20,653 research outputs found
Superconductivity and Lattice Instability in Compressed Lithium from Fermi Surface Hot Spots
The highest superconducting temperature T observed in any elemental metal
(Li with T ~ 20 K at pressure P ~ 40 GPa) is shown to arise from critical
(formally divergent) electron-phonon coupling to the transverse T phonon
branch along intersections of Kohn anomaly surfaces with the Fermi surface.
First principles linear response calculations of the phonon spectrum and
spectral function reveal (harmonic) instability already at
25 GPa. Our results imply that the fcc phase is anharmonically stabilized in
the 25-38 GPa range.Comment: 4 pages, 3 embedded figure
Potential and efficiency of statistical learning closely intertwined with individuals’ executive functions: A mathematical modeling study
Statistical learning (SL) is essential in enabling humans to extract probabilistic regularities from the world. The ability to accomplish ultimate learning performance with training (i.e., the potential of learning) has been known to be dissociated with performance improvement per amount of learning time (i.e., the efficiency of learning). Here, we quantified the potential and efficiency of SL separately through mathematical modeling and scrutinized how they were affected by various executive functions. Our results showed that a high potential of SL was associated with poor inhibition and good visuo-spatial working memory, whereas high efficiency of SL was closely related to good inhibition and good set-shifting. We unveiled the distinct characteristics of SL in relation to potential and efficiency and their interaction with executive functions
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Perceptual image quality assessment for various viewing conditions and display systems
From complete darkness to direct sunlight, real-world dis-
plays operate in various viewing conditions often resulting in a
non-optimal viewing experience. Most existing Image Quality
Assessment (IQA) methods, however, assume ideal environments
and displays, and thus cannot be used when viewing conditions
differ from the standard. In this paper, we investigate the influence
of ambient illumination level and display luminance on human
perception of image quality. We conduct a psychophysical study
to collect a novel dataset of over 10000 image quality preference
judgments performed in illumination conditions ranging from 0 lux
to 20000 lux. We also propose a perceptual IQA framework that
allows most existing image quality metrics (IQM) to accurately
predict image quality for a wide range of illumination conditions
and display parameters 1 . Our analysis demonstrates strong cor-
relation between human IQA and the predictions of our proposed
framework combined with multiple prominent IQMs and across a
wide range of luminance values
Dynamical Compactification and Inflation in Einstein-Yang-Mills Theory with Higher Derivative Coupling
We study cosmology of the Einstein-Yang-Mills theory in ten dimensions with a
quartic term in the Yang-Mills field strength. We obtain analytically a class
of cosmological solutions in which the extra dimensions are static and the
scale factor of the four-dimensional Friedmann-Lemaitre-Robertson-Walker metric
is an exponential function of time. This means that the model can explain
inflation. Then we look for solutions that describe dynamical compactification
of the extra dimensions. The effective cosmological constant in the
four-dimensional universe is determined from the gravitational coupling,
ten-dimensional cosmological constant, gauge coupling and higher derivative
coupling. By numerical integration, the solution with is found to
behave as a matter-dominated universe which asymptotically approaches flat
space-time, while the solution with a non-vanishing approaches de
Sitter space-time in the asymptotic future.Comment: 30 pages, 7 figure
Influence of gravitational field on quantum-nondemolition measurement of atomic momentum in the dispersive Jaynes-Cummings model
We present a theoretical scheme based on su(2) algebra to investigate the
influence of homogeneous gravitational field on the quantum nondemolition
measurement of atomic momentum in dispersive Jaynes-Cummings model. In the
dispersive Jaynes-Cummings model, when detuning is large and the atomic motion
is in a propagating light wave, we consider a two-level atom with quantized
cavity-field in the presence of a homogeneous gravitational field. We derive an
effective Hamiltonian describing the dispersive atom-field interaction in the
presence of gravitational field. We can see gravitational influence both on the
momentum filter and momentum distribution. Moreover, gravitational field
decreases both tooth spacing of momentum and the width of teeth of momentum.Comment: 21 pages, 8 figure
The Mre11-Rad50-Nbs1 complex mediates activation of TopBP1 by ATM
The activation of ATR-ATRIP in response to double-stranded DNA breaks (DSBs) depends upon ATM in human cells and Xenopus egg extracts. One important aspect of this dependency involves regulation of TopBP1 by ATM. In Xenopus egg extracts, ATM associates with TopBP1 and thereupon phosphorylates it on S1131. This phosphorylation enhances the capacity of TopBP1 to activate the ATR-ATRIP complex. We show that TopBP1 also interacts with the Mre11-Rad50-Nbs1 (MRN) complex in egg extracts in a checkpoint-regulated manner. This interaction involves the Nbs1 subunit of the complex. ATM can no longer interact with TopBP1 in Nbs1-depleted egg extracts, which suggests that the MRN complex helps to bridge ATM and TopBP1 together. The association between TopBP1 and Nbs1 involves the first pair of BRCT repeats in TopBP1. In addition, the two tandem BRCT repeats of Nbs1 are required for this binding. Functional studies with mutated forms of TopBP1 and Nbs1 suggested that the BRCT-dependent association of these proteins is critical for a normal checkpoint response to DSBs. These findings suggest that the MRN complex is a crucial mediator in the process whereby ATM promotes the TopBP1-dependent activation of ATR-ATRIP in response to DSBs
Transfverter: Imbuing Transformer-Like Properties in an Interlink Converter for Robust Control of a Hybrid AC–DC Microgrid
In a hybrid ac-dc microgrid, stiff voltage sources may appear in either the dc or ac subgrids which gives rise to multiple operation modes as power dispatch changes. This creates a challenge for designing the interlink converter between the ac and dc subgrids since the different modes require different interlink controls. To solve this problem, this paper proposes the concept of a transfverter inspired by how transformers link ac grids. Like a transformer, a transfverter can react to the presence of stiff voltage sources on either the dc or ac side and reflect the “stiffness” and voltage stabilizing capability to the other side. A back-to-back converter with droop control is used as the underlying technology to implement this concept. A novel optimization method called model bank synthesis is proposed to find control parameters for the interlink converter that offer the best controller performance across the different microgrid modes without requiring mode-changing of the controller. The effectiveness of the proposed solution is validated through both simulation and experiments
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