22,662 research outputs found
NASA/MSFC FY88 Global Scale Atmospheric Processes Research Program Review
Interest in environmental issues and the magnitude of the environmental changes continues. One way to gain more understanding of the atmosphere is to make measurements on a global scale from space. The Earth Observation System is a series of new sensors to measure globally atmospheric parameters. Analysis of satellite data by developing algorithms to interpret the radiance information improves the understanding and also defines requirements for these sensors. One measure of knowledge of the atmosphere lies in the ability to predict its behavior. Use of numerical and experimental models provides a better understanding of these processes. These efforts are described in the context of satellite data analysis and fundamental studies of atmospheric dynamics which examine selected processes important to the global circulation
Molecular Simulation of MoS2 Exfoliation.
A wide variety of two-dimensional layered materials are synthesized by liquid-phase exfoliation. Here we examine exfoliation of MoS2 into nanosheets in a mixture of water and isopropanol (IPA) containing cavitation bubbles. Using force fields optimized with experimental data on interfacial energies between MoS2 and the solvent, multimillion-atom molecular dynamics simulations are performed in conjunction with experiments to examine shock-induced collapse of cavitation bubbles and the resulting exfoliation of MoS2. The collapse of cavitation bubbles generates high-speed nanojets and shock waves in the solvent. Large shear stresses due to the nanojet impact on MoS2 surfaces initiate exfoliation, and shock waves reflected from MoS2 surfaces enhance exfoliation. Structural correlations in the solvent indicate that shock induces an ice VII like motif in the first solvation shell of water
Toward Making the Constraint Hypersurface an Attractor in Free Evolution
There is an abundance of empirical evidence in the numerical relativity
literature that the form in which the Einstein evolution equations are written
plays a significant role in the lifetime of numerical simulations. This paper
attempts to present a consistent framework for modifying any system of
evolution equations by adding terms that push the evolution toward the
constraint hypersurface. The method is, in principle, applicable to any system
of partial differential equations which can be divided into evolution equations
and constraints, although it is only demonstrated here through an application
to the Maxwell equations.Comment: 6 pages, 3 figures, 1 table. Uses REVTeX
Wavelet-Based High-Order Adaptive Modeling of Lossy Interconnects
Abstract—This paper presents a numerical-modeling strategy for simulation of fast transients in lossy electrical interconnects. The proposed algorithm makes use of wavelet representations of voltages and currents along the structure, with the aim of reducing the computational complexity of standard time-domain solvers. A special weak procedure for the implementation of possibly dynamic and nonlinear boundary conditions allows to preserve stability as well as a high approximation order, thus leading to very accurate schemes. On the other hand, the wavelet expansion allows the computation of the solution by using few significant coefficients which are automatically determined at each time step. A dynamically refinable mesh is then used to perform a sparse time-stepping. Several numerical results illustrate the high efficiency of the proposed algorithm, which has been tuned and optimized for best performance in fast digital applications typically found on modern PCB structures. Index Terms—Finite difference methods, time-domain analysis, transmission lines, wavelet transforms. I
Quantum properties of atomic-sized conductors
Using remarkably simple experimental techniques it is possible to gently
break a metallic contact and thus form conducting nanowires. During the last
stages of the pulling a neck-shaped wire connects the two electrodes, the
diameter of which is reduced to single atom upon further stretching. For some
metals it is even possible to form a chain of individual atoms in this fashion.
Although the atomic structure of contacts can be quite complicated, as soon as
the weakest point is reduced to just a single atom the complexity is removed.
The properties of the contact are then dominantly determined by the nature of
this atom. This has allowed for quantitative comparison of theory and
experiment for many properties, and atomic contacts have proven to form a rich
test-bed for concepts from mesoscopic physics. Properties investigated include
multiple Andreev reflection, shot noise, conductance quantization, conductance
fluctuations, and dynamical Coulomb blockade. In addition, pronounced quantum
effects show up in the mechanical properties of the contacts, as seen in the
force and cohesion energy of the nanowires. We review this reseach, which has
been performed mainly during the past decade, and we discuss the results in the
context of related developments.Comment: Review, 120 pages, 98 figures. In view of the file size figures have
been compressed. A higher-resolution version can be found at:
http://lions1.leidenuniv.nl/wwwhome/ruitenbe/review/QPASC-hr-ps-v2.zip (5.6MB
zip PostScript
Generalized Warped Disk Equations
The manner in which warps in accretion disks evolve depends on the magnitude of the viscosity. ... See full text for complete abstract
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