A fracture criterion for three-dimensional crack problems

A criterion for predicting the growth of three-dimensional cracks is developed on the basis of the strain energy density concept which has been used successfully for treating two-dimensional crack problems. Fracture is assumed to initiate from the nearest neighbor element located by a set of spherical coordinates (r, θ, φ) attached to the crack border. The new fracture surface is described by a locus of these elements whose locations correspond to the strain energy function, dW/dV, being a minimum. The function dW/dV is found to be singular of the type 1/r and is of quadratic form in the three stress intensity factors k₁, k₂ and k₃ expressed through the strain energy density factor S. It is postulated that unstable crack propagation initiates from a region where S reaches a critical value S_cr = r₀(dW/dV)_cr. The locations of failure lying on the fracture surface is determined by holding (dW/dV)_cr = S_min/r₀ constant. The quantity S_min stands for the value of S minimized with respect to θ and φ and r₀ is a radial distance measured from the crack border.

An example of failure prediction for an embedded elliptical crack subjected to both normal and shear loads is presented. According to the S-criterion, fracture initiation takes place at the ends of the minor axis. An unexpected result is that for a narrow elliptical crack and Poisson's ratio of 1/3 the lowest failure load occurs when the uniaxial tensile load makes an angle of approximately 60° with the crack surface and is in the plane of the major axis. This is in contrast to the expectation that the lowest critical load occurs when the uniaxial tension is perpendicular to the crack surface. In the limit as the elliptical crack becomes increasingly narrower, the result reduces to the two dimensional line crack case of Mode I and III loading. The S-criterion is also applied to the failure prediction of three dimensional cracks under compressive loads.     

A 2.4-GHz Low-Power Low-IF Receiver and Direct-Conversion Transmitter in 0.18-μm CMOS for IEEE 802.15.4 WPAN Applications

In this paper, a low-power low-IF receiver and a direct-conversion transmitter (DCT) suitable for the IEEE standard 802.15.4 radio system at the 2.4-GHz band are presented in 0.18-mum deep n-well CMOS technology. By using vertical NPN (V-NPN) bipolar junction transistors in the baseband analog circuits of the low-IF receiver, the image rejection performance is improved and the power consumption is reduced. In addition, by applying the V-NPN current mirrored technique in a DCT, the carrier leakage is reduced and the linearity performance is improved. The receiver has 10 dB of noise figure, -15 dBm of third-order input intercept point, and 35 dBc of image rejection. The transmitter has more than -2 dBm of transmit output power, -35 dBc of local oscillator leakage, and -46 dBc of the transmit third harmonic component. The receiver and transmitter dissipate 6 and 9 mA from a 1.8-V supply, respectively     

A 20 GHz Steerable Array Antenna Using 3-bit Dielectric Slab Phase Shifters on a Coplanar Waveguide

A simple steerable array antenna is designed and developed using a movable dielectric phase shifter. The change of effective dielectric constant at different dielectric slab positions on a coplanar waveguide is used as the phase shifter. The impedance matching and desired phase shift conditions are satisfied at two slab heights, and the reflection is designed to be minimized at these slab positions. The low-loss dielectric material is used as the dielectric slab and is placed close to a coplanar transmission line with airgap. The 4times4 steerable array antenna with the phase shifters is designed and fabricated at 20 GHz. The H-plane radiation patterns are measured at different phase shift positions and compared with the expected results     

Optimized microwave dielectric properties of Co- and Ca-substituted Mg0.6Zn0.4TiO3

The system of (1 − y)(Mg_0.6Zn_0.4)_1−xCo_xTiO₃-yCaTiO₃ was investigated to optimize its microwave dielectric properties by adopting appropriate contents of Co and Ca and by controlling sintering conditions. The effect of Co substitution was to enhance densification and Qf value, while the addition of CaTiO₃ resulted in increases of dielectric constant and TCF. As an optimal compositions, 0.93(Mg_0.6Zn_0.4)_0.95Co_0.05TiO₃-0.07CaTiO₃ successfully demonstrated a dielectric constant of 23.04, a Qf of 79,460 GHz and a TCF value of +1.4 ppm/°C after firing at a relatively lower sintering temperature of 1200 °C. The increase of sintering temperature beyond 1200 °C tended to degrade overall microwave dielectric properties presumably due to Zn volatilization as evidenced by the presence of a Zn-deficient phase (MgTi₂O₅) at 1400 °C. An attempt to establish the correlation between microstructure characteristics and dielectric properties was made in this dielectric system where the extensive range of firing temperature up to 1400 °C was evaluated.     

Development and evaluation of Zigbee node module for USN

This study aims at securing technology to develop a multisensor and complex position-tracking Zigbee node module for USN (ubiquitous sensor network). In a concrete way, it aims at developing military (invader detection module and system) and industrial (transformer-tracking and thermo-measurement module and system) Zigbee telecommunication node module, and developing wireless monitoring and tracking technology based on such modules. In addition, it aims at building up the foundation of interface test for various sensors (thermo sensors, pressure sensors, vibration sensors and vision sensors) and the foundation of a comprehensive interlocking device to which GIS (Geographic Information System) and GPS (Global Positioning System) were applied, for industrial devices are mostly installed in mountains. Moreover, it aims at developing a roaming-type variable Zigbee node module to the end that it stands against unfavorable conditions (extreme temperatures, dust, winds, electromagnetism, noise, etc.). In case such aims are achieved, Zigbee communications will not be limited to normal and stable conditions (home networks, building automation, etc.) but will be applied to the industrial field under noises and unfavorable conditions. In such a case, the application of Zigbee node modules is expected to be unlimited.     

