measurements with the Koldewey Aerosol Raman LIDAR in Ny-{\AA}lesund provide the opportunity to study Arctic aerosols in the troposphere and the stratosphere not only in case studies but on longer time scales. In this PhD thesis, both, tropospheric aerosols in the Arctic spring and stratospheric aerosols following volcanic eruptions have been described qualitatively and quantitatively. Case studies and comparative studies with data of other instruments on site allowed for the analysis of microphysical aerosol characteristics and their temporal evolution.}, language = {en} } @article{HobanCampbellLoukopoulosetal.2011, author = {Hoban, Matty J. and Campbell, Earl T. and Loukopoulos, Klearchos and Browne, Dan E.}, title = {Non-adaptive measurement-based quantum computation and multi-party Bell inequalities}, series = {New journal of physics : the open-access journal for physics}, volume = {13}, journal = {New journal of physics : the open-access journal for physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/13/2/023014}, pages = {18}, year = {2011}, abstract = {Quantum correlations exhibit behaviour that cannot be resolved with a local hidden variable picture of the world. In quantum information, they are also used as resources for information processing tasks, such as measurement-based quantum computation (MQC). In MQC, universal quantum computation can be achieved via adaptive measurements on a suitable entangled resource state. In this paper, we look at a version of MQC in which we remove the adaptivity of measurements and aim to understand what computational abilities remain in the resource. We show that there are explicit connections between this model of computation and the question of non-classicality in quantum correlations. We demonstrate this by focusing on deterministic computation of Boolean functions, in which natural generalizations of the Greenberger-Horne-Zeilinger paradox emerge; we then explore probabilistic computation via, which multipartite Bell inequalities can be defined. We use this correspondence to define families of multi-party Bell inequalities, which we show to have a number of interesting contrasting properties.}, language = {en} } @article{GruberChakravartyBaehtzetal.2011, author = {Gruber, W. and Chakravarty, S. and Baehtz, C. and Leitenberger, Wolfram and Bruns, M. and Kobler, A. and K{\"u}bel, Christian and Schmidt, H.}, title = {Strain relaxation and vacancy creation in thin platinum films}, series = {Physical review letters}, volume = {107}, journal = {Physical review letters}, number = {26}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.107.265501}, pages = {5}, year = {2011}, abstract = {Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 degrees C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.}, language = {en} } @article{GreenKliemWallace2011, author = {Green, Luci M. and Kliem, Bernhard and Wallace, A. J.}, title = {Photospheric flux cancellation and associated flux rope formation and eruption}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {526}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {2}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201015146}, pages = {10}, year = {2011}, abstract = {Aims. We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The aim is to investigate the quantity of flux cancellation that is involved in flux rope formation in the time period leading up to the eruption. Methods. The active region is studied using its extreme ultraviolet and soft X-ray emissions as it evolves from a sheared arcade to flux rope configuration. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. Results. About one third of the active region flux cancels at the internal polarity inversion line in the 2.5 days leading up to the eruption. In this period, the coronal structure evolves from a weakly to a highly sheared arcade and then to a sigmoid that crosses the inversion line in the inverse direction. These properties suggest that a flux rope has formed prior to the eruption. The amount of cancellation implies that up to 60\% of the active region flux could be in the body of the flux rope. We point out that only part of the cancellation contributes to the flux in the rope if the arcade is only weakly sheared, as in the first part of the evolution. This reduces the estimated flux in the rope to similar to 30\% or less of the active region flux. We suggest that the remaining discrepancy between our estimate and the limiting value of similar to 10\% of the active region flux, obtained previously by the flux rope insertion method, results from the incomplete coherence of the flux rope, due to nonuniform cancellation along the polarity inversion line. A hot linear feature is observed in the active region which rises as part of the eruption and then likely traces out the field lines close to the axis of the flux rope. The flux cancellation and changing magnetic connections at one end of this feature suggest that the flux rope reaches coherence by reconnection immediately before and early in the impulsive phase of the associated flare. The sigmoid is destroyed in the eruption but reforms quickly, with the amount of cancellation involved being much smaller than in the course of its original formation.}, language = {en} } @article{GrassdosSantosPelster2011, author = {Grass, T. D. and dos Santos, Francisca E. A. and Pelster, Axel}, title = {Real-time Ginzburg-Landau theory for bosons in optical lattices}, series = {Laser physics}, volume = {21}, journal = {Laser physics}, number = {8}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1054-660X}, doi = {10.1134/S1054660X11150096}, pages = {1459 -- 1463}, year = {2011}, abstract = {Within the Schwinger-Keldysh formalism we derive a Ginzburg-Landau theory for the Bose-Hubbard model which describes the real-time dynamics of the complex order parameter field. Analyzing the excitations in the vicinity of the quantum phase transitions it turns out that particle/hole dispersions in the Mott phase map continuously onto corresponding amplitude/phase excitations in the superfluid phase. Furthermore, in the superfluid phase we find a sound mode, which is in accordance with recent Bragg spectroscopy measurements in the Bogoliubov regime, as well as an additional gapped mode, which seems to have been detected via lattice modulation.