TY  - JOUR
A1  - Rychkov, Dmitry
A1  - Yablokov, M.
A1  - Rychkov, A.
T1  - Chemical and physical surface modification of PTFE films-an approach to produce stable electrets
JF  - Applied physics : A, Materials science & processing
N2  - The thermal stability of positive charge has been investigated in chemically and physically treated polytetrafluoroethylene (PTFE) films. It has been found that virgin films, oriented by the manufacturer, display an increase in thermal stability of positive charge with an increase of the initial value of surface potential. Such an anomalous behavior is explained by the influence of a negative tribocharge, trapped some small distance below the surface. In PTFE samples treated with orthophosphoric acid and with tetraethoxysilane, a considerable improvement of positive charge stability has been achieved, but no influence of the initial value of surface potential has been observed. However, this influence should be kept in mind when comparing charge stability in virgin and modified samples. In nonoriented PTFE films, no influence of the initial value of surface potential on charge stability has been observed. This could be due to the fact that these films did not possess a noticeable negative tribocharge. After the treatment in glow-discharge defluorination, oxidation and appearance of polar groups have been detected on the surface. These changes in chemical composition of a PTFE surface resulted in a noticeable improvement in thermal stability of positively charged electrets. This improvement is attributed to the formation of deeper traps on the modified surface.
Y1  - 2012
U6  - https://doi.org/10.1007/s00339-012-6834-5
SN  - 0947-8396
VL  - 107
IS  - 3
SP  - 589
EP  - 596
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Garz, Andreas
A1  - Sandmann, Michael
A1  - Rading, Michael
A1  - Ramm, Sascha
A1  - Menzel, Ralf
A1  - Steup, Martin
T1  - Cell-to-cell diversity in a synchronized chlamydomonas culture as revealed by single-cell analyses
JF  - Biophysical journal
N2  - In a synchronized photoautotrophic culture of Chlamydomonas reinhardtii, cell size, cell number, and the averaged starch content were determined throughout the light-dark cycle. For single-cell analyses, the relative cellular starch was quantified by measuring the second harmonic generation (SHG). In destained cells, amylopectin essentially represents the only biophotonic structure. As revealed by various validation procedures, SHG signal intensities are a reliable relative measure of the cellular starch content. During photosynthesis-driven starch biosynthesis, synchronized Chlamydomonas cells possess an unexpected cell-to-cell diversity both in size and starch content, but the starch-related heterogeneity largely exceeds that of size. The cellular volume, starch content, and amount of starch/cell volume obey lognormal distributions. Starch degradation was initiated by inhibiting the photosynthetic electron transport in illuminated cells or by darkening. Under both conditions, the averaged rate of starch degradation is almost constant, but it is higher in illuminated than in darkened cells. At the single-cell level, rates of starch degradation largely differ but are unrelated to the initial cellular starch content. A rate equation describing the cellular starch degradation
Y1  - 2012
U6  - https://doi.org/10.1016/j.bpj.2012.07.026
SN  - 0006-3495
VL  - 103
IS  - 5
SP  - 1078
EP  - 1086
PB  - Cell Press
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Mattos, Thiago G.
A1  - Mejia-Monasterio, Carlos
A1  - Metzler, Ralf
A1  - Oshanin, Gleb
T1  - First passages in bounded domains When is the mean first passage time meaningful?
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We study the first passage statistics to adsorbing boundaries of a Brownian motion in bounded two-dimensional domains of different shapes and configurations of the adsorbing and reflecting boundaries. From extensive numerical analysis we obtain the probability P(omega) distribution of the random variable omega = tau(1)/(tau(1) + tau(2)), which is a measure for how similar the first passage times tau(1) and tau(2) are of two independent realizations of a Brownian walk starting at the same location. We construct a chart for each domain, determining whether P(omega) represents a unimodal, bell-shaped form, or a bimodal, M-shaped behavior. While in the former case the mean first passage time (MFPT) is a valid characteristic of the first passage behavior, in the latter case it is an insufficient measure for the process. Strikingly we find a distinct turnover between the two modes of P(omega), characteristic for the domain shape and the respective location of absorbing and reflective boundaries. Our results demonstrate that large fluctuations of the first passage times may occur frequently in two-dimensional domains, rendering quite vague the general use of the MFPT as a robust measure of the actual behavior even in bounded domains, in which all moments of the first passage distribution exist.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevE.86.031143
SN  - 1539-3755
VL  - 86
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Makarava, Natallia
A1  - Bettenbühl, Mario
A1  - Engbert, Ralf
A1  - Holschneider, Matthias
T1  - Bayesian estimation of the scaling parameter of fixational eye movements
JF  - epl : a letters journal exploring the frontiers of physics
N2  - In this study we re-evaluate the estimation of the self-similarity exponent of fixational eye movements using Bayesian theory. Our analysis is based on a subsampling decomposition, which permits an analysis of the signal up to some scale factor. We demonstrate that our approach can be applied to simulated data from mathematical models of fixational eye movements to distinguish the models' properties reliably.
