10,791 research outputs found
Exact Random Walk Distributions using Noncommutative Geometry
Using the results obtained by the non commutative geometry techniques applied
to the Harper equation, we derive the areas distribution of random walks of
length on a two-dimensional square lattice for large , taking into
account finite size contributions.Comment: Latex, 3 pages, 1 figure, to be published in J. Phys. A : Math. Ge
Entropic Barriers, Frustration and Order: Basic Ingredients in Protein Folding
We solve a model that takes into account entropic barriers, frustration, and
the organization of a protein-like molecule. For a chain of size , there is
an effective folding transition to an ordered structure. Without frustration,
this state is reached in a time that scales as , with
. This scaling is limited by the amount of frustration which
leads to the dynamical selectivity of proteins: foldable proteins are limited
to monomers; and they are stable in {\it one} range of temperatures,
independent of size and structure. These predictions explain generic properties
of {\it in vivo} proteins.Comment: 4 pages, 4 Figures appended as postscript fil
Dimensional analysis and Rutherford Scattering
Dimensional analysis, and in particular the Buckingham theorem is
widely used in fluid mechanics. In this article we obtain an expression for the
impact parameter from Buckingham's theorem and we compare our result with
Rutherford's original discovery found in the early twentieth century
Electron and ion stagnation at the collision front between two laser produced plasmas
We report results from a combined optical interferometric and spectrally resolved imaging study on colliding laser produced aluminium plasmas. A Nomarski interferometer was used to probe the spatio-temporal distribution of electron densities at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a localized electron density feature with a well-defined profile reminiscent of a stagnation layer. Electron stagnation begins at a time delay of 10 ns after the peak of the plasma generating laser pulse. The peak electron density was found to exceed 10^19 cm^â3 and the layer remained well defined up to a time delay of ca 100 ns. Temporally and spectrally resolved optical imaging was also undertaken, to compare the Al^+ ion distribution with that of the 2D electron density profile. This revealed nascent stagnation of singly charged ions at a delay time of 20 ns. We attribute these results to the effects of space charge separation in the seed plasma plumes
Path integral approach to no-Coriolis approximation in heavy-ion collisions
We use the two time influence functional method of the path integral approach
in order to reduce the dimension of the coupled-channels equations for
heavy-ion reactions based on the no-Coriolis approximation. Our method is
superior to other methods in that it easily enables us to study the cases where
the initial spin of the colliding particle is not zero. It can also be easily
applied to the cases where the internal degrees of freedom are not necessarily
collective coordinates. We also clarify the underlying assumptions in our
approach.Comment: 11 pages, Latex, Phys. Rev. C in pres
FastContact: a free energy scoring tool for proteinâprotein complex structures
âFastContactâ is a server that estimates the direct electrostatic and desolvation interaction free energy between two proteins in units of kcal/mol. Users submit two proteins in PDB format, and the output is emailed back to the user in three files: one output file, and the two processed proteins. Besides the electrostatic and desolvation free energy, the server reports residue contact free energies that rapidly highlight the hotspots of the interaction and evaluates the van der Waals interaction using CHARMm. Response time is âŒ1âmin. The server has been successfully tested and validated, scoring refined complex structures and blind sets of docking decoys, as well as proven useful predicting protein interactions. âFastContactâ offers unique capabilities from biophysical insights to scoring and identifying important contacts
Gravitomagnetism in Metric Theories: Analysis of Earth Satellites Results, and its Coupling with Spin
Employing the PPN formalism the gravitomagnetic field in different metric
theories is considered in the analysis of the LAGEOS results. It will be shown
that there are several models that predict exactly the same effect that general
relativity comprises. In other words, these Earth satellites results can be
taken as experimental evidence that the orbital angular momentum of a body does
indeed generate space--time geometry, notwithstanding they do not endow general
relativity with an outstanding status among metric theories. Additionally the
coupling spin--gravitomagnetic field is analyzed with the introduction of the
Rabi transitions that this field produces on a quantum system with spin 1/2.
Afterwards, a continuous measurement of the energy of this system is
introduced, and the consequences upon the corresponding probabilities of the
involved gravitomagnetic field will be obtained. Finally, it will be proved
that these proposals allows us, not only to confront against future experiments
the usual assumption of the coupling spin--gravotimagnetism, but also to
measure some PPN parameters and to obtain functional dependences among them.Comment: 10 page
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