38,598 research outputs found
The mass of the black hole in LMC X-3
New high resolution, optical spectroscopy of the high mass X-ray binary LMC X-3, shows the spectral type of the donor star changes with phase due to irradition by the X-ray source. We find the spectral type is likely to be B5V, and only appears as B3V when viewing the heated side of the donor. Combining our measurements with those previously published, and taking into account the effects of X-ray irradiation, results in a value for the donor star radial velocity semi-amplitude of ~km~s. We find the mass of the black hole lies in the range
The Abelian Higgs Model as an Ensemble of Vortex Loops
In the London limit of the Ginzburg-Landau theory (Abelian Higgs model),
vortex dipoles (small vortex loops) are treated as a grand canonical ensemble
in the dilute gas approximation. The summation over these objects with the most
general rotation- and translation invariant measure of integration over their
shapes leads to effective sine-Gordon theories of the dual fields. The
representations of the partition functions of both grand canonical ensembles
are derived in the form of the integrals over the vortex dipoles and the small
vortex loops, respectively. By virtue of these representations, the bilocal
correlator of the vortex dipoles (loops) is calculated in the low-energy limit.
It is further demonstrated that once the vortex dipoles (loops) are considered
as such an ensemble rather than individual ones, the London limit of the
Ginzburg-Landau theory (Abelian Higgs model) with external monopoles is
equivalent up to the leading order in the inverse UV cutoff to the compact QED
in the corresponding dimension with the charge of Cooper pairs changed due to
the Debye screening.Comment: 17 pages, LaTeX2e, no figures, dedicated to Prof. Yu.A. Simonov on
the occasion of his 65-th birthday, final published version (minor
corrections, references added
A modified Oster-Murray-Harris mechanical model of morphogenesis
There are two main modeling paradigms for biological pattern formation in developmental biology: chemical prepattern models and cell aggregation models. This paper focuses on an example of a cell aggregation model, the mechanical model developed by Oster, Murray, and Harris [Development, 78 (1983), pp. 83--125]. We revisit the Oster--Murray--Harris model and find that, due to the infinitesimal displacement assumption made in the original version of this model, there is a restriction on the types of boundary conditions that can be prescribed. We derive a modified form of the model which relaxes the infinitesimal displacement assumption. We analyze the dynamics of this model using linear and multiscale nonlinear analysis and show that it has the same linear behavior as the original Oster--Murray--Harris model. Nonlinear analysis, however, predicts that the modified model will allow for a wider range of parameters where the solution evolves to a bounded steady state. The results from both analyses are verified through numerical simulations of the full nonlinear model in one and two dimensions. The increased range of boundary conditions that are well-posed, as well as a wider range of parameters that yield bounded steady states, renders the modified model more applicable to, and more robust for, comparisons with experiments
Agribusiness Capstone Courses Design: Objectives and Strategies
This paper discusses the benefits of using strategic management principles as the cornerstone for building the agribusiness capstone experience. The necessity for agribusiness firms to create and implement strategies that build a sustainable competitive advantage in turn necessitates the development of strategic management skills in the leaders/managers of the future. As such, the objectives of a capstone course lean heavily toward the integrative development of strategic decision-making competence. This has a number of implications for the capstone professor in terms of course content, pedagogies, and subsequent measurement of student performance.Agribusiness, Teaching/Communication/Extension/Profession,
Non-Linear N-Parameter Spacetime Perturbations: Gauge Transformations
We introduce N-parameter perturbation theory as a new tool for the study of
non-linear relativistic phenomena. The main ingredient in this formulation is
the use of the Baker-Campbell-Hausdorff formula. The associated machinery
allows us to prove the main results concerning the consistency of the scheme to
any perturbative order. Gauge transformations and conditions for gauge
invariance at any required order can then be derived from a generating
exponential formula via a simple Taylor expansion. We outline the relation
between our novel formulation and previous developments.Comment: 7 pages, no figures, RevTeX 4.0. Revised version to match version
published in PR
New results for hadronic collisions in the framework of the Parton-Based Gribov-Regge Theory
We recently proposed a new approach to high energy nuclear scattering, which
treats hadronic collisions in a sophisticated way. Demanding theoretical
consistency as a minimal requirement for a realistic model, we provide a
solution for the energy conservation, screening problems and identical
elementary interactions, the so-called "Parton-Based Gribov-Regge Theory"
including enhanced diagrams. We can now present some of our results for SPS and
RHIC energies.Comment: 4 pages, 3 figures, To appear in the proceedings of Quark Matter 2002
(QM 2002), Nantes, France, 18-24 Jul 200
A Guide to Precision Calculations in Dyson's Hierarchical Scalar Field Theory
The goal of this article is to provide a practical method to calculate, in a
scalar theory, accurate numerical values of the renormalized quantities which
could be used to test any kind of approximate calculation. We use finite
truncations of the Fourier transform of the recursion formula for Dyson's
hierarchical model in the symmetric phase to perform high-precision
calculations of the unsubtracted Green's functions at zero momentum in
dimension 3, 4, and 5. We use the well-known correspondence between statistical
mechanics and field theory in which the large cut-off limit is obtained by
letting beta reach a critical value beta_c (with up to 16 significant digits in
our actual calculations). We show that the round-off errors on the magnetic
susceptibility grow like (beta_c -beta)^{-1} near criticality. We show that the
systematic errors (finite truncations and volume) can be controlled with an
exponential precision and reduced to a level lower than the numerical errors.
We justify the use of the truncation for calculations of the high-temperature
expansion. We calculate the dimensionless renormalized coupling constant
corresponding to the 4-point function and show that when beta -> beta_c, this
quantity tends to a fixed value which can be determined accurately when D=3
(hyperscaling holds), and goes to zero like (Ln(beta_c -beta))^{-1} when D=4.Comment: Uses revtex with psfig, 31 pages including 15 figure
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