}, language = {en} } @article{GogolinMuellerEisert2011, author = {Gogolin, Christian and M{\"u}ller, Markus P. and Eisert, Jens}, title = {Absence of thermalization in nonintegrable systems}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.040401}, pages = {4}, year = {2011}, abstract = {We establish a link between unitary relaxation dynamics after a quench in closed many-body systems and the entanglement in the energy eigenbasis. We find that even if reduced states equilibrate, they can have memory on the initial conditions even in certain models that are far from integrable. We show that in such situations the equilibrium states are still described by a maximum entropy or generalized Gibbs ensemble, regardless of whether a model is integrable or not, thereby contributing to a recent debate. In addition, we discuss individual aspects of the thermalization process, comment on the role of Anderson localization, and collect and compare different notions of integrability.}, language = {en} } @article{GiewekemeyerKruegerKalbfleischetal.2011, author = {Giewekemeyer, K. and Krueger, S. P. and Kalbfleisch, S. and Bartels, Meike and Beta, Carsten and Salditt, T.}, title = {X-ray propagation microscopy of biological cells using waveguides as a quasipoint source}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {83}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.83.023804}, pages = {7}, year = {2011}, abstract = {We have used x-ray waveguides as highly confining optical elements for nanoscale imaging of unstained biological cells using the simple geometry of in-line holography. The well-known twin-image problem is effectively circumvented by a simple and fast iterative reconstruction. The algorithm which combines elements of the classical Gerchberg-Saxton scheme and the hybrid-input-output algorithm is optimized for phase-contrast samples, well-justified for imaging of cells at multi-keV photon energies. The experimental scheme allows for a quantitative phase reconstruction from a single holographic image without detailed knowledge of the complex illumination function incident on the sample, as demonstrated for freeze-dried cells of the eukaryotic amoeba Dictyostelium discoideum. The accessible resolution range is explored by simulations, indicating that resolutions on the order of 20 nm are within reach applying illumination times on the order of minutes at present synchrotron sources.}, language = {en} } @article{GerhardtGroegerMacCarthy2011, author = {Gerhardt, Matthias and Groeger, Gillian and MacCarthy, Niall}, title = {Monopolar vs. bipolar subretinal stimulation-An in vitro study}, series = {Journal of neuroscience methods}, volume = {199}, journal = {Journal of neuroscience methods}, number = {1}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0165-0270}, doi = {10.1016/j.jneumeth.2011.04.017}, pages = {26 -- 34}, year = {2011}, abstract = {This study uses an in vitro rd10 mouse model to quantify and compare the ability of the monopolar and the (concentric) bipolar electrode configurations for subretinal stimulation. To allow for results which can be directly compared an identical region of the retina was stimulated due to the circumstance that the bipolar electrode configuration allows also for monopolar stimulation, if the concentric counter-electrode is set potential-free (floating). A ganglion cell, located centrally over the bipolar electrode configuration was selected to extracellularly record action potentials during stimulation. To analyse the recorded action potentials, we introduce a new method which combines the advantages of (a) singular value decomposition (SVD) for weighting similar modulation patterns with which the recorded action potentials are characterized and (b) multi curve fitting to identify a common threshold level, required to finally assemble a strength-duration relationship (SDR). By directly comparing the obtained SDR curves, we found that the efficiency of stimulation with the monopolar electrode configuration is significantly higher than with the bipolar electrode configuration. All obtained SDR curves were fitted using the Lapicque model to estimate the chronaxie times and the rheobase currents. Liquid inclusions, eventually separating the retina from the electrodes are discussed to be a major cause for low ganglion cell responses during stimulation with the bipolar electrode configuration.}, language = {en} } @misc{Gerhard2011, author = {Gerhard, Reimund}, title = {Honoring Professor Gerhard M. Sessler on his 80th Birthday (15th of February 2011)}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {18}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {1}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2011.5704485}, pages = {1 -- 2}, year = {2011}, language = {en} } @article{GagneFehonSavoyetal.2011, author = {Gagne, Marc and Fehon, Garrett and Savoy, Michael R. and Cohen, David H. and Townsley, Leisa K. and Broos, Patrick S. and Povich, Matthew S. and Corcoran, Michael F. and Walborn, Nolan R. and Evans, Nancy Remage and Moffat, Anthony F. J. and Naze, Yael and Oskinova, Lida}, title = {Carina ob stars: x-ray signatures of wind shocks and magnetic FIELDS}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series}, volume = {194}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0067-0049}, doi = {10.1088/0067-0049/194/1/5}, pages = {26}, year = {2011}, abstract = {The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L-X/L-bol relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with a period of > 30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403, and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high L-X cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star.}, language = {en} } @article{FuhrmannSeehaferValorietal.2011, author = {Fuhrmann, Marcel and Seehafer, Norbert and Valori, Gherardo and Wiegelmann, Thomas}, title = {A comparison of preprocessing methods for solar force-free magnetic field extrapolation}, issn = {0004-6361}, year = {2011}, language = {en} } @article{FuhrmannSeehaferValorietal.2011, author = {Fuhrmann, Marcel and Seehafer, Norbert and Valori, Gherardo and Wiegelmann, T.