Study of Umbrella-Type Erectable Paraboloidal Solar Concentrators for Generation of Spacecraft Auxiliary Power

An investigation was made of some aspects of erectable umbrella-type paraboloidal solar-energy concentrators for use in spacecraft auxiliary power systems. An analysis is presented for the design of concentrators employing radial ribs and membrane-type coverings. The rib stiffness necessary to give a desired parabolic curvature upon erection is determined. Rib contour measurements were made in an upright and inverted position on an experimental 10-foot-diameter concentrator giving a focal length of 30.78 inches and 30.6 inches, respectively, as compared with a design focal length of 30 inches. Calorimetric tests employing spherical heat receivers showed a maximum geometrical concentrator efficiency of 75.3 percent with a concentration ratio of 92.2 at a focal length of approximately 30.5 inches. Within the scope of this investigation, it was found that, as the concentrator size increases, the weight per unit projected area increases, time to damp to one-half amplitude increases, and the natural frequency decreases. Umbrella-type solar concentrators appear to be feasible for power conversion systems using low concentration ratios; however, for large concentrators the time required to damp out disturbances may be a problem

American bison: relic symbol, domesticated novelty, rewilding dream

Presented at the 9th international wildlife ranching symposium: wildlife - the key to prosperity for rural communities, held on 12-16 September 2016 at Hotel Safari & the Safari Court, Windhoek, Namibia.The US Congress and President unanimously agreed on a national mammalian symbol with the National Bison Legacy Act of 2016. The law is entirely symbolic and could mean nothing to socially and ecologically rewild bison which might have totaled 30-60 million: the last clause of the bill reads "Nothing in this act or the adoption of the North American bison as the national mammal of the United States shall be construed or used as a reason to alter, change, modify, or otherwise affect any plan, policy, management decision, regulation, or other action by the federal government." Approximately 500,000 bison (20,000 plains and 10,000 wood bison) live in 62 conservation herds in the Great Plains and boreal forests of North America. Perhaps 15,000 bison are free-ranging and able to function ecologically. Relic extant populations persisted since near extirpation during the 1800s in Yellowstone National Park (4,900), and were restored on other public lands. Most numbers, 90 percent, were introduced to fenced private and tribal lands, bred for meat, husbanded as novelties and exhibits, or fostered for ecological and social considerations. The rewilding dream is limited by human populations and infrastructures, land uses, fragmented suitable landscapes, and attitudes that are incompatible with free-roaming wild herds of 1/2 to one ton ungulates. Mangers with governments, tribes, organizations, and private lands seek uncertain futures for bison considering legislation, land use alternatives, economics, social perspectives, dreams, and actions that not all can agree. Must we accept symbolic management of relics or ecologically rewild our dreams

Bose-Einstein Condensation of Excitons: Reply to Tikhodeev's Criticism

The extended version of our reply to Comment on ``Critical Velocities in Exciton Superfluidity'' by S. G. Tikhodeev (Phys. Rev. Lett., 84 (2000), 3502 or from http://prl.aps.org/) is presented here. The principal question is discussed: does the moving exciton-phonon packet contain the coherent `nucleus', or the exciton-phonon condensate?Comment: 3 pages in LaTe

Mechanisms of fragmentation of Al-W granular composites under dynamic loading

Numerical simulations of Aluminum (Al) and Tungsten (W) granular composite rings under various dynamic loading conditions caused by explosive loading were examined. Three competing mechanisms of fragmentation were observed: a continuum level mechanism generating large macrocracks described by the Grady-Kipp fragmentation mechanism, a mesoscale mechanism generating voids and microcracks near the initially unbonded Al/W interfaces due to tensile strains, and a mesoscale jetting due to the development of large velocity gradients between the W particles and adjacent Al. These mesoscale mechanisms can be used to tailor the size of the fragments by selecting an appropriate initial mesostructure for a given loading condition.Comment: 10 pages, 3 figures, submitted to AP

The Motion of a Body in Newtonian Theories

A theorem due to Bob Geroch and Pong Soo Jang ["Motion of a Body in General Relativity." Journal of Mathematical Physics 16(1), (1975)] provides the sense in which the geodesic principle has the status of a theorem in General Relativity (GR). Here we show that a similar theorem holds in the context of geometrized Newtonian gravitation (often called Newton-Cartan theory). It follows that in Newtonian gravitation, as in GR, inertial motion can be derived from other central principles of the theory.Comment: 12 pages, 1 figure. This is the version that appeared in JMP; it is only slightly changed from the previous version, to reflect small issue caught in proo

Three dimensional viscous analysis of a hypersonic inlet

The flow fields in supersonic/hypersonic inlets are currently being studied at NASA Lewis Research Center using 2- and 3-D full Navier-Stokes and Parabolized Navier-Stokes solvers. These tools have been used to analyze the flow through the McDonnell Douglas Option 2 inlet which has been tested at Calspan in support of the National Aerospace Plane Program. Comparisons between the computational and experimental results are presented. These comparisons lead to better overall understanding of the complex flows present in this class of inlets. The aspects of the flow field emphasized in this work are the 3-D effects, the transition from laminar to turbulent flow, and the strong nonuniformities generated within the inlet

