2008半导体库存仍然居高不下

据iSuppli公司报告,2008年第一季度多数厂商在季中降低或者缩窄了营业收入预期,与当时相比,第二财季的情况比较正面.在第二财季季中展望中,多数厂商重申了季度营业收入预期或者只是略微收紧了预估区间.     

Impact of computers on professional practice: A survey of current practices and attitudes.

Surveyed 227 practicing psychologists to explore the impact of computers on the everyday practice of psychology and practitioners' attitudes toward specific uses of computers. Whereas more than half of the respondents reported using computers in their practices, most restricted their use to clerical applications. Few practitioners used their computer for more clinical applications. Reasons most frequently reported for not using computers related to lacking the necessary skills and experience and to financial considerations. Overall, practitioners had positive attitudes toward a variety of specific applications of computers. Implications of these findings for facilitating the appropriate use of computers by practitioners are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoluminescence of copper ion exchange BK7 glass planar waveguides

Copper–alkali ion exchange technology was used to prepare BK7 glass planar waveguides. The photoluminescence spectra of the waveguides were studied with fluorescence spectrophotometer. It was observed that there were strong emission peaks at around 520 nm, which were strongly influenced by the ion-exchange times. Besides the time, the ion-exchange temperature was important factor as well, the higher ion-exchange temperature was found to bring a blue shift of emission spectra. The blue–green emission band originates from different transition mechanism of energy level. The spectroscopy features of copper within the glass host were also affected by the excitation wavelength, which resulted in a shift of the emission band peaks.     

Accuracy of the diffusion approximation in determining the optical properties of a two-layer turbid medium

We have examined the possibility of determining the optical properties of a two-layer medium by using a diffusion approximation radiation transport model [Appl. Opt. 37, 779 (1998)]. Continuous-wave and frequency-domain (FD) low-noise Monte Carlo (MC) data were fitted to the model. Marquardt-Levenberg and a simulated annealing algorithm were used and compared as optimization techniques. Our particular choice of optical properties for the two-layer model was consistent with skin and underlying fat in the presence of an exogenous chromophore [Appl. Opt. 37, 1958 (1998)]. The results are therefore specific to this set of optical properties. It was found that the cw diffusion solution could never be used to estimate all optical properties reliably. The combined cw and FD solutions could not be used to estimate some of the top-layer optical properties to an accuracy of better than 10%, although the absorption and the transport scattering coefficients of the bottom layer could be estimated to within 7% and 0.5%, respectively. No improvement was found from simultaneously fitting MC data at three different modulation frequencies. These results point to the need for a more accurate radiation transfer model at small source-detector separations.     

Synthesis of linear aliphatic polycarbonate macroglycols using dimethylcarbonate

A series of linear aliphatic polycarbonate polyols were synthesized using dimethylcarbonate and a linear alkane diol or specific combinations of linear alkane diols. Polyol synthesis was carried out in a two‐stage process using dimethylcarbonate and a linear alkane diol to prepare a series of homopolymer polycarbonate polyols. Polyol grades were characterized using Fourier transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetery techniques. Suitable reaction conditions were developed to yield polycarbonate polyols of number average molecular weight between 700 and 1700. The crystallinity of the polycarbonate polyols was shown to reduce as the molecular weight of the alkane diols used in the polycarbonate synthesis was increased. These polymers offer the potential for use in the synthesis of ether free polyurethane elastomers for biomedical applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Chemical Interactions and Their Role in the Microphase Separation of Block Copolymer Thin Films

The thermodynamics of self-assembling systems are discussed in terms of the chemical interactions and the intermolecular forces between species. It is clear that there are both theoretical and practical limitations on the dimensions and the structural regularity of these systems. These considerations are made with reference to the microphase separation that occurs in block copolymer (BCP) systems. BCP systems self-assemble via a thermodynamic driven process where chemical dis-affinity between the blocks driving them part is balanced by a restorative force deriving from the chemical bond between the blocks. These systems are attracting much interest because of their possible role in nanoelectronic fabrication. This form of self-assembly can obtain highly regular nanopatterns in certain circumstances where the orientation and alignment of chemically distinct blocks can be guided through molecular interactions between the polymer and the surrounding interfaces. However, for this to be possible, great care must be taken to properly engineer the interactions between the surfaces and the polymer blocks. The optimum methods of structure directing are chemical pre-patterning (defining regions on the substrate of different chemistry) and graphoepitaxy (topographical alignment) but both centre on generating alignment through favourable chemical interactions. As in all self-assembling systems, the problems of defect formation must be considered and the origin of defects in these systems is explored. It is argued that in these nanostructures equilibrium defects are relatively few and largely originate from kinetic effects arising during film growth. Many defects also arise from the confinement of the systems when they are ‘directed’ by topography. The potential applications of these materials in electronics are discussed.     

Secondary structural studies of bovine caseins: temperature dependence of β-casein structure as analyzed by circular dichroism and FTIR spectroscopy and correlation with micellization

To obtain a molecular basis for the similarities and dissimilarities in the functional, chemical, and biochemical properties between β-casein and the other caseins, three-dimensional models have been presented. Secondary structural prediction algorithms and molecular modeling techniques were used to predict β-casein structure. The secondary structure of bovine β-casein was re-examined using Fourier transform infrared and circular dichroism spectroscopies to test these predictions. Both methods predict a range of secondary structures for β-casein (28–32% turns, 32–34% extended) at 25°C. These elements were highly stable from 5 to 70°C as viewed by circular dichroism. More flexible conformational elements, tentatively identified as loops, helix and short segments of polyproline II, were influenced by temperature, increasing with elevated temperatures. Another view is that as temperature decreases, these elements are lost (cold denaturation). Several distinct transitions were observed by circular dichroism at 10, 33 and 41°C, and another transition, extrapolated to occur at 78°C. Calculations from analytical ultracentrifugation indicate that the 10, 33 and 41°C transitions occur primarily in the monomeric form of the protein. As β-casein polymers are formed, and increase in size, the transitions at higher temperature may reflect changes in the more flexible conformational elements as they adjust to changes in surface charge during polymer formation. The transition at 10°C may represent an actual general conformational change or cold denaturation. Over the range of temperatures studied, the sheet and turn areas remain relatively constant, perhaps forming a supporting hydrophobic core for the monomers within the micelle-like polymer. This interpretation is in accord with the known properties of β-casein, and those predicted from molecular modeling.