724 research outputs found
Writhing Geometry of Open DNA
Motivated by recent experiments on DNA torsion-force-extension
characteristics we consider the writhing geometry of open stiff molecules. We
exhibit a cyclic motion which allows arbitrarily large twisting of the end of a
molecule via an activated process. This process is suppressed for forces larger
than femto-Newtons which allows us to show that experiments are sensitive to a
generalization of the Calugareanu-White formula for the writhe. Using numerical
methods we compare this formulation of the writhe with recent analytic
calculations.Comment: 12 pages 10 figures. Revtex
Comment on "Elasticity Model of a Supercoiled DNA Molecule"
We perform simulations to numerically study the writhe distribution of a
stiff polymer. We compare with analytic results of Bouchiat and Mezard (PRL 80
1556- (1998); cond-mat/9706050).Comment: 1 page, 1 figure revtex
Writhing Photons and Berry Phases in Diffusive Wave Scattering
We study theoretically the polarization state of light in multiple scattering
media in the limit of weak gradients in refractive index. Linearly polarized
photons are randomly rotated due to the Berry phase associated with the
scattering path. For circularly polarized light independent speckle patterns
are found for the two helical states. The statistics of the geometric phase is
related to the writhe distribution of semiflexible polymers such as DNA.Comment: 4 pages, 1 figur
The Global Earthquake Model Physical Vulnerability Database
There are almost 50 years of research on fragility and vulnerability assessment, both key
elements in seismic risk or loss estimation. This paper presents the online database of
physical vulnerability models that has been created as part of the Global Earthquake Model
(GEM) initiative. The database comprises fragility and vulnerability curves, damage-to-loss
models, and capacity curves for various types of structures. The attributes that have been
selected to characterize each function, the constraints of setting up a usable database, the
challenges in collecting these models, and the current trends in the development of
vulnerability models are discussed in this study. The current collection of models leverages
upon the outputs of several initiatives, such as GEM’s Global Vulnerability Consortium and
the European Syner-G project. This database is publicly available through the web-based
GEM OpenQuake-platform http://doi.org/10.13117/GEM.DATASET.VULN.WEB-V1.
Development and first operation of a Cavity Ring Down Spectroscopy diagnostic in the negative ion source SPIDER
The Neutral Beam Injectors of the ITER experiment will rely on negative ion
sources to produce 16.7 MW beams of H/D particles accelerated at 1 MeV. The
prototype of these sources was built and is currently operated in the SPIDER
experiment (Source for the Production of Ions o Deuterium Extracted from an RF
plasma), part of the Neutral Beam Test Facility of Consorzio RFX, Padua. In
SPIDER, the H-/D- ion source is coupled to a three grids 100 kV acceleration
system. One of the main targets of the experimentation in SPIDER is to
uniformly maximize the extracted current density; to achieve this it is
important to study the density of negative ions available in proximity of the
ion acceleration system. In SPIDER, line-integrated measurements of negative
ion density are performed by a Cavity Ring Down Spectroscopy (CRDS) diagnostic.
Its principle of operation is based on the absorption of the photons of a laser
beam pulse by H-/D- photo-detachment; the absorption detection is enhanced by
trapping the laser pulse in an optical cavity, containing the absorbing medium
(i.e. negative ions). The paper presents and discusses the CRDS diagnostic
setup in SPIDER, including the first measurements of negative ion density,
correlated to the main source parameters.Comment: 5 pages, 7 figures. Contributer paper for the HTPD 2020 conference.
Accepted manuscrip
Pitangueira leaves effects on enteric methane emission in adult sheep.
On a global scale, the production of methane (CH4) from ruminant animals is responsible for 8% of total anthropogenic greenhouse gas emissions (Beauchenin et al., 2008).Coordenador: Roberto Giolo de Almeida. II SIGEE
Local Simulation Algorithms for Coulomb Interaction
Long ranged electrostatic interactions are time consuming to calculate in
molecular dynamics and Monte-Carlo simulations. We introduce an algorithmic
framework for simulating charged particles which modifies the dynamics so as to
allow equilibration using a local Hamiltonian. The method introduces an
auxiliary field with constrained dynamics so that the equilibrium distribution
is determined by the Coulomb interaction. We demonstrate the efficiency of the
method by simulating a simple, charged lattice gas.Comment: Last figure changed to improve demonstration of numerical efficienc
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