System Design Issues Research Articles

Analysis of uncertainty in natural ventilation predictions of high-rise apartment buildings

Quantification of natural ventilation rates is an important issue in HVAC system design. Natural ventilation in buildings depends on many parameters whose uncertainty varies significantly, and hence the results from a standard deterministic simulation approach could be unreliable and provide a false sense of security that natural ventilation will supply adequate amounts of fresh air. This study performed an uncertainty analysis to predict natural airflow rates. The paper presents relevant uncertainty in model and input parameters such as meteorological data, building properties (leakage areas of windows, doors, etc.), etc. Uncertainties of the aforementioned parameters were quantified based on data available from literature and on-site visits. The Monte-Carlo method with Latin Hypercube Sampling (LHS) was used for uncertainty propagation. The CONTAMW was chosen to simulate natural ventilation phenomena in a high-rise apartment building that is typical of residential buildings in Korea. It is shown that the uncertainty propagated through this process is not negligible and may significantly influence the prediction of the airflow rates. In the paper, the result of a sensitivity analysis is also addressed. Practical application: The paper describes a probablistic approach to predict the natural airflow rates of high-rise apartment buildings under uncertainty and could eventually replace the current conventional deterministic approach.

Exploring criteria for successful query expansion in the genomic domain

Query Expansion is commonly used in Information Retrieval to overcome vocabulary mismatch issues, such as synonymy between the original query terms and a relevant document. In general, query expansion experiments exhibit mixed results. Overall TREC Genomics Track results are also mixed; however, results from the top performing systems provide strong evidence supporting the need for expansion. In this paper, we examine the conditions necessary for optimal query expansion performance with respect to two system design issues: IR framework and knowledge source used for expansion. We present a query expansion framework that improves Okapi baseline passage MAP performance by 185%. Using this framework, we compare and contrast the effectiveness of a variety of biomedical knowledge sources used by TREC 2006 Genomics Track participants for expansion. Based on the outcome of these experiments, we discuss the success factors required for effective query expansion with respect to various sources of term expansion, such as corpus-based cooccurrence statistics, pseudo-relevance feedback methods, and domain-specific and domain-independent ontologies and databases. Our results show that choice of document ranking algorithm is the most important factor affecting retrieval performance on this dataset. In addition, when an appropriate ranking algorithm is used, we find that query expansion with domain-specific knowledge sources provides an equally substantive gain in performance over a baseline system.

The Compact Polarimetry Alternative for Spaceborne SAR at Low Frequency

In spaceborne synthetic aperture radar (SAR), a single-polarization on-transmit offers twice the swath width compared to full polarization. This is linked to SAR system design issues, and, without getting into the technical details deserving by themselves a full paper, we can just mention the swath characteristics of ALOS PALSAR (the Advanced Land Observing Satellite, Phased Array L-Band Synthetic Aperture Radar), reducing from 70 km for the dual-pol mode to 30 km for the full polarization mode. The reduced coverage in the full polarization mode has a harmful impact on the revisit time, which is always a major drive for the Earth-observing community. The options chosen up to now for dual-pol system designs (or single-polarization on-transmit) rely on a linear polarization on-transmit [either horizontal (H) or vertical (V)], with two orthogonal polarizations on-receive. Souyris and Raney in earlier papers proposed more pertinent alternatives for the selection of the transmit polarization leading to a better characterization of the scattering mechanisms. In this paper, the analysis is pursued in more depth by including the effect of the ionosphere on the wave propagation and extending the applications to polarimetric interferometry SAR (PolInSAR). A compact mode is developed where the transmit polarization is circular, whereas the only constraint on the two receiving polarizations is independence. Indeed, the choice of the polarizations of the two receive channels does not matter, as any polarization on-receive can be synthesized from these two measurements. This is, however, not the case for the unique transmit polarization. At a low frequency, where the ionosphere has a significant effect, the circular transmit polarization is the only sensible option, as it provides an effective constant polarization as seen by the scattering surface. This is an essential condition for a meaningful multitemporal analysis. Both the polarimetric SAR applications and the PolInSAR applications in the context of this compact polarimetry (CP) mode are explored. A pseudocovariance matrix can be reconstructed following Souyris' proposed approach for distributed targets and is shown to be very similar to the full polarimetric (FP) covariance matrix. The reconstruction of the cross-polarized Sigma0 is shown to be reliable and to have very low sensitivity to Faraday rotation. A PolInSAR vegetation height inversion for P-band is presented and applied to the CP data with a level of performance that is similar to the one derived from FP (a 1.2-m root-mean-square height error on the ONERA Airborne radar (RAMSES) data over the Landes Forest). A procedure is developed to correct for the ionospheric effects for the PolInSAR acquisition in the FP or CP mode and is assessed on the data simulated from an airborne acquisition. The results demonstrate that the technique is efficient and robust. The calibration of CP data is identified as an important challenge to be solved, and some clues are provided to address the problem.

