Critical Design Issues Research Articles

Water supply development for a new 17.5 MGD (66,200 m3/d) brackish-water RO facility for the City of Hialeah, Florida

Freshwater supply limitations in Southeast Florida have caused a change in the water supply strategy for the next 30 years. As a result of the move away from the use of fresh groundwater, a 17.5 MGD (66,200 m3/d) brackish-water desalination plant is under design for the City of Hialeah, Florida. Feedwater for this facility will be developed from the upper part of the Floridan Aquifer System at depths ranging from 1,080 to 1,480 ft (329–451 m) below surface. The initial water quality is mildly brackish with a total dissolved solids concentration (TDS) of about 2,300 mg/l. The anticipated volume of raw water required to operate the RO plant will be about 23.3 MGD (88,200 m3/d). The raw water will be obtained from 12 primary production wells and two backup capacity wells. A critical design issue for any RO plant is the maintenance of feedwater quality over the operating life-cycle of the facility. The wellfield water quality is anticipated to change in time because of the upward leakage of greater salinity w...

Long-Term Reinforcement Load of Geosynthetic-Reinforced Soil Retaining Walls

As increasing number of geosynthetic-reinforced soil (GRS) retaining walls are built for permanent purpose, and their long-term behaviors have become one of the most critical issues in design. However, there has been very limited study on long-term reinforcement load and its relation to various parameters of GRS walls. A finite-element procedure for the long-term response of geosynthetic-reinforced soil structures with granular backfills was first validated against the long-term model test. Extensive finite-element analyses considering the viscous properties of geosynthetic reinforcements were then carried out to investigate the load distributions in geosynthetic reinforcements of GRS walls under operational condition. Construction sequence was simulated and a creep analysis of 10 years was subsequently conducted on each model wall. The effects of wall parameters, including backfill soil, reinforcement length, reinforcement spacing, reinforcement stiffness, and creep rate of reinforcement were investigate...

Optimization of multilevel power adjustment in wireless sensor networks

Restricted to the limited battery power of nodes, energy conservation becomes a critical design issue in wireless sensor networks (WSNs). Transmission with excess power not only reduces the lifetime of sensor nodes, but also introduces immoderate interference in the shared radio channel. It is ideal to transmit packets with just enough power. In this paper, we propose a multilevel power adjustment (MLPA) mechanism for WSNs to prolong the individual node lifetime and the overall network lifetime. The energy conservation is achieved by reducing the average transmission power. The analytical model is built for the MLPA mechanism enabled with k distinct power levels (k-LPA). Under a free space loss (path loss exponent ?=2) model, the closed-form expression of optimal power setting is derived and the average transmission power can be minimized as (k+1)/2k of original fixed power. For wireless environment other than the free space loss model (??2), a recursive formula expression set is established to acquire the optimal power configuration and the minimum average transmission power, which is 2P/(?+2) as k approaches infinity. Furthermore, to reduce the computing complexity and the effort of measuring path loss exponent, two approximated power configuration methods are proposed. The analytical results show that both the proposed approximate methods are near-optimal solutions for most of the wireless communication environments. It can be shown that lim? k?? P avg ~I (k,?)=lim? k?? P avg ~II (k,?)=lim? k?? P avg min? (k,?)=2P/(?+2).

Design of the Dubai Metro light rail viaducts—substructure

The Dubai Metro light rail scheme is a flagship project in the United Arab Emirates which is currently one of the largest civil engineering projects under construction and, when completed, will be the longest fully automated rail system in the world. The first section of the rail system is due to be opened in September 2009. This paper describes the scheme outline and contractual set-up for the viaduct design and discusses the design and construction of the viaduct substructure. In particular, the design methodologies used for the piled foundations, single reinforced concrete columns and prestressed concrete pier heads are discussed as well as the design of elastomeric bearings that were used extensively for most of the viaduct spans. Seismic loading governed the design of many of the foundations and the seismic analysis and design methodology adopted is discussed, together with specific reinforcement detailing requirements. Rail–structure interaction analysis and design is also covered. Other critical design issues resolved included the fatigue performance of cranked reinforcement and the treatment of the onerous construction loading from overhead gantries used to erect the precast deck segments.

Evidence synthesis as the key to more coherent and efficient research

BackgroundSystematic review and meta-analysis currently underpin much of evidence-based medicine. Such methodologies bring order to previous research, but future research planning remains relatively incoherent and inefficient.MethodsTo outline a framework for evaluation of health interventions, aimed at increasing coherence and efficiency through i) making better use of information contained within the existing evidence-base when designing future studies; and ii) maximising the information available and thus potentially reducing the need for future studies.ResultsThe framework presented insists that an up-to-date meta-analysis of existing randomised controlled trials (RCTs) should always be considered before future trials are conducted. Such a meta-analysis should inform critical design issues such as sample size determination. The contexts in which the use of individual patient data meta-analysis and mixed treatment comparisons modelling may be beneficial before further RCTs are conducted are considered. Consideration should also be given to how any newly planned RCTs would contribute to the totality of evidence through its incorporation into an updated meta-analysis. We illustrate how new RCTs can have very low power to change inferences of an existing meta-analysis, particularly when between study heterogeneity is taken into consideration.ConclusionWhile the collation of existing evidence as the basis for clinical practice is now routine, a more coherent and efficient approach to planning future RCTs to strengthen the evidence base needs to be developed. The framework presented is a proposal for how this situation can be improved.

