6,583 research outputs found
The Impact of Science on Society
Four speeches delivered as part of a public lecture series to assess the impact of science on society are presented. The computerization of society, space exploration and habitation, the mechanisms of technological change, and cultural responses are addressed
Heterogeneity and Disorder: Contributions of Rolf Landauer
Rolf Landauer made important contributions to many branches of science.
Within the broad area of transport in disordered media, he wrote seminal papers
on electrical conduction in macroscopically inhomogeneous materials, as well as
fundamental analyses of electron transport in quantum mechanical systems with
disorder on the atomic scale. We review here some of these contributions. We
also briefly describe some main events in his personal and scientific life.Comment: 10 pages, 3 figures; presented on the occasion when Rolf Landauer was
awarded, posthumously, the inaugural ETOPIM Medal at the ETOPIM 8 Conference,
which took place during 7--12 June, 2009 in Rethymnon, Cret
Transient and chaotic low-energy transfers in a system with bistable nonlinearity
The low-energy dynamics of a two-dof system composed of a grounded linear oscillator coupled to
a lightweight mass by means of a spring with both cubic nonlinear and negative linear components
is investigated. The mechanisms leading to intense energy exchanges between the linear oscillator,
excited by a low-energy impulse, and the nonlinear attachment are addressed. For lightly damped
systems, it is shown that two main mechanisms arise: Aperiodic alternating in-well and cross-well
oscillations of the nonlinear attachment, and secondary nonlinear beats occurring once the dynamics
evolves solely in-well. The description of the former dissipative phenomenon is provided in a
two-dimensional projection of the phase space, where transitions between in-well and cross-well
oscillations are associated with sequences of crossings across a pseudo-separatrix. Whereas the second
mechanism is described in terms of secondary limiting phase trajectories of the nonlinear
attachment under certain resonance conditions. The analytical treatment of the two aformentioned
low-energy transfer mechanisms relies on the reduction of the nonlinear dynamics and consequent
analysis of the reduced dynamics by asymptotic techniques. Direct numerical simulations fully
validate our analytical predictions
Structure of human transthyretin complexed with bromophenols: a new mode of binding
The binding of two organohalogen substances, pentabromophenol (PBP) and 2,4,6-tribromophenol (TBP), to human transthyretin (TTR), a thyroid hormone transport protein, has been studied by in vitro competitive binding assays and by X-ray crystallography. Both compounds bind to TTR with high affinity, in competition with the natural ligand thyroxine (
Generalized Paraxial Ray Trace Procedure Derived from Geodesic Deviation
Paraxial ray tracing procedures have become widely accepted techniques for
acoustic models in seismology and underwater acoustics. To date a generic form
of these procedures including fluid motion and time dependence has not appeared
in the literature. A detailed investigation of the characteristic curves of the
equations of hydrodynamics allows for an immediate generalization of the
procedure to be extracted from the equation form geodesic deviation. The
general paraxial ray trace equations serve as an ideal supplement to ordinary
ray tracing in predicting the deformation of acoustic beams in random
environments. The general procedure is derived in terms of affine
parameterization and in a coordinate time parameterization ideal for
application to physical acoustic ray propagation. The formalism is applied to
layered media, where the deviation equation reduces to a second order
differential equation for a single field with a general solution in terms of a
depth integral along the ray path. Some features are illustrated through
special cases which lead to exact solutions in terms of either ordinary or
special functions.Comment: Original; 40 pages (double spaced), 1 figure Replaced version; 36
pages single spaced, 7 figures. Expanded content; Complete derivation of the
equations from the equations of hydrodynamics, introduction of an auxiliary
basis for three dimensional wave-front modeling. Typos in text and equations
correcte
Closed Bosonic String Partition Function in Time Independent Exact PP-Wave Background
The modular invariance of the one-loop partition function of the closed
bosonic string in four dimensions in the presence of certain homogeneous exact
pp-wave backgrounds is studied. In the absence of an axion field the partition
function is found to be modular invariant. In the presence of an axion field
modular invariace is broken. This can be attributed to the light-cone gauge
which breaks the symmetry in the -, -directions. Recovery of this
broken modular invariance suggests the introduction of twists in the
world-sheet directions. However, one needs to go beyond the light-cone gauge to
introduce such twists.Comment: 17 pages, added reference
Universality and Clustering in 1+1 Dimensional Superstring-Bit Models
We construct a 1+1 dimensional superstring-bit model for D=3 Type IIB
superstring. This low dimension model escapes the problems encountered in
higher dimension models: (1) It possesses full Galilean supersymmetry; (2) For
noninteracting polymers of bits, the exactly soluble linear superpotential
describing bit interactions is in a large universality class of superpotentials
which includes ones bounded at spatial infinity; (3) The latter are used to
construct a superstring-bit model with the clustering properties needed to
define an -matrix for closed polymers of superstring-bits.Comment: 11 pages, Latex documen
Scalable Parallel Numerical Constraint Solver Using Global Load Balancing
We present a scalable parallel solver for numerical constraint satisfaction
problems (NCSPs). Our parallelization scheme consists of homogeneous worker
solvers, each of which runs on an available core and communicates with others
via the global load balancing (GLB) method. The parallel solver is implemented
with X10 that provides an implementation of GLB as a library. In experiments,
several NCSPs from the literature were solved and attained up to 516-fold
speedup using 600 cores of the TSUBAME2.5 supercomputer.Comment: To be presented at X10'15 Worksho
Absorption of dilaton s-wave in type 0B string theory
We find the absorption probability of dilaton field in type 0B string theory.
Since the background solutions are of the form on both
regions, we use the semiclassical formalism adopted in type IIB theory to find
the absorption cross section. The background tachyon field solution was used as
a reference to relate the solutions of the two regions. We also consider the
possible corrections to absorption probability and the form of the
correction is expected as in the calculation of the confinement solution.Comment: minor corrections, reference added, version to appear PR
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