An experimental study of random knapsack problems

The size of the Pareto curve for the bicriteria version of the knapsack problem is polynomial on average. This has been shown for various random input distributions. We experimentally investigate the number of Pareto points for knapsack instances overn elements whose profits and weights are chosen at random according to various classes of input distributions. The numbers observed in our experiments are significantly smaller than the known upper bounds. For example, the upper bound for so-called uniform instances isO(n ³). Based on our experiments, we conjecture that the number of Pareto points for these instances is only Θ(n ²). We also study other structural properties for random knapsack instances that have been used in theoretical studies to bound the average-case complexity of the knapsack problem. Furthermore, we study advanced algorithmic techniques for the knapsack problem. In particular, we review several ideas that originate from theory as well as from practice. Most of the concepts that we use are simple and have been known for at least 20 years, but apparently have not been used in this combination. Surprisingly, the result of our study is a very competitive code that outperforms the best previous implementationCombo by orders of magnitude for various classes of random instances, including harder random knapsack instances in which profits and weights are chosen in a correlated fashion. This research was supported in part by the EU within the 6th Framework Programme under Contract 0019007 (DELIS), by DFG Grant Vo889/2-1, and by a postdoctoral fellowship by the German Academic Exchange Service (DAAD).     

An upper bound model for TCP and UDP throughput in IPv4 and IPv6

Due to the shortage of public IPv4 addresses, the IETF has developed a new version of the Internet Protocol called IPv6. Many institutions all over the world had already started the migration to IPv6. Since this migration has to be done slowly, the first step is the coexistence of the two protocols (IPv4 and IPv6) for some years. One important issue for IPv6 to gain acceptance, is its performance in end-user applications. Hence, due to the availability of a variety of IPv6 implementations on different operating systems, it is important to evaluate the performance of the different IPv6 stacks, and compare it to the one shown by IPv4. In this paper, we present an upper bound model to compute TCP and UDP throughput for IPv4 and IPv6, in a full-duplex point-to-point connection. Our model can be used for any variant of Ethernet technology (10, 100, and 1000 Mbps). To validate this model, we did experiments and compared the maximum theoretical throughput with the experimental ones. Experiments were done with Windows XP SP2, Solaris 10, and Debian 3.1, which are very popular operating systems. The results show that 10 Mbps Ethernet technology is already very mature, since it gave performance very close to the maximum theoretical throughput. Experiments with FastEthernet (100 Mbps) show a TCP and UDP throughput close to the maximum theoretical throughput, especially for large payload. In the case of GigaEthernet (1000 Mbps), experimental results are not far from the maximum throughput for large TCP and UDP payload. However, for small TCP and UDP payload, the differences between our model (the maximum throughput) and the experiments are important. These differences should significantly decrease with the release of faster technology (processors and RAM).     

An experimental study of processor thrashing in multiprocessor systems

A special occurrence of a phenomenon calledprocessor thrashing caused by processor lockouts within the dispatcher of a symmetric multiprocessor system is studied. Results derived from simulation experiments involving up to 16 processors show that the potential danger of processor thrashing can be reduced noticably by locking only parts of the dispatcher's data during a specific dispatcher operation. The algorithms and data structure of a highly efficient implementation are outlined based on this principle and its performance is compared with a simple monitor realization of a dispatcher.     

On the nonconcavity of throughput in certain closed queueing networks

Analytic queueing network models are being used to analyze various optimization problems such as server allocation, design and capacity issues, optimal routing, and workload allocation. The mathematical properties of the relevant performance measures, such as throughput, are important for optimization purposes and for insight into system performance.We show that for closed queueing networks of m arbitrarily connected single server queues with n customers, throughput, as a function of a scaled, constrained workload, is not concave. In fact, the function appears to be strictly quasiconcave. There is a constraint on the total workload that must be allocated among the servers in the network. However, for closed networks of two single server queues, we prove that our scaled throughput is concave when there are two customers in the network and strictly quasi-concave when there are more than two customers. The mathematical properties of both the scaled throughput and reciprocal throughput are demonstrated graphically for closed networks of two and three single server queues.     

