23,851 research outputs found
Diagnostic techniques in deflagration and detonation studies
Advances in experimental, high-speed techniques can be used to explore the processes occurring within energetic materials. This review describes techniques used to study a wide range of processes: hot-spot formation, ignition thresholds, deflagration, sensitivity and finally the detonation process. As this is a wide field the focus will be on small-scale experiments and quantitative studies. It is important that such studies are linked to predictive models, which inform the experimental design process. The stimuli range includes, thermal ignition, drop-weight, Hopkinson Bar and Plate Impact studies. Studies made with inert simulants are also included as these are important in differentiating between reactive response and purely mechanical behaviour
Spectroscopic Interpretation: The High Vibrations of CDBrClF
We extract the dynamics implicit in an algebraic fitted model Hamiltonian for
the deuterium chromophore's vibrational motion in the molecule CDBrClF. The
original model has 4 degrees of freedom, three positions and one representing
interbond couplings. A conserved polyad allows in a semiclassical approach the
reduction to 3 degrees of freedom. For most quantum states we can identify the
underlying motion that when quantized gives the said state. Most of the
classifications, identifications and assignments are done by visual inspection
of the already available wave function semiclassically transformed from the
number representation to a representation on the reduced dimension toroidal
configuration space corresponding to the classical action and angle variables.
The concentration of the wave function density to lower dimensional subsets
centered on idealized simple lower dimensional organizing structures and the
behavior of the phase along such organizing centers already reveals the atomic
motion. Extremely little computational work is needed.Comment: 23 pages, 6 figures. Accepted for publication in J. Chem. Phy
Quartic oscillator potential in the {\gamma}-rigid regime of the collective geometrical model
A prolate -rigid version of the Bohr-Mottelson Hamiltonian with a
quartic anharmonic oscillator potential in collective shape variable is
used to describe the spectra for a variety of vibrational-like nuclei.
Speculating the exact separation between the two Euler angles and the
variable, one arrives to a differential Schr\"{o}dinger equation with a quartic
anharmonic oscillator potential and a centrifugal-like barrier. The
corresponding eigenvalue is approximated by an analytical formula depending
only on a single parameter up to an overall scaling factor. The applicability
of the model is discussed in connection to the existence interval of the free
parameter which is limited by the accuracy of the approximation and by
comparison to the predictions of the related and -
models. The model is applied to qualitatively describe the spectra for nine
nuclei which exhibit near vibrational features.Comment: 9 pages, 7 figures, 1 tabl
Adaptive Strain-Boost Hyperdynamics Simulations of Stress-Driven Atomic Processes
The deformation and failure phenomena of materials are the results of stress-driven, thermally activated processes at the atomic scale. Molecular-dynamics (MD) simulations can only span a very limited time range which hinders one from gaining full view of the deformation physics. Inspired by the Eshelby transformation formalism, we present here a transformation “strain-boost” method for accelerating atomistic simulations, which is often more efficient and robust than the bond-boost hyperdynamics method [R. A. Miron and K. A. Fichthorn, J. Chem. Phys. 119, 6210 (2003)] for exploring collective stress-driven processes such as dislocation nucleation, that have characteristic activation volumes larger than one atomic volume. By introducing an adaptive algorithm that safely maximizes the boost factor, we directly access the finite-temperature dynamical process of dislocation nucleation in compressed Cu nanopillar over time scale comparable to laboratory experiments. Our method provides stress- and temperature-dependent activation enthalpy, activation entropy and activation volume for surface-dislocation nucleation with no human guidance about crystallography or deformation physics. Remarkably, the accelerated MD results indicate that harmonic transition-state theory and the empirical Meyer-Neldel compensation rule give reasonable approximations of the dislocation nucleation rate
Gauge theory in dimension
We first review the notion of a -manifold, defined in terms of a
principal ("gauge") bundle over a -dimensional manifold, before
discussing their relation to supergravity. In a second thread, we focus on
associative submanifolds and present their deformation theory. In particular,
we elaborate on a deformation problem with coassociative boundary condition.
Its space of infinitesimal deformations can be identified with the solution
space of an elliptic equation whose index is given by a topological formula.Comment: 15 page
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