}, title = {A comparison of preprocessing methods for solar force-free magnetic field extrapolation}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {526}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201015453}, pages = {12}, year = {2011}, abstract = {Context. Extrapolations of solar photospheric vector magnetograms into three-dimensional magnetic fields in the chromosphere and corona are usually done under the assumption that the fields are force-free. This condition is violated in the photosphere itself and a thin layer in the lower atmosphere above. The field calculations can be improved by preprocessing the photospheric magnetograms. The intention here is to remove a non-force-free component from the data. Aims. We compare two preprocessing methods presently in use, namely the methods of Wiegelmann et al. (2006, Sol. Phys., 233, 215) and Fuhrmann et al. (2007, A\&A, 476, 349). Methods. The two preprocessing methods were applied to a vector magnetogram of the recently observed active region NOAA AR 10 953. We examine the changes in the magnetogram effected by the two preprocessing algorithms. Furthermore, the original magnetogram and the two preprocessed magnetograms were each used as input data for nonlinear force-free field extrapolations by means of two different methods, and we analyze the resulting fields. Results. Both preprocessing methods managed to significantly decrease the magnetic forces and magnetic torques that act through the magnetogram area and that can cause incompatibilities with the assumption of force-freeness in the solution domain. The force and torque decrease is stronger for the Fuhrmann et al. method. Both methods also reduced the amount of small-scale irregularities in the observed photospheric field, which can sharply worsen the quality of the solutions. For the chosen parameter set, the Wiegelmann et al. method led to greater changes in strong-field areas, leaving weak-field areas mostly unchanged, and thus providing an approximation of the magnetic field vector in the chromosphere, while the Fuhrmann et al. method weakly changed the whole magnetogram, thereby better preserving patterns present in the original magnetogram. Both preprocessing methods raised the magnetic energy content of the extrapolated fields to values above the minimum energy, corresponding to the potential field. Also, the fields calculated from the preprocessed magnetograms fulfill the solenoidal condition better than those calculated without preprocessing.}, language = {en} } @article{FlossKlamrothSaalfrank2011, author = {Floss, Gereon and Klamroth, Tillmann and Saalfrank, Peter}, title = {Laser-controlled switching of molecular arrays in an dissipative environment}, series = {Physical review : B, Condensed matter and materials physics}, volume = {83}, journal = {Physical review : B, Condensed matter and materials physics}, number = {10}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.83.104301}, pages = {9}, year = {2011}, abstract = {The optical switching of molecular ensembles in a dissipative environment is a subject of various fields of chemical physics and physical chemistry. Here we try to switch arrays of molecules from a stable collective ground state to a state in which all molecules have been transferred to another stable higher-energy configuration. In our model switching proceeds through electronically excited intermediates which are coherently coupled to each other through dipolar interactions, and which decay incoherently within a finite lifetime by coupling to a dissipative environment. The model is quite general, but parameters are chosen to roughly resemble the all-trans -> all-cis isomerization of an array of azobenzene molecules on a surface. Using analytical and optimal control pulses and the concept of "laser distillation," we demonstrate that for various aggregates (dimers up to hexamers), controlled and complete switching should be possible.}, language = {en} } @phdthesis{FloresSuarez2011, author = {Flores Su{\´a}rez, Rosaura}, title = {Three-dimensional polarization probing in polymer ferroelectrics, polymer-dispersed liquid crystals, and polymer ferroelectrets}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-60173}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {A key non-destructive technique for analysis, optimization and developing of new functional materials such as sensors, transducers, electro-optical and memory devices is presented. The Thermal-Pulse Tomography (TPT) provides high-resolution three-dimensional images of electric field and polarization distribution in a material. This thermal technique use a pulsed heating by means of focused laser light which is absorbed by opaque electrodes. The diffusion of the heat causes changes in the sample geometry, generating a short-circuit current or change in surface potential, which contains information about the spatial distribution of electric dipoles or space charges. Afterwards, a reconstruction of the internal electric field and polarization distribution in the material is possible via Scale Transformation or Regularization methods. In this way, the TPT was used for the first time to image the inhomogeneous ferroelectric switching in polymer ferroelectric films (candidates to memory devices). The results shows the typical pinning of electric dipoles in the ferroelectric polymer under study and support the previous hypotheses of a ferroelectric reversal at a grain level via nucleation and growth. In order to obtain more information about the impact of the lateral and depth resolution of the thermal techniques, the TPT and its counterpart called Focused Laser Intensity Modulation Method (FLIMM) were implemented in ferroelectric films with grid-shaped electrodes. The results from both techniques, after the data analysis with different regularization and scale methods, are in total agreement. It was also revealed a possible overestimated lateral resolution of the FLIMM and highlights the TPT method as the most efficient and reliable thermal technique. After an improvement in the optics, the Thermal-Pulse Tomography method was implemented in polymer-dispersed liquid crystals (PDLCs) films, which are used in electro-optical applications. The results indicated a possible electrostatic interaction between the COH group in the liquid crystals and the fluorinate atoms of the used ferroelectric matrix. The geometrical parameters of the LC droplets were partially reproduced as they were compared with Scanning Electron Microscopy (SEM) images. For further applications, it is suggested the use of a non-strong-ferroelectric polymer matrix. In an effort to develop new polymerferroelectrets and for optimizing their properties, new multilayer systems were inspected. The results of the TPT method showed the non-uniformity of the internal electric-field distribution in the shaped-macrodipoles and thus suggested the instability of the sample. Further investigation on multilayers ferroelectrets was suggested and the implementation of less conductive polymers layers too.}, language = {en} } @article{FilimonKopfSchmidtetal.2011, author = {Filimon, Marlena and Kopf, Ilona and Schmidt, Dietrich A. and Bruendermann, Erik and R{\"u}he, J{\"u}rgen and Santer, Svetlana and Havenith, Martina}, title = {Local chemical composition of nanophase-separated polymer brushes}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {24}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp02756a}, pages = {11620 -- 11626}, year = {2011}, abstract = {Using scattering scanning nearfield infrared microscopy (s-SNIM), we have imaged the nanoscale phase separation of mixed polystyrene-poly(methyl methacrylate) (PS-PMMA) brushes and investigated changes in the top layer as a function of solvent exposure. We deduce that the top-layer of the mixed brushes is composed primarily of PMMA after exposure to acetone, while after exposure to toluene this changes to PS. Access to simultaneously measured topographic and chemical information allows direct correlation of the chemical morphology of the sample with topographic information. Our results demonstrate the potential of s-SNIM for chemical mapping based on distinct infrared absorption properties of polymers with a high spatial resolution of 80 nm x 80 nm.