Y1  - 2012
U6  - https://doi.org/10.1209/0295-5075/100/40003
SN  - 0295-5075
VL  - 100
IS  - 4
PB  - EDP Sciences
CY  - Mulhouse
ER  - 
TY  - JOUR
A1  - Aliu, E.
A1  - Archambault, S.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Bouvier, A.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Decerprit, G.
A1  - Dickherber, R.
A1  - Duke, C.
A1  - Dumm, J.
A1  - Dwarkadas, Vikram V.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Feng, Q.
A1  - Finley, J. P.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Huan, H.
A1  - Hughes, G.
A1  - Humensky, T. B.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Khassen, Y.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - Lee, K.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Millis, J.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Nunez, P. D.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Pandel, D.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pohl, M.
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Ruppel, J.
A1  - Saxon, D. B.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Skole, C.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Telezhinsky, Igor O.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Welsing, R.
A1  - Williams, D. A.
A1  - Zitzer, B.
T1  - Veritas observations of the nova in V407 CYGNI
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We report on very high energy (E > 100 GeV) gamma-ray observations of V407 Cygni, a symbiotic binary that underwent a nova outburst producing 0.1-10 GeV gamma rays during 2010 March 10-26. Observations were made with the Very Energetic Radiation Imaging Telescope Array System during 2010 March 19-26 at relatively large zenith angles due to the position of V407 Cyg. An improved reconstruction technique for large zenith angle observations is presented and used to analyze the data. We do not detect V407 Cygni and place a differential upper limit on the flux at 1.6 TeV of 2.3 x 10(-12) erg cm(-2) s(-1) (at the 95% confidence level). When considered jointly with data from Fermi-LAT, this result places limits on the acceleration of very high energy particles in the nova.
KW  - gamma rays: general
KW  - novae, cataclysmic variables
KW  - white dwarfs
Y1  - 2012
U6  - https://doi.org/10.1088/0004-637X/754/1/77
SN  - 0004-637X
VL  - 754
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Zurita-Sanchez, Jorge R.
A1  - Henkel, Carsten
T1  - Acoustic waves from mechanical impulses due to fluorescence resonant energy (Forster) transfer Blowing a whistle with light
JF  - epl : a letters journal exploring the frontiers of physics
N2  - We present a momentum transfer mechanism mediated by electromagnetic fields that originates in a system of two nearby molecules: one excited (donor D*) and the other in ground state (acceptor A). An intermolecular force related to fluorescence resonant energy or Forster transfer (FRET) arises in the unstable D* A molecular system, which differs from the equilibrium van der Waals interaction. Due to the its finite lifetime, a mechanical impulse is imparted to the relative motion in the system. We analyze the FRET impulse when the molecules are embedded in free space and find that its magnitude can be much greater than the single recoil photon momentum, getting comparable with the thermal momentum (Maxwell-Boltzmann distribution) at room temperature. In addition, we propose that this FRET impulse can be exploited in the generation of acoustic waves inside a film containing layers of donor and acceptor molecules, when a picosecond laser pulse excites the donors. This acoustic transient is distinguishable from that produced by thermal stress due to laser absorption, and may therefore play a role in photoacoustic spectroscopy. The effect can be seen as exciting a vibrating system like a string or organ pipe with light; it may be used as an opto-mechanical transducer.
