The effect of rapid rotation on a vertical bridgman furnace at large Rayleigh number

In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate.     

Divinylsiloxane‐bisbenzocyclobutene‐based polymer modified with polystyrene–polybutadiene–polystyrene triblock copolymers

Divinylsiloxane‐bisbenzocyclobutene (DVS‐bisBCB) polymer has very low dielectric constant and dissipation factor, good thermal stability, and high chemical resistance. The fracture toughness of the thermoset polymer is moderate due to its high crosslink density. A thermoplastic elastomer, polystyrene–polybutadiene–polystyrene triblock copolymer, was incorporated into the matrix to enhance its toughness. The cured thermoset matrix showed different morphology when the elastomer was added to the B‐staged prepolymer or when the elastomer was B‐staged with the DVS‐bisBCB monomer. Small and uniformly distributed elastomer domains were detected by transmission electron micrographs (TEM) in the former case, but TEM did not detect a separate domain in the latter case. A high percentage of the polystyrene–polybutadiene–polystyrene triblock copolymer could be incorporated into the DVS‐bisBCB thermoset matrix by B‐staging the triblock copolymer with the BCB monomer. The elastomer increased the fracture toughness of DVS‐bisBCB polymer as indicated by enhanced elongation at break and increased K1c values obtained by the modified edge‐lift‐off test. Elastomer modified DVS‐bisBCB maintained excellent electrical properties, high T_g and good thermal stability, but showed higher coefficient of linear thermal expansion values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1591–1599, 2006     

Effects of osmotic manipulation of intracellular hydration of HeLa S-3 cells on their proton NMR relaxation times

Pellets of HeLa from suspension cultured cells in isotonic medium (300 mosmolar) were introduced into a Bruker CXP100 NMR spectrophotometer at 80 mHz within 5 min of the start of centrifugation. T1 and T2 times were measured within a total elapsed time of 20-25 min at 80 mHz and 37 degrees C, and averaged 1430 msec and 120 msec, respectively. Extrapolation to zero extracellular space gave a corrected T1 of 1370 msec. For cells collected after 10 min in hypotonic medium (down to 30 mosmolar) increased proton density correlated well with increased cell water content, but relaxation times did not rise in proportion to that predicted for the entry of "bulk" water (T1 of 4700 msec), except when swelling approached lysis point. Cells partially dehydrated by 10 min in hypertonic medium of up to 1500 mosmolar have also been analyzed, but once again the shortening of T1 was not proportional to the loss of "free" (bulk phase) water. At the upper limit of hypertonic treatment, lacunae or vacuoles of a watery nature separated within the cytomatrix, preventing maximum dehydration. The relationship of cell water to T1 is complex over the whole range of tonicity that HeLa S-3 cells tolerate. The data indicate, however, that hypotonically induced water probably has an average T1 time considerably lower than bulk phase water. In contrast, raising the total extracellular volume with medium had precisely the predicted effect on T1 time, further strengthening the case that water taken up by cell acquires a shorter T1 time. Cells adapting to hypotonic conditions oscillated in size and water content over 2-3 hr before returning to near their initial volume. Under these circumstances, T1 oscillated in the same way but with a reduced amplitude, consistent with the above findings.     

Surfactant displacement of human serum albumin adsorbed on loosely packed self-assembled monolayers: cetyltrimethylammonium bromide versus sodium dodecyl sulfate

The surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) displace human serum albumin (HSA) from loosely packed self-assembled monolayers (SAM) of hydrophobic alkyl chains by different means. Removal of HSA is of interest because previous work has suggested that the adsorption of HSA to such loosely packed SAMs may be sufficiently tenacious to offer opportunities for surface passivation. While HSA remains on the surface after exposure to SDS and rinsing, no protein remains after exposure to CTAB and rinsing. X-ray reflectivity and X-ray photoelectron spectroscopy measurements indicate that CTAB molecules remain interdigitated in the loosely packed SAM after rinsing, suggesting that CTAB is more effective in removing the HSA because it interacts more strongly with the SAM.     

