Thermal Annealing and Propagation of Shockley Stacking Faults in 4H-SiC PiN Diodes

Stacking faults within 4H-SiC PiN diodes are known to be detrimental to device operation. Here, we present electroluminescence (EL) images of 4H-SiC PiN diodes providing evidence that electrically and optically stimulated Shockley stacking fault (SSF) propagation is a reversible process at temperatures as low as 210°C. Optical beam induced current (OBIC) images taken following complete optical stressing of a PiN diode and that lead to a small number of completely propagated SSFs provide evidence that such defects propagate across the n–/p+ interface and continue to grow throughout the p+ layer. These observations bring about questions regarding the validity of the currently accepted driving force mechanism for SSF propagation.     

Fractionation of Hydrophobic Organic Materials in Surface Microlayers

Organic microlayers occur naturally on the surfaces of most bodies of water. Hydrophobic organic materials such as longchain acids and hydrocarbons are constituents of these surface films and may be essential for their formation. Studies of these microlayer components have been primarily of marine locations, although several reports describing freshwater locations exist. Results of these studies are generally consistent with those of Lake Michigan surface films. Fractionation of fatty acids and alkanes according to differential solubility occurs to some extent but is complicated by other processes. Partitioning between dissolved and particulate phases appears to modify both input and removal effects, and purely physical phenomena such as sinking processes and turbulent mixing are also quite important. Evidence of aquatic, terrigenous, and eolian sources is preserved in microlayer components. Their relative contributions vary considerably but provide more information about surface/subsurface fractionation.     

Influence of Temperature on Shockley Stacking Fault Expansion and Contraction in SiC PiN Diodes

While Shockley stacking fault (SSF) creation and expansion within 4H-SiC bipolar devices is well known, only recently was it observed that this expansion and the associated increase in the forward voltage drop (V _f) could be completely reversed via low-temperature annealing. Here we report the temperature dependence of the recovery rate of the V _f drift via annealing, reporting an activation energy of 1.3 ± 0.3 eV. The V _f drift was observed to saturate following extended electrical stressing, and it was observed that the value of V _f at this saturation was inversely proportional to the stressing temperature. We also observed that SSF and V _f drift recovery could occur in highly stressed diodes at elevated temperatures even under high current injection conditions (14 A/cm²).     

Measuring End-to-End Delay in Low Energy SDN IoT Platform

In this paper, we developed a new customizable low energy Software Defined Networking (SDN) based Internet of Things (IoT) platform that can be reconfigured according to the requirements of the target IoT applications. Technically, the platform consists of a set of low cost and energy efficient single-board computers, which are interconnected within a network with the software defined configuration. The proposed SDN switch is deployed on Raspberry Pi 3 board using Open vSwitch (OvS) software, while the Floodlight controller is deployed on the Orange Pi Prime board. We firstly presented and implemented the method for measuring a delay introduced by each component of the IoT infrastructure, ranging from the sensor, the core of SDN, the IoT broker, to an IoT subscriber. Thus, we presented the approach for estimating energy efficiency for SDN based IoT platform proportional to the traffic. The experiments carried out on a real SDN topology based on single-board computers show that our approach not only saves up to 53.56% of energy at low traffic intensity, but also provides QoS guarantee for IoT applications.     

Comparative study on the densification process of different titanium powders

In the powder metallurgy of titanium and titanium alloys, titanium powders produced through hydrogenation/dehydrogenation (HDH) approach and titanium hydride powder are extensively used. The choice of initial powder greatly influences the properties and performance of as-sintered materials. In the present study, comparative experiments were performed on two powders of various sizes to elucidate the peculiarities of their densification process and the characteristics (as-sintered density, impurity content, and tensile properties) of the processed materials. As expected, the sintering performance of both powder-type compacts were greatly affected by the specific surface and contact areas, so finer powders and higher compaction pressures were used to achieve higher densities upon sintering. However, the systematic results clearly indicated the advantage of using titanium hydride powder as a starting material in titanium powder metallurgy. At equal size, compaction, and sintering parameters, materials processed from titanium hydride powder had higher density and lower impurity content, thereby providing better balance of tensile properties compared with materials processed from HDH titanium powder. This advantage is explained by the higher relative density of green compacts made of brittle titanium hydride powder and by the higher sintering ability of such compacts activated by powder-released hydrogen.     