Y1  - 2012
U6  - https://doi.org/10.1209/0295-5075/97/43002
SN  - 0295-5075
VL  - 97
IS  - 4
PB  - EDP Sciences
CY  - Mulhouse
ER  - 
TY  - JOUR
A1  - Haakh, Harald Richard
A1  - Henkel, Carsten
T1  - Magnetic near fields as a probe of charge transport in spatially dispersive conductors
JF  - The European physical journal : B, Condensed matter and complex systems
N2  - We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to a reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behaviour is common to a wide range of materials, including semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturised atom traps and matter-wave interferometers.
Y1  - 2012
U6  - https://doi.org/10.1140/epjb/e2011-20567-1
SN  - 1434-6028
VL  - 85
IS  - 1
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Bödecker, Geesche
A1  - Henkel, Carsten
T1  - Validity of the quantum regression theorem for resonance fluorescence in a photonic crystal
JF  - Annalen der Physik
N2  - Correlation functions of a driven two-level system embedded in a photonic crystal are analyzed. The spectral density of the photonic bands near a gap makes this system non-Markovian. The equations of motion for two-time correlations are derived by two different methods, the quantum regression theorem and the fluctuation dissipation theorem, and found to be the same.
KW  - Resonance fluorescence
KW  - fluctuation dissipation theorem
KW  - quantum regression theorem
KW  - non-Markovian dynamics
KW  - open quantum system
KW  - photonic bandgap
Y1  - 2012
U6  - https://doi.org/10.1002/andp.201200135
SN  - 0003-3804
VL  - 524
IS  - 12
SP  - 805
EP  - 813
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Wirges, Werner
A1  - Raabe, Sebastian
A1  - Qiu, Xunlin
T1  - Dielectric elastomer and ferroelectret films combined in a single device how do they reinforce each other?
JF  - Applied physics : A, Materials science & processing
N2  - Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies ( ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the of ferroelectrets, while the can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application.
Y1  - 2012
U6  - https://doi.org/10.1007/s00339-012-6833-6
SN  - 0947-8396
SN  - 1432-0630
VL  - 107
IS  - 3
SP  - 583
EP  - 588
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Jeon, Jae-Hyung
A1  - Metzler, Ralf
T1  - Inequivalence of time and ensemble averages in ergodic systems: exponential versus power-law relaxation in confinement
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Single-particle tracking has become a standard tool for the investigation of diffusive properties, especially in small systems such as biological cells. Usually the resulting time series are analyzed in terms of time averages over individual trajectories. Here we study confined normal as well as anomalous diffusion, modeled by fractional Brownian motion and the fractional Langevin equation, and show that even for such ergodic systems time-averaged quantities behave differently from their ensemble-averaged counterparts, irrespective of how long the measurement time becomes. Knowledge of the exact behavior of time averages is therefore fundamental for the proper physical interpretation of measured time series, in particular, for extraction of the relaxation time scale from data.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevE.85.021147
SN  - 1539-3755
VL  - 85
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Riera, Arnau
A1  - Gogolin, Christian
A1  - Eisert, Jens
T1  - Thermalization in nature and on a quantum computer
JF  - Physical review letters
N2  - In this work, we show how Gibbs or thermal states appear dynamically in closed quantum many-body systems, building on the program of dynamical typicality. We introduce a novel perturbation theorem for physically relevant weak system-bath couplings that is applicable even in the thermodynamic limit. We identify conditions under which thermalization happens and discuss the underlying physics. Based on these results, we also present a fully general quantum algorithm for preparing Gibbs states on a quantum computer with a certified runtime and error bound. This complements quantum Metropolis algorithms, which are expected to be efficient but have no known runtime estimates and only work for local Hamiltonians.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevLett.108.080402
SN  - 0031-9007
VL  - 108
IS  - 8
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Caravelli, Francesco
A1  - Hamma, Alioscia
A1  - Markopoulou, Fotini
A1  - Riera, Arnau
T1  - Trapped surfaces and emergent curved space in the Bose-Hubbard model
JF  - Physical review : D, Particles, fields, gravitation, and cosmology
N2  - A Bose-Hubbard model on a dynamical lattice was introduced in previous work as a spin system analogue of emergent geometry and gravity. Graphs with regions of high connectivity in the lattice were identified as candidate analogues of spacetime geometries that contain trapped surfaces. We carry out a detailed study of these systems and show explicitly that the highly connected subgraphs trap matter. We do this by solving the model in the limit of no back-reaction of the matter on the lattice, and for states with certain symmetries that are natural for our problem. We find that in this case the problem reduces to a one-dimensional Hubbard model on a lattice with variable vertex degree and multiple edges between the same two vertices. In addition, we obtain a (discrete) differential equation for the evolution of the probability density of particles which is closed in the classical regime. This is a wave equation in which the vertex degree is related to the local speed of propagation of probability. This allows an interpretation of the probability density of particles similar to that in analogue gravity systems: matter inside this analogue system sees a curved spacetime. We verify our analytic results by numerical simulations. Finally, we analyze the dependence of localization on a gradual, rather than abrupt, falloff of the vertex degree on the boundary of the highly connected region and find that matter is localized in and around that region.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevD.85.044046
SN  - 1550-7998
VL  - 85
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Bergner, Andre
A1  - Frasca, M.
