SXRP: an X-ray polarimeter for the SPECTRUM-X-Gamma Mission

Summary TheStellar X-ray Polarimeter (SXRP) is a focal plane instrument which will be flown on the SPECTRUM-X-Gamma mission in 1993. The polarimeter is composed of two separate instruments: the first exploits the dependence on the polarization of the Bragg reflection from a graphite crystal, and of the Thomson scattering from a metallic lithium target. The second instrument makes use of the recently discovered polarization dependence of X-ray photoemission from CsI. The SXRP will permit sensitive measurements of several hundreds of known X-ray sources. X-ray polarization measurements will allow us to constrain the physical mechanisms and the geometries of several classes of galactic X-ray sources, such as X-ray pulsars, black-hole candidates and supernova remnants. Moreover, and for the first time, SXRP will be able to perform highly sensitive measurements of the brightest extragalactic sources. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Analysis of three-dimensional grids: Cubic equations for nine-point prismatic arrays

Four polynomial equations for interpolating the nine-point cube are compared. All of the equations estimate first-, second- and third-order coefficients. Fidelity to monotonic test surfaces, as measured by sums-of-squares of deviations, depends on the distribution of the center point datum among the coefficients. Linear-term coefficients rendered by the equations are often more accurate than the like coefficients rendered by main-effects formulas.     

Preparation and unit cell dimensions of new-perovskite materials of the formula K(MM′)F3(MMn,Fe,Co,Zn,M′Mn,Co,Ni,Zn)

Materials of the type K(MM′)F₃ are prepared by a simple solution method. The simple replacement of one M²⁺ ion with another without distortion of the cubic unit cell is demonstrated from X-ray powder diffraction data. Unit cell dimensions are reported.     

Condensation of injected electrons and holes in silicon

We report that the condensed electron—hole phase in silicon has been produced by electrical carrier injection. The condensed phase recombination radiation occured at 1.082 ± 0.001 eV with a linewidth of 0.012 eV. Hence the line position and linewidth appear to be independent of whether the semiconductor is excited by optical of electrical injection. Joule heating is shown to be important by analyses of time resolved recombination radiation spectra and double pulse experiments.     

A normal-incidence reflective polariscope for viscoelasticity measurements

A normal-incidence reflective polariscope, together with some auxiliary instrumentation, is described. The instrument consists of eight unit polariscopes, relatively oriented, which are indexed into position within a short period of time to obtain a set of eight data. These data provide sufficient information to separate the principal strains obtained at different time intervals. The primary experimental objective was to design an inflated-cylinder test, analogous to the loading experienced in a solid-propellant rocket, that would enable reasonable measurements of the triaxial surfacelayer strains of a viscoelastic material as a function of time. The stress geometry imposed on the viscoelastic material was that of an unrestricted, biaxially pressurized, thick-walled tubular cylinder. The material investigated was polyurethane solid propellant. Two different methods to reduce the biaxial strains in a low-modulus birefringent polyurethane coating are also described.     

Plutonium and intrinsic predominance-region diagrams

Four intrinsic predominance-region diagrams for aqueous plutonium are described. They are easily prepared from an existing diagram by changing the oxidation-state fractions on the axes of the diagram and renaming the predominance regions. Not all combinations of oxidation-state fractions can be used to prepare the diagrams.     

Protein crystals make it big at electrode surfaces

Enhanced and rapid growth of lysozyme crystals at the surface of a platinum electrode, using an applied current and a simplified crystallizing solution, is demonstrated.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

The Role of Visual Representations in Advanced Mathematical Problem Solving: An Examination of Expert-Novice Similarities and Differences

Expert mathematicians are contrasted with undergraduate students through a two-part analysis of the potential and actual use of visual representations in problem solving. In the first part, a classification task is used to indicate the extent to which visual representations are perceived as having potential utility for advanced mathematical problem solving. The analysis reveals that both experts and novices perceive visual representation use as a viable strategy. However, the two groups judge visual representations likely to be useful with different sets of problems. Novices generally indicate that visual representations would likely be useful mostly for geometry problems, whereas the experts indicate potential application to a wider variety of problems. In the second part, written solutions to problems and verbal protocols of problem-solving episodes are analyzed to determine the frequency, nature, and function of the visual representations actually used during problem solving. Experts construct visual representations more frequently than do novices and use them as dynamic objects to explore the problem space qualitatively, to develop a better understanding of the problem situation, and to guide their solution planning and enactment of problem-solving activity. In contrast, novices typically make little use of visual representations.