Dilaton Dynamics from Production of Tensionless Membranes

In this paper we consider classical and quantum corrections to cosmological solutions of 11D SUGRA coming from dynamics of membrane states. We first consider the supermembrane spectrum following the approach of Russo and Tseytlin for consistent quantization. We calculate the production rate of BPS membrane bound states in a cosmological background and find that such effects are generically suppressed by the Planck scale, as expected. However, for a modified brane spectrum possessing enhanced symmetry, production can be finite and significant. We stress that this effect could not be anticipated given only a knowledge of the low-energy effective theory. Once on-shell, inclusion of these states leads to an attractive force pulling the dilaton towards a fixed point of S-duality, namely $g_s=1$. Although the SUGRA description breaks down in this regime, inclusion of the enhanced states suggests that the center of M-theory moduli space is a dynamical attractor. Morever, our results seem to suggest that string dynamics does indeed favor a vacuum near fixed points of duality.Comment: 39 pages, 7 figures, minor corrections and reference adde

Starting Small in an Unfamiliar Environment

Motivated by a characteristic way in which firms in developed countries make their decisions regarding cooperation with potential partners from less developed countries, we design a simple model of a DC firm's search for an LDC partner/supplier and the subsequent relationship between the two parties. Matched firms can "start small" with a trial order or pilot project of variable size in order to gain information about the ability of the LDC firm to successfully carry out a large project. We derive results relating whether and how the parties start small to the characteristics of the large project and to the matching environment. Among other results, we show how risk and search cost are associated with the propensity to start small and we establish a connection between starting small and the expected longevity of successful partnerships. We also address methods of contract enforcement and demonstrate the relationship between starting small and monitoring.

Entrepreneurship in International Trade

Motivated by evidence on the importance of incomplete information and networks in international trade, we investigate the supply of 'network intermediation.' We hypothesize that the agents who become international trade intermediaries first accumulate networks of foreign contacts while working as employees in production or sales, then become entrepreneurs who sell access to and use of the networks they accumulated. We report supportive results regarding this hypothesis from a pilot survey of international trade intermediaries. We then build a simple general-equilibrium model of this type of entrepreneurship, and use it for comparative statics and welfare analysis. One welfare conclusion is that intermediaries may have inadequate incentives to maintain or expand their networks, suggesting a rationale for the policies followed by some countries to encourage large-scale trading companies that imitate the Japanese sogo shosha.

Germanium:gallium photoconductors for far infrared heterodyne detection

Highly compensated Ge:Ga photoconductors have been fabricated and evaluated for high bandwidth heterodyne detection. Bandwidths up to 60 MHz have been obtained with corresponding current responsivity of 0.01 A/W

High temperature spark plug Patent

High temperature spark plug for igniting liquid rocket propellant

Materials technology for an advanced space power nuclear reactor concept: Program summary

The results of a materials technology program for a long-life (50,000 hr), high-temperature (950 C coolant outlet), lithium-cooled, nuclear space power reactor concept are reviewed and discussed. Fabrication methods and compatibility and property data were developed for candidate materials for fuel pins and, to a lesser extent, for potential control systems, reflectors, reactor vessel and piping, and other reactor structural materials. The effects of selected materials variables on fuel pin irradiation performance were determined. The most promising materials for fuel pins were found to be 85 percent dense uranium mononitride (UN) fuel clad with tungsten-lined T-111 (Ta-8W-2Hf)

Electric arc apparatus Patent

Electric arc heater with supersonic nozzle and fixed arc length for use in high temperature wind tunnel

Kelvin-Helmholtz Instability in a Weakly Ionized Medium

Ambient interstellar material may become entrained in outflows from massive stars as a result of shear flow instabilities. We study the linear theory of the Kelvin - Helmholtz instability, the simplest example of shear flow instability, in a partially ionized medium. We model the interaction as a two fluid system (charged and neutral) in a planar geometry. Our principal result is that for much of the relevant parameter space, neutrals and ions are sufficiently decoupled that the neutrals are unstable while the ions are held in place by the magnetic field. Thus, we predict that there should be a detectably narrower line profile in ionized species tracing the outflow compared with neutral species since ionized species are not participating in the turbulent interface with the ambient ISM. Since the magnetic field is frozen to the plasma, it is not tangled by the turbulence in the boundary layer.Comment: 21 pages, 4 figure

The extended hypergeometric class of L\'evy processes

With a view to computing fluctuation identities related to stable processes, we review and extend the class of hypergeometric L\'evy processes explored in Kuznetsov and Pardo (arXiv:1012.0817). We give the Wiener-Hopf factorisation of a process in the extended class, and characterise its exponential functional. Finally, we give three concrete examples arising from transformations of stable processes.Comment: 22 page