6,715 research outputs found
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 Effect of Climate Change on Transportation Flows and Inland Waterways Due to Climate-Induced Shifts in Crop Production Patterns
This study was funded by the the University Transportation Center for Mobility, Texas Transportation InstituteGrain Transportation, Climate change and agriculture, Climate change and transportation, Land use change, Supply of grain, Demand for grain, Crop production patterns, Inland waterways, Mississippi River Basin, Climate change adaptation, Welfare distribution, Corn transportation, Soybeans transportation, Crop Production/Industries, Demand and Price Analysis, Environmental Economics and Policy, International Relations/Trade, Land Economics/Use, C61, L91, L92, Q15, Q17, Q54, R14, R41, R13,
Frequency shift of hyperfine transitions due to blackbody radiation
We have performed calculations of the size of the frequency shift induced by
a static electric field on the clock transition frequencies of the hyperfine
splitting in Yb+, Rb, Cs, Ba+, and Hg+. The calculations are used to find the
frequency shifts due to blackbody radiation which are needed for accurate
frequency measurements and improvements of the limits on variation of the fine
structure constant, alpha. Our result for Cs (delta nu E^2=-2.26 times
10^{-10}Hz/(V/m)^2) is in good agreement with early measurements and ab initio
calculations. We present arguments against recent claims that the actual value
might be smaller. The difference (approx 10%) is due to the contribution of the
continuum spectrum in the sum over intermediate states.Comment: Added discussion of Cs results and reference
An Iterative and Toolchain-Based Approach to Automate Scanning and Mapping Computer Networks
As today's organizational computer networks are ever evolving and becoming
more and more complex, finding potential vulnerabilities and conducting
security audits has become a crucial element in securing these networks. The
first step in auditing a network is reconnaissance by mapping it to get a
comprehensive overview over its structure. The growing complexity, however,
makes this task increasingly effortful, even more as mapping (instead of plain
scanning), presently, still involves a lot of manual work. Therefore, the
concept proposed in this paper automates the scanning and mapping of unknown
and non-cooperative computer networks in order to find security weaknesses or
verify access controls. It further helps to conduct audits by allowing
comparing documented with actual networks and finding unauthorized network
devices, as well as evaluating access control methods by conducting delta
scans. It uses a novel approach of augmenting data from iteratively chained
existing scanning tools with context, using genuine analytics modules to allow
assessing a network's topology instead of just generating a list of scanned
devices. It further contains a visualization model that provides a clear, lucid
topology map and a special graph for comparative analysis. The goal is to
provide maximum insight with a minimum of a priori knowledge.Comment: 7 pages, 6 figure
A Spatial Equilibrium Model of the Impact of Bio-Fuels Energy Policy on Grain Transportation Flows
Traffic flows in the U.S. have been affected by the substantial increase and, as of January 2009, decrease in biofuel production and use. This paper considers a framework to study the effect on grain transportation flows of the 2005 Energy Act and subsequent legislation, which mandated higher production levels of biofuels, e.g. ethanol and biodiesels. Future research will incorporate changes due to the recent economic slowdown.ethanol, biodiesel, spatial equilibrium, quadratic programming, Agricultural and Food Policy, Crop Production/Industries, Resource /Energy Economics and Policy,
Monitoring wolf populations using howling points combined with sign survey transects
Wolves respond to simulated howling, especially during the mating and breeding seasons. Simulated howling points are, therefore, commonly used by many wolf researchers around the world to estimate pack numbers in a given area. A large amount of information is available on various pack breeding
areas in Asturias, the only region in north-western Spain where the Iberian wolf (Canis lupus signatus, Cabrera 1907) is not classed as a game species. Wolf research began there in the early 1980s. We present the results of the latest study on population status, conducted between July and November, 2001. Using sampling transects to detect wolf scat and scratch marks and designated howling and observation points, twenty one (21) wolf packs were
definitely located, with two others considered “likely”. Nineteen (19) packs were detected using howling points (n=314). The results of this study show that simulated howling points and sampling transects are reliable and
inexpensive way of detecting wolf packs
Spin Dynamics near the Superconductor-to-Insulator Transition in Impurity-Doped YBa2Cu4O8
We studied low-frequency spin dynamics near the impurity-induced
superconductor-to-insulator transition for underdoped high-Tc superconductor
YBa2(Cu1-xMx)4O8 (M=Ni, Zn) using the Cu nuclear quadrupole resonance (NQR)
spin-echo technique. We observed remarkable suppression of the normal-state
pseudo spin-gap and a loss of Cu NQR spectrum intensity at low temperatures
around the critical impurity concentration.Comment: 6 pages, 4 figures. To be published in J. Phys. Soc. Jpn. Vol.70,
No.7 (2001
Quantum effective potential, electron transport and conformons in biopolymers
In the Kirchhoff model of a biopolymer, conformation dynamics can be
described in terms of solitary waves, for certain special cross-section
asymmetries. Applying this to the problem of electron transport, we show that
the quantum effective potential arising due to the bends and twists of the
polymer enables us to formalize and quantify the concept of a {\it conformon}
that has been hypothesized in biology. Its connection to the soliton solution
of the cubic nonlinear Schr\"{o}dinger equation emerges in a natural fashion.Comment: to appear in J. Phys.
No-horizon theorem for spacetimes with spacelike G1 isometry groups
We consider four-dimensional spacetimes which obey the
Einstein equations , and admit a global spacelike
isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
which guarantees that cannot contain apparent
horizons. Given any (3+1) spacetime with spacelike translational isometry, the
no-horizon condition can be readily tested without the need for dimensional
reduction. This provides thus a useful and encompassing apparent horizon test
for -symmetric spacetimes. We argue that this adds further evidence
towards the validity of the hoop conjecture, and signals possible violations of
strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra
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