Cap-layer and charge sheet effect in InP based pnp δ-doped heterojunction bipolar transistor

Microsystem Technologies - The effect of varying the cap layer and the δ doped charge sheet has been investigated for an InP based heterojunction bipolar transistor (HBT) using the SILVACO...     

Application of bacteria foraging algorithm in designing log periodic dipole array for entire UHF TV spectrum

In this article, an attempt has been made to revisit the design of well‐established log periodic dipole array (LPDA) in light of recent optimization technique, the bacteria foraging algorithm (BFA). Although there are many works published in the literatures based on various optimization techniques, this article deals with the optimization of the LPDA for the entire ultra high frequency (UHF) television (TV) spectrum (470–870 MHz) covering 400 MHz bandwidth and accommodating 49 channels. The challenges of this design lie in selecting suitable values of τ and σ for 134 frequency points for which different sets of all the output parameters such as gain, input impedance (Z_in), front‐to‐back ratio (FTBR), first side lobe level (FSLL), voltage standing wave ratio (VSWR), and so forth are obtained and then averaged over to get Gain_av, Z_inAav, FTBR_av, FSLL_av, and VSWR_av close to the desired values. These average values are used to design suitable fitness function. Another important aspect of this article is to provide exhaustive design details for LPDA using network theory that would couple to the BFA for getting the optimized number of elements to satisfy the desired values of Z_inav, Gain_av, FTBR_av, FSLL_av, and VSWR_av, set as 50 Ω, 9 dBi, 40 dB, 40 dB, and 1.1, respectively. Moreover, this LPDA design considers the standard wire gauge dipole elements, which is just a very practical approach in the design procedure. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Tribological Behavior of Acrylic Acid–Modified Date Palm Leaf–Reinforced Polyvinyl Alcohol Composite

Most machine components are frequently exposed to tribological loadings during their service life. Hence, the tribological performance of materials is an essential element to be considered in the design of mechanical parts in addition to mechanical properties. Previously, authors have studied the mechanical properties of date palm leaf–reinforced polyvinyl alcohol composite. In the present investigation, an attempt has been made to investigate the tribological behavior of the composite under a multipass abrasion condition. The composite was prepared by reinforcing randomly oriented acrylic acid–modified date palm leaf fibers with varying weight percentages of 10, 20, 28, and 30%. The performances of the specific wear rate and wear weight loss were investigated as a function of applied loads and abrading distances. It was observed that 28 wt% is the optimum fiber loading to achieve maximum tribological properties similar to mechanical properties obtained from previous work. Scanning electron microscopy was used to understand the wear mechanisms of the composite at optimum fiber loading.     

Wear damage of cemented carbides with different combinations of WC mean grain size and Co content. Part I: ASTM wear tests

In the present work we made and examined cemented carbides characterized by very different WC grain sizes varying from near-nano with a WC mean grain size of about 200 nm to coarse-grain with a WC mean grain size of about 4.5 μm and Co contents varying from 3 to 24 wt.%. The major objective of the present work was to examine the wear damage, wear behavior and wear mechanisms of cemented carbides having nearly the same hardness but greatly varying with respect to their WC grain size and Co content in the high-load ASTM B611 test and low-load G65 test.Both the hardness and resistance to fracture and micro-fatigue of cemented carbides play an important role in the wear damage by use of the high-stress ASTM B611 test when the carbide surface is subjected to alumina particles at high loads. In this case, the wear-resistance increases with increasing the WC mean grain size and decreasing the Co content at nearly the same hardness of the different cemented carbides. The submicron and near-nano cemented carbides are characterized by lower wear-resistance in comparison with the coarse-grain grade due to their reduced fracture toughness, fracture resistance and resistance to micro-fatigue.The Co mean free path in the carbide microstructure plays an important role with respect to wear-resistance in the low-stress ASTM G65 test when the carbide surface is subjected to gentle scratching by abrasive silica particles. The predominant wear of the thick Co interlayers leaving unsupported WC grains plays the decisive role in the wear behavior of the coarse-grain grade resulting in its low wear-resistance. In contrast to the ASTM B611 test the wear rate decreases with decreasing the WC mean grain size and increasing the Co content due to the corresponding reduction of Co mean free path in the carbide microstructure. As a result, the wear-resistance of the near-nano grade in the ASTM G65 test is the best of all in spite of its reduced fracture toughness.Phenomena of micro-fatigue, micro-fracturing and micro-chipping are found to play a decisive role in the wear damage of cemented carbides if they are subjected to abrasion wear, high loads and severe fatigue.     

