Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Electrolytes and interphases in Li-ion batteries and beyond.

National Institute of Standards and Technology における超伝導研究及び生活

The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

THE subject of quantum electrodynamics is extremely difficult, even for the case of a single electron. The usual method of solving the corresponding wave equation leads to divergent integrals. To avoid these, Prof. P. A. M. Dirac* uses the method of redundant variables. This does not abolish the difficulty, but presents it in a new form, which may be dealt with in two ways. The first of these needs only comparatively simple mathematics and is directly connected with an elegant general scheme, but unfortunately its wave functions apply only to a hypothetical world and so its physical interpretation is indirect. The second way has the advantage of a direct physical interpretation, but the mathematics is so complicated that it has not yet been solved even for what appears to be the simplest possible case. Both methods seem worth further study, failing the discovery of a third which would combine the advantages of both.

http://ieeexplore.ieee.org/iel5/3/22993/01069961.pdf

Quantum electrodynamics

Extreme ultraviolet (EUV) emission from laser-produced plasmas (LPP) centered at 13.5 nm is considered a leading
candidate for the light source in future lithography systems. Tin is currently the best material for generating this EUV
emission since it emits strongly within the 13.5 nm region due to its various ionic states (Sn 8+ -Sn 14+ ). Highly efficient
and low-debris LPPs are a pre-requisite for their use as light sources for EUV lithography. Tin plasmas generate debris
that can damage collection optics over time. Techniques to mitigate debris are needed to extend the lifetime of these
components and the system. Optimization of plasma conditions is necessary for increasing EUV emission and enhancing
conversion efficiency (CE). Improving the source CE is necessary in order to reduce the cost of ownership and hence,
develop a commercially viable lithography system for the semiconductor industry. One method to accomplish this is to
reheat pre-formed plasma with a laser pulse to enhance EUV emission. This enhancement is achieved by controlling
those plasma conditions necessary for optimizing EUV emission. We investigated the role of prepulse laser wavelength
on prepulse plume formation and EUV in-band signal enhancement. A 6 ns Nd:YAG laser operating at 1064 nm and 266
nm was used for generating the prepulse plume. The expanding plume was then reheated by a 35 ns CO 2 laser operating
at 10.6 μm. The role of prepulse wavelength and energy on EUV conversion efficiency is discussed.

Wavelength dependence of prepulse laser beams on EUV emission from CO2 reheated Sn plasma

Thermoelastic response of liquid metal targets exposed to high-volumetric-energy deposition in times shorter than the target hydrodynamic response time (i.e., sound travel time) is of interest to several research areas, including first walls of fusion reactors (especially inertially confined fusion reactors), targets for high-power accelerators such as the Spallation Neutron Source, muon collider targets, etc. Under conditions that exist in these reactors, accelerators, etc., the deposited energy is considered instant in time from the hydrodynamic point of view. Because thermal heat conduction requires a longer than instant response time for energy redistribution, only hydrodynamic phenomena should be taken into account when modeling and simulating the fragmentation of suddenly heated liquid metal jets. Sudden energy deposition causes an instant rise in temperature that leads to a corresponding rise in the thermal pressure that causes excitation of sound waves, i.e., shock waves and rarefaction waves. During this excitation of sound waves, pressure oscillates with magnitude {+-} {Delta}P that corresponds to an initial thermal pressure of tens of katm. Liquids are frequently observed to withstand significant negative pressures (hydrostatic tensile stresses). Yet, a liquid subjected to a negative pressure is metastable. The formation and behavior of cavities (empty voids) under negative pressures wasmore » previously studied. Theoretically, the obtained fracture (failure) pressure of mercury is in good agreement with experimental results. Cavitation, or spontaneous formation of cavities, in stressed liquid metal targets is of interest to engineers and physicists who operate high-power targets in fusion reactors, nuclear accelerators, and particle colliders. The problems of liquid target oscillation in the presence of large magnitudes of negative pressure, and the mechanism of fragmentation and its consequences are considered in this analysis. It is shown that a cavity coming into existence will initiate a shock wave that is actually a relaxation shock wave initiated when the stretched medium reverts to normal density from the low-density state. The nature of this relaxation wave is similar to that of the detonation wave. It is also shown that a cavity born at the high-negative-pressure stage expands permanently and does not disappear. This permanent expansion and failure to disappear is a major difference between the cavity dynamics in stretched media and the dynamics observed in the usual cavitation processes that occur when vapor bubbles collapse during a phase of increased pressure, and is the result of ''unloading'' or ''discharging'' of the medium by the relaxation shock wave initiated by the appearance of the cavity. Detailed calculations of cavity dynamics are presented for both spherical and cylindrical liquid metal target systems.« less

/pdf/modeling-and-simulation-of-fragmentation-of-suddenly-heated-2fap0afytu.pdf

Modeling and simulation of fragmentation of suddenly heated liquid metal jets

Predicting hydrogen isotope inventory in plasma-facing components during normal and abnormal operations in fusion devices

The structure of a collisionless scrape-off-layer (SOL) plasma in tokamak reactors is being studied to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. The collisionless model is shown to be valid during the thermal phase of a plasma disruption, as well as during the newly desired low-recycling normal phase of operation with low-density, high-temperature, edge plasma conditions. An analytical solution is developed by solving the Fokker-Planck equation for electron distribution and balance in the SOL. The solution is in good agreement with numerical studies using Monte-Carlo methods. The analytical solutions provide an insight to the role of different physical and geometrical processes in a collisionless SOL during disruptions and during the enhanced phase of normal operation over a wide range of parameters.

/pdf/physics-of-collisionless-scrape-off-layer-plasma-during-1rk8zvueov.pdf

Ahmed Hassanein

Papers

Wavelength dependence of prepulse laser beams on EUV emission from CO2 reheated Sn plasma

Modeling and simulation of fragmentation of suddenly heated liquid metal jets

Predicting hydrogen isotope inventory in plasma-facing components during normal and abnormal operations in fusion devices

Physics of collisionless scrape-off-layer plasma during normal and off-normal Tokamak operating conditions.

Effect of surface segregation and mobility on erosion of plasma-facing materials in magnetic fusion systems