@article{HaakhIntravaiaHenkel2010, author = {Haakh, Harald Richard and Intravaia, Francesco and Henkel, Carsten}, title = {Temperature dependence of the plasmonic Casimir interaction}, issn = {1050-2947}, doi = {10.1103/Physreva.82.012507}, year = {2010}, abstract = {We investigate the role of surface plasmons in the electromagnetic Casimir effect at finite temperature, including situations out of global thermal equilibrium. The free energy is calculated analytically and expanded for different regimes of distances and temperatures. Similar to the zero-temperature case, the interaction changes from attraction to repulsion with distance. Thermal effects are shown to be negligible for small plate separations and at room temperature but become dominant and repulsive at large values of these parameters. In configurations out of global thermal equilibrium, we show that the selective excitation of surface plasmons can create a repulsive Casimir force between metal plates.}, language = {en} } @article{GvaramadzeKniazevHamannetal.2010, author = {Gvaramadze, Vasily V. and Kniazev, Alexei Y. and Hamann, Wolf-Rainer and Berdnikov, Leonid N. and Fabrika, Sergei Nikolaevich and Valeev, Azamat F.}, title = {A new Wolf-Rayet star and its circumstellar nebula in Aquila}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2009.16126.x}, year = {2010}, abstract = {We report the discovery of a new Wolf-Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR121b). We analysed the spectrum of WR 121b by using the Potsdam Wolf-Rayet model atmospheres, obtaining a stellar temperature of similar or equal to 50 kK. The stellar wind composition is dominated by helium with similar to 20 per cent of hydrogen. The stellar spectrum is highly reddened [E(B - V) = 2.85 mag]. Adopting an absolute magnitude of M-v = 5.7, the star has a luminosity of log L/L-circle dot = 5.75 and a mass-loss rate of 10(-4.7)M(circle dot)yr(-1), and resides at a distance of 6.3 kpc. We searched for a possible parent cluster of WR 121b and found that this star is located at similar or equal to 1 degrees from the young star cluster embedded in the giant HII region W43 (containing a WN7+a/OB? star - WR121a). We also discovered a bow shock around the O9.5III star ALS 9956, located at similar or equal to 0 degrees.5 from the cluster. We discuss the possibility that WR121b and ALS 9956 are runaway stars ejected from the cluster in W43.}, language = {en} } @article{GrossMuellerColbecketal.2010, author = {Gross, David and Mueller, Markus and Colbeck, Roger and Dahlsten, Oscar C. O.}, title = {All reversible dynamics in maximally nonlocal theories are trivial}, issn = {0031-9007}, doi = {10.1103/Physrevlett.104.080402}, year = {2010}, abstract = {A remarkable feature of quantum theory is nonlocality ( Bell inequality violations). However, quantum correlations are not maximally nonlocal, and it is natural to ask whether there are compelling reasons for rejecting theories in which stronger violations are possible. To shed light on this question, we consider post-quantum theories in which maximally nonlocal states ( nonlocal boxes) occur. We show that reversible transformations in such theories are trivial: they consist solely of local operations and permutations of systems. In particular, no correlations can be created; nonlocal boxes cannot be prepared from product states and classical computers can efficiently simulate all such processes.}, language = {en} } @article{GrossLiuFlammiaetal.2010, author = {Gross, David and Liu, Yi-Kai and Flammia, Steven T. and Becker, Stephen and Eisert, Jens}, title = {Quantum state tomography via compressed sensing}, issn = {0031-9007}, doi = {10.1103/Physrevlett.105.150401}, year = {2010}, abstract = {We establish methods for quantum state tomography based on compressed sensing. These methods are specialized for quantum states that are fairly pure, and they offer a significant performance improvement on large quantum systems. In particular, they are able to reconstruct an unknown density matrix of dimension d and rank r using O(rdlog(2)d) measurement settings, compared to standard methods that require d(2) settings. Our methods have several features that make them amenable to experimental implementation: they require only simple Pauli measurements, use fast convex optimization, are stable against noise, and can be applied to states that are only approximately low rank. The acquired data can be used to certify that the state is indeed close to pure, so no a priori assumptions are needed.