Finding efficient assignments: An innovative DEA approach

Finding and classifying all efficient assignments for a Multi-Criteria Assignment Problem (MCAP) is one of the controversial issues in Multi-Criteria Decision Making (MCDM) problems. The main aim of this study is to utilize Data Envelopment Analysis (DEA) methodology to tackle this issue. Toward this end, we first state and prove some theorems to clarify the relationships between DEA and MCAP and then design a new two-phase approach to find and classify a set of efficient assignments. In Phase I, we formulate a new Mixed Integer Linear Programming (MILP) model, based on the Additive Free Disposal Hull (FDH) model, to gain an efficient assignment and then extend it to determine a Minimal Complete Set (MCS) of efficient assignments. In Phase II, we use the BCC model to classify all efficient solutions obtained from Phase I as supported and non-supported. A 4 × 4 assignment problem, containing two cost-type and single profit-type of objective functions, is solved using the presented approach.     

Determination of effective electrode configuration for electrical measurements of carbon thin conductive coatings

When electrical characterization of thin conductive coating is carried out, it requires an effective electrode configuration that prevents design problems due to low thickness, such as short circuits or electrode diffusion. In this work, two electrode configurations were carried out, surface and volume configurations, in order to compare and demonstrate the efficiency of surface electrode configuration for thin films. Highly conductive coatings based on carbon black (CB) have been prepared by the sol–gel method, and electrical properties were measured for both configurations, indicating that when the thickness of the film is low enough, the electrical conduction with the electrodes disposed on the surface is produced for the entire volume. This effect facilitates the design and treatment of the coating. This configuration could be very useful for many technological applications.     

Self-healable,Eu~(3+)-based polymeric gels containing terpyridyl groups with tunable luminescence based on ion recognition

Novel luminescent materials that change their emission colors in responding to external stimuli have attracted increasing attentions in the past decades.Herein,we report the preparation of a novel kind of Eu~(3+)-based polymeric organogel with three networks.With dynamic coordination interactions,the organogel shows fast self-healing and adjustable fluorescent emission properties in the presence of different metal ions via coordination interaction competition effect.Dynamic coordination interaction also endows the gel with multiple stimuli-responsive properties such as water,base and acid.The multistimuli responsive fluorochromic organogel demonstrates a new way of preparing optical materials and bio-relevant sensors.     

Use of shadows for extracting buildings in aerial images

Two new methods integrating region growing and edge detection are presented to extract buildings in aerial images. In the domain we are considering, building shadows play an important role in enhancing the detection accuracy and reliability. In both methods, interpretations of buildings are only based on the reliable features (shadows and shapes of buildings in our case) obtained by segmentation and are not affected by artifacts or sementation errors. We also propose algorithms to correct the segmentation errors or to enhance resultant contours based on local edge information (contrast and smoothness along contours) and global shape information. In the first method we start with an edge detection to loacte shadowed boundaries, then combine region growing to find boundaries without shadows. In the second method, we use region growing to obtain a primary segmentation. Edge information is then used to eliminate false boundaries or to modify the contours. Further modification of contour artifacts can be achieved by using domain knowledge (most boundaries are smooth enough to be approximated by straight segments.)     

The Future of Electric Transmission

Transmission sector problems require a new business and regulatory paradigm if electric power restructuring is to succeed. Performance-based regulation of for-profit transmission seems to be the best alternative.     

Effectiveness of fly ash for strength and durability of concrete

The effectiveness, K, of a fly ash can be defined as the ratio of the amount of cement replaced to the amount of fly ash added, provided the specified requirements of the concrete are maintained. It is generally assumed that the effectiveness of a fly ash can be treated as a constant. This paper presents results on concrete made with various mix proportions using three different cements and fly ash from three different sources. It was found that the K factor of each fly ash in achieving common 28-day compressive strength varies over a wide range depending on the amount of fly ash used, the type of cement, the incorporation of chemical admixtures and the particular strength level chosen. Besides strength, K can also be calculated for other properties. For the materials used in this investigation, the K factors with respect to carbonation were found to be unequal to K factors for strength.