Development of a special purpose spacecraft coating, phase 4

Coating formulations based on a fluorocarbon resin were evaluated for use on spacecraft exteriors. Formulations modified with an acrylic resin were found to have excellent offgassing properties. A much less expensive process for increasing to solid content of the fluorocarbon latex was developed

Development of a special purpose spacecraft interior coating, phase 3

A variety of intumescent coatings based on a fluorocarbon latex resin modified with either an acrylic resin or an epoxy resin were prepared. Several intumescent systems were used for these studies including some based on ammonium polyphosphate and others based on sulfanilamide. The best coatings developed had a high concentration (60-70% by wt.) of intumescent additives and had to be applied thick, approximately 100 mils, in order to have adequate intumescent/fire protection properties

Indecomposable modules and Gelfand rings

It is proved that a commutative ring is clean if and only if it is Gelfand with a totally disconnected maximal spectrum. Commutative rings for which each indecomposable module has a local endomorphism ring are studied. These rings are clean and elementary divisor rings

Mirror Movements in Essential Tremor: Prevalence and Relationship to Mini-Mental Status Test Scores

Background: Mirror movements (MM) are mirror reversals of contralateral, voluntary alternating or repetitive limb movements. MM have been described in age-related neurological diseases, including essential tremor (ET). MM could represent a motor release sign. Cognitive dysfunction (especially executive dysfunction) and dementia have also been reported among ET patients. It is conceivable that MM and cognitive dysfunction in ET arise from the same underlying anatomical or physiological substrate. Hence, the underlying clinical question is whether MM are a simple and easily elicited motor marker for incipient cognitive change or dementia in ET? Identifying such a marker would have value to clinicians, and we are unaware of prior studies that have assessed this issue. Methods: The Folstein Mini-Mental State Exam (FMMSE) and the Modified Mini-Mental Status Examination (mMMSE) were administered to 148 ET cases enrolled in a cross-sectional clinical study. Results: MM were present in 115 out of 148 (77.7%) ET cases. In analyses that considered age, there were no differences in FMMSE or mMMSE scores between participants with vs. without MMs (all p values >0.05). Discussion: These data suggest that MM, while present in a considerable number of ET cases, would not be a useful motor marker for incipient cognitive change in ET cases

MV3: A new word based stream cipher using rapid mixing and revolving buffers

MV3 is a new word based stream cipher for encrypting long streams of data. A direct adaptation of a byte based cipher such as RC4 into a 32- or 64-bit word version will obviously need vast amounts of memory. This scaling issue necessitates a look for new components and principles, as well as mathematical analysis to justify their use. Our approach, like RC4's, is based on rapidly mixing random walks on directed graphs (that is, walks which reach a random state quickly, from any starting point). We begin with some well understood walks, and then introduce nonlinearity in their steps in order to improve security and show long term statistical correlations are negligible. To minimize the short term correlations, as well as to deter attacks using equations involving successive outputs, we provide a method for sequencing the outputs derived from the walk using three revolving buffers. The cipher is fast -- it runs at a speed of less than 5 cycles per byte on a Pentium IV processor. A word based cipher needs to output more bits per step, which exposes more correlations for attacks. Moreover we seek simplicity of construction and transparent analysis. To meet these requirements, we use a larger state and claim security corresponding to only a fraction of it. Our design is for an adequately secure word-based cipher; our very preliminary estimate puts the security close to exhaustive search for keys of size < 256 bits.Comment: 27 pages, shortened version will appear in "Topics in Cryptology - CT-RSA 2007

Review of Leading Approaches for Mitigating Hypersonic Vehicle Communications Blackout and a Method of Ceramic Particulate Injection Via Cathode Spot Arcs for Blackout Mitigation

Vehicles flying at hypersonic velocities within the atmosphere become enveloped in a "plasma sheath" that prevents radio communication, telemetry, and most importantly, GPS signal reception for navigation. This radio "blackout" period has been a problem since the dawn of the manned space program and was an especially significant hindrance during the days of the Apollo missions. An appropriate mitigation method must allow for spacecraft to ground control and ground control to spacecraft communications through the reentry plasma sheath. Many mitigation techniques have been proposed, including but not limited to, aerodynamic shaping, magnetic windows, and liquid injection. The research performed on these mitigation techniques over the years will be reviewed and summarized, along with the advantages and obstacles that each technique will need to overcome to be practically implemented. A unique approach for mitigating the blackout communications problem is presented herein along with research results associated with this method. The novel method involves the injection of ceramic metal-oxide particulate into a simulated reentry plasma to quench the reentry plasma. Injection of the solid ceramic particulates is achieved by entrainment within induced, energetic cathode spot flows

Health risk appraisal in older people 7: long-acting benzodiazepine use in community-dwelling older adults in London: is it related to physical or psychological factors?

To investigate whether the use of long-acting benzodiazepines, in individuals aged 65 and over is mediated by physical or psychological factors. Long-acting benzodiazepine consumption among older people has implications for mortality, morbidity and cost-effective prescribing. Two models explain benzodiazepine use in this age group, one linked to physical illness and disability and one to psychological factors. Secondary analysis of baseline data from a study of 1059 community-dwelling non-disabled people aged 65 years and over recruited from three general practices in London. For this analysis, use of long-acting benzodiazepines was defined as any self-reported use of diazepam or nitrazepam in the last four weeks. Associations between demographic factors, health service use, and physical and psychological characteristics and benzodiazepine use were investigated. The prevalence of benzodiazepine use in this sample was 3.3% (35/1059). In univariate analyses, benzodiazepine use was associated with female gender, low income, high consultation rates, physical factors (medication for arthritis or joint pain, polypharmacy, difficulties in instrumental activities of daily living, recent pain) and psychological factors (poor self-perceived health, social isolation, and symptoms of anxiety or agitation). In a multivariate logistic regression analysis only two factors retained statistically significant independent associations with benzodiazepine use: receiving only the state pension (OR=4.0, 95% CI: 1.70, 9.80) and pain in the past four weeks (OR=3.79, 95% CI: 1.36, 10.54)