On positivity of solutions of degenerate boundary value problems for second-order elliptic equations

In this paper we study thedegenerate mixed boundary value problem:Pu=f in Ω,B _u =gon Ω∂Г where ω is a domain in ℝ ⁿ ,P is a second order linear elliptic operator with real coefficients, Γ⊆∂Ω is a relatively closed set, andB is an oblique boundary operator defined only on ∂Ω/Γ which is assumed to be a smooth part of the boundary. The aim of this research is to establish some basic results concerning positive solutions. In particular, we study the solvability of the above boundary value problem in the class of nonnegative functions, and properties of the generalized principal eigenvalue, the ground state, and the Green function associated with this problem. The notion of criticality and subcriticality for this problem is introduced, and a criticality theory for this problem is established. The analogs for the generalized Dirichlet boundary value problem, where Γ=∂Ω, were examined intensively by many authors.     

Interferences in the density of two Bose-Einstein condensates consisting of identical or different atoms

The density of two initially independent condensates which are allowed to expand and overlap can show interferences as a function of time due to interparticle interaction. Two situations are separately discussed and compared: (1) all atoms are identical and (2) each condensate consists of a different kind of atoms. Illustrative examples are presented.     

Deletion of nondominant effects in modeling transport in porous media

A methodology for eliminating nondominant effects in models that describe transport phenomena in porous media is presented. The methodology is based on the introduction of dimensionless numbers and on a proper evaluation of the order of magnitude of terms. These dimensionless numbers are redefined as characteristics of transport and transformation phenomena in porous media. It is shown that different time scales and different length scales may have to be employed for different variables. A method for evaluating the order of magnitude of the error of prediction when terms are deleted, is presented.     

Currency options as theoretical and practical instrument in hedging the exchange risk in excess of loss reinsurance

The paper demonstrates that a ceding company can fully hedge itself against adverse movements of the exchange rate in the case of excess of loss foreign reinsurance by using the currency option markets.     

Vibrational relaxation of biacetyl studied by a visible—infrared double resonance technique

The vibrational relaxation of biacetyl following excitation by a highly intense laser pulse at 10.6 micron is studied. The changes in vibrational population are monitored by visible absorption from the ground electronic state to the excited n-π* state. The results indicate that thermal disequilibrium persists for at least 10^?5 seconds after the laser pulse at pressures in the range of 1–40 torr.The implications of these results for the use of high-power infrared lasers in inducing selective chemical reactions are briefly discussed.     

Serum Levels of 25‐Hydroxy‐Vitamin D3 Among Sun‐protected Outdoor Workers in Israel

The objective of this study was to evaluate the effect of reduced sun exposure of outdoor workers on vitamin D status using different modalities of sun protection, for primary prevention of skin cancer. 25‐OH‐D3 measurements were performed in two successive winters, 8 (interim) and 20 months after initiation of the study, in three groups of male outdoor workers, enrolled in either a complete, partial or minimal sun protection program. Ambient solar UVB radiation was monitored simultaneously. No intragroup or intergroup differences were observed between the interim‐ and postintervention measurements of mean 25‐OH‐D3, which were close to 30 ng mL^?1. Significant risk factors for postintervention 25‐OH‐D3 levels >33.8 ng mL^?1 (a surrogate for reduced sun protection) were: previous sunburn episodes (OR 2.5; 95% CI 1.01–6.3; P = 0.05) and younger age (OR 0.92; 95 CI 0.86–0.98; P = 0.009). Outdoor workers of Western, compared with those of Eastern paternal origin had a borderline significant risk (OR 2.4; 95% CI 0.9–6.3; P = 0.07). A borderline significant effect (OR 2.9; 95% CI 0.97–10.1; P = 0.085) was also noted for those in the minimal intervention group. In conclusion, sun protection among outdoor workers following a successful intervention did not suppress mean winter 25‐OH‐D3.     

Classical stochastic diffusion theory for desorption from solid surfaces

We present a theory of desorption of atoms and molecules from solid surfaces based on a classical stochastic diffusion formulation. We obtain a simple rate expression which has the form $\text{R = (}\text{Ω}{}_{\mathrm{o}}\text{2π}$f(T) exp($\text{?D}{}_{\mathrm{e}}\text{K}{}_{\mathrm{T}}$), where T is the temperature, k is Boltzmann's constant, the bond enthalpy, and Ω_o is the surface-adsorbate vibrational frequency. For atoms √(T) = 1, while for molecules f(T) depends on the parameters for the frustrated rotations at the surface. Application of this theory is reported for the desorption of atoms and molecules. We find that molecules lead to a greatly increased (factor of 100) Arrhenius preexponential factor in excellent agreement with experiment.