593 research outputs found
Getting DNA twist rigidity from single molecule experiments
We use an elastic rod model with contact to study the extension versus
rotation diagrams of single supercoiled DNA molecules. We reproduce
quantitatively the supercoiling response of overtwisted DNA and, using
experimental data, we get an estimation of the effective supercoiling radius
and of the twist rigidity of B-DNA. We find that unlike the bending rigidity,
the twist rigidity of DNA seems to vary widely with the nature and
concentration of the salt buffer in which it is immerged
Multivariate Fitting and the Error Matrix in Global Analysis of Data
When a large body of data from diverse experiments is analyzed using a
theoretical model with many parameters, the standard error matrix method and
the general tools for evaluating errors may become inadequate. We present an
iterative method that significantly improves the reliability of the error
matrix calculation. To obtain even better estimates of the uncertainties on
predictions of physical observables, we also present a Lagrange multiplier
method that explores the entire parameter space and avoids the linear
approximations assumed in conventional error propagation calculations. These
methods are illustrated by an example from the global analysis of parton
distribution functions.Comment: 13 pages, 5 figures, Latex; minor clarifications, fortran program
made available; Normalization of Hessian matrix changed to HEP standar
Questions on uncertainties in parton distributions
A discussion is presented of the manner in which uncertainties in parton distributions
and related quantities are determined. One of the central problems
is the criteria used to judge what variation of the parameters describing a set
of partons is acceptable within the context of a global fit. Various ways of
addressing this question are outlined
Termination Casts: A Flexible Approach to Termination with General Recursion
This paper proposes a type-and-effect system called Teqt, which distinguishes
terminating terms and total functions from possibly diverging terms and partial
functions, for a lambda calculus with general recursion and equality types. The
central idea is to include a primitive type-form "Terminates t", expressing
that term t is terminating; and then allow terms t to be coerced from possibly
diverging to total, using a proof of Terminates t. We call such coercions
termination casts, and show how to implement terminating recursion using them.
For the meta-theory of the system, we describe a translation from Teqt to a
logical theory of termination for general recursive, simply typed functions.
Every typing judgment of Teqt is translated to a theorem expressing the
appropriate termination property of the computational part of the Teqt term.Comment: In Proceedings PAR 2010, arXiv:1012.455
Lower bounds for open charm and beauty contributions to F_2
On the basis of some peculiar scaling properties of the OPE coefficient
functions, we give the lower bounds for F_2^{c\bar{c}} and F_2^{b\bar{b}}
independently of the properties of the gluon density function. Predictions for
F_2^{b\bar{b}} within reach of HERA are made.Comment: 10 pages, 4 eps figures. Misprints are corrected and comment is
added. To appear in JHE
QCD-supression by Black Hole Production at the LHC
Possible consequences of the production of small black holes at the LHC for
different scenarios with large extra dimensions are investigated. The effects
from black hole production on some standard jet observables are examined,
concentrating on the reduction of the QCD cross section. It is found that black
hole production of partons interacting on a short enough distance indeed seem
to generate a drastic drop in the QCD cross section. However from an
experimental point of view this will in most cases be camouflaged by energetic
radiation from the black holes
Heavy Quark Mass Effects in Deep Inelastic Scattering and Global QCD Analysis
A new implementation of the general PQCD formalism of Collins, including
heavy quark mass effects, is described. Important features that contribute to
the accuracy and efficiency of the calculation of both neutral current (NC) and
charged current (CC) processess are explicitly discussed. This new
implementation is applied to the global analysis of the full HERA I data sets
on NC and CC cross sections, with correlated systematic errors, in conjunction
with the usual fixed-target and hadron collider data sets. By using a variety
of parametrizations to explore the parton parameter space, robust new parton
distribution function (PDF) sets (CTEQ6.5) are obtained. The new quark
distributions are consistently higher in the region x ~ 10^{-3} than previous
ones, with important implications on hadron collider phenomenology, especially
at the LHC. The uncertainties of the parton distributions are reassessed and
are compared to the previous ones. A new set of CTEQ6.5 eigenvector PDFs that
encapsulates these uncertainties is also presented.Comment: 32 pages, 12 figures; updated, Publication Versio
Higgs boson production with one bottom quark jet at hadron colliders
We present total rates and kinematic distributions for the associated
production of a single bottom quark and a Higgs boson at the Tevatron and the
LHC. We include next-to-leading order QCD corrections and compare the results
obtained in the four and five flavor number schemes for parton distribution
functions.Comment: 4 pages, 8 figures, RevTeX
Lunar lander conceptual design
This paper is a first look at the problems of building a lunar lander to support a small lunar surface base. A series of trade studies was performed to define the lander. The initial trades concerned choosing number of stages, payload mass, parking orbit altitude, and propellant type. Other important trades and issues included plane change capability, propellant loading and maintenance location, and reusability considerations. Given a rough baseline, the systems were then reviewed. A conceptual design was then produced. The process was carried through only one iteration. Many more iterations are needed. A transportation system using reusable, aerobraked orbital transfer vehicles (OTV's) is assumed. These OTV's are assumed to be based and maintained at a low Earth orbit (LEO) space station, optimized for transportation functions. Single- and two-stage OTV stacks are considered. The OTV's make the translunar injection (TLI), lunar orbit insertion (LOI), and trans-Earth injection (TEI) burns, as well as midcourse and perigee raise maneuvers
Probing Topcolor-Assisted Technicolor from Like-sign Top Pair Production at LHC
The topcolor-assisted technicolor (TC2) theory predicts tree-level
flavor-changing neutral-current (FCNC) top quark Yukawa couplings with
top-pions. Such FCNC interactions will induce like-sign top quark pair
productions at CERN Large Hadron Collider (LHC). While these rare productions
are far below the observable level in the Standard Model and other popular new
physics models such as the Minimal Supersymmetric Model, we find that in a
sound part of parameter space the TC2 model can enhance the production cross
sections to several tens of fb and thus may be observable at the LHC due to
rather low backgrounds. Searching for these productions at the LHC will serve
as an excellent probe for the TC2 model.Comment: 10 pages, 6 fig
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