1,954 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
Changing Times, Changing Opinions: History Informing the Family Presence Debate
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75754/1/j.aem.2005.05.027.pd
Slipping friction of an optically and magnetically manipulated microsphere rolling at a glass-water interface
The motion of submerged magnetic microspheres rolling at a glass-water
interface has been studied using magnetic rotation and optical tweezers
combined with bright-field microscopy particle tracking techniques. Individual
microspheres of varying surface roughness were magnetically rotated both in and
out of an optical trap to induce rolling, along either plain glass cover slides
or glass cover slides functionalized with polyethylene glycol. It has been
observed that the manipulated microspheres exhibited nonlinear dynamic
rolling-while-slipping motion characterized by two motional regimes: At low
rotational frequencies, the speed of microspheres free-rolling along the
surface increased proportionately with magnetic rotation rate; however, a
further increase in the rotation frequency beyond a certain threshold revealed
a sharp transition to a motion in which the microspheres slipped with respect
to the external magnetic field resulting in decreased rolling speeds. The
effects of surface-microsphere interactions on the position of this threshold
frequency are posed and investigated. Similar experiments with microspheres
rolling while slipping in an optical trap showed congruent results.Comment: submitted to Journal of Applied Physics, 11 figure
Inter-Particle Distribution Functions for One-Species Diffusion-Limited Annihilation, A+A->0
Diffusion-limited annihilation, , and coalescence, , may
both be exactly analyzed in one dimension. While the concentrations of
particles in the two processes bear a simple relation, the inter-particle
distribution functions (IPDF) exhibit remarkable differences. However, the IPDF
is known exactly only for the coalescence process. We obtain the IPDF for the
annihilation process, based on the Glauber spin approach and assuming that the
IPDF's of nearest-particle pairs are statistically independent. This assumption
is supported by computer simulations. Our analysis sheds further light on the
relationship between the annihilation and the coalescence models.Comment: 15 pages, plain TeX, 3 figures - available upon request (snail mail
Too Many Cooks Spoil the Broth: How the Tragedy of the Anticommons Emerges in Organizations
In organizations, conflict often revolves around commons resources because they are critical for influence, performance, and organizational survival. Research on property rights, territoriality, and social dilemmas suggests that to reduce such conflict, organizations should facilitate the (psychological) privatization of commons resources. We complement these three literatures by drawing from the legal, organizational, and social psychology literatures to model how psychologically privatizing organizational commons resources – to prevent a tragedy of the commons (an overuse problem) – can lead to the emergence of equivalently problematic tragedy in organizations: the tragedy of the anticommons (an underuse problem). Our model contributes to these literatures by conceptualizing a bottom-up behavioral process (in contrast to institutional allocation) of property distribution that leads to the emergence of the tragedy of the anticommons. The implications of this bottom-up behavioral process for property rights theory, territoriality theory, and the social dilemma paradigm are discussed
Two weeks delayed bleeding in blunt liver injury: case report and review of the literature
Most cases of blunt hepatic trauma are treated nowadays non-operatively. This type of conservative treatment has resulted in increased complication rate. Delayed complications occur in cases that didn't require surgical intervention during the first 24 hours. The most common late complication is hemorrhage. We report a case of two weeks delayed hemorrhage after blunt hepatic trauma in an adult. We describe the diagnostic procedures, the surgical treatment and review the relevant literature
Mentalizing the body: spatial and social cognition in anosognosia for hemiplegia
Following right-hemisphere damage, a specific disorder of motor awareness can occur called anosognosia for hemiplegia, i.e. the denial of motor deficits contralateral to a brain lesion. The study of anosognosia can offer unique insights into the neurocognitive basis of awareness. Typically, however, awareness is assessed as a first person judgement and the ability of patients to think about their bodies in more ‘objective’ (third person) terms is not directly assessed. This may be important as right-hemisphere spatial abilities may underlie our ability to take third person perspectives. This possibility was assessed for the first time in the present study. We investigated third person perspective taking using both visuospatial and verbal tasks in right-hemisphere stroke patients with anosognosia ( n = 15) and without anosognosia ( n = 15), as well as neurologically healthy control subjects ( n = 15). The anosognosic group performed worse than both control groups when having to perform the tasks from a third versus a first person perspective. Individual analysis further revealed a classical dissociation between most anosognosic patients and control subjects in mental (but not visuospatial) third person perspective taking abilities. Finally, the severity of unawareness in anosognosia patients was correlated to greater impairments in such third person, mental perspective taking abilities (but not visuospatial perspective taking). In voxel-based lesion mapping we also identified the lesion sites linked with such deficits, including some brain areas previously associated with inhibition, perspective taking and mentalizing, such as the inferior and middle frontal gyri, as well as the supramarginal and superior temporal gyri. These results suggest that neurocognitive deficits in mental perspective taking may contribute to anosognosia and provide novel insights regarding the relation between self-awareness and social cognition
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
Fractal-like exciton transport and fusion in disordered naphthalene
Steady-state fluorescence and phosphorescence spectra od semi-crystalline naphthalene are presented. Singlet and triplet exciton transport are strongly dependent on temperature and degree of annealing. Analysis of delayed fluorescence decays reveals fractal-like transport in the more disordered samples.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24628/1/0000038.pd
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
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