}, language = {en} } @article{GrossEisert2010, author = {Gross, David and Eisert, Jens}, title = {Quantum computational webs}, issn = {1050-2947}, doi = {10.1103/Physreva.82.040303}, year = {2010}, abstract = {We discuss the notion of quantum computational webs: These are quantum states universal for measurement-based computation, which can be built up from a collection of simple primitives. The primitive elements-reminiscent of building blocks in a construction kit-are (i) one-dimensional states (computational quantum wires) with the power to process one logical qubit and (ii) suitable couplings, which connect the wires to a computationally universal web. All elements are preparable by nearest-neighbor interactions in a single pass, of the kind accessible in a number of physical architectures. We provide a complete classification of qubit wires, a physically well-motivated class of universal resources that can be fully understood. Finally, we sketch possible realizations in superlattices and explore the power of coupling mechanisms based on Ising or exchange interactions.}, language = {en} } @article{GrecoWangWegener2010, author = {Greco, Tonino and Wang, Feipeng and Wegener, Michael}, title = {Multifunctional silver poly(vinylidene fluoride) nanocomposites : nanoparticle synthesis, film processing, and structural characterization}, issn = {0015-0193}, doi = {10.1080/00150193.2010.482896}, year = {2010}, abstract = {Scope of this work was the synthesis of homogeneously dispersed silver nanoparticles in the ferroelectric polymer poly(vinylidene fluoride) (PVDF) and the study of the resulting properties affecting both the electro-active matrix and the optically-active nanofiller. In the nanocomposites surface plasmon resonances can be tuned across the UV- vis to the NIR spectral range. From IR spectra and DSC measurements it is concluded that the - to -phase transformation is observed and no degradation of the polymer matrix occurs. Finally, electrical poling was performed in order to investigate the influence of the embedded silver particles on the polarization behavior of the ferroelectric polymer.}, language = {en} } @article{FoxWakkerSmokeretal.2010, author = {Fox, Andrew J. and Wakker, Bart P. and Smoker, Jonathan V. and Richter, Philipp and Savage, Blair D. and Sembach, Kenneth R.}, title = {Exploring the origin and fate of the Magellanic stream with ultraviolet and optical absorption}, issn = {0004-637X}, doi = {10.1088/0004-637x/718/2/1046}, year = {2010}, abstract = {We present an analysis of ionization and metal enrichment in the Magellanic Stream (MS), the nearest gaseous tidal stream, using Hubble Space Telescope/STIS and FUSE ultraviolet spectroscopy of two background active galactic nuclei. The targets are NGC 7469, lying directly behind the MS with log N(H I)(MS) = 18.63 +/- 0.03(stat) +/- 0.08(syst), and Mrk 335, lying 24 degrees.7 away with log N(H I)(MS) = 16.67 +/- 0.05. For NGC 7469, we include optical spectroscopy from VLT/UVES. In both sight lines, the MS is detected in low-ion (O I, C II, C III, Si II, Si III, Al II, Ca II) and high-ion (O VI, C IV, Si IV) absorption. Toward NGC 7469, we measure an MS oxygen abundance [O/H](MS) = [O I/ H I]= -1.00 +/- 0.05(stat) +/- 0.08(syst), supporting the view that the Stream originates in the Small Magellanic Cloud rather than the Large Magellanic Cloud. We use CLOUDY to model the low-ion phase of the Stream as a photoionized plasma using the observed Si III/Si II and C III/C II ratios. Toward Mrk 335, this yields an ionization parameter between log U= -3.45 and -3.15, a gas density log (n(H)/cm(-3)) between-2.51 and -2.21, and a hydrogen ionization fraction of 98.9\%- 99.5\%. Toward NGC 7469, we derive sub-solar abundance ratios for [Si/O], [Fe/O], and [Al/O], indicating the presence of dust in the MS. The high-ion column densities are too large to be explained by photoionization, but also cannot be explained by a single-temperature collisional ionization model (equilibrium or non-equilibrium). This suggests that