Single development project

An often-cited problem in undergraduate software engineering courses states that some topics are difficult to teach in a university setting and, although laboratory work is a useful supplement to the lectures, it is difficult to make projects realistic and relevant. In recognition of this problem, and based on our past experience, we started preparing a new course by examining the pedagogies and curricular aspects of software engineering that are important for the Net Generation of software engineers.The course project described in this paper concentrates on those aspects that can be dealt with effectively within the environment, i.e., the software lifecycle, system interdependences, teamwork, and realistic yet manageable project dynamics, all supported by various means of communication. The workload per students must be balanced with their lack of knowledge and skills, so that their unpreparedness to deal with complex issues does not abate their motivation.The approach was tested on six large projects over the period of one semester. We believe that the results reflect the students’ strong interest and commitment, and demonstrate their ability to stay focused and work at a level that is well above the obvious.     

Determinants of conflict detection: a model of risk judgments in air traffic control

OBJECTIVE: A model of conflict judgments in air traffic control (ATC) is proposed. BACKGROUND: Three horizontal distances determine risk judgments about conflict between two aircraft: (a) Dt(o) is the distance between the crossing of the aircraft trajectories and the first aircraft to reach that point; (b) Dt(h) is the distance between the two aircraft when they are horizontally closest; and (c) Dt(v) is the horizontal distance between the two aircraft when their growing vertical distance reaches 1000 feet. METHODS: Two experiments tested whether the variables in the model reflect what controllers do. In Experiment 1, 125 certified controllers provided risk judgments about situations in which the model variables were manipulated. Experiment 2 investigated the relationship between the model and expertise by comparing a population of certified controllers with a population of ATC students. RESULTS: Across both experiments, the model accounted for 44% to 50% of the variance in risk judgments by certified controllers (N=161) but only 20% in judgments by ATC students (N=88). There were major individual differences in the predictive power of the model as well as in the contributions of the three variables. In Experiment 2, the model described experts better than novices. CONCLUSION: The model provided a satisfying account of the data, albeit with substantial individual differences. It is argued that an individual-differences approach is required when investigating the strategies involved in conflict judgment in ATC. APPLICATION: These findings should have implications for developing user-friendly interfaces with conflict detection devices and for devising ATC training programs.     

Overlapping decentralized approach to automation generation control of multi-area power systems

An overlapping decentralized control scheme is presented and applied to automatic generation control (AGC) for multi-area power systems. Based on the inclusion principle, the system is first decomposed in the expanded space as a group of pair-wise subsystems (areas). Then, the decentralized controllers designed, by standard linear quadratic (LQ) control laws are implemented in each pair-wise subsystem. Finally, the overlapping decentralized controller is obtained by coordinating and contracting the pair-wise decentralized controllers from the expanded space to the original space, preserving the inclusion conditions. When applied to AGC of a four-area power system, the proposed methodology not only guarantees AGC qualities, but also increases the system reliability with respect to a wide variety of structured perturbations. Simulation results illustrate the effectiveness of the presented approach both in the general case of information structure constraints and in the cases when some pairs of subsystems are disconnected by unpredicted faults.     

On accurate and efficient statistical counting in sensor-based surveillance systems

Sensor networks have been used in many surveillance systems, providing statistical information about monitored areas. Accurate counting information (e.g., the distribution of the total number of targets) is often important for decision making. As a complementary solution to double-counting in communication, this paper presents the first work that deals with double-counting in sensing for wireless sensor networks. The probability mass function (pmf) of target counts is derived first. This, however, is shown to be computationally prohibitive when a network becomes large. A partitioning algorithm is then designed to significantly reduce computation complexity with a certain loss in counting accuracy. Finally, two methods are proposed to compensate for the loss. To evaluate the design, we compare the derived probability mass function with ground truth obtained through exhaustive enumeration in small-scale networks. In large-scale networks, where pmf ground truth is not available, we compare the expected count with true target counts. We demonstrate that accurate counting within 1%–3% relative error can be achieved with orders of magnitude reduction in computation, compared with an exhaustive enumeration-based approach.     

Efficient channel code rate selection algorithms for forward error correction of packetized multimedia bitstreams in varying channels

We study joint source-channel coding systems for the transmission of images over varying channels without feedback. We consider the situation where the channel statistics are unknown to the transmitter and focus on systems that enable good performance over a wide range of channel conditions. We first propose a linear-time channel code rate selection algorithm for a hybrid transmission system that combines packetization of an embedded wavelet bitstream into independently decodable packets and forward error correction with a concatenated cyclic redundancy check/rate-compatible punctured convolutional (RCPC) channel coder. We then consider an extension of this hybrid system with additional Reed-Solomon (RS) coding across the packets and give a linear-time algorithm for the efficient selection of both the RS and RCPC code rates. Experimental results for a wireline/wireless link modeled as the combination of a packet erasure channel and a Rayleigh flat-fading channel showed that our schemes significantly outperformed the best previous forward error correction systems in many situations where the actual channel parameter values deviated from the ones used in the optimization of the source-channel rate allocation.     

Randomized modulation in power electronic converters

This article reviews analytical results and practical experience with randomized modulation in power electronic converters. After providing a brief overview of power electronics and of relevant switching patterns, the authors present performance specifications for converters (in terms of electromagnetic interference, vibrations and acoustic noise), and classify various randomized switching schemes. They review the most directly related references next, and introduce the mathematical objects of primary interest-averaged autocorrelation and power spectrum. They then list some results for the (simpler) case of stationary modulation and consider in detail the more general case of randomized switching based on Markov chains. Their aim is twofold-to present results important for practice and to establish connections with several areas of applied probability. Finally, they consider the synthesis task for the two cases of randomized modulation, followed by brief conclusions     

Autonomic straightening after gravitropic curvature of cress roots

Few studies have documented the response of gravitropically curved organs to a withdrawal of a constant gravitational stimulus. The effects of stimulus withdrawal on gravitropic curvature were studied by following individual roots of cress (Lepidium sativum L.) through reorientation and clinostat rotation. Roots turned to the horizontal curved down 62 degrees and 88 degrees after 1 and 5 h, respectively. Subsequent rotation on a clinostat for 6 h resulted in root straightening through a loss of gravitropic curvature in older regions and through new growth becoming aligned closer to the prestimulus vertical. However, these roots did not return completely to the prestimulus vertical, indicating the retention of some gravitropic response. Clinostat rotation shifted the mean root angle -36 degrees closer to the prestimulus vertical, regardless of the duration of prior horizontal stimulation. Control roots (no horizontal stimulation) were slanted at various angles after clinostat rotation. These findings indicate that gravitropic curvature is not necessarily permanent, and that the root retains some commitment to its equilibrium orientation prior to gravitropic stimulation.     

Dissipativity-based adaptive and robust control of UPS

In this paper, we investigate the output voltage control for a three-phase uninterruptible power supply (UPS) using controllers based on ideas of dissipativity. To provide balanced sinusoidal output voltages, even in the presence of nonlinear and unbalanced loads, we first derive a dissipativity-based controller using a frequency-domain representation of system dynamics. Adaptive refinements have been added to the controller to cope with parametric uncertainties. Second, based on the first adaptive controller, we propose a controller which turns out to have the proportional-plus-integral-type structure on rotating-frame variables, but with a special design of gain matrices. A sufficient condition in terms of the design parameters is presented for this controller that guarantees stability of the desired equilibrium and robustness against parameter uncertainties. Finally, simulation and experimental results on a three-phase prototype show effectiveness and advantages of the proposed approach