The Endomorphisms of a Finite Chain Form a Rees Congruence Semigroup

Rees congruence semigroup , is one for which every non-identity congruence is a Rees congruence. We show that the widely studied semigroup of endomorphisms of a finite chain is a Rees congruence semigroup. Communicated by     

Spatial versus quantum confinement in porous amorphous silicon nanostructures

Light-emitting porous amorphous silicon has been produced by anodization in HF of hydrogenated amorphous silicon films. The maximal thickness of the porous films is limited by the onset of an instability which results in the formation of large channels short-circuiting the amorphous layer. This is due to the high resistivity of the amorphous silicon films as compared to that of the electrolyte. Confinement effects on the electron wavefunction are analyzed in situ using photoluminescence measurements in hydrofluoric acid and compared to those observed in porous crystalline silicon. For crystalline silicon, a huge blue shift of the photoluminescence is observable upon reducing the size of the structures by photo-etch, showing clear evidence of quantum confinement effects in this material. No shift has been observed when carrying out the same experiment with amorphous silicon. This indicates that the extent of the wavefunction in the bandtail states involved in luminescence is too small to be sensitive to confinement down to the minimum sizes of our porous material ( 3 nm). Measurements of the width and the temperature dependence of the photoluminescence demonstrate that the Urbach energy does not change upon increasing the porosity, i.e., upon decreasing the size of the a-Si:H nanostructures, in contradiction with what has been reported in ultrathin a-Si:H multilayers. Received: 3 August 1998     

The implications of demographic changes for publicly funded medical insurance costs

This paper explores the changes in public expenditures for Medicare and Medicaid that would result between 1980 and 2040 under the ceteris paribus assumption, under the age, sex, and family structure projections of John Wilkin of the Social Security Administration. Inflation aside, costs are shown to approximately double as a percent of the payroll of active workers. The most dramatic increases occur in nursing home costs: Costs for welfare recipients under age 65 change little except for medical care inflation. This latter results from the assumed low birth rates assumed in the population forecast.     

Simplicial K(G,1)'s

We describe a subcomplex S_* (G) of a K(G,1) which depends on a given presentation of the group G. We prove that under a certain condition S_* (G) is a K(G,1). Complexes of the type S_* (G) arise in the homotopy theory of the classifying space for foliations.This research was partially supported by the N.S.F.     

On the origin of photocontraction effect in amorphous chalcogenide films

Large photocontraction of up to 26% has been observed in some chalcogenide films. Conditions necessary for the occurrence of large photocontraction are indicated to be: ability to form a glass, high bond ionicity, strong electron-phonon coupling, low density of the bulk material, and a large density difference between the bulk and the thin-film. These studies suggest that contraction (densification) is due to the mechanical collapse of the columns resulting from the large internal stresses caused by the interaction of the photogenerated carriers and the charged dangling bonds.     

Single step oxidative binding of antibodies to hydrazide-modified eupergit C

A single step periodate oxidative binding of glycoproteins to synthetic polymeric matrices is proposed. By this procedure, the glycoprotein to be immobilized is simultaneously mixed with sodium periodate and a hydrazide-containing matrix. The carbohydrate moieties of the protein are oxidized and react with matrix. The single step reaction is faster than the commonly-used multistep procedure and it allows conjugation of minute amounts of glycoproteins to the matrix.     

Synthesis of spiro[4′,5′,10,11-tetrahydro-5H-dibenzo[a,d]cyclohepten-5-yl-2′(3′H)-furans] as potential cytokine inhibitors

A synthesis of novel spiro[4′,5′,10,11-tetrahydro-5H-dibenzo[a,d]cyclohepten-5-yl-2′(3′H)-furans] is described. The key reaction was formation of the tetrahydrofuran ring by cyclization of the diol 3 or the protected diol 10. These compounds were investigated as potential TNF-α inhibitors.