the high-ion plasma is multi-phase, with an Si IV region, a hotter O VI region, and C IV potentially contributing to each. Summing over the low-ion and high-ion phases, we derive conservative lower limits on the ratio N(total H II)/N(H I) of greater than or similar to 19 toward NGC 7469 and greater than or similar to 330 toward Mrk 335, showing that along these two directions the vast majority of the Stream has been ionized. The presence of warm-hot plasma together with the small-scale structure observed at 21 cm provides evidence for an evaporative interaction with the hot Galactic corona. This scenario, predicted by hydrodynamical simulations, suggests that the fate of the MS will be to replenish the Galactic corona with new plasma, rather than to bring neutral fuel to the disk.}, language = {en} } @article{FilimonKopfBalloutetal.2010, author = {Filimon, Marlena and Kopf, Ilona and Ballout, Fuad and Schmidt, Dietrich A. and Bruendermann, Erik and R{\"u}he, J{\"u}rgen and Santer, Svetlana and Havenith, Martina}, title = {Smart polymer surfaces : mapping chemical landscapes on the nanometre scale}, issn = {1744-683X}, doi = {10.1039/C0sm00098a}, year = {2010}, abstract = {We show that Scattering Infrared Near-field Microscopy (SNIM) allows chemical mapping of polymer monolayers that can serve as designed nanostructured surfaces with specific surface chemistry properties on a nm scale. Using s- SNIM a minimum volume of 100 nm x 100 nm x 15 nm is sufficient for a recording of a "chemical'' IR signature which corresponds to an enhancement of at least four orders of magnitudes compared to conventional FT-IR microscopy. We could prove that even in cases where it is essentially difficult to distinguish between distinct polymer compositions based solely on topography, nanophase separated polymers can be clearly distinguished according to their characteristic near-field IR response.}, language = {en} } @article{FangQiuWirgesetal.2010, author = {Fang, Peng and Qiu, Xunlin and Wirges, Werner and Gerhard, Reimund and Zirkel, Larissa}, title = {Polyethylene-naphthalate (PEN) ferroelectrets : cellular structure, piezoelectricity and thermal stability}, issn = {1070-9878}, doi = {10.1109/TDEI.2010.5539678}, year = {2010}, abstract = {Cellular polyethylene-naphthalate (PEN) ferroelectrets are useful as soft and flexible electromechanical transducer materials. Improved cellular PEN foams are prepared by means of a "voiding + inflation + stretching" process and investigated with respect to their structure and their applications-relevant properties. It is found that most of the cellular voids have heights below 8 mu m. The polymer walls do not allow sufficient gas exchange between the voids and the ambient atmosphere, when the cellular films are exposed to atmospheric pressures between a millibar and a few bars. As expected for ferroelectrets, a threshold voltage for charging is observed: A reasonable piezoelectric coefficient d(33) is only found when the charging voltage is higher than 4 kV. Furthermore, d(33) increases with charging voltage and reaches saturation at approximately 8 kV. Annealing after charging or charging at elevated temperatures may enhance the thermal stability of the PEN ferroelectrets. The d(33) of properly annealed samples is stable up to the respective annealing temperatures, but the annealing process reduces the piezoelectric activity of charged ferroelectret films to some extent. Samples charged at suitable elevated temperatures show much better thermal stability than those charged at room temperature, but the charging temperature should be limited to values below the material's glass-transition temperature T-g. Furthermore, the relevant elastic modulus c(33) of PEN ferroelectrets may decrease upon thermal treatment.}, language = {en} } @article{EnquistNavirianNueskeetal.2010, author = {Enquist, Henrik and Navirian, Hengameh and Nueske, Ralf and von Korff Schmising, Clemens and Jurgilaitis, Andrius and Herzog, Marc and Bargheer, Matias and Sondhauss, Peter and Larsson, Joergen}, title = {Subpicosecond hard x-ray streak camera using single-photon counting}, issn = {0146-9592}, doi = {10.1364/OL.35.003219}, year = {2010}, abstract = {We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons.}, language = {en} }