Thermogravimetry of the analytical precipitates M2Pb[Co(NO2)6] AND MPb[Co(NO2)6]

Thermogravimetric studies are reported for analytical precipitates of the types MPb[Co(NO₂)₆] and M₂Pb[Co(NO₂)₆], where M represents the univalent cations NH⁺₄, K⁺, Rb⁺, Cs⁺, and Tl⁺. Compounds of the latter series are consitently more stable to higher temperatures. For either series increasing the radius of M increases thermal stability. Decomposition to temperatures approaching 500°C involves some four separate processes.     

Poly-Sugar: Modification of Poly(vinyl Alcohol)

This paper describes the attachment of sugar (sucrose) onto low molecular weight poly(vinyl alcohols) (etherification) to produce a new class of synthetic sweetener. Because of its regulated molecular weight, the new sweetener would pass through the digestive tract and be excreted in its original molecular form. We have termed the new class of sweeteners poly-sugar. The etherification of sucrose with poly(vinyl alcohol) can be carried out either in dimethyl sulfoxide or water. We have prepared poly-sugars with varying degrees of etherification (3.4–5.4). Highly etherified products were bitter, but a poly-sugar with a 4.23 degree of etherification was sweet without any bitter aftertaste.     

Solution properties of ethylene-vinyl acetate copolymers

High-pressure ethylene–vinyl acetate copolymers of four different chemical compositions(9%, 15%, 45%, and 70% VA) were characterized to determine molecular weight and distribution. The four samples were fractionated by solvent–nonsolvent precipitation methods. Light-scattering, osmometry, and viscosity measurements were made on these fractionated copolymers to determine weight-average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_w } $\end{document}, number-average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_n } $\end{document}, molecular size in solution, and interaction constants. Dilute solution viscosity was measured on the fractions to determine intrinsic viscosity and Huggins' constant k′. Viscosity–molecular weight equations were established for the four copolymer compositions. The log intrinsic viscosity versus log molecular weight diagrams were analyzed and the average length of branches calculated. The composition of the polymer fractions, determined by C and H combustion analysis, was found not to vary significantly with molecular weight. The uniformly random character of the E/VA copolymers was thereby confirmed. The density of the fractions was determined by density-gradient column method. Chain sequence distribution of monomer units for the four copolymers was calculated by using IBM 704 computations involving the actual monomer reactivity ratios. Long sequences of either ethylene or vinyl acetate are improbable, except at the extremes of copolymer composition.     

Primary lymphoma of the breast: MR imaging features. A case report

Primary non-Hodgkin's lymphoma (NHL) of the breast are rare and represent less than 0.6% of all mammary malignancies. Secondary involvement of the breast in patients with diffuse disease occurs more frequently. The radiologic features of breast lymphoma are nonspecific, and the diagnosis is based on histologic criteria. We present the MR-imaging features of a case of primary NHL of the breast.     

Coordinated Thematic Science in the Classroom: A View from Pilot Teachers

The purpose of this paper is threefold. First, we set out to describe a context for understanding events that fuel the need to reform secondary science education in Texas. Next, we present the results of a survey of the knowledge, beliefs, and attitudes of a group of central Texas science teachers related to implementing Coordinated Thematic Science (CTS) instruction, who were surveyed after field testing preliminary CTS instructional materials. Last, we argue that caution must be exercised in the design of inservice programs to prepare life science teachers in Texas to teach a coordinated thematic Science I course to rising Grade 7 students by the target date of Fall, 1994.     

Structure and property relationships in ethylene–vinyl acetate copolymers

The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.     

Lithium niobium disulfide,Li0.63NbS2

Lithium niobium di­sulfide, Li_0.63NbS₂, has been prepared by a metathesis reaction between physically separated solid reactants, i.e. separated reactant metathesis (SRM). Single‐crystal data were collected at reduced temperature [150 (2) K], yielding a refined Li content of y = 0.63 (6). The Li content in the crystalline samples was also determined analytically by flame photometry. The compound crystallizes in hexagonal space group P6₃/mmc (No. 194), with Li⁺ ions situated in octahedral sites between NbS₂ layers.     

Deflated GMRES for systems with multiple shifts and multiple right-hand sides

We consider solution of multiply shifted systems of nonsymmetric linear equations, possibly also with multiple right-hand sides. First, for a single right-hand side, the matrix is shifted by several multiples of the identity. Such problems arise in a number of applications, including lattice quantum chromodynamics where the matrices are complex and non-Hermitian. Some Krylov iterative methods such as GMRES and BiCGStab have been used to solve multiply shifted systems for about the cost of solving just one system. Restarted GMRES can be improved by deflating eigenvalues for matrices that have a few small eigenvalues. We show that a particular deflated method, GMRES-DR, can be applied to multiply shifted systems.In quantum chromodynamics, it is common to have multiple right-hand sides with multiple shifts for each right-hand side. We develop a method that efficiently solves the multiple right-hand sides by using a deflated version of GMRES and yet keeps costs for all of the multiply shifted systems close to those for one shift. An example is given showing this can be extremely effective with a quantum chromodynamics matrix.