115,403 research outputs found
Low-Temperature Thermal Conductivity of Superconductors With Gap Nodes
We report a detailed analytic and numerical study of electronic thermal
conductivity in d-wave superconductors. We compare theory of the cross over at
low temperatures from T-dependence to T^3-dependence for increasing temperature
with recent experiments on YBCO in zero magnetic field for temperatures from
0.04K to 0.4K by Hill et al., Phys. Rev. Lett. 92, 027001 (2004). Transport
theory, including impurity scattering and inelastic scattering within strong
coupling superconductivity, can consistently fit the temperature dependence of
the data in the lower half of the temperature regime. We discuss the conditions
under which we expect power-law dependences over wide temperature intervals.Comment: 4 pages, 3 figure
On Horizontal and Vertical Separation in Hierarchical Text Classification
Hierarchy is a common and effective way of organizing data and representing
their relationships at different levels of abstraction. However, hierarchical
data dependencies cause difficulties in the estimation of "separable" models
that can distinguish between the entities in the hierarchy. Extracting
separable models of hierarchical entities requires us to take their relative
position into account and to consider the different types of dependencies in
the hierarchy. In this paper, we present an investigation of the effect of
separability in text-based entity classification and argue that in hierarchical
classification, a separation property should be established between entities
not only in the same layer, but also in different layers. Our main findings are
the followings. First, we analyse the importance of separability on the data
representation in the task of classification and based on that, we introduce a
"Strong Separation Principle" for optimizing expected effectiveness of
classifiers decision based on separation property. Second, we present
Hierarchical Significant Words Language Models (HSWLM) which capture all, and
only, the essential features of hierarchical entities according to their
relative position in the hierarchy resulting in horizontally and vertically
separable models. Third, we validate our claims on real-world data and
demonstrate that how HSWLM improves the accuracy of classification and how it
provides transferable models over time. Although discussions in this paper
focus on the classification problem, the models are applicable to any
information access tasks on data that has, or can be mapped to, a hierarchical
structure.Comment: Full paper (10 pages) accepted for publication in proceedings of ACM
SIGIR International Conference on the Theory of Information Retrieval
(ICTIR'16
Ferromagnetic resonance study of polycrystalline Fe_{1-x}V_x alloy thin films
Ferromagnetic resonance has been used to study the magnetic properties and
magnetization dynamics of polycrystalline FeV alloy films with
. Films were produced by co-sputtering from separate Fe and V
targets, leading to a composition gradient across a Si substrate. FMR studies
were conducted at room temperature with a broadband coplanar waveguide at
frequencies up to 50 GHz using the flip-chip method. The effective
demagnetization field and the Gilbert damping
parameter have been determined as a function of V concentration. The
results are compared to those of epitaxial FeV films
Entanglement between two fermionic atoms inside a cylindrical harmonic trap
We investigate quantum entanglement between two (spin-1/2) fermions inside a
cylindrical harmonic trap, making use of the von Neumann entropy for the
reduced single particle density matrix as the pure state entanglement measure.
We explore the dependence of pair entanglement on the geometry and strength of
the trap and on the strength of the pairing interaction over the complete range
of the effective BCS to BEC crossover. Our result elucidates an interesting
connection between our model system of two fermions and that of two interacting
bosons.Comment: to appear in PR
Probing and modelling the localized self-mixing in a GaN/AlGaN field-effect terahertz detector
In a GaN/AlGaN field-effect terahertz detector, the directional photocurrent
is mapped in the two-dimensional space of the gate voltage and the drain/source
bias. It is found that not only the magnitude, but also the polarity, of the
photocurrent can be tuned. A quasistatic self-mixing model taking into account
the localized terahertz field provides a quantitative description of the
detector characteristics. Strongly localized self-mixing is confirmed. It is
therefore important to engineer the spatial distribution of the terahertz field
and its coupling to the field-effect channel on the sub-micron scale.Comment: 12 pages, 4 figures, submitted to AP
Dynamics of coherence, localization and excitation transfer in disordered nanorings
Self-assembled supramolecular aggregates are excellent candidates for the
design of efficient excitation transport devices. Both artificially prepared
and natural photosynthetic aggregates in plants and bacteria present an
important degree of disorder that is supposed to hinder excitation transport.
Besides, molecular excitations couple to nuclear motion affecting excitation
transport in a variety of ways. We present an exhaustive study of exciton
dynamics in disordered nanorings with long-range interactions under the
influence of a phonon bath and take the LH2 system of purple bacteria as a
model. Nuclear motion is explicitly taken into account by employing the Davydov
ansatz description of the polaron and quantum dynamics are obtained using a
time-dependent variational method. We reveal an optimal exciton-phonon coupling
that suppresses disorder-induced localization and facilitate excitation
de-trapping. This excitation transfer enhancement, mediated by environmental
phonons, is attributed to energy relaxation toward extended, low-energy
excitons provided by the precise LH2 geometry with anti-parallel dipoles and
long-range interactions. An analysis of localization and spectral statistics is
followed by dynamical measures of coherence and localization, transfer
efficiency and superradiance. Linear absorption, 2D photon-echo spectra and
diffusion measures of the exciton are examined to monitor the diffusive
behavior as a function of the strengths of disorder and exciton-phonon
coupling.Comment: 18 pages, 13 figure
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