A novel symmetrical 4H–SiC MESFET: an effective way to improve the breakdown voltage

In this paper, a novel symmetrical structure (SS) of 4H–SiC metal semiconductor field effect transistor (MESFET) as an effective way to improve the breakdown voltage is presented. The key idea in this work is to improve the breakdown voltage, maximum output power density, and frequency parameters of the device using a symmetrical structure with recessed gate. The SS-MESFET modifies the electric field in the drift layer significantly. The influence of the SS-MESFET on the saturation current, breakdown voltage \((\hbox {V}_{\mathrm{BR}})\), and small-signal characteristics of the SS-MESFET are studied by numerical device simulation. Using two-dimensional device simulation, we demonstrate that the breakdown voltage \((\hbox {V}_{\mathrm{BR}})\) improved by factors 2.5 and 3.3 in comparison with an asymmetrical conventional MESFET structure (AC-MESFET) and a symmetrical conventional MESFET structure (SC-MESFET), respectively. Also, the maximum output power density \((\hbox {P}_{\mathrm{max}})\) improved about by 93 and 250 % in comparison with the AC-MESFET and SC-MESFET structures, respectively. So, the SS-MESFET shows the superior maximum available gain (MAG), unilateral power gain (U), and current gain \((\hbox {h}_{12})\) which is presenting the proposed structure is more suitable device for high power microwave applications.     

Cured melamine systems as thick fire-retardant layers deposited by combination of plasma technology and dip-coating

Melamine and melamine resins are widely used as fire-retardants for polymer building materials. Cured melamine systems are used in heat-sensitive items, such as furniture and window frames and sills. In this work, differently cured methylated poly(melamine-co-formaldehyde) (cmPMF) resins were used as fire-retardant coverage for poly(styrene) (PS) and poly(ethylene) (PE) building materials. Such polymer layers should have several tenths of micrometers thickness to produce sufficient fire retardancy. These thick layers were produced by dip-coating. To promote sufficient adhesion of such thick coating to the polyolefin substrates, also in the case of high temperatures occurring at fire exposure, the polymer substrates were firstly coated with a few hundred nanometer thick adhesion-promoting plasma polymer layer. Such thin plasma polymer layers were deposited by low-pressure plasma polymerization of allyl alcohol (ppAAl). It was assumed that the hydroxyl groups of ppAAl interact with the melamine resin; therefore, ppAAl was well suited as adhesion promoter for thick melamine resin coatings. Chemical structure and composition of polymer films were investigated using infrared-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). Peel strengths of coatings were measured. After peeling, the peeled polymer surfaces were also investigated using optical microscopy and XPS the layers for identification of the locus of peel front propagation. Thermal properties were analyzed using TGA (thermo-gravimetric analyses). Finally, the fire-retardant properties of such thick coated polymers were evaluated by exposure to flames.     

The quantitative comparison of wash fastness improvement of acid and direct dyes on wool using full backtan,syntan, and syntan/cation system

Natural tannin, synthetic tanning agent (syntan), and syntan/cationic agent were applied on wool fabric dyed with different acid and direct dyes to improve the wash fastness of dyes. In this study, a method for quantitative and exact assessment of dye removal after washing from dyed samples was used. Firstly, the optimum operating parameters for application of full backtan and syntan were determined. Then the dyed wool samples were aftertreated, using natural tannin, syntan, and syntan/cationic agent. It was found that all aftertreatments improved the wash fastness. However, aftertreatment with natural tannin improved wash fastness to the greatest extent. In the case of syntan, sequential application of cationic agent on syntaned fabric obtained further improvement in wash fastness.     

One-factor-at-a-time (OFAT) optimization of hemicellulases production from Fusarium moniliforme in submerged fermentation

Hemicellulose degrading enzymes play an important role in bioconversion of lignocellulosic and agro-industrial wastes. In this study, production of hemicellulase by six fungal isolates was determined under submerged culture using corn cobs xylan as a carbon source and enzyme inducer at different incubation periods. The results indicated that Alternaria tenuis showed the lowest enzyme productivity (156.95 ± 2.07U/l) while the highest enzyme production (2,594.44 ± 62.25 U/l) was obtained by Fusarium moniliforme. One-factor-at-a-time revealed maximum enzyme productivity of 10,950.11 ± 98.45 U/l at corn cobs xylan (6 g/l), yeast extract (4 g/l), inorganic salts (1.5 g/l KH₂PO₄, 1.0 g/l MgSO₄.7H₂O, 0.2 g/l CaCl₂, 0.4 g/l FeSO₄.7H₂O, and 0.3 g/l MnSO₄.5H₂O), initial pH (5), initial inoculum size (4%), 150 rpm, and temperature (30°C) in a submerged fermentation process.     

