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Search Results: 1 - 10 of 55639 matches for " David Klein "
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Advanced Placement Calculus AB Evaluation
David Klein
Nonpartisan Education Review , 2007,
Abstract: no abstract
International Baccalaureate Diploma Programme: Mathematics SL, A Review
David Klein
Nonpartisan Education Review , 2007,
Abstract: no abstract
Maximal Fermi charts and geometry of inflationary universes
David Klein
Mathematics , 2012, DOI: 10.1007/s00023-012-0227-3
Abstract: A proof is given that the maximal Fermi coordinate chart for any comoving observer in a broad class of Robertson-Walker spacetimes consists of all events within the cosmological event horizon, if there is one, or is otherwise global. Exact formulas for the metric coefficients in Fermi coordinates are derived. Sharp universal upper bounds for the proper radii of leaves of the foliation by Fermi spaceslices are found, i.e., for the proper radii of the spatial universe at fixed times of the comoving observer. It is proved that the radius at proper time $\tau$ diverges to infinity for non inflationary cosmologies as $\tau\to\infty$, but not necessarily for cosmologies with periods of inflation. It is shown that any spacelike geodesic orthogonal to the worldline of a comoving observer has finite proper length and terminates within the cosmological event horizon (if there is one) at the big bang. Geometric properties of inflationary versus non inflationary cosmologies are compared, and opposite inequalities for the inflationary and non inflationary cases, analogous to Hubble's law, are obtained for the Fermi relative velocities of comoving test particles. It is proved that the Fermi relative velocities of radially moving test particles are necessarily subluminal for inflationary cosmologies in contrast to non inflationary models, where superluminal relative Fermi velocities necessarily exist.
Variation in quality of caribou and reindeer forage plants associated with season, plant part, and phenology
David R. Klein
Rangifer , 1990,
Abstract: Plant parts used as forage by caribou and reindeer (Rangifer tarandus) have been collected in conjunction with studies of foraging dynamics, nutrition, growth, and population ecology of this arctic ungulate over the course of several years in Alaska and other circumpolar areas. These samples were subjected to proximal analyses for percent nitrogen, phosphorus, sodium, carbohydrate, cell wall (NDF), acid detergent fiber (ADF), lignin, cellulose, and residual ash, and treated to determine in vitro and nylon bag dry matter digestibility (DMD). Among winter vascular plant forage only carbohydrates showed a positive correlation with digestibility, wheras in summer nitrogen, phosphorus, and in some cases sodium, also are positively correlated with digestibility. Forage from shrubs and forbs in early summer had higher nitrogen and carbohydrate levels than later in the season, wheras graminoids show an increase in these levels during the first few weeks of growth. Floral parts during anthesis showed higher nitrogen, phosphorus, and carbohydrate levels and higher digestibility than corresponding leaf material. The annual dietary cycle is the product of adjustment of the physiological cycle to seasonal fluctuation in forage quality and quantity.
Arctic ungulates at the northern edge of terrestrial life
David R. Klein
Rangifer , 1996,
Abstract: The two ungulate species that occur in the High Arctic, Rangifer tarandus and Ovibos moschatus, exhibit considerable adaptive plasticity in response to habitat variability throughout their circumpolar distribution. R. tarandus, however, has a much wider latitudinal distribution and occurs within a wider range of both forest and tundra habitat types than 0. moschatus, reflecting greater morphological, physiological, and behavioral plasticity. As a consequence, muskoxen have been less successful than caribou and reindeer in maintaining populations at their southern limits. Muskoxen, however, existed throughout Pleistocene glaciations in the cold periglacial steppes of Eurasia and North America and find the closest analog to this vegetation type in the High Arctic, where they have been more successful than R. tarandus in maintaining their populations.
Comparative ecological and behavioral adaptations of Ovibos moschatus and Rangifer tarandus
David R. Klein
Rangifer , 1992,
Abstract: Caribou/reindeer and muskoxen are the only two ungulate species that have successfully occupied arctic tundra habitats. Although confronted with similar environmental constraints, their morphological dissimilarities have enabled them to develop unique behavioral and ecological adaptations that under most circumstances result in minimal overlap in use of forage resources. The large body and gut capacity of muskoxen have enabled them to adopt a strategy maximizing rate of forage intake and energy conservation, whereas caribou/reindeer of substantially smaller body size must pursue selective feeding, requiring high mobility and high energy expenditure. Responses to predators and insects by the two species show similar contrasts in associated energy costs. When confronted with environmental extremes that limit forage availability, competition for food may occur and the resulting differential success is a reflection of their divergent evolutionary routes.
Limiting factors in caribou population ecology
David R. Klein
Rangifer , 1991,
Abstract: Caribou and wild reindeer populations fluctuate over time. On this fact there is general agreement. Factors responsible for population limitation and subsequent declines have been examined within the framework of animal population theory. There is, however, little agreement when factors limiting specific populations are generalized to Rangifer populations over broad geographic regions. Comparative examinations of wild Rangifer populations worldwide discloses that factors that have regulated those populations are highly variable between populations, apparently as a reflection of the differences in environmental variables unique to each population. Examples exist of populations where major regulating factors have been climatic extremes, predation, hunting mortality, food limitation, insects, parasites, disease, interspecific competition, and human developmental impacts or combinations of these factors. This diversity of limiting factors affecting caribou and wild reindeer populations is a reflection of the ecologial complexity of the species, a concept that has often been ignored in past efforts to reach management decisions by extrapolation from the limited localized knowledge available on the species.
Reindeer on South Georgia: The ecology of an introduced species
David R. Klein
Rangifer , 1989,
Abstract: N. Leader-Williams. "Reindeer on South Georgia: The ecology of an introduced species." Cambridge University Press (Studies in Polar Research). 1988. 319pp. ISBN 0 521 24271 1.
The challenge of preparation for a chemical, biological, radiological or nuclear terrorist attack
Alexander David,Klein S
Journal of Postgraduate Medicine , 2006,
Abstract: Terrorism is not a new phenomenon, but, in the contemporary scene, it has established itself in a manner which commands the most serious attention of the authorities. Until relatively recently, the major threat has been through the medium of conventional weaponry and explosives. Their obvious convenience of use and accessibility guarantees that such methods will continue to represent a serious threat. However, over the last few years, terrorists have displayed an enthusiasm for higher levels of carnage, destruction and publicity. This trend leads inexorably to the conclusion that chemical, biological, radiological and nuclear (CBRN) methods will be pursued by terrorist organisations, particularly those which are well organised, are based on immutable ideological principles, and have significant financial backing. Whilst it is important that the authorities and the general public do not risk over-reacting to such a threat (otherwise, they will do the work of the terrorists for them), it would be equally ill-advised to seek comfort in denial. The reality of a CBRN event has to be accepted and, as a consequence, the authorities need to consider (and take seriously) how individuals and the community are likely to react thereto and to identify (and rehearse in a realistic climate) what steps would need to be taken to ameliorate the effects of such an event.
Exact Fermi coordinates for anti-de Sitter and other spacetimes
David Klein,Peter Collas
Physics , 2009,
Abstract: This paper has been withdrawn by the authors, an improved version with the title "Exact Fermi coordinates for a class of spacetimes", arXiv:0912.2779, replaces it.
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