Design of filter banks using transformation of variables: newresults

The design problem of multirate filter banks can be divided into two parts. The first part involves the issue of reconstruction errors. The second part involves the issue of designing good quality subband filters. There is a class of techniques that we refer to as transformation of variables which satisfactorily addresses the two parts of the design problem. This class of filter banks is specified by its prototype filters and transformation (kernel). It is the flexibility and relative ease in designing the kernel that enables the technique to satisfactorily address the second part of the design problem. We present two new methods of designing the kernel that will enhance the design techniques' flexibility and effectiveness. The first is the combination of the McClellan transformation and rotation operators. The second introduces and uses the concept of directional singular value decomposition (SVD)     

Fast alternating direction implicit method for efficient transient thermal simulation of integrated circuits

This paper presents fast alternating direction implicit (FADI) method for efficient transient thermal simulation of integrated circuits. The FADI method is formulated from Peaceman–Rachford's ADI and Douglas–Gunn's ADI methods. The update procedure of the proposed method has basic implicit form that features derivative‐free right‐hand side and hence, better efficiency and conciseness. Subsequently, through the basic implicit form of FADI method, the relationship between classical Peaceman–Rachford's and Douglas–Gunn's ADI methods can be clarified and elucidated in detail. A unified boundary condition that can cater to common kinds of boundary conditions in thermal simulation is also introduced. To further accelerate FADI method, the graphics processing unit is also utilized through Compute Unified Device Architecture implementation. It is shown that high efficiency gain can be achieved using the proposed FADI method through large time step size and data parallelism, while maintaining stability and good accuracy. As numerical illustration, an integrated circuit structure with microchannel cooling is demonstrated. Numerical results further ascertain the cooling effect of the microchannels. Copyright © 2015 John Wiley & Sons, Ltd.     

Production of hydrogen in a granular sludge-based anaerobic continuous stirred tank reactor

An investigation on biohydrogen production was conducted in a granular sludge-based continuous stirred tank reactor (CSTR). The reactor performance was assessed at five different glucose concentrations of 2.5, 5, 10, 20 and 40 g/L and four hydraulic retention times (HRTs) of 0.25, 0.5, 1 and 2 h, resulting in the organic loading rates (OLRs) ranged between 2.5 and 20 g-glucose/L h. Carbon flow was traced by analyzing the composition of gaseous and soluble metabolites as well as the cell yield. Butyrate, acetate and ethanol were found to be the major soluble metabolite products in the biochemical synthesis of hydrogen. Carbon balance analysis showed that more than half of the glucose carbon was converted into unidentified soluble products at an OLR of 2.5 g-glucose/L h. It was found that high hydrogen yields corresponded to a sludge loading rate in between 0.6 and 0.8 g-glucose/g-VSS h. Substantial suppression in hydrogen yield was noted as the sludge loading rate fell beyond the optimum range. It is deduced that decreasing the sludge loading rate induced the metabolic shift of biochemical reactions at an OLR of 2.5 g-glucose/L h, which resulted in a substantial reduction in hydrogen yield to 0.36–0.41 mol-_H2${\mathrm{H}}_2$/mol-glucose. Optimal operation conditions for peak hydrogen yield (1.84 mol-_H2${\mathrm{H}}_2$/mol-glucose) and hydrogen production rate (3.26 L/L h) were achieved at an OLR of 20 g-glucose/L h, which corresponded to an HRT of 0.5 h and an influent glucose concentration of 10 g/L. Influence of HRT and substrate concentration on the reactor performance was interrelated and the adverse impact on hydrogen production was noted as substrate concentration was higher than 20 g/L or HRT was shorter than 0.5 h. The experimental study indicated that a higher OLR derived from appropriate HRTs and substrate concentrations was desirable for hydrogen production in such a granule-based CSTR.     

Experimental and modeling studies of particle removal in post silicon chemical mechanical planarization cleaning process

Experiments were carried out in order to evaluate the particle removal efficiency from a wafer surface by means of a buffing disk in a process for flow rates of chemical media ranging from 3.33 × 10⁻⁶ m³/s to 6.67 × 10^− 6 m³/s, buffing disc pressures of 6.894 kPa to 20.684 kPa and three relative speeds were used in the experiments. A mathematical model which considered the toppling of a particle as a result of forces due to friction, hydrodynamic drag, adhesion and capillary phenomena was developed in order to correlate the particle removal efficiency with the flow rate, buffing disc pressure and relative rotational speed. Results of simulations of the model showed a good agreement with the experimental data with satisfactory correlation coefficients.     

