THERMAL SHOCK PROBLEMS OF ELASTIC BODIES WITH A CRACK

This paper deals with thermal shock, problems of elastic bodies with a crack. The case considered is that of an infinitely long circular cylinder with an edge crack, and a homogeneous flat plate with an edge crack initially at uniform temperature and suddenly immersed into a medium of lower temperature. The thermal disturbance near the crack tip is assumed to be neglible in the analysis of the temperature field because thermal shocks occur very quickly. We analyze the transient thermal stress problems of elastic solids with a crack and determine the stress intensity factor at the crack tip. The nondimensional maximum transient stress intensity factor is expressed as a function of the Biot number and the nondimensional crack length. Then we propose simplified formulations of the nondimensional maximum transient stress intensity factor as a function of the Biot number and the nondimensional crack length.     

Advanced Reactive Power Control at Individual Residences to Smooth Energy Loss Fluctuation for a Clustered Grid-Interconnected PV System

Reactive power control can control voltage within the proper range from the power network side or from the distribution generation （PV （photovoltaic）） side. Reactive power control from the power network side is simpler because little controlled object apparatus, such as STATCOM, is required. However, it is difficult to optimize the individual voltages of residential consumers because few data have been obtained by the power network side as compared with the power generation side. Energy loss at each residence with PV is different due to the difference in the grid-interconnection condition, such as distribution line impedance when the same operating voltage is set at all residences. Therefore, in this paper, the authors propose an advanced reactive power control method for residential PV systems in order to optimally control the voltage at individual residences so as to minimize energy loss fluctuation. The effectiveness of the proposed reactive power control is demonstrated by numerical simulation.     

Study for pulse stress NBTI characteristics degradation stress

NBTI characteristic degradation of MOSFET is still one of important reliability physics in semiconductor device. Although it is well recognized that its degradation is recovered immediately after releasing DC test stress, it is also fact that the voltage which is applied to the gate electrode in most semiconductor device is an intermittent stress like pulse, not consecutive DC stress as NBTI test. Accurate NBTI lifetime prediction method under this pulse stress condition can afford an actual reliable lifetime. In this work, we considered the characteristic recovery phenomenon in pulse NBTI stress with MOSFET of TOSHIBA 40 nm and 90 nm CMOS process technology and examined a more realistic life prediction method.     

Novel contact probing method using single fiber optical trapping probe

A novel contact probing method for microdevices with high aspect ratio or biological samples is proposed. In this technique, a dielectric microsphere is optically trapped by an optical fiber and used as a touch probe. In the simulations, the finite difference time domain (FDTD) method and Maxwell stress theory are applied to obtain a suitable shape for the tip of the optical fiber. The results show that it is possible to trap the microsphere by using a single optical fiber. In experiments, single fiber optical trapping is successfully demonstrated by considering the simulation results. In order to use the trapped microsphere in the touch probe, the intensity of the reentered beam that is reflected from the surface of the microsphere is monitored. When the probe is in contact with the surface of the object, the intensity of the beam changes and this change is used as the contact signal. Because the probe is trapped optically and the trapping force is very small, this system can be used in a low invasive method.     

Thermal Conductivity Measurements of Some Synthetic Al2O3-CaO-SiO2 Slags by Means of a Front-Heating and Front-Detection Laser-Flash Method

The thermal conductivities of some synthetic slags containing Al₂O₃, CaO, and SiO₂ have been determined in the temperature range between 1623?K (1350?°C) and 1823?K (1550?°C) by applying a front-heating front-detection laser-flash method. In this method, the temperature response curve is measured in the short initial time period immediately after irradiating a laser pulse. The resultant values obtained by this method are unaffected by the radiative heat transfer. The temperature dependence of the thermal conductivity values were found not to be significant for all slag samples currently investigated. The thermal conductivity (??) of samples is represented with standard deviation less than 2?pct of its value as a function of compositions as follows: $$ \lambda = - 0.48\left[ {{\text{Al}}_{ 2} {\text{O}}_{ 3} } \right] - 0.57\left[ {\text{CaO}} \right] - 0.55\left[ {{\text{SiO}}_{2} } \right] + 57.1{\text{ W m}}^{ - 1} {\text{ K}}^{ - 1} $$ where [Al₂O₃], [CaO], and [SiO₂] are molar percent of Al₂O₃, CaO and SiO₂, respectively. The equation is suggested to cover the region of the following compositions: 8.0?mol pct < Al₂O₃ <21.0?mol pct, 31.5?mol pct < CaO <41.5?mol pct and 43.0?mol pct < SiO₂ <58.1?mol pct. The addition of Al₂O₃ to slags with a constant CaO/SiO₂ molar ratio resulted in an increase in thermal conductivity. In contrast, the effects of addition of SiO₂ and CaO are found to be insignificant.     

