First Order Semiclassical Thermal String in the AdS Spacetime

We formulate the finite temperature theory for the free thermal excitations of the bosonic string in the anti-de Sitter (AdS) spacetime in the Thermo Field Dynamics (TFD) approach. The spacetime metric is treated exactly while the string and the thermal reservoir are semiclassically quantized at the first order perturbation theory with respect to the dimensionless parameter \epsilon = \a ' H^{-2}. In the conformal $D=2+1$ black-hole AdS background the quantization is exact. The method can be extended to the arbitrary AdS spacetime only in the first order perturbation. This approximation is taken in the center of mass reference frame and it is justified by the fact that at the first order the string dynamics is determined only by the interaction between the {\em free} string oscillation modes and the {\em exact} background. The first order thermal string is obtained by thermalization of the $T = 0$ system carried on by the TFD Bogoliubov operator. We determine the free thermal string states and compute the local entropy and free energy in the center of mass reference frame.Comment: Minor typos corrected. Two references added. LATeX file, 19 page

Current Algebra of Super WZNW Models

We derive the current algebra of supersymmetric principal chiral models with a Wess-Zumino term. At the critical point one obtains two commuting super Kac-Moody algebra as expected, but in general there are intertwining fields connecting both right and left sectors, analogously to the bosonic case. Moreover, in the present supersymmetric extension we have a quadratic algebra, rather than an affine Lie algebra, due to the mixing between bosonic and fermionic fields since the purely fermionic sector displays a Lie algebra as well.Comment: 13 page

Thermal DD-Brane Boundary States from Green-Schwarz Superstrings

In this paper we thermalize the type II superstrings in the GS formulation by applying the TFD formalism. The thermal boundary conditions on the thermal Hilbert space are obtained from the BPS $D$-brane boundary conditions at zero temperature. We show that thermal boundary states can be obtained by thermalization from the BPS $D$-branes at zero temperature. These new states can be interpreted as thermal $D$-branes. Next, we discuss the supersymmetry breaking of the thermal string in the TFD approach. We identify the broken supersymmetry with the $\epsilon$-transformation while the $\eta$-transformation is preserved. Also, we compute the thermal partition function and the entropy of the thermal string.Comment: 23 pages, LATeX fil

Integrable models: from dynamical solutions to string theory

We review the status of integrable models from the point of view of their dynamics and integrability conditions. Some integrable models are discussed in detail. We comment on the use it is made of them in string theory. We also discuss the Bethe Ansatz solution of the SO(6) symmetric Hamiltonian with SO(6) boundary. This work is especially prepared for the seventieth anniversaries of Andr\'{e} Swieca (in memoriam) and Roland K\"{o}berle.Comment: 24 pages, to appear in Brazilian Journal of Physic

Area Quantization in Quasi-Extreme Black Holes

We consider quasi-extreme Kerr and quasi-extreme Schwarzschild-de Sitter black holes. From the known analytical expressions obtained for their quasi-normal modes frequencies, we suggest an area quantization prescription for those objects.Comment: Final version to appear in Mod. Phys. Lett.

An effective Hamiltonian for 2D black hole Physics

In another application of the methods of Henneaux, Teitelboim, and Vergara developed for diffeomorphisms invariant models, the CGHS theory of 2D black holes is focused in order to obtain the true degrees of freedom, the simplectic structure and the {\it effective} Hamiltonian that rules the dynamics in reduced phase-space.Comment: To appear in Europhysics Letter

Possible Impacts of the Expected Shift From Cow-Calf to Cow-Calf-Yearling Enterprises on Beef Production and Beef Prices

Retention of young cattle and marketing older cattle from the range has been suggested as one of the profitable means of adjustment for the cow-calf operator. This study was to determine the impacts of the shift from cow-calf ranching operation to cow-calf-yearling operation on the feed energy budget of the ranch, cow herd size, beef production and market price of beef. Ten alternative livestock management options involving cow-calf-yearling operations were tested for these impacts, using two representative Utah size ranches (150 and 300 cow ranches). The extra feed needed to accomodate the increased number of yearlings and the decrease required in brood cow herd size were estimated. Changes in beef production in Utah, the Western eleven States, and the change on national price of beef were estimated from marketing projections of four types of beef. These projections were based on three levels of adoption for the management options by producers in each area. Under complete retention of home grown calves, the total amount of feed required to support the typical cow-calf operation was 93% of the total feed needed for the cow~calf short yearling and 85% of the total feed required for the cow-calf long-yearling operation. Only the production of long-yearlings resulted in a considerable decrease in brood cow carrying capacity (8 to 31%)· Marketing baby-beef and grass-fed beef produced a substantial decrease in beef tonnage and a corresponding increase in beef price. Light-fed short-yearlings and heavy-fed beef (from both short and long yearlings) showed a considerable beef increase in Utah and the western region. Only the marketing of heavy-fed short-yearlings produced a positive change in the beef produced nationally and a slight decrease in beef price (0.3 to 2 %)

Effects of Planting Dates on Yield and Quality of Garlic )Allium sativum L.) in Northern Sudan

Field experiments were conducted for three consecutive seasons starting 1991/92 at Hudeiba Research Station, northern Sudan. Seven planting dates between 15 Sept. and 15 Dec, were tested. Planting in I Oct. resulted in the highest yield ( 10263 kg/ha). followed by 15 Sept. (9980)kg/ha) and then I Nov. (8860 kg/ha). The lowest yields were found in the late planting dates.  The higher yields in early planting dates were due to the short days and low temperatures prevailing during the early stages of crop development to produce vigorous vegetative growth which is a prerequisite high garlic yields