Static thermal conductivity methods for solid materials

Various experimental arrangements for the determination of steady-state thermal conductivities, as adopted for different situations, are reviewed. The case where the sample geometry and dimensions are imposed is treated distinctly from that where they may be chosen by the experimenter. In the latter case, it is shown that the set-up adopted may vary significantly according to the magnitude of the conductivity, the temperature range investigated, the geometry, and the dimensions of the samples available. Some devices which were recently developed in the author's laboratory are taken as illustrative examples and briefly discussed.     

Shear force microscopy with a nanoscale resolution

This paper presents a shear force microscope having a nanometric resolution at high scan rates. Current techniques were reviewed and tested, and a design based on the use of a tuning fork is described. The use of a low quality factor enabled us to decrease the response time and increase the stability of the tracking. The microscope was coupled with a tunneling current detection, in order to study the interactions between the sample and the probe during scanning. As an example, a sharp nickel nanotip was used to image a gold surface, showing details down to a few nanometers, even at scanning rates of 4Hz.     

Structure and thermal stability of zinc–nickel electrodeposits

ZnNi alloys were electrodeposited from a chloride bath on steel substrates. The effect of nickel bath concentration on chemical composition, structure and microstructure of the deposits is demonstrated. From 0 to 13 nickel, the phases obtained do not correspond to that reported on the thermodynamic phase diagram. It is shown that the substitution of zinc by nickel is responsible for the formation of distorted _d and _d phases corresponding to the supersaturated hexagonal phase of zinc and to the unsaturated cubic phase of Zn–Ni alloy, respectively. Differential scanning calorimetry indicates that the thermal instability of the alloys containing up to 13 wt of nickel, results from the crystallization of the phase from the _d and _d phases at around 200 °C and 250 °C, respectively.     

<Emphasis Type="Italic">Santalum </Emphasis><Emphasis Type="Italic">insulare</Emphasis> Acetylenic Fatty Acid Seed Oils: Comparison within the <Emphasis Type="Italic">Santalum</Emphasis> Genus

The sandalwood kernels of Santalum insulare (Santalaceae) collected in French Polynesia give seed oils containing significant amounts of ximenynic acid, E-11-octadecen-9-oic acid (64–86%). Fatty acid (FA) identifications were performed by gas chromatography/mass spectrometry (GC/MS) of FA methyl esters. Among the other main eight identified fatty acids, oleic acid was found at a 7–28% level. The content in stearolic acid, octadec-9-ynoic acid, was low (0.7–3.0%). An inverse relationship was demonstrated between ximenynic acid and oleic acid using 20 seed oils. Results obtained have been compared to other previously published data on species belonging to the Santalum genus, using multivariate statistical analysis. The relative FA S. insulare composition, rich in ximenynic acid is in the same order of those given for S. album or S. obtusifolium. The other compared species (S. acuminatum, S. lanceolatum, S. spicatum and S. murrayanum) are richer in oleic acid (40–59%) with some little differences in linolenic content.     

(4R)-5,6,7,9-四-O-乙酰基-4,8-脱水-4-氯-2,3-二脱氧-D-葡糖壬腈的合成

以乙酰基保护的葡萄糖为原料 ,经氯化 ,溴化反应 ,再与丙烯腈在中压汞灯( 4 50 W)下发生自由基反应 ,高选择性地合成了 ( 4 R) - 5,6,7,9-四 - O-乙酰基 - 4,8-脱水 - 4-氯 - 2 ,3-二脱氧 - D-葡糖壬腈。     

Profiles and Sources of PAHs in Sediments from an Open-Pit Mining Area in the Peruvian Andes

The Peruvian Andes are one of the most productive areas for mining and therefore also one of the most exposed to these sources of pollution. This article reports the characterization of Polycyclic Aromatic Hydrocarbons (PAHs) in sediments of Cerro de Pasco area (Peru) located close to a large open-pit mine and, in recent years, several reports have provided evidence of environmental contamination and related health problems. Investigations were carried out into the fifteen PAHs identified by the US-Environment Protection Agency (US-EPA) as requiring priority monitoring, other non US-EPA listed PAHs and perylene were also investigated in order to obtain further information on their origins. By considering the results of all the analysis, the total PAHs concentration varies from 13–1009 μg/Kg with a mean value of 224 μg/Kg. The concentrations of PAHs found in all 12 stations were lower than the effect range low (ERL). PAHs, in the most of the samples, have origin from high temperature processes. Taking into consideration that perylene concentrations were low, a small quantity of polycyclic hydrocarbons may be originated from biological activity.     