Design of a CO preferential oxidation reactor for PEFC systems: A modelling approach

Abstract This paper presents a two-dimensional model of a preferential oxidation (PROX) reactor to be used in a beta 5 kWe hydrogen generator (HYGen II), to integrate with Polymer Electrolyte Fuel Cells (PEFCs). PROX reactors require careful temperature control systems, in order to enhance optimization and control of the unit. The model concerns chemical kinetics and heat/mass transfer phenomena occurring in the reactor. Aim of the model is to investigate the effects of the molar ratio O2/CO, the gas hourly space velocity (GHSV) and the inlet temperature on process performance of the reactor, in order to obtain high CO conversion and high selectivity with respect to the undesired H2 oxidation. The model plays a key role in overcoming the issues of system design, by evaluating the temperature and the gas concentration profiles in the reactor. Simulation results showed the strong dependence of the overall performance upon the operating conditions examined.

A Quantitative Study on Risk Issues in Safety Feature Control System Design in Digitalized Nuclear Power Plant

Risk assessment for the engineered safety feature component control system (ESF-CCS) designed as part of the Korean Nuclear Instrumentation and Control (I&C) System project for application to the advanced pressurized reactor (APR1400) by using newly developed safety-class microprocessor-based modules was performed for risk-informed design feedback. The fault-tree models were developed to assess the failure probability of a system function, which is used to generate an automated control signal for complicated accident-mitigation equipment. The developed fault trees were combined with a plant risk model. This study aims at providing risk information of design issues: the risk effects of the ESF-CCS failure in consideration of an operator's manual action failure, the effect of input-signal diversity on ESF-CCS unavailability, and the risk effects of the network communication used for safety-critical information transmission in the ESF-CCS. Based on the case studies and cutset analysis, we quantitatively address these risk issues.

A Senior-Level Course in Hardware–Software Codesign

Modern electronic system design makes extensive use of programmable architectures, and requires designers to consider hardware and software jointly in their design. A senior-level course named hardware/software codesign provides a practical introduction to these complex system design issues. The challenge is to bring a subject, which is traditionally covered as a graduate-level course, to senior undergraduate students without overly narrowing down the scope, and without turning the course into an ad-hoc design project. The course combines an incremental, structured overview of hardware/software codesign with practical assignments that emphasize key concepts. This paper reviews the motivations for this course, the curriculum, the lab materials and tools used, and the results of the first offering of the course in fall 2006.

Analyzing Functional Coverage in Bounded Model Checking

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Formal verification is an important issue in circuit and system design. In this context, bounded model checking (BMC) is one of the most successful techniques. However, even if all the specified properties can be verified, it is difficult to determine whether they cover the complete functional behavior of a design. We propose a practical approach to analyze coverage in BMC. The approach can easily be integrated in a BMC tool with only minor changes. In our approach, a coverage property is generated for each important signal. If the considered properties do not describe the signal's entire behavior, the coverage property fails, and a counter example is generated. From the counter example, an uncovered scenario can be derived. This way, the approach also helps in design understanding. We demonstrate our method for a reduced instruction set computer (RISC) CPU. First, the coverage of the block-level verification is considered. Second, it is demonstrated how the technique can be applied on a higher level. Therefore, we investigate the instruction set verification of the RISC CPU. The experiments show that the costs for coverage analysis are comparable to the verification costs. Based on the results, we identified coverage gaps during the verification. We were able to close all of them and achieved 100% functional coverage in total. </para>

