124 research outputs found
Manufactured Solutions for Verification of a Coupled Flow and Material Response Code
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106457/1/AIAA2013-2646.pd
Quantum repeaters and quantum key distribution: analysis of secret key rates
We analyze various prominent quantum repeater protocols in the context of
long-distance quantum key distribution. These protocols are the original
quantum repeater proposal by Briegel, D\"ur, Cirac and Zoller, the so-called
hybrid quantum repeater using optical coherent states dispersively interacting
with atomic spin qubits, and the Duan-Lukin-Cirac-Zoller-type repeater using
atomic ensembles together with linear optics and, in its most recent extension,
heralded qubit amplifiers. For our analysis, we investigate the most important
experimental parameters of every repeater component and find their minimally
required values for obtaining a nonzero secret key. Additionally, we examine in
detail the impact of device imperfections on the final secret key rate and on
the optimal number of rounds of distillation when the entangled states are
purified right after their initial distribution.Comment: Published versio
Thrust at N^3LL with Power Corrections and a Precision Global Fit for alphas(mZ)
We give a factorization formula for the e+e- thrust distribution dsigma/dtau
with tau=1-T based on soft-collinear effective theory. The result is applicable
for all tau, i.e. in the peak, tail, and far-tail regions. The formula includes
O(alphas^3) fixed-order QCD results, resummation of singular partonic alphas^j
ln^k(tau)/tau terms with N^3LL accuracy, hadronization effects from fitting a
universal nonperturbative soft function defined in field theory, bottom quark
mass effects, QED corrections, and the dominant top mass dependent terms from
the axial anomaly. We do not rely on Monte Carlo generators to determine
nonperturbative effects since they are not compatible with higher order
perturbative analyses. Instead our treatment is based on fitting
nonperturbative matrix elements in field theory, which are moments Omega_i of a
nonperturbative soft function. We present a global analysis of all available
thrust data measured at center-of-mass energies Q=35 to 207 GeV in the tail
region, where a two parameter fit to and the first moment
Omega_1 suffices. We use a short distance scheme to define Omega_1, called the
R-gap scheme, thus ensuring that the perturbative dsigma/dtau does not suffer
from an O(Lambda_QCD) renormalon ambiguity. We find alphas(mZ)=0.1135 \pm
(0.0002)_{expt} \pm (0.0005)_{hadr} \pm (0.0009)_{pert}, with chi^2/dof=0.91,
where the displayed 1-sigma errors are the total experimental error, the
hadronization uncertainty, and the perturbative theory uncertainty,
respectively. The hadronization uncertainty in alphas is significantly
decreased compared to earlier analyses by our two parameter fit, which
determines Omega_1=0.323 GeV with 16% uncertainty.Comment: 45 pages, 21 figures, v2: added discussion of bin integration vs.
cumulant differences; comparison to Becher & Schwartz improved; typo in Eq.55
fixe
A field-theoretic approach to the Wiener Sausage
The Wiener Sausage, the volume traced out by a sphere attached to a Brownian
particle, is a classical problem in statistics and mathematical physics.
Initially motivated by a range of field-theoretic, technical questions, we
present a single loop renormalised perturbation theory of a stochastic process
closely related to the Wiener Sausage, which, however, proves to be exact for
the exponents and some amplitudes. The field-theoretic approach is particularly
elegant and very enjoyable to see at work on such a classic problem. While we
recover a number of known, classical results, the field-theoretic techniques
deployed provide a particularly versatile framework, which allows easy
calculation with different boundary conditions even of higher momenta and more
complicated correlation functions. At the same time, we provide a highly
instructive, non-trivial example for some of the technical particularities of
the field-theoretic description of stochastic processes, such as excluded
volume, lack of translational invariance and immobile particles. The aim of the
present work is not to improve upon the well-established results for the Wiener
Sausage, but to provide a field-theoretic approach to it, in order to gain a
better understanding of the field-theoretic obstacles to overcome.Comment: 45 pages, 3 Figures, Springer styl
Emergent Properties of Tumor Microenvironment in a Real-life Model of Multicell Tumor Spheroids
Multicellular tumor spheroids are an important {\it in vitro} model of the
pre-vascular phase of solid tumors, for sizes well below the diagnostic limit:
therefore a biophysical model of spheroids has the ability to shed light on the
internal workings and organization of tumors at a critical phase of their
development. To this end, we have developed a computer program that integrates
the behavior of individual cells and their interactions with other cells and
the surrounding environment. It is based on a quantitative description of
metabolism, growth, proliferation and death of single tumor cells, and on
equations that model biochemical and mechanical cell-cell and cell-environment
interactions. The program reproduces existing experimental data on spheroids,
