The Neveu-Schwarz Five-Brane and its Dual Geometries

In this paper we discuss two aspects of duality transformations on the Neveu-Schwarz (NS) 5-brane solutions in type II and heterotic string theories. First we demonstrate that the non-extremal NS 5-brane background is U-dual to its CGHS limit, a two-dimensional black hole times $S^3\times T^5$; an intermediate step is provided by the near horizon geometry which is given by the three-dimensional $BTZ_3$ black hole (being closely related to $AdS_3$) times $S^3\times T^4$. In the second part of the paper we discuss the T-duality between $k$ NS 5-branes and the Taub-NUT spaces respectively ALE spaces, which are related to the resolution of the $A_{k-1}$ singularities of the non-compact orbifold ${\bf C}^2/{\bf Z}_{k}$. In particular in the framework of N=1 supersymmetric gauge theories related to brane box constructions we give the metric dual to two sets of intersecting NS 5-branes. In this way we get a picture of a dual orbifold background ${\bf C}^3/ \Gamma$ which is fibered together out of two N=2 models ($\Gamma={\bf Z}_k\times {\bf Z}_{k'}$). Finally we also discuss the intersection of NS 5-branes with D branes, which can serve as probes of the dual background spaces.Comment: 18pp, added reference

Heterotic String Theory on non-Kaehler Manifolds with H-Flux and Gaugino Condensate

We discuss compactifications of heterotic string theory to four dimensions in the presence of H-fluxes, which deform the geometry of the internal manifold, and a gaugino condensate which breaks supersymmetry. We focus on the compensation of the two effects in order to obtain vacua with zero cosmological constant and we comment on the effective superpotential describing these vacua.Comment: 6 page

BPS Action and Superpotential for Heterotic String Compactifications with Fluxes

We consider N =1 compactifications to four dimensions of heterotic string theory in the presence of fluxes. We show that up to order O(\alpha'^2) the associated action can be written as a sum of squares of BPS-like quantities. In this way we prove that the equations of motion are solved by backgrounds which fulfill the supersymmetry conditions and the Bianchi identities. We also argue for the expression of the related superpotential and discuss the radial modulus stabilization for a class of examples.Comment: LaTeX, 28 pages. Minor changes, one more reference added. Final version to appear on JHE

Duality Symmetries and Supersymmetry Breaking in String Compactifications

We discuss the spontaneous supersymetry breaking within the low-energy effective supergravity action of four-dimensional superstrings. In particular, we emphasize the non-universality of the soft supersymmetry breaking parameters, the $\mu$-problem and the duality symmetries.Comment: (invited talk to the 27th ICHEP, Glasgow, July 1994), 11 page

Multi-year Water Allocation: A Policy Analysis for Groundwater Management and Conservation for Irrigated Agriculture

Heavy withdrawals from the most dependable source of groundwater in the Texas Panhandle, the Ogallala Aquifer, create an impending need for implementing water conservation policies. This study evaluates the policy option of multi-year water allocation coupled with water use restriction in four water deficit counties of Castro, Deafsmith, Parmer and Swisher over a sixty year planning horizon. Results indicate that the water use in the study area declines with progressive restriction rates accompanied by a substantial decrease in the net present value of net returns over sixty years and therefore it is important to analyze the socio-economic effects of implementing such a policy alternative.Multi-year allocation, Ogallala Aquifer, Texas Panhandle, Water conservation, Environmental Economics and Policy, Farm Management, Resource /Energy Economics and Policy,

Black Hole Formation and Classicalization in Ultra-Planckian 2 -> N Scattering

We establish a connection between the ultra-Planckian scattering amplitudes in field and string theory and unitarization by black hole formation in these scattering processes. Using as a guideline an explicit microscopic theory in which the black hole represents a bound-state of many soft gravitons at the quantum critical point, we were able to identify and compute a set of perturbative amplitudes relevant for black hole formation. These are the tree-level N-graviton scattering S-matrix elements in a kinematical regime (called classicalization limit) where the two incoming ultra-Planckian gravitons produce a large number N of soft gravitons. We compute these amplitudes by using the Kawai-Lewellen-Tye relations, as well as scattering equations and string theory techniques. We discover that this limit reveals the key features of the microscopic corpuscular black hole N-portrait. In particular, the perturbative suppression factor of a N-graviton final state, derived from the amplitude, matches the non-perturbative black hole entropy when N reaches the quantum criticality value, whereas final states with different value of N are either suppressed or excluded by non-perturbative corpuscular physics. Thus we identify the microscopic reason behind the black hole dominance over other final states including non-black hole classical object. In the parameterization of the classicalization limit the scattering equations can be solved exactly allowing us to obtain closed expressions for the high-energy limit of the open and closed superstring tree-level scattering amplitudes for a generic number N of external legs. We demonstrate matching and complementarity between the string theory and field theory in different large-s and large-N regimes.Comment: 55 pages, 7 figures, LaTeX; v2: typos removed; final version to appear in Nucl. Phys.

