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

I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Principles of Neural Science

The organization of behavior: A neuropsychological theory

QUANTUM gravitational effects are usually ignored in calculations of the formation and evolution of black holes. The justification for this is that the radius of curvature of space-time outside the event horizon is very large compared to the Planck length (Għ/c3)1/2 ≈ 10−33 cm, the length scale on which quantum fluctuations of the metric are expected to be of order unity. This means that the energy density of particles created by the gravitational field is small compared to the space-time curvature. Even though quantum effects may be small locally, they may still, however, add up to produce a significant effect over the lifetime of the Universe ≈ 1017 s which is very long compared to the Planck time ≈ 10−43 s. The purpose of this letter is to show that this indeed may be the case: it seems that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ≈ 10−6 (M/M)K where κ is the surface gravity of the black hole1. As a black hole emits this thermal radiation one would expect it to lose mass. This in turn would increase the surface gravity and so increase the rate of emission. The black hole would therefore have a finite life of the order of 1071 (M/M)−3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs. It is often said that nothing can escape from a black hole. But in 1974, Stephen Hawking realized that, owing to quantum effects, black holes should emit particles with a thermal distribution of energies — as if the black hole had a temperature inversely proportional to its mass. In addition to putting black-hole thermodynamics on a firmer footing, this discovery led Hawking to postulate 'black hole explosions', as primordial black holes end their lives in an accelerating release of energy.

Black Hole Explosions

The task of quantizing general relativity raises serious questions about the meaning of the present formulation and interpretation of quantum mechanics when applied to so fundamental a structure as the space-time geometry itself. This paper seeks to clarify the foundations of quantum mechanics. It presents a reformulation of quantum theory in a form believed suitable for application to general relativity. The aim is not to deny or contradict the conventional formulation of quantum theory, which has demonstrated its usefulness in an overwhelming variety of problems, but rather to supply a new, more general and complete formulation, from which the conventional interpretation can be deduced. The relationship of this new formulation to the older formulation is therefore that of a metatheory to a theory, that is, it is an underlying theory in which the nature and consistency, as well as the realm of applicability, of the older theory can be investigated and clarified.

"relative State" Formulation of Quantum Mechanics

Evolution of an interstitial 1/2〈111〉 dislocation loop under tensile, shear, and torsion stresses is studied with molecular statics method. Under a tensile stress, the dependence of ultimate tensile strength on size of loop is calculated. The formation of small shear loops around the initial prismatic loop is confirmed as an intermediate state to form the final dislocation network. Under a shear stress, the rotation of a loop is observed not only by a change of the habit plane but also through a transformation between a shear and a prismatic loop. Under torsion, a perfect BCC crystal may undergo a BCC to FCC or BCC to HCP transformation. The present work indicates that a 1/2〈111〉 loop can delay these transformations, resulting in the formation of micro-crack on the surface.

Atomistic Simulation of Interstitial Dislocation Loop Evolution under Applied Stresses in BCC Iron

The first hard X-ray free electron laser (XFEL) facility in China, the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility (SHINE), is under construction, which allows for generating X-ray pulses in the photon energy range from 3 keV to 25 keV. To produce X-ray pulses with photon energy up to 25 keV, FEL-III undulator line of SHINE employs superconducting undulators. However, the smaller gap of the superconducting undulator poses serious wakefield effect reducing the FEL power, compared to the normal planar undulator. For a setup design optimization, the design and performance of the FEL-III undulator line are presented using start-to-end beam simulations at self-amplified spontaneous emission (SASE) and self-seeding mode. The wakefield impact on FEL performance is then investigated. A linear undulator tapering technique is adopted for recovering the FEL power to the non-wakefield level.

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Physical Design and FEL Performance Study for FEL-III Beamline of SHINE

Exploration of quantum correlations in an open system with Unruh effect under a Schwarzschild space-time

Entropic uncertainty relation (EUR) quantifies the precision of measurements for arbitrary two non-commuting observables within a specified system. Due to exposure in a noisy environment, a practical system unavoidably suffers from decay by interacting with the environment. Inthis paper, we investigate the dynamic behaviors of EUR for a pair of non-commuting observables under two typical dissipative environments. Specifically, we study the dynamics features of EUR in a single-qubit system under the degradation induced by amplitude damping (AD) and depolarizing noises, respectively. It has been found that AD and depolarizing noises do not always cause the increase of the uncertainty, and can reduce the amount in a relative long-time regime. Remarkably, it has been shown that there exists a critical phenomenon that AD noise can always lead to the reducing of the uncertainty when the ratio of ground state and excited state is beyond a threshold in the system. Furthermore, we propose a general and effective approach to steer EUR by means of a kind of non-unitary operations, namely, quantum weak measurements. It is verified that quantum weak measurements can effectively reduce the entropic uncertainty in the dissipative environment.

Dong Wang

Papers

Atomistic Simulation of Interstitial Dislocation Loop Evolution under Applied Stresses in BCC Iron

Physical Design and FEL Performance Study for FEL-III Beamline of SHINE

Exploration of quantum correlations in an open system with Unruh effect under a Schwarzschild space-time

Entropic Uncertainty Relation Under Dissipative Environments and Its Steering by Local Non-unitary Operations

Tunable High-Intensity Electron Bunch Train Production Based on Nonlinear Longitudinal Space Charge Oscillation