26,100 research outputs found
The role of vibrationalārotational coupling in VāV and VāR,T energy transfer
The effect of neglecting vibrationalārotational coupling in energy transfer calculations is studied for collisions of HF (v=1ā7) with HF (v=0). An analog of a "classical path" method is considered in which rigid-rotor trajectories are used to determine a time-dependent forcing term on the vibrational motion of each molecule. The results are compared with our quasiclassical calculations in which no such approximation was used. At higher vibrational states the rigid-rotor forced-oscillator model is found to predict substantially smaller VāR,T rate constants than those found in the exact study
Collisional broadening and spectral line shape of an entire rotational band
The impact approximation is applied to the classical binary collision operator making it possible to derive an expression for the dipole correlation function for real systems in a form which is computationally tractable and contains no adjustable parameters. Trajectory calculations are performed (in order to evaluate the microscopic expression for the relaxation parameter in the correlation function) for the system CO in dense Ar gas. Comparison is made with experimental data and excellent agreement is found for certain densities when a quantum correction is included. At higher densities (i.e., Ļ^(ā1/3)< "the range of the potential") one approximation is not valid and comparison with experiment illustrates this point
Cluster algebras in scattering amplitudes with special 2D kinematics
We study the cluster algebra of the kinematic configuration space
of a n-particle scattering amplitude restricted to the
special 2D kinematics. We found that the n-points two loop MHV remainder
function found in special 2D kinematics depend on a selection of
\XX-coordinates that are part of a special structure of the cluster algebra
related to snake triangulations of polygons. This structure forms a necklace of
hypercubes beads in the corresponding Stasheff polytope. Furthermore in , the cluster algebra and the selection of \XX-coordinates in special 2D
kinematics replicates the cluster algebra and the selection of \XX-coordinates
of two loop MHV amplitude in 4D kinematics.Comment: 22 page
Three-isotope plot of fractionation in photolysis: A perturbation theoretical expression
The slope of the three-isotope plot for the isotopomer fractionation by direct or nearly direct photodissociation is obtained using a perturbation theoretical analysis. This result, correct to first order in the mass difference, is the same as that for equilibrium chemical exchange reactions, a similarity unexpected a priori. A comparison is made with computational results for N2O photodissociation. This theoretical slope for mass-dependent photolytic fractionation can be used to analyze the data for isotopic anomalies in spin-allowed photodissociation reactions. Earlier work on chemical equilibria is extended by avoiding a high-temperature approximation
Modular structure in C. elegans neural network and its response to external localized stimuli
Synchronization plays a key role in information processing in neuronal
networks. Response of specific groups of neurons are triggered by external
stimuli, such as visual, tactile or olfactory inputs. Neurons, however, can be
divided into several categories, such as by physical location, functional role
or topological clustering properties. Here we study the response of the
electric junction C. elegans network to external stimuli using the partially
forced Kuramoto model and applying the force to specific groups of neurons.
Stimuli were applied to topological modules, obtained by the ModuLand
procedure, to a ganglion, specified by its anatomical localization, and to the
functional group composed of all sensory neurons. We found that topological
modules do not contain purely anatomical groups or functional classes,
corroborating previous results, and that stimulating different classes of
neurons lead to very different responses, measured in terms of synchronization
and phase velocity correlations. In all cases, however, the modular structure
hindered full synchronization, protecting the system from seizures. More
importantly, the responses to stimuli applied to topological and functional
modules showed pronounced patterns of correlation or anti-correlation with
other modules that were not observed when the stimulus was applied to ganglia.Comment: 23 pages, 6 figure
Energy Dissipation Via Coupling With a Finite Chaotic Environment
We study the flow of energy between a harmonic oscillator (HO) and an
external environment consisting of N two-degrees of freedom non-linear
oscillators, ranging from integrable to chaotic according to a control
parameter. The coupling between the HO and the environment is bilinear in the
coordinates and scales with system size with the inverse square root of N. We
study the conditions for energy dissipation and thermalization as a function of
N and of the dynamical regime of the non-linear oscillators. The study is
classical and based on single realization of the dynamics, as opposed to
ensemble averages over many realizations. We find that dissipation occurs in
the chaotic regime for a fairly small N, leading to the thermalization of the
HO and environment a Boltzmann distribution of energies for a well defined
temperature. We develop a simple analytical treatment, based on the linear
response theory, that justifies the coupling scaling and reproduces the
numerical simulations when the environment is in the chaotic regime.Comment: 7 pages, 10 figure
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