Fluorides, orthodontics and demineralization: a systematic review

Objectives: To evaluate the effectiveness of fluoride in preventing white spot lesion (WSL) demineralization during orthodontic treatment and compare all modes of fluoride delivery. Data sources: The search strategy for the review was carried out according to the standard Cochrane systematic review methodology. The following databases were searched for RCTs or CCTs: Cochrane Clinical Trials Register, Cochrane Oral Health Group Specialized Trials Register, MEDLINE and EMBASE. Inclusion and exclusion criteria were applied when considering studies to be included. Authors of trials were contacted for further data. Data selection: The primary outcome of the review was the presence or absence of WSL by patient at the end of treatment. Secondary outcomes included any quantitative assessment of enamel mineral loss or lesion depth. Data extraction: Six reviewers independently, in duplicate, extracted data, including an assessment of the methodological quality of each trial. Data synthesis: Fifteen trials provided data for this review, although none fulfilled all the methodological quality assessment criteria. One study found that a daily NaF mouthrinse reduced the severity of demineralization surrounding an orthodontic appliance (lesion depth difference –70.0 µm; 95% CI –118.2 to –21.8 µm). One study found that use of a glass ionomer cement (GIC) for bracket bonding reduced the prevalence of WSL (Peto OR 0.35; 95% CI 0.15–0.84) compared with a composite resin. None of the studies fulfilled all of the methodological quality assessment criteria. Conclusions: There is some evidence that the use of a daily NaF mouthrinse or a GIC for bonding brackets might reduce the occurrence and severity of WSL during orthodontic treatment. More high quality, clinical research is required into the different modes of delivering fluoride to the orthodontic patient

The Removal of Flourides from Water by Ionic Exchange

Mottled enamel is the term originated by McKay to describe the disfigurement of teeth which Smith and others discovered was caused by the presence of fluorides in drinking water. Since then considerable time, energy and money have been spent in an effort to find an economical method of removing fluorides from drinking water. At first the use of activated carbon and activated alumina were rather promising; but more recently the use of tricalcium phosphate to remove fluorides from water has been developed (2). A patent by Adams and Holmes (1), wherein it was claimed that the sulphate ion concentration could be reduced nearly to zero, suggested that the fluoride content of water might be reduced to a permissible value by anionic exchange. Such a method of fluoride removal was investigated as a part of the research program concerning water treatment which has been in progress for many years at Iowa State College

On Critical Velocities in Exciton Superfluidity

The presence of exciton phonon interactions is shown to play a key role in the exciton superfluidity. We apply the Landau criterion for an exciton-phonon condensate moving uniformly at zero temperature. It turns out that there are essentially two critical velocities in the theory. Within the range of these velocities the condensate can exist only as a bright soliton. The excitation spectrum and differential equations for the wave function of this condensate are derived.Comment: 7 pages, Latex; to be published in Phys.Rev.Lett (1997

Experiences With Surgical Treatment of Chronic Lower Limb Ulcers at a Tertiary Hospital in Northwestern Tanzania: A Prospective Review of 300 Cases.

Chronic lower limb ulcers constitute a major public health problem of great important all over the world and contribute significantly to high morbidity and long-term disabilities. There is paucity of information regarding chronic lower limb ulcers in our setting; therefore it was necessary to conduct this study to establish the patterns and outcome of chronic lower limb ulcers and to identify predictors of outcome in our local setting. This was a descriptive prospective study of patients with chronic lower limb ulcers conducted at Bugando Medical Centre between November 2010 and April 2012. Ethical approval to conduct the study was sought from relevant authorities. Statistical data analysis was done using SPSS version 17.0 and STATA version 11.0. A total of 300 patients were studied. Their ages ranged from 3 months to 85 years (median 32 years). The male to female ratio was 2:1. The median duration of illness was 44 days. Traumatic ulcer was the most frequent type of ulcer accounting for 60.3% of patients. The median duration of illness was 44 days. The leg was commonly affected in 33.7% of cases and the right side (48.7%) was frequently involved. Out of 300 patients, 212 (70.7%) had positive aerobic bacterial growth within 48 hours of incubation. Pseudomonas aeruginosa (25.5%) was the most frequent gram negative bacteria isolated, whereas gram positive bacteria commonly isolated was Staphylococcus aureus (13.7%). Twenty (6.7%) patients were HIV positive with a median CD4+ count of 350 cells/μl. Mycological investigation was not performed. Bony involvement was radiologically reported in 83.0% of cases. Histopathological examination performed in 56 patients revealed malignancy in 20 (35.7%) patients, of which malignant melanoma (45.0%) was the most common histopathological type. The vast majority of patients, 270 (90.0%) were treated surgically, and surgical debridement was the most common surgical procedure performed in 24.1% of cases. Limb amputation rate was 8.7%. Postoperative complication rate was 58.3% of which surgical site infection (77.5%) was the most common post-operative complications. The median length of hospital stay was 23 days. Mortality rate was 4.3%. Out of the two hundred and eighty-seven (95.7%) survivors, 253 (91.6%) were treated successfully and discharged well (healed). After discharge, only 35.5% of cases were available for follow up at the end of study period. Chronic lower limb ulcers remain a major public health problem in this part of Tanzania. The majority of patients in our environment present late when the disease is already in advanced stages. Early recognition and aggressive treatment of the acute phase of chronic lower limb ulcers at the peripheral hospitals and close follow-up are urgently needed to improve outcomes of these patients in our environment