Synthesis and characterization of novel antimicrobial polymers containing pendent triclosan moieties

Novel antimicrobial copolymers were produced by first converting the commodity biocide, triclosan (TCS), to an epoxy-functional derivative, 2-((5-chloro-2-(2,4-dichlorophenoxy)phenoxy) methyl)oxirane (ETCS), and then reacting ETCS with polyethylenimine (PEI). While neither ETCS or PEI showed high antimicrobial activity toward either the Gram-positive bacterium, Staphylococcus epidermidis, or the Gram-negative bacterium, Escherichia coli, some the copolymers showed very high activity toward both bacteria. Antimicrobial activity for these copolymers was found to be highly dependent on both the molecular weight of the PEI utilized and the concentration of pendent groups derived from ETCS. In general, decreasing PEI molecular weight and increasing TCS pendent group concentration increased antimicrobial activity. Surface tension measurements showed that the molecular parameters affecting antimicrobial activity also affected surface activity in a similar fashion. Thus, it was speculated that the mechanism of antimicrobial activity associated with these copolymers involves interaction of the copolymers with the bacterial cell wall. A comparison of the antimicrobial activity of the most effective copolymers to TCS showed that the copolymers were more effective toward E. coli than pure TCS when compared using an equivalent TCS content (i.e. TCS pendent group content for the copolymers). This characteristic coupled with the fact that the TCS-containing copolymers are highly aqueous soluble liquids as opposed to a crystalline solid of limited solubility may afford utility of these copolymers for a variety of applications.     

Microprocessor Adaptive Control of Oil Temperature for Robot Arm Valves: A Practical Implementation

An assembly line quality control robotic arm has to have a very accurate regulation of the hydraulic oil temperature. An adaptive control strategy is designed and implemented, based on on-line parameter identification and optimum integral compensation realization. Design details, implementation, and performance data are presented.     

Synthesis and properties of 4‐(ω‐methoxyoligodimethylsiloxanyl)butyl maleate: A new surfmer

Anionic reactive maleate with hydrophobic oligosiloxane chain was synthesized to use as a stabilizer in the batch and seeded emulsion polymerization of traditional monomers (acrylates, methacrylates, styrene, etc.). Polymerizable surfactant is obtained in a three‐step synthesis, starting from the anionic polymerization of cyclic siloxanes, followed by the silylation of methanol with the obtained cyclic oligomer, and finishing with the acylation of the linear oligomer by maleic anhydride. The improved technique of the synthesis of 4‐chlorobutoxydimethylchlorosilane, one of the initial substances for obtaining siloxane monomer, was elaborated. The anionic polymerization of octamethylcyclotetrasiloxane using cyclic alkoxysilane was carried out to form siloxane cyclic oligomer for the first time. The chemical structure of the monomer synthesized was confirmed by IR spectroscopy and functional analysis. Critical micelle concentration of the obtained surfactant was measured. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 310–313, 2004     

Synthesis and Properties of Novel Surface Active Maleic Monomer Containing Phosphate Group

A novel surface active monomer （surfmer） containing poly（ethylene glycol） chain and terminated phosphate group was synthesized. The copolymerization of synthesized surfmer with NVP （N-vinylpyrrolidone） and with NVP and VEP （5-tert-butylperoxy-5-methyl-2-hexene-3-yne monomer） led to formation of corresponding surface-active copolymers. The capability of application of resulted copolymers as surface active macroinitiators of emulsion polymerization of styrene and as components of polymeric scaffolds was investigated.     

J-spectral factorization and equalizing vectors

For the Wiener class of matrix-valued functions we provide necessary and sufficient conditions for the existence of a J-spectral factorization. One of these conditions is in terms of equalizing vectors. The second one states that the existence of a J-spectral factorization is equivalent to the invertibility of the Toeplitz operator associated to the matrix to be factorized. Our proofs are simple and only use standard results of general factorization theory (Clancey and Gohberg, Factorization of Matrix Functions and Singular Integral Operators, Operator Theory: Advances and Applications, Vol. 3, Birkhäuser, Basel, 1981). Note that we do not use a state space representation of the system. However, we make the connection with the known results for the Pritchard–Salamon class of systems where an equivalent condition with the solvability of an algebraic Riccati equation is given.