Analysis of energy recovery transformer in DC choppers and inverters

In dc choppers and variable frequency inverters, the commutation of the conducting thyristors must be achieved. In most of the techniques used for commutation, the stored energy in the commutation capacitor at the end of the commutation is higher than the initial stored energy. This paper describes a commutation scheme which uses an energy recovery transformer to feed back the excess energy to the dc supply. The differential equations for the different modes of operation of the commutation system are derived. The solutions of the equations are used to optimize the system for minimum stored energy. Effects of the leakage inductance and turns ratio of the energy recovery transformer are also considered.     

The genome of wine yeast Dekkera bruxellensis provides a tool to explore its food-related properties

The yeast Dekkera/Brettanomyces bruxellensis can cause enormous economic losses in wine industry due to production of phenolic off-flavor compounds. D. bruxellensis is a distant relative of baker's yeast Saccharomyces cerevisiae. Nevertheless, these two yeasts are often found in the same habitats and share several food-related traits, such as production of high ethanol levels and ability to grow without oxygen. In some food products, like lambic beer, D. bruxellensis can importantly contribute to flavor development. We determined the 13.4 Mb genome sequence of the D. bruxellensis strain Y879 (CBS2499) and deduced the genetic background of several "food-relevant" properties and evolutionary history of this yeast. Surprisingly, we find that this yeast is phylogenetically distant to other food-related yeasts and most related to Pichia (Komagataella) pastoris, which is an aerobic poor ethanol producer. We further show that the D. bruxellensis genome does not contain an excess of lineage specific duplicated genes nor a horizontally transferred URA1 gene, two crucial events that promoted the evolution of the food relevant traits in the S. cerevisiae lineage. However, D. bruxellensis has several independently duplicated ADH and ADH-like genes, which are likely responsible for metabolism of alcohols, including ethanol, and also a range of aromatic compounds.     

Assessing the utility of airborne hyperspectral and LiDAR data for species distribution mapping in the coastal Pacific Northwest, Canada

To effectively manage forested ecosystems an accurate characterization of species distribution is required. In this study we assess the utility of hyperspectral Airborne Imaging Spectrometer for Applications (AISA) imagery and small footprint discrete return Light Detection and Ranging (LiDAR) data for mapping 11 tree species in and around the Gulf Islands National Park Reserve, in coastal South-western Canada. Using hyperspectral imagery yielded producer's and user's accuracies for most species ranging from > 52-95.4 and > 63-87.8%, respectively. For species dominated by definable growth stages, pixel-level fusion of hyperspectral imagery with LiDAR-derived height and volumetric canopy profile data increased both producer's (+ 5.1-11.6%) and user's (+ 8.4-18.8%) accuracies. McNemar's tests confirmed that improvements in overall accuracies associated with the inclusion of LiDAR-derived structural information were statistically significant (p < 0.05). This methodology establishes a specific framework for mapping key species with greater detail and accuracy then is possible using conventional approaches (i.e., aerial photograph interpretation), or either technology on its own. Furthermore, in the study area, acquisition and processing costs were lower than a conventional aerial photograph interpretation campaign, making hyperspectral/LiDAR fusion a viable replacement technology.     

Command and Control in Policing: A Systems Assessment of the Gold,Silver and Bronze Structure

A police force exhibits characteristics that are typical of those that can be found in many large, formal, bureaucratic organisations. It has a profound sense of hierarchy and shows a strong awareness of the power of procedure and the benefits to be gained from being systematic. It can be argued that such values and beliefs are entirely appropriate. Rules of evidence, for example, require a very strong discipline and offer very little opportunity for individual interpretation. In the context of such an orderly, systematic approach, the application of systems thinking, with its emphasis on Weltanschauung, viewpoint and perspective, may at first appear inappropriate to police activity. However, this paper argues that this is not the case. It uses systems thinking to examine one important aspect of policing where method and procedure are very important -the command and control of major incidents/operations - and shows that its application enables important lessons to be drawn about the strengths and weaknesses of the mechanisms in place.     

Facet Grammars: Towards static semantic analysis by context-free parsing

Use of executable declarative metalanguages has simplified programming language syntax specification and implementation, whereas existing formalisms for static semantics are still relatively procedural. A working hypothesis is that the context-sensitivity of languages (under static semantic rules) is derived in significant part from the interleaved presences therein of sentences in implicitly-defined and effectively invisible context-free languages. Procedures by which these sentences and context-free grammars for their languages can be respectively derived from the original sentence and the combination of the original language's grammar and semantic rules, lead to the possibility of automatic generation of static semantic analysers from the purely context-free specifications of “Facet Grammars” (FG)!

We show that the utility of FG for static semantic analysis has a non-trivial lower bound, by specifying the relatively complicated identifier scope and accessibility rules for Dijkstra's Guarded Commands Language.     

Durban’s pursuit of economic development in the post-apartheid era

The city in South Africa has “been forced to engage in serious soul-searching about their role in a new political order while facing up to complex and dynamic global economic forces” (Hall and Robbins, 2002, p. 43)     

DSP技术协助进行高速串行数据分析

经过验证的第一代串行总线技术目前正被广泛部署.目前面市的许多新型消费品中内置了PCIExpress、串行ATA及其它串行实现技术.     

Behavior of molybdenum in pyrochemical reprocessing: A spectroscopic study of the chlorination of molybdenum and its oxides in chloride melts

The high temperature reactions of molybdenum and its oxides with chlorine and hydrogen chloride in molten alkali metal chlorides were investigated between 400 and 700 °C. The melts studied were LiCl-KCl, NaCl-CsCl and NaCl-KCl and the reactions were followed by in situ electronic absorption spectroscopy measurements. In these melts Mo reacts with Cl₂ and initially produces MoCl₆²⁻ and then a mixture of Mo(III) and Mo(V) chlorocomplexes, the final proportion depending on the reaction conditions. The Mo(V) content can be removed as MoCl₅ from the melt under vacuum or be reduced to Mo(III) by Mo metal. The reaction of Mo when HCl gas is bubbled into alkali chloride melts yields only MoCl₆³⁻. MoO₂ reacts in these melts with chlorine to form soluble MoOCl₅²⁻ and volatile MoO₂Cl₂. MoO₃ is soluble in chloride melts and then decomposes into the oxychloride MoO₂Cl₂, which sublimes or can be sparged from the melt, and molybdate. Pyrochemical reprocessing can thus be employed for molybdenum since, after various intermediates, the end-products are chloride melts containing chloro and oxychloro anions of molybdenum plus molybdate, and volatile chlorides and oxychlorides that can be readily separated off. The reactions were fastest in the NaCl-KCl melt. The X-ray diffraction pattern of MoO₂Cl₂ is reported for the first time.     

A simple high efficiency solar water purification system

A new passive solar water pasteurization system based on density difference flow principles has been designed, built and tested. The system contains no valves and regulates flow based on the density difference between two columns of water. The new system eliminates boiling problems encountered in previous designs. Boiling is undesirable because it may contaminate treated water. The system with a total absorber area of 0.45 m² has achieved a peak flow rate of 19.3 kg/h of treated water. Experiments with the prototype systems presented in this paper show that density driven systems are an attractive option to existing solar water pasteurization approaches.     

USB热门应用②海量存储等级vs.媒体传输协议

数字版权管理(DRM)与内容保护需要运用特别的通讯协议,在微软的DRM引擎Janus中,底层采用的技术为MTP.MTP可被视为取代传统MSC的方案,能传送受保护的内容.图1是传统海量存储装置应用以及相关的软件堆栈.