Design and analysis of a self-testing-and-repairing random access memory “STAR–RAM” with error correction

This paper presents the philosophy and design of a fault-tolerant dynamically-reconfigurable random access memory (RAM) system with a built-in Self-Testing-And-Repairing “STAR” engine. The STAR engine, supported by SEC–DED capability, provides on-line fault detection, correction, analysis and repair without destroying useful data stored in the memory. Reliability analysis of the presented system has been accomplished using a SMART simulation approach[1], and results show significant reliability enhancement over SEC–DED RAM designs. The memory system employs a hardware parallel address-comparison mechanism for rapid processing of incoming addresses during normal read/write operations to minimize memory access delay. The flexible STAR architecture and the low hardware overhead enables utilization of the proposed approach in VLSI memory chips as well as in WSI and large memory modules.     

The digestibility and chemical composition of plant parts in Italian and perennial ryegrass during primary growth

Italian ryegrass (cv. S22) and perennial ryegrass (cv. S24) were sampled duringprimary growth at head emergence, pollen shedding and seed shedding in each of 2 years. Each sample was separated into approximately 19 plant parts and for each part the true dry matter digestibility, digestibility of cell wall and percentages of cell content, nitrogen, water-soluble carbohydrate and lignin were determined. Trends reported in the literature, based on a smaller number of plant parts, were generally confirmed, but were shown to conceal appreciable variation. Thus, while, on average, stem declined in digestibility faster than leaf sheath, the upper sheaths declined in digestibility faster than the lower internodes and nodes; similarly, the proportion of cell content declined at a rather similar rate to digestibility in leaf blade and much less than digestibility in stem but the position was reversed between pollen shedding and seed shedding in the case of dead leaf blade and internodes. While the N content of the inflorescence as a whole did not decline greatly with advancing maturity, the N content of the rachis was nearly halved. The upper part of the crop was more digestible than the lower part at head emergence, but not at seed shedding. Italian ryegrass had a higher proportion of cell content than perennial ryegrass in all types of plant part. The digestibility of cell wall declined with advancing maturity in all the plant parts examined. The lower portions of internodes had a higher proportion of cell content than the upper portions. There were gradients from top to bottom of the plant, e.g. percentage N declined and percentage water-soluble carbohydrate increased from top to bottom.     

Sewer asset management – state of the art and research needs

ABSTRACT

Sewer asset management gained momentum and importance in recent years due to economic considerations, since infrastructure maintenance and rehabilitation directly represent major investments. Because physical urban water infrastructure has life expectancies of up to 100 years or more, contemporary urban drainage systems are strongly influenced by historical decisions and implementations. The current decisions taken in sewer asset management will, therefore, have a long-lasting impact on the functionality and quality of future services provided by these networks. These decisions can be supported by different approaches ranging from various inspection techniques, deterioration models to assess the probability of failure or the technical service life, to sophisticated decision support systems crossing boundaries to other urban infrastructure. This paper presents the state of the art in sewer asset management in its manifold facets spanning a wide field of research and highlights existing research gaps while giving an outlook on future developments and research areas.     

The effect of field modifier blocks on the fast photoneutron dose equivalent from two high-energy medical linear accelerators

High-energy linear accelerators (linacs) have several advantages, including low skin doses and high dose rates at deep-seated tumours. But, at energies more than 8 MeV, photonuclear reactions produce neutron contamination around the therapeutic beam, which may induce secondary malignancies. In spite of improvements achieved in medical linac designs, many countries still use conventional (non-intensity-modulated radiotherapy) linacs. Hence, in these conventional machines, fitting the beam over the treatment volume may require using blocks. Therefore, the effect of these devices on neutron production of linacs needs to be studied. The aim of this study was to investigate the effect of field shaping blocks on photoneutron dose in the treatment plane for two high-energy medical linacs. Two medical linacs, a Saturn 43 (25 MeV) and an Elekta SL 75/25 (18 MeV), were studied. Polycarbonate (PC) films were used to measure the fluence of photoneutrons produced by these linacs. After electrochemical etching of the PC films, the neutron dose equivalent was calculated at the isocentre and 50 cm away from the isocentre. It was noted that by increasing the distance from the centre of the X-ray beam towards the periphery, the photoneutron dose equivalent decreases rapidly for both the open and blocked fields. Increasing the energy of the photons causes an increase in the amount of photoneutron dose equivalent. At 25 MeV photon energy, the lead blocks cause a meaningful increase in the dose equivalent of photoneutrons. In this research, a 30% increase was seen in neutron dose contribution to central axis dose at the isocentre of a 25 MeV irregular field shaped by lead blocks. It is concluded that lead blocks must be considered as a source of photoneutron production when treating irregular fields with high-energy photons.     