A model for calculating channel share of 802.11 access points with overlapping wireless cells

Consider a collection of 802.11 access points. Each serves as the gateway to the Internet for clients in its WiFi cell. These cells have an arbitrary interference pattern, and reception at a client may be corrupted by transmissions nearby. The popularity of WiFi has made such dense deployment increasingly common. As interference can seriously degrade performance, there is much interest in optimizing the configuration of these cells. One factor to consider in optimization is channel share, defined as the useful fraction of channel bandwidth that an access point gets when there is downlink traffic saturation. Interference affects channel share on the sender side through carrier sensing and transmission deferral, and on the receiver side through collisions, which result in exponential backoff and retransmission. There exists a simple, “back-of-the-envelope” (BoE) technique to model the impact of pairwise sender-side interference. This paper tackles the harder task of determining the impact of receiver-side and non-pairwise sender-side interference. It proposes a technique for modeling the channel share of wireless links, and the accuracy is demonstrated with Qualnet simulation.     

Effects of roadside memorials on traffic flow

Despite their growing popularity in North America, little research has been conducted on understanding the effects of roadside memorials on drivers’ behaviour. In this study, we examined the short-term effects of roadside memorials on traffic speed and headways on a high speed intercity freeway as well as its long-term effect on traffic speed on a high speed urban freeway. Our study found that the placement of roadside memorials did not have any significant effect on traffic speeds or headways, either in the short or long term. Therefore, concerns about the negative effects on driver behaviour were not supported by this research, at least with regards to speeding and following too closely. However, no positive effects on safety were found either.     

Surface profile measurement in white-light scanning interferometry using a three-chip color CCD

White-light scanning interferometry (WLSI) is a useful technique to measure surface profile when a test object contains discontinuous structures or microstructures. A black and white CCD camera is usually utilized to capture interferograms, and a series of corresponding algorithms is used to achieve the profile measurement. However, the color information in the interferograms is lost. A novel profile measurement method that uses phase information in different color channels (red-green-blue) of an interferogram obtained using a three-chip color CCD in WLSI is proposed. The phase values are extracted by a windowed Fourier transform algorithm. Simulation and experimental results are presented to demonstrate the validity of the proposed method.     

Outcome of obstructive uropathy after pelvic irradiation in patients with carcinoma of the uterine cervix

A prospective, randomized study was performed to assess the effectiveness of postoperative closed suction drainage. One hundred and twelve consecutive procedures involving autologous iliac-crest bone graft were performed, from December 29, 1992, to July 1, 1993, following a traumatic injury of the spine in 108 patients. Sixty of the sites from which the bone graft had been obtained were drained with a single large Hemovac device. The drains were maintained for two to five days postoperatively. The remaining fifty-two incisions were closed without a drainage device. All patients were evaluated clinically for problems with wound-healing. The incisions were considered to be healed when they had been asymptomatic for one year. Of eleven patients who had problems with wound-healing, six had been managed with a drain and five had not. The findings of this study do not support the routine use of drainage at the donor sites of iliac-crest bone grafts.     

Media-Induced Hydraulic Behavior and Performance of Upflow Biofilters

Laboratory studies were conducted to assess the influence of media-related factors such as porosity, specific surface, and pore size on hydraulic behavior and performance of upflow anaerobic biofilters (ABFs). Three 15-L upflow biofilters, each packed with different support media, were subject to identical synthetic protein-carbohydrate substrate with chemical oxygen demand (COD) concentrations ranging from 2,500 to 10,000 mg∕L, and hydraulic retention times from 15 to 30 hours, corresponding to organic loading rates (OLRs) varying from 2 to 16 g COD∕L∕d. Tracer studies were carried out to characterize hydraulic behavior of the biofilters containing media with and without biomass, designated as dirty-bed and clean-bed, respectively. The results indicate that hydraulic flow regimes in all biofilters were characterized by a plug-flow pattern with a large extent of dispersion under clean-bed conditions. The tracer response curve under dirty-bed conditions operating at an OLR of 16 g COD∕L∕d reflects more closely the response of a mixed-flow reactor than that of a plug-flow unit, which suggests that there is significant short-circuiting in the ABFs. Waste treatment performance indicates that the biofilter associated with media of the largest pore size and porosity consistently demonstrated the highest COD removal from 96% to 73% at loadings varying from 2 to 16 g COD∕L∕d. The same reactor exhibited the lowest magnitude of dispersion along with minimum dead space within the bed from the tracer analysis. This implies that the use of support media with larger pore size and porosity may reduce the extent of short-circuiting, leading to better waste treatment performance. Increasing the media specific surface at the expense of media porosity may result in lower treatment performance in upflow anaerobic biofilters.