Low-bias performance of avalanche photodetector. A time-domainapproach

The performance of the InP-InGaAs avalanche photodiode (APD) at low bias voltages has been investigated directly from its impulse response without using any fitting parameters. The important mechanisms responsible for low-bias performance are the emission of holes from the InP-InGaAs interface potential-trap in the valence band, the velocity of the carriers, and the diffusion of photogenerated holes from the undepleted region to the depleted region of the absorption layer. A time-recurrence relation for the emission of holes from the trap has been derived and special attention has been paid to the velocity of carriers at low fields. The delay in the process of diffusion of photogenerated holes has been taken into account in obtaining the impulse response. The bandwidth at different gains have been calculated by taking the fast Fourier transform (FFT) of the current impulse response. The gain-bias and gain-bandwidth characteristics show reasonably good agreement between the data from the model and the experimental data of an earlier published work on InP-InGaAs APD     

Ki-1 large cell anaplastic lymphoma--a clinicopathological study

Ki-1 large cell anaplastic lymphoma is a recently described variant of malignant lymphoma. A retrospective study of 10 cases of Ki-1 lymphoma was carried out at the Armed Forces Institute of Pathology (AFIP) Rawalpindi to document its clinical and morphological features. The morphological features were evaluated by a study of paraffin embedded sections stained with haematoxylin and eosin stains. Immunohistochemical stains for BER-H2 and leucocyte common antigen (LCA) were performed in all cases. The age of the patients ranged from 2 to 60 years and male to female ratio was 2.3:1. Cervical lymphadenopathy was the most common presentation. Histologically, there was a complete effacement of the lymph node architecture in 8 cases. The Reed-Sternberg like cells were seen in 2 and histiocyte like cells in 7 cases. Immunohistochemically all cases were positive for BER-H2. It is suggested that the possibility of Ki-1 lymphoma should be considered in all cases of lymphoma with pleomorphic morphology.     

A lapping and polishing process to achieve high quality alumina surfaces for applications in device fabrication

A lapping process for achieving high quality alumina (Al₂O₃) surfaces was investigated. Alumina films were sputter deposited on thick TiC---Al₂O₃ ceramic wafers. Polishing of these films was carried out on pitch plates (organic resin melted and set on the circular disk of a lapping machine). Abrasives with different grit sizes, 0.05–1.0 μm, were tried together with different lapping process parameters. Qualitu of the lapped surface was studied in terms of roughness and flatness. Stock removal rates were also measured. Correlation of surface quality with lapping parameters was established to achieve process optimization.

Scratch-free polished alumina surfaces were obtained by using this technique. Specific applications of the process in the fabrication of magnetic recording devices are indicated.     

Architecture of a multipurpose simulator

This paper presents the development of a multipurpose simulator with the general model describing a four-component, three-phase (oil, aqua, gas), multi-dimensional, finite-difference polymer injection simulator. The model uses a block-centered grid and a seven-point finite-difference scheme. Fluid saturations and pressure distributions are obtained from a fully implicit formulation using Newton's method, whereas polymer concentration is obtained, in a subsequent step, explicitly using the method of cascade. Practical features of the present simulator include: (1) a truly multipurpose simulation; and (2) ease of preparing a batch data file required for the simulator. A novel and simple procedure is implemented to reduce the general model of the polymer injection simulator (polymer, oil, aqua, and gas) to: (1) three-phase black-oil simulator (oil, water, and gas); (2) two-phase black-oil simulators (oil and water, oil and gas, or water and gas); (3) two-phase polymer injection simulator (polymer, oil, and aqua); and (4) one-phase simulators (oil, water, or gas) with only the relevant equations being solved at the matrix level for each simulator. Guidelines for other practical features are also presented.The simulator was tested and verified using a polymer injection test problem and a gas injection bench mark test problem both reported in the literature. The simulator was also used to model a field case and some results are highlighted.     

