192 research outputs found
Geometric Universality of Currents
We discuss a non-equilibrium statistical system on a graph or network.
Identical particles are injected, interact with each other, traverse, and leave
the graph in a stochastic manner described in terms of Poisson rates, possibly
dependent on time and instantaneous occupation numbers at the nodes of the
graph. We show that under the assumption of constancy of the relative rates,
the system demonstrates a profound statistical symmetry, resulting in geometric
universality of the statistics of the particle currents. This phenomenon
applies broadly to many man-made and natural open stochastic systems, such as
queuing of packages over the internet, transport of electrons and
quasi-particles in mesoscopic systems, and chains of reactions in bio-chemical
networks. We illustrate the utility of our general approach using two enabling
examples from the two latter disciplines.Comment: 15 pages, 5 figure
Anomalous Hall effect in a two-dimensional electron gas
The anomalous Hall effect in a magnetic two-dimensional electron gas with
Rashba spin-orbit coupling is studied within the Kubo-Streda formalism in the
presence of pointlike potential impurities. We find that all contributions to
the anomalous Hall conductivity vanish to leading order in disorder strength
when both chiral subbands are occupied. In the situation that only the majority
subband is occupied, all terms are finite in the weak scattering limit and the
total anomalous Hall conductivity is dominated by skew scattering. We compare
our results to previous treatments and resolve some of the discrepancies
present in the literature.Comment: 11 pages, 5 figure
The Campanian Ignimbrite and Codola tephra layers: Two temporal/stratigraphic markers for the Early Upper Palaeolithic in southern Italy and eastern Europe
Tephra layers from archaeological sites in southern Italy and eastern Europe stratigraphically associated with
cultural levels containing Early Upper Palaeolithic industry were analysed. The results confirm the
occurrence of the Campanian Ignimbrite tephra (CI; ca. 40 cal ka BP) at Castelcivita Cave (southern Italy),
Temnata Cave (Bulgaria) and in the Kostenki–Borshchevo area of the Russian Plain. This tephra, originated
from the largest eruption of the Phlegrean Field caldera, represents the widest volcanic deposit and one of
the most important temporal/stratigraphic markers of western Eurasia. At Paglicci Cave and lesser sites in the
Apulia region we recognise a chemically and texturally different tephra, which lithologically, chronologically
and chemically matches the physical and chemical characteristics of the Plinian eruption of Codola; a poorly
known Late Pleistocene explosive event from the Neapolitan volcanoes, likely Somma–Vesuvius. For this
latter, we propose a preliminary age estimate of ca. 33 cal ka BP and a correlation to the widespread C-10
marine tephra of the central Mediterranean. The stratigraphic position of both CI and Codola tephra layers at
Castelcivita and Paglicci help date the first and the last documented appearance of Early Upper Palaeolithic
industries of southern Italy to ca. 41–40 and 33 cal ka BP, respectively, or between two interstadial
oscillations of the Monticchio pollen record – to which the CI and Codola tephras are physically correlated –
corresponding to the Greenland interstadials 10–9 and 5. In eastern Europe, the stratigraphic and
chronometric data seem to indicate an earlier appearance of the Early Upper Palaeolithic industries, which
would predate of two millennia at least the overlying CI tephra. The tephrostratigraphic correlation indicates
that in both regions the innovations connected with the so-called Early Upper Palaeolithic – encompassing
subsistence strategy and stone tool technology – appeared and evolved during one of the most unstable
climatic phases of the Last Glacial period. On this basis, the marked environmental unpredictability
characterising this time-span is seen as a potential ecological factor involved in the cultural changes
observed
Restrictions on modeling spin injection by resistor networks
Because of the technical difficulties of solving spin transport equations in
inhomogeneous systems, different resistor networks are widely applied for
modeling spin transport. By comparing an analytical solution for spin injection
across a ferromagnet - paramagnet junction with a resistor model approach, its
essential limitations stemming from inhomogeneous spin populations are
clarified.Comment: To be published in a special issue of Semicond. Sci. Technol., Guest
editor Prof. G. Landweh
Symmetry adapted finite-cluster solver for quantum Heisenberg model in two-dimensions: a real-space renormalization approach
We present a quantum cluster solver for spin- Heisenberg model on a
two-dimensional lattice. The formalism is based on the real-space
renormalization procedure and uses the lattice point group-theoretical analysis
and nonabelian SU(2) spin symmetry technique. The exact diagonalization
procedure is used twice at each renormalization group step. The method is
applied to the spin-half antiferromagnet on a square lattice and a calculation
of local observables is demonstrated. A symmetry based truncation procedure is
suggested and verified numerically.Comment: willm appear in J. Phys.
Spin-Hall effect and spin-Coulomb drag in doped semiconductors
In this review, we describe in detail two important spin-transport phenomena:
the extrinsic spin-Hall effect (coming from spin-orbit interactions between
electrons and impurities) and the spin-Coulomb drag. The interplay of these two
phenomena is analyzed. In particular, we discuss the influence of scattering
between electrons with opposite spins on the spin current and the spin
accumulation produced by the spin-Hall effect. Future challenges and open
questions are briefly discussed.Comment: Topical revie
Generally covariant state-dependent diffusion
Statistical invariance of Wiener increments under SO(n) rotations provides a
notion of gauge transformation of state-dependent Brownian motion. We show that
the stochastic dynamics of non gauge-invariant systems is not unambiguously
defined. They typically do not relax to equilibrium steady states even in the
absence of extenal forces. Assuming both coordinate covariance and gauge
invariance, we derive a second-order Langevin equation with state-dependent
diffusion matrix and vanishing environmental forces. It differs from previous
proposals but nevertheless entails the Einstein relation, a Maxwellian
conditional steady state for the velocities, and the equipartition theorem. The
over-damping limit leads to a stochastic differential equation in state space
that cannot be interpreted as a pure differential (Ito, Stratonovich or else).
At odds with the latter interpretations, the corresponding Fokker-Planck
equation admits an equilibrium steady state; a detailed comparison with other
theories of state-dependent diffusion is carried out. We propose this as a
theory of diffusion in a heat bath with varying temperature. Besides
equilibrium, a crucial experimental signature is the non-uniform steady spatial
distribution.Comment: 24 page
Preparation and Study of Sulfonated Co-Polynaphthoyleneimide Proton-Exchange Membrane for a H2/Air Fuel Cell
The sulfonated polynaphthoyleneimide polymer (co-PNIS70/30) was prepared by copolymerization
of 4,40
-diaminodiphenyl ether-2,20
-disulfonic acid (ODAS) and 4,4’-methylenebisanthranilic acid
(MDAC) with ODAS/MDAC molar ratio 0.7/0.3. High molecular weight co-PNIS70/30 polymers
were synthesized either in phenol or in DMSO by catalytic polyheterocyclization in the presence of
benzoic acid and triethylamine. The titration reveals the ion-exchange capacity of the polymer equal
to 2.13 meq/g. The membrane films were prepared by casting polymer solution. Conductivities of
the polymer films were determined using both in- and through-plane geometries and reached ~96
and ~60 mS/cm, respectively. The anisotropy of the conductivity is ascribed to high hydration of the
surface layer compared to the bulk. SFG NMR diffusometry shows that, in the temperature range from
213 to 353 K, the 1H self-diffusion coefficient of the co-PNIS70/30 membrane is about one third of the
diffusion coefficient of Nafion® at the same humidity. However, temperature dependences of proton
conductivities of Nafion® and of co-PNIS70/30 membranes are nearly identical. Membrane–electrode
assemblies (MEAs) based on co-PNIS70/30 were fabricated by different procedures. The optimal MEAs
with co-PNIS70/30 membranes are characterized by maximum output power of ~370 mW/cm² at
80 °C. It allows considering sulfonated co-PNIS70/30 polynaphthoyleneimides membrane attractive
for practical applications
ВОЗМОЖНОСТИ КОМПЬЮТЕРНОЙ И МАГНИТНО-РЕЗОНАНСНОЙ ТОМОГРАФИИ В СУДЕБНО-МЕДИЦИНСКОЙ ЭКСПЕРТИЗЕ МЕХАНИЧЕСКОЙ ТРАВМЫ И СКОРОПОСТИЖНОЙ СМЕРТИ (ОБЗОР ЛИТЕРАТУРЫ)
ABSTRACT. The review analyzes the possibility of multislice computed tomography (MSCT) and magnetic resonance imaging (MRI) use in the forensic examination of corpses of adults. We present the critical analysis of literature on post-mortem imaging in terms of forensic thanatology. The review is based on basic Internet resources: Scientific Electronic Library (elibrary), Scopus, PubMed. The review includes articles that discuss both advantages and limitations of post-mortem MSCT and MRI imaging in forensic examination of the corpse.Through studying the available literature, the authors attempted to answer two questions: 1) which method was more suitable for the purposes of forensic examination of the corpse - MSCT or MRI; 2) whether the virtual autopsy replaced the traditional autopsy in the near future?Conclusion: comprehensive study of the corpse often requires both imaging methods; in cases of death under mechanical damage, MSCT exceeds the range of possibilities of MRI; today, virtual autopsy cannot completely replace traditional autopsy in forensic science, since there are no convincing evidence-based comparative studies, as well as the legal framework of the method. РЕЗЮМЕ. В обзоре проанализирована возможность использования мультиспиральной компьютерной томографии (МСКТ) и магнитно-резонансной томографии (МРТ) в судебно-медицинской экспертизе трупов взрослых лиц. Представлен критический анализ литературы по проблеме посмертной визуализации с точки зрения судебно-медицинской танатологии. При подготовке обзора были использованы основные интернет-ресурсы: научная электронная библиотека (elibrary), Scopus, PubMed. В обзор включены статьи, в которых обсуждались как преимущества, так и ограничения посмертной МСКТ- и МРТ-визуализации в судебно-медицинской экспертизе трупа.В ходе анализа доступной литературы авторы попытались ответить на два вопроса: 1) какой лучевой метод, МСКТ или МРТ, в большей степени подходит для целей судебно-медицинской экспертизы трупа; 2) сможет ли виртуальная аутопсия заменить традиционное вскрытие в ближайшей перспективе?Выводы: для всестороннего исследования трупа часто требуются оба метода визуализации; в случаях смерти от механических повреждений диапазон возможностей МСКТ превышает МРТ; в настоящее время виртуальная аутопсия не может полностью заменить традиционное вскрытие в судебно-медицинской экспертизе, поскольку отсутствуют убедительные, основанные на принципах доказательной медицины, сравнительные исследования, а также правовая база использования метода.
Fast noise in the Landau-Zener theory
We study the influence of a fast noise on Landau-Zener transitions. We
demonstrate that a fast colored noise much weaker than the conventional white
noise can produce transitions itself or can change substantially the
Landau-Zener transition probabilities. In the limit of fast colored or strong
white noise we derive asymptotically exact formulae for transition
probabilities and study the time evolution of a spin coupled to the noise and a
sweeping magnetic field.Comment: 28 pages, 5 figure
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