Electrochemical performance, biocompatibility, and adhesion of new polymer matrices for solid-state ion sensors.

Ammonium and potassium ion-selective membranes formulated with PVC/hydroxylated PVC, polyurethane/hydroxylated PVC, and moisture-curable silicone rubber matrices are studied in an effort to extend the lifetime of solid-state ion sensors through improved membrane adhesion. The PVC/membranes exhibit electrochemical performance equivalent to that of conventional PVC membranes in terms of slope, detection limit, and selectivity. The polyurethane- and silicone-rubber-based membranes have better adhesion to silicon nitride than do PVC or hydroxylated PVC matrices. Incorporating a silanizing reagent (silicon tetrachloride) significantly improves the adhesion of the polyurethane matrix. The use of silicon tetrachloride in membrane matrices also enhances the electrochemical stability of the interfacial potential between ion-selective polymer-matrix membranes and silver epoxy inner reference electrodes of solid-state sensors. The biocompatibility of the polymer matrices is examined via radiotracer protein adsorption studies and whole blood clotting time measurements. The polyurethane- and silicone-rubber-based membranes exhibit less overall nonspecific protein adsorption than the PVC or hydroxylated PVC matrices.     

Electrolyte optimization for a Li ion battery by charge profile analysis

Electrolyte design for Li ion batteries was approached by means of comparison of faradaic and non-faradaic currents. The faradaic current by the movement of Li⁺ ions was dependent on the composition of the electrolyte and was related to the battery capacity; the higher the capacity, the greater the current by the faradaic reaction. The open circuit potential of the electrode with a greater faradaic current decreased at a slower rate than that of the electrode with a smaller faradaic current. This analysis method can be used to prepare an optimal electrolyte of an actual Li ion battery, especially when developing batteries with excellent high-rate discharge capabilities and low temperature discharge properties.     

High-resolution crystal structures of delta5-3-ketosteroid isomerase with and without a reaction intermediate analogue

Bacterial Delta5-3-ketosteroid isomerase (KSI) catalyzes a stereospecific isomerization of steroid substrates at an extremely fast rate, overcoming a large disparity of pKa values between a catalytic residue and its target. The crystal structures of KSI from Pseudomonas putida and of the enzyme in complex with equilenin, an analogue of the reaction intermediate, have been determined at 1.9 and 2.5 A resolution, respectively. The structures reveal that the side chains of Tyr14 and Asp99 (a newly identified catalytic residue) form hydrogen bonds directly with the oxyanion of the bound inhibitor in a completely apolar milieu of the active site. No water molecule is found at the active site, and the access of bulk solvent is blocked by a layer of apolar residues. Asp99 is surrounded by six apolar residues, and consequently, its pKa appears to be elevated as high as 9.5 to be consistent with early studies. No interaction was found between the bound inhibitor and the residue 101 (phenylalanine in Pseudomonas testosteroni and methionine in P. putida KSI) which was suggested to contribute significantly to the rate enhancement based on mutational analysis. This observation excludes the residue 101 as a potential catalytic residue and requires that the rate enhancement should be explained solely by Tyr14 and Asp99. Kinetic analyses of Y14F and D99L mutant enzymes demonstrate that Tyr14 contributes much more significantly to the rate enhancement than Asp99. Previous studies and the structural analysis strongly suggest that the low-barrier hydrogen bond of Tyr14 (>7.1 kcal/mol), along with a moderate strength hydrogen bond of Asp99 ( approximately 4 kcal/mol), accounts for the required energy of 11 kcal/mol for the transition-state stabilization.     

Plasma etching optimization of oxide/nitride/oxide interpolydielectric breakdown time in flash memory devices

The breakdown time of flash memory oxide/nitride/oxide (ONO) layer t_bd under positive constant current stressing has been found to be closely related to the cumulative extent of (over)etch of the tungsten silicide, control polysilicon, and ONO layers, i.e., Σ(ΛOE). An empirical first-order relation between t_bd and Σ(ΛOE) has been derived to facilitate the plasma etch recipe optimization. This has led to a four-fold increase in the average t_bd across a 200-mm wafer to 208 s. More importantly, the spread in t_bd has been tightened to ~5%, which is down from ~54%     

Microstructure and mechanical properties of Ti 45Al 5Nb + (0–0.5C) sheets

The possible application of gamma titanium aluminides in aerospace industry requires a detailed understanding of the microstructure–property relationship of sheets made from this material. This paper reports the mechanical properties of sheets up to 1000 °C, based on alloy concepts with high Nb concentrations and small additions of C. Sheets were manufactured by rolling powder metallurgical compacts with compositions Ti 45Al 5Nb and Ti 45Al 5Nb 0.5C. The microstructures of both sheets are “near gamma” and consist of γ-TiAl and ₂-Ti₃Al phases. The texture of both phases is very weak. The strengths levels are very high and that of the C-containing sheet exceeds that of the C-free material at RT by 200 MPa. The mechanical properties of Ti 45Al 5Nb are independent of the direction in the sheet, in the whole temperature range from RT to 1000 °C. However, for the C-containing sheet this is true only in the upper temperature range.