1,933 research outputs found
Semi-classical Green kernel asymptotics for the Dirac operator
We consider a semi-classical Dirac operator in arbitrary spatial dimensions
with a smooth potential whose partial derivatives of any order are bounded by
suitable constants. We prove that the distribution kernel of the inverse
operator evaluated at two distinct points fulfilling a certain hypothesis can
be represented as the product of an exponentially decaying factor involving an
associated Agmon distance and some amplitude admitting a complete asymptotic
expansion in powers of the semi-classical parameter. Moreover, we find an
explicit formula for the leading term in that expansion.Comment: 46 page
In-plane elastic wave propagation and band-gaps in layered functionally graded phononic crystals
AbstractIn-plane wave propagation in layered phononic crystals composed of functionally graded interlayers arisen from the solid diffusion of homogeneous isotropic materials of the crystal is considered. Wave transmission and band-gaps due to the material gradation and incident wave-field are investigated. A classification of band-gaps in layered phononic crystals is proposed. The classification relies on the analysis of the eigenvalues of the transfer matrix for a unit-cell and the asymptotics derived for the transmission coefficient. Two kinds of band-gaps, where the transmission coefficient decays exponentially with the number of unit-cells are specified. The so-called low transmission pass-bands are introduced in order to identify frequency ranges, in which the transmission is sufficiently low for engineering applications, but it does not tend to zero exponentially as the number of unit-cells tends to infinity. A polyvalent analysis of the geometrical and physical parameters on band-gaps is presented
Wildfire evidence from the Middle and Late Permian Hanxing Coalfield, North China Basin
Earth has a long geological history and palaeo-wildfire is one of the key factors which is responsible for the evolution and extinction of our earth systems. Thus, it is important to establish the history in order to gain more understanding about Permian-Triassic mass extinction. It is also related to the carbon cycle of the earth in which the whole life system depends. The objective of this paper is to evaluate the product of wildfire in terms of distribution and occurrences from the Late Permian North China basin. Hence, fourteen (14) rock samples were collected from a drill core of Hanxing Coalfield of North China basin. The samples were analyzed by macro and micro petrography, scanning electron microscopy (SEM), gas chromatography (GC), and gas chromatography-mass spectrometry (GC-MS) in order to study the evidence of wildfire. Charcoal (inertinite) particles are observed in the samples, which established the occurrences of wildfire during the Upper Middle and Late Permian time in North China. Additionally, high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) were detected in the studied samples which also reinforce the presence of palaeo - wildfire events in the North China basin in Late Permian due to the fact that the these aromatic compounds were formed under high temperatures
Wildfire evidence from the Middle and Late Permian Hanxing Coalfield, North China Basin
Earth has a long geological history and palaeo-wildfire is one of the key factors which is responsible for the evolution and extinction of our earth systems. The most important extinction of our earth systems is the Permian-Triassic mass extinction. The objective of this paper is to evaluate the product of wildfire in terms of distribution and occurrences from the Late Permian North China basin. Fourteen rock samples were collected from a drill core of Hanxing Coalfield of North China basin. The samples were analyzed by macro and micro petrography, Scanning Electron Microscopy (SEM), Gas Chromatography (GC) and Gas Chromatography–Mass Spectrometry (GC-MS) in order to study the evidence of wildfire. Charcoal (inertinite) particles are observed in the samples, which established the occurrences of wildfire during the upper Middle and Late Permian time in North China. Additionally, high-molecular-weight Polycyclic Aromatic Hydrocarbons (PAHs) were detected in the studied samples which also reinforce the presence of palaeo–wildfire events in the North China basin in Late Permian due to the fact that these aromatic compounds were formed under high temperatures
The Sigma 13 (10-14) twin in alpha-Al2O3: A model for a general grain boundary
The atomistic structure and energetics of the Sigma 13 (10-14)[1-210]
symmetrical tilt grain boundary in alpha-Al2O3 are studied by first-principles
calculations based on the local-density-functional theory with a mixed-basis
pseudopotential method. Three configurations, stable with respect to
intergranular cleavage, are identified: one Al-terminated glide-mirror twin
boundary, and two O-terminated twin boundaries, with glide-mirror and two-fold
screw-rotation symmetries, respectively. Their relative energetics as a
function of axial grain separation are described, and the local electronic
structure and bonding are analysed. The Al-terminated variant is predicted to
be the most stable one, confirming previous empirical calculations, but in
contrast with high-resolution transmission electron microscopy observations on
high-purity diffusion-bonded bicrystals, which resulted in an O-terminated
structure.
