2,701 research outputs found
Explicit determination of a 727-dimensional root space of the hyperbolic Lie algebra
The 727-dimensional root space associated with the level-2 root \bLambda_1
of the hyperbolic Kac--Moody algebra is determined using a recently
developed string theoretic approach to hyperbolic algebras. The explicit form
of the basis reveals a complicated structure with transversal as well as
longitudinal string states present.Comment: 12 pages, LaTeX 2
Applying the extended molecule approach to correlated electron transport: important insight from model calculations
Theoretical approaches of electronic transport in correlated molecules
usually consider an extended molecule, which includes, in addition to the
molecule itself, parts of electrodes. In the case where electron correlations
remain confined within the molecule, and the extended molecule is sufficiently
large, the current can be expressed by means of Laudauer-type formulae.
Electron correlations are embodied into the retarded Green function of a
sufficiently large but isolated extended molecule, which represents the key
quantity that can be accurately determined by means of ab initio quantum
chemical calculations. To exemplify these ideas, we present and analyze
numerical results obtained within full CI calculations for an extended molecule
described by the interacting resonant level model. Based on them, we argue that
for organic electrodes the transport properties can be reliably computed,
because the extended molecule can be chosen sufficiently small to be tackled
within accurate ab initio methods. For metallic electrodes, larger extended
molecules have to be considered in general, but a (semi-)quantitative
description of the transport should still be possible particularly in the
typical cases where electron transport proceeds by off-resonant tunneling. Our
numerical results also demonstrate that, contrary to the usual claim, the ratio
between the characteristic Coulomb strength and the level width due to
molecule-electrode coupling is not the only quantity needed to assess whether
electron correlation effects are strong or weak
Energetic Materials at High Compression: First-Principles Density Functional Theory and Reactive Force Field Studies
We report the results of a comparative study of pentaerythritol tetranitrate (PETN) at high compression using classical reactive interatomic potential ReaxFF and first-principles density functional theory (DFT). Lattice parameters of PETN I, the ground state structure at ambient conditions, is obtained by ReaxFF and two different density functional methods (plane wave and LCAO pseudopotential methods) and compared with experiment. Calculated energetics and isothermal equation of state (EOS) upon hydrostatic compression obtained by DFT and ReaxFF are both in good agreement with available experimental data. Our calculations of the hydrostatic EOS at zero temperature are extended to high pressures up to 50 GPa. The anisotropic characteristics of PETN upon uniaxial compression were also calculated by both ReaxFF and DFT
The 1998 Center for Simulation of Dynamic Response in Materials Annual Technical Report
Introduction:
This annual report describes research accomplishments for FY 98 of the Center for Simulation
of Dynamic Response of Materials. The Center is constructing a virtual shock physics facility
in which the full three dimensional response of a variety of target materials can be computed
for a wide range of compressive, tensional, and shear loadings, including those produced by
detonation of energetic materials. The goals are to facilitate computation of a variety of
experiments in which strong shock and detonation waves are made to impinge on targets
consisting of various combinations of materials, compute the subsequent dynamic response
of the target materials, and validate these computations against experimental data
Cinematic and aesthetic cartographies of subjective mutation
This article exmaines the use of cinema as a mapping of subjective mutation in the work of Deleuze, Gauttari and Berardi. Drawing on Deleuze's distinciton between the reduction of the art-work to the symptom and the idea of art as symptomatology, the article focuses on Berardi's use of cinematic examples, posing the quesiton in each case of to what extent they function as symptomatologies or mere symptoms of cultural and subjective mutations in examples ranging from Bergman's Persona to Van Sant's Elephant to finish on speculations about Fincher's The Social Network as a cirtical engagement with subjective mutation in the 21st Century
Analysis of dynamics, stability, and flow fields' structure of an accelerated hydrodynamic discontinuity with interfacial mass flux by a general matrix method
We develop a general matrix method to analyze from a far field the dynamics of an accelerated interface between incompressible ideal fluids of different densities with interfacial mass flux and with negligible density variations and stratification. We rigorously solve the linearized boundary value problem for the dynamics conserving mass, momentum, and energy in the bulk and at the interface. We find a new hydrodynamic instability that develops only when the acceleration magnitude exceeds a threshold. This critical threshold value depends on the magnitudes of the steady velocities of the fluids, the ratio of their densities, and the wavelength of the initial perturbation. The flow has potential velocity fields in the fluid bulk and is shear-free at the interface. The interface stability is set by the interplay of inertia and gravity. For weak acceleration, inertial effects dominate, and the flow fields experience stable oscillations. For strong acceleration, gravity effects dominate, and the dynamics is unstable. For strong accelerations, this new hydrodynamic instability grows faster than accelerated Landau-Darrieus and Rayleigh-Taylor instabilities. For given values of the fluids' densities and their steady bulk velocities, and for a given magnitude of acceleration, we find the critical and maximum values of the initial perturbation wavelength at which this new instability can be stabilized and at which its growth is the fastest. The quantitative, qualitative, and formal properties of the accelerated conservative dynamics depart from those of accelerated Landau-Darrieus and Rayleigh-Taylor dynamics. New diagnostic benchmarks are identified for experiments and simulations of unstable interfaces
Superlubricity mechanism of diamond-like carbon with glycerol. Coupling of experimental and simulation studies
We report a unique tribological system that produces superlubricity under boundary lubrication conditions with extremely little wear. This system is a thin coating of hydrogen-free amorphous Diamond-Like-Carbon (denoted as ta-C) at 353 K in a ta-C/ta-C friction pair lubricated with pure glycerol. To understand the mechanism of friction vanishing we performed ToF-SIMS experiments using deuterated glycerol and 13C glycerol. This was complemented by first-principles-based computer simulations using the ReaxFF reactive force field to create an atomistic model of ta-C. These simulations show that DLC with the experimental density of 3.24 g/cc leads to an atomistic structure consisting of a 3D percolating network of tetrahedral (sp3) carbons accounting for 71.5% of the total, in excellent agreement with the 70% deduced from our Auger spectroscopy and XANES experiments. The simulations show that the remaining carbons (with sp2 and sp1 character) attach in short chains of length 1 to 7. In sliding simulations including glycerol molecules, the surface atoms react readily to form a very smooth carbon surface containing OH-terminated groups. This agrees with our SIMS experiments. The simulations find that the OH atoms are mostly bound to surface sp1 atoms leading to very flexible elastic response to sliding. Both simulations and experiments suggest that the origin of the superlubricity arises from the formation of this OH-terminated surface
Persistence to high temperatures of interlayer coherence in an organic superconductor
The interlayer magnetoresistance of the organic metal \cuscn is
studied in fields of up to 45 T and at temperatures from 0.5 K to 30 K. The
peak in seen in in-plane fields, a definitive signature of
interlayer coherence, remains to s exceeding the Anderson criterion for
incoherent transport by a factor . Angle-dependent magnetoresistance
oscillations are modeled using an approach based on field-induced quasiparticle
paths on a 3D Fermi surface, to yield the dependence of the scattering rate
. The results suggest that does not vary strongly over
the Fermi surface, and that it has a dependence due to electron-electron
scattering
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