A statistical analysis of weight and cost parameters of spacecraft with special reference to ‘Aryabhata’

The available data on the weights of several NASA and ESRO spacecraft have been statistically analysed using the regression analysis technique and empirical relationships of the type W_T = AW{kx/β} have been established, where W_T is the total weight of the spacecraft, W_x is the weight of one of its chosen subsystems andA and β are constants for the chosen subsystem. It is found that the weight data ofAryabhata show a fairly good fit with these empirical relationships. Further, using an established statistically derived relationship for NASA satellites, involving the cost of a spacecraft and its weight parameters, it is found that the cost ofAryabhata is much lower than that of other NASA satellites of comparable weight. The implications of these results are briefly discussed.     

Design optimisation for weight, stress and cost on Airbus using epoxy resin models

Scale modelling is used to perform experimental stress analysis on aircraft components in order to iteratively reduce stress peaks and remove material in low stress areas. The scaling technique used is to model the components in CT200 epoxy resin and analyse them using reflective photoelastic coatings. This technique leads to structurally efficient or optimised components early in the design programme. Costs are reduced by obviating stress problems which would normally only be found much later during the fatigue testing of the real component, by that time of course expensive tooling will have been made and forgings produced. It is also sometimes possible that a less expensive manufacturing technique may be employed as a result of the high confidence stress data produced. Loading rigs etc. are also much lighter and cheaper than the equivalent for testing the metal components.     

Estimated cost of crashes in commercial drivers supports screening and treatment of obstructive sleep apnea

Sleep apnea among commercial drivers may increase the risk of fall-asleep crashes, which incur large expenses. Drivers of passenger cars whose apnea is treated experience lower crash risk. Among community-based holders of commercial driver's licenses, we considered three methods for identifying sleep apnea syndrome: (1) in-lab polysomnography; (2) selective in-lab polysomnography for high-risk drivers, where high risk is first identified by body mass index, age and gender, followed by oximetry in a subset of drivers; (3) not screening. The costs for each of these three programs equaled the sum of the costs of testing, treatment of identified cases, and crashes. Assuming that treatment prevents apnea-related crashes, polysomnography is not cost-effective, because it was more expensive than the cost of crashes when no screening is done. Screening with BMI, age and gender, however, with confirmatory in-lab polysomnography only on high-risk drivers was cost-effective, as long as a high proportion (73.8%) of screened drivers accepts treatment. These findings indicate that strategies that reduce reliance on in-laboratory polysomnography may be more cost-effective than not screening, and that treatment acceptance may need to be a condition of employment for affected drivers.     

Reliability of a computer network in case capacity weight varying with arcs, nodes and types of commodity

The computer network can be modeled as a capacitated-flow network. This paper concentrates on a two-commodity capacitated-flow network with three characters: (1) nodes as well as arcs have multiple possible capacities and may fail, (2) each component (arc/node) has both capacity and cost attributes; and (3) the capacity weight varies with arcs, nodes and types of commodity (or named file). We study the possibility that a given quantity of two types of files can be transmitted through this network simultaneously under the budget constraint. Such a possibility is named the system reliability which is a performance index to measure the quality level of supply demand systems such as computer, telecommunication, electric-power transmission and transportation systems. The approach of minimal paths is applied to describe the relationship among flow assignments and capacity vectors. A simple algorithm in terms of minimal paths is proposed to evaluate the system reliability.     

Effects of green supply chain integration and green innovation on environmental and cost performance

This paper argues that mechanisms such as information sharing and collaboration used in green supply chain integration (GSCI) to improve information processing capacity can reduce uncertain outcomes of green product and process innovation. Based on data from a survey of Chinese (Hong Kong) firms, the paper tests whether the three dimensions of GSCI (green internal, customer and supplier integration) improve environmental performance and cost reduction by facilitating green product and process innovation. The results show that green customer integration improves cost and environmental performance through green process innovation (not green product innovation). Both green product and process innovations are facilitated by green customer integration (not green supplier integration), while both green customer and supplier integration significantly depend on green internal integration. These suggest that the distinctive information processing capacity created by green internal and customer integration can facilitate the green process innovation required to improve environmental and cost efficiency, while green product innovation and green supplier integration cannot create such efficiencies.     

