954 research outputs found
A Coarse-grained model for diffusion in zeolites based on clustering of short MD trajectories
Zeolites form a class of microporous aluminosilicates of great interest due to their multifarious applications in industry and everyday life. Their porous structure allows small molecules to be adsorbed and to diffuse inside crystals, and depending on the zeolite type and on the diffusant species a variety of behaviours is possible. Molecular Dynamics is now widely used in order to understand the microscopic mechanisms of adsorption and diffusion occurring within these materials as well as in MOFs and ZIFs. A major drawback of MD for this kind of systems is its high computational cost, so that coarse-grained methods, speeding up simulations without losing
the essential features of dynamics, are valuable tools for exploring the behaviour of guest molecules on time and space scales hardly, if at all, reachable with ordinary MD.
The first step in our proposed method is the clustering of MD trajectories to obtain a discretized version of the motion of adsorbed molecules within the zeolite. Each pore in the aluminosilicate is partitioned in a number of regions and each point in the original trajectory is mapped to the proper region based on a distance criterion. The regions correspond roughly to the main basins in the
potential energy surface (PES)
Fault Sneaking Attack: a Stealthy Framework for Misleading Deep Neural Networks
Despite the great achievements of deep neural networks (DNNs), the
vulnerability of state-of-the-art DNNs raises security concerns of DNNs in many
application domains requiring high reliability.We propose the fault sneaking
attack on DNNs, where the adversary aims to misclassify certain input images
into any target labels by modifying the DNN parameters. We apply ADMM
(alternating direction method of multipliers) for solving the optimization
problem of the fault sneaking attack with two constraints: 1) the
classification of the other images should be unchanged and 2) the parameter
modifications should be minimized. Specifically, the first constraint requires
us not only to inject designated faults (misclassifications), but also to hide
the faults for stealthy or sneaking considerations by maintaining model
accuracy. The second constraint requires us to minimize the parameter
modifications (using L0 norm to measure the number of modifications and L2 norm
to measure the magnitude of modifications). Comprehensive experimental
evaluation demonstrates that the proposed framework can inject multiple
sneaking faults without losing the overall test accuracy performance.Comment: Accepted by the 56th Design Automation Conference (DAC 2019
Rogue wave formation scenarios for the focusing nonlinear Schr\"odinger equation with parabolic-profile initial data on a compact support
We study the (1+1) focusing nonlinear Schroedinger (NLS) equation for an
initial condition with concave parabolic profile on a compact support and phase
depending quadratically on the spatial coordinate. In the absence of
dispersion, using the natural class of self-similar solutions of the resulting
elliptic system, we generalise a result by Talanov, Guervich and Shvartsburg,
finding a criterion on the chirp and modulus coefficients at time equal zero to
determine whether the dispersionless solution features asymptotic relaxation or
a blow-up at fine time, providing an explicit formula for the time of
catastrophe. In the presence of dispersion, we numerically show that the same
criterion determines, even beyond the semi-classical regime, whether the
solution relaxes or develops a higher order rogue wave, whose amplitude can be
several multiples of the height of the initial parabola. In the latter case,
for small dispersion, the time of catastrophe for the corresponding
dispersionless solution predicts almost exactly the onset time of the rogue
wave. In our numerical experiments, the sign of the chirp appears to determine
the prevailing scenario, among two competing mechanisms leading to the
formation of a rogue wave. For negative values, the simulations are suggestive
of the dispersive regularisation of a gradient catastrophe described by Bertola
and Tovbis for a different class of smooth, bell-shaped initial data. As the
chirp becomes positive, the rogue wave seem to result from the interaction of
counter-propagating dispersive dam break flows, as described for the box
problem by El, Khamis and Tovbis. As the chirp and amplitude of the initial
profile are relatively easy to manipulate in optical devices and water tank
wave generators, we expect our observation to be relevant for experiments in
nonlinear optics and fluid dynamics.Comment: 17 pages, 5 figures, 1 tabl
A metabolomic approach to animal vitreous humor topographical composition: A pilot study
The purpose of this study was to evaluate the feasibility of a 1H-NMR-based metabolomic approach to explore the
metabolomic signature of different topographical areas of vitreous humor (VH) in an animal model. Five ocular globes were
enucleated from five goats and immediately frozen at 280uC. Once frozen, three of them were sectioned, and four samples
corresponding to four different VH areas were collected: the cortical, core, and basal, which was further divided into a
superior and an inferior fraction. An additional two samples were collected that were representative of the whole vitreous
body. 1H-NMR spectra were acquired for twenty-three goat vitreous samples with the aim of characterizing the
metabolomic signature of this biofluid and identifying whether any site-specific patterns were present. Multivariate
statistical analysis (MVA) of the spectral data were carried out, including Principal Component Analysis (PCA), Hierarchical
Cluster Analysis (HCA), and Partial Least Squares Discriminant Analysis (PLS-DA). A unique metabolomic signature belonging
to each area was observed. The cortical area was characterized by lactate, glutamine, choline, and its derivatives, N-acetyl
groups, creatine, and glycerol; the core area was characterized by glucose, acetate, and scyllo-inositol; and the basal area
was characterized by branched-chain amino acids (BCAA), betaine, alanine, ascorbate, lysine, and myo-inositol. We propose