An investigation of myocardial aerobic capacity as a measure of both physical and cognitive workloads

With increased automation and supervisory control, the physical content of jobs has decreased while cognitive workload has increased. The cardiovascular system responds to both physical and cognitive stresses, and their combination, by causing an increase in both heart rate (HR) and blood pressure. The increase in HR and blood pressure cause an increase in myocardial contractility, which results in an increase in myocardial oxygen consumption (MV_O2). The rate–pressure product (RPP), given by the product of HR and systolic blood pressure, is a very reliable indirect measure of MV_O2. With this in mind, an experiment was conducted on 12 able-bodied male students from the University population. Subjects were required to perform three cognitive tasks (Stroop Incongruent Color-Word Test, simulated public speaking, and calculating task) under two physical conditions (riding a Schwinn Airdyne at a constant speed of 1/3 of their estimated maximum HR, and seated at rest on the Schwinn Airdyne). HR and blood pressure were monitored throughout the testing period. Results of the analysis of the randomized block design indicated that both cognitive and physical tasks had a significant effect on RPP. Additionally, the findings from this study indicated that RPP can be used as an objective measure to separate the components of cognitive workload and cognitive stress in combined tasks.

Relevance to industry

Rate–pressure product may be used as a measure of occupational workload, both cognitive and physical. It may be possible to use RPP measures to set limits on workloads and for establishing work allowance.     

Definition, modelling and simulation of a grid computing scheduling system for high throughput computing

In this paper, we study and compare grid and global computing systems and outline the benefits of having a hybrid system called DIRAC. To evaluate the DIRAC scheduling for high throughput computing, a new model is presented and a simulator was developed for many clusters of heterogeneous nodes belonging to a local network. These clusters are assumed to be connected to each other through a global network and each cluster is managed via a local scheduler which is shared by many users. We validate our simulator by comparing the experimental and analytical results of a M/M/4 queuing system. Next, we do the comparison with a real batch system and we obtain an average error of 10.5% for the response time and 12% for the makespan. We conclude that the simulator is realistic and well describes the behaviour of a large-scale system. Thus we can study the scheduling of our system called DIRAC in a high throughput context. We justify our decentralized, adaptive and opportunistic approach in comparison to a centralized approach in such a context.     

An ergonomics study at an information department of the computer center at National Autonomous University of Mexico

This paper reports the analysis of an ergonomical study carried out in the Information Department of the Computer Center at National Autonomous University of Mexico. This department is in charge of providing information to the users about services provided by the center. For the majority of the users, the service provided by the department staff satisfies their expectations, but there are some users not satisfied with the quality of the service and the quantity and quality of the information received. In order to improve their service, an ergonomical study about the activities of the department was carried out. This study included a questionnaire about the users’ opinion and an analysis of the mental workload of the activities carried out by the department members. The results suggested that the service provided by the department staff can be considered good, but there are some organizational factors that reduce the level of performance of their service. A reorganization of some of the tasks, procedures and support on the department are recommended in order to improve their performance.

Relevance to the industry

The study provides the opportunity to evaluate the level of mental workload for office workers, by the assignation of the second task while carrying out their job.     

Development and validation of a computer expertise questionnaire for older adults

Prior computer expertise represents one of the most important predictors of performance when interacting with ICT (Information and Communication Technologies) and acquiring computer skills. Due to demographic changes, the older adult will become increasingly important as a potential user. However, there is a lack of instruments for the assessment of computer expertise in older adults, especially for novice users with restricted prior computer knowledge. A computer expertise (CE) questionnaire for older adults was developed, analysed (Study I) and validated (Study II). Item-analysis showed that the CE-questionnaire is particularly appropriate for the computer knowledge level of older adults and measures computer expertise sufficiently. Furthermore, it was found that computer experience (in terms of frequency of computer usage) is a poor predictor of actual computer performance, which has important implications for the theoretical conceptualization of computer expertise and its assessment.     

Development and validation of a computer expertise questionnaire for older adults

Prior computer expertise represents one of the most important predictors of performance when interacting with ICT (Information and Communication Technologies) and acquiring computer skills. Due to demographic changes, the older adult will become increasingly important as a potential user. However, there is a lack of instruments for the assessment of computer expertise in older adults, especially for novice users with restricted prior computer knowledge. A computer expertise (CE) questionnaire for older adults was developed, analysed (Study I) and validated (Study II). Item-analysis showed that the CE-questionnaire is particularly appropriate for the computer knowledge level of older adults and measures computer expertise sufficiently. Furthermore, it was found that computer experience (in terms of frequency of computer usage) is a poor predictor of actual computer performance, which has important implications for the theoretical conceptualization of computer expertise and its assessment.     