Reactions of metal carbonyl cluster complexes with multidentate phosphine ligands; reactions with bis(diphenylphosphino)methane

Reactions of Rh₆(CO)₁₆ with bis(diphenylphosphino)methane (dppm) gave Rh₆(CO)₁₄(dppm), Rh₆(CO)₁₂(dppm)₂, or Rh₆(CO)₁₀(dppm)₃, depending upon the reaction conditions. Rh₄(CO)₁₀(dppm) may be obtained from the reaction of Rh₄(CO)₁₂ with dppm, but this derivative rapidly decomposes in solution to give Rh₄(CO)₈(dppm)₂, Rh₆(CO)₁₄(dppm), and Rh₆(CO)₁₂(dppm)₂. Ir₄(CO)₁₀(dppm) and Ir₄(CO)₈(dppm)₂ have also been prepared, and their structures are discussed on the basis of infrared and ³¹P NMR spectroscopic data.     

The effect of the t-butyl substituent on polymer properties in homopolymer systems

The effect of a bulky substituent on properties of different homopolymers has been examined. The substituent is the t-butyl moiety attached to a benzene ring found in the repeat units of the homopolymers of polyesters, polyarylates, polyamides, and polyaramides. These polymers have been prepared by melt, solution, or interfacial techniques. The source of the t-butyl group is mainly from 5-t-butylisophthalic acid (5TBIA) and comparisons are generally made with corresponding homopolymers based on isophthalic acid. The effect of the t-butyl group is shown by comparison of the properties of these homopolymers. Thermal and mechanical (tensile and impact) properties, density, water absorption, solubility, and processability are discussed. Differences in these properties are attributed to the t-butyl group and are based on intermolecular and intramolecular interactions that include increased free volume, chain stiffening, and conformational changes.     

Determination of copper in medicinal plants used as dietary supplements by atomic absorption spectrometry with direct flame solid analysis

An alternative device for the direct solid analysis (DSA) for copper determination by flame atomic absorption spectrometry (FAAS) is proposed. Copper was directly determined in commercial medicinal plants used as dietary supplements. The determination of copper in solid samples by DSA–FAAS was made by using a conventional air–acetylene flame. Between 0.05 and 1.5 mg of each test, sample was weighed directly into a small polyethylene vial connected to the device used for solid introduction into the flame. Test samples were introduced into the flame as a dry aerosol using a T-quartz cell set between the burner and the optical path. The T-quartz cell has a slit in the superior part by which the solid aerosol passes to the flame. A transient signal, evaluated as integrated absorbance, is produced and it is totally integrated in 2 s. Background signals always presented absorbance values less than 0.1. It was found a characteristic mass of 0.8 ng Cu and absolute limit of detection of 1.2 ng (3 s), or 1.2 μg g⁻¹ if a sample mass of 1 mg was used. Optimized conditions for air flow rate, flame stoichiometry, and so on were established as well. No excessive grinding of the samples was needed and samples with particle of size less than 80 μm were used throughout. No statistical difference between the results from the proposed system and those obtained by sample digestion and determination by conventional FAAS was observed. With the proposed procedure, more than 50 test samples can be analyzed in 1 h and it can be easily adapted to conventional spectrometers for FAAS.     

EFFICACY OF PHOTODYNAMIC THERAPY ON ORIGINAL AND RECURRENT RAT MAMMARY TUMORS

Abstract— Photodynamic therapy has demonstrated efficacy toward primary, metastatic and recurrent human tumors. Here, we investigated the ability of photodynamic therapy, using Photofrin, to inhibit growth of R3230AC mammary adenocarcinomas when tumors were treated as original implants and again as lesions recurring at the initial treatment site. The results demonstrate that both initial implants and lesions recurring after the first photodynamic treatment respond similarly to the same photodynamic therapy protocol, with mean tumor volume doubling times of ˜ 11 days in both cases. Cells cultured from original tumor implants or tumors that recurred after photodynamic treatment accumulate equivalent amounts of [¹⁴C]polyhematoporphyrin. Single cell suspensions prepared from either original or recurrent tumors from animals administered 5 mg/kg Photofrin and exposed to light in vitro displayed comparable phototoxicity. Additionally, examination of tumors by light microscopy revealed no morphological differences between the original tumor implants and the recurrent lesions. Taken together, these data indicate that lesions which recurred at the site of the initial photodynamic treatment were not resistant to a second identical course of photodynamic therapy.