Synthesis,spectral characterization,properties and structure of dinuclear rhenium complex containing bis[4-(2-pyridylmethyleneamino)phenyl]methane ligand

The synthesis, characterization, properties and crystal structure of {(bis[4-(2-pyridylmethyleneamino)phenyl]methane)[Re(CO)₃Br]₂} complex are reported. The ¹H NMR data for this complex shows downfield shift of the bis-diimine ligand protons upon coordination to the Re center. The molecular structure of the dinuclear rhenium(I) complex exhibits distorted octahedral geometries around the each metal center with one Br and facial arrangement of three CO and a cis-bonded diimine ligands. The bis-diimine ligand, twists via a half-turn around the metal–metal axis. Electrochemical investigation reveals two oxidation waves and two irreversible reduction waves.     

The in-vitro digestibility and chemical composition of plant parts in white clover,red clover and lucerne during primary growth

White clover (cv. Grasslands Huia), red clover (cv. Norseman) and lucerne (cv. Sabilt) were sampled during primary growth at the flower bud, near full flowering and seeds formed stages in each of 2 years. Each sample was separated into 2–11 plant parts, depending on species and stage of growth, and for each part the in-vitro true dry matter digestibility, digestibility of cell wall and percentages of cell content, nitrogen, water-soluble carbohydrate and lignin were determined. Green leaflets of all three species were consistently high in digestibility. The cell wall fraction of green leaflets was less digestible in red clover than in white clover and lucerne. The digestibility of the upper part of the stem of lucerne and red clover was high at the flower bud stage but declined considerably thereafter, whereas the digestibility of the lower part of the stem was much lower at the flower bud stage and declined relatively little. The green leaf stalks and inflorescences were generally rather less digestible than green leaflets and, in lucerne and red clover, more digestible than stems. In white clover the inflorescence stalks were less digestible than the leaf stalks. The digestibility of plant parts was strongly correlated with the proportion of cell content, and less strongly with the digestibility of cell wall. The proportion of cell content was positively correlated with N%, and the digestibility of cell wall was negatively correlated with the proportion of lignin in cell wall.     

Estimating regions of asymptotic stability with sliding for relay-control systems

The object of this article is the estimation of stability boundaries and regions of asymptotic stability with sliding for a class of single-input relay-control systems. The direct method of Lyapunov is used to obtain these estimates. A coordinate transformation that brings the system into a special canonical form is utilized to facilitate the stability analysis. The proposed approach to stability regions estimation is applied to a class of second-order systems, and analytical expressions for stability regions are derived.Recommended by K. Mizukami     

Characterization of High-Fracture Toughness K-Fluorrichterite-Fluorapatite Glass Ceramics

Stoichiometric K-fluorrichterite (Glass A) and the same composition with 2 mol% P₂O₅ added (Glass B) were prepared and then heat-treated isothermally from 550°–1000°C with 50°C intervals. Samples were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The biaxial flexural strength and indentation fracture toughness of heat-treated glass specimens were also determined for both materials. XRD traces and TEM images showed similar phase evolution and fine microstructures for both systems at ≤950°C, with mica and diopside reacting with residual glass to form K-fluorrichterite as the temperature was increased from 650°C. However, in Glass B, fluorapatite was also present at >800°C. In contrast, coarser microstructures were observed at 1000°C, with larger K-fluorrichterite (20 μm) and enstatite (10 μm) crystals in Glasses A and B, respectively. The highest fracture toughness (2.69 ± 0.01 MPa·m^1/2) and biaxial strength (242.6 ± 3.6 MPa) were recorded for Glass B heat-treated at 1000°C. This was attributed to the presence of enstatite coupled with an interlocked lath-like crystalline microstructure.     

Effect of CaF2 and CaO Substituted for MgO on the Phase Evolution and Mechanical Properties of K-Fluorrichterite Glass Ceramics

Chain silicate glass ceramics based on K-fluorrichterite (KNaCaMg₅Si₈O₂₂F₂, KFR) have potential for use in restorative dentistry and biomedical applications because they may be cast to shape and, when cerammed, have high biaxial flexural strength and fracture toughness. Excess CaO in canasite-based chain silicate compositions is known to enhance their bioactivity. Therefore, two new glass ceramic compositions have been fabricated with 5 mol% CaF₂ (Glass A) and 5 mol% CaO (Glass B) substituted for MgO in the KFR formula unit. The phase evolution of Glasses A and B was studied in detail using X-ray diffraction and transmission electron microscopy. In addition, their mechanical properties were assessed. For Glass A, the fracture toughness (FT=2.66±0.02 MPa·m^1/2) and biaxial flexural strength (BFS=227.3±24.5 MPa) were optimized for samples heat treated at 900°C for 4 h. In Glass B, however, the best FT (2.08±0.02 MPa·m^1/2) and BFS (217.4±4.4 MPa) were obtained at 950°C. In view of their excellent mechanical properties and castability, Glasses A and B are considered potential candidates for fabrication of custom medical devices in restorative dentistry and moderate load-bearing reconstructive bone surgery.     

