3,139 research outputs found
Three Bead Rotating Chain model shows universality in the stretching of proteins
We introduce a model of proteins in which all of the key atoms in the protein
backbone are accounted for, thus extending the Freely Rotating Chain model. We
use average bond lengths and average angles from the Protein Databank as input
parameters, leaving the number of residues as a single variable. The model is
used to study the stretching of proteins in the entropic regime. The results of
our Monte Carlo simulations are found to agree well with experimental data,
suggesting that the force extension plot is universal and does not depend on
the side chains or primary structure of proteins
Transverse spectral functions and Dzyaloshinskii-Moriya interactions in XXZ spin chains
Recently much progress has been made in applying field theory methods, first
developed to study X-ray edge singularities, to interacting one dimensional
systems in order to include band curvature effects and study edge singularities
at arbitrary momentum. Finding experimental confirmations of this theory
remains an open challenge. Here we point out that spin chains with uniform
Dzyaloshinskii-Moriya (DM) interactions provide an opportunity to test these
theories since these interactions may be exactly eliminated by a gauge
transformation which shifts the momentum. However, this requires an extension
of these X-ray edge methods to the transverse spectral function of the xxz spin
chain in a magnetic field, which we provide
On factorizations in perturbative quantum gravity
Some features of Einstein gravity are most easily understood from string
theory but are not manifest at the level of the usual Lagrangian formulation.
One example is the factorization of gravity amplitudes into gauge theory
amplitudes. Based on the recently constructed `double field theory' and a
geometrical frame-like formalism developed by Siegel, we provide a framework of
perturbative Einstein gravity coupled to a 2-form and a dilaton in which, as a
consequence of T-duality, the Feynman rules factorize to all orders in
perturbation theory. We thereby establish the precise relation between the
field variables in different formulations and discuss the Lagrangian that, when
written in terms of these variables, makes a left-right factorization manifest.Comment: 18 pages, v2: reference added, to appear in JHE
Model-based Control of the Scanning Tunneling Microscope: Enabling New Modes of Imaging, Spectroscopy, and Lithography
The invention of scanning tunneling microscope (STM) dates back to the work
of Binnig and Rohrer in the early 1980s, whose seminal contribution was
rewarded by the 1986 Nobel Prize in Physics for the design of the scanning
tunneling microscope. Forty years later, the STM remains the best existing tool
for studying electronic, chemical, and physical properties of conducting and
semiconducting surfaces with atomic precision. It has opened entirely new
fields of research, enabling scientists to gain invaluable insight into
properties and structure of matter at the atomic scale. Recent breakthroughs in
STM-based automated hydrogen depassivation lithography (HDL) on silicon have
resulted in the STM being considered a viable tool for fabrication of
error-free silicon-based quantum-electronic devices. Despite the STM's unique
ability to interrogate and manipulate matter with atomic precision, it remains
a challenging tool to use. It turns out that many issues can be traced back to
the STM's feedback control system, which has remained essentially unchanged
since its invention about 40 years ago. This article explains the role of
feedback control system of the STM and reviews some of the recent progress made
possible in imaging, spectroscopy, and lithography by making appropriate
changes to the STM's feedback control loop. We believe that the full potential
of the STM is yet to be realized, and the key to new innovations will be the
application of advanced model-based control and estimation techniques to this
system
Little Higgs Model Completed with a Chiral Fermionic Sector
The implementation of the little Higgs mechanism to solve the hierarchy
problem provides an interesting guiding principle to build particle physics
models beyond the electroweak scale. Most model building works, however, pay
not much attention to the fermionic sector. Through a case example, we
illustrate how a complete and consistent fermionic sector of the TeV effective
field theory may actually be largely dictated by the gauge structure of the
model. The completed fermionic sector has specific flavor physics structure,
and many phenomenological constraints on the model can thus be obtained beyond
gauge, Higgs, and top physics. We take a first look on some of the quark sector
constraints.Comment: 14 revtex pages with no figure, largely a re-written version of
hep-ph/0307250 with elaboration on flavor sector FCNC constraints; accepted
for publication in Phys.Rev.
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