Critical issues in telecollaborative task design

In this article we examine how instructors make decisions about task design in telecollaboration and the factors that influence these decisions during the actual implementation of the tasks. We begin with a review of the recent literature of online intercultural exchanges to identify and describe a typology of 12 different types of tasks and task sequences. Next, we illustrate through two case studies – both post-secondary telecollaborative exchanges between learners of English and Spanish – how such decisions about task design are reached by partner instructors prior to an exchange, and how that task design is negotiated throughout the exchange with different consequences on the learning outcomes. Finally, based on this two-step analysis, we make recommendations about factors that instructors and researchers should consider when designing and implementing tasks for their telecollaborative exchanges.

Mobile business models: organizational and financial design issues that matter

Designing viable mobile services and business models that capture value for all the organizations involved is a challenge. There are many design issues that can be taken into account, and it is often unclear what their ultimate effect is on the performance of a business model. This paper offers a framework for relating critical design issues to success factors and tests the causal relationship between these core concepts in the organizational and financial domain of mobile business models, based on an international survey among 120 practitioners and experts in the mobile Internet services domain, most of them from EU countries. According to our findings, addressing organizational design issues (i.e. partner selection, governance and relation management) leads to an acceptable division of roles among actors, while addressing financial design issues (i.e., pricing, division of investments and costs among partners) results in risk levels that are perceived to be acceptable. The level of profitability that is perceived to be acceptable is influenced indirectly by these design issues, because the relationships are mediated through the risk level that the actors involved perceive to be acceptable and through the way the roles are divided among the actors.

Can Driving Simulators Contribute to Solving Critical Issues in Geometric Design?

Research on driving simulation in virtual reality has not been recommended by strategic documents for solving critical issues in geometric design. However, several research efforts have demonstrated the usefulness of driving simulators in road design. The objective of this paper is to initiate a discussion on the effective contribution of driving simulators to issues of geometric design. The paper gives an overview of the main experiences acquired in geometric design using advanced driving simulators and points out their potential as well as their limits. It then outlines the critical issues in promoting their use in geometric design and provides recommendations for overcoming these issues.

A hybrid 5-axis CNC milling machine

Abstract 5-Axis CNC milling machines are important in a number of industries ranging from aerospace to consumer-die-mold machining because they can deliver high machining accuracy with a spindle tilting capacity. Most of these machines have serial mechanisms so that modest static and dynamic stiffness become very critical design issues when high speed machining capability is required. Parallel mechanisms have recently received attention from machine tool designers because of their inherent potential for stiffness and because of their compactness. However, much of the promised advantages of parallel machines only occur within a very small region of their workspace. We discuss some of the kinematic and structural challenges to extract machining performance from serial and parallel machines. We compare a hybrid machine, which combines serial and parallel mechanisms, with typical serial and parallel machines such as Euler angle machines and a hexapod. In particular, we consider singularities, reversal characteristics, and manufacturability. We show that hybrid machines can benefit from the advantages of serial and parallel mechanisms while avoiding most potential pitfalls. However, hybrid structures can suffer from the manufacturing problem of over-constraint. We show that the degree of over-constraint depends on machine size. We have designed a small hybrid 5-axis motion platform, the MIT-SS-1, which can tolerate this over-constraint through a novel layout of axes. We show that this structure has potential as a small 5-axis CNC milling machine.

Frame Buffer Access Reduction for MPEG Video Decoder

Frame buffer power consumption and bandwidth requirement are two critical design issues in MPEG video decoders due to the overwhelming amount of frame data accesses. This paper proposes a reusable macroblock detector (RMD) which exploits the characteristic of a stationary macroblock (MB) to identify the reusable MBs in the frame buffer and avoid unnecessary data transfers. The RMD on average reduces about one quarter of the frame buffer accesses for 18 video sequences.

Automated module assignment in stacked-Vdd designs for high-efficiency power delivery

With aggressive reductions in feature sizes and the integration of multiple functionalities on the same die, bottlenecks due to I/O pin limitations have become a critical issue in today's VLSI designs, especially for 3D IC technologies. To alleviate the pin limitation problem, a stacked-Vdd circuit paradigm has recently been proposed in the literature. However, for a circuit designed using this paradigm, a significant amount of power may be wasted if modules are not carefully assigned to different Vdd domains. In this article, we present a partition-based algorithm for efficiently assigning modules at the floorplanning level, so as to reuse currents between Vdd domains and minimize the power wasted during the operation of the circuit. Experimental results on both 3D and 2D ICs show that compared with assigning modules to different Vdd domains using enumeration and simulated annealing, our algorithm can generate circuits with competitive power and IR noise performance, while being orders of magnitude faster.

Model-based analysis of reactor geometrical configuration on CO preferential oxidation performance

Abstract Modeling studies have been conducted on Preferential Oxidation (PROX) Reaction, covering chemical kinetics and heat/mass transfer phenomena that occur in a shell and tube system, to be used in a beta 5 kWe hydrogen generator for Polymer Electrolyte Fuel Cells (PEFCs). The critical issue in the PROX reactor design is to achieve temperature control along the catalyst bed, because poor selectivities primarily result from excess reactor temperature. Aim of the model is to investigate the effects of the reactor dimensions on process performance, in order to obtain high CO conversion and high selectivity with respect to the undesired H 2 oxidation. The CO removal from simulated reformate was examined, by evaluating the temperature and the gas concentration profiles along the reactor. The sensitivity analysis showed that the overall performance is strongly dependent upon the geometrical configurations examined.

Photonic Networks-on-Chip for Future Generations of Chip Multiprocessors

The design and performance of next-generation chip multiprocessors (CMPs) will be bound by the limited amount of power that can be dissipated on a single die. We present photonic networks-on-chip (NoC) as a solution to reduce the impact of intra-chip and off-chip communication on the overall power budget. A photonic interconnection network can deliver higher bandwidth and lower latencies with significantly lower power dissipation. We explain why on-chip photonic communication has recently become a feasible opportunity and explore the challenges that need to be addressed to realize its implementation. We introduce a novel hybrid micro-architecture for NoCs combining a broadband photonic circuit-switched network with an electronic overlay packet-switched control network. We address the critical design issues including: topology, routing algorithms, deadlock avoidance, and path-setup/tear-down procedures. We present experimental results obtained with POINTS, an event-driven simulator specifically developed to analyze the proposed idea, as well as a comparative power analysis of a photonic versus an electronic NoC. Overall, these results confirm the unique benefits for future generations of CMPs that can be achieved by bringing optics into the chip in the form of photonic NoCs.

A frequent-pattern approach for optical networks routing planning

Optical burst switching (OBS) networks have been receiving much attention as a promising approach to build the next generation optical Internet. In the bufferless DWDM switching technology, burst loss that should be minimized is the key design parameter. One of the critical design issues in OBS network is how to plan the optimal routing path in order to minimize burst dropping due to network resource contention. This study proposes the burst frequent-pattern tree (BFP-Tree) approach to pre-determine a suitable routing path in the OBS network. The BFP-Tree approach essentially is a learning-based mechanism that is able to determine a suitable transmission path from the historical network transaction data. The experiment results show that the successful rates of routing paths obtained by the BFP-Tree approach are able to converge to those of the optimal results.

Treating obstructive sleep apnea in adults with epilepsy

Small uncontrolled series suggest that treatment of obstructive sleep apnea (OSA) in patients with epilepsy may improve seizure control. Prior to conducting a definitive randomized controlled trial, we addressed critical design issues in a pilot study. We identified a cohort of adult patients with medically refractory epilepsy and coexisting OSA, documented by polysomnography (PSG). After an 8-week baseline period, subjects with OSA were randomized to therapeutic or sham continuous positive airway pressure (CPAP) for 10 weeks. Subjects maintained seizure calendars and antiepileptic drug dosages were held constant. Sixty-eight subjects with suspected OSA were enrolled and 35 subjects randomized to therapeutic CPAP (22 subjects) or sham (13 subjects) CPAP. Male gender and an elevated sleep apnea questionnaire score were predictive of OSA on PSG. Nineteen subjects in the therapeutic group and all 13 subjects in the sham group completed the trial. Baseline apnea-hypopnea index (AHI) and CPAP adherence were comparable between groups. A significant reduction in AHI was observed in the therapeutic CPAP group as compared to the sham group. Subjects, study coordinators, and principal investigators were unable to predict treatment allocation. This pilot study provided critical information related to study design and feasibility for planning a comprehensive trial to test the hypothesis that treating obstructive sleep apnea in patients with epilepsy improves seizure control.