Analysis and Design of Warning Delivery Service in Intervehicular Networks

This paper focuses on inter-vehicular networks providing warning delivery service. As soon as a danger is detected, the propagation of a warning message is triggered, with the aim of guaranteeing a safety area around the point in which the danger is located. Multiple broadcast cycles can be generated so that a given lifetime of the safety area is guaranteed. The service is based on multi-hop ad hoc inter-vehicular communications with a probabilistic choice of the relay nodes. The scenario we consider consists of high speed streets, such as highways, in which vehicles exhibit one-dimensional movements along the direction of the road. We propose an analytical model for the study of this service and derive performance indices such as the probability that a vehicle is informed, the average number of duplicate messages received by a vehicle and the average delay. Moreover, we use the model to discuss system design issues, which include the proper setting of the forwarding probability at each vehicle, so that a given probability to receive the warning can be guaranteed to all vehicles in the safety area. The model is validated against simulation results. Since it is very accurate, the model can be instrumental to the performance evaluation and design of broadcasting techniques in inter-vehicular networks.

What is Systems Engineering for Embedded Systems?

AbstractThis paper asks the question “What is Systems Engineering for Embedded Systems?” First the scene is set by discussing the prevalence of embedded systems in the world around us including examples, design metrics, and technology issues such as processor architecture. Then the aspects of Systems Engineering that apply to embedded systems are discussed in some detail with a focus on requirements issues such as end product utility and power management. This is followed by a discussion of the System Design issues relating to embedded systems such as real time operation, size &amp; weight and cost. Some focus is applied to the issue of data management for embedded systems. Finally some tool related issues are discussed.

Evaluation of existing sound system designs in mosques and alternative modern solutions

Sound intelligibly and audibility was from the old days and will remain a central issue in any sound system design especially in mosques. In other worship spaces sound system may not be needed during specific worshiping modes like congregational prayers. In mosques all worshiping modes require professionally designed sound system to maintain the needed intelligibility and audibility levels in such spaces. Here the current used sound systems in mosques will be discussed and pro and cons will be highlighted. Also, the effect of these systems on mosques applicable sound parameter will be introduced. In the same time, modern sound system design solution for different mosques architectural form and size will be suggested. Case study examples will be used to show the advantages of the new suggested sound system configurations.

Energy Minimization of Portable Video Communication Devices Based on Power-Rate-Distortion Optimization

Portable video communication devices operate on batteries with limited energy supply. However, video compression is computationally intensive and energy-demanding. Therefore, one of the central challenging issues in portable video communication system design is to minimize the energy consumption of video encoding so as to prolong the operational lifetime of portable video devices. In this work, based on power-rate-distortion (P-R-D) optimization, we develop a new approach for energy minimization by exploring the energy tradeoff between video encoding and wireless communication and exploiting the nonstationary characteristics of input video data. Both analytically and experimentally, we demonstrate that incorporating the third dimension of power consumption into conventional R-D analysis gives us one extra dimension of flexibility in resource allocation and allows us to achieve significant energy saving. Within the P-R-D analysis framework, power is tightly coupled with rate, enabling us to trade <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bits</i> for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">joules</i> and perform energy minimization through optimum bit allocation. We analyze the energy saving gain of P-R-D optimization. We develop an adaptive scheme to estimate P-R-D model parameters and perform online resource allocation and energy optimization for real-time video encoding. Our experimental studies show that, for typical videos with nonstationary scene statistics, using the proposed P-R-D optimization technology, the energy consumption of video encoding can be significantly reduced (by up to 50%), especially in delay-tolerant portable video communication applications.

Robust design of battery/fuel cell hybrid systems—Methodology for surrogate models of Pt stability and mitigation through system controls

With increasing interest in energy storage and conversion devices for automobile applications, the necessity to understand and predict life behavior of rechargeable batteries, PEM fuel cells and super capacitors is paramount. These electrochemical devices are most beneficial when used in hybrid configurations rather than as individual components. A system model helps us to understand the interactions between components and enables us to determine the response of the system as a whole. However, system models that are available predict just the performance and neglect degradation. The objective of this research is to provide a framework to account for the durability phenomena that are prevalent in fuel cells and batteries in a hybrid system. Toward this end, the methodology for development of surrogate models is provided, and Pt catalyst dissolution in proton exchange membrane fuel cells (PEMFCs) is used as an example to demonstrate the approach. Surrogate models are more easily integrated into higher level system models than the detailed physics-based models. As an illustration, the effects of changes in control strategies and power management approaches in mitigating platinum instability in fuel cells are reported. A system model that includes a fuel cell stack, a storage battery, power-sharing algorithm, and dc/dc converter has been developed; and preliminary results have been presented. These results show that platinum stability can be improved with only a small impact on system efficiency. Thus, this research will elucidate the importance of degradation issues in system design and optimization as opposed to just initial performance metrics.

