Search Results - (Author, Cooperation:J. E. Cohen)

2011-12-17

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Communication ; *Disaster Planning ; *Earthquakes ; Italy ; *Public Policy ; *Science/education ; United States

1089-7666

AIP Digital Archive

Physics

It is shown how fluid velocities along heavy-particle trajectories in a turbulent flow, which are neither purely Lagrangian nor purely Eulerian in character, can be simulated using a fractional Langevin equation; the analogy of the Langevin equation but with fractional Gaussian noise as the source of randomness. A modified Fokker–Planck equation is derived for such stochastic processes and Thomson's well-mixed condition is generalized accordingly. Heavy-particle trajectories in grid turbulence are then simulated by combining the fractional Langevin equation with the equation of motion for a heavy-particle in a turbulent flow. Model predictions for the mean concentrations and root-mean-square velocities of heavy-particles are shown to be in reasonable agreement with the experimental data of Snyder and Lumley (1971). © 2002 American Institute of Physics.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The simplest neo-darwinian model for the evolution of the population mean ? of a genetically determined character expresses the change dx in time interval d ?s the sum of a natural selection term and a random variation term: dx(t) = F'(x(t)) + adW(t) (1) F(x), a one-dimensional genotypic3 or ...

Electronic Resource

1432-1416

Springer Online Journal Archives 1860-2000

Biology

Mathematics

Abstract A logistic matrix model for age-structured population dynamics is constructed. This model discretizes a continuous, density-dependent model with age structure, i.e. it is an extension of the logistic model to the case of age-dependence. We prove the existence and uniqueness of its equilibrium and give a necessary and sufficient condition for the local stability of the equilibrium.

Electronic Resource

1588-2861

Springer Online Journal Archives 1860-2000

Information Science and Librarianship

Nature of Science, Research, Systems of Higher Education, Museum Science

Conclusions Laboratory size may affect the number of scientific publications per capita. However, no analysis I have seen of my data or of other data has demonstrated the existence of such an effect convincingly. An analysis5 of patentable research among 500 leading industrial firms concluded that the number of patents filed per year divided by annual sales is independent of the annual sales, i.e., on the average, small, medium and large industrial firms are all equally inventive. If patents are viewed as a measure of research productivity in the commercial sector, and if sales are viewed as a measure of size or research effort (a company's research budget would be a better measure), then this finding that the ratio of patents to total sales is independent of total sales exactly parallels my finding that publications per capita are independent of laboratory size. The parallelism of these findings suggests the possibility that, in general, the productivity per capita of a research effort is independent of the total size of the research effort, whether the setting is academic or commercial. Whether or not this empirical generalization is ultimately confirmed, the methodological message of this note seems to me less arguable.

Electronic Resource

1588-2861

Springer Online Journal Archives 1860-2000

Information Science and Librarianship

Nature of Science, Research, Systems of Higher Education, Museum Science

Abstract At the Rockefeller University in 1977–78, the number of all publications of a research group in a year was approximately proportional to the number of individuals in that group during the year. The number of primary research publications of a group in a year was also approximately proportional to the number of individuals in that group during the year. The observed frequency distribution of laboratory size was statistically indistinguishable from a 0-truncated negative binomial distribution, which is the equilibrium frequency distribution of size predicted by stochastic models for the dynamics of freely-forming primate social groups.

Electronic Resource

1588-2861

Springer Online Journal Archives 1860-2000

Information Science and Librarianship

Nature of Science, Research, Systems of Higher Education, Museum Science

Abstract Varied empirical studies show that the average output (measured in various ways) of a scientific or technical research group is directly proportional to its size (also measured in various ways), when the size and output are measured independently. Hence groups of different sizes have the same average output per unit of size. There is no reliable evidence for the existence of a size or a range of sizes for a research group that maximizes output per unit of size. Present theoretical explanations for the proportionality between size and output are largely inadequate or untested. Similarly, among reported results on group age and output, the only consistency so far is that age, measured as years since the founding or first functioning of the group, is uncorrelated with output per capita. Again, there is no evidence for the existence of an age or a range of ages for a research group that is optimal.

Electronic Resource

1588-2861

Springer Online Journal Archives 1860-2000

Information Science and Librarianship

Nature of Science, Research, Systems of Higher Education, Museum Science

Abstract In three biomedical research institutions, there is no indication of a single laboratory size at which the number of publications per scientist is maximal or minimal. In a scattergram of the number of publications of a laboratory against laboratory size, the horizontal coordinate measures the number of scientists in a laboratory, the vertical axis measures the number of publications from the laboratory (counting each publication once regardless of the number of authors), and each laboratory is represented by one point. Scattergrams for the Rockefeller University (RU), New York, the National Institute for Medical Research (NIMR), London, and the National Cancer Institute (NCI), Bethesda, are each described well by a straight line through the origin. The slopes of the lines for the three institutions are not significantly different. In these laboratories, ranging in size from 1 to 46 scientists, one additional scientist increases the expected annual number of publications of a laboratory by approximately 1.1, regardless of the size of the laboratory. Although the three institutions have significantly different mean laboratory sizes, the frequency distribution of laboratory size in each institution is described well by a 0-truncated negative binomial distribution, as predicted by a simple model of laboratory population dynamics.

Electronic Resource