Environmentally friendly methods of water disinfection: The chemistry of alternative disinfectants

The risk of disease from microbiological organisms far surpasses any chemical risk associated with water treatment by chemical oxidation. Giardia lamblia and Cryptosporidium parvum, common microbiological contaminants, sometimes have fatal consequences to individuals with weak immune systems. Because effective environmentally friendly oxidants are available and accessible for treating drinking water, utilities throughout the industrialized world are investigasting alternative disinfection/oxidation practices. Chlorine dioxide and ozone are frequently used to remove taste and odor problems, color and to inactive problem microbiological species. To understand the unique value of ozone and chlorine dioxide in water treatment, one must start with the chemistry.     

Steady-State Analysis of a Permanent Magnet Synchronous Motor Drive with Current Source Inverter

A steady-state analysis is presented of a permanent magnet (PM) synchronous motor drive with a current source inverter (CSI). The torque-speed profile required of the drive is a constant torque region from zero to base speed and a constant power region above base speed. The analysis assumes position feedback control. Optimum control strategies are obtained for the two regions of the torque-speed profile. Using these optimum strategies, performance curves of the drive are predicted and experimentally verified. The time harmonics in the motor are a function of the presence and configuration of the dampers in the motor. An expression is obtained for the equivalent inductance seen by the harmonics for different damper configurations. A Fourier series approach is used to predict the line-to-line voltage waveforms. Even though the presence of the dampers is not essential to the operation of the drive, their presence reduces the voltage spikes present in the line-to-line voltage.     

L2imbo: A distributed systems platform for mobile computing

Mobile computing environments increasingly consist of a range of supporting technologies offering a diverse set of capabilities to applications and end-systems. Such environments are characterised by sudden and dramatic changes in the quality-of-service (QoS) available to applications and users. Recent work has shown that distributed systems platforms can assist applications to take advantage of these changes in QoS and, more specifically, facilitate applications to adapt to their environment. However, the current state-of-the-art in these platforms reflects their fixed network origins through their choice of synchronous connection-oriented communications paradigms. In this paper we argue that these paradigms are not well suited to operation in the emerging mobile environments. Furthermore, we offer an alternative programming paradigm based on tuple spaces which, we believe, offers a number of benefits within a mobile context. The paper presents the design, implementation and evaluation of a new platform based on this paradigm. This revised version was published online in June 2006 with corrections to the Cover Date.     

Chromatographic analysis of species specific odor profiles inMastomys natalensis andM. coucha (Rodentia: Muridae)

Whole-body volatiles from males of the cryptic multimammate mouse speciesMastomys natalensis andM. coucha were analyzed by dynamic solvent effect sampling and capillary gas chromatography. One compound, 3-nonene-2-one, was always present, sometimes as the major component, in volatiles fromM. coucha and absent, or present only at low levels, in volatiles fromM. natalensis. The mean ±SD of the 3-nonen-2-one peak area forM. coucha was 8599 ±9630 and forM. natalensis 148 ±486. Chromatographic analysis was more reliable in identifying a male's species than were a female's in a two-choice olfactorium.     

Energy Storage in Ceramic Dielectrics

Historically, multilayer ceramic capacitors (MLC's) have not been considered for energy storage applications for two primary reasons. First, physically large ceramic capacitors were very expensive and, second, total energy density obtainable was not nearly so high as in electrolytic capacitor types. More recently, the fabrication technology for MLC's has improved significantly, permitting both significantly higher energy density and significantly lower costs. Simultaneously, in many applications, total energy storage has become smaller, and the secondary requirements of very low effective series resistance and effective series inductance (which, together, determine how efficiently the energy may be stored and recovered) have become more important. It is therefore desirable to reexamine energy storage in ceramics for contemporary commercial and near-commercial dielectrics. Stored energy is proportional to voltage squared only in the case of paraelectric insulators, because only they have capacitance that is independent of bias voltage. High dielectric constant materials, however, are ferroics (that is ferroelectric and/or antiferroelectric) and display significant variation of effective dielectric constant with bias voltage. The common ferroelectric materials, whether based upon barium titanate or lead manganese niobate (PMN), in the high-field limit, exhibit an energy storage which increases linearly with bias voltage. Mixed phase, ferroelectric plus antiferroelectric, dielectrics from the lead lanthanum zirconate titanate (PLZT) system, as predicted theoretically, show the best energy density at low to moderate fields. Surprisingly, maximum energy storage is not obtained in high dielectric constant materials but in those materials which display intermediate dielectric constant and the highest ultimate breakdown voltages.     

