Identification of relaxation and diffusion mechanisms in amorphous silicon

The dynamics of amorphous silicon at low temperatures can be characterized by a sequence of discrete activated events, through which the topological network is locally reorganized. Using the activation-relaxation technique, we create more than 8000 events, providing an extensive database of relaxation and diffusion mechanisms. The generic properties of these events - size, number of atoms involved, activation energy, etc. - are discussed and found to be compatible with experimental data. We introduce a complete and unique classification of defects based on their topological properties and apply it to study of events involving only four-fold coordinated atoms. For these events, we identify and present in detail three dominant mechanisms.Comment: 4 pages, three figures, submitted to PR

Cost-Offsets of New Medications for Treatment of Schizophrenia

Broad claims are frequently made that new medications will offset all or part of their costs by reducing other areas of Medicaid spending. In this paper we examine the net impact on spending for new drugs used to treat schizophrenia. We extend research in this area by taking a new approach to identification of spending impacts of new drugs. We specify and estimate models of spending on treatment of schizophrenia using 7 years of Florida Medicaid data. The estimates indicate that use of the new drugs result in net spending increases. This may be due to increased adherence to treatment.

Thermally-activated charge reversibility of gallium vacancies in GaAs

The dominant charge state for the Ga vacancy in GaAs has been the subject of a long debate, with experiments proposing $-$1, $-$2 or $-$3 as the best answer. We revisit this problem using {\it ab initio} calculations to compute the effects of temperature on the Gibbs free energy of formation, and we find that the thermal dependence of the Fermi level and of the ionization levels lead to a reversal of the preferred charge state as the temperature increases. Calculating the concentrations of gallium vacancies based on these results, we reproduce two conflicting experimental measurements, showing that these can be understood from a single set of coherent LDA results when thermal effects are included.Comment: 4 pages, 4 figure

The ability of fifth grade children to discriminate between fact and opinion statement

Thesis (Ed.M.)--Boston Universit

Discrete ordinates-Monte Carlo coupling: A comparison of techniques in NERVA radiation analysis

In the radiation analysis of the NERVA nuclear rocket system, two-dimensional discrete ordinates calculations are sufficient to provide detail in the pressure vessel and reactor assembly. Other parts of the system, however, require three-dimensional Monte Carlo analyses. To use these two methods in a single analysis, a means of coupling was developed whereby the results of a discrete ordinates calculation can be used to produce source data for a Monte Carlo calculation. Several techniques for producing source detail were investigated. Results of calculations on the NERVA system are compared and limitations and advantages of the coupling techniques discussed

Le rôle de la végétation sur la morphologie d’un petit cours d’eau

Dans cette étude, on démontre que la forme du chenal le long d'un petit affluent de la rivière au Saumon (Québec) varie en fonction des propriétés des racines des végétaux qui bordent les berges. Le cours d'eau est étroit et profond lorsque les deux berges sont occupées par des graminées, alors qu'il est plus large et moins profond lorsqu'au moins une des deux berges est couverte d'aulnes. Ces variations morphologiques sont en partie expliquées par la forme des berges, qui est elle-même contrôlée par la densité, la taille et le déploiement des racines des plantes qui y poussent.Along a segment of a small tributary of the Rivière au Saumon (Québec), channel shape is affected by the root sysiem of the vegetation growing on the top of the channel banks. The stream is narrow and deep under pasture while it becomes wider and shallower when alder grows on at least one of its bank. These morphometric changes are related to changes in the shape of the banks which in turn are controlled by the density, size and spatial organization of the plants root system

Real Output in Mental Health Care During the 1990s

Health accounts document changes over time in the level and composition of health spending. There has been a continued evolution in the ability to track such outlays. Less rapid has been the ability to interpret changes in spending. In this paper we apply quality adjusted price indexes for several major mental disorders to national mental health account estimates to assess changes in real "output". We show that using the new price indexes reveals large gains in real output relative to application of BLS indexes.