Risks and performance in supply chain: the push effect

A risk, when it occurs, causes negative effects on outputs. Typically risks are not independent, as multiple risks occur simultaneously. These risks have links, creating a ‘push’ effect, thus increasing the severity of each and all risk(s) on outputs. This paper aims to verify the mechanism of the push effect that is a new approach in the supply chain risk management literature. In this study, two models were compared: (1) only exists in direct effects of risks on supply chain performance, i.e. the competitive model. The other, (2), contains relationships among risks that show the mechanism of the push effect, i.e. the hypothesised model. Empirical evidence found in the Vietnam construction sector proved that the hypothesised model is better suited and has greater effect on supply chain performance in terms of each and all risk(s). Comparing 55% variance of the competitive model, the hypothesised one can explain up to 73% variance of supply chain performance. These results confirm our hypotheses of the push effect. Furthermore, findings achieved from this research can be used as ‘a guideline’ for reducing the impact of this mechanism.     

Effective expediting to improve project due date and cost performance through buffer management

The rapidly changing marketplace together with the increasing complexity of contemporary projects makes it more likely that project activities will have uncertain durations, incurring a generally low probability of on-time delivery. Thus, project control that aims to track the project performance and to expedite relevant activities when necessary has become the main aspect within the scope of project management in order to ensure a successful scheduling outcome. The Critical Chain Scheduling and Buffer Management (CC/BM) has shown to provide a popular approach to build robust project schedules and to offer a valuable control tool for coping with schedule variability. However, the most current buffer management (BM) practice faces a problem of neglecting the cost information when taking expediting actions. In view of this defect, we introduce a new control procedure on the basis of CC/BM that evaluates the probability of successful project completion relative to the cost of crashing and that determines when to expedite which activities in a cost-effective manner. Results of an experimental application of the proposed method present its relative dominance over the currently widely adopted BM approach with respect to project time and cost performance.     

小管径铜管换热器的性能及成本分析

对比分析采用R410A制冷剂的Ф7mm铜管换热器与Ф5mm铜管换热器的性能与成本。测试结果表明,在相同的测试工况和迎风尺寸下,Ф5mm铜管换热器的换热效果比Ф7mm铜管换热器的好,可以节约大量铜材和铝材,且制冷剂充注量减少。     

Availability and cost functions for periodically inspected preventively maintained units

Unavailability and cost rate functions are developed for components whose failures can occur randomly but they are detected only by periodic testing or inspections. If a failure occurs between consecutive inspections, the unit remains failed until the next inspection. Components are renewed by preventive maintenance periodically, or by repair or replacement after a failure, whichever occurs first (age-replacement). The model takes into account finite repair and maintenance durations as well as costs due to testing, repair, maintenance and lost production or accidents. For normally operating units the time-related penalty is loss of production. For standby safety equipment it is the expected cost of an accident that can happen when the component is down due to a dormant failure, repair or maintenance. The objective of maintenance optimization is to minimize the total cost rate by proper selection of two intervals, one for inspections and one for replacements. General conditions and techniques are developed for solving optimal test and maintenance intervals, with and without constraints on the production loss or accident rate. Insights are gained into how the optimal intervals depend on various cost parameters and reliability characteristics.     

Risk‐based metrics for performance evaluation of control charts

Control charts are commonly evaluated in terms of their average run length (ARL). However, since run length distributions are typically strongly skewed, the ARL gives a very limited impression about the actual run length performance. In this study, it is proposed to evaluate a control chart's performance using risk metrics, specifically the value at risk and the tail conditional expectation. When a control chart is evaluated for an in‐control performance, the risk is an early occurrence of a false alarm, whereas in an out‐of‐control state, there is a risk of a delayed detection. For these situations, risk metric computations are derived and exemplified for diverse types of control charts. It is demonstrated that the use of such risk metrics leads to important new insights into a control chart's performance. In addition to the cases of known process parameters for control chart design, these risk metrics are further used to analyze the estimation uncertainty in evaluating a control chart's performance if the design parameters rely on a phase 1 analysis. Benefits of the risk‐based metrics are discussed thoroughly, and these are recommended as supplements to the traditional ARL metric.     

