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Anharmonic multi-phonon nonradiative transition: An ab initio calculation approach
Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering. In this article, we provide a revised analysis of Huang’s original nonradiative multi-phonon (NMP) theory with ab initio calculations. First, we confirmed at the first-principles level that Huang’s concise formula gives the same results as the matrix-based formula, and that Huang’s high-temperature formula provides an analytical expression for the coupling constant in Marcus theory. Secondly, we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect. The corrected capture rates for defects in GaN and SiC agree well with experiments
Understanding the Persistence of Caste: A Commentary on Cotterill, Sidanius, Bhardwaj and Kumar (2014)
We contextualise Cotterill, Sidanius, Bhardwaj, and Kumar’s (2014) paper within a broader literature on caste and collective mobilisation. Cotterill and colleagues’ paper represents a fresh and timely attempt to make sense of the persistence of caste from the perspective of Social Dominance Theory. Cotterill and colleagues, however, do not examine caste differences in the endorsement of karma, and take behavioural asymmetry among lower castes for granted. Cotterill and colleagues also adhere to a Varna model of the caste system that arguably is simplistic and benefits the upper castes of Indian society. We caution that emphasising behavioural asymmetry and endorsing the Varna model might further stigmatise lower castes, especially Dalits, and feed into a conformity bias already predominant in caste-related psychological research. We argue that the conceptualisation and operationalisation of Right-Wing Authoritarianism, Social Dominance Orientation and legitimising myths in the Indian context needs to take into account the particular meaning and functions of these constructs in specific intergroup contexts, and for identity positions salient within these contexts. We contend that any examination aimed at better understanding the nature of social hierarchy and oppression within the caste system and Indian society in general remains inconclusive without including a focus on the construction and contestation of social categories and social identities
P2X receptors: epithelial ion channels and regulators of salt and water transport.
When the results from electrophysiological studies of renal epithelial cells are combined with data from in vivo tubule microperfusion experiments and immunohistochemical surveys of the nephron, the accumulated evidence suggests that ATP-gated ion channels, P2X receptors, play a specialized role in the regulation of ion and water movement across the renal tubule and are integral to electrolyte and fluid homeostasis. In this short review, we discuss the concept of P2X receptors as regulators of salt and water salvage pathways, as well as acknowledging their accepted role as ATP-gated ion channels
Jet quenching in shock waves
We study the propagation of an ultrarelativistic light quark jet inside a
shock wave using the holographic principle. The maximum stopping distance and
its dependency on the energy of the jet is obtained
On the Beaming of Gluonic Fields at Strong Coupling
We examine the conditions for beaming of the gluonic field sourced by a heavy
quark in strongly-coupled conformal field theories, using the AdS/CFT
correspondence. Previous works have found that, contrary to naive expectations,
it is possible to set up collimated beams of gluonic radiation despite the
strong coupling. We show that, on the gravity side of the correspondence, this
follows directly (for arbitrary quark motion, and independently of any
approximations) from the fact that the string dual to the quark remains
unexpectedly close to the AdS boundary whenever the quark moves
ultra-relativistically. We also work out the validity conditions for a related
approximation scheme that proposed to explain the beaming effect though the
formation of shock waves in the bulk fields emitted by the string. We find that
these conditions are fulfilled in the case of ultra-relativistic uniform
circular motion that motivated the proposal, but unfortunately do not hold for
much more general quark trajectories.Comment: 1+33 pages, 2 figure
The Gluonic Field of a Heavy Quark in Conformal Field Theories at Strong Coupling
We determine the gluonic field configuration sourced by a heavy quark
undergoing arbitrary motion in N=4 super-Yang-Mills at strong coupling and
large number of colors. More specifically, we compute the expectation value of
the operator tr[F^2+...] in the presence of such a quark, by means of the
AdS/CFT correspondence. Our results for this observable show that signals
propagate without temporal broadening, just as was found for the expectation
value of the energy density in recent work by Hatta et al. We attempt to shed
some additional light on the origin of this feature, and propose a different
interpretation for its physical significance. As an application of our general
results, we examine when the quark undergoes oscillatory motion,
uniform circular motion, and uniform acceleration. Via the AdS/CFT
correspondence, all of our results are pertinent to any conformal field theory
in 3+1 dimensions with a dual gravity formulation.Comment: 1+38 pages, 16 eps figures; v2: completed affiliation; v3: corrected
typo, version to appear in JHE
Refractive index in holographic superconductors
With the probe limit, we investigate the behavior of the electric
permittivity and effective magnetic permeability and related optical properties
in the s-wave holographic superconductors. In particular, our result shows that
unlike the strong coupled systems which admit a gravity dual of charged black
holes in the bulk, the electric permittivity and effective magnetic
permeability are unable to conspire to bring about the negative
Depine-Lakhtakia index at low frequencies, which implies that the negative
phase velocity does not appear in the holographic superconductors under such a
situation.Comment: JHEP style, 1+15 pages, 11 figures, version to appear in JHE
Alkylated-C-60 based soft materials: regulation of self-assembly and optoelectronic properties by chain branching
Derivatization of fullerene (C60) with branched aliphatic chains softens C60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84 °C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 ± 0.1%) in comparison with another compound, 10 (PCE: 0.5 ± 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices
Holographic Phase Transition to Topological Dyons
The dynamical stability of a Julia-Zee solution in the AdS background in a
four dimensional Einstein-Yang-Mills-Higgs theory is studied. We find that the
model with a vanishing scalar field develops a non-zero value for the field at
a certain critical temperature which corresponds to a topological dyon in the
bulk and a topological phase transition at the boundary.Comment: 18 pages, 2 figures, 2 tables, sections 2 and 4 are shortened, an
error in the last part of section 5 is corrected and equations are modified.
This version to be published in JHE
Collaborative Layer-wise Discriminative Learning in Deep Neural Networks
Intermediate features at different layers of a deep neural network are known
to be discriminative for visual patterns of different complexities. However,
most existing works ignore such cross-layer heterogeneities when classifying
samples of different complexities. For example, if a training sample has
already been correctly classified at a specific layer with high confidence, we
argue that it is unnecessary to enforce rest layers to classify this sample
correctly and a better strategy is to encourage those layers to focus on other
samples.
In this paper, we propose a layer-wise discriminative learning method to
enhance the discriminative capability of a deep network by allowing its layers
to work collaboratively for classification. Towards this target, we introduce
multiple classifiers on top of multiple layers. Each classifier not only tries
to correctly classify the features from its input layer, but also coordinates
with other classifiers to jointly maximize the final classification
performance. Guided by the other companion classifiers, each classifier learns
to concentrate on certain training examples and boosts the overall performance.
Allowing for end-to-end training, our method can be conveniently embedded into
state-of-the-art deep networks. Experiments with multiple popular deep
networks, including Network in Network, GoogLeNet and VGGNet, on scale-various
object classification benchmarks, including CIFAR100, MNIST and ImageNet, and
scene classification benchmarks, including MIT67, SUN397 and Places205,
demonstrate the effectiveness of our method. In addition, we also analyze the
relationship between the proposed method and classical conditional random
fields models.Comment: To appear in ECCV 2016. Maybe subject to minor changes before
camera-ready versio
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