Distinct element modelling of fracture plan control in continuum and jointed rock mass in presplitting method of surface mining

Controlled blasting techniques are used to control overbreak and to aid in the stability of the remaining rock formation. Presplitting is one of the most common methods which is used in many open pit m...     

Enhancing the learning process with expert systems

The purpose of this paper is to show how expert systems are used to enhance the learning process or improve basic skills of students. It provides resource material to business faculty for the teaching of a one or two session module on expert systems in a graduate or undergraduate statistics class. After briefly introducing the concept of expert systems and discussing their potential uses in education, a student exercise involves using STAT-EXPERT, an expert system designed to help students in selecting the appropriate statistical analysis technique for a mini case situation described in the exercise.     

A new feature subset selection using bottom-up clustering

Feature subset selection and/or dimensionality reduction is an essential preprocess before performing any data mining task, especially when there are too many features in the problem space. In this paper, a clustering-based feature subset selection (CFSS) algorithm is proposed for discriminating more relevant features. In each level of agglomeration, it uses similarity measure among features to merge two most similar clusters of features. By gathering similar features into clusters and then introducing representative features of each cluster, it tries to remove some redundant features. To identify the representative features, a criterion based on mutual information is proposed. Since CFSS works in a filter manner in specifying the representatives, it is noticeably fast. As an advantage of hierarchical clustering, it does not need to determine the number of clusters in advance. In CFSS, the clustering process is repeated until all features are distributed in some clusters. However, to diffuse the features in a reasonable number of clusters, a recently proposed approach is used to obtain a suitable level for cutting the clustering tree. To assess the performance of CFSS, we have applied it on some valid UCI datasets and compared with some popular feature selection methods. The experimental results reveal the efficiency and fastness of our proposed method.     

A new order splitting model with stochastic lead times for deterioration items

In unreliable supply environments, the strategy of pooling lead time risks by splitting replenishment orders among multiple suppliers simultaneously is an attractive sourcing policy that has captured the attention of academic researchers and corporate managers alike. While various assumptions are considered in the models developed, researchers tend to overlook an important inventory category in order splitting models: deteriorating items. In this paper, we study an order splitting policy for a retailer that sells a deteriorating product. The inventory system is modelled as a continuous review system (s, Q) under stochastic lead time. Demand rate per unit time is assumed to be constant over an infinite planning horizon and shortages are backordered completely. We develop two inventory models. In the first model, it is assumed that all the requirements are supplied by only one source, whereas in the second, two suppliers are available. We use sensitivity analysis to determine the situations in which each sourcing policy is the most economic. We then study a real case from the European pharmaceutical industry to demonstrate the applicability and effectiveness of the proposed models. Finally, more promising directions are suggested for future research.     

Analysis and modeling of unipolar junction transistor with excellent performance: a novel DG MOSFET with $${N}^{+}{-}{P}^{-}$$ junction

We propose herein a new dual-gate metal–oxide–semiconductor field-effect transistor (MOSFET) with just a unipolar junction (UJ-DG MOSFET) on the source side. The UJ-DG MOSFET structure is constructed from an \({N}^{+}\) region on the source side with the rest consisting of a \({P}^{-}\) region over the gate and drain, forming an auxiliary gate over the drain region with appropriate length and work function (named A-gate), converting the drain to an \({N}^{+}\) region. The new structure behaves as a MOSFET, exhibiting better efficiency than the conventional double-gate MOSFET (C-DG MOSFET) thanks to the modified electric field. The amended electric field offers advantages including improved electrical characteristics, reliability, leakage current, \({I}_{\mathrm{ON}}/I_{\mathrm{OFF}}\) ratio, gate-induced drain leakage, and electron temperature. Two-dimensional analytical models of the surface potential and electric field over the channel and drain are applied to investigate the drain current in the UJ-DG MOSFET. To confirm their accuracy, the MOSFET characteristics obtained using the 2D Atlas simulator for the UJ-DG and C-DG are analyzed and compared.     

Trapping polystyrene and latex nanospheres inside hollow nanostructures using Staphylococcus aureus cells

A new methodology was developed to trap polystyrene or latex nanospheres in nanocrystalline nickel columnar nanostructures with various cross-sectional geometries. After filling the column interiors with polystyrene or latex nanospheres with diameters of ～300 and 500 nm, respectively, the top openings of these small metallic nanopillars were capped with Staphylococcus aureus (S. aureus) bacterial cells. High resolution scanning electron microscopy inspection revealed that these bacterial cells were able to cover the top openings of C-shaped pillars within an hour of incubation at 37 °C. Results also demonstrated that capping S. aureus adhesive strengths to the nickel structures are greater than the cell wall cohesive strengths.