Design of a flexure mount for optics in dynamic and cryogenic environments

The design of a flexure mount for a mirror operating in a cryogenic environment is presented. This structure represents a design effort recently submitted to NASA Ames for the support of the primary mirror of the Space Infrared Telescope Facility (SIRTF). The support structure must passively accommodate the differential thermal contraction between the glass mirror and the aluminium structure of the telescope during cryogenic cooldown. Further, it must support the one meter diameter, 116 kilogram (258 pound) primary mirror during a severe launch to orbit without exceeding the micro-yield of the material anywhere in the flexure mount. Procedures used to establish the maximum allowable radial stiffness of the flexural mount, based on the finite element program NASTRAN and the optical program FRINGE, are discussed. Early design concepts were evaluated using a parametric design program, and the development of that program is presented. Dynamic loading analyses performed with NASTRAN are discussed. Methods of combining modal responses resulting from a displacement response spectrum analysis are discussed, and a combination scheme called MRSS, modified root of sum of squares, is presented. Model combination schemes using MRSS, SRSS, and ABS are compared to the results of the modal frequency response analysis performed with NASTRAN

INJURIES IN AUSTRALIAN RULES FOOTBALL: A Review of the Literature

Background: Australian Rules Football is one of the most popular sports in Australia. Successful injury prevention relies on injury surveillance to establish the extent of injuries, to monitor injury patterns and to evaluate prevention strategies. Despite the popularity of participation at the community level, few injury surveillance studies have been published, so a detailed review of the literature is vital. There is limited information available outside of the elite level. Injury statistics for any professional sport may not necessarily be translatable to community sport level

Successful management of hamstring injuries in Australian Rules footballers: two case reports

Hamstring injuries are the most prevalent injury in Australian Rules football. There is a lack of evidence based literature on the treatment, prevention and management of hamstring injuries, although it is agreed that the etiology is complicated and multi-factorial. We present two cases of hamstring injury that had full resolution after spinal manipulation and correction of lumbar-pelvic biomechanics. There was no recurrence through preventative treatment over a twelve and sixteen week period. The use of spinal manipulation for treatment or prevention of hamstring injury has not been documented in sports medicine literature and should be further investigated in prospective randomized controlled trials

Cervical stenosis in a professional rugby league football player: a case report

BACKGROUND: This paper describes a case of C7 radiculopathy in a professional rugby league player after repeated cervical spine trauma. The report outlines the management of the patient following an acute cervical hyperflexion injury with chiropractic manipulation and soft tissue therapies. It also presents a change in approach to include distractive techniques on presentation of a neurological deficit following re-injury. The clinical outcomes, while good, were very dependent upon the athlete restricting himself from further trauma during games, which is a challenge for a professional athlete. CASE PRESENTATION: A 30-year old male front row Australian rugby league player presented complaining of neck pain after a hyperflexion and compressive injury during a game. Repeated trauma over a four month period resulted in radicular pain. Radiographs revealed decreased disc height at the C5-C6 and C6-C7 levels and mild calcification within the anterior longitudinal ligament at the C6-C7 level. MRI revealed a right postero-lateral disc protrusion at the C6-C7 level causing a C7 nerve root compression. CONCLUSION: Recommendations from the available literature at the present time suggest that conservative management of cervical discogenic pain and disc protrusion, including chiropractic manipulation and ancillary therapies, can be successful in the absence of progressive neurological deficit. The current case highlights the initial successful management of a football athlete, and the later unsuccessful management. This case highlights the issues involvement in the management of a collision sport athlete with a serious neck injury

Submerged Aquatic Bryophytes in Colour Lake, a Naturally Acidic Polar Lake with Occasional Year-round Ice-cover

Colour Lake is a small, naturally acidic (pH 3.7) lake on Axel Heiberg Island (Canadian High Arctic) that experiences occasional year-round ice cover. We investigated the benthic vegetation of this lake, with a specific aim of determining whether the annual growth of benthic bryophytes reflects the state of summer ice cover. We found the bed of the lake to be almost completely covered by mosses or liverworts to a depth of 22 m. The mosses showed annual growth bands 10-30 mm in length, visible as changes in leaf density and size. Four to five bands retained recognizable leaves and measurable amounts of chlorophyll-a (chla), and up to 12 bands were recognizable from leaf scars. We could not find a consistent relationship between band length and persistence of ice cover for a given year. We suggest that this lack is due to the complex effects of ice cover on moss growth conditions, specifically on the water temperature and irradiance at depth. Photosynthetic characteristics of Calliergon over a range of light and temperature conditions, determined using pulse amplitude-modulated fluorometry, are presented in support of this argument. We conclude that moss banding patterns are an unreliable method of hindcasting episodic failure of ice to melt in Arctic lakes.Le lac Colour est un petit lac de l'île Axel Heiberg, située dans l'Extrême-Arctique canadien, dont l'acidité (pH = 3,7) est naturelle et qui reste parfois englacé toute l'année. On a étudié la végétation benthique de ce lac, dans le but précis de déterminer si la croissance annuelle des bryophytes benthiques reflète l'état de la couverture de la glace en été. On a trouvé que le lit du lac est presque entièrement recouvert de mousses ou d'hépatiques jusqu'à une profondeur de 22 m. Les mousses affichaient des bandes de croissance annuelles de 10 à 30 mm de longueur, visibles sous la forme d'un changement dans la densité et la taille de la feuille. De 4 à 5 bandes conservaient des feuilles reconnaissables et des quantités mesurables de chlorophylle-a (chla), et jusqu'à 12 bandes étaient reconnaissables d'après les cicatrices foliaires. On n'a pu trouver de rapport constant entre la longueur de la bande et la persistance du manteau glaciel pour une année donnée. On suggère que ce manque est dû aux effets complexes du manteau glaciel sur les conditions de croissance de la mousse, en particulier sur la température de l'eau et l'irradiance en profondeur. Les attributs photosynthétiques de Calliergon pour une gamme de conditions d'éclairement et de température données, déterminés par fluorimétrie par impulsions à amplitude modulée, sont présentés à l'appui de cette thèse. On conclut que les schémas de rubanement de la mousse constituent une méthode peu fiable de prévision a posteriori des interruptions épisodiques de fonte de la glace dans les lacs arctiques

