Mapping X-ray heliometer for Orbiting Solar Observatory-8

An instrument combining mechanical collimators and proportional counter detectors was designed to record solar X-rays with energies of 2-30 keV with good temperal, spectral, and spatial resolution. The overall operation of the instrument is described to the degree needed by personnel who interact with the experimenter during SC/experiment interfacing, experiment testing, observatory integration and testing, and pre/post launch data processing. The general layout of the instrument is given along with a summary of the instrument characteristics

Energy Loss from a Moving Vortex in Superfluid Helium

We present measurements on both energy loss and pinning for a vortex terminating on the curved surface of a cylindrical container. We vary surface roughness, cell diameter, fluid velocity, and temperature. Although energy loss and pinning both arise from interactions between the vortex and the surface, their dependences on the experimental parameters differ, suggesting that different mechanisms govern the two effects. We propose that the energy loss stems from reconnections with a mesh of microscopic vortices that covers the cell wall, while pinning is dominated by other influences such as the local fluid velocity.Comment: 8 pages, 6 figure

The Lockheed OSO-8 program. Analysis of data from the mapping X-ray heliometer experiment

The final report describes the extent of the analysis effort, and other activities associated with the preservation and documentation of the data set are described. The main scientific results, which are related to the behavior of individual solar activity regions in the energy band 1.5 - 15 keV, are summarized, and a complete bibliography of publications and presentations is given. Copies of key articles are also provided

The dynamics of measles in sub-Saharan Africa.

Although vaccination has almost eliminated measles in parts of the world, the disease remains a major killer in some high birth rate countries of the Sahel. On the basis of measles dynamics for industrialized countries, high birth rate regions should experience regular annual epidemics. Here, however, we show that measles epidemics in Niger are highly episodic, particularly in the capital Niamey. Models demonstrate that this variability arises from powerful seasonality in transmission-generating high amplitude epidemics-within the chaotic domain of deterministic dynamics. In practice, this leads to frequent stochastic fadeouts, interspersed with irregular, large epidemics. A metapopulation model illustrates how increased vaccine coverage, but still below the local elimination threshold, could lead to increasingly variable major outbreaks in highly seasonally forced contexts. Such erratic dynamics emphasize the importance both of control strategies that address build-up of susceptible individuals and efforts to mitigate the impact of large outbreaks when they occur

Student conceptions about energy transformations: progression from general chemistry to biochemistry

Students commencing studies in biochemistry must transfer and build on concepts they learned in chemistry and biology classes. It is well established, however, that students have difficulties in transferring critical concepts from general chemistry courses; one key concept is “energy.” Most previous work on students’ conception of energy has focused on their understanding of energy in the context of physics (including the idea of “work”) and/or their understanding of energy in classical physical and inorganic chemistry contexts (particularly Gibbs Free Energy changes, the second law of thermodynamics, and equilibrium under standard conditions within a closed system). For biochemistry, students must go beyond those basic thermodynamics concepts of work, standard energy changes, and closed systems, and instead they must consider what energy flow, use, and transformation mean in living, open, and dynamic systems. In this study we explored students’ concepts about free energy and flow in biological chemical reactions and metabolic pathways by surveys and in-depth interviews. We worked with students in general chemistry classes and biochemistry courses in both an Australian and a US tertiary institution. We address three primary questions (i) What are the most common alternative conceptions held by students when they explain energy-related phenomena in biochemistry?, (ii) What information do students transfer from introductory chemistry and biology when they are asked to consider energy in a biological reaction or reaction pathway?, and (iii) How do students at varying levels of competence articulate their understandings of energy in pathways and biological reactions? The answers to these questions are used to build a preliminary learning progression for understanding “energy” in biochemistry. We also propose crucial elements of content knowledge that instructors could apply to help students better grasp this threshold concept in biochemistry

Estimates of measles case fatality ratios: a comprehensive review of community-based studies.

BACKGROUND: Global deaths from measles have decreased notably in past decades, due to both increases in immunization rates and decreases in measles case fatality ratios (CFRs). While some aspects of the reduction in measles mortality can be monitored through increases in immunization coverage, estimating the level of measles deaths (in absolute terms) is problematic, particularly since incidence-based methods of estimation rely on accurate measures of measles CFRs. These ratios vary widely by geographic and epidemiologic context and even within the same community from year-to-year. METHODS: To understand better the variations in CFRs, we reviewed community-based studies published between 1980 and 2008 reporting age-specific measles CFRs. RESULTS: The results of the search consistently document that measles CFRs are highest in unvaccinated children under age 5 years; in outbreaks; the lowest CFRs occur in vaccinated children regardless of setting. The broad range of case and death definitions, study populations and geography highlight the complexities in extrapolating results for global public health planning. CONCLUSIONS: Values for measles CFRs remain imprecise, resulting in continued uncertainty about the actual toll measles exacts

Transversality of Electromagnetic Waves in the Calculus-Based Introductory Physics Course

Introductory calculus-based physics textbooks state that electromagnetic waves are transverse and list many of their properties, but most such textbooks do not bring forth arguments why this is so. Both physical and theoretical arguments are at a level appropriate for students of courses based on such books, and could be readily used by instructors of such courses. Here, we discuss two physical arguments (based on polarization experiments and on lack of monopole electromagnetic radiation), and the full argument for the transversality of (plane) electromagnetic waves based on the integral Maxwell equations. We also show, at a level appropriate for the introductory course, why the electric and magnetic fields in a wave are in phase and the relation of their magnitudes.Comment: 10 pages, 6 figure