Sensemaking in military planning: a methodological study of command teams

Sensemaking, understanding how to deal with the situation at hand, has a central role in military command. This paper presents a method for measuring sensemaking performance in command teams during military planning. The method was tested in two experiments with Army captains serving as participants. The task was to produce parts of a brigade order within 6 h. The participants worked in teams of 5–7 individuals, 16 teams in the first experiment and 8 teams in the second experiment, with one team member acting as brigade commander. The independent variables were amount of information and type of communication, respectively. The characteristics of each team’s sensemaking process were assessed from video recordings of their planning sessions. The quality of their plans was judged by military experts. Although plan quality was unaffected by the experimental manipulations, the quality of the sensemaking process was related to the quality of the plans.

An experimental study on the role of 3D sound in augmented reality environment

Investigation of augmented reality (AR) environments has become a popular research topic for engineers, computer and cognitive scientists. Although application oriented studies focused on audio AR environments have been published, little work has been done to vigorously study and evaluate the important research questions of the effectiveness of three-dimensional (3D) sound in the AR context, and to what extent the addition of 3D sound would contribute to the AR experience.

Thus, we have developed two AR environments and performed vigorous experiments with human subjects to study the effects of 3D sound in the AR context. The study concerns two scenarios. In the first scenario, one participant must use vision only and vision with 3D sound to judge the relative depth of augmented virtual objects. In the second scenario, two participants must cooperate to perform a joint task in a game-based AR environment.

Hence, the goals of this study are (1) to access the impact of 3D sound on depth perception in a single-camera AR environment, (2) to study the impact of 3D sound on task performance and the feeling of ‘human presence and collaboration’, (3) to better understand the role of 3D sound in human–computer and human–human interactions, (4) to investigate if gender can affect the impact of 3D sound in AR environments. The outcomes of this research can have a useful impact on the development of audio AR systems, which provide more immersive, realistic and entertaining experiences by introducing 3D sound. Our results suggest that 3D sound in AR environment significantly improves the accuracy of depth judgment and improves task performance. Our results also suggest that 3D sound contributes significantly to the feeling of human presence and collaboration and helps the subjects to ‘identify spatial objects’.     

An experimental evaluation of capture-recapture in software inspections

The use of capture-recapture to estimate the residual faults in a software artifact has evolved as a promising method. However, the assumptions needed to make the estimates are not completely fulfilled in software development, leading to an underestimation of the residual fault content. Therefore, a method employing a filtering technique with an experience factor to improve the estimate of the residual faults is proposed in this paper. An experimental study of the capture-recapture method with this correction method has been conducted. It is concluded that the correction method improves the capture-recapture estimate of the number of residual defects in the inspected document.     

A field study of sleep and fatigue in a regular rotating 12-h shift system

The aim of this study was to examine a regular rotating 12-h shift system (2D2N4Off) at an Australian Smelter. Sleep behavior, subjective fatigue and neurobehavioral performance were investigated over a 14-day period for 20 employees. Activity monitors, sleep/wake diaries, and 5-min psychomotor vigilance tasks were used. Sleep data showed differences between day and night shifts. While sleep prior to night1 was increased relative to day shifts, a reduced sleep length carried into the period leading to night2. Total wakefulness at the end of shift, and subjective fatigue were increased for night shifts, particularly night1. Decrements in performance data supported these findings. Both prior wakefulness and prior sleep are important in a 12-h shift system. Employees may “sleep in” after day shifts, rather than taking extra sleep prior to night work. Thus, sleep between day and night shifts is based on recovery rather than preparation.     

Stochastic control of processes having moving boundaries—An experimental study

A general state estimator requiring only discrete time measurements has been developed for nonlinear distributed parameter systems having moving boundaries. The state estimator has been combined with an optimal linear-quadratic feedback controller to provide a stochastic feedback control scheme for this class of problem. Both the state estimation and control algorithms were implemented in real time for a laboratory casting process and were found to perform well. The state estimation scheme would seem to hold the most interest for industrial applications.     