}, language = {en} } @article{FiehlerBannertBischoffetal.2011, author = {Fiehler, Katja and Bannert, Michael M. and Bischoff, Matthias and Blecker, Carlo and Stark, Rudolf and Vaitl, Dieter and Franz, Volker H. and Roesler, Frank}, title = {Working memory maintenance of grasp-target information in the human posterior parietal cortex}, series = {NeuroImage : a journal of brain function}, volume = {54}, journal = {NeuroImage : a journal of brain function}, number = {3}, publisher = {Elsevier}, address = {San Diego}, issn = {1053-8119}, doi = {10.1016/j.neuroimage.2010.09.080}, pages = {2401 -- 2411}, year = {2011}, abstract = {Event-related functional magnetic resonance imaging was applied to identify cortical areas involved in maintaining target information in working memory used for an upcoming grasping action. Participants had to grasp with their thumb and index finger of the dominant right hand three-dimensional objects of different size and orientation. Reaching-to-grasp movements were performed without visual feedback either immediately after object presentation or after a variable delay of 2-12 s. The right inferior parietal cortex demonstrated sustained neural activity throughout the delay, which overlapped with activity observed during encoding of the grasp target. Immediate and delayed grasping activated similar motor-related brain areas and showed no differential activity. The results suggest that the right inferior parietal cortex plays an important functional role in working memory maintenance of grasp-related information. Moreover, our findings confirm the assumption that brain areas engaged in maintaining information are also involved in encoding the same information, and thus extend previous findings on working memory function of the posterior parietal cortex in saccadic behavior to reach-to-grasp movements.}, language = {en} } @article{FeudelBergemannTuckermanetal.2011, author = {Feudel, Fred and Bergemann, Kay and Tuckerman, Laurette S. and Egbers, C. and Futterer, B. and Gellert, Marcus and Hollerbach, Rainer}, title = {Convection patterns in a spherical fluid shell}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {83}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.83.046304}, pages = {8}, year = {2011}, abstract = {Symmetry-breaking bifurcations have been studied for convection in a nonrotating spherical shell whose outer radius is twice the inner radius, under the influence of an externally applied central force field with a radial dependence proportional to 1/r(5). This work is motivated by the GeoFlow experiment, which is performed under microgravity condition at the International Space Station where this particular central force can be generated. In order to predict the observable patterns, simulations together with path-following techniques and stability computations have been applied. Branches of axisymmetric, octahedral, and seven-cell solutions have been traced. The bifurcations producing them have been identified and their stability ranges determined. At higher Rayleigh numbers, time-periodic states with a complex spatiotemporal symmetry are found, which we call breathing patterns.}, language = {en} } @misc{FedericiPohlRuppeletal.2011, author = {Federici, S. and Pohl, Martin and Ruppel, J. and Telezhinsky, Igor O. and Hofmann, Werner and Martinez, M. and Knapp, J.}, title = {Design concepts for the Cherenkov Telescope Array CTA}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, volume = {32}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1325}, issn = {1866-8372}, doi = {10.25932/publishup-43014}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-430149}, pages = {124}, year = {2011}, abstract = {Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.}, language = {en} } @article{Fechner2011, author = {Fechner, Cora}, title = {Reconstructing the intergalactic UV background with QSO absorption lines}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {532}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {2}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201117080}, pages = {15}, year = {2011}, abstract = {We present a new approach to observationally constraining the spectral energy distribution of the intergalactic UV background by studying metal absorption systems. We study single-component metal line systems that exhibit various well-measured species. Among the observed transitions, at least two ratios of ionization stages from the same element are required, e. g. C III/C IV and Si III/Si IV. For each system photoionization models are constructed by varying the spectrum of the ionizing radiation. The spectral energy distribution can then be constrained by comparing the models with the observed column density ratios. Extensive tests with artificial absorbers show that the spectrum of the ionizing radiation cannot be reconstructed unambiguously, but it is possible to constrain the main characteristics of the spectrum. Furthermore, the resulting physical parameters of the absorber, such as ionization parameter, metallicity, and relative abundances, may depend strongly on the adopted ionizing spectrum. Even in case of well-fitting models, the uncertainties can be as high as similar to 0.5 dex for the ionization parameter and up to similar to 1.5 dex for the metallicity. Therefore, it is essential to know the hardness of the UV background when estimating the metallicity of the intergalactic medium. Applying the procedure to a small sample of 3 observed single-component metal line systems yields a soft ionizing radiation at z > 2 and a slightly harder spectrum at z < 2. The resulting energy distributions exhibit strong He II Lya re-emission features, suggesting that reprocessing by intergalactic He II is important. Comparing the observed systems to UV background spectra from the literature indicates that a recent model that includes sawtooth modulation due to reprocessing by intergalactic He II with delayed helium reionization fits the investigated systems very well.