A1  - Sciuto, G.
A1  - Buscarino, A.
A1  - Ngamga, Eulalie Joelle
A1  - Fortuna, L.
A1  - Kurths, Jürgen
T1  - Remote synchronization in star networks
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We study phase synchronization in a network motif with a starlike structure in which the central node's (the hub's) frequency is strongly detuned against the other peripheral nodes. We find numerically and experimentally a regime of remote synchronization (RS), where the peripheral nodes form a phase synchronized cluster, while the hub remains free with its own dynamics and serves just as a transmitter for the other nodes. We explain the mechanism for this RS by the existence of a free amplitude and also show that systems with a fixed or constant amplitude, such as the classic Kuramoto phase oscillator, are not able to generate this phenomenon. Further, we derive an analytic expression which supports our explanation of the mechanism.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevE.85.026208
SN  - 1539-3755
VL  - 85
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Lange, Dietrich
A1  - Tilmann, Frederik
A1  - Barrientos, Sergio E.
A1  - Contreras-Reyes, Eduardo
A1  - Methe, Pascal
A1  - Moreno, Marcos
A1  - Heit, Ben
A1  - Agurto, Hans
A1  - Bernard, Pascal
A1  - Vilotte, Jean-Pierre
A1  - Beck, Susan
T1  - Aftershock seismicity of the 27 February 2010 Mw 8.8 Maule earthquake rupture zone
JF  - Earth & planetary science letters
N2  - On 27 February 2010 the M-w 8.8 Maule earthquake in Central Chile ruptured a seismic gap where significant strain had accumulated since 1835. Shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity. Here, we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines. By processing the seismic data between 15 March and 30 September 2010 from stations from IRIS, IPGP, GFZ and University of Liverpool we determined 20,205 hypocentres with magnitudes M-w between 1 and 5.5. Seismic activity occurs in six groups: 1.) Normal faulting outer rise events 2.) A shallow group of plate interface seismicity apparent at 25-35 km depth and 50-120 km distance to the trench with some variations between profiles. Along strike, the aftershocks occur largely within the zone of coseismic slip but extend similar to 50 km further north, and with predominantly shallowly dipping thrust mechanisms. Along dip, the events are either within the zone of coseismic slip, or downdip from it, depending on the coseismic slip model used. 3.) A third band of seismicity is observed further downdip at 40-50 km depth and further inland at 150-160 km trench perpendicular distance, with mostly shallow dipping (similar to 28 degrees) thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture, and presumably above the intersection of the continental Moho with the plate interface. 4.) A deep group of intermediate depth events between 80 and 120 km depth is present north of 36 degrees S. Within the Maule segment, a large portion of events during the inter-seismic phase originated from this depth range. 5.) The magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the M-w 8.8 Maule 2010 earthquake. 6.) Pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of Pichilemu (similar to 34.5 degrees S). These crustal events occur in a similar to 30 km wide region with sharp inclined boundaries and oriented oblique to the trench. The best-located events describe a plane dipping to the southwest, consistent with one of the focal planes of the large normal-faulting aftershock (M-w = 6.9) on 11 March 2010.
KW  - Maule 2010 earthquake
KW  - local seismicity
KW  - aftershock distribution
KW  - subduction zone
KW  - Central Chile
KW  - seismogenic zone
Y1  - 2012
U6  - https://doi.org/10.1016/j.epsl.2011.11.034
SN  - 0012-821X
VL  - 317
IS  - 2
SP  - 413
EP  - 425
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Baushev, Anton N.
