Nonexistence of a class of variate generation schemes

Motivated by a problem arising in the regenerative analysis of discrete-event system simulation, we ask whether a certain class of random variate generation schemes exists or not. Under very reasonable conditions, we prove that such variate generation schemes do not exist. The implications of this result for regenerative steady-state simulation of discrete-event systems are discussed.     

PIXE analysis of prehistoric and protohistoric Caborn-Welborn phase copper artifacts from the lower Ohio River Valley

Particle-induced X-ray emission (PIXE) spectrometry is being used to nondestructively determine the elemental composition of copper-based artifacts excavated from prehistoric/protohistoric sites in the Ohio River Valley. Copper objects from Caborn-Welborn (C-W) and contemporary Fort Ancient sites are being studied so as to differentiate between native American and European copper. The trace element analysis of metal artifacts enables archaeologists to more accurately assess the material culture and chronological development of C-W society (A.D. 1400–1700) with particular reference to geological sources of copper and brass.     

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Crystallization behavior of poly(3,3-bisethoxymethyl oxetane) and poly(3,3-bisazidomethyl oxetane)

Two crystal modifications have been found for poly(3,3-bisethoxymethyl oxetane) [poly- (BEMO)] by wide-angle x-ray powder diffraction and differential scanning calorimetry, while only one modification has been found for poly(3,3-bisazidomethyl oxetane) [poly(BAMO)]. Melting temperatures for the two polymers were nearly the same, varying from about 70 to about 90°C depending on the thermal treatment; higher crystallization temperatures resulted in higher melting temperatures. The equilibrium melting temperature T was found to be 125 and 128°C for poly(BEMO) and poly(BAMO), respectively, by using the Hoffman-Weeks extrapolation procedure. Measurement of the melting-point depression of Poly(BEMO) and poly(BAMO) in dibutyl phthalate yielded enthalpy of fusion values of 2.25 and 12.8 kcal/mol, respectively. The percent crystallinity for poly(BEMO) and poly(BAMO), respectively, was calculated to be 55-60 and 13-30% based on DSC and x-ray analysis.     

The vector refraction law for shock waves

The law is formulated in vector form and is shown to be a powerful principle for studying the refraction of shock waves. A variety of criteria for the onset of irregular refraction are discussed. The refraction index matrix is defined and it is shown that it arises naturally from the law. A projection matrix is also defined and it is found to be useful for operating on the vector wave impedance. It is expected that the methods described here will be useful for the numerical solution of problems in the refraction of shocks by materials with continuous changes in properties. The refraction law is violated in fast-slow refraction by the reflected wave over-running the incident shock to produce an irregular refraction which is either the anomalous type or the Mach-reflection-refraction type. For slow-fast refraction the law is violated by the transmitted wave becoming a precursor and also over-running the incident shock. The precursor may either be a shock or an evanescent compression wave band.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

BIODISTRIBUTION AND PDT EFFICACY OF A KETOCHLORIN PHOTOSENSITIZER AS A FUNCTION OF THE DELIVERY VEHICLE

Abstract C8KC is a new ketochlorin photosensitizer that must be formulated with an emulsifier because of its poor water solubility. In this report, we compare properties of Cremophor EL (CRM) and Tween 80 as delivery vehicles for C8KC. Unlike Tween 80, CRM altered the physical properties of both human and mouse plasma lipoproteins, resulting in decreased electrophoretic mobility of the individual lipoproteins along with the formation of a l ipoprotein degradation product: a phospholipid fraction of low buoyant density. In human plasma, where there was sufficient low-density lipoprotein (LDL) for a distinction to be made, CRM caused a shift in binding of a ketochlorin from albumin to LDL and the degraded lipoprotein fraction. In mice bearing the RIF tumor, the use of CRM for drug formulation was associated with longer plasma and tissue persistence of C8KC, and enhanced photodynamic therapy (PDT) efficacy. These results indicate the importance of both sensitizer and vehicle as determinants of PDT efficacy.     

Laser radiation hazards

Lasers are being employed in an increasingly diverse range of applications, but laser safety is rightly a topic of current concern. This paper considers the radiometry of laser exposure, briefly reviews the biological mechanisms of laser damage, and discusses the ways in which laser safety standards are applied to ensure safe operation of laser equipment.