Production Profitability of Ethanol from Alternative Feedstocks in the Texas Panhandle

The potential of three feedstocks: grain sorghum, sweet sorghum, and switchgrass for ethanol production in the top 26 counties of the Texas Panhandle Region is analyzed using yield and production costs of feedstock, processing cost of feedstock, final demand for ethanol, farm to wholesale marketing margin, and the derived demand price of feedstock. The calculated economic returns per acre of grain sorghum, sweet sorghum, and switchgrass are -$45.37, -$410.19, and -$150.17 respectively under irrigated condition and -$38.25, -$145.09, and -$29.04 respectively under dryland condition. The evaluation in this study demonstrates that ethanol production from grain sorghum, sweet sorghum, and switchgrass in the Texas Panhandle Region is not economically feasible given the current price for ethanol in Texas. This is consistent with the status of the ethanol industry in the Texas Panhandle.Ethanol production, Texas Panhandle, Grain sorghum, Sweet sorghum, and Switchgrass, Feedstock, Crop Production/Industries, Production Economics, Resource /Energy Economics and Policy, Q16, Q25, Q27, and Q42,

Evaluating Dryland Crop/Livestock System Alternatives for Risk Management under Declining Irrigation in the Texas Panhandle

Production budgets for dryland crop and crop/livestock systems are developed to estimate yields, costs and returns for dryland wheat and sorghum and for alternative dryland crop/livestock systems. A crop simulation model aids yield estimation. The yield and return distributions are used to estimate risk and relative risk for included alternatives.Relative Risk, Ogallala Aquifer, Crop-Livestock Systems, Wheat, Sorghum, Crop Production/Industries, Farm Management, Livestock Production/Industries, Production Economics, Productivity Analysis,

Intercellular signaling as a cause of cell death in cyclically impacted cartilage explants

AbstractRecently, in vitro cartilage studies have shown that impact loading can produce structural damage and osteoarthritis-like changes, including tissue swelling, collagen denaturation, and cell death.Objective This study was to determine whether a signal for cell death moves through the cartilage matrix, resulting in the spread of cell death over time from impacted to unimpacted regions.Design Cyclic impacts were applied to the 2mm core of 4mm cartilage discs. Post-impact culturing extended for 3, 6 or 21 days and occurred in one of two ways. In one, discs were cultured intact. In the second, cores were removed immediately after cessation of impact and cores and rings cultured separately. Cells in apoptosis and later stage necrosis were monitored using the TUNEL assay.Results The extent of cell death in impacted samples increased with increased duration of post-impact culturing. At the early time, the majority of cell death was located in the regions of direct impact whereas after extended culture, the extent of cell death was similar in the surrounding unimpacted regions and in the impacted core region. However, the physical separation of the impacted core from the surrounding, non-impacted ring regions immediately after impact, and prior to independent culture, kept the level of cell death in the surrounding ring close to control levels, even after 21 days of incubation.Discussion These findings indicate that soluble intercellular signalling is involved in the spreading of cell death through the cartilage matrix, and that its effects can be prevented by physical isolation of the surrounding ring from the impacted core

Structured Random Matrices

Random matrix theory is a well-developed area of probability theory that has numerous connections with other areas of mathematics and its applications. Much of the literature in this area is concerned with matrices that possess many exact or approximate symmetries, such as matrices with i.i.d. entries, for which precise analytic results and limit theorems are available. Much less well understood are matrices that are endowed with an arbitrary structure, such as sparse Wigner matrices or matrices whose entries possess a given variance pattern. The challenge in investigating such structured random matrices is to understand how the given structure of the matrix is reflected in its spectral properties. This chapter reviews a number of recent results, methods, and open problems in this direction, with a particular emphasis on sharp spectral norm inequalities for Gaussian random matrices.Comment: 46 pages; to appear in IMA Volume "Discrete Structures: Analysis and Applications" (Springer