网络性能的分析、评价模型及其软件实现

通过网络参数设置、建立性能分析模型、采用新网络测试技术和使用开源网络测试软件Cacti进行具体网络测试与分析。搭建一个小型的骨干网络来模拟运营商的IP承载网,在IP网络的核心,以具体的网络故障排除作为分析实例,使用Cacti对网络流量进行监控和对流量图进行分析,以及性能测试与网络性能瓶颈分析,最后提出相关优化解决方案。     

Application potential of high performance steels for weight reduction and efficiency increase in commercial vehicles

The fast-growing economy and the gradually established highway system have boosted the road transportation for both passenger and cargo over the last decade in China.From 2000 to 2010 Chinese GDP increased by around10.15%annually and the sales of medium and heavy trucks by around 18.87%(sales increased from 0.2 million in 2000 to 1.3 million in 2010) according to the National Bureau of Statistics of People's Republic of China.Today commercial vehicles consume almost the same amount of fuel as passenger cars in China although the number of commercial vehicles is only about one fourth of passenger cars.It is estimated that around 50%of imported fuel to China each year will be consumed by vehicle transportation.This situation will worsen fuel shortage problems in the long run and at the same time it is partially responsible for the everworsening air pollution in China.Due to the widespread overloading in China,lightweight development in commercial vehicles has fallen far behind that of passenger cars with the consequences that Chinese commercial vehicles consume in average about 20%more fuel,especially the heavy trucks,compared to European models.Under these circumstances it is essential to reduce the vehicle fuel consumption and increase the transport efficiency.The key solution thereby is to implement lightweight design in commercial vehicles as it has been successfully practiced over the last decade in the passenger cars.This paper summarizes highlights given in presentations during the "International seminar on the application of high strength steels in light weight commercial vehicles" with the focus on the development and application of Nb alloyed high performance steels made for lightweight commercial vehicles.     

Innovation dimensions and firm performance synergy in the emerging market: A perspective from Dynamic Capability Theory & Signaling Theory

ContextIn this rapidly changing business environment, innovation is the key requirement to gain a sustained advantage over competitors. Innovation helps firms grow more quickly than others grow, survive in the harsh & highly competitive business environment, and eventually become a market leader.PurposeIndia is an emerging market, and many companies are entering here and making it highly competitive. The limited study is available to measure the effect of innovation in Indian Business. Thus, the study establishes a relationship between innovation and firm performance in the Indian setting.Design/methodology/approachThis is a perception-based study and used established subjective scales to measure innovation and firm performance. I validated the scale using the measurement model in AMOS. The survey used to collect around 250 cross-sectional data from middle & higher management executives of Indian firms. Structural equation modeling in AMOS was used to test the hypothesis.FindingsThe results showed that product and marketing innovation has a significant and positive impact on the dimensions of firm performance. In contrast, Process innovation showed an indirect effect mediated through marketing innovation. These outcomes will be beneficial for the industries for taking proactive measures.Originality/valueThe examination of mediation relationships between Marketing innovation and Product & Process innovation is limited. Novelty also lies in analyzing the impact of multiple innovation types on multiple dimensions of firm performance in Indian firms to verify dynamic capability and mediating effect of marketing innovation in Indian demography to validate the signaling theory perspective. Rigor in research methods like Scale and sampling method verification test, i.e., CMB. Heteroscedasticity and Endogeneity test for applicability of OLS and verifying exogenous variables.     

Stress intensity factors and weight functions for deep semi-elliptical surface cracks in finite-thickness plates

ABSTRACT Three-dimensional finite element analyses have been conducted to calculate the stress intensity factors for deep semi-elliptical cracks in flat plates. The stress intensity factors are presented for the deepest and surface points on semi-elliptic cracks with a/t -values of 0.9 and 0.95 and aspect ratios ( a/c ) from 0.05 to 2. Uniform, linear, parabolic or cubic stress distributions were applied to the crack face. The results for uniform and linear stress distributions were combined with corresponding results for surface cracks with a/t = 0.6 and 0.8 to derive weight functions over the range 0.05 ≤  a/c  ≤ 2.0 and 0.6 ≤  a/t  ≤ 0.95. The weight functions were then verified against finite element data for parabolic or cubic stress distributions. Excellent agreements are achieved for both the deepest and surface points. The present results complement stress intensity factors and weight functions for surface cracks in finite thickness plate developed previously.     

Limits of spatial attention in three-dimensional space and dual-task driving performance

The present study examined the limits of spatial attention while performing two driving relevant tasks that varied in depth. The first task was to maintain a fixed headway distance behind a lead vehicle that varied speed. The second task was to detect a light-change target in an array of lights located above the roadway. In Experiment 1 the light detection task required drivers to encode color and location. The results indicated that reaction time to detect a light-change target increased and accuracy decreased as a function of the horizontal location of the light-change target and as a function of the distance from the driver. In a second experiment the light change task was changed to a singleton search (detect the onset of a yellow light) and the workload of the car following task was systematically varied. The results of Experiment 2 indicated that RT increased as a function of task workload, the 2D position of the light-change target and the distance of the light-change target. A multiple regression analysis indicated that the effect of distance on light detection performance was not due to changes in the projected size of the light target. In Experiment 3 we found that the distance effect in detecting a light change could not be explained by the location of eye fixations. The results demonstrate that when drivers attend to a roadway scene attention is limited in three-dimensional space. These results have important implications for developing tests for assessing crash risk among drivers as well as the design of in vehicle technologies such as head-up displays.     