T1  - Interaction of clumpy dark matter with interstellar medium in astrophysical systems
JF  - Monthly notices of the Royal Astronomical Society
N2  - Contemporary cosmological conceptions suggest that the dark matter in haloes of galaxies and galaxy clusters has most likely a clumpy structure. If a stream of gas penetrates through it, a small-scale gravitational field created by the clumps disturbs the flow resulting in momentum exchange between the stream and the dark matter. In this article, we perform an analysis of this effect, based on the hierarchical halo model of the dark matter structure and Navarro-Frenk-White density profiles. We consider the clumps of various masses, from the smallest up to the highest ones M = 10(9) M circle dot. It has been found that in any event the effect grows with the mass of the clump: not only the drag force F acting on the clump but also its acceleration w = F/M increases.
 We discuss various astrophysical systems. The mechanism proved to be ineffective in the case of galaxy or galaxy cluster collisions. On the other hand, it played an important role during the process of galaxy formation. As a result, the dark matter should have formed a more compact, oblate and faster rotating substructure in the halo of our Galaxy. We have shown that this thick disc should be more clumpy than the halo. This fact is very important for the indirect detection experiments since it is the clumps that give the main contribution to the annihilation signal. Our calculations show that the mechanism of momentum exchange between the dark and baryon matter is ineffective on the outskirts of the galactic halo. It means that the clumps from there were not transported to the thick disc, and this region should be more clumpy than the halo on the average.
KW  - elementary particles
KW  - cosmology: theory
KW  - dark matter
Y1  - 2012
U6  - https://doi.org/10.1111/j.1365-2966.2011.20067.x
SN  - 0035-8711
VL  - 420
IS  - 1
SP  - 590
EP  - 595
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Draganova, Nadya
A1  - Richter, Philipp
A1  - Fechner, Cora
T1  - High-resolution observations of two O VI absorbers at z approximate to 2 toward PKS 1448-232
JF  - Astronomy and astrophysics : an international weekly journal
N2  - To explore the ionization conditions in highly-ionized absorbers at high redshift, we study in detail two intervening O vi absorbers at z approximate to 2 toward the quasar PKS 1448-232, based on high (R approximate to 75 000) and intermediate (R approximate to 45 000) resolution optical VLT/UVES spectra. We find that both absorption systems are composed of several narrow subcomponents with typical Civ/O VI Doppler-parameters of b < 10 km s(-1). This implies that the gas temperatures are T < 10(5) K and that the absorbers are photoionized by the UV background. The system at z = 2.1098 represents a simple, isolated O VI absorber that has only two absorption components and is relatively metal-rich (Z similar to 0.6 solar). Ioinization modeling implies that the system is photoionized with O VI, C IV, and H I coexisting in the same gas phase. The second system at z = 2.1660 represents a complicated, multi-component absorption system with eight O VI components spanning almost 300 km s(-1) in radial velocity. The photoionization modeling implies that the metallicity is non-uniform and relatively low (<= 0.1 solar) and that the O VI absorption must arise in a gas phase that differs from that traced by C IV, C III, and H I. Our detailed study of the two O VI systems towards PKS 1448-232 shows that multi-phase, multi-component high-ion absorbers similar to the one at z = 2.1660 can be described by applying a detailed ionization modeling of the various subcomponents to obtain reliable measurements of the physical conditions and the metal abundances in the gas.
KW  - intergalactic medium
KW  - quasars: absorption lines
KW  - cosmology: observations
Y1  - 2012
U6  - https://doi.org/10.1051/0004-6361/201116730
SN  - 0004-6361
VL  - 538
IS  - 1
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Cubitt, Toby S.
A1  - Eisert, Jens
A1  - Wolf, Michael M.
T1  - The complexity of relating quantum channels to master equations
JF  - Communications in mathematical physics
N2  - Completely positive, trace preserving (CPT) maps and Lindblad master equations are both widely used to describe the dynamics of open quantum systems. The connection between these two descriptions is a classic topic in mathematical physics. One direction was solved by the now famous result due to Lindblad, Kossakowski, Gorini and Sudarshan, who gave a complete characterisation of the master equations that generate completely positive semi-groups. However, the other direction has remained open: given a CPT map, is there a Lindblad master equation that generates it (and if so, can we find its form)? This is sometimes known as the Markovianity problem. Physically, it is asking how one can deduce underlying physical processes from experimental observations.
