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We study the performance of CdS/CdTe thin-film devices contacted with ZnTe:Cu/Ti of various thickness at a higher-than-optimum temperature of {approx}360 C. At this temperature, optimum device performance requires the same thickness of ZnTe:Cu as for similar contacts formed at a lower temperature of 320 C. C-V analysis indicates that a ZnTe:Cu layer thickness of {approx}< 0.5 mu m does not yield the degree of CdTe net acceptor concentration necessary to reduce space charge width to its optimum value for n-p device operation. The thickest ZnTe:Cu layer investigated (1 mu m) yields the highest CdTe net acceptor concentration, lowest value of Jo, and highest Voc. However, performance is limited for this device by poor fill factor. We suggest poor fill factor is due to Cu-related acceptors compensating donors in CdS.

The warming temperatures and increased drought predicted to occur over the course of the next century have the potential to profoundly impact the composition and structure of global plant communities. Because of the relevance of forest ecosystems in storing a large amount of the planet’s carbon and thus in regulating the earth’s climate, there is a major effort to forecast forest composition, structure, and functioning. Accurate predictions will require the application of studies that identify how climate drivers (and interactions between multiple drivers) affect physiological processes that underlie patterns of demography and assembly. In forest systems, community composition is strongly shaped by bottleneck effects that occur during recruitment at small size classes, size classes that are highly vulnerable to climate change. In this dissertation, I investigated how climate change will affect the seedling demography of two temperate tree species that commonly co-occur across eastern North America: Acer saccharum (sugar maple) and Quercus rubra (northern red oak). In chapter 2 I investigated how potential climate-driven shifts in seedling foliar phenology (in relation to shifts in canopy phenology) could affect the ability of seedlings to maintain positive net carbon assimilation over the growing season, a dynamic that is commonly referred to as phenological escape. I also modeled how environmental conditions drive photosynthetic rates and used that information to estimate the relative proportion of carbon that is assimilated in different seasons. In my third chapter I used the same photosynthesis models to estimate annual carbon assimilation for individual tree seedlings and then modeled the relationship between carbon assimilation and demographic performance (growth and survival). I used results from both chapters to project how climate change in my study region could affect seedling demography directly (e.g., via changes in respiration rates associated with higher temperatures) and indirectly (e.g., via ...

2019 Summer. ; Includes bibliographical references. ; Concerns over depleting oil reserves and national security have spurred renewed vigor in developing bio-based products. One specific area of growing concern is the consumption of petroleum based plastics, which is expected to consume 20% of global annual oil by 2050. Algae systems represent a promising pathway for the development of a bioplastic feedstock but have many technological challenges. Algae-based plastics offer a promising alleviate that would decrease oil consumption, improve environmental impact, and in some cases even improve plastic performance. This study investigates the economic viability and environmental impact of an algae biorefinery that integrates the complementary functions of bioplastic and fuel production. The bioplastic and biofuel biorefinery modeled herein includes nine different production scenarios. Performance of the facility was validated based on experimental systems with modeling work focusing on mass and energy balances of all required sub-processes in the production pathway. Results show the minimum selling price of the bioplastic feedstock is within the realm of economic competition with prices as low as $970 USD tonne-1. Additionally, LCA results indicate drastic improvements in environmental performance of the produced bioplastic feedstock, with reductions ranging between 67-116% compared to petroleum based plastics. These results indicate that an algae biorefinery focused on bioplastic feedstock production and fuels has the potential to operate both economically and sustainably. Sensitivity analysis results, alternative co-products (given that fuels represent minimal value) and product market potential are discussed.

The Tidd PFBC Demonstration Plant, located in Brilliant, Ohio, is in its third year of operation and testing. The plant has achieved many of its original performance goals and test objectives; however, current emissions standards and the projected performance of competing technologies have caused a reassessment of the program goals. This paper provides a review of PFBC technology and discusses project goals and milestones achieved. Emphasis is placed on environmental performance and on projected modifications to be undertaken to improve sulfur capture and reduce calcium/sulfur molar ratio. A large-scale hot gas clean up demonstration is also in progress at Tidd. The demonstration has been providing information on ceramic barrier filter technology since its commissioning in October 1992. The Tidd Plant has met both its performance guarantees for emissions and its environmental permit limits. However, the tightening of government environmental standards and the projected performance of competing technologies have required a reassessment of the goals of AEP`s PFBC program. Efforts are focusing on achieving better environmental performance, particularly with respect to sulfur capture and sorbent utilization.

Pseudorapidity distributions of multiplicity and transverse energy are a useful probe of nuclear stopping. Emulsion results at the AGS and CERN, as well as E/sub T/ measurements at both laboratories are discussed, and show that the fireball model with crisp and precise predictions of the pseudorapidity distributions, utterly fails to reproduce the measurements. By stark contrast, the fireball model is very successful in predicting the observed ratio of E/sub T/ production in central /sup 32/S and /sup 16/O interactions in Au and other heavy targets. This conundrum is explored and explained, leading to a systematic comparison of measurements from all the RHI experiments at the AGS and CERN. 14 refs., 3 figs.

