31,601 research outputs found
Anomalous Lorentz and CPT violation from a local Chern-Simons-like term in the effective gauge-field action
We consider four-dimensional chiral gauge theories defined over a spacetime
manifold with topology and periodic boundary
conditions over the compact dimension. The effective gauge-field action is
calculated for Abelian gauge fields which depend on all
four spacetime coordinates (including the coordinate of the
compact dimension) and have vanishing components (implying trivial
holonomies in the 4-direction). Our calculation shows that the effective
gauge-field action contains a local Chern-Simons-like term which violates
Lorentz and CPT invariance. This result is established perturbatively with a
generalized Pauli-Villars regularization and nonperturbatively with a lattice
regularization based on Ginsparg-Wilson fermions.Comment: 48 pages, v7: published versio
Thermal elastohydrodynamic lubrication of line contacts
A numerical solution to the problem of thermal elastohydrodynamic lubrication of line contacts was obtained by using a finite difference formulation. The solution procedure consists of simultaneous solution of the thermal Reynolds equation, the elasticity equation, and the energy equation subject to appropriate boundary conditions. Pressure distribution, film shape, and temperature distribution were obtained for fully flooded conjunctions, a paraffinic lubricant, and various dimensionless speed parameters while the dimensionless load and materials parameters were held constant. Reduction in the minimum film thickness due to thermal effects (as a ratio of thermal to isothermal minimum film thickness) is given by a simple formula as a function of the thermal loading parameter Q: H(min)/H(min,I) = 10/10+ Q(0.4). Plots of pressure distribution, film shape, temperature distribution, and flow are shown for some representative cases
Modeling Censored Data Using Mixture Regression Models with an Application to Cattle Production Yields
This research develops a mixture regression model that is shown to have advantages over the classical Tobit model in model fit and predictive tests when data are generated from a two step process. Additionally, the model is shown to allow for flexibility in distributional assumptions while nesting the classic Tobit model. A simulated data set is utilized to assess the potential loss in efficiency from model misspecification, assuming the Tobit and a zero-inflated log-normal distribution, which is derived from the generalized mixture model. Results from simulations key on the finding that the proposed zero-inflated log-normal model clearly outperforms the Tobit model when data are generated from a two step process. When data are generated from a Tobit model, forecasts are more accurate when utilizing the Tobit model. However, the Tobit model will be shown to be a special case of the generalized mixture model. The empirical model is then applied to evaluating mortality rates in commercial cattle feedlots, both independently and as part of a system including other performance and health factors. This particular application is hypothesized to be more appropriate for the proposed model due to the high degree of censoring and skewed nature of mortality rates. The zero-inflated log-normal model clearly models and predicts with more accuracy that the tobit model.censoring, livestock production, tobit, zero-inflated, bayesian, Livestock Production/Industries,
A Multivariate Evaluation of Ex-ante Risks Associated with Fed Cattle Production
The purpose of this study is to evaluate the risks faced by fed cattle producers. With the development of livestock insurance programs as part of the Agricultural Risk Protection Act of 2000, a thorough investigation into the probabilistic measures of individual risk factors is needed. This research jointly models cattle production yield risk factors, using a multivariate dynamic regression model. A multivariate framework is necessary to characterize yield risk in terms of four yield factors (dry matter feed conversion, averaged daily gain, mortality, and veterinary costs), which are highly correlated. Additionally, a conditional Tobit model is used to handle censored yield variables (e.g., mortality). The proposed econometric model estimates parameters that influence the mean and variance of each production yield factor, as well as the covariance between variables. Following the model fitting using a maximum likelihood approach, simulation methods allow for profits, revenue, and gross margins to be evaluated given different assumptions concerning volatility among other shocks. The profit function is composed of random draws, based on conditioning variables, as well as parameter estimates. Shocks to variability, yield factors, or prices allow for a visual representation of the vulnerability of cattle feeder profits to these shocks.Livestock Production/Industries,
Solitons in 1+1 Dimensional Gauged Sigma Models
We study soliton solutions in 1+1 dimensional gauged sigma models, obtained
by dimensional reduction from its 2+1 dimensional counterparts. We show that
the Bogomol'nyi bound of these models can be expressed in terms of two
conserved charges in a similar way to that of the BPS dyons in 3+1 dimensions.
Purely magnetic vortices of the 2+1 dimensional completely gauged sigma model
appear as charged solitons in the corresponding 1+1 dimensional theory. The
scale invariance of these solitons is also broken because of the dimensional
reduction. We obtain exact static soliton solutions of these models saturating
the Bogomol'nyi bound.Comment: 21 pages, RevTeX, minor changes, version to appear in Physical Review
Three flavour Quark matter in chiral colour dielectric model
We investigate the properties of quark matter at finite density and
temperature using the nonlinear chiral extension of Colour Dielectric Model
(CCM). Assuming that the square of the meson fields devlop non- zero vacuum
expectation value, the thermodynamic potential for interacting three flavour
matter has been calculated. It is found that remain zero
in the medium whereas changes in the medium. As a result, and
quark masses decrease monotonically as the temperature and density of the quark
matter is increased.In the present model, the deconfinement density and
temperature is found to be lower compared to lattice results. We also study the
behaviour of pressure and energy density above critical temperature.Comment: Latex file. 5 figures available on request. To appear in Phys. Rev.
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