Evaluation of the Residence Time of a Moving Fuel Bed on a Forward Acting Grate

The objective of this study is to identify numerical approaches and to employ them to evaluate the residence time of a moving bed on a forward acting grate. Obtaining residence times of fuel particles on a grate favours more reliable design of grate furnaces. The moving bed was represented by spherical particles, whereby a varying size accounts for the variety of particle geometries in a combustion chamber. In order to describe accurately the motion of a moving bed e.g. its particles, the discrete element method was applied. Thus, detailed data on all the particle’s paths and velocities are available. These data were used within two statistical approaches to estimate the residence time of a moving bed. One approach is based on a spatial averaging procedure, while the other relies on tracking the particle’s path. Both methods yielded satisfactory agreement with measurements, however, better predictions were obtained by tracking particles.Academic visitor to the Lithuanian Energy Institute     

Direct laser writing of microoptical structures using a Ge-containing hybrid material

We present our investigations into the direct laser writing of a novel germanium-containing hybrid sol–gel photosensitive material for optical applications at micro scale. We employ this material in the fabrication of photonic micro-structures, such as aspheric lenses and prisms; these are well-shaped and provided good optical performance. The material exhibits good transparency and structurability, and three-dimensional structures with sub-100 nm resolution are achieved. We demonstrate the suitability of the direct laser writing method for the rapid production of custom shaped microoptical components. Since germanium glasses are widely used in fiber optics, the combination of direct laser writing with this specially designed, functional material opens an interesting way in fabricating structures for controlling light flow.     

Cardiac and visual responses to stimuli presented both foveally and peripherally as a function of moving stimuli.

Measured heart rate (HR) and visual fixation responses as indices of attention getting (AG) and attention holding (AH) in 17 15-wk-old infants. The stimulus situation was one in which a brief central stimulus was followed by either a brief peripheral stimulus (AG trials) or a prolonged peripheral stimulus (AH trials). The stimuli for both central and peripheral presentations were moving black and white bar patterns. The speed for the central stimulus was constant over trials and groups (at 6.6°/sec), whereas the peripheral stimuli were either 6.6 or 26°/sec. Results suggest that much of the observed HR change can be accounted for by the AG phase, whereas the AH phase was reflected in the time it took for the cardiac responses to return to prestimulus baseline values. Stimulus speed also affected both attention behaviors; the faster speed produced the greatest HR change. Latency of 1st fixation and duration of looking measures did not show any discrimination between stimuli of different speeds. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

钯和铂中痕量杂质元素锭状固体标准样品制备的研究

详细介绍了制备钯和铂锭状固体标准样品的实验方法。该固体标样可用于测定固体样品的电弧/火花发射光谱、火花烧蚀发射光谱和辉光放电质谱(GD-MS)等仪器分析方法。在标准样品的制备过程中,首先将含有33种待测杂质元素的钯或铂溶液进行沉淀和共沉淀得到“贮备”粉末,然后将粉末与99.999%纯金属钯或铂进行熔炼,从而获得杂质元素含量在(5~10)×10-6的固体标准样品。部分杂质元素在沉淀和共沉淀过程、热处理环节会发生损失,在最终得到的锭中,钯标准样品有25个元素、铂标准样品有26个元素得到定量回收,发生污染的元素主要包括金、硼、铁和硅。     

The role of friction in mixing and segregation of granular material

We use discrete element modelling to investigate the processes of mixing and size segregation in a polydisperse mixture of spherical particles in a three-dimensional rectangular box and analyze the influence of friction between the particles on segregation. The packed bed is stirred by a rectangular bar moving periodically in the horizontal direction. The parameters were introduced to characterise the segregation and mixing intensities, and a differential equation was proposed to describe the evolution of segregation intensity approaching exponentially a certain steady state value. It was found that the dynamic friction coefficient has a non-monotonous influence on the processes of mixing and size segregation in poly-disperse granular systems. Critical value of the dynamic friction coefficient μ_crit was identified. For the values of friction μ > μ_crit, behaviour of granular material can be characterised as a “laminar” flow with dominating convective motion of packed bed. For values of friction μ < μ_crit, behaviour of granular mattter can be characterised as “turbulent” flow with dominating “local” mixing inside the packed bed.     

An approach to qualify the intensity of mixing on a forward acting grate

The objective of this study is to derive methods on a statistical basis to describe quantitatively the mixing process of a packed bed on a forward acting grate. The packed bed was represented by spherical particles, whereby a varying size accounts for the variety of particle geometries in a combustion chamber. In order to describe accurately the motion of a packed bed e.g. its particles, the discrete element method (DEM) was applied. Thus, detailed data on all the particle's paths and velocities are available. These data were used for the two proposed methods based on particles’ velocities and trajectories to assess mixing and segregation of a packed bed. Both methods describe the mixing process very satisfactorily, whereby the trajectory based method is more favourable to describe segregation.     

