22,002 research outputs found
Ideal strengths and bonding properties of PuO2 under tension
We perform a first-principles computational tensile test on PuO based
on density-functional theory within local density approximation (LDA)+\emph{U}
formalism to investigate its structural, mechanical, magnetic, and intrinsic
bonding properties in the four representative directions: [001], [100], [110],
and [111]. The stress-strain relations show that the ideal tensile strengths in
the four directions are 81.2, 80.5, 28.3, and 16.8 GPa at strains of 0.36,
0.36, 0.22, and 0.18, respectively. The [001] and [100] directions are
prominently stronger than other two directions since that more PuO bonds
participate in the pulling process. Through charge and density of states
analysis along the [001] direction, we find that the strong mixed
ionic/covalent character of PuO bond is weakened by tensile strain and
PuO will exhibit an insulator-to-metal transition after tensile stress
exceeds about 79 GPa.Comment: 11 pages, 6 figure
Reversible Embedding to Covers Full of Boundaries
In reversible data embedding, to avoid overflow and underflow problem, before
data embedding, boundary pixels are recorded as side information, which may be
losslessly compressed. The existing algorithms often assume that a natural
image has little boundary pixels so that the size of side information is small.
Accordingly, a relatively high pure payload could be achieved. However, there
actually may exist a lot of boundary pixels in a natural image, implying that,
the size of side information could be very large. Therefore, when to directly
use the existing algorithms, the pure embedding capacity may be not sufficient.
In order to address this problem, in this paper, we present a new and efficient
framework to reversible data embedding in images that have lots of boundary
pixels. The core idea is to losslessly preprocess boundary pixels so that it
can significantly reduce the side information. Experimental results have shown
the superiority and applicability of our work
Flat bidifferential ideals and semihamiltonian PDEs
In this paper we consider a class of semihamiltonian systems characterized by
the existence of a special conservation law.
The density and the current of this conservation law satisfy a second order
system of PDEs which has a natural interpretation in the theory of flat
bifferential ideals. The class of systems we consider contains important
well-known examples of semihamiltonian systems. Other examples, like genus 1
Whitham modulation equations for KdV, are related to this class by a
reciprocal trasformation.Comment: 18 pages. v5: formula (36) corrected; minor change
Theory of localization and resonance phenomena in the quantum kicked rotor
We present an analytic theory of quantum interference and Anderson
localization in the quantum kicked rotor (QKR). The behavior of the system is
known to depend sensitively on the value of its effective Planck's constant
\he. We here show that for rational values of \he/(4\pi)=p/q, it bears
similarity to a disordered metallic ring of circumference and threaded by
an Aharonov-Bohm flux. Building on that correspondence, we obtain quantitative
results for the time--dependent behavior of the QKR kinetic energy, (this is an observable which sensitively probes the system's localization
properties). For values of smaller than the localization length , we
obtain scaling , where is
the quasi--energy level spacing on the ring. This scaling is indicative of a
long time dynamics that is neither localized nor diffusive. For larger values
, the functions saturates (up to exponentially
small corrections ), thus reflecting essentially localized
behavior.Comment: 27 pages, 3 figure
Multiphoton Coincidence Spectroscopy
We extend the analysis of photon coincidence spectroscopy beyond bichromatic
excitation and two-photon coincidence detection to include multichromatic
excitation and multiphoton coincidence detection. Trichromatic excitation and
three-photon coincidence spectroscopy are studied in detail, and we identify an
observable signature of a triple resonance in an atom-cavity system.Comment: 6 page, REVTeXs, 6 Postscript figures. The abstract appeared in the
Proceedings of ACOLS9
Predicting students' emotions using machine learning techniques
Detecting students' real-time emotions has numerous benefits, such as helping lecturers understand their students' learning behaviour and to address problems like confusion and boredom, which undermine students' engagement. One way to detect students' emotions is through their feedback about a lecture. Detecting students' emotions from their feedback, however, is both demanding and time-consuming. For this purpose, we looked at several models that could be used for detecting emotions from students' feedback by training seven different machine learning techniques using real students' feedback. The models with a single emotion performed better than those with multiple emotions. Overall, the best three models were obtained with the CNB classiffier for three emotions: amused, bored and excitement
How do foreign institutional investors enhance firm innovation?
We examine the effect of foreign institutional investors on firm innovation. Using firm-level data across 26 non-U.S. economies between 2000 and 2010, we show that foreign institutional ownership has a positive, causal effect on firm innovation. We further explore three possible underlying mechanisms through which foreign institutions affect firm innovation: Foreign institutions act as active monitors, provide insurance for firm managers against innovation failures, and promote knowledge spillovers from high-innovation economies. Our article sheds new light on the real effects of foreign institutions on firm innovation
A discrete time relativistic Toda lattice
Four integrable symplectic maps approximating two Hamiltonian flows from the
relativistic Toda hierarchy are introduced. They are demostrated to belong to
the same hierarchy and to examplify the general scheme for symplectic maps on
groups equiped with quadratic Poisson brackets. The initial value problem for
the difference equations is solved in terms of a factorization problem in a
group. Interpolating Hamiltonian flows are found for all the maps.Comment: 32 pages, LaTe
Local free-fall temperature of a RN-AdS black hole
We use the global embedding Minkowski space (GEMS) geometries of a
(3+1)-dimensional curved Reissner-Nordstr\"om(RN)-AdS black hole spacetime into
a (5+2)-dimensional flat spacetime to define a proper local temperature, which
remains finite at the event horizon, for freely falling observers outside a
static black hole. Our extended results include the known limiting cases of the
RN, Schwarzschild--AdS, and Schwarzschild black holes.Comment: 18 pages, 11 figures, version to appear in Int. J. Mod. Phys.
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