and yields unique views of their microenvironment. Simulations show complex
internal flows and motions of nutrients, metabolites and cells, that are
otherwise unobservable with current experimental techniques, and give novel
clues on tumor development and strong hints for future therapies.Comment: 20 pages, 10 figures. Accepted for publication in PLOS One. The
published version contains links to a supplementary text and three video
file
All stationary axi-symmetric local solutions of topologically massive gravity
We classify all stationary axi-symmetric solutions of topologically massive
gravity into Einstein, Schr\"odinger, warped and generic solutions. We
construct explicitly all local solutions in the first three sectors and present
an algorithm for the numerical construction of all local solutions in the
generic sector. The only input for this algorithm is the value of one constant
of motion if the solution has an analytic centre, and three constants of motion
otherwise. We present several examples, including soliton solutions that
asymptote to warped AdS.Comment: 42 pages, 9 figures. v2: Changed potentially confusing labelling of
one sector, added references. v3: Minor changes, matches published versio
Theory and Computation of the Spheroidal Wave Functions
In this paper we report on a package, written in the Mathematica computer
algebra system, which has been developed to compute the spheroidal wave
functions of Meixner [J. Meixner and R.W. Schaefke, Mathieusche Funktionen und
Sphaeroidfunktionen, 1954] and is available online
(www.physics.uwa.edu.au/~falloon/spheroidal/spheroidal.html). This package
represents a substantial contribution to the existing software, since it
computes the spheroidal wave functions to arbitrary precision for general
complex parameters mu, nu, gamma and argument z; existing software can only
handle integer mu, nu and does not give arbitrary precision. The package also
incorporates various special cases and computes analytic power series and
asymptotic expansions in the parameter gamma. The spheroidal wave functions of
Flammer [C. Flammer, Spheroidal Wave Functions, 1957] are included as a special
case of Meixner's more general functions. This paper presents a concise review
of the general theory of spheroidal wave functions and a description of the
formulas and algorithms used in their computation, and gives high-precision
numerical examples.Comment: 26 pages, 4 Appendices, 5 Table
Quantum fluctuations of one-dimensional free fermions and Fisher-Hartwig formula for Toeplitz determinants
We revisit the problem of finding the probability distribution of a fermionic
number of one-dimensional spinless free fermions on a segment of a given
length. The generating function for this probability distribution can be
expressed as a determinant of a Toeplitz matrix. We use the recently proven
generalized Fisher--Hartwig conjecture on the asymptotic behavior of such
determinants to find the generating function for the full counting statistics
of fermions on a line segment. Unlike the method of bosonization, the
Fisher--Hartwig formula correctly takes into account the discreteness of
charge. Furthermore, we check numerically the precision of the generalized
Fisher--Hartwig formula, find that it has a higher precision than rigorously
proven so far, and conjecture the form of the next-order correction to the
existing formula.Comment: 17 pages, 2 figures, Latex, iopart.cl
An assessment of existing models for individualized breast cancer risk estimation in a screening program in Spain
Background: The aim of this study was to evaluate the calibration and discriminatory power of three predictive
models of breast cancer risk.
Methods: We included 13,760 women who were first-time participants in the Sabadell-Cerdanyola Breast Cancer
Screening Program, in Catalonia, Spain. Projections of risk were obtained at three and five years for invasive cancer
using the Gail, Chen and Barlow models. Incidence and mortality data were obtained from the Catalan registries.
The calibration and discrimination of the models were assessed using the Hosmer-Lemeshow C statistic, the area
under the receiver operating characteristic curve (AUC) and the Harrell’s C statistic.
Results: The Gail and Chen models showed good calibration while the Barlow model overestimated the number of
cases: the ratio between estimated and observed values at 5 years ranged from 0.86 to 1.55 for the first two models
and from 1.82 to 3.44 for the Barlow model. The 5-year projection for the Chen and Barlow models had the highest
discrimination, with an AUC around 0.58. The Harrell’s C statistic showed very similar values in the 5-year projection
for each of the models. Although they passed the calibration test, the Gail and Chen models overestimated the
number of cases in some breast density categories.
Conclusions: These models cannot be used as a measure of individual risk in early detection programs to
customize screening strategies. The inclusion of longitudinal measures of breast density or other risk factors in joint
models of survival and longitudinal data may be a step towards personalized early detection of BC.This study was funded by grant PS09/01340 and The Spanish Network on Chronic Diseases REDISSEC (RD12/0001/0007) from the Health Research Fund (Fondo de InvestigaciĂłn Sanitaria) of the Spanish Ministry of Health
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