Dietary manipulation of long-chain polyunsaturated fatty acids in the retina and brain of guinea pigs

High levels of n−6 docosapentaenoic acid (22∶5n−6) have been reported in the retina of guinea pigs fed commercially-prepared grain-based rations (commercial diet). In rats and monkeys, high levels of 22∶5n−6 are an indicator of n−3 polyunsaturated fatty acid (PUFA) deficiency. We have examined the fatty acid composition of the retina and brain in guinea pigs fed a commercial diet or one of three semi-purified diets containing three different levels of n−3 PUFA. The diets comprised a diet deficient in n−3 PUFA (semi-purified diet containing safflower oil), two diets containing α-linolenic acid (standard commercial laboratory diet and semi-purified diet containing canola oil), and a diet containing α-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid (DHA) (semi-purified diet containing canola oil, safflower oil, and fish oil). Two groups of guinea pigs were given the diets from day 1 to 4 wk or day 1 to 8 wk, when they were sacrificed and the retinal tissues were extracted and analyzed for PUFA content by gas-liquid chromatography. Fatty acid analyses of the retinal phospholipids of the four-week-old animals revealed that the group fed DHA (from the fish oil) had the highest level of DHA (32%), compared with values of 19 and 13% for the groups fed canola oil diet and commercial diet, respectively, and 2% for the group fed the diet deficient in n−3 PUFA. The levels of 22∶5n−6 in the retinal lipids were inversely related to the DHA values, being 0.6, 6.6, 11.4, and 20.6 for the fish oil, canola oil, commercial diet, and safflower oil diet groups, respectively. The long-chain PUFA profiles in the brain phospholipids of the four-week-old group were similar to those from the retina. The retinal PUFA values for the eight-week-old animals were similar to the four-week-old group. The safflower oil diet induced a greater deficit of DHA in retinal lipids than has been reported in rats and monkeys fed similar diets. The guinea pigs fed the commercial diet had retinal and brain PUFA patterns similar to that produced by n−3 PUFA-deficient diets in rats and monkeys. Guinea pigs fed the canola oil diet had significantly greater retinal DHA levels than those fed the commercial diet, but lower than those fed fish oil. The data suggest that the guinea pig has a reduced capacity for DHA synthesis from α-linolenic acid as compared with other mammals. Supplementation of guinea pig diets with fish oil produced high retinal and brain DHA levels and prevented the accumulation of 22∶5n−6.     

Epistemology and Adolescents' Conceptions of Procedural Justice in School.

When evaluating instructional practices, adolescents (n = 128, ages 14-19) coordinated knowledge of epistemology, fairness, and motivation in their conceptions of procedural justice. Adolescents ranked the fairness and effectiveness of instructional practices differently for controversial and noncontroversial topics. They raised epistemological, moral, and motivational concerns in their justifications but coordinated these issues differently for each science topic. Using prototypical practices as a stimulus, adolescents described how students could practice the scientific method, remember current scientific positions, or invent their own theories and methods. The proportion of adolescents offering different conceptions for each science topic was significantly different from chance, but 50% relied on one conception to evaluate all instructional practices. Adolescents' conceptions reflected their standards for evaluating educational experiences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Robotics-Based Location Sensing Using Wireless Ethernet

A key subproblem in the construction of location-aware systems is the determination of the position of a mobile device. This article describes the design, implementation and analysis of a system for determining position inside a building from measured RF signal strengths of packets on an IEEE 802.11b wireless Ethernet network. Previous approaches to location-awareness with RF signals have been severely hampered by non-Gaussian signals, noise, and complex correlations due to multi-path effects, interference and absorption. The design of our system begins with the observation that determining position from complex, noisy and non-Gaussian signals is a well-studied problem in the field of robotics. Using only off-the-shelf hardware, we achieve robust position estimation to within a meter in our experimental context and after adequate training of our system. We can also coarsely determine our orientation and can track our position as we move. Our results show that we can localize a stationary device to within 1.5 meters over 80% of the time and track a moving device to within 1 meter over 50% of the time. Both localization and tracking run in real-time. By applying recent advances in probabilistic inference of position and sensor fusion from noisy signals, we show that the RF emissions from base stations as measured by off-the-shelf wireless Ethernet cards are sufficiently rich in information to permit a mobile device to reliably track its location. An earlier version of this article was published as A.M. Ladd, K.E. Bekris, A. Rudys, G. Marceau, L.E. Kavraki and D.S. Wallach, Robotics-based location sensing using wireless Ethernet, at the 8th ACM International Conference on Mobile Computing and Networking (MOBICOM) (September 2002, Atlanta, GA).