Temperature-dependent nonlinearities in GaN/AlGaN HEMTs

Temperature-dependent nonlinearities of GaN/AlGaN HEMTs are reported. The large-signal device model of the transistor is obtained by using a physics-based analysis. The model parameters are obtained as functions of bias voltages and temperature. The analysis of the device has been carried out using a time-domain technique. f_max for a 0.23 μm×100 μm Al_0.13Ga_0.87N/GaN FET is calculated as 69 GHz at 300 K, while at 500 K, f_max decreases to 30 GHz, which are in agreement with the experimental data within 7% error. f_max as obtained from calculated unilateral gain, decreases monotonically with increasing temperature. For shorter gate lengths irrespective of the operating temperature f_max is less sensitive to bias voltage scaling. For longer gate length devices, f_max becomes less sensitive to the bias voltage scaling at elevated temperatures. 1-dB compression point (P_1-dB ) at 4 GHz for a 1 μm×500 μm Al_0.15Ga_0.85N/GaN FET is 13 dBm at 300 K. At 500 K, P_1-dB decreases to 2.5 dBm for the same operating frequency. Similar results for output referred third intercept point (OIP3) are reported for different gate length devices     

Behaviour of pyrite during hydrogenation of graphite at atmospheric pressure

The pyrite behaviour during hydrogenation of graphite is investigated. Kinetic experiments were carried out using thermogravimetry. The solid burn up residue was examined by SEM, and by X-Ray and electronic diffraction. The results show how graphite hydrogenation at temperatures lower than 1000 °C can be achieved in the presence of metallic iron obtained from pyrite. Pyrite, or its reduced form pyrrhotite, appears to have no catalytic behaviour during hydrogenation of graphite.     

A new on-chip digital BIST for analog-to-digital converters

A fully digital built-in self-test (BIST) for analog-to-digital converters is presented in this paper. This test circuit is capable of measuring the DNL, INL, offset error and gain error, and mainly consists of several registers and some digital subtracters. The main advantage of this BIST is the ability to test DNL and INL for all codes in the digital domain, which in turn eliminates the necessity of calibration. On the other hand, some parts of the analog-to-digital converter with minor modifications are used in the BIST simultaneously. This also reduces the area overhead and the cost of the test. The proposed BIST structure presents a compromise between test accuracy, area overhead and test cost. The BIST circuitry has been designed using Mitel CMOS 1.5 μm technology. The simulation results of the test show that it can be applied to medium resolution analog-to-digital converters or high resolution pipelined analog-to-digital converters. The presented BIST shows satisfactory results for a nine-bit pipe-lined analog-to-digital converter.     

Design and analysis of a self-testing-and-repairing random access memory “STAR–RAM” with error correction

This paper presents the philosophy and design of a fault-tolerant dynamically-reconfigurable random access memory (RAM) system with a built-in Self-Testing-And-Repairing “STAR” engine. The STAR engine, supported by SEC–DED capability, provides on-line fault detection, correction, analysis and repair without destroying useful data stored in the memory. Reliability analysis of the presented system has been accomplished using a SMART simulation approach[1], and results show significant reliability enhancement over SEC–DED RAM designs. The memory system employs a hardware parallel address-comparison mechanism for rapid processing of incoming addresses during normal read/write operations to minimize memory access delay. The flexible STAR architecture and the low hardware overhead enables utilization of the proposed approach in VLSI memory chips as well as in WSI and large memory modules.     

The digestibility and chemical composition of plant parts in Italian and perennial ryegrass during primary growth

Italian ryegrass (cv. S22) and perennial ryegrass (cv. S24) were sampled duringprimary growth at head emergence, pollen shedding and seed shedding in each of 2 years. Each sample was separated into approximately 19 plant parts and for each part the true dry matter digestibility, digestibility of cell wall and percentages of cell content, nitrogen, water-soluble carbohydrate and lignin were determined. Trends reported in the literature, based on a smaller number of plant parts, were generally confirmed, but were shown to conceal appreciable variation. Thus, while, on average, stem declined in digestibility faster than leaf sheath, the upper sheaths declined in digestibility faster than the lower internodes and nodes; similarly, the proportion of cell content declined at a rather similar rate to digestibility in leaf blade and much less than digestibility in stem but the position was reversed between pollen shedding and seed shedding in the case of dead leaf blade and internodes. While the N content of the inflorescence as a whole did not decline greatly with advancing maturity, the N content of the rachis was nearly halved. The upper part of the crop was more digestible than the lower part at head emergence, but not at seed shedding. Italian ryegrass had a higher proportion of cell content than perennial ryegrass in all types of plant part. The digestibility of cell wall declined with advancing maturity in all the plant parts examined. The lower portions of internodes had a higher proportion of cell content than the upper portions. There were gradients from top to bottom of the plant, e.g. percentage N declined and percentage water-soluble carbohydrate increased from top to bottom.