Analysis of a prioritized CSMA protocol based on staggered delays

Summary Carrier sense multiple access (CSMA) protocols were originally conceived for use in digital radio communication. Such protocols are, however, quite applicable in a variety of distributed computing and local networking configurations based on a shared bus. The CSMA protocols are characterized by the fact that message collisions can occur only in a very small time window whose duration corresponds to the propagation delay of the bus. They are further characterized by the technique used to subsequently serialize the transmission of the colliding messages. In this paper we analyze the situation wherein colliding messages are serialized by using a set of staggered retry delays which are associated with the sources that may generate the colliding messages. Our analysis produces both path throughput (utilization) curves and message delay curves, as a function of message generation rate. These curves show that the protocol is in a sense self stabalizing, serve to quantify its behaviour, and indicate loading levels which result in unacceptable message delays.     

Nitrous oxide "analgesia": resemblance to opiate action

Nitrous oxide produced a dose-related "analgesia" in mice (median effective dose, 55 percent). The analgesia was evaluated by means of a phenylquinone writhing test. Narcotic antagonists or chronic morphinization reduced nitrous oxide analgesia. Either nitrous oxide releases an endogenous analgesic or narcotic antagonists have analgesic antagonist properties heretofore unappreciated.     

A novel method for measuring induction machine magnetizing inductance

This paper presents a novel method for measuring the magnetizing inductance of an induction machine. The approach uses a static DC excitation technique which can be employed whenever the neutral of the machine is accessible. The proposed method measures only the magnetizing inductance and not the self inductance which normally includes the effect of the stator leakage inductance. Because this test uses a DC excitation, the iron losses in the motor are considerably reduced as well and minimally influence the measurement when compared to the traditional 60-Hz no-load test. By using the proposed method for measuring only the magnetizing inductance, the stator leakage inductance can be later individually determined by performing a separate no-load test. Test results using the method are compared with theoretical values and confirm its feasibility.     

Effect of lactic acid on nucleation morphology and surface roughness of electroless Ni–P deposition in nanoscale

The present work aims to study effect of lactic acid concentration as complexing agent on surface roughness and nucleation morphology of electroless N?CP deposition. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to study nucleation morphology and surface roughness of deposition. Deposition process started at some initial priority growing centres independently distributed on the substrate. We found that the morphology and surface roughness of deposition strongly depends on the complexing agent concentration. Morphology of initial deposited centres with no concentration of lactic acid was in coniform structure. By increasing the complexing agent concentration, the structure of initial growing centres changed from coniform to nodular shape and the surface roughness of depositions decreased.     

Thermal analysis of randomly oriented carbon nanotube reinforced functionally graded timoshenko beam

The unique thermal properties of carbon nanotubes (CNT) are utilized to increase the use of functionally graded material (FGM) at higher temperatures which resulted in introduction of a new type of material called as functionally graded carbon nanotube-reinforced composites (FG-CNTRCs). To use the FG-CNTRCs at elevated temperatures, their thermal analysis is very important. In this context, this article presents the thermal analysis of a CNT based FG Timoshenko beam. Material properties distribution is assumed to vary along the thickness direction according to power law distribution and linear distributions. Finite difference method is implemented to find out the temperature distribution. Using first order shear deformation theory (FSDT), expressions for strains and stresses are obtained. The results are compared with temperature distribution according to power law. The effect of CNT distribution on strains and stresses is also observed. Based on these results important conclusions have been drawn.     

A Quantitative Study of the Relationship between Project Performance and BIM Use on Commercial Construction Projects in the USA

This article reports the findings of a quantitative study on the relationship between various project performance outcomes and the use of Building Information Modeling (BIM), within the commercial construction industry. The literature review identified inconsistent results among prior qualitative and quantitative work concerning the relationships of key project performance measures and BIM use. Data on 13 variables from 93 completed construction projects were collected and examined through a causal comparative research design. Projects that used BIM (in design or construction) were not found to experience significant performance outcomes when controlling for the contribution of other independent variables and covariates at the 95% confidence level (CL). At the lower 90% CL, however, projects using BIM in construction experienced significantly higher levels of schedule growth than projects that did not use BIM in construction. Recommendations are made for training of construction management staff as a step to avoid unwanted schedule growth associated with BIM use during construction. This study is one of a very small group of rigorous quantitative analyses of BIM project performance outcomes conducted to date; additionally, it is the only study that has analyzed BIM in a multivariate context that controlled for the contribution of other project variables not directly related to BIM use.     

Metal interactions in contaminated freshwater sediments from the fly river floodplain,Papua New Guinea

Field data for sediment pH, Eh, sulphur and organic matter were analysed to determine their relationship with measured dissolved and particulate metals from sites in the Fly River affected by mine‐derived wastes. The above‐background concentrations of dissolved metals correspond to various concentration groups as demonstrated by copper for background (< 70 mg/kg), moderate (70–500mg/kg) and severe (> 500mg/kg), respectively. Dissolved Cu (r = 0.7431, p < 0.0005) and Mo (r = 0.7133,/> < 0.0005) were significantly correlated with their sediment component. Dissolved Al, Cd, Cu and Mo were positively correlated with sediment pH. Significant negative correlation between dissolved copper and sediment (SOM) organic matter (r = ‐0.3821, p < 0.05), and positive correlation with dissolved Al (r = 0.9358, p < 0.0005) suggest that dissolved Cu is present as a complex with either organic matter, Al/Fe oxyhydroxides, or oxyhydroxide‐organic matter colloids. Significant interrelations between dissolved Al, Cu and Mo with organic matter and the ratio of Fe/SOM also suggests that sediment physico‐chemical characteristics are important in the processes occurring in the Fly River floodplain sediments. These processes appear to be responsible for the significantly increased metal concentration in the water column.     

真空缓冷铸渣机冷却炉渣选铜的研究

介绍了真空缓冷炉渣的工艺矿物学特性。试验研究结果表明，该炉渣属于中等可碎性偏难，硬度系数在８￣１６之间，在磨矿细度为－０．０１６ｍｍ占８９％时，粗、扫选抛尾粗精矿再磨再选，以Ｚ－２００、ＳＮ－９和丁胺为混合捕收剂，最终得到铜精矿产率为４．５９％，精矿含铜２３．４８％，含金５．８ｇ／ｔ，铜回收率为８３．７０％；尾矿含铜０．２２％，含金０．１８ｇ／ｔ。     

扭摆式微硅隧道加速度传感器

本文介绍了扭摆式隧道加速度传感器的结构、工作原理、简化的力学模型,设计了版图、工艺流程及关键工艺,并制备出样品,最后给出测试电路和结果。     

Full-wafer technology-A new approach to large-scale laserfabrication and integration

A concept for full-wafer processing (FWP) and full-wafer testing (FWT) for semiconductor laser fabrication in the AlGaAs-GaAs material system is presented. The approach is based on chemically assisted ion beam etching for the laser-mirror formation. Record values for mirror scattering, optimum mirror reflectivity, and equivalence to cleaved mirrors in terms of laser threshold and efficiency have been achieved. Promising results for uniformity and reproducibility for major laser diode characteristics on processed 2-in wafers have been found. The FWP technology has been extensively used for designing test sites to determine various materials, process, and laser parameters, such as sheet resistance, ridge dimensions, lithographic alignment errors, mirror surface leakage, etc