The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved

Two sets of polyether-polyurethane block polymers based on poly(tetramethylene oxide) (PTMO), 4,4'-methylenebis(phenyl isocyanate) (MDI), and butanediol (BD) were prepared in different ways to produce materials with equivalent stoichiometries but different hard segment length distributions. One set of materials was prepared by a one-step polymerization with butanediol as the chain extender. The second series was synthesized by a multistep method using butanediol and/or bis(4-hydroxybutyl) 4,4'-methylenebis(phenylcarbamate) (BMB) as the chain extender. The single-step polymers are shown to have fewer hard segments containing a single MDI unit than the corresponding multistep samples. The result of this is that the multistep materials exhibit a greater degree of phase mixing, as the very short hard segments are more likely to be dissolved in the soft phase than are longer hard segments. The evidence for this comes from the behavior of the sample ET-20M, an MDI/PTMO alternating copolymer. The hard phase volume fraction and crystallinity are greater in the single-step materials due to the lower degree of phase mixing in these polymers. The results of infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, stress-strain testing, and small-angle X-ray scattering are all shown to be consistent with the differences in hard segment length distributions and the differences in phase mixing which accompany the distributional differences. diffraction to study the crystal structure of MDI/BD/ PTMO-2000 polyurethanes. These materials had the same chemical constituents as those studied by Seymour et al.but had longer segmental lengths. Abouzahr found no detectable crystalline diffraction for samples with less than 35 wt % MDI. On the basis of small-angle X-ray scattering and stress relaxation studies, Abouzahr et al. also proposed that polyurethanes have an interlocked domain morphology at moderate MDI content (35 and 45 wt %).Bonart5,6 also examined the packing of MDI/BD hard segments using X-ray scattering and suggested that hard segments were laterally associated forming lamellae with a thickness limited by the average hard segment length. Using electron microscopy and X-ray diffraction analysis, Schneider et al.7 proposed that the MDI/BD hard segment domain existed in a micelle-like structure which was made

The low-ball technique, a tactic often used by automobile sales dealers to produce compliance from customers, was examined in a set of three experiments. In all three studies, a requester who induced subjects to make an initial decision to perform a target behavior and who then made performance of the behavior more costly obtained greater final compliance than a requester who informed subjects of the full costs of the target behavior from the outset. The low-ball phenomenon-that an active preliminary decision to take an action tends to persevere even after the costs of performing the action have been increased-was found to be reliable (Experiment 1), different from the foot-in-the-door effect (Experiment 2), and effective only when the preliminary decision was made with a high degree of choice (Experiment 3). In competition with three other conceptual explanations, a formulation based on the concept of commitment was seen to best account for the results. An ecologically derived strategy for the identification and investigation of research questions was used and discussed.

The efficient and cost-effective direct conversion of solar photons into solar electricity and solar fuels is one of the most important scientific and technological challenges of this century. It is estimated that at least 20 terawatts of carbonfree energy (1 1 / 2 times the total amount of all forms of energy consumed today globally), in the form of electricity and liquid and gaseous fuels, will be required by 2050 in order to avoid the most serious consequences of global climate change and to ensure adequate global energy supply that will avoid economic chaos. But in order for solar energy to contribute a major fraction of future carbon-free energy supplies, it must be priced competitively with, or perhaps even be less costly than, energy from fossil fuels and nuclear power as well as other renewable energy resources. The challenge of delivering very low-cost solar fuels and electricity will require groundbreaking advances in both fundamental and applied science. This Thematic Issue on Solar Photon Conversion will provide a review by leading researchers on the present status and prognosis of the science and technology of direct solar photoconversion to electricity and fuels. The topics covered include advanced and novel concepts for lowcost photovoltaic (PV) energy based on chemistry (dyesensitized photoelectrodes, organic and molecular PV, multiple exciton generation in quantum dots, singlet fission), solar water splitting, redox catalysis for water oxidation and reduction, the role of nanoscience and nanocrystals in solar photoconversion, photoelectrochemical energy conversion, and photoinduced electron transfer.The direct conversion of solar photons to electricity via photovoltaic (PV) cells is a vital present-day commercial industry, with PV module production growing at about 75%/ year over the past 3 years. However, the total installed yearly averaged energy capacity at the end of 2009 was about 7 GW-year (0.2% of global electricity usage). Thus, there is potential for the PV industry to grow enormously in the