An anomalous alloy: Y_x Si_{1-x}

We study via density functional-based molecular dynamics the structural and dynamical properties of the rare earth silicon amorphous alloy Y_xSi_{1-x} for x=0.093 and x=0.156. The Si network forms cavities in which a Y^{3+} cation is entrapped. Its electrons are transferred to the Si network and are located in the dangling bonds of the Si atoms that line the Y cavities. This leads to the presence of low coordinated Si atoms that can be described as monovalent or divalent anions. For x=0.156, the cavities touch each other and share Si atoms that have two dangling bonds. The vibrational spectrum is similar to that of amorphous Si. However, doping induces a shoulder at 70 cm^{-1} and a pronounced peak at 180 cm^{-1} due to low coordinated Si.Comment: 4 pages, 4 figure

Giant negative magnetoresistance in semiconductors doped by multiply charged deep impurities

A giant negative magnetoresistance has been observed in bulk germanium doped with multiply charged deep impurities. Applying a magnetic field the resistance may decrease exponentially at any orientation of the field. A drop of the resistance as much as about 10000% has been measured at 6 T. The effect is attributed to the spin splitting of impurity ground state with a very large g-factor in the order of several tens depending on impurity.Comment: 4 pages, 4 figure

The optical response of Ba_{1-x}K_xBiO_3: Evidence for an unusual coupling mechanism of superconductivity?

We have analysed optical reflectivity data for Ba_{1-x}K_xBiO_3 in the far-infrared region using Migdal-Eliashberg theory and found it inconsistent with standard electron-phonon coupling: Whereas the superconducting state data could be explained using moderate coupling, \lambda=0.7, the normal state properties indicate \lambda \le 0.2. We have found that such behaviour could be understood using a simple model consisting of weak standard electron-phonon coupling plus weak coupling to an unspecified high energy excitation near 0.4 eV. This model is found to be in general agreement with the reflectivity data, except for the predicted superconducting gap size. The additional high energy excitation suggests that the dominant coupling mechanism in Ba_{1-x}K_xBiO_3 is not standard electron-phonon.Comment: 5 pages REVTex, 5 figures, 32 refs, accepted for publication in Phys. Rev.

Processing and Transmission of Information

Contains research objectives, summary of research and reports on two research projects.National Aeronautics and Space Administration (Grant NGL 22-009-013)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E)U. S. Army Research Office - Durham (Contract DAHCO4-69-C-0042

Glucose metabolism and oscillatory behavior of pancreatic islets

A variety of oscillations are observed in pancreatic islets.We establish a model, incorporating two oscillatory systems of different time scales: One is the well-known bursting model in pancreatic beta-cells and the other is the glucose-insulin feedback model which considers direct and indirect feedback of secreted insulin. These two are coupled to interact with each other in the combined model, and two basic assumptions are made on the basis of biological observations: The conductance g_{K(ATP)} for the ATP-dependent potassium current is a decreasing function of the glucose concentration whereas the insulin secretion rate is given by a function of the intracellular calcium concentration. Obtained via extensive numerical simulations are complex oscillations including clusters of bursts, slow and fast calcium oscillations, and so on. We also consider how the intracellular glucose concentration depends upon the extracellular glucose concentration, and examine the inhibitory effects of insulin.Comment: 11 pages, 16 figure

Economic transition and elections in Poland 1

Poland's economic and political transition, one of the most successful, has depended very heavily on job creation in new firms to replace the jobs lost in the formerly state-owned enterprises. This paper uses survey and aggregate data from three Polish elections to suggest that these de novo firms, the individuals they employ, and the residents in the local areas where they exist become an important constituency supporting pro-reform political parties and constraining the actions of parties less sympathetic to the reforms. The creation of this political constituency helps explain how countries can successfully pursue both economic and political reforms. JEL classification: D72, P26.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72227/1/1468-0351.00139.pd