Modeling and performance analysis of two phase service systems

Abstract

A Markovian queuing system is used to model a Two Phase Service (TPS) system. In this system, there are two queues, batch queue and individual queue, and a central server switching service between them. Expressions of mean task response time in the TPS are derived from the Markov‐Chain concept and the Z‐transform technique. Other performance parameters, such as the concept of power and speedup, and the optimization issues have also been taken into consideration. The relation between the TPS system and the other queuing system is compared and described. Furthermore, the performance improvement issue is investigated and the speedup upper bound is obtained. Finally, numerical results are provided to verify the analytical model.     

太阳能吸收式串联流程制冷系统与性能分析

本文提出了一种串联流程的以太阳能与燃气双热源供热的溴化锂吸收式制冷系统。介绍了当前太阳能吸收式制冷的发展概况。对双热源制冷系统原理进行介绍,简述了制冷机内工质循环流程,并模拟分析了系统的热力性能,得到高压发生器与低压发生器在不同放气范围时系统制冷系数与双热源的供热分配情况。分析了一天内不同时段制冷系统运行特性在不同太阳辐照度下的变化特点。结果证明太阳能与燃气双热源串联流程溴化锂吸收式制冷方案具有节能高效的优势。     

Local improvements that degrade system performance: case studies and discussion for throughput analysis

Much of our intuition about production system performance dynamics is grounded in an understanding of simple serial lines. For this reason, practitioners tend to rely on concepts and principles that have successfully guided the design and improvement of these lines, even in the analysis of significantly more complex systems. Based on this intuition, there is a natural tendency to believe that improving any specific feature of a system will result in comparable or improved overall performance. Unfortunately, this is not always the case. In this paper, we present three case study examples which demonstrate that local improvements to station speed or buffer capacity can result in an overall degradation of system performance for non-serial production systems.     

Comparative study of wear performance of particulate and fiber-reinforced nano-ZnO/ultra-high molecular weight polyethylene hybrid composites using response surface methodology

The effects of two types of filler reinforcements i.e. particulate (talc particles) and fiber (Glass Fiber (GF)) as secondary reinforcements in ultra-high molecular weight polyethylene (UHMWPE)-based composites on the wear and friction properties were discussed in this paper. These UHMWPE hybrid composites were fabricated by the addition of 10 wt% of talc and glass fiber at a fixed nano-ZnO loading of 10 wt% using a hot compression moulding technique. The wear and friction properties of these hybrid composites were investigated using a pin-on-disc tester with different operating conditions of applied loads, sliding speeds and sliding distances based on response surface Box–Behnken design. Response Surface Methodology (RSM) was applied to model the effects of various variables of applied load, sliding speed and distance on the wear volume loss and average coefficient of friction (COF) of UHMWPE hybrid composites. The mathematical regression models of the wear volume and average COF were derived from the analysis of variance (ANOVA). Optimization of the independent variables to minimize the wear and friction responses of both UHMWPE composites was estimated using RSM. The mathematical models showed that applied load, sliding speed and distance have significant effects on the wear and friction properties of both UHMWPE composites in the tested range of variables. The most significant, in order of the variables that affect the volume loss and friction of UHMWPE composites is load, followed by sliding distance and speed. In addition, the combined effects of load and distance indicate the highest significance on volume loss and average COF for both UHMWPE hybrid composites as compared to other variable interactions. GF/ZnO/UHMWPE exhibited better wear performance compared to talc/ZnO/UHMWPE hybrid composites. The severity of worn surfaces of the GF/ZnO/UHMWPE was less than that of talc/ZnO/UHMWPE. The GF/ZnO/UHMWPE produced transfer films that were more uniform and had better coverage compared to talc/ZnO/UHMWPE.     

Conceptual design and performance analysis of absorption heat pumps for waste heat utilization

The potential of the absorption cycle for recovering low temperature waste heat (60°C) as a first step towards the construction of a working system to provide process heat is assessed. The system is considered with lithium chloride-, lithium bromide-water solutions as working fluids.