Preparation and properties of core–shell alginate–carboxymethylchitosan hydrogels

BACKGROUND: Hydrogels of alginate (ALG) with partially carboxymethylated chitosan (CMCHI) have been produced for drug delivery, based on the interactions between the negative groups and an ionic crosslinker. In the present work, CMCHI was used to evaluate the influence of amino groups that are positively charged at pH = 4 and 6 on the ALG–CMCHI core–shell hydrogel preparation. An ANOVA statistics tool was used to evaluate the effect of composition, pH and chitosan chemical nature on the morphology and swelling properties of the hydrogels in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). RESULTS: The ALG–CMCHI core–shell hydrogels presented smaller (ca 2.3 µm) and more homogeneous microparticles than those with unmodified chitosan (ca 5.5 µm). The ALG–CMCHI hydrogels showed higher thermal stability and lower degree of swelling in SGF (314%) compared to those with chitosan (708%), since in the former hydrogels the protective layers that surround the particles are negatively charged. CONCLUSION: CMCHI can replace chitosan in the production of core–shell hydrogels with improved properties since the negative charge surrounding the ALG–CMCHI particles favours a lower degree of swelling. The results point out a possible prevention of burst release in SGF, sustaining the swelling ability of the ALG–CMCHI core–shell hydrogels in SIF, promising appropriate drug release. Copyright © 2009 Society of Chemical Industry     

Characterization and evaluation of supported rac‐dimethylsilylenebis(indenyl)zirconium dichloride on ethylene polymerization

rac‐Dimethylsilylenebis(indenyl)zirconium dichloride was grafted onto commercial methyl aluminoxane modified silica (SMAO) at different loadings (0.1–1.5 wt % Zr/SMAO). Supported catalysts were evaluated in ethylene polymerization with isoprenylaluminum as a cocatalyst. The characterization of two supported catalysts bearing 0.3 and 0.8 wt % Zr/SiO₂ by extended X‐ray absorption fine structure indicated that the number and the intensity of the peaks beyond the coordination shell, associated with the next nearest neighbors, depended on the Zr concentration. For the catalyst with a higher Zr content, only one peak (2.8 Å) was observed. The catalyst with 0.3 wt % Zr/SMAO presented two small peaks at 2.8 and 3.8 Å. Polymers produced with the supported catalysts presented lower crystallinity and higher molar mass and polydispersity values in comparison to that produced by the homogeneous one. Gel permeation chromatogram deconvolution suggested the presence of four catalyst sites for the supported systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The MIT Alewife Machine

A variety of models for parallel architectures, such as shared memory, message passing, and data flow, have converged in the recent past to a hybrid architecture form called distributed shared memory (DSM). Alewife, an early prototype of such DSM architectures, uses hybrid software and hardware mechanisms to support coherent shared memory, efficient user level messaging, fine grain synchronization, and latency tolerance. Alewife supports up to 512 processing nodes connected over a scalable and cost effective mesh network at a constant cost per node. Four mechanisms combine to achieve Alewife's goals of scalability and programmability: software extended coherent shared memory provides a global, linear address space; integrated message passing allows compiler and operating system designers to provide efficient communication and synchronization; support for fine grain computation allows many processors to cooperate on small problem sizes; and latency tolerance mechanisms-including block multithreading and prefetching-mask unavoidable delays due to communication. Extensive results from microbenchmarks, together with over a dozen complete applications running on a 32-node prototype, demonstrate that integrating message passing with shared memory enables a cost efficient solution to the cache coherence problem and provides a rich set of programming primitives. Our results further show that messaging and shared memory operations are both important because each helps the programmer to achieve the best performance for various machine configurations