Identification of Gravity-Related Effects on Crystal Growth From Melts With an Immiscibility Gap

This work involves an experimental-numerical approach to study the effects of natural and Marangoni convections on solidification of single crystals from a silicate melt with a liquid-liquid immiscibility gap. Industrial use of crystals grown from silicate melts is becoming increasingly important in electronic, optical, and high temperature structural applications. Even the simplest silicate systems like Al203-SiO2 have had, and will continue to have, a significant role in the development of traditional and advanced ceramics. A unique feature of crystals grown from the silicate systems is their outstanding linear electro-optic properties. They also exhibit exceptionally high optical rotativity. As a result, these crystals are attractive materials for dielectric, optical, and microwave applications. Experimental work in our laboratory has indicated that directional solidification of a single crystal mullite appears to be preceded by liquid-liquid phase separation in the melt. Disruption of the immiscible state results in crystallization of a two phase structure. There is also evidence that mixing in the melt caused by density-driven convection can significantly affect the stability of the immiscible liquid layers and result in poly-crystalline growth. On earth, the immiscible state has only been observed for small diameter crystals grown in float zone systems where natural convection is almost negligible. Therefore, it is anticipated that growth of large single crystals from silicate melts would benefit from microgravity conditions because of the reduction of the natural convective mixing. The main objective of this research is to determine the effects of transport processes on the phase separation in the melt during growth of a single crystal while addressing the following issues: (1) When do the immiscible layers form and are they real?; (2) What are the main physical characteristics of the immiscible liquids?; and (3) How mixing by natural or Marangoni convection affects the stability of the phase separated melt

Progress Towards III-V Photovoltaics on Flexible Substrates

Presented here is the recent progress of the NASA Glenn Research Center OMVPE group's efforts in the development of high efficiency thin-film polycrystalline III-V photovoltaics on optimum substrates. By using bulk polycrystalline germanium (Ge) films, devices of high efficiency and low mass will be developed and incorporated onto low-cost flexible substrates. Our progress towards the integration of high efficiency polycrystalline III-V devices and recrystallized Ge films on thin metal foils is discussed

On the transport capacity of a multiple access gaussian channel, in

Abstract-We address the problem of maximizing the transport capacity of a wireless network, defined as the sum, over all transmitters, of the products of the transmission rate with a reward r(x), which is a function of the distance x separating the transmitter and its receiver. When r(x) = x, this product is measured in bps × meters, and is the natural measure of the usefulness of a transmission in a multihop wireless ad hoc network. We first consider a single transmitter-receiver pair, and determine the optimal distance between the two that maximizes the rate-reward product, for reward functions of the form r(x) = x ρ and when the signal power decays with distance according to a power law. We then calculate the scheme that maximizes the transport capacity in a multiple access network consisting of a single receiver and a number of transmitters, each placed at a fixed distance from the receiver, and each with a fixed power constraint. We conclude by showing that when the per-transmitter power constraints are substituted with a single constraint on the sum of the powers, the maximum transport capacity and the power allocation scheme that achieves it can be found by solving a convex optimization problem

Capacity results for asymmetric wireless networks

Abstract — We study wireless ad hoc networks that consist of n source nodes and m destination nodes, placed randomly in a two dimensional area. Each source node is creating data trafÞc that must be delivered to one of the m destination nodes, chosen at random. When m is on the order of n d with 0 <d< 1 2, the capacity of the network is affected by the formation of bottlenecks around the destinations, and the maximum aggregate throughput is on the order of n d. If, however, 1 < d < 1, 2 an aggregate throughput on the order of n 1 2 is achievable. The scheme that achieves this aggregate throughput does not suffer from the formation of bottlenecks. These results hold under a general model of channel fading, and with probability going to 1 as n →∞. Index Terms — Asymmetric trafÞc, capacity, wireless ad hoc networks. I

Surgical treatment of right middle lobe syndrome in children

Objective: Right middle lobe syndrome is a rare entity in children, causing high morbidity. Our experience of these patients including their clinical and laboratory characteristics, indications forsurgical management, postoperative courses, and follow-up results was evaluated. Methods: A retrospective analysis was performed involving 20 children with right middle lobe syndrome who were hospitalized and treated with surgical resection of the right middle lobe in Van Training and Research Hospital and Yüzüncüyil university hospital, Turkey, between January 2002 and January 2011. Results: The mean age of the patients was 10.5 years (range, 5 to 15 years). Twelve patients were boys and eight were girls. The most frequent symptom was chronic cough (75%). Hemoptysis was present in two (10%) patients. One patient was being treated for asthma. 25% positive cultures were identified among the patients. Streptococcus pneumoniae was the most frequently identified agent in sputum. All patients underwent chest computed tomography. There were bronchiectasis in 11 (55%) patients, atelectasis and bronchiectasis in five (25%) patients, and destroyed lung in four (20%) patients. A narrowed middle lobe bronchus was shown in 15 (75%) patients. Bronchoscopy was performed in 18 (90%) patients. Stenosis due to external compression was seen in 12 (60%) patients, hyperemia and bronchitis in two (10%) patients, granulation tissue in two (10%) patients, and dense secretions in two (10%) patients. A history of doctor-diagnosed tuberculosis was present in two (10%) patients. These patients had completed antituberculous treatment. The patients had been symptomatic for the last 1 to 10 years (mean, 4 years) and had received several medical treatments. All patients (totally 20 patients) underwent right middle lobe resection. In one patient, a bronchial abnormality was found intraoperatively. One patient died on postoperative day 10 due to a brain abscess. Three other patients had postoperative complications (15%). Mean duration of follow-up of the patients was 4.5 years (range, 2 months to 12 years). Seventeen patients were asymptomatic, and two patients had improved. Conclusions: Children with right middle lobe syndrome unresponsive to medical treatment should undergo early lobe resection to avoid serious complications and the progression of the disease to other segments or lobes