}, language = {en} } @article{FangWangWirgesetal.2011, author = {Fang, Peng and Wang, Feipeng and Wirges, Werner and Gerhard, Reimund and Basso, Heitor Cury}, title = {Three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films}, series = {Applied physics : A, Materials science \& processing}, volume = {103}, journal = {Applied physics : A, Materials science \& processing}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-010-6008-2}, pages = {455 -- 461}, year = {2011}, abstract = {A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d (33) coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140A degrees C keep their piezoelectric activity up to at least 120A degrees C and retain 70\% of their initial d (33) even at 130A degrees C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz.}, language = {en} } @article{EvansDeGioiaEastwoodGagneetal.2011, author = {Evans, Nancy Remage and DeGioia-Eastwood, Kathleen and Gagne, Marc and Townsley, Leisa and Broos, Patrick S. and Wolk, Scott J. and Naze, Yael and Corcoran, Michael and Oskinova, Lida and Moffat, Anthony F. J. and Wang, Junfeng and Walborn, Nolan R.}, title = {The search for low-mass companions of b stars in the Carina Nebula cluster trumpler 16}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series}, volume = {194}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0067-0049}, doi = {10.1088/0067-0049/194/1/13}, pages = {9}, year = {2011}, abstract = {We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of eta Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M-circle dot are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39\% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32\% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M-circle dot) primaries, such as would be found by random pairing from the initial mass function.}, language = {en} } @article{EichlerPohl2011, author = {Eichler, David and Pohl, Martin}, title = {Can ultrahigh-energy cosmic rays come from Gamma-ray bursts? - cosmic rays below the ankle and galactic gamma-ray bursts}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {738}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.1088/2041-8205/738/2/L21}, pages = {4}, year = {2011}, abstract = {The maximum cosmic-ray energy achievable by acceleration by a relativistic blast wave is derived. It is shown that forward shocks from long gamma-ray bursts (GRBs) in the interstellar medium accelerate protons to large enough energies, and have a sufficient energy budget, to produce the Galactic cosmic-ray component just below the ankle at 4 x 10(18) eV, as per an earlier suggestion. It is further argued that, were extragalactic long GRBs responsible for the component above the ankle as well, the occasional Galactic GRB within the solar circle would contribute more than the observational limits on the outward flux from the solar circle, unless an avoidance scenario, such as intermittency and/or beaming, allows the present-day local flux to be less than 10(-3) of the average. Difficulties with these avoidance scenarios are noted.}, language = {en} } @article{DoeringKolloscheRabeetal.2011, author = {D{\"o}ring, Sebastian and Kollosche, Matthias and Rabe, Torsten and Stumpe, Joachim and Kofod, Guggi}, title = {Electrically tunable polymer DFB laser}, series = {Advanced materials}, volume = {23}, journal = {Advanced materials}, number = {37}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201102465}, pages = {4265 -- 4269}, year = {2011}, language = {en} } @phdthesis{Doering2011, author = {D{\"o}ring, Sebastian}, title = {Oberfl{\"a}chengitter in azobenzenhaltigen Schichten f{\"u}r organische DFB-Laser}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59211}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Ein neuentwickeltes azobenzenhaltiges Material, das auf einem supramolekularen Konzept basiert, wird bez{\"u}glich seiner Strukturbildung w{\"a}hrend einer holografischen Belichtung bei 488 nm untersucht. Im Mittelpunkt stehen dabei eindimensionale, sinusf{\"o}rmige Reliefs mit Periodizit{\"a}ten kleiner 500 nm. Es wird gezeigt, wie der Grad der Vernetzung der photosensitiven Schicht die Strukturbildung in diesem Gr{\"o}ßenbereich beeinflusst. Zur Maximierung der Strukturtiefe werden gezielt Prozessparameter der Belichtung sowie Materialparameter variiert. Unter Standardbedingungen und moderaten Belichtungsintensit{\"a}ten von ca. 200 mW/cm² bilden sich innerhalb weniger Minuten bei einer Periode von 400 nm Strukturtiefen von bis zu 80nm aus. Durch die Beeinflussung von Materialparametern, wie Oberfl{\"a}chenspannung und Viskosit{\"a}t, wird die maximale Strukturtiefe auf 160nm verdoppelt. Durch Mehrfachbelichtungen wird auch die Bildung von zweidimensionalen Gittern untersucht. Die Originalstrukturen werden in einem Abformverfahren kopiert und in Schichten von unter UV-Licht aush{\"a}rtenden Polymeren {\"u}bertragen. Durch das Abformen kommt es zu einer geringf{\"u}gigen Verschlechterung der Oberfl{\"a}chenqualit{\"a}t sowie Abnahme der Strukturtiefe. Dieser Verlust wird durch eine Verringerung der Prozesstemperatur verringert. Mithilfe kopierter Oberfl{\"a}chengitter werden organische Distributed Feedback-(DFB)-Laser zweiter Ordnung hergestellt, um den Einfluss von Gitterparametern auf die Emissionseigenschaften dieser Laser zu untersuchen. Dazu erfolgt zun{\"a}chst die Charakterisierung der optischen Verst{\"a}rkungseigenschaften ausgew{\"a}hlter organischer Emittermaterialien mittels der Variablen Strichl{\"a}ngenmethode. Das mit dem Laserfarbstoff Pyrromthen567 (PM567) dotierte Polystyrol (PS) zeigt dabei trotz konzentrationsbedingter geringer Absorption eine vergleichsweise geringe Gewinnschwelle von 50µJ/cm² bei ca. 575 nm. Das aktive Gast-Wirt-System der konjugierten Polymere MEH-PPV und F8BT* weist eine hohe Absorption und eine kleine Gewinnschwelle von 2,5 µJ/cm² bei 630 nm auf. Dieses Verhalten spiegelt sich auch in den Emissionseigenschaften der damit hergestellten DFB-Laser wieder. Die Dicke der aktiven Schichten liegen im Bereich hunderter Nanometer und wird so eingestellt, dass sich nur die transversalen Grundmoden im Wellenleiter ausbreiten k{\"o}nnen. Die Gitterperiode sind so gew{\"a}hlt, dass ein Lichtmode im Verst{\"a}rkungsbereich des Emittermaterials liegt. Die Emissionslinien der Laser sind mit FWHM-Werten von bis zu 0,3 nm spektral sehr schmalbandig und weisen auf eine sehr gute Gitterqualit{\"a}t hin. Die Untersuchungen liefern minimale Laserschwellen und maximale differentielle Effizienzen von 4,0µJ/cm² und 8,4\% f{\"u}r MEH-PPV in F8BT* (bei ca. 640nm) sowie 80 µJ/cm² und 0,9\% f{\"u}r PM567 in PS (bei ca. 575 nm). Die Vergr{\"o}ßerung der Strukturtiefe von 40nm auf 80nm in mit MEH-PPV dotierten F8BT*-Lasern zu einem deutlichen Anstieg der ausgekoppelten Energie sowie der differentiellen Effizienz und einem geringen Absinken der Laserschwelle. Dies