A shipboard study of a four-crew rotating watchkeeping system

Abstract

Body-temperatures and subjective alertness ratings were obtained at 2-hourly intervals in a shipboard study of six subjects watchkeeping on a rapidly rotating system with a 4-day cycle. The results were compared with those from an earlier study of this system conducted on land in ‘laboratory’ conditions. The similarity of the temperature curves from the two studies indicated that prolonged exposure to shipboard conditions made no difference to the underlying circadian rhythm in this variable, which appeared to be near-normal in form. Subjective alertness showed a clear rhythm of considerable amplitude; the phasing of this rhythm suggested that, under the present system, operational effectiveness is likely to be reduced in watches held in night hours. Further analyses indicated that it was also likely to be reduced in daytime hours following these night watches, because of the disruption of sleep that results from them. An alternative ‘fixed hours’ watchkeeping system is proposed to overcome these unwanted effects.     

Scheduling a dynamic job shop production system with sequence-dependent setups: An experimental study

This paper presents the salient aspects of a simulation-based experimental study of scheduling rules for scheduling a dynamic job shop in which the setup times are sequence dependent. A discrete event simulation model of the job shop system is developed for the purpose of experimentation. Seven scheduling rules from the literature are incorporated in the simulation model. Five new setup-oriented scheduling rules are proposed and implemented. Simulation experiments have been conducted under various experimental conditions characterized by factors such as shop load, setup time ratios and due date tightness. The results indicate that setup-oriented rules provide better performance than ordinary rules. The difference in performance between these two groups of rules increases with increase in shop load and setup time ratio. One of the proposed rules performs better for mean flow time and mean tardiness measures.     

Topological design of a distributed computer communication network in a noisy environment

The effect of noisy links is considered in the design of a computer communication network topology. Because of noisy links, and the consequent probability of bit error, additional network traffic in the form of acknowledgement packets and retransmission packets are generated which load the network. A topological design procedure for obtaining a minimum cost network is proposed which satisfies given constraints of overall network delay, maximum delay on a link, throughput and reliability. Traffic priority for different classes of traffic is also taken into consideration in the design. As expected, the network cost increases as the bit error probability of the links increases.     

An experimental evaluation of a higher-ordered-typed-functional specification-based test-generation technique

HOTTest is a model based test automation technique of software systems based on models of the system described using HaskellDB. HaskellDB is an embedded domain specific language derived from Haskell. HOTTest enforces a systematic abstraction process and exploits system invariants for automatically producing test cases for domain specific requirements. Use of functional languages for system modeling is a new concept and hence HOTTest is subject to concerns of usability, like any other new technique. Also, the syntax and the declarative style of Haskell based languages make them difficult to learn. Similar concerns can be raised for HOTTest as it shares the same syntax with Haskell. In this paper we describe an experiment designed to study the usability of HOTTest and to compare it with existing model based test design techniques. The results show that HOTTest is more usable than the traditional technique and demonstrate that the test suites produced by HOTTest are more effective and efficient than those generated using the traditional model based test design technique. Editor: James Miller     

TD-LTE系统中一种AMC方案的研究

当信道SNR变化较快而导致BLER较高时,现有的LTE-AMC性能严重下降,不能满足系统要求。针对这种情况,提出了一种可靠性好的AMC方案。该方案通过相同资源对数下选择最小的CQI,使系统更加适应SNR变化较快的情况。理论和仿真分析结果表明,该方案大大提高了系统吞吐量,满足协议上对吞吐量的要求。     

An evaluation of voice stress analysis techniques in a simulated AWACS environment

Fundamental frequency, frequency jitter, and amplitude shimmer voice algorithms were employed to measure the effects of stress in crewmember communications data in simulated AWACS mission scenarios. Two independent workload measures were used to identify levels of stress: 1) a predictor model developed by the simulation author based upon scenario-generated stimulus events, and 2) the duration of communication for each weapons director, representative of the individual's response to the induced stress. Results identified fundamental frequency and frequency jitter as statistically significant vocal indicators of stress, while amplitude shimmer showed no signs of any significant relationship with workload or stress. Consistent with previous research, the frequency algorithm was identified as the most reliable measure. However, the results did not reveal a sensitive discrimination measure between levels of stress, but rather, did distinguish between the presence or absence of stress.