1,601 research outputs found
Nature of segregation of reactants in diffusion controlled A+B reactions: Role of mobility in forming compact clusters
We investigate the A+B=0 bimolecular chemical reaction taking place in
low-dimensional spaces when the mobilities of the two reacting species are not
equal. While the case of different reactant mobilities has been previously
reported as not affecting the scaling of the reactant densities with time, but
only the pre-exponential factor, the mechanism for this had not been explained
before. By using Monte-Carlo simulations we show that the nature of segregation
is very different when compared to the normal case of equal reactant
mobilities. The clusters of the mobile species are statistically homogeneous
and randomly distributed in space, but the clusters of the less mobile species
are much more compact and restricted in space. Due to the asymmetric
mobilities, the initial symmetric random density fluctuations in time turn into
asymmetric density fluctuations. We explain this trend by calculating the
correlation functions for the positions of particles for the several different
cases
Reply to Comment on ‘‘Experimental test of the Anderson–Mott transition model for excitation transport’’
It is argued that the critical electronic energy transfer EET concentrations observed in naphthalene2,4 are not accounted for by the Klafler and Fortner1,3,5 models of an Anderson transition. (AIP)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70450/2/JCPSA6-73-2-1005-1.pd
Experimental test of the Anderson–Mott transition model for excitation transporta)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69648/2/JCPSA6-70-6-3133-1.pd
Finite-Size Scaling Studies of Reaction-Diffusion Systems Part III: Numerical Methods
The scaling exponent and scaling function for the 1D single species
coagulation model are shown to be universal, i.e. they are
not influenced by the value of the coagulation rate. They are independent of
the initial conditions as well. Two different numerical methods are used to
compute the scaling properties: Monte Carlo simulations and extrapolations of
exact finite lattice data. These methods are tested in a case where analytical
results are available. It is shown that Monte Carlo simulations can be used to
compute even the correction terms. To obtain reliable results from finite-size
extrapolations exact numerical data for lattices up to ten sites are
sufficient.Comment: 19 pages, LaTeX, 5 figures uuencoded, BONN HE-94-0
Context Memory in Korsakoff’s Syndrome
Memory for contextual information and target-context integration are crucial for successful episodic memory formation and are impaired in patients with Korsakoff’s syndrome. In this paper we review the evidence for the notion that a context memory deficit makes an important contribution to the amnesia in these patients. First, we focus on anterograde memory for contextual (spatial and temporal) information. Next, the use of contextual cues in memory retrieval is examined and their role in retrograde amnesia and confabulation. Evidence on the role of contextual cues and associations in working memory is discussed in relation to the underlying neurocognitive mechanisms and their dissociation from long-term encoding. Finally, we focus on implicit learning of contextual information in Korsakoff patients. It can be concluded that Korsakoff patients are impaired in the explicit processing of contextual information and in target-context binding, both in long-term (retrograde and anterograde) memory and in working memory. These results extend the context memory deficit hypothesis. In contrast, implicit contextual learning is relatively preserved in these patients. These findings are discussed in relation to evidence of dysfunction of the extended diencephalic-hippocampal memory circuit in Korsakoff’s syndrome
Phonon sidebands of localized excitons in molecular crystals with methyl torsions: Hexamethylbenzene
Fluorescence and phosphorescence phonon sidebands of isotopic mixed hexamethylbenzene crystals at 2°K are presented. The external phonons can be observed separately from the semi‐internal (methyl torsion) ones. The nature of the electronic or vibronic state has observable but not drastic effects on the exciton‐phonon coupling function. Likewise, the exciton delocalization is of minor importance to the exciton‐phonon function in hexamethylbenzene. The coupling between external and internal vibrations is also weak in this system. The exciton‐phonon coupling appears comparable for the optical and acoustic phonons in hexamethylbenzene. The phonon sidebands give some of the phonon singularities of the low‐temperature crystal.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70173/2/JCPSA6-60-6-2365-1.pd
Diffusion-Limited Coalescence with Finite Reaction Rates in One Dimension
We study the diffusion-limited process in one dimension, with
finite reaction rates. We develop an approximation scheme based on the method
of Inter-Particle Distribution Functions (IPDF), which was formerly used for
the exact solution of the same process with infinite reaction rate. The
approximation becomes exact in the very early time regime (or the
reaction-controlled limit) and in the long time (diffusion-controlled)
asymptotic limit. For the intermediate time regime, we obtain a simple
interpolative behavior between these two limits. We also study the coalescence
process (with finite reaction rates) with the back reaction , and in
the presence of particle input. In each of these cases the system reaches a
non-trivial steady state with a finite concentration of particles. Theoretical
predictions for the concentration time dependence and for the IPDF are compared
to computer simulations. P. A. C. S. Numbers: 82.20.Mj 02.50.+s 05.40.+j
05.70.LnComment: 13 pages (and 4 figures), plain TeX, SISSA-94-0
Concentration for One and Two Species One-Dimensional Reaction-Diffusion Systems
We look for similarity transformations which yield mappings between different
one-dimensional reaction-diffusion processes. In this way results obtained for
special systems can be generalized to equivalent reaction-diffusion models. The
coagulation (A + A -> A) or the annihilation (A + A -> 0) models can be mapped
onto systems in which both processes are allowed. With the help of the
coagulation-decoagulation model results for some death-decoagulation and
annihilation-creation systems are given. We also find a reaction-diffusion
system which is equivalent to the two species annihilation model (A + B ->0).
Besides we present numerical results of Monte Carlo simulations. An accurate
description of the effects of the reaction rates on the concentration in
one-species diffusion-annihilation model is made. The asymptotic behavior of
the concentration in the two species annihilation system (A + B -> 0) with
symmetric initial conditions is studied.Comment: 20 pages latex, uuencoded figures at the en
Universality and critical exponents of energy transport in binary crystals: 3B2u naphthalene
Exciton migration experiments on isotopically mixed naphthalene crystals reveal a universal behavior with reduced donor concentration, irrespective of temperature, acceptor species or acceptor concentration, giving a very wide scaling region, with critical exponents [gamma] = 2.1 +/- 0.22 and [beta] = 0.13 +/- 0.05, consistent with two-dimensional dynamic exciton percolation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24518/1/0000797.pd
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