Metadata only record Within the last thirty years in the West African Sahel, farmers have started to implement agroenvironmental practices which have allowed them to improve the soil quality and increase crop yields. Using two examples of land rehabilitation in Africa, this paper examines the technical and institutional innovations and their impacts on the ability to meet food demand for the growing population. Agroenvironmental techniques incorporate trees into the agricultural landscape, which improves water retention in the soil, increases the supply of nutrients, reduces wind erosion, and provides other marketable tree products. This large-scale effort has created income opportunities for farmers, benefited women, and increased food supply for many African families.

Cement production is the second most carbon dioxide intensive industry, accounting for 5% of anthropogenic emissions. As the key binding agent in concrete it is integral to the modern infrastructure our society depends on. The U.S. invests more than 260 megatonnes of concrete at a cost of nearly $65 billion annually in its road and highway infrastructure alone. Despite this, road and highway infrastructure remains in poor condition. A new approach to how cement materials are used and produced is needed to improve its sustainability. This dissertation develops methods for quantifying and characterizing the sustainability of different options in cement production and its use in concrete infrastructure applications. Four methods are presented, (1) life cycle modeling of concrete infrastructure comparing new designs and engineered cementitious composite (ECC) materials to conventional designs and materials, (2) life cycle modeling applied to the development of greener ECC materials, (3) overlay analysis of constraints on mineral resource extraction to assesses the feasibility of siting large consolidated cement plants and quarries, or megaquarries, and (4) network analysis of freight transportation to quantify energy and cost implications of megaquarries. Life cycle modeling showed adopting a novel design for the concrete bridge deck using an ECC link slab design improved environmental and cost performance. The modeled deck experienced high traffic flow, and the novel design showed a 40% improvement in sustainability indicators, with traffic-related impacts dominating results. Life cycle modeling was extended to enhance the sustainability performance of ECC materials used as link slabs. Results showed the key driver for material performance is sufficient durability, and alternative constituent materials perceived as environmentally friendly should only be used if ECC durability meets infrastructure design needs. Overlay analysis showed constraints on limestone extraction, cement's primary raw material, eliminated ...

Shipping list no.: 2001-0115-P. ; "Department of Defense, Department of Energy, Department of the Interior, nondepartmental witnesses." ; Includes bibliographical references and indexes. ; Mode of access: Internet.

This paper discussed general thermal engineering problems and specific categories of thermal design issues for high photon flux beam lines at the LBL Advanced Light Source: thermal distortion of optical surfaces and elevated temperatures of thermal absorbers receiving synchrotron radiation. A generic design for water-cooled heat absorbers is described for use with ALS photon shutters, beam defining apertures, and heat absorbing masks. Also, results of in- situ measurements of thermal distortion of a water-cooled mirror in a synchrotron radiation beam line are compared with calculated performance estimates. 17 refs., 2 figs.

This work focuses on the development of ternary and quaternary chalcogenide compounds featuring transition metal cations through careful engineering of the electronic and thermal transport as well as magnetic properties by traditional solid-state doping techniques and novel template structure synthesis methods for improvements in thermoelectric performance, diluted magnetic semiconductors, and photovoltaic conversion. Presented here is an innovative low-temperature batch synthesis that was developed to create hexagonal nanoplatelets of thermoelectrically interesting CuAgSe. This process utilized room temperature ion exchange reactions to convert cubic Cu2-xSe nanoplatelets into CuAgSe by replacing a portion of the Cu+ ions with Ag+ while maintaining the morphology of the nanoplatelet. This simple reaction process offers an energy efficient and versatile strategy to create interesting materials with superior thermoelectric performance. An investigation of the thermal and electronic transport of CuAl(SxSe1-x)2 solid solutions was also conducted. While these compounds yielded low thermal conductivity, they also exhibited low electronic conductivity. Doping with transition metals Ag, Hf, and Ti further reduced the thermal conductivity below 1 W/mK; however, most exciting was the determination that the thermal transport of the system could be modified by doping at the Al3+ site without affecting the electronic structure of the system, potentially leading to the use of CuAl(SxSe1-x)2 as a heavily doped thermoelectric material. The effect of local carrier concentration in the diluted magnetic semiconductor FeSb2Se4 was studied by substitution of In3+ for Sb3+. Using systematic Rietveld refinement, it was determined that In3+ resides in the semiconducting layer of the structure for concentrations of x ≤ 0.1, and the magnetic layer for x > 0.1. The increase in local carrier concentration has an appreciable effect on the electronic and magnetic properties of the material in a predictable manner based on the ...