The Importance of Incorporating Landscape Change for Predictions of Climate-Induced Plant Phenological Shifts

Warming in the high Arctic is occurring at the fastest rate on the planet, raising concerns over how this global change driver will influence plant community composition, the timing of vegetation phenological events, and the wildlife that rely on them. In this region, as much as 50% of near-surface permafrost is composed of thermally sensitive ground ice that when melted produces substantial changes in topography and microbiome conditions. We take advantage of natural variations in permafrost melt to conduct a space-for-time study on Ellesmere Island in northern Canada. We demonstrate that phenological timing can be delayed in thermokarst areas when compared to stable ground, and that this change is a function of shifting species composition in these vegetation communities as well as delayed timing within species. These findings suggest that a warming climate could result in an overall broadening of blooming and leafing windows at the landscape level when these delayed timings are taken into consideration with the projected advance of phenological timings in ice-poor areas. We emphasize that the impacts of geomorphic processes on key phenological drivers are essential for enhancing our understanding of community response to climate warming in the high Arctic, with implications for ecosystem functioning and trophic interactions.ISSN:1664-462

Dynamic analysis and design of the SIRTF primary mirror mount

The criteria and considerations for the design of the support system for the Space Infrared Telescope Facility (SIRTF) primary mirror are presented. A flexural-gimbal-baseplate design for the 0.5 m primary mirror was developed. Preliminary studies have indicated that this design may be further improved by replacing the flexures by a post-gimbal system wherein the gimbal design accomodates both the cryogenic cool down effects, the dynamic launch loads, and manufacturing tolerance effects. Additionally, a prestressed baseplate concept had evolved and was presented for the full scale 1.0 m mirror. However, preliminary design studies indicate that this concept will not be required, and the post-gimbal-baseplate design similar to the 0.5 m alternate support system will meet the cryogenic cool down, dynamic launch load criteria, and manufacturing tolerance effects

Low back pain in junior Australian Rules football: a cross-sectional survey of elite juniors, non-elite juniors and non-football playing controls

<p>Abstract</p> <p>Background</p> <p>Low back pain in junior Australian Rules footballers has not been investigated despite findings that back pain is more prevalent, severe and frequent in senior footballers than non-athletic controls and findings that adolescent back pain is a strong predictor for adult back pain. The aim of this study was to determine the prevalence, intensity, quality and frequency of low back pain in junior Australian Rules footballers and a control group and to compare this data between groups.</p> <p>Methods</p> <p>A cross-sectional survey of male non-elite junior (n = 60) and elite junior players (n = 102) was conducted along with a convenience sample of non-footballers (school children) (n = 100). Subjects completed a self-reported questionnaire on low back pain incorporating the Quadruple Visual Analogue Scale and McGill Pain Questionnaire (short form), along with additional questions adapted from an Australian epidemiological study. Linear Mixed Model (Residual Maximum Likelihood) methods were used to compare differences between groups. Log-linear models were used in the analysis of contingency tables.</p> <p>Results</p> <p>For current, average and best low back pain levels, elite junior players had higher pain levels (p < 0.001), with no difference noted between non-elite juniors and controls for average and best low back pain. For low back pain at worst, there were significant differences in the mean pain scores. The difference between elite juniors and non-elite juniors (p = 0.040) and between elite juniors and controls (p < 0.001) was significant, but not between non-elite juniors and controls. The chance of suffering low back pain increases from 45% for controls, through 55% for non-elite juniors to 66.7% for elite juniors. The chance that a pain sufferer experiences chronic pain is 16% for controls and 41% for non-elite junior and elite junior players. Elite junior players experienced low back pain more frequently (p = 0.002), with no difference in frequency noted between non-elite juniors and controls. Over 25% of elite junior and non-elite junior players reported that back pain impacted their performance some of the time or greater.</p> <p>Conclusions</p> <p>This study demonstrated that when compared with non-elite junior players and non-footballers of a similar age, elite junior players experience back pain more severely and frequently and have higher prevalence and chronicity rates.</p