Discoloration of spark–plasma–sintered transparent MgAl2O4 spinel

It is reported that the spark-plasma-sintered (SPSed) transparent oxides exhibit a discoloration. The discoloration is known to be more remarkable in the SPSed oxides than the HIP/HP processed ones. In order to understand the discoloration phenomena, the discoloration was investigated by spectroscopic techniques using a spinel (MgAl2O4) as the reference material. The discoloration is explained by the combination of carbon contaminations and lattice defects (color centers), which are introduced in the spinel matrix depending on the SPS conditions. For high heating rate of ³50°C/min, carbon contamination occurred by evaporating the carbon phases from the carbon papers and graphite dies during the heating process and tended to be enhanced by the increasing heating rate. For the high heating rate of α = 100 °C/min, although the carbon contamination occurs over almost the entire region of the spinel plate with a 3 mm thickness, the amount of the contamination is significant around the surfaces. The color center (F+-center) may be generated by the formation of oxygen vacancies, which are mainly introduced by dislocation motion depending on the sintering conditions. Since the rate of sintering, namely the deformation rate, increased with the heating rate, the concentration of the dislocation-related color centers increased with the heating rate, but decreased with the sintering temperature due to the bleaching of the oxygen vacancies. For the present spinel, the discoloration due to the carbon contamination and the formation of F+-centers deteriorates the light transmission depending on the sintering conditions

Nucleus from String Theory

In generic holographic QCD, we find that baryons are bound to form a nucleus, and that its radius obeys the empirically-known mass number (A) dependence r A^{1/3} for large A. Our result is robust, since we use only a generic property of D-brane actions in string theory. We also show that nucleons are bound completely in a finite volume. Furthermore, employing a concrete holographic model (derived by Hashimoto, Iizuka, and Yi, describing a multi-baryon system in the Sakai-Sugimoto model), the nuclear radius is evaluated as O(1) x A^{1/3} [fm], which is consistent with experiments.Comment: 4 pages; Ver.2: terminology on nuclear density saturation modified, a reference adde

Bounded cohomology of subgroups of mapping class groups

We show that every subgroup of the mapping class group MCG(S) of a compact surface S is either virtually abelian or it has infinite dimensional second bounded cohomology. As an application, we give another proof of the Farb-Kaimanovich-Masur rigidity theorem that states that MCG(S) does not contain a higher rank lattice as a subgroup.Comment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol6/paper4.abs.htm

構造材料の粒界構造とその破壊強度に関する研究

第1章 序論 第2章 粒界構造の解析法 第3章 実験方法 第4章 モリブデンの粒界破壊強度とそのエネルギー 第5章 モリブデンの粒界構造とそのエネルギー 第6章 モリブデンの粒界構造とその破壊強度に及ぼす不純物元素(炭素､酸素)の効果 第7章 炭化チタンの粒界構造 第8章 総括Made available in DSpace on 2012-07-04T00:27:40Z (GMT). No. of bitstreams: 2 morita1.pdf: 9313031 bytes, checksum: 836a58010ca376d69498b0637a3201c6 (MD5) morita2.pdf: 13410196 bytes, checksum: 49411d7c0280fb09da77eca16cf4af82 (MD5) Previous issue date: 1997-03-2

Grain growth behavior during spark plasma sintering of ceramics

During sintering, most of densification process proceeds in the intermediate stage where channel-like open pores and large isolated pores shrink by the movement of particles or grains towards the pores. The grain rearrangement without significant shape change, one of the characteristics of sintering, is a result of the grain-boundary sliding which is the most important mechanism for high-temperature deformation, such as superplastic deformation. The grain-boundary sliding is an essential process during densification. During spark plasma sintering of alumina, the effects of heating rate, pressure and loading schedule on the grain size were examined. Usually, high heating rates results in small grain sizes because of short heating time. However, when alumina was densified at low temperatures, high heating rates accelerated grain growth, though the total heating time was reduced. The grain growth rate after full densification was also accelerated for high heating rates. The accelerated grain growth might result from the generation of defects during densification. The densification in the intermediate stage of sintering includes the deformation of powder particles, and the deformation occurs mainly by grain-boundary sliding or grain re-arrangement. The defects generated during grain-boundary sliding may enhance the grain-boundary mobility and accelerate the grain growth rate, that is the dynamic grain growth. It is considered, therefore, that the high deformation rate at high heating rates accelerated grain growth during sintering. The accelerated grain growth also appeared for high-pressure sintering. The grain size after sintering increased with the applied pressure. High pressures lowered the deformation temperature and increased the deformation rate. As a result, the high deformation rate during heating may generate defects and enhance the grain-boundary mobility. Lastly, the loading schedule during heating also affected the deformation and the grain growth. Applying pressure at low temperatures or at high rates may generate more defects and resultantly accelerate the grain growth. These unusual grain growth behaviors during spark plasma sintering are explained by using a concept of dynamic grain growth [1]. Hence, one of our conclusions is that the deformation of grain-boundary sliding plays an important role in both densification and grain growth during sintering. [1] BN Kim et al., Scripta Mater., 80 (2014) 29

