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排序方式: 共有1620条查询结果,搜索用时 131 毫秒
101.
Cho SW Hwang HJ Kim JY Song WC Song SJ Yamamoto H Jung HS 《Journal of electron microscopy》2003,52(6):567-571
The tooth is one of the ectodermal organs controlled by reciprocal interactions between the epithelium and the mesenchyme. Mesenchymal cells in the developing tooth, so-called dental mesenchymal cells, are derived from two different origins: the cranial neural crest (CNC) and the non-CNC. These CNC-derived cells migrate, proliferate and differentiate into odontoblasts, cementoblasts, fibroblasts, osteoblasts and chondroblasts. Tooth germs of wild-type mice were transplanted into the kidney of adult lacZ-transgenic mice. After 1 week of transplantation, a few lacZ-expressing cells and many red blood cells were found near or inside the blood vessels in the pulp of wild-type tooth germs. This result shows that circulating cells of the adult host could invade the dental pulp during tooth development, through the blood vessels, and be a part of dental pulp tissue. Therefore, it can be suggested that these circulating progenitor cells could be the origin of non-CNC-derived cells in tooth germ and their migration pathways would be the blood vessels invading the dental pulp during tooth development. If variations of this experiment were suitably adjusted, such as the embryonic stage of the tooth germ, duration of transplantation, etc., this transplantation experiment using adult lacZ-transgenic mice could be a good system to reveal the origin and migration pathway of cells in developing organs as well as in dental mesenchymal cells. 相似文献
102.
A laser-induced breakdown spectroscopy (LIBS) technique has been applied for detection of unburned carbon in fly ash, and an automated LIBS unit has been developed and applied in a 1000-MW pulverized-coal-fired power plant for real-time measurement, specifically of unburned carbon in fly ash. Good agreement was found between measurement results from the LIBS method and those from the conventional method (Japanese Industrial Standard 8815), with a standard deviation of 0.27%. This result confirms that the measurement of unburned carbon in fly ash by use of LIBS is sufficiently accurate for boiler control. Measurements taken by this apparatus were also integrated into a boiler-control system with the objective of achieving optimal and stable combustion. By control of the rotating speed of a mill rotary separator relative to measured unburned-carbon content, it has been demonstrated that boiler control is possible in an optimized manner by use of the value of the unburned-carbon content of fly ash. 相似文献
103.
An improvement of Fourier synthesis optics for hard x-ray imaging is described, and the basic performance of the new optics is confirmed through numerical simulations. The original concept of the Fourier synthesis imager utilizes nonposition-sensitive hard x-ray detectors coupled to individual bigrid modulation collimators. The improved concept employs a one-dimensional position-sensitive detector (such as a CdTe strip detector) instead of the second grid layer of each bigrid modulation collimator. This improves the imaging performance in several respects over the original design. One performance improvement is a two-fold increase in the average transmission, from 1/4 to 1/2. The second merit is that both the sine and cosine components can be derived from a single grid-detector module, and hence the number of imaging modules can be halved. Furthermore, it provides information along the depth direction simultaneously. This in turn enables a three-dimensional imaging hard x-ray microscope for medical diagnostics, incorporating radioactive tracers. A conceptual design of such a microscope is presented, designed to provide a field of view of 4 mm and a spatial resolution of 400 microm. 相似文献
104.
Y. Kohsaka T. Hanaguri K. Kitazawa M. Azuma M. Takano H. Takagi 《Journal of Low Temperature Physics》2003,131(3-4):299-303
Scanning tunneling microscopy (STM) has been performed on underdoped Ca2–x
Na
x
CuO2Cl2 (Na-CCOC) single crystals to investigate the electronic states of doped Mott insulators near the metal-insulator transition. STM images taken at 7 K show patch-like or river-like irregular features superposed on the atomic corrugations. The irregular structure has a characteristic length scale of 20 Å, which is unchanged in different samples and at different doping levels studied (0.08<x<0.12). Bias voltage dependence of the STM image suggests that Na-CCOC consists of two distinct phases with different electronic states. 相似文献
105.
