128 research outputs found
Stochastic quasi-Newton molecular simulations
Article / Letter to editorLeiden Institute of Chemistr
A stochastic quasi Newton method for molecular simulations
In this thesis the Langevin equation with a space-dependent alternative mobility matrix has been considered. Simulations of a complex molecular system with many different length and time scales based on the fundamental equations of motion take a very long simulation time before capturing the functional and relevant motions. This problem is called critical slowing down. To avoid this problem multi-scale simulation methods are applied, which permits the use of different size time steps and thus enables acceleration of the relevant (slow) movements. The aim of this thesis is to develop a stochastic quasi Newton method, such that by incorporating multi-scaling the relevant motions are effectively taken with larger time step. Due to the integration of the slow motions with a larger time step, critical slowing down can be avoided. The proposed stochastic quasi Newton method enables automatic multi-scaling in the Langevin dynamics and contributes to efficient calculation of the noise term. The construction of the proposed method also enables the construction of a limited memory version for the mobility. This results in a method where less storage is needed. Together with the reduction of the computation time and the multi-scaling property, a powerful method for molecular simulations has been provided.UBL - phd migration 201
Stochastic quasi-Newton method: Application to minimal model for proteins
Soft Matter Chemistr
Stochastic quasi-Newton molecular simulations
Soft Matter Chemistr
Unitary designs and codes
A unitary design is a collection of unitary matrices that approximate the
entire unitary group, much like a spherical design approximates the entire unit
sphere. In this paper, we use irreducible representations of the unitary group
to find a general lower bound on the size of a unitary t-design in U(d), for
any d and t. We also introduce the notion of a unitary code - a subset of U(d)
in which the trace inner product of any pair of matrices is restricted to only
a small number of distinct values - and give an upper bound for the size of a
code of degree s in U(d) for any d and s. These bounds can be strengthened when
the particular inner product values that occur in the code or design are known.
Finally, we describe some constructions of designs: we give an upper bound on
the size of the smallest weighted unitary t-design in U(d), and we catalogue
some t-designs that arise from finite groups.Comment: 25 pages, no figure
Branching ratios of decays in perturbative QCD approach
We study the rare decays , which can occur only via
annihilation type diagrams in the standard model. We calculate all of the four
modes, , in the framework of perturbative QCD approach
and give the branching ratios of the order about .Comment: 18 pages, 1 figure, Revte
Branching ratio and CP asymmetry of decays in the perturbative QCD approach
In this paper, we calculate the decay rate and CP asymmetry of the decay in perturbative QCD approach with Sudakov resummation. Since
none of the quarks in final states is the same as those of the initial
meson, this decay can occur only via annihilation diagrams in the standard
model. Besides the current-current operators, the contributions from the QCD
and electroweak penguin operators are also taken into account. We find that (a)
the branching ratio is about ; (b) the penguin diagrams
dominate the total contribution; and (c) the direct CP asymmetry is small in
size: no more than ; but the mixing-induced CP asymmetry can be as large
as ten percent testable in the near future LHC-b experiments.Comment: 12 pages, 4 figures included, RevTe
Test of Factorization Hypothesis from Exclusive Non-leptonic B decays
We investigate the possibility of testing factorization hypothesis in
non-leptonic exclusive decays of B-meson. In particular, we considered the non
factorizable \bar{B^0} -> D^{(*)+} D_s^{(*)-} modes and \bar{B^0} -> D^{(*)+}
(\pi^-, \rho^-) known as well-factorizable modes. By taking the ratios
BR(\bar{B^0}-> D^{(*)+}D_s^{(*)-})/BR(\bar{B^0}-> D^{(*)+}(\pi^-,\rho^-)), we
found that under the present theoretical and experimental uncertainties there's
no evidence for the breakdown of factorization description to heavy-heavy
decays of the B meson.Comment: 11 pages; submitted to PR
Measurements of Cabibbo Suppressed Hadronic Decay Fractions of Charmed D0 and D+ Mesons
Using data collected with the BESII detector at storage ring
Beijing Electron Positron Collider, the measurements of relative branching
fractions for seven Cabibbo suppressed hadronic weak decays ,
, and , , and are presented.Comment: 11 pages, 5 figure
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