84 research outputs found
Ultrafast absorption kinetics of NADH in folded and unfolded conformations
The non-radiative energy transfer is shown to occur on a ~3ps time scale for NADH in the folded form in H2O. Addition of methanol thermodynamically favours the open form, for which energy transfer does not occur
Variational approach in dislocation theory
A variational approach is presented to calculate the stress field generated
by a system of dislocations. It is shown that in the simplest case, when the
material containing the dislocations obeys Hooke's law the variational
framework gives the same field equations as Kr\"oner's theory. However, the
variational method proposed allows to study many other problems like
dislocation core regularisation, role of elastic anharmonicity and
dislocation--solute atom interaction. The aim of the paper is to demonstrate
that these problems can be handled on a systematic manner.Comment: 16 pages, 4 figures. Minor changes in the text and few numerical
corrections. Few references also adde
Fluorescence kinetics of flavin adenine dinucleotide in different microenvironments
Fluorescence kinetics of flavin adenine dinucleotide was measured in a wide time and spectral range in different media, affecting its intra- end extramolecular interactions, and analyzed by a new method based on compressed sensing
Global existence for a system of non-linear and non-local transport equations describing the dynamics of dislocation densities
In this paper, we study the global in time existence problem for the
Groma-Balogh model describing the dynamics of dislocation densities. This model
is a two-dimensional model where the dislocation densities satisfy a system of
transport equations such that the velocity vector field is the shear stress in
the material, solving the equations of elasticity. This shear stress can be
expressed as some Riesz transform of the dislocation densities. The main tool
in the proof of this result is the existence of an entropy for this syste
Intermittent dislocation flow in viscoplastic deformation
The viscoplastic deformation (creep) of crystalline materials under constant
stress involves the motion of a large number of interacting dislocations.
Analytical methods and sophisticated `dislocation-dynamics' simulations have
proved very effective in the study of dislocation patterning, and have led to
macroscopic constitutive laws of plastic deformation. Yet, a statistical
analysis of the dynamics of an assembly of interacting dislocations has not
hitherto been performed. Here we report acoustic emission measurements on
stressed ice single crystals, the results of which indicate that dislocations
move in a scale-free intermittent fashion. This result is confirmed by
numerical simulations of a model of interacting dislocations that successfully
reproduces the main features of the experiment. We find that dislocations
generate a slowly evolving configuration landscape which coexists with rapid
collective rearrangements. These rearrangements involve a comparatively small
fraction of the dislocations and lead to an intermittent behavior of the net
plastic response. This basic dynamical picture appears to be a generic feature
in the deformation of many other materials. Moreover, it should provide a
framework for discussing fundamental aspects of plasticity, that goes beyond
standard mean-field approaches that see plastic deformation as a smooth laminar
flow
Nanocrystalline materials studied by powder diffraction line profile analysis
X-ray powder diffraction is a powerful tool for characterising the microstructure of crystalline materials in terms of size and strain. It is widely applied for nanocrystalline materials, especially since other methods, in particular electron microscopy is, on the one hand tedious and time consuming, on the other hand, due to the often metastable states of nanomaterials it might change their microstructures. It is attempted to overview the applications of microstructure characterization by powder diffraction on nanocrystalline metals, alloys, ceramics and carbon base materials. Whenever opportunity is given, the data provided by the X-ray method are compared and discussed together with results of electron microscopy. Since the topic is vast we do not try to cover the entire field
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