System Design Issues for Harsh Environment Electronics Employing Metal-Backed Laminate Substrates

Designing harsh environment electronics continue to increase in difficulty to a rapid increase in feature content while electronics packaging technologies are often providing less reliability. In addition, restricted under-the-hood airflow and integrated (mechatronic) designs are significantly increasing operating temperatures toward their maximum operating capability. To provide a cost effective design, automotive electronics designers are pursuing circuit board assemblies directly attached to a metal plate. For cost purposes, this metal plate can also be used as part of the module housing to provide protection, as well as thermal efficiency. Unfortunately, the metal backing can often further reduce component reliability due to increases in substrate coefficient of thermal expansion. The paper investigates the impact of metal attachment on component reliability as it investigates the use of several board attachment options. These analyses are compared to finite element modeling to further understand the causes of earlier failure. In addition, the impact of additional component encapsulants and conformal coatings are investigated. Because all attachment materials must meet a certain thermal performance (both initial design and long-term performance) the thermal efficiencies of these design options are investigated, as well as the delamination due to product life. Finally, failure analyses are presented and ensure that failures match expected characteristics.

Sense through the wall system development and design considerations

This paper presents system design challenges and issues with sensing through walls at different standoff distances and wall types. Efforts for developing sense through the wall (STTW) systems, such as those undertaken by the US Army Technology Objective (ATO) program, aim at providing the soldier with situational awareness information before breaching a building in a military operations in urban terrain (MOUT) environment. STTW capabilities also support law enforcement and search and rescue applications. Since 2002, extensive evaluations of STTW technologies, most notably those performed by the Communications Electronics, Research, Development and Engineering Center (CERDEC) Intelligence and Information Warfare Directorate (I2WD), have been made to determine which technology could be the most viable solution. After conducting comprehensive studies, I2WD initiated several Phase I efforts and Phase II efforts. The purpose behind both efforts was to develop various STTW technology demonstrators under a 5 year ATO. Many lessons learned during the development of Phase I systems were incorporated into the considerations for Phase II developments. This paper discusses design challenges and issues with sensing through walls at different standoff distances and wall types through lessons learned and results from modeling and simulations performed by the Army Research Laboratory.

On Robustness against Measurement Noise of Iterative Learning Control based Identification

One of the most important issues in control system design is to obtain an accurate model of the plant to be controlled. Though most of the existing identification methods are described in discrete-time, it would be more appropriate to have continuous-time models directly from the sampled I/O data. From this viewpoint, the authors have developed such a direct identification method based on ILC (Iterative Learning Control) approach. This is a new application area of ILC. The method often yields accurate models even in the presence of heavy measurement noise. The robustness against noise is achieved through (i) projection of continuous-time I/O signals onto a finite dimensional parameter space, (ii) initial models through preparatory experiment and (iii) noise tolerant learning laws. This paper examines the accuracy of the initial models and convergence property of ILC in the presence of heavy colored noise through detailed simulations, which demonstrates the robustness of the ILC based identification method.

A Quantitative Study on Risk Issues in Safety Feature Control System Design in Digitalized Nuclear Power Plant

A Quantitative Study on Risk Issues in Safety Feature Control System Design in Digitalized Nuclear Power Plant

System Design Issues and Performance Evaluations for Adaptive Modulation in New Wireless Access Systems

This paper discusses system design strategies and performance evaluation for adaptive modulation techniques used in new and up-and-coming wireless access systems. After a brief discussion on basic modulation parameter (MP) settings as well as functionalities specific for adaptive modulation systems, this paper discusses how to design a narrowband time-division multiple-access/time-division duplex (TDMA/TDD)-based adaptive modulation system and confirms through laboratory experiments that the narrowband TDMA/TDD-based adaptive modulation system dramatically enhances system robustness to multipath fading and flexibility in throughput and transmission quality control. Next, as an extension to many fields of application for adaptive modulation, this paper discusses subcarrier-level adaptive modulation for orthogonal frequency-division multiplexing (OFDM)-based one-cell reuse broadband cellular systems. One key result is that nonsubcarrier transmit power control (TPC) applied adaptive modulation systems can achieve almost the same performance as subcarrier TPC applied adaptive modulation systems provided that the required signal-to-noise-plus-interference power ratio increment in the MP sets is designed to be sufficiently small. Finally, this paper explains the dynamic parameter controlled OFDM/TDMA system as an example of a practical scheme for one-cell reuse broadband wireless access systems. The analysis confirms that this adaptive system can achieve a spatial reuse efficiency defined by (average throughput in multicell conditions)/(average throughput in single cell conditions) of 0.8 as well as an average media access control payload throughput of about 150 Mb/s using about 100 MHz of bandwidth.