 We give a complexity theoretic answer to this problem: it is NP-hard. We also give an explicit algorithm that reduces the problem to integer semi-definite programming, a well-known NP problem. Together, these results imply that resolving the question of which CPT maps can be generated by master equations is tantamount to solving P = NP: any efficiently computable criterion for Markovianity would imply P = NP; whereas a proof that P = NP would imply that our algorithm already gives an efficiently computable criterion. Thus, unless P does equal NP, there cannot exist any simple criterion for determining when a CPT map has a master equation description.
 However, we also show that if the system dimension is fixed (relevant for current quantum process tomography experiments), then our algorithm scales efficiently in the required precision, allowing an underlying Lindblad master equation to be determined efficiently from even a single snapshot in this case.
 Our work also leads to similar complexity-theoretic answers to a related long-standing open problem in probability theory.
Y1  - 2012
U6  - https://doi.org/10.1007/s00220-011-1402-y
SN  - 0010-3616
VL  - 310
IS  - 2
SP  - 383
EP  - 418
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Gross, David
A1  - Nesme, V.
A1  - Vogts, H.
A1  - Werner, Reinhard F.
T1  - Index theory of one dimensional quantum walks and cellular automata
JF  - Communications in mathematical physics
N2  - If a one-dimensional quantum lattice system is subject to one step of a reversible discrete-time dynamics, it is intuitive that as much "quantum information" as moves into any given block of cells from the left, has to exit that block to the right. For two types of such systems - namely quantum walks and cellular automata - we make this intuition precise by defining an index, a quantity that measures the "net flow of quantum information" through the system. The index supplies a complete characterization of two properties of the discrete dynamics. First, two systems S-1, S-2 can be "pieced together", in the sense that there is a system S which acts like S-1 in one region and like S-2 in some other region, if and only if S-1 and S-2 have the same index. Second, the index labels connected components of such systems: equality of the index is necessary and sufficient for the existence of a continuous deformation of S-1 into S-2. In the case of quantum walks, the index is integer-valued, whereas for cellular automata, it takes values in the group of positive rationals. In both cases, the map S bar right arrow. ind S is a group homomorphism if composition of the discrete dynamics is taken as the group law of the quantum systems. Systems with trivial index are precisely those which can be realized by partitioned unitaries, and the prototypes of systems with non-trivial index are shifts.
Y1  - 2012
U6  - https://doi.org/10.1007/s00220-012-1423-1
SN  - 0010-3616
VL  - 310
IS  - 2
SP  - 419
EP  - 454
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Bodrova, Anna
A1  - Schmidt, Jürgen
A1  - Spahn, Frank
A1  - Brilliantov, Nikolai V.
T1  - Adhesion and collisional release of particles in dense planetary rings
JF  - Icarus : international journal of solar system studies
N2  - We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn's dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn's rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for "Saturn after Cassini-Huygens" Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system.
KW  - Planetary rings
KW  - Saturn, Rings
KW  - Collisional physics
Y1  - 2012
U6  - https://doi.org/10.1016/j.icarus.2011.11.011
SN  - 0019-1035
SN  - 1090-2643
VL  - 218
IS  - 1
SP  - 60
EP  - 68
PB  - Elsevier
CY  - San Diego
ER  - 
TY  - JOUR
A1  - Palyulin, Vladimir V.
A1  - Metzler, Ralf
T1  - How a finite potential barrier decreases the mean first-passage time
JF  - Journal of statistical mechanics: theory and experiment
N2  - We consider the mean first-passage time of a random walker moving in a potential landscape on a finite interval, the starting and end points being at different potentials. From analytical calculations and Monte Carlo simulations we demonstrate that the mean first-passage time for a piecewise linear curve between these two points is minimized by the introduction of a potential barrier. Due to thermal fluctuations, this barrier may be crossed. It turns out that the corresponding expense for this activation is less severe than the gain from an increased slope towards the end point. In particular, the resulting mean first-passage time is shorter than for a linear potential drop between the two points.
KW  - diffusion
Y1  - 2012
U6  - https://doi.org/10.1088/1742-5468/2012/03/L03001
SN  - 1742-5468
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -