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Coherent phenomena in mesoscopic systems
A mesoscopic system of cylindrical geometry made of a metal or a
semiconductor is shown to exhibit features of a quantum coherent state. It is
shown that magnetostatic interaction can play an important role in mesoscopic
systems leading to an ordered ground state. The temperature below the
system exhibits long-range order is determined. The self-consistent mean field
approximation of the magnetostatic interaction is performed giving the
effective Hamiltonian from which the self-sustaining currents can be obtained.
The relation of quantum coherent state in mesoscopic cylinders to other
coherent systems like superconductors is discussed.Comment: REVTeX, 4 figures, in print in Supercond. Sci. Techno
On Abelian Multi-Chern-Simons Field Theories
In this paper a class of multi-Chern-Simons field theories which is relevant
to the statistical mechanics of polymer systems is investigated. Motivated by
the problems which one encounters in the treatment of these theories, a general
procedure is presented to eliminate the Chern-Simons fields from their action.
In this way it has been possible to derive an expression of the partition
function of topologically linked polymers which depends explicitly on the
topological numbers and does not have intractable nonlocal terms as it happened
in previous approaches. The new formulation of multi-Chern-Simons field
theories is then used to remove and clarify some inconsistencies and
ambiguities which apparently affect field theoretical models of topologically
linked polymers. Finally, the limit of disentangled polymers is discussed.Comment: 18 pages, plain LaTe
Using failed supernovae to constrain the Galactic r-process element production
Rapid neutron capture process (r-process) elements have been detected in a
large fraction of metal-poor halo stars, with abundances relative to iron (Fe)
that vary by over two orders of magnitude. This scatter is reduced to less than
a factor of 3 in younger Galactic disc stars. The large scatter of r-process
elements in the early Galaxy suggests that the r-process is made by rare
events, like compact binary mergers and rare sub-classes of supernovae.
Although being rare, neutron star mergers alone have difficulties to explain
the observed enhancement of r-process elements in the lowest metallicity stars
compared to Fe. The supernovae producing the two neutron stars already provide
a substantial Fe abundance where the r-process ejecta from the merger would be
injected. In this work we investigate another complementary scenario, where the
r-process occurs in neutron star-black hole mergers in addition to neutron star
mergers. Neutron star-black hole mergers would eject similar amounts of
r-process matter as neutron star mergers, but only the neutron star progenitor
would have produced Fe. Furthermore, a reduced efficiency of Fe production from
single stars significantly alters the age-metallicity relation, which shifts
the onset of r-process production to lower metallicities. We use the
high-resolution [(20 pc)3/cell] inhomogeneous chemical evolution tool `ICE' to
study the outcomes of these effects. In our simulations, an adequate
combination of neutron star mergers and neutron star-black hole mergers
qualitatively reproduces the observed r-process abundances in the Galaxy
Microbiology and atmospheric processes: Biological, physical and chemical characterization of aerosol particles
The interest in bioaerosols has traditionally been linked to health hazards for humans, animals and plants. However, several components of bioaerosols exhibit physical properties of great significance for cloud processes, such as ice nucleation and cloud condensation. To gain a better understanding of their influence on climate, it is therefore important to determine the composition, concentration, seasonal fluctuation, regional diversity and evolution of bioaerosols. In this paper, we will review briefly the existing techniques for detection, quantification, physical and chemical analysis of biological particles, attempting to bridge physical, chemical and biological methods for analysis of biological particles and integrate them with aerosol sampling techniques. We will also explore some emerging spectroscopy techniques for bulk and single-particle analysis that have potential for in-situ physical and chemical analysis. Lastly, we will outline open questions and further desired capabilities (e. g., in-situ, sensitive, both broad and selective, on-line, time-resolved, rapid, versatile, cost-effective techniques) required prior to comprehensive understanding of chemical and physical characterization of bioaerosols
Mental Activity as the Bridge between Neural Biomarkers and Symptoms of Psychiatric Illness
The Research Domain Criteria (RDoC) initiative challenges researchers to build neurobehavioral models of psychiatric illness with the hope that such models identify better targets that will yield more effective treatment. However, a guide for building such models was not provided and symptom heterogeneity within Diagnostic Statistical Manual categories has hampered progress in identifying endophenotypes that underlie mental illness. We propose that the best chance to discover viable biomarkers and treatment targets for psychiatric illness is to investigate a triangle of relationships: severity of a specific psychiatric symptom that correlates to mental activity that correlates to a neural activity signature. We propose that this is the minimal model complexity required to advance the field of psychiatry. With an understanding of how neural activity relates to the experience of the patient, a genuine understanding for how treatment imparts its therapeutic effect is possible. After the discovery of this three-fold relationship, causal testing is required in which the neural activity pattern is directly enhanced or suppressed to provide causal, instead of just correlational, evidence for the biomarker. We suggest using non-invasive brain stimulation (NIBS) as these techniques provide tools to precisely manipulate spatial and temporal activity patterns. We detail how this approach enabled the discovery of two orthogonal electroencephalography (EEG) activity patterns associated with anhedonia and anxiosomatic symptoms in depression that can serve as future treatment targets. Altogether, we propose a systematic approach for building neurobehavioral models for dimensional psychiatry
Dynamics of epileptiform activity in mouse hippocampal slices
Increase of the extracellular K + concentration mediates seizure-like synchronized activities in vitro and was proposed to be one of the main factors underlying epileptogenesis in some types of seizures in vivo. While underlying biophysical mechanisms clearly involve cell depolarization and overall increase in excitability, it remains unknown what qualitative changes of the spatio-temporal network dynamics occur after extracellular K + increase. In this study, we used multi-electrode recordings from mouse hippocampal slices to explore changes of the network activity during progressive increase of the extracellular K + concentration. Our analysis revealed complex spatio-temporal evolution of epileptiform activity and demonstrated a sequence of state transitions from relatively simple network bursts into complex bursting, with multiple synchronized events within each burst. We describe these transitions as qualitative changes of the state attractors, constructed from experimental data, mediated by elevation of extracellular K + concentration
Stability of Chiral Luttinger Liquids and Abelian Quantum Hall States.
A criterion is given for topological stability of Abelian quantum Hall
states, and of Luttinger liquids at the boundaries between such states; this
suggests a selection rule on states in the quantum Hall hierarchy theory. The
linear response of Luttinger liquids to electromagnetic fields is described:
the Hall conductance is quantized, irrespective of whether edge modes propagate
in different directions.Comment: 12 pages, LaTeX (RevTeX 3.0
Single-Particle Green Functions in Exactly Solvable Models of Bose and Fermi Liquids
Based on a class of exactly solvable models of interacting bose and fermi
liquids, we compute the single-particle propagators of these systems exactly
for all wavelengths and energies and in any number of spatial dimensions. The
field operators are expressed in terms of bose fields that correspond to
displacements of the condensate in the bose case and displacements of the fermi
sea in the fermi case.
Unlike some of the previous attempts, the present attempt reduces the answer
for the spectral function in any dimension in both fermi and bose systems to
quadratures.
It is shown that when only the lowest order sea-displacement terms are
included, the random phase approximation in its many guises is recovered in the
fermi case, and Bogoliubov's theory in the bose case. The momentum distribution
is evaluated using two different approaches, exact diagonalisation and the
equation of motion approach.
The novelty being of course, the exact computation of single-particle
properties including short wavelength behaviour.Comment: Latest version to be published in Phys. Rev. B. enlarged to around 40
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