The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines

The objective of this study is the characterization of the fretting fatigue strength in a hydrogen gas environment. The test materials were a low alloy steel SCM435H, super alloy A286 and two kinds of austenitic stainless steels, SUS304 and SUS316L. The test was performed in hydrogen gas at 0.12 MPa absolute pressure. The purity of the hydrogen gas was 99.9999%. The fretting fatigue limit was defined by the fretting fatigue strength at 30 million cycles. For all materials, the fretting fatigue strength in the hydrogen gas environment increased in the short-life region. However, the fretting fatigue strength in the hydrogen gas environment decreased in the long-life region when exceeding 10 million cycles except for SCM435H, while there was no reduction in the fretting fatigue strength in air between 10 and 30 million cycles. The reduction rate was 18% for A286, 24% for SUS304 and 7% for SUS316L. The tangential force coefficient in the hydrogen gas environment increased when compared to that in air. It can be estimated that this increase is one of the causes of the reduced fretting fatigue strength found in a hydrogen gas environment. In order to discuss the extension of the fretting fatigue life in hydrogen gas observed at the stress level above the fretting fatigue limit in air, continuous measurement of the fretting fatigue crack propagation was performed in a hydrogen gas environment using the direct current potential drop method. As a result, it was found that the extension of the fretting fatigue life was caused by the delay in the start of the stable crack propagation.     

MRT letter: In situ observation method for microstructural changes of steel during hot deformation

We report on the result of an in situ method for observing microstructural changes during hot deformation. The observation of microstructural changes of steel at 1,473 K under tensile strain is demonstrated using the reported method. The development of deformed structures and the formation of a new grain boundary, which subsequently moved with increased strain, were clearly observed. The effectiveness of this method was confirmed by the results of several examples. © 2009 Wiley‐Liss, Inc.     

The relationship between solid-state fluorescence intensity and molecular packing of coumarin dyes

The solid-state fluorescence intensity of coumarin dyes depends on the substituents present at the 4- and 7-positions. 7-(Diethylamino)coumarins showed higher solid-state fluorescence quantum yield (Φ_f(ss) = 0.29–0.40) than 7-aminocoumarins (0.01). In the case of julolydyl coumarins, a 4-methyltetramethyljulolydyl derivative also displayed high Φ_f(ss) (0.34), this being greater than that observed for both 4-(perfluoroalkyl)tetramethyljulolydyl (0.09 and 0.10) and 4-methyljulolydyl derivatives (0.01). X-ray crystallographic analysis suggested that coumarin dyes bearing network hydrogen bonds and/or π–π stacking show weak solid-state fluorescence whereas coumarin dyes having isolated monomer- and dimer-type stacking show intense fluorescence. 4-(Perfluoroalkyl)tetramethyljulolydyl derivatives displayed medium fluorescence intensity owing to isolated monomer-type packing with little intermolecular interactions operating between adjacent molecules.     

Michael Reactions Catalyzed by Basic Alkylamines and Dialkylaminopyridine Immobilized on Acidic Silica–Alumina Surfaces

Acid–base bifunctional catalysts were prepared by immobilization of basic amines on acidic silica–alumina (SA) surfaces. Silane-coupling reagents with various amino-functional groups, such as primary, secondary, and tertiary alkylamines, alkyldiamine, and dialkylaminopyridine, were examined as anchoring reagents for the amines in the preparation of catalysts. The obtained immobilized catalysts (SA–NR′R′′) were characterized by solid-state ¹³C and ²⁹Si MAS NMR and elemental analysis. The catalytic activity of tertiary alkylamines for Michael reactions increased dramatically by the immobilization on silica–alumina, whereas a homogeneous tertiary amine scarcely promoted the reaction. Regarding the kind of amines, the dialkylaminopyridine immobilized silica–alumina with low Al content (SA_L) showed the highest catalytic performance among the amine immobilized catalysts. The solid-state ¹³C NMR analysis revealed the interaction between the nitrogen atom on pyridine ring and a surface strong acid site of the silica–alumina support.