3,144 research outputs found
Wind-engineering study of Seattle Hotel, Seattle
CER78-79JEC-JAP-AK13.Prepared for John Graham and Company.Includes bibliographical references (pages 32-33).September 1978
Wind-tunnel study of block 259 building, Houston
CER78-79JEC-JAP-AK18.Prepared for Colaco Engineers, Inc.Includes bibliographical references (pages 32-33).January 1979
The bend stiffness of S-DNA
We formulate and solve a two-state model for the elasticity of nicked,
double-stranded DNA that borrows features from both the Worm Like Chain and the
Bragg--Zimm model. Our model is computationally simple, and gives an excellent
fit to recent experimental data through the entire overstretching transition.
The fit gives the first value for the bending stiffness of the overstretched
state as about 10 nm*kbt, a value quite different from either B-form or
single-stranded DNA.Comment: 7 pages, 1 figur
Dissipation enhanced vibrational sensing in an olfactory molecular switch
Motivated by a proposed olfactory mechanism based on a
vibrationally-activated molecular switch, we study electron transport within a
donor-acceptor pair that is coupled to a vibrational mode and embedded in a
surrounding environment. We derive a polaron master equation with which we
study the dynamics of both the electronic and vibrational degrees of freedom
beyond previously employed semiclassical (Marcus-Jortner) rate analyses. We
show: (i) that in the absence of explicit dissipation of the vibrational mode,
the semiclassical approach is generally unable to capture the dynamics
predicted by our master equation due to both its assumption of one-way
(exponential) electron transfer from donor to acceptor and its neglect of the
spectral details of the environment; (ii) that by additionally allowing strong
dissipation to act on the odorant vibrational mode we can recover exponential
electron transfer, though typically at a rate that differs from that given by
the Marcus-Jortner expression; (iii) that the ability of the molecular switch
to discriminate between the presence and absence of the odorant, and its
sensitivity to the odorant vibrational frequency, are enhanced significantly in
this strong dissipation regime, when compared to the case without mode
dissipation; and (iv) that details of the environment absent from previous
Marcus-Jortner analyses can also dramatically alter the sensitivity of the
molecular switch, in particular allowing its frequency resolution to be
improved. Our results thus demonstrate the constructive role dissipation can
play in facilitating sensitive and selective operation in molecular switch
devices, as well as the inadequacy of semiclassical rate equations in analysing
such behaviour over a wide range of parameters.Comment: 12 pages, 6 figures, close to published version, comments welcom
Residual entropy in a model for the unfolding of single polymer chains
We study the unfolding of a single polymer chain due to an external force. We
use a simplified model which allows to perform all calculations in closed form
without assuming a Boltzmann-Gibbs form for the equilibrium distribution.
Temperature is then defined by calculating the Legendre transform of the
entropy under certain constraints. The application of the model is limited to
flexible polymers. It exhibits a gradual transition from compact globule to
rod. The boundary line between these two phases shows reentrant behavior. This
behavior is explained by the presence of residual entropy.Comment: 5 pages, 4 figures, extended version of arXiv:cond-mat/061225
Matter collineations of Spacetime Homogeneous G\"odel-type Metrics
The spacetime homogeneous G\"odel-type spacetimes which have four classes of
metrics are studied according to their matter collineations. The obtained
results are compared with Killing vectors and Ricci collineations. It is found
that these spacetimes have infinite number of matter collineations in
degenerate case, i.e. det, and do not admit proper matter
collineations in non-degenerate case, i.e. det. The degenerate
case has the new constraints on the parameters and which characterize
the causality features of the G\"odel-type spacetimes.Comment: 12 pages, LaTex, no figures, Class. Quantum.Grav.20 (2003) 216
Separation-dependent localization in a two-impurity spin-boson model
Using a variational approach we investigate the delocalized to localized
crossover in the ground state of an Ohmic two-impurity spin-boson model,
describing two otherwise non-interacting spins coupled to a common bosonic
environment. We show that a competition between an environment-induced Ising
spin interaction and externally applied fields leads to variations in the
system-bath coupling strength, , at which the delocalized-localized
crossover occurs. Specifically, the crossover regime lies between
and depending upon the spin separation and the
strength of the transverse tunneling field. This is in contrast to the
analogous single spin case, for which the crossover occurs (in the scaling
limit) at fixed . We also discuss links between the
two-impurity spin-boson model and a dissipative two-spin transverse Ising
model, showing that the latter possesses the same qualitative features as the
Ising strength is varied. Finally, we show that signatures of the crossover may
be observed in single impurity observables, as well as in the behaviour of the
system-environment entanglement.Comment: 12 pages, 9 figures. Published version. Expanded discussion of the
distance dependence between the impurities, and added a related figur
About the computation of the signature of surface singularities z^N+g(x,y)=0
In this article we describe our experiences with a parallel
SINGULAR-implementation of the signature of a surface singularity defined by
z^N+g(x,y)=0.Comment: 6 page
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