Cosmological evolution of cosmic strings with time-dependent tension

We discuss the cosmological evolution of cosmic strings with time-dependent tension. We show that, in the case that the tension changes as a power of time, the cosmic string network obeys the scaling solution: the characteristic scale of the string network grows with the time. But due to the time dependence of the tension, the ratio of the energy density of infinite strings to that of the background universe is {\it not} necessarily constant.Comment: 9 pages, to appear in Phys. Rev.

X-ray stress measurement of carbide in tool steel

金沢大学大学院自然科学研究科システム創成科学専攻Thin films deposited by physical vapor deposition (PVD) were studied in terms of residual stress by the authors. The final purpose of our study is to evaluate the stress state at the interface between a substrate and a thin film. In this study, JIS-SKH55 tool steel without thin-film deposition was used as the specimen. SKH55 is a dual-phase steel consisting of martensite α\u27Fe and alloyed carbide M6C2. The specimens were heated to 573K, 798K, 843K and 893K. Recently, the relationship between the misfit of plastic strain and stress obtained by X-ray stress measurement has been proposed by the authors using the Eshelby/Mori-Tanaka model (EMT model). The residual stress and the misfit of plastic strain were determined by X-ray stress measurement using the EMT model. Results showed that as annealing temperature increased, the compressive residual stress remained nearly constant up to about 800K, and decreased above 800K in both phases. The misfit of plastic strain also remained nearly constant up to about 800K, and reached zero above 800K

Improving sinterability of ceramics using hybrid microwave heating

金沢大学大学院自然科学研究科 金沢大学信頼性システム工学（工学部）Microwave processing, as a new method for sintering ceramics, has key advantages such as increased heating rate, uniform heating and reduced cost compared to conventional methods. It is generally accepted that microwave sintering can improve the macroscopic mechanical performances of ceramics, however, the performances of microwave-sintered ceramics on the microscopic scale are rarely investigated. In the present study, the ceramics are sintered by hybrid microwave sintering (HMS), which combines the characteristics of microwave heating and conventional heating. To evaluate the homogeneous performance of the sintered ceramics, the behaviors of thermal residual stress distribution in the microwave-sintered and conventionally sintered ceramics were investigated by X-ray diffraction technique. The thermal residual stress investigation shows microwaves can sinter ceramics in entire volume while offering improved mechanical properties. Subsequently, the distribution behaviors of pore ratio and hardness in the ceramics were investigated, respectively. The experiment results confirm that the sinterability of ceramics is homogenously improved by hybrid microwave sintering. © 2008 Elsevier B.V. All rights reserved.in pres

PVDによるセラミックス硬質膜を有する工具材料の残留応力に関するX線的研究

取得学位：博士(工学)，学位授与番号：博甲第680号，学位授与年月日：平成16年9月30日,学位授与年：200

Scratch test of TiCN thin films with different preferred orientation

The purpose of this study is to examine the effect of crystallite preferred orientation on the mechanical strength of TiCN thin films in highly compressive residual stress. TiCN thin films were deposited by PVD on JIS-SKH55 (AISI M35) steel. The applied substrate bias voltages were set for -50, -80, -100,-120 and -150V. Subsequently, residual stress and crystalline preferred orientation of these specimens were investigated by X-ray diffraction methodology. The crystalline preferred orientation in thin films was evaluated by the ODF calculated from pole figures. On the other hand, dynamic hardness test (DH) and scratch test were executed to evaluate the mechanical strength of thin films. In our study, it was observed that negative bias voltages had an effect on the preferred orientation. The orientation density at -120 V was the highest of all specimens. In addition, the value of scratch section area at -120V was the largest of all specimens. As a conclusion, the relation between the scratch area and the negative bias voltages corresponded to the relation between the preferred orientation and the bias voltages

Microstructure-based computational simulation and experimental measurement of stresses in spheroidized steels

金沢大学大学院自然科学研究科Carbon steel is the most popular engineering material, usually consisted of ferrite and cementite phases. Internal stress state of the steel under thermal or mechanical loading is strongly affected by the amount and morphology in the cementite phase. With this aim, a computational model which applies the finite element method at the microscale was used in present study. Effects of volume fraction and particle size of the spheriodal cementite on the internal stress states in carbon steels under the mechanical and thermal loadings are investigated. To verify the reliability of the computational simulations, the residual stresses in the constituent phases are measured by means of X-ray stress diffraction technique. The computational simulations fit well with the experimental data, and the microstructure-based model is validated

Influence of interfacial neighborhood on residual stress due to deposition of TiN thin films made by PVD

金沢大学大学院自然科学研究科システム創成科学専攻In depositing the TiN thin films to the substrate by Physical Vapor Deposition (PVD), it influences the substrate interface. Change of the residual stress and the full-width at half maximum (FWHM) in each process of the TiN deposition of thin film was measured by the X-ray stress measurement. As a result of the X-ray stress measurement, there are no changes in the residual stress and the FWHM. It is thought that there is a difference in the penetration depth to the substrate of X-rays and Ti ion

X-ray study on Mg-Sm alloy produced by HPT

金沢大学大学院自然科学研究科システム創成科学専攻The purpose of this study is to reveal the cause of hardening of magnesium base alloys by the high pressure torsion processing (HPT) using X-ray diffraction. HPT was applied to Mg base alloys of the Mg-Sm system (2.8-5.5 mass %Sm). HPT was performed under pressure 4GPa at 20°C and 200°C. HPT results in significant strengthening of the Mg-Sm alloys due to the formation of sub microcrystalline structure. The dynamic recrystallization was realized through the pole figure measurement and the photograph of X-ray back scattering. The Mg supersaturated solid solution decomposition during HPT was observed by the X-ray profile analysis and the calculation of lattice constants of the Mg phase

Investigation of the Utility and Safety of Dynamic Computed Tomography with Vasodilators

Background: Dynamic computed tomography (CT) angiography is useful for evaluating of hepatic vascularity. Although vasodilators increase hepatic blood flow, the utility of dynamic CT with vasodilators is unclear. Here we investigated the utility and safety of dynamic CT with vasodilators. Methods: A prospective case-control radiographic evaluation using abdominal dynamic CT with and without vasodilator was performed at a single center between October 2015 and September 2016. We compared the CT values in Hounsfield units of the aorta; celiac artery; and common, right, and left hepatic arteries in the arterial phase and the main trunk; right and left branches of the portal vein; and right, middle, and left hepatic veins in the portal phase with and without vasodilators. The region of interest was set in each element of the liver vasculature. Four radiological technologists independently and visually compared the scores of the portal vein (P-score) and hepatic vein (V-score) on a 5-point scale with and without vasodilators. Results: The CT values of arteries and veins using vasodilators were significantly higher than those without vasodilators. With and without vasodilators, the P-scores were 3.1 ± 1.2 and 4.0 ± 1.1 (P < 0.05) and the V-scores were 3.3 ± 1.4 and 4.3 ± 1.0 (P < 0.05). Only one patient with vasodilator use had transient hypotension and recovered immediately without medication. Conclusion: Dynamic CT with vasodilators can provides better visualization of vascular structures