Fatigue crack monitoring of riveted aluminium strap joints by Lamb wave analysis and acoustic emission measurement techniques

Statistics show that fatigue crack development comes first and foremost as a damage source in aerospace metallic structures. Currently, widespread methods are available to inspect these structures, but they are quite time-consuming, costly and require the structural system to be idle. Next, attempts to develop damage detection integrated systems are paramount for the safety and cost of such structures. This paper describes an investigation into the feasibility of using an integrated system based on Lamb waves in order to assess the integrity of riveted aluminium joints during cyclical loading. In this experimental analysis, Lamb waves are excited and received outside the joint area using piezoelectric transducers coupled onto the plates. The detected damage is cracks in joint resulting from fatigue loading. The collected signals on the piezoelectric transducers are analysed using Hilbert transform and time–frequency analysis. It is shown that the final interpretation of Lamb wave analysis may provide a means of sizing the defects and following the crack development. In addition to that, an acoustic emission system is used jointly with the Lamb wave analysis in order to discuss results and damage development. Finally, it is demonstrated that both methods can work together and the results obtained are in good agreement.     

Flower-like architecture of CoSn4 nano structure as anode in lithium ion batteries

CoSn₄ nano-particles were synthesized on Cu and Ni substrates through pulsed current electrodeposition and used as anode in lithium ion batteries. Nano particles with Flower-like morphology were obtained through applying an average current density of 85 mA/cm² on Ni substrate while the particles formed using constant current electrodeposition are greater in size ca. 500 nm. Optimum discharge capacity of synthesized CoSn₄ was obtained 848 mAh g^?1 which reduced to 500 mAh g^?1 at 120th cycle indicating an enhanced electrochemical performance compared to anode films synthesized through other pulsed current densities and also constant current electrodeposition. This high discharge capacity and cycleability is attributed to finer crystal grains and flower-like morphology of nano particles. Also, the sample synthesized on Ni substrate showed higher cycleability and noticeably lower resistance. High resistance of anode film synthesized on Cu substrate is due to the corrosion and passivation of copper occurred by HF formation in LiPF₆ electrolyte.     

Oxy‐fuel combustion technology: current status,applications, and trends

The increased level of emissions of carbon dioxide into the atmosphere due to burning of fossil fuels represents one of the main barriers toward the reduction of greenhouse gases and the control of global warming. In the last decades, the use of renewable and clean sources of energies such as solar and wind energies has been increased extensively. However, due to the tremendously increasing world energy demand, fossil fuels would continue in use for decades which necessitates the integration of carbon capture technologies (CCTs) in power plants. These technologies include oxycombustion, pre‐combustion, and post‐combustion carbon capture. Oxycombustion technology is one of the most promising carbon capture technologies as it can be applied with slight modifications to existing power plants or to new power plants. In this technology, fuel is burned using an oxidizer mixture of pure oxygen plus recycled exhaust gases (consists mainly of CO₂). The oxycombustion process results in highly CO₂‐concentrated exhaust gases, which facilitates the capture process of CO₂ after H₂O condensation. The captured CO₂ can be used for industrial applications or can be sequestrated. The current work reviews the current status of oxycombustion technology and its applications in existing conventional combustion systems (including gas turbines and boilers) and novel oxygen transport reactors (OTRs). The review starts with an introduction to the available CCTs with emphasis on their different applications and limitations of use, followed by a review on oxycombustion applications in different combustion systems utilizing gaseous, liquid, and coal fuels. The current status and technology readiness level of oxycombustion technology is discussed. The novel application of oxycombustion technology in OTRs is analyzed in some details. The analyses of OTRs include oxygen permeation technique, fabrication of oxygen transport membranes (OTMs), calculation of oxygen permeation flux, and coupling between oxygen separation and oxycombustion of fuel within the same unit called OTR. The oxycombustion process inside OTR is analyzed considering coal and gaseous fuels. The future trends of oxycombustion technology are itemized and discussed in details in the present study including: (i) ITMs for syngas production; (ii) combustion utilizing liquid fuels in OTRs; (iii) oxy‐combustion integrated power plants and (iv) third generation technologies for CO₂ capture. Techno‐economic analysis of oxycombustion integrated systems is also discussed trying to assess the future prospects of this technology. Copyright © 2017 John Wiley & Sons, Ltd.     

Electrophoretic deposition of graphene oxide on carbon brush as bioanode for microbial fuel cell operated with real wastewater

Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm^?2 to 381 mWm^?2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements.