Variations in the compressive strength of dental cements stored in ionic or acidic solutions

The compressive strengths of various dental cements (a zinc polycarboxylate, a zinc phosphate, a glass-ionomer and two resin-modified glass ionomers, RMGICs) have been determined following storage in pure water, 0.9% sodium chloride solution or 20 mmol dm^–3 lactic acid solution for periods of time ranging from 24 h to 3 months. The glass-ionomer cement showed no differences between different storage solutions or at different storage times, whereas the zinc polycarboxylate, zinc phosphate and the resin-modified glass ionomer cements showed significant differences following storage in the solutions for 24 h compared with pure water. The zinc polycarboxylate cement was significantly weaker at 24 h in 0.9% NaCl and lactic acid than in pure water, whereas most of the other cements were significantly stronger in both 0.9% NaCl and lactic acid. One of the RMGICs (Vitremer luting, ex. 3M), however, was significantly stronger only in the NaCl solution, not in the lactic acid. In general, by 1 week, the strengths all reverted to being essentially the same as for specimens stored in pure water for most subsequent storage times, and did not change significantly on storage for up to 3 months. This effect of storage medium on the early strength has not been reported previously and since the media were chosen to model certain characteristics of natural saliva, the changes observed seem likely to occur in vivo. It is concluded that pure water is not the best medium for storing these cements if they are to behave as they do under clinical conditions. © 2001 Kluwer Academic Publishers     

Desorption-ionization mass spectrometry using deposited nanostructured silicon films

We present a method for desorption ionization on silicon based on novel column/void-network-deposited silicon thin films. A number of different peptides and proteins in the < or = 6000 Daltons range are analyzed by time-of-flight mass spectrometry in this demonstration of our approach. A variety of sample preparation conditions, including the use of chemical additives, surface treatments, and sample purification are used to show the potential of mass analysis using deposited column/void-network silicon films for high throughput proteomic screening.     

Joint transform optical correlator designed and analyzed by use of two- and one-dimensional hilbert transforms

Novel real-time joint transform, Hilbert transform optical correlators are proposed in which only a half or a quarter of the Fourier plane is written onto an optically addressable spatial light modulator. A point source is used to recover the result for the whole plane. As a result, images with a two- or four-times larger space-bandwidth product can be matched in amplitude and phase. The effect of truncating the transform plane is explained with two- and one-dimensional Hilbert transform analysis. Results of computer simulation are shown.     

Three-dimensional confocal microscopy of colloids

Confocal microscopy is used in the study of colloidal gels, glasses, and binary fluids. We measure the three-dimensional positions of colloidal particles with a precision of approximately 50 nm (a small fraction of each particle's radius) and with a time resolution sufficient for tracking the thermal motions of several thousand particles at once. This information allows us to characterize the structure and the dynamics of these materials in qualitatively new ways, for example, by quantifying the topology of chains and clusters of particles as well as by measuring the spatial correlations between particles with high mobilities. We describe our experimental technique and describe measurements that complement the results of light scattering.     

自动数据采集在电池行业中的应用

固定资产管理工作对于避免资产流失、提高资产利用效率,有重大意义。目前,条码技术是自动识别技术在固定资产管理中应用的重点。我们组织了两篇有关自动识别技术在固定资产管理工作中应用的案例,供读者参考、借鉴。     

活塞式制冷压缩机工质替代的应用分析

近年来，由于CFCS问题的正式公认，由绿色环保制冷剂取代传统制冷剂，寻求安全、高效、环保的替代制冷剂成为制冷界一项紧迫而重要的任务。在冷藏冷冻半封闭活塞式制冷压缩机上，使用新制冷剂R404A的机组已经得到广泛的应用。我国由于成本和施工工艺的限制，新制冷剂的产品还没有广泛推广，但对新制冷剂产品的需求已经呼声四起。本文对活塞式制冷压缩机在R404A替代R22过程中需要关注的润滑油的选择，零部件的改进，以及制造工艺和制冷系统的改进等进行了分析，为使用环保型制冷剂R404A替换R22的应用打下基础。     

3G通信标准比较及在煤矿的应用

介绍几种3G通信标准的比较,及其在煤矿的应用。     

Oxidation of Cr(III) in tannery sludge to Cr(VI): field observations and theoretical assessment

Sludge, soil and leachate samples collected from a chromium-contaminated tannery waste dumping site in Kanpur, India, were found to contain considerable amounts of Cr(VI), despite the fresh tannery sludge containing little or no Cr(VI). Literature reports suggested that dry Cr(III) precipitates could be converted to Cr(VI) when heated in the presence of oxygen. Also, Cr(III) in aqueous phase could be oxidized through interaction with manganese dioxide (MnO2) surface to Cr(VI). Measurement of manganese in the sludge samples collected from the site showed concentrations up to 0.6 mg/g. Based on equilibrium calculations, it was determined that both dry phase Cr(III) oxidation by atmospheric oxygen and aqueous phase Cr(III) oxidation by MnO2 surface were thermodynamically feasible. It was further suggested that in aqueous phase, manganese may act effectively as an electron transporter between Cr(III) and dissolved oxygen during Cr(III) oxidation, leading to regeneration of MnO2 solid phase. Further, as dissolved Cr(III) is oxidized, dissolution of Cr(OH3) will take place to maintain the equilibrium between the dissolved and solid phases of Cr(III). In the pH range of 3-10, and at oxygen partial pressure (P(O2)) of 10(-6) atm or higher, equilibrium conditions stipulate nearly complete conversion of Cr(III) to Cr(VI). At P(O2) of 10(-20) atm or lower, very little Cr(VI) is expected to be present under equilibrium conditions. In the intermediate P(O2) regions, incomplete dissolution of the Cr(OH3) solid phase and only partial conversion of chromium from +3 to the +6 oxidation state is expected, especially at lower pH values.     

胆机装配一·二·三

在最近数年里,电子管机（又称胆机）似有掀起热潮之趋势,越来越多的音响发烧友视胆机为瑰宝。更有甚者,说听过胆机之后会上瘾,以后就非“胆”不欢云云。其实胆机与晶体管机也是各有优点和不足地,目前还不能说也不应该说谁可取代谁,不过胆机的声音的确颇有其本身之特色。