Bibliothek

Notizen: Using a new technique to generate cold electron beams, an electron-beam positron-plasma experiment was performed in a previously unexplored range of energies. An electron beam, formed from a thermalized room-temperature electron plasma, is transmitted through a positron plasma stored in a quadrupole Penning trap geometry. The transit-time instability, which is excited by the beam, was previously studied using a hot-cathode electron gun. The large beam energies produced by the cathode did not permit an investigation of the instability in the interesting range of energies near its onset. Using a new 0.1 eV energy width electron beam, we have reinvestigated the system. The experimental data are compared with the results of a theoretical model, also described in this paper. The theory employs a linearized cold fluid and Vlasov approach to model the plasma and beam dynamics, respectively. The data and predictions are in good agreement over the broad range of energies and beam currents studied. © 2001 American Institute of Physics.

Notizen: Abstract Public health genetics is an exciting interdisciplinary area that brings all the public health sciences to bear on the emerging challenge of interpreting the medical and public health significance of genetic variation within populations. Sequencing of the human genome will generate an avalanche of genetic information to be linked with information about microbial, chemical, and physical exposures; nutrition, metabolism, lifestyle behaviors, and medications. The public health genetics mini-symposium in this volume includes articles dealing with educational innovations, host-pathogen interactions in infectious diseases, nutrition/genetic interactions in cancers, and population screening for hemochromatosis. Additional topics addressed here are ecogenetics and risk assessment, the genetics of unhealthful behaviors, and ethical and policy issues. Finally, a set of principles for community-based health research in populations is presented as a public health-oriented counterpart to the principle of autonomy and the practice of informed consent that have become key elements of ethics in medical care and medical research with individuals.

Notizen: Genetic differences (polymorphisms) among members of a population are thought to influence susceptibility to various environmental exposures. In practice, however, this information is rarely incorporated into quantitative risk assessment and risk management. We describe an analytic framework for predicting the risk reduction and value-of-information (VOI) resulting from specific risk management applications of genetic biomarkers, and we apply the framework to the example of occupational chronic beryllium disease (CBD), an immune-mediated pulmonary granulomatous disease. One described Human Leukocyte Antigen gene variant, HLA-DPβ1*0201, contains a substitution of glutamate for lysine at position 69 that appears to have high sensitivity (∼94%) but low specificity (∼70%) with respect to CBD among individuals occupationally exposed to respirable beryllium. The expected postintervention CBD prevalence rates for using the genetic variant (1) as a required job placement screen, (2) as a medical screen for semiannual in place of annual lymphocyte proliferation testing, or (3) as a voluntary job placement screen are 0.08%, 0.8%, and 0.6%, respectively, in a hypothetical cohort with 1% baseline CBD prevalence. VOI analysis is used to examine the reduction in total social cost, calculated as the net value of disease reduction and financial expenditures, expected for proposed CBD intervention programs based on the genetic susceptibility test. For the example cohort, the expected net VOI per beryllium worker for genetically based testing and intervention is $13,000, $1,800, and $5,100, respectively, based on a health valuation of $1.45 million per CBD case avoided. VOI results for alternative CBD valuations are also presented. Despite large parameter uncertainty, probabilistic analysis predicts generally positive utility for each of the three evaluated programs when avoidance of a CBD case is valued at $1 million or higher. Although the utility of a proposed risk management program may be evaluated solely in terms of risk reduction and financial costs, decisions about genetic testing and program implementation must also consider serious social, legal, and ethical factors.