Liquid oxygen-compatible filament-winding matrix resin

Polyurethanes derived from hydroxy terminated polyperfluoro propylene oxide prepolymers were evaluated as matrix resins for filament wound composites which would be exposed to liquid (and 100% gaseous) oxygen environments. A number of structural modifications were brought about by variations in prepolymer molecular weight, and alternative curing agents which allowed retention of the oxygen compatibility. Although satisfactory performance was achieved at sub-ambient temperatures, the derived composites suffered considerable property loss at ambient or slightly elevated temperatures. To attain overall effectiveness of the composite system, upgrading of the polymer thermomechanical properties must first be achieved

Polymeric foams from cross-linkable poly-N-ary lenebenzimidazoles

Foamed cross-linked poly-N-arylenebinzimidazoles are prepared by mixing an organic tetraamine and an ortho substituted aromatic dicarboxylic acid anhydride in the presence of a blowing agent, and then heating the prepolymer to a temperature sufficient to complete polymerization and foaming of the reactants. In another embodiment of the process, the reactants are heated to form a prepolymer. The prepolymer is then cured at higher temperatures to complete foaming and polymerization

Dirac nodal pockets in the antiferromagnetic parent phase of FeAs superconductors

We show that previously measured small Fermi surface pockets within the antiferromagnetic phase of SrFe2As2 and BaFe2As2 are consistent with a Dirac dispersion modulated by interlayer hopping, giving rise to a Dirac point in k-space and a cusp in the magnetic field angle-dependent magnetic quantum oscillation frequencies. These findings support the existence of a nodal spin-density wave in these materials, which could play an important role in protecting the metallic state against localization effects. The speed of the Dirac fermions in SrFe2As2 and BaFe2As2 is found to be 14-20 times slower than in graphene, suggesting that the pnictides provide a laboratory for exploring the effects of strongly interacting Dirac fermions.Comment: 4 page

Does Direct Foreign Investment Affect Domestic Firms' Credit Constraints?

Firms in developing countries cite credit constraints as one of their primary obstacles to investment. Direct foreign investment, by bringing in scarce capital, may ease domestic firms' credit constraints. Alternatively, if foreign firms borrow heavily from domestic banks, they may exacerbate domestic firms' credit constraints by crowding them out of domestic capital markets. One plausible mechanism by which this may happen is indirect. Foreign firms may be more experienced and have better financial ratios and thus, be a safer bet for lending institutions. Using firm-level data from the Ivory Coast for the period 1974-1987 we test the following hypotheses: (1) domestic firms are more credit constrained than foreign firms and (2) borrowing by foreign firms exacerbates the credit constraints of domestic firms. Results suggest that domestic firms are significantly more credit constrained that foreign firms and that borrowing by foreign firms aggravates domestic firms' credit constraints. By splitting the sample into state-owned (SOE) and privately owned domestic enterprises we are able to show that SOEs are less financially constrained than other domestic enterprises, consistent with the notion of a 'soft budget constraint'. Borrowing by foreign firms affects only privately owned enterprises. Finally, we explore possible explanations for the crowding out effect.

Outsourcing Jobs? Multinationals and US Employment

Critics of globalization claim that US manufacturing firms are being driven to shift employment abroad by the prospects of cheaper labor. Others argue that the availability of low-wage labor has allowed US based firms to survive and even prosper. Yet evidence for either hypothesis, beyond anecdotes, is slim. Using firm-level data collected by the US Bureau of Economic Analysis (BEA), we estimate the impact on US manufacturing employment of changes in foreign affiliate wages, controlling for changing demand conditions and technological change. We find that the evidence supports both perspectives on globalization. For firms most likely to perform the same tasks in foreign affiliates and at home ("horizontal" foreign investment), foreign and domestic employees appear to be substitutes. For these firms, lower wages in affiliate locations are associated with lower employment in the US. However, for firms which do significantly different tasks at home and abroad ("vertical" foreign investment), foreign and domestic employment are complements. For vertical foreign investment, lower wages abroad are associated with higher US manufacturing employment. These offsetting effects may be combined to show that offshoring is associated with a quantitatively small decline in manufacturing employment. Other factors, such as declining prices for consumer goods, import competition, and falling prices for investment goods (which substitute for labor) play a more important role.