2,418 research outputs found
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
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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)
Teacher perspectives on the introduction of linguistics in the languages classroom. Evidence from a co-creation project on French, German and Spanish
Linguistics is conspicuously absent from language teaching in UK schools. A-level cultural topics cover a range of themes such as cyber-society, cultural heritage and multiculturalism, but the approach taken to these topics is not informed by linguistics. In previous work, we have argued that this is an unfortunate omission not only because linguistics is appealing to many language students and perceived by them to be useful, but also because the existing cultural topics could be significantly enriched by the inclusion of the critical/analytical study of language itself. In this paper, we provide concrete examples of how linguistics can be integrated into the existing A-level curriculum for Modern Foreign Languages (MFL) in England and Wales. Reporting on a project in which teachers trialled linguistics materials co-created by us (a group of academics) and experienced languages teachers, we present evidence that linguistics materials are perceived to be both highly novel and nonetheless compatible with the existing A-level curriculum. Data from questionnaires and semi-structured interviews with participating teachers also show that: (i) these new materials can be taught with little or no prior experience of linguistics; and (ii) adding linguistics materials to the curriculum leads to significant impacts on teacher and pupil attitudes towards language(s). Despite some challenges, which we also discuss, the results highlight again the great potential of linguistics as a component of language teaching and the contribution that it can make to the enrichment of the discipline. (DIPF/Orig.
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