An experiment to prove the concept of the downhole coaxial heat exchanger (DCHE) in Hawaii

The first experiment for the Downhole Coaxial Heat Exchanger (DCHE, see Fig. 1) was carried out successfully at the HGP-A well on the island of Hawaii using an interval from the surface down to a depth of 876.5m. The temperature at the bottom of the DCHE before the onset of the experiment was 110°C. The observed highest hot water temperature during the experiment was 98°C, and the maximum gross and net thermal outputs were 540 kW and 370 kW, respectively. The experiment proceeded smoothly and excellent agreement between measured values and computed values was obtained in the analysis (Morita et a/., 1992). Thus, the concept of the DCHE was proved to be sound

Quantitative ultrasonic assessment for detecting microscopic cartilage damage in osteoarthritis

Osteoarthritis (OA) is one of the most prevalent chronic conditions. The histological cartilage changes in OA include surface erosion and irregularities, deep fissures, and alterations in the staining of the matrix. The reversibility of these chondral alterations is still under debate. It is expected that clinical and basic science studies will provide the clinician with new scientific information about the natural history and optimal treatment of OA at an early stage. However, a reliable method for detecting microscopic changes in early OA has not yet been established. We have developed a novel system for evaluating articular cartilage, in which the acoustic properties of the articular cartilage are measured by introducing an ultrasonic probe into the knee joint under arthroscopy. The purpose of this study was to assess microscopic cartilage damage in OA by using this cartilage evaluation system on collagenase-treated articular cartilage in vivo and in vitro. Ultrasonic echoes from articular cartilage were converted into a wavelet map by wavelet transformation. On the wavelet map, the maximum magnitude and echo duration were selected as quantitative indices. Using these indices, the articular cartilage was examined to elucidate the relationships of the ultrasonic analysis with biochemical, biomechanical and histological analyses. In the in vitro study, the maximum magnitude decreased as the duration of collagenase digestion increased. Correlations were observed between the maximum magnitude and the proteoglycan content from biochemical findings, and the maximum magnitude and the aggregate modulus from biomechanical findings. From the histological findings, matrix staining of the surface layer to a depth of 500 μm was closely related to the maximum magnitude. In the in vivo study, the maximum magnitude decreased with increasing duration of the collagenase injection. There was a significant correlation between the maximum magnitude and the aggregate modulus. The evaluation system therefore successfully detected microscopic changes in degenerated cartilage with the use of collagen-induced OA

An improved apparent polar wander path for southwest Japan: post-Cretaceous multiphase rotations with respect to the Asian continent

To construct the Mesozoic apparent polar wander path (APWP) for the inner arc of the southwestern Japanese islands (referred to as southwest Japan) and compare it to that of East Asia, a 110 Ma paleomagnetic pole for southwest Japan was determined. Mudstone and sandstone samples were collected from 16 sites for paleomagnetic analysis in the Lower Cretaceous Inakura Formation of the Inakura area in the central part of southwest Japan. A high-temperature magnetization component, with unblocking temperatures of 670-695 degrees C, was isolated from 12 sites of red mudstone. Of these, 11 sites revealed a primary remanent magnetization during the Early Cretaceous. The primary directions combined with the previously reported ones provide a new mean direction (D = 79.7 degrees, I = 47.4 degrees, alpha(95) = 6.5 degrees, N = 17), and a corresponding paleomagnetic pole that is representative of southwest Japan (24.6 degrees N, 203.1 degrees E, A(95) = 6.8 degrees). The Early Cretaceous paleomagnetic pole, together with the Late Cretaceous and Cenozoic poles, constitute a new APWP for southwest Japan. The new APWP illustrates a standstill polar position during 110-70 Ma, suggesting tectonic quiescence of this region. This standstill was followed by two large tracks during the Cenozoic. We interpret these tracks as clockwise tectonic rotations of southwest Japan that occurred twice during the Cenozoic. The earlier tectonic rotation occurred for a tectonic unit positioned below northeast China, the Liaodong and Korean Peninsulas, and southwest Japan (East Tan-Lu Block) during the Paleogene. The later rotation took place only under southwest Japan during the Neogene. Cenozoic multiphase rifting activity in the eastern margin of the Asian continent was responsible for the tectonic rotations that are observed from the paleomagnetic studies. Intermittent rifting may constitute a series of phenomena due to asthenospheric convection, induced by the growth of the Eurasian mega-continent in the Mesozoic

Athermally Enhanced High Temperature Plastic Flow in Zirconia Ceramics under Flash Event

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