An explanation of this discrepancy is proposed, based on the different
relative energetics of the internal interfaces with respect to the free
surfaces
Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation
Rate theory of the radiation-induced precipitation in solids is modified with
account of non-equilibrium fluctuations driven by the gas of lattice solitons
(a.k.a. quodons) produced by irradiation. According to quantitative
estimations, a steady-state density of the quodon gas under sufficiently
intense irradiation can be as high as the density of phonon gas. The quodon gas
may be a powerful driver of the chemical reaction rates under irradiation, the
strength of which exponentially increases with irradiation flux and may be
comparable with strength of the phonon gas that exponentially increases with
temperature. The modified rate theory is applied to modelling of copper
precipitation in FeCu binary alloys under electron irradiation. In contrast to
the classical rate theory, which disagrees strongly with experimental data on
all precipitation parameters, the modified rate theory describes quite well
both the evolution of precipitates and the matrix concentration of copper
measured by different methodsComment: V. Dubinko, R. Shapovalov, Theory of a quodon gas. With application
to precipitation kinetics in solids under irradiation. (Springer
International Publishing, Switzerland, 2014
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Travel app shopping: understanding the success factors influencing in-app travel purchase intentions
Purpose - While many benefits are purported by travel app developers, there is scant research on the factors driving behaviour when using travel apps. With the diffusion of innovation theory (DOI) and theory of planned behaviour (TPB) as the guiding theoretical perspectives, this research identifies the factors motivating user attitudes and in-app purchase intentions. The moderating impact of user inertia towards TPB constructs was also explored.
Design/methodology/approach - A total of 500 responses were received via an online-survey fielded from July to October 2021. The data were then analyzed using Partial Least Squares Structural Equation Modelling (PLS-SEM).
Findings - The results indicated that attitudes toward travel app shopping were predominantly determined by perceived relative advantages, compatibility, and complexity. While findings also suggested that in-app purchase intentions are positively influenced by attitudes, communicability, and perceived behavioural control, and are moderated by user inertia.
Originality/Value - A holistic framework integrating theoretical foundations from two disciplines (information systems and psychology) was designed to explain factors motivating user intentions to purchase travel products and services from apps. This research found a missing link in previous studies by showing the indirect role of attitudes that bridges the diffusion of innovation (DOI) and theory of planned behaviour (TPB), and the importance of inertia as a key boundary condition
Metabarcoding read abundances of orchid mycorrhizal fungi are correlated to copy numbers estimated using ddPCR
Environmental Biolog
Efficient convolutional hierarchical autoencoder for human motion prediction
© 2019, The Author(s). Human motion prediction is a challenging problem due to the complicated human body constraints and high-dimensional dynamics. Recent deep learning approaches adopt RNN, CNN or fully connected networks to learn the motion features which do not fully exploit the hierarchical structure of human anatomy. To address this problem, we propose a convolutional hierarchical autoencoder model for motion prediction with a novel encoder which incorporates 1D convolutional layers and hierarchical topology. The new network is more efficient compared to the existing deep learning models with respect to size and speed. We train the generic model on Human3.6M and CMU benchmark and conduct extensive experiments. The qualitative and quantitative results show that our model outperforms the state-of-the-art methods in both short-term prediction and long-term prediction
Theory of bound polarons in oxide compounds
We present a multilateral theoretical study of bound polarons in oxide
compounds MgO and \alpha-Al_2O_3 (corundum). A continuum theory at arbitrary
electron-phonon coupling is used for calculation of the energies of thermal
dissociation, photoionization (optically induced release of an electron (hole)
from the ground self-consistent state), as well as optical absorption to the
non-relaxed excited states. Unlike the case of free strong-coupling polarons,
where the ratio \kappa of the photoionization energy to the thermal
dissociation energy was shown to be always equal to 3, here this ratio depends
on the Froehlich coupling constant \alpha and the screened Coulomb interaction
strength \beta. Reasonable variation of these two parameters has demonstrated
that the magnitude of \kappa remains usually in the narrow interval from 1 to
2.5. This is in agreement with atomistic calculations and experimental data for
hole O^- polarons bound to the cation vacancy in MgO. The thermal dissociation
energy for the ground self-consistent state and the energy of the optically
induced charge transfer process (hops of a hole between O^{2-} ions) have been
calculated using the quantum-chemical method INDO. Results obtained within the
two approaches for hole O polarons bound by the cation vacancies (V^-) in
MgO and by the Mg^{2+} impurity (V_{Mg}) in corundum are compared to
experimental data and to each other. We discuss a surprising closeness of the
results obtained on the basis of independent models and their agreement with
experiment.Comment: 13 pages, 2 figures, 2 tables, E-mail addresses:
[email protected], [email protected]
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