a speculative approach on the topographic role of these molecules that are mainly responsible for metabolic differences
among the as-identified areas. 1H-NMR-based metabolomic analysis has shown to be an important tool for investigating the
VH. In particular, this approach was able to assess in the samples here analyzed the presence of different functional areas on
the basis of a different metabolite distribution.The purpose of this study was to evaluate the feasibility of a 1H-NMR-based metabolomic approach to explore the metabolomic signature of different topographical areas of vitreous humor (VH) in an animal model. Five ocular globes were enucleated from five goats and immediately frozen at -80°C. Once frozen, three of them were sectioned, and four samples corresponding to four different VH areas were collected: the cortical, core, and basal, which was further divided into a superior and an inferior fraction. An additional two samples were collected that were representative of the whole vitreous body. 1H-NMR spectra were acquired for twenty-three goat vitreous samples with the aim of characterizing the metabolomic signature of this biofluid and identifying whether any site-specific patterns were present. Multivariate statistical analysis (MVA) of the spectral data were carried out, including Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and Partial Least Squares Discriminant Analysis (PLS-DA). A unique metabolomic signature belonging to each area was observed. The cortical area was characterized by lactate, glutamine, choline, and its derivatives, N-acetyl groups, creatine, and glycerol; the core area was characterized by glucose, acetate, and scyllo-inositol; and the basal area was characterized by branched-chain amino acids (BCAA), betaine, alanine, ascorbate, lysine, and myo-inositol. We propose a speculative approach on the topographic role of these molecules that are mainly responsible for metabolic differences among the as-identified areas. 1H-NMR-based metabolomic analysis has shown to be an important tool for investigating the VH. In particular, this approach was able to assess in the samples here analyzed the presence of different functional areas on the basis of a different metabolite distribution. © 2014 Locci et al
Rogue wave formation scenarios for the focusing nonlinear Schrödinger equation with parabolic-profile initial data on a compact support
We study the (1+1) focusing nonlinear Schrödinger equation for an initial condition with compactly supported parabolic profile and phase depending quadratically on the spatial coordinate. In the absence of dispersion, using the natural class of self-similar solutions, we provide a criterion for blowup in finite time, generalizing a result by Talanov et al. In the presence of dispersion, we numerically show that the same criterion determines, even beyond the semiclassical regime, whether the solution relaxes or develops a high-order rogue wave, whose onset time is predicted by the corresponding dispersionless catastrophe time. The sign of the chirp appears to determine the prevailing scenario among two competing mechanisms for rogue wave formation. For negative values, the numerical simulations are suggestive of the dispersive regularization of a gradient catastrophe described by Bertola and Tovbis for a different class of smooth, bell-shaped initial data. As the chirp becomes positive, the rogue wave seems to result from the interaction of counterpropagating dispersive dam break flows, as in the box problem recently studied by El, Khamis, and Tovbis. As the chirp and amplitude of the initial profile are relatively easy to manipulate in optical devices and water tank wave generators, we expect our observation to be relevant for experiments in nonlinear optics and fluid dynamics
Exact solutions to the focusing nonlinear Schrodinger equation
A method is given to construct globally analytic (in space and time) exact
solutions to the focusing cubic nonlinear Schrodinger equation on the line. An
explicit formula and its equivalents are presented to express such exact
solutions in a compact form in terms of matrix exponentials. Such exact
solutions can alternatively be written explicitly as algebraic combinations of
exponential, trigonometric, and polynomial functions of the spatial and
temporal coordinates.Comment: 60 pages, 18 figure
ZnSe Nanoparticles for Thermoelectrics: Impact of Cu-Doping
The present study investigates the impact of copper doping on the thermoelectric properties of zinc selenide (ZnSe) nanoparticles synthesized by the hydrothermal method. Nanoparticle samples with varying copper concentrations were prepared and their thermoelectric performances were evaluated by measuring the electrical transport properties, the Seebeck coefficient, and extracting the power factor. The results demonstrate that the thermoelectric properties of Cu-doped ZnSe nanoparticles are significantly enhanced by doping, mainly as an effect of an improved electrical conductivity, providing a promising avenue for energy applications of these nanomaterials. To gain further insights into the fundamental mechanisms underlying the observed improvements in thermoelectric performance of the samples, the morphological, structural, and vibrational properties were characterized using a combination of scanning electron microscopy, X-ray diffraction, and Raman spectroscopy
A unified approach to Darboux transformations
We analyze a certain class of integral equations related to Marchenko
equations and Gel'fand-Levitan equations associated with various systems of
ordinary differential operators. When the integral operator is perturbed by a
finite-rank perturbation, we explicitly evaluate the change in the solution. We
show how this result provides a unified approach to Darboux transformations
associated with various systems of ordinary differential operators. We
illustrate our theory by deriving the Darboux transformation for the
Zakharov-Shabat system and show how the potential and wave function change when
a discrete eigenvalue is added to the spectrum.Comment: final version that will appear in Inverse Problem
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