Advanced Low-Noise X-Ray Readout ASIC for Radiation Sensor Interfaces

A VLSI readout front-end architecture, dedicated for X-ray imaging, using specific capacitive silicon detectors, with capacitance ranging from 2 to 10 pF, is described. Critical design issues such as the noise optimization and the shaper implementation technique are addressed and the first performance - test results of a fabricated prototype in a 0.35-mum 3.3-V CMOS process, are presented. Important feature of the design is the novel CR - RC2 pulse-shaper configuration since in this section, transconductor circuits are used in order to provide a broad range of continuous variable peaking time, programmable gain and adjustable undershoot while still maintaining the noise performance and the required linearity of the specific radiation detection application. Regarding the readout ASIC performance characteristics, the power consumption is 1 mW per channel, the equivalent noise charge at 1.81-mus peaking time is 382 e- plus 21 e- per picofrard of detector capacitance. The topology achieves a conversion gain equal to 3.31 mV/fC and a linearity of 0.69%.

Magnetically and optoelectronically isolated trigger for pulse-power applications

In this article the design of a magnetically and optically isolated trigger is discussed. Critical issues for trigger design are presented together with some experimental usages. In this trigger, an optical coupler is used to cut off the ground loop between the circuits of the preceding control system and the power supplies of the double functional device KT-5D (as a simple magnetic torus or a tokamak). A magnetic coupler is used to provide a pulse-power output for the silicon controlled rectifier. The output is a 230 mus transistor-transistor logic (TTL) with an amplitude of 3.0 V. The rising time and the trailing time are no more than 4.0 mus. The delay time between the input and the output of the trigger is 6.8+/-0.2 mus. A resistance-capacity branch is integrated into the trigger to provide an adjustable delay time of up to 72 ms. The zero quiescent dissipation character endows the trigger with a long lifetime of years dispensing with any charging or replacing batteries. It is observed that the trigger has a good stability even in a high electromagnetic circumstance (at the order of 1 T). Using it as a trigger for the silicon controlled rectifier, we realized the compatible operation of the steady state mode and the pulse mode in KT-5D.

Route-following assistance for travelers with cognitive impairments: A comparison of four prompt modes

Navigational skills, which are fundamental to community travel and hence, personal independence, are often disrupted in people with cognitive impairments. Assistive technology, in the form of navigation devices, are being developed that can support community navigation by delivering directional information. Selecting an effective mode to provide route-prompts is a critical design issue. This study evaluated the differential effects on pedestrian route following using different modes of prompting delivered via an electronic device for travelers with severe cognitive impairments. The research design used was a within subject comparison to evaluate potential differences in route-following performance when travelers received directions using four different prompt modes: (1) aerial map image, (2) point of view map image, (3) audio direction/no image and (4) text-based instructions/no image. Twenty travelers with severe cognitive impairments due to acquired brain injury walked four equivalent routes using four different prompting modes delivered via a wrist-worn navigation device. Navigation scores were computed that captured accuracy and confidence during navigation. Results of the repeated measures analysis of variance suggested that participants performed best when given prompts via speech-based audio directions. The majority of the participants also preferred this prompting mode. Findings are interpreted in the context of cognitive resource allocation theory.

Efficient tag detection in RFID systems

Recent technological advances have motivated large-scale deployment of RFID systems. However, a number of critical design issues relating to efficient detection of tags remain unresolved. In this paper, we address three important problems associated with tag detection in RFID systems: (i) accurately detecting RFID tags in the presence of reader interference ( reader collision avoidance problem); (ii) eliminating redundant tag reports by multiple readers ( optimal tag reporting problem); and (iii) minimizing redundant reports from multiple readers by identifying a minimal set of readers that cover all tags present in the system ( optimal tag coverage problem). The underlying difficulties associated with these problems arise from the lack of collision detection mechanisms, the potential inability of RFID readers to relay packets generated by other readers, and severe resource constraints on RFID tags. In this paper we present a randomized, distributed and localized Reader Collision Avoidance (RCA) algorithm and provide detailed probabilistic analysis to establish the accuracy and the efficiency of this algorithm. Then, we prove that the optimal tag coverage problem is NP-hard even with global knowledge of reader and tag locations. We develop a distributed and localized Redundant Reader Elimination (RRE) algorithm, that efficiently identifies redundant readers and avoids redundant reporting by multiple readers. In addition to rigorous analysis of performance and accuracy, we provide results from elaborate simulations for a wide range of system parameters, demonstrating the correctness and efficiency of the proposed algorithms under various scenarios.

The development of medical microrobots: a review of progress

PurposeThe purpose of this paper is to provide a review of recent progress in the development of medical microrobots.Design/methodology/approachThe paper first considers some of the critical aspects of medical microrobot design and then illustrates the present state of development through examples of prevailing research.FindingsThis paper shows that medical microrobot developments are at an early stage and involve a disparate family of technologies and disciplines, such as MEMS, nanotechnology, biomimetics and hydrodynamics. Critical design issues include power sources, propulsion and location, and many different schemes have been proposed. These are the topic of a growing body of academic research.Originality/valueThis paper provides a detailed insight into the present‐day state of medical microrobot technology and development.