Semiconductor nanowires (NWs) represent a new class of materials and a shift from conventional two-dimensional bulk thin films to three-dimensional devices. Unlike thin film technology, lattice mismatch strain in NWs can be relaxed elastically at the NW free surface without dislocations. This capability can be used to grow unique heterostructures and to grow III-V NWs directly on inexpensive substrates, such as Si, rather than lattice-matched but more expensive III-V substrates. This capability, along with other unique properties (quantum confinement and light trapping), makes NWs of great interest for next generation optoelectronic devices with improved performance, new functionalities, and reduced cost. One of the many applications of NWs includes energy conversion. This review will outline applications of NWs in photovoltaics, thermoelectrics, and betavoltaics (direct conversion of solar, thermal, and nuclear energy, respectively, into electrical energy) with an emphasis on III-V materials. By transitioning away from bulk semiconductor thin films or wafers, high efficiency photovoltaic cells comprised of III-V NWs grown on Si would improve performance and take advantage of cheaper materials, larger wafer sizes, and improved economies of scale associated with the mature Si industry. The thermoelectric effect enables a conversion of heat into electrical power via the Seebeck effect. NWs present an opportunity to increase the figure of merit (ZT) of thermoelectric devices by decreasing the thermal conductivity (κ) due to surface phonon backscattering from the NW surface boundaries. Quantum confinement in sufficiently thin NWs can also increase the Seebeck coefficient by modification of the electronic density of states. Prospects for III-V NWs in thermoelectric devices, including solar thermoelectric generators, are discussed. Finally, betavoltaics refers to the direct generation of electrical power in a semiconductor from a radioactive source. This betavoltaic process is similar to photovoltaics in which photon energy is converted to electrical energy. In betavoltaics, however, energetic electrons (beta particles) are used instead of photons to create electron-hole pairs in the semiconductor by impact ionization. NWs offer the opportunity for improved beta capture efficiency by almost completely surrounding the radioisotope with semiconductor material. Improving the efficiency is important in betavoltaic design because of the high cost of materials and manufacturing, regulatory restrictions on the amount of radioactive material used, and the enabling of new applications with higher power requirements.
I explored the efficacy of alternative actions to recover threatened Snake River chinook salmon ( Onchorhyncus tshawytscha ). I compared the potential to increase population growth rates from two different actions: (1) habitat restoration efforts, aimed at increasing egg-to-smolt survival rate, and (2) dam breaching, intended to improve smolt-to-spawner survival. Eight dams obstruct the migration corridor these populations traverse as juveniles (downstream) and as adults (upstream), and a large portion of the juvenile migrants are collected and transported past most of the dams on barges or trucks. I applied sensitivity, elasticity, and direct perturbation analyses to an age-structured projection matrix to predict potential effects from simultaneous, nonproportional changes in multiple survival rates. Throughout the analyses, I explicitly incorporated alternative assumptions about the effectiveness of transportation, which is known to be influential. Results of the numerical experiments suggest that dam breaching has more potential to increase population growth rates than habitat restoration, except for the most optimistic assumption about the efficacy of transportation. I then fit the matrix to historical data to identify life stages in which actual decreases in survival rates have caused the observed declines in abundance. There was no reduction in egg-to-smolt survival, indicating that neither habitat deterioration nor hatchery impacts (in that life stage) caused the stocks to decline. The large decrease in smolt-to-adult survival rate from the historical period, when there were fewer dams, is consistent with the hypothesis that increased stress from transportation and passage through additional dams on the Snake River has elevated delayed mortality levels. Análisis Matricial de la Recuperación de Salmón en el Río SnakeResumen: Exploré la eficacia de acciones alternativas para recuperar al salmón ( Onchorhyncus tshawytscha ) amenazado en el Río Snake. Comparé el incremento potencial de las tasas de crecimiento poblacional mediante dos acciones diferentes: (1) esfuerzos para la restauración del hábitat, enfocados a incrementar la tasa de supervivencia de huevo a juvenil y (2) apertura de represas con la intención de mejorar la supervivencia de juvenil a reproductor. Ocho represas obstruyen el corredor migratorio que recorren estas poblaciones cuando son juveniles (aguas abajo) y cuando son adultos (aguas arriba), por lo cual se recolecta y transporta una gran porción de los juveniles migrantes en barcazas o camiones para que puedan atravesar la mayoría de las represas. Apliqué un análisis de sensibilidad, elasticidad y perturbación directa a una proyección matricial estructurada por edades para predecir los efectos de cambios no proporcionales, simultáneos sobre tasas de supervivencia múltiples. Durante los análisis, se incorporaron explícitamente supuestos alternativos sobre la efectividad del transporte, cuya influencia se conoce. Los resultados de los experimentos numéricos sugieren que la apertura de presas...
The retruded contact position (RCP) is an important maxillomandibular relation in restorative dentistry. This review will describe RCP and consider its importance and use in the restorative dental treatment of the dentate and edentulous subject. A comparative account of the various mandibular guidance methods used to obtain a RCP record will be presented, followed by recommendations for fixed and removable clinical prosthodontic practice.
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