Glycosidic linkages of legume,grass and cereal straw cell walls before and after extensive degradation by rumen microorganisms

The technique of methylation analysis for the location of glycosidic linkages in cell wall polysaccharides was applied directly (after dry milling in liquid nitrogen) to whole wheat and barley straws, cell wall preparations from early- and late-cut perennial ryegrass and white clover, and their extensively degraded residues recovered from the rumen. The addition of an internal standard, methyl-β-D-allo-pyranose, to milled samples enabled the recovery of partially-methylated sugars to be quantified, and the recovery of parent sugars from methylated material to be compared with values obtained by direct estimation of monosaccharides by the alditol acetate method. Recovery of sugars from methylated samples was generally higher than that predicted by the alditol acetate method, particularly from digested residues. All four samples of Gramineae showed similar proportions of glycosidic linkages in which (1 →4)-linked xylose and glucose units accounted for more than 80% of total identified partially-methylated sugars. The proportions of glycosidic linkages found in digested residues of straws were essentially the same as those found in the parent material. In residues of the more digestible ryegrass there was a two- to three-fold increase in (1→4)-linked xylose units without branch points at the O-2/O-3 positions, the proportions of these branch points being substantially reduced. A corresponding reduction in the proportion of (1→2)-, (1→3)-and terminally-linked arabinose units was also found. The proportion of both (1→4)- and (1→3)-linked glucose units were also reduced in digested residues. These changes were greater in the early-cut than in the late-cut sample. White clover differed from the Gramineae in a number of respects. Galactose units predominantly in the form of (1→4)-, (1→6)- and terminally-linked units, were the major non-cellulosic sugars present. The proportion of all forms of galactose was reduced in digested residues, but (1→6)-linked units appeared more resistant to degradation than (1→4)-linked units. Like ryegrass, the proportion of xylose units increased in digested residues from clover, while the proportion of glucose decreased. The proportion of (1→4)-linked mannose units, initially present at levels ten times as great as in the Gramineae, was also substantially reduced.     

Nevoscopy: three-dimensional computed tomography of nevi and melanomas in situ by transillumination

The thickness of a malignant nevus has been found to be an important prognostic factor for patients with melanoma. We have designed a new method of imaging nevi that permits their thickness to be measured in situ. Using fiber optics directed into the surrounding skin, we transilluminate the nevus. Three images are picked up by a digitizing TV camera: the vertical image (90 degrees ), a glancing image (180 degrees ), and one at 45 degrees , obtained by using two front-silvered mirrors held next to the nevus in a "nevoscope." The digitized images are used in a computed tomography algorithm to calculate approximate vertical cross sections of the nevus. The algorithm is one we recently developed to permit reconstruction from a very few projections. Our method is completely noninvasive. It may be used to check all the nevi on a patient. Without excisions, we could establish a baseline three-dimensional shape for each nevus, follow any changes in time, and obtain an early warning of increase in thickness and possible malignancy.     

Proposal for Compact Optical Filters Using Large Index Step Binary Supergratings

Compact optical filters are proposed using an aperiodic grating of fixed element size [i.e., a binary supergrating (BSG)] with a large refractive index step. These filters allow for almost arbitrary wavelength filtering, yet they are more compact than previous demonstrations of BSG. The filters are designed using a combination of Boolean particle swarm optimization (B-PSO) and a one-dimensional transfer matrix method. To demonstrate the compact device size, several 50-mum-long single-wavelength transmission filters are demonstrated theoretically, each having a different wavelength while using the same structural parameters. A multiwavelength filter is also proposed in an 80-mum-long structure to show the versatility of the large refractive index step BSG. A genetic algorithm is substituted for the B-PSO; however, B-PSO shows better performance here. This work may be applied to produce compact optical filters for intrachip optical networks and compact tunable lasers, while using existing single-step photolithography processes.     

管理RoHS资源的策略

很不幸，我们在生活中经常会碰到这样的场景：在电子产品制造公司里，当人们第一次提出要贯彻从产品中消除有害物质的规定时，却无法说服管理层下决心拿出公司的资源来做这件事。相反，他们倒是听到了“这件事与我无关”的几个不同说法。