ist ein Resultat der erh{\"o}hten Kopplung von Lasermode und Gitter. Die Emission von DFB-Lasern mit zweidimensionalen Oberfl{\"a}chengittern zeigen eine Verringerung der Divergenz aber kein Einfluss auf die Laserschwelle. Abschließend erfolgt eine Vermessung der Photostabilit{\"a}t von DFB-Lasern unter verschiedenen Bedingungen. Das Einbringen eines konjugierten Polymers in eine aktive Matrix sowie der Betrieb in einer Stickstoffatmosph{\"a}re f{\"u}hren dabei zu einer Erh{\"o}hung der Lebensdauer auf {\"u}ber eine Million Pulse. Durch die Kombination von Oberfl{\"a}chengittern in PDMS-Filmen mit elektroaktiven Substraten wird eine elektrisch steuerbare Deformation des Beugungsgitters erreicht und auf einen DFB-Laser {\"u}bertragen. Die spannungsinduzierte Verformung wird zun{\"a}chst in Beugungsexperimenten charakterisiert und ein optimaler Arbeitspunkt bestimmt. Mit den beiden Elastomeren SEBS12 und VHB4910 werden in den Gittern maximale Perioden{\"a}nderungen von 1,3\% bzw. 3,4\% bei einer Steuerspannung von 2 kV erreicht. Der Unterschied resultiert aus den verschiedenen Elastizit{\"a}tsmoduln der Materialien. {\"U}bertragen auf DFB-Laser resultiert eine Variation der Gitterperiode senkrecht zu den Gitterlinien in einer kontinuierlichen Verschiebung der Emissionswellenl{\"a}nge. Mit einem Spannungssignal von 3,25 kV wird die schmalbandige Emission eines elastischen DFB-Lasers kontinuierlich um fast 50nm von 604 nm zu 557 nm hin verschoben. Aus dem Deformationsverhalten sowohl der reinen Beugungsgitter als auch der Laser werden R{\"u}ckschl{\"u}sse auf die Elastizit{\"a}t der verwendeten Materialien gezogen und erlauben Verbesserungen der Bauteile.}, language = {de} } @article{DouceSuisseGuillonetal.2011, author = {Douce, Laurent and Suisse, Jean-Moise and Guillon, Daniel and Taubert, Andreas}, title = {Imidazolium-based liquid crystals a modular platform for versatile new materials with finely tuneable properties and behaviour}, series = {Liquid crystals : an international journal of science and technology}, volume = {38}, journal = {Liquid crystals : an international journal of science and technology}, number = {11-12}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0267-8292}, doi = {10.1080/02678292.2011.610474}, pages = {1653 -- 1661}, year = {2011}, abstract = {Ionic liquid Crystals constitute highly versatile materials that have drawn much interest these past few years in the fields of academic research and industrial development. In this respect, the present article is intended as an update of K. Binnemans review published in 2005, but focusing exclusively on the imidazolium cation - the most widely studied. Herein, imidazolium-containing thermotropic liquid crystalline materials will be sorted by molecular structure (mono-, bis-, poly-imidazolium compounds, with symmetrical and non-symmetrical structures) and discussed. Their physico-chemical properties will be exposed in order to adduce the relevancy and potential of the imidazolium platform in various fields of research.}, language = {en} } @phdthesis{Dosche2011, author = {Dosche, Carsten}, title = {Funktionale Farbstoffe und ihre Photophysik und Anwendung in komplexen Matrizes}, address = {Potsdam}, pages = {151 S.}, year = {2011}, language = {de} } @article{DongesDonnerTrauthetal.2011, author = {Donges, Jonathan and Donner, Reik Volker and Trauth, Martin H. and Marwan, Norbert and Schellnhuber, Hans Joachim and Kurths, J{\"u}rgen}, title = {Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {108}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {51}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1117052108}, pages = {20422 -- 20427}, year = {2011}, abstract = {Potential paleoclimatic driving mechanisms acting on human evolution present an open problem of cross-disciplinary scientific interest. The analysis of paleoclimate archives encoding the environmental variability in East Africa during the past 5 Ma has triggered an ongoing debate about possible candidate processes and evolutionary mechanisms. In this work, we apply a nonlinear statistical technique, recurrence network analysis, to three distinct marine records of terrigenous dust flux. Our method enables us to identify three epochs with transitions between qualitatively different types of environmental variability in North and East Africa during the (i) Middle Pliocene (3.35-3.15 Ma B. P.), (ii) Early Pleistocene (2.25-1.6 Ma B. P.), and (iii) Middle Pleistocene (1.1-0.7 Ma B. P.). A deeper examination of these transition periods reveals potential climatic drivers, including (i) large-scale changes in ocean currents due to a spatial shift of the Indonesian throughflow in combination with an intensification of Northern Hemisphere glaciation, (ii) a global reorganization of the atmospheric Walker circulation induced in the tropical Pacific and Indian Ocean, and (iii) shifts in the dominating temporal variability pattern of glacial activity during the Middle Pleistocene, respectively. A reexamination of the available fossil record demonstrates statistically significant coincidences between the detected transition periods and major steps in hominin evolution. This result suggests that the observed shifts between more regular and more erratic environmental variability may have acted as a trigger for rapid change in the development of humankind in Africa.}, language = {en} } @article{DiGuglielmoSamblowskiHageetal.2011, author = {DiGuglielmo, J. and Samblowski, A. and Hage, B. and Pineda, Carlos and Eisert, Jens and Schnabel, R.}, title = {Experimental Unconditional Preparation and Detection of a Continuous Bound Entangled State of Light}, series = {Physical review letters}, volume = {107}, journal = {Physical review letters}, number = {24}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.107.240503}, pages = {5}, year = {2011}, abstract = {Among the possibly most intriguing aspects of quantum entanglement is that it comes in free and bound instances. The existence of bound entangled states certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this Letter, we present a first unconditional, continuous-variable preparation and detection of a bound entangled state of light. We use convex optimization to identify regimes rendering its bound character well certifiable, and continuously produce a distributed bound entangled state with an extraordinary and unprecedented significance of more than 10 standard deviations away from both separability and distillability. Our results show that the approach chosen allows for the efficient and precise preparation of multimode entangled states of light with various applications in quantum information, quantum state engineering, and high precision metrology.}, language = {en} } @article{DelahayeFiassonPohletal.2011, author = {Delahaye, T. and Fiasson, A. and Pohl, Martin and Salati, P.}, title = {The GeV-TeV Galactic gamma-ray diffuse emission I. Uncertainties in the predictions of the hadronic component}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {531}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {4}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201116647}, pages = {19}, year = {2011}, abstract = {Context. The Galactic gamma-ray diffuse emission is currently observed in the GeV-TeV energy range with unprecedented accuracy by the Fermi satellite. Understanding this component is crucial because it provides a background to many different signals, such as extragalactic sources or annihilating dark matter. It is timely to reinvestigate how it is calculated and to assess the various uncertainties that are likely to affect the accuracy of the predictions. Aims. The Galactic gamma-ray diffuse emission is mostly produced above a few GeV by the interactions of cosmic ray primaries impinging on the interstellar material. The theoretical error on that component is derived by exploring various potential sources of uncertainty. Particular attention is paid to cosmic ray propagation. Nuclear cross sections, the proton and helium fluxes at the Earth's position, the Galactic radial profile of supernova remnants, and the hydrogen distribution can also severely affect the signal. Methods. The propagation of cosmic ray species throughout the Galaxy is described in the framework of a semi-analytic two-zone diffusion/convection model. The gamma-ray flux is reliably and quickly determined. This allows conversion of the constraints set by the boron-to-carbon data into a theoretical uncertainty on the diffuse emission. New deconvolutions of the HI and CO sky maps are also used to get the hydrogen distribution within the Galaxy. Results. The thickness of the cosmic ray diffusive halo is found to have a significant effect on the Galactic gamma-ray diffuse emission, while the interplay between diffusion and convection has little influence on the signal. The uncertainties related to nuclear cross sections and to the primary cosmic ray fluxes at the Earth are significant. The radial distribution of supernova remnants along the Galactic plane turns out to be a key ingredient. As expected, the predictions are extremely sensitive to the spatial distribution of hydrogen within the Milky Way. Conclusions. Most of the sources of uncertainty are likely to be reduced in the near future. The stress should be put (i) on better determination of the thickness of the cosmic ray diffusive halo; and (ii) on refined observations of the radial profile of supernova remnants.}, language = {en} } @article{CockburnNegrettiProukakisetal.2011, author = {Cockburn, S. P. and Negretti, Antonio and Proukakis, N. P. and Henkel, Carsten}, title = {Comparison between microscopic methods for finite-temperature Bose gases}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {83}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.83.043619}, pages = {29}, year = {2011}, abstract = {We analyze the equilibrium properties of a weakly interacting, trapped quasi-one-dimensional Bose gas at finite temperatures and compare different theoretical approaches. We focus in particular on two stochastic theories: a number-conserving Bogoliubov (NCB) approach and a stochastic Gross-Pitaevskii equation (SGPE) that have been extensively used in numerical simulations. Equilibrium properties like density profiles, correlation functions, and the condensate statistics are compared to predictions based upon a number of alternative theories. We find that due to thermal phase fluctuations, and the corresponding condensate depletion, the NCB approach loses its validity at relatively low temperatures. This can be attributed to the change in the Bogoliubov spectrum, as the condensate gets thermally depleted, and to large fluctuations beyond perturbation theory. Although the two stochastic theories are built on different thermodynamic ensembles (NCB, canonical; SGPE, grand-canonical), they yield the correct condensate statistics in a large Bose-Einstein condensate (BEC) (strong enough particle interactions). For smaller systems, the SGPE results are prone to anomalously large number fluctuations, well known for the grand-canonical, ideal Bose gas. Based on the comparison of the above theories to the modified Popov approach, we propose a simple procedure for approximately extracting the Penrose-Onsager condensate from first-and second-order correlation functions that is both computationally convenient and of potential use to experimentalists. This also clarifies the link between condensate and quasicondensate in the Popov theory of low-dimensional systems.}, language = {en} } @article{Campbell2011, author = {Campbell, Earl T.}, title = {Catalysis and activation of magic states in fault-tolerant architectures}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {83}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.83.032317}, pages = {12}, year = {2011}, abstract = {In many architectures for fault-tolerant quantum computing universality is achieved by a combination of Clifford group unitary operators and preparation of suitable nonstabilizer states, the so-called magic states. Universality is possible even for some fairly noisy nonstabilizer states, as distillation can convert many noisy copies into fewer purer magic states. Here we propose protocols that exploit multiple species of magic states in surprising ways. These protocols provide examples of previously unobserved phenomena that are analogous to catalysis and activation well known in entanglement theory.}, language = {en} } @article{BurylkoPikovskij2011, author = {Burylko, Oleksandr and Pikovskij, Arkadij}, title = {Desynchronization transitions in nonlinearly coupled phase oscillators}, series = {Physica :D, Nonlinear phenomena}, volume = {240}, journal = {Physica :D, Nonlinear phenomena}, number = {17}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-2789}, doi = {10.1016/j.physd.2011.05.016}, pages = {1352 -- 1361}, year = {2011}, abstract = {We consider the nonlinear extension of the Kuramoto model of globally coupled phase oscillators where the phase shift in the coupling function depends on the order parameter. A bifurcation analysis of the transition from fully synchronous state to partial synchrony is performed. We demonstrate that for small ensembles it is typically mediated by stable cluster states, that disappear with creation of heteroclinic cycles, while for a larger number of oscillators a direct transition from full synchrony to a periodic or a quasiperiodic regime occurs.}, language = {en} } @book{Brehmer2011, author = {Brehmer, Ludwig}, title = {Die Brandeburgische Landeshochschule zu Potsdam im Jahre eins : die Hochschule in Potsdamer Schulen ; Daten und Fakten ; Kommentare und Dokumente}, volume = {4}, publisher = {Eigenverl. des Verf}, address = {Potsdam}, isbn = {978-3-00-034135-9}, pages = {174 S.}, year = {2011}, language = {de} } @article{BrandaoEisertHorodeckietal.2011, author = {Brandao, F. G. S. L. and Eisert, Jens and Horodecki, M. and Yang, Dong}, title = {Entangled inputs cannot make imperfect quantum channels perfect}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.230502}, pages = {4}, year = {2011}, abstract = {Entangled inputs can enhance the capacity of quantum channels, this being one of the consequences of the celebrated result showing the nonadditivity of several quantities relevant for quantum information science. In this work, we answer the converse question (whether entangled inputs can ever render noisy quantum channels to have maximum capacity) to the negative: No sophisticated entangled input of any quantum channel can ever enhance the capacity to the maximum possible value, a result that holds true for all channels both for the classical as well as the quantum capacity. This result can hence be seen as a bound as to how "nonadditive quantum information can be.'' As a main result, we find first practical and remarkably simple computable single-shot bounds to capacities, related to entanglement measures. As examples, we discuss the qubit amplitude damping and identify the first meaningful bound for its classical capacity.}, language = {en} } @phdthesis{Boeche2011, author = {Boeche, Corrado}, title = {Chemical gradients in the Milky Way from unsupervised chemical abundances measurements of the RAVE spectroscopic data set}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52478}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The present thesis was born and evolved within the RAdial Velocity Experiment (RAVE) with the goal of measuring chemical abundances from the RAVE spectra and exploit them to investigate the chemical gradients along the plane of the Galaxy to provide constraints on possible Galactic formation scenarios. RAVE is a large spectroscopic survey which aims to observe spectroscopically ~10^6 stars by the end of 2012 and measures their radial velocities, atmospheric parameters and chemical abundances. The project makes use of the UK Schmidt telescope at Australian Astronomical Observatory (AAO) in Siding Spring, Australia, equipped with the multiobject spectrograph 6dF. To date, RAVE collected and measured more than 450,000 spectra. The precision of the chemical abundance estimations depends on the reliability of the atomic and atmosphere parameters adopted (in particular the oscillator strengths of the absorption lines and the effective temperature, gravity, and metallicity of the stars measured). Therefore we first identified 604 absorption lines in the RAVE wavelength range and refined their oscillator strengths with an inverse spectral analysis. Then, we improved the RAVE stellar parameters by modifying the RAVE pipeline and the spectral library the pipeline rely on. The modifications removed some systematic errors in stellar parameters discovered during this work. To obtain chemical abundances, we developed two different processing pipelines. Both of them perform chemical abundances measurements by assuming stellar atmospheres in Local Thermodynamic Equilibrium (LTE). The first one determines elements abundances from equivalent widths of absorption lines. Since this pipeline showed poor sensibility on abundances relative to iron, it has been superseded. The second one exploits the chi^2 minimization technique between observed and model spectra. Thanks to its precision, it has been adopted for the creation of the RAVE chemical catalogue. This pipeline provides abundances with uncertains of about ~0.2dex for spectra with signal-to-noise ratio S/N>40 and ~0.3dex for spectra with 20>S/N>40. For this work, the pipeline measured chemical abundances up to 7 elements for 217,358 RAVE stars. With these data we investigated the chemical gradients along the Galactic radius of the Milky Way. We found that stars with low vertical velocities |W| (which stay close to the Galactic plane) show an iron abundance gradient in agreement with previous works (~-0.07\$ dex kpc^-1) whereas stars with larger |W| which are able to reach larger heights above the Galactic plane, show progressively flatter gradients. The gradients of the other elements follow the same trend. This suggests that an efficient radial mixing acts in the Galaxy or that the thick disk formed from homogeneous interstellar matter. In particular, we found hundreds of stars which can be kinetically classified as thick disk stars exhibiting a chemical composition typical of the thin disk. A few stars of this kind have already been detected by other authors, and their origin is still not clear. One possibility is that they are thin disk stars kinematically heated, and then underwent an efficient radial mixing process which blurred (and so flattened) the gradient. Alternatively they may be a transition population" which represents an evolutionary bridge between thin and thick disk. Our analysis shows that the two explanations are not mutually exclusive. Future follow-up high resolution spectroscopic observations will clarify their role in the Galactic disk evolution.}, language = {en} } @article{BlakesleySchubertSteyrleuthneretal.2011, author = {Blakesley, James C. and Schubert, Marcel and Steyrleuthner, Robert and Chen, Zhihua and Facchetti, Antonio and Neher, Dieter}, title = {Time-of-flight measurements and vertical transport in a high electron-mobility polymer}, series = {Applied physics letters}, volume = {99}, journal = {Applied physics letters}, number = {18}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3657827}, pages = {3}, year = {2011}, abstract = {We investigate charge transport in a high-electron mobility polymer, poly(N, N-bis 2-octyldodecyl-naphthalene-1,4,5,8-bis dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) [P(NDI2OD-T2), Polyera ActivInk (TM) N2200]. Time-of-flight measurements reveal electron mobilities approaching those measured in field-effect transistors, the highest ever recorded in a conjugated polymer using this technique. The modest temperature dependence and weak dispersion of the transients indicate low energetic disorder in this material. Steady-state electron-only current measurements reveal a barrier to injection of about 300 meV. We propose that this barrier is located within the P(NDI2OD-T2) film and arises from molecular orientation effects.}, language = {en} }