229 research outputs found
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Symmetry of laser driven implosions
The achievement of significant nuclear energy yields from laserheated pellets of thermonuclear fuel requires that the fuel be compressed to at least several orders of magnitude above initial density. Such compressions can be attained by spherical implosions, but because of the large compression ratios required, these implosions must be highly symmetrical. Calculations of the behavior of imploding spheres and shells by a spherical harmonic perturbation method, and by two-dimensional hydrodynamic codes within their limitations, have shown the importance of electron thermal conduction in the low-density ablation cloud of a pellet in bringing about the required symmetry. These calculations show that, at early time in the heating of a pellet when the ablation cloud is relatively small and cold, the symmetry requirements are most severe and call for as many as four laser beams. However, symmetry requirements at later times, when most of the laser energy must be deposited, may be met by as few as one beam. (auth
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Structure and scaling laws of laser-driven ablative implosions
A stationary, spherical flow model gives the form of laser-driven ablation fronts and scaling laws for the dependence of implosion parameters on laser wavelength, pusher atomic number, and other input quantities. (auth
Energy, Central Charge, and the BPS Bound for 1+1 Dimensional Supersymmetric Solitons
We consider one-loop quantum corrections to soliton energies and central
charges in the supersymmetric and sine-Gordon models in 1+1
dimensions. In both models, we unambiguously calculate the correction to the
energy in a simple renormalization scheme and obtain ,
in agreement with previous results. Furthermore, we show that there is an
identical correction to the central charge, so that the BPS bound remains
saturated in the one-loop approximation. We extend these results to arbitrary
1+1 dimensional supersymmetric theories.Comment: 15 pages, RevTeX; v2: generalized energy result, added minor
clarifications, and fixed typos; v3: more minor clarifications and
corrections; v4: fixed factor of 2 in eq. (25); v5: fixed minor error in eq.
(55
Exact solutions of the radial Schrodinger equation for some physical potentials
By using an ansatz for the eigenfunction, we have obtained the exact
analytical solutions of the radial Schrodinger equation for the pseudoharmonic
and Kratzer potentials in two dimensions. The energy levels of all the bound
states are easily calculated from this eigenfunction ansatz. The normalized
wavefunctions are also obtained.Comment: 13 page
Deformation of Small Compressed Droplets
We investigate the elastic properties of small droplets under compression.
The compression of a bubble by two parallel plates is solved exactly and it is
shown that a lowest-order expansion of the solution reduces to a form similar
to that obtained by Morse and Witten. Other systems are studied numerically and
results for configurations involving between 2 and 20 compressing planes are
presented. It is found that the response to compression depends on the number
of planes. The shear modulus is also calculated for common lattices and the
stability crossover between f.c.c.\ and b.c.c.\ is discussed.Comment: RevTeX with psfig-included figures and a galley macr
Impaired cellular immune response in rats exposed perinatally to Baltic Sea herring oil or 2,3,7,8-TCDD
While the immunotoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been well established, the effects of complex environmental mixtures of polyhalogenated aromatic hydrocarbons (PHAHs) are poorly understood. Many PHAHs, including the polychlorinated-biphenyls (PCBs), -dibenzofurans (PCDFs), and dibenzo-p-dioxins (PCDDs), possess 'dioxin-like' activities, and accumulate in the aquatic food chain. Organisms occupying high trophic levels may therefore be exposed to concentrations which may present an immunotoxic risk. In this study, pregnant PVG rats were administered a daily oral dose of 1 ml of the following during pregnancy and lactation: (1) oil extracted from herring caught in the relatively uncontaminated Atlantic Ocean; (2) oil extracted from herring caught in the contaminated Baltic Sea; or (3) the Atlantic herring oil extract spiked with 2,3,7,8-TCDD. The daily intakes of aryl hydrocarbon (Ah)-receptor dependent toxic equivalents (TEQ) for mothers were 0.3 in the Atlantic group, 2.1 in the Baltic group, and 134 ng/kg body wt. in the 2,3,7,8-TCDD positive control group. Immune function and host resistance to rat cytomegalovirus (RCMV) we
Statistical Theory of Spin Relaxation and Diffusion in Solids
A comprehensive theoretical description is given for the spin relaxation and
diffusion in solids. The formulation is made in a general
statistical-mechanical way. The method of the nonequilibrium statistical
operator (NSO) developed by D. N. Zubarev is employed to analyze a relaxation
dynamics of a spin subsystem. Perturbation of this subsystem in solids may
produce a nonequilibrium state which is then relaxed to an equilibrium state
due to the interaction between the particles or with a thermal bath (lattice).
The generalized kinetic equations were derived previously for a system weakly
coupled to a thermal bath to elucidate the nature of transport and relaxation
processes. In this paper, these results are used to describe the relaxation and
diffusion of nuclear spins in solids. The aim is to formulate a successive and
coherent microscopic description of the nuclear magnetic relaxation and
diffusion in solids. The nuclear spin-lattice relaxation is considered and the
Gorter relation is derived. As an example, a theory of spin diffusion of the
nuclear magnetic moment in dilute alloys (like Cu-Mn) is developed. It is shown
that due to the dipolar interaction between host nuclear spins and impurity
spins, a nonuniform distribution in the host nuclear spin system will occur and
consequently the macroscopic relaxation time will be strongly determined by the
spin diffusion. The explicit expressions for the relaxation time in certain
physically relevant cases are given.Comment: 41 pages, 119 Refs. Corrected typos, added reference
Dualities and dilemmas: contending with uncertainty in large-scale safety-critical projects
© 2016, Informa UK Limited, trading as Taylor & Francis Group. Uncertainty is a fact of project life. Most decisions that are made on a safety-critical project involve uncertainty, the consequences of which may be highly significant to the safe and timely delivery of the project. Based on interviews with project management practitioners on nine large-scale civil nuclear and aerospace projects, we explore how uncertainty emerges, and how project management practitioners identify, analyse and act on it. We make three important contributions. First, we present three approaches – structural, behavioural and relational – that individuals and organizations can adopt when contending with project uncertainty. Secondly, we characterize nine dualities at play in the management of project uncertainty and thirdly, we identify key differences between how civil nuclear and aerospace project managers confront project uncertainty, which have important implications for how projects might be organized in both these industry sectors. Drawing attention to the structural, behavioural and relational approaches to project uncertainty and the tensions that manifest themselves in each approach should enable the project management community to make progress in environments of high uncertainty where situations are often complex, rapidly changing and confusing, and yet where, for reasons of safety, failure is not an option
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