Grouping based bit-slot ALOHA protocol for tag anti-collision in RFID systems

Tag collision arbitration is a significant issue in RFID system design. This letter presents an efficient stochastic scheme based protocol which is characterized by the fact that both idle and collisional timeslots are reduced obviously. Utilizing of reservation sequence and controlling the number of tags to respond ensure the protocol works stably and efficiently. Simulation results show that the proposed protocol has a good performance and requires less time consumption than other stochastic scheme based protocols.

Planetary protection implementation on Mars Reconnaissance Orbiter mission

In August 2005 NASA launched a large orbiting science observatory, the Mars Reconnaissance Orbiter (MRO), for what is scheduled to be a 5.4-year mission. High resolution imaging of the surface is a principal goal of the mission. One consequence of this goal however is the need for a low science orbit. Unfortunately this orbit fails the required 20-year orbit life set in NASA Planetary Protection (PP) requirements [NASA. Planetary protection provisions for robotic extraterrestrial missions, NASA procedural requirements NPR 8020.12C, NASA HQ, Washington, DC, April 2005.]. So rather than sacrifice the science goals of the mission by raising the science orbit, the MRO Project chose to be the first orbiter to pursue the bio-burden reduction approach. Cleaning alone for a large orbiter like MRO is insufficient to achieve the bio-burden threshold requirement in NASA PP requirements. The burden requirement for an orbiter includes spores encapsulated in non-metallic materials and trapped in joints, as well as located on all internal and external surfaces (the total spore burden). Total burden estimates are dominated by the mated and encapsulated burden. The encapsulated burden cannot be cleaned. The total burden of a smaller orbiter (e.g., Mars Odyssey) likely could not have met the requirement by cleaning; for the large MRO it is clearly impossible. Of course, a system-level partial sterilization, with its attendant costs and system design issues, could have been employed. In the approach taken by the MRO Project, hardware which will burn up (completely vaporize or ablate) before reaching the surface or will at least attain high temperature (500 °C for 0.5 s or more) due to entry heating was exempt from burden accounting. Thus the bio-burden estimate was reduced. Lockheed Martin engineers developed a process to perform what is called breakup and burn-up (B&B) analysis. 2 Lockheed Martin Corporation. 2 The use of the B&B analysis to comply with the spore burden requirement is the main subject of this article. However, several components aboard the orbiter were predicted to fail the minimum time at temperature requirements (or could not conservatively be shown to meet the conditions). An implementation plan was generated to address the highest contributors to the bio-burden assessment that fail to meet the requirements. The spore burden for these components was estimated by direct and proxy burden assays, NASA PP specifications, and dry heat microbial reduction, as appropriate. Items on the orbiter that required rework during assembly were also individually assessed. MRO met the spore burden requirement based on the B&B analysis, the MRO Planetary Protection Implementation Plan, and verification by the NASA Planetary Protection Officer’s (PPO) independent assays. The compliance was documented in the MRO PP Pre-Launch Report. MRO was approved for flight by the NASA PPO.

Model-based investigation of a CO preferential oxidation reactor for polymer electrolyte fuel cell systems

This paper deals with a two-dimensional model of a preferential oxidation (PROX) reactor to be used in a beta 5 kWe hydrogen generator, named HYGen II, to integrate with polymer electrolyte fuel cells (PEFCs) for residential applications. The reactor geometrical configuration developed is a single-stage multi-tube configuration, in which a cocurrent air flow in the interspace is aimed at improving heat transfer and consequently controlling the temperature of the reactor. The aim of the model is to investigate the process performance of the reactor in order to enhance optimization and control of the PROX unit. The model concerns chemical kinetics and heat and mass transfer phenomena in the reactor. The model plays a key role in overcoming the issues of system design, by evaluating the temperature and the gas concentration profiles in the reactor. The CO removal from simulated reformate was examined with varying inlet temperature. Simulation results showed the strong dependence of the overall performance upon the reactor geometrical configuration.