A more general model for the analysis of the rock slope stability

The slope stability analysis has many applications in the engineering projects such as the dams, the roads and open pits structures. The method of analysis is usually based on the equilibrium conditions of the potential plane and wedge failures. The zone of the potential failure is stable whenever the stability forces dominate instability characteristics of the slope. In most of the classic methods of slope stability analysis, the joint surfaces are assumed to be continuous along the potential failure zone. These can cause an underestimated solution to the analysis. In this research the joint trace length is considered to be discontinuous across the potential surface of failure as it happens in nature. Therefore, there exists a rock bridge between the local joint traces. Because of the numerous problems related to the rock slope stability the above assumption is satisfied and the shear strength characteristics of intact rock have taken part in the analysis. The analysis presented here gives a better concept, view, and idea of understanding the physical nature of rock slopes and includes more parameters governing the stability of the potential failure zone.     

Control of H2S emission from swine manure using Na-nitrite and Na-molybdate

Biogenic production of hydrogen sulphide (H2S) in oil reservoirs (souring) has been shown to be controlled effectively using nitrite and molybdate salts. In the present work the effects of addition of nitrite and molybdate on reducing the emission of H2S from swine manure slurry was investigated in the laboratory and semi-pilot scale systems. Addition of 80 mM nitrite or 2 mM molybdate (final concentration in the manure slurry) to fresh manure in the laboratory scale closed systems (125 mL and 4 L) reduced the concentration of H2S in the headspace gas from 1500 microL L(-1) to 10 microL L(-1) which maintained during the remaining period of trials (40-60 days). With aged manure, similar results were achieved with a lower level of nitrite (10 mM). Simultaneous or sequential additions of nitrite and molybdate to fresh manure had similar effects. Contrary to the systems simulating biological conditions in oil reservoirs in which simultaneous addition of nitrite and molybdate has been reported to have a synergistic effect, no synergism was observed when nitrite and molybdate were added to the manure simultaneously. Experiments with fresh manure slurry in the semi-pilot scale systems (200 L) confirmed the effectiveness of this approach in which addition of 80 mM nitrite or 2 mM molybdate or a combination of 80 mM nitrite and 2 mM molybdate decreased the concentration of the H2S in the headspace gas from an initial value of 500 microL L(-1) to a low level in the range 2-25 microL L(-1) and maintained these low levels during the remaining period of trials (16 days). The concentration of ammonia (NH3) in the headspace gas of the treated systems was similar to that observed in the control system (untreated), indicating that the treatment did not have an effect on the level of present NH3. Although the addition of nitrite or molybdate reduced emissions of H2S from swine manure and the associated health and safety concerns, it had little impact on the intensity of odour in the headspace gas samples from the semi-pilot scale system.     

基于并行组合进化算法的光伏阵列最大功率点追踪

针对光伏阵列在局部遮阴时功率的多峰输出,提出了一种新型并行组合进化算法(GA-DE-PSO),解决了传统采用的单一进化算法以及单一改进算法追踪最大功率时的不稳定性和精确性不足的缺点。该方法将所有的可行解个体随机分为两个子种群,并行采用向量的差分进化模式和染色体的遗传模式,产生新型个体和备选个体。再通过粒子群算法进行混合选择,得到更为有效的可行域的指导信息,从而更快速地收敛到最优点,实现最大功率点追踪。仿真结果表明,组合算法保留了三种进化算法的优点,具有较高的寻优精度与稳定性。     

GAC adsorber design protocol for the removal of off-flavors

This paper investigates the effectiveness of granular activated carbon (GAC) for removing off-flavor compounds of water—geosmin and 2-methylisoborneol (MIB). More specifically, it focuses on the development of an appropriate modeling approach and experimental protocol for the design of fixed-bed GAC adsorbers. Adsorption equilibrium, rate and long-term mini-column studies were conducted on a bench-scale for geosmin and MIB to estimate the equilibrium and mass-transfer parameters required for adsorber modeling. The dispersed flow homogeneous surface diffusion model (DFHSDM) was used for the prediction/simulation of the adsorber dynamics. Scale-up procedures based on dimensional analysis and similitude were employed for the design of full-scale adsorbers from bench-scale adsorbers, and for performance forecasting of full-scale adsorbers under different operating conditions. More importantly, operation and maintenance (O & M) costs were estimated for full-scale adsorbers directed at the removal of off flavor compounds, based on carbon utilization rates and disposal costs. These estimates were obtained for different plant capacities and empty bed contact times (EBCTs).     

Degree of polarization estimation in the presence of nonuniform illumination and additive Gaussian noise

Within the general framework of active imaging we address the degree of polarization (DOP) estimation in the presence of additive Gaussian detector noise. We first study the performance of standard DOP estimators and propose a method to increase estimation precision using physically relevant a priori information. We then consider the realistic case of nonuniform illumination distribution. We derive the Cramer-Rao lower bound and determine a profile likelihood-based estimator. We demonstrate the efficiency of this new estimator and compare its performance with other standard estimators as a function of the degree of nonuniformity of the illumination.