Analysis of phosphorus removal and anaerobic selector performance in a full-scale activated sludge process in Singapore.

This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed.     

用于控制变速电动机的功率模块

改善洗衣机、电冰箱以及空调等家用电器能源使用效率的需求正在增加。从传统的固定转速马达转换到变速马达可以节省能耗30％之多。但这种设计的难度较大，虽已经出现了几种方案来降低此类项目的数字设计工作难度，但是设计人员仍需要集成模块和相关的设计工具来促进功率级的设计。为了使低成本变速马达控制器成为可能，元器件供应商设法通过简化设计和降低结构复杂度来减少变速控制器的成本。例如，已经出现了几种数字信号控制平台，它们结合了DSP和集成PWM和马达控制外围设备的RISC处理器。这些平台可运行第三方或者自行开发的马达控制算法。     

A radix-8 wafer scale FFT processor

Wafer Scale Integration promises radical improvements in the performance of digital signal processing systems. This paper describes the design of a radix-8 systolic (pipeline) fast Fourier transform processor for implementation with wafer scale integration. By the use of the radix-8 FFT butterfly wafer that is currently under development, continuous data rates of 160 MSPS are anticipated for FFTs of up to 4096 points with 16-bit fixed point data.     

Simulation of leachate migration in leaky aquifers

A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect.     

BATCH SEQUENCING

Consider the single machine scheduling problem where there are a number of part types to be processed. A part type is defined as follows: Two parts are of the same part type if the machine does not require a setup in between the processing of these parts. The problem investigated in this paper is to find a sequence of batches of parts (if there are any) where all the requirements for parts are met. A heuristic and an exact algorithm are developed, and computational analysis is performed to measure the performance of the heuristic. The time complexity function of the heuristic is O(n²), and the exact algorithm runs in polynomial time given a fixed upper bound on the number of setups.     

Microstructural effects on the tensile properties and deformation behavior of a Ti-48Al gamma titanium aluminide

The effects of microstructure on the tensile properties and deformation behavior of a binary Ti-48Al gamma titanium aluminide were studied. Tensile-mechanical properties of samples with microstructures ranging from near γ to duplex to fine grained, near- and fully-lamellar were determined at a range of temperatures, and the deformation structures in these characterized by transmission electron microscopy (TEM). Microstructure was observed to exert a strong influence on the tensile properties, with the grain size and lamellar volume fraction playing connected, but complex, roles. Acoustic emission response monitored during the tensile test revealed spikes whose amplitude and frequency increased with an increase in the volume fraction of lamellar grains in the microstructure. Analysis of failed samples suggested that microcracking was the main factor responsible for the spikes, with twinning providing a minor contribution in the near-lamellar materials. The most important factor that controls ductility of these alloys is grain size. The ductility, yield stress, and work-hardening rate of the binary Ti-48Al alloy exhibit maximum values between 0.50 and 0.60 volume fraction of the lamellar constituent. The high work-hardening rate, which is associated with the low mobility of dislocations, is the likely cause of low ductility of these alloys. In the near-γ and duplex structures, slip by motion of 1/2<110] unit dislocations and twinning are the prevalent deformation modes at room temperature (RT), whereas twinning is more common in the near- and fully-lamellar structures. The occurrence of twinning is largely dictated by the Schmid factor. The 1/2<110] unit dislocations are prevalent even for grain orientations for which the Schmid factor is higher for <101] superdislocations, though the latter are observed in favorably oriented grains. The activity of both of these systems is responsible for the higher ductility at ambient temperatures compared with Al-rich single-phase γ alloys. A higher twin density is observed in lamellar grains, but their propagation depends on the orientation and geometry of the individual γ lamellae. The increase in ductility at high temperatures correlates with increased activity of 1/2<110] dislocations (including their climb motion) and twin thickening. The role of microstructural variables on strength, ductility, and fracture are discussed. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Morphological changes in poly(?-caprolactone) in dense carbon dioxide

Morphological changes that take place in poly(?-caprolactone) upon exposure to carbon dioxide at high pressures have been explored as a function of pressure and temperature. SEM and DSC results point to a competition between CO₂-modulated crystallization and pressure-induced phase separation which leads to unique morphologies. At 293 K, exposure to CO₂ at pressures up to 45 MPa leads to recrystallization resulting in higher level of crystallinity and higher melting temperatures. Highest crystallinity levels along with distinct crystal morphology were observed after exposure to CO₂ at 308 K and 21 MPa. At a higher pressure at this temperature (308 K/34 MPa) polymer undergoes melting, and foaming is achieved during depressurization prior to solidification. At 323 K, the polymer is found to display unique crystal morphology with concave crystal geometry as well as porous domains. The results are discussed in terms of the crystallization and phase separation paths that are followed during exposure to CO₂ and the depressurization stages.     

Optimal operation of a multibasin reservoir system

A simulation-optimization procedure is presented for evaluating the extent of interbasin transfer of water in the Peninsular Indian river system consisting of 15 reservoirs on four river basins. A system-dependent simulation model is developed incorporating the concept of reservoir zoning to facilitate releases and transfers. The simulation model generates a larger number of solutions which are then screened by the optimization model. The Box complex nonlinear programming algorithm is used for the optimization. The performance of the system is evaluated through simulation with the optimal reservoir zones with respect to four indices, reliability, resiliency, vulnerability and deficit ratio. The results indicate that by operating the system of 15 reservoirs as a single unit the existing utilization of water may be increased significantly.     

Densely connected convolutional networks-based COVID-19 screening model

The extensively utilized tool to detect novel coronavirus (COVID-19) is a real-time polymerase chain reaction (RT-PCR). However, RT-PCR kits are costly and consume critical time, around 6 to 9 hours to classify the subjects as COVID-19(+) or COVID-19(-). Due to the less sensitivity of RT-PCR, it suffers from high false-negative results. To overcome these issues, many deep learning models have been implemented in the literature for the early-stage classification of suspected subjects. To handle the sensitivity issue associated with RT-PCR, chest CT scans are utilized to classify the suspected subjects as COVID-19 (+), tuberculosis, pneumonia, or healthy subjects. The extensive study on chest CT scans of COVID-19 (+) subjects reveals that there are some bilateral changes and unique patterns. But the manual analysis from chest CT scans is a tedious task. Therefore, an automated COVID-19 screening model is implemented by ensembling the deep transfer learning models such as Densely connected convolutional networks (DCCNs), ResNet152V2, and VGG16. Experimental results reveal that the proposed ensemble model outperforms the competitive models in terms of accuracy, f-measure, area under curve, sensitivity, and specificity.

     

Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Partially crystalline Si₃N₄, with nanosized crystals and a specific surface area greater than 200 m²/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH₃ to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si₃N₄ proceeds with additional heating above 1400°C under N₂. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N₂, are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes.