Investigation of acceptor levels and hole scattering mechanisms in p-gallium selenide by means of transport measurements under pressure

The effect of pressure on acceptor levels and hole scattering mechanisms in p-GaSe is investigated through Hall effect and resistivity measurements under quasi-hydrostatic conditions up to 4 GPa. The pressure dependence of the hole concentration is interpreted through a carrier statistics equation with a single (nitrogen) or double (tin) acceptor whose ionization energies decrease under pressure due to the dielectric constant increase. The pressure effect on the hole mobility is also accounted for by considering the pressure dependencies of both the phonon frequencies and the hole-phonon coupling constants involved in the scattering rates.Comment: 13 pages, Latex, 4 ps figures. to appear in High Pressure Research 69 (1997

Rotating Stars and the Formation of Bipolar Planetary Nebulae II: Tidal Spin-up

We present new binary stellar evolution models that include the effects of tidal forces, rotation, and magnetic torques with the goal of testing Planetary Nebulae (PNe) shaping via binary interaction. We explore whether tidal interaction with a companion can spin up the AGB envelope. To do so we have selected binary systems with main sequence masses of 2.5 \Mo and of 0.8 \Mo and evolve them allowing initial separations of 5, 6, 7, and 8 AU. The binary stellar evolution models have been computed all the way to the PNe formation phase or until Roche lobe overflow (RLOF) is reached, whatever happens first. We show that with initial separations of 7 and 8 AU, the binary avoids entering into RLOF, and the AGB star reaches moderate rotational velocities at the surface ($\sim 3.5$ and $\sim 2$ \kms respectively) during the inter-pulse phases, but after the thermal pulses it drops to a final rotational velocity of only $\sim 0.03$ \kms. For the closest binary separations explored, 5 and 6 AU, the AGB star reaches rotational velocities of $\sim 6$ and $\sim 4$ \kms respectively when the RLOF is initiated. We conclude that the detached binary models that avoid entering the RLOF phase during the AGB will not shape bipolar PNe, since the acquired angular momentum is lost via the wind during the last two thermal pulses. This study rules out tidal spin-up in non-contact binaries as a sufficient condition to form bipolar PNe.Comment: 25 pages, 3 figures, accepted by The Astrophysical Journa

How does the North American Free Trade Agreement (NAFTA) affect Central America?

Most Central American economies experienced slower growth in the 1980s than in the 1960s and 1970s, trailing far behind the Asian Tigers. Contributing to slow growth were severe external shocks, sizable macroeconomic disturbances, and widespread political instability. The challenges Central America faces now may be even greater, conclude the authors, because of Mexican liberalization, continuing instability of the real exchange rate, low savings rates, and, finally, the North American Free Trade Agreement (NAFTA). Improvements in per capita income are closely linked with exports to North America of labor-intensive manufactures. Earnings from the export of tropical agricultural products are important, but the Central American labor force is unlikely to earn higher wagers unless countries diversify more into manufacturing. The Asian Tigers began their economic miracles by shifting into such labor-intensive manufactures as apparel and footwear, which they could export to a vast high-wage market. But the US market for such exports is now more crowded and threatens to become more so, with exports from China and other very low-wage countries. With Asian competition hurting Central America's chances, it could be said that wages in Central America are set in Beijing, not in San Jose. The authors examine the critical drivers of Central America's future competitiveness: economic liberalization, uncertainty about the real exchange rate, distance from key markets, savings rates and NAFTA. Central American economies have low wage rates, and considerable advantage of location over Asia in selling in North American markets, especially Mexico. But real exchange rates in Central America are more unpredictable than those in Asian countries. Central America faces a chicken-and-egg problem. To stabilize its terms of trade, it must expand exports of manufactures. But instability in the terms of trade deters the investments that would lead to expanded exports of manufactures. By greatly increasong Mexico's attractiveness to foreign investors, NAFTA could be the straw that breaks the camel's back, as far as Central America is concerned. For this reason, the governments of Central America need to do all in their power to increase domestic savings and reduce investment risks. Exchange rate stabilization should be carried out obviously with appropriate macroeconomic policies -- but also by encouraging exports of labor-intensive manufactures with appropriate incentives, supporting infrastructure and educational investments. The key conclusion is that the future of Central America rests importantly on exports to Mexico, a market today which is pretty much untapped. Investments in transportation infrastructure that can facilitate this emerging trade are likely to have very large payoffs for the Central American economies.Trade Policy,Economic Theory&Research,Environmental Economics&Policies,Labor Policies,Banks&Banking Reform,Environmental Economics&Policies,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Economic Growth,Banks&Banking Reform,Economic Theory&Research

Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass

Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution

SUPPLY CHAIN MANAGEMENT AND THE ROMANIAN TRANSITION

Supply Chain Management (SCM), defined here as the construction of productive systems spanning over organizational borders with suppliers and customers and integrated via human-based and information technology systems to satisfy final customer requirements, is introduced as a key concept to accelerate Romania’s economic transition as it approaches EU membership, as well as to develop a modern supplier network. We introduce SCM from a system perspective along three broad areas: input, operations, output and system integration activities. We close by introducing constraints to SCM implementation in Romania. The first major constraint involves a lack of appropriate physical and human capital. Modernization of antiquated equipment and training employees in modern operations practices are prime requisites. The second major constraint, and perhaps the more difficult to change, deals with a lack of social capital among Romanian firms and adapting to appropriate managerial and worker values and attitudes.Supply Chain Management; Social Capital; Transition Economy; Economic Development.

Fast microwave-assisted synthesis of Li-stuffed garnets and insights into Li diffusion from muon spin spectroscopy

Lithium-stuffed garnets attract huge attention due to their outstanding potential as solid-state electrolytes for lithium batteries. However, there exists a persistent challenge in the reliable synthesis of these complex functional oxides together with a lack of complete understanding of the lithium-ion diffusion mechanisms in these important materials. Addressing these issues is critical to realizing the application of garnet materials as electrolytes in all solid-state lithium-ion batteries. In this work, a cubic phase garnet of nominal composition Li6.5Al0.25La2.92Zr2O12 is synthesized through a microwave-assisted solid-state route for the first time, reducing considerably the reaction times and heating temperatures. Lithium-ion diffusion behavior is investigated by electrochemical impedance spectroscopy (EIS) and state-of-art muon spin relaxation (μSR) spectroscopy, displaying activation energies of 0.55 ± 0.03 eV and 0.19 ± 0.01 eV respectively. This difference arises from the high inter-grain resistance, which contributes to the total resistance in EIS measurements. In contrast, μSR acts as a local probe providing insights on the order of the lattice, giving an estimated value of 4.62 × 10−11 cm2 s−1 for the lithium diffusion coefficient. These results demonstrate the potential of this lithium-stuffed garnet as a solid-state electrolyte for all-solid state lithium-ion batteries, an area of growing interest in the energy storage community

Echo Emission From Dust Scattering and X-Ray Afterglows of Gamma-Ray Bursts

We investigate the effect of X-ray echo emission in gamma-ray bursts (GRBs). We find that the echo emission can provide an alternative way of understanding X-ray shallow decays and jet breaks. In particular, a shallow decay followed by a "normal" decay and a further rapid decay of X-ray afterglows can be together explained as being due to the echo from prompt X-ray emission scattered by dust grains in a massive wind bubble around a GRB progenitor. We also introduce an extra temporal break in the X-ray echo emission. By fitting the afterglow light curves, we can measure the locations of the massive wind bubbles, which will bring us closer to finding the mass loss rate, wind velocity, and the age of the progenitors prior to the GRB explosions.Comment: 25 pages, 3 figures, 2 tables. Accepted for publication in Ap