Chunqing?HeEmail author Takenori?Suzuki Eisaku?Hamada Hitoshi?Kobayashi Kenjiro?Kondo Victor?P.?Shantarovich Yasuo?Ito 《Materials Research Innovations》2003,7(1):37-41
Polymer structures have been investigated using positron annihilation lifetime spectroscopy (PALS) with a slow positron beam
as well as a conventional radioactive source (22Na). The properties of the free volume holes near the polymer surface were studied as a function of the positron implantation
energy. The longest lifetime was associated with ortho-positronium (o-Ps) annihilation in the free volume holes. In polytetrafluoroethylene film, the lifetime of o-Ps was observed to decrease with increasing positron implantation depth, and a significant change in the o-Ps lifetime was found at a short distance (about 10 nm) from the surface, while its intensity increased. This result implies
that near the polymer surface the free volume holes become larger that in the bulk. The effect of temperature on the polymer
sub-surface layers was also studied. For high molecular weight polystyrene, the glass transition temperature for the sub-surface
was lower than that for the bulk and thermal expansion coefficient of the sub-surface layers was found to be larger than the
bulk value.
Electronic Publication 相似文献
106.
Songlan?Yang Zheng-Ming?SunEmail author Hitoshi?Hashimoto 《Materials Research Innovations》2003,7(4):225-230
Ti/Si/TiC powder mixture with molar ratios of 2:2:3 were sintered at various temperatures from 700–1300 °C for 15 min by PDS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the evaluation of phase composition in different samples for the understanding of the sintering mechanism for this system. Results showed that Ti5Si3 formed as the intermediate phase during sintering. The reaction between Ti5Si3 and TiC as well as Si induces the formation of Ti3SiC2, and TiSi2 appears as the byproduct in this process. At temperature above 1000 °C, TiSi2 reacts with TiC to form Ti3SiC2. High Ti3SiC2 phase content bulk material can be synthesized at 1300 °C for 15 min. 相似文献
107.
Chinatsu Yonezawa Masahiro Negishi Kenta Azuma Manabu Watanabe Naoki Ishitsuka Shigeo Ogawa 《International journal of remote sensing》2013,34(18):5696-5711
Spaceborne synthetic aperture radar (SAR) can be used for agricultural monitoring. In this study, three single-polarimetric and four full-polarimetric observation data sets were analysed. A rice paddy field in northern Japan was used as the study site; the data for this site were obtained using RADARSAT-2, which carries a full-polarimetric C-band SAR. Soybean and grass fields were also present within the paddy fields. The temporal change in the backscattering coefficient of the rice paddy fields for the single-polarization data agreed with the temporal change obtained for a rice growth model based on radiative transfer theory. A three-component decomposition approach was applied to the full-polarimetric data. With each rice growth stage, the volume scattering component ratio increased, whereas the surface scattering component ratio generally decreased. The soybean and grass fields showed a smaller double-bounce scattering component than the rice fields for all the acquired data. The results of this study show that multitemporal observation by full-polarimetric SAR has great potential to be utilized for estimating rice-planted areas and monitoring rice growth. 相似文献
108.
Shun-ichi Azuma Yosuke Tanaka Toshiharu Sugie 《International journal of control》2013,86(6):1103-1116
This paper addresses multi-agent control under an environment where both agent-to-agent communication and one-to-all broadcast are available. The problem studied here is a consensus problem for a pre-specified location, i.e. collecting the agents at a desired location in an n-dimensional space, with a limited communication range and an unlimited broadcast range, which is a nice example to be solved under the mixed environment. For solving this, we first introduce a concept of the connected agent group. Using this notion, the problem is reduced to a consensus problem for the group-to-group relation and that for the agent-to-agent relation in the groups, from which we derive a controller achieving the consensus with probability 1. Finally, the performance of the proposed controller is demonstrated by numerical simulation. 相似文献
109.
Cubic Co3O4 nanocrystals (NCs) were synthesized by a one-pot hydrothermal reaction in the presence of the oxidant KClO3 and the capping reagent polyvinylpyrrolidone (PVP). The as-prepared Co3O4 NCs were uniformly cubic with sharp edges and good crystallinity and showed flat surfaces with {100} facets. The capped PVP could be removed without losing cubic shape by heating the NCs at 300 °C. 相似文献
110.
Guanbin Song Yang Ju Hitoshi Soyama 《Materials science & engineering. C, Materials for biological applications》2008,28(8):1467-1471
Bone marrow mesenchymal stem cells (MSCs) can differentiate into a various type cells. It has been identified that MSCs are an attractive cell source for various tissue engineering and play a central role in the repair and regeneration of mesenchymal tissue. Expansion of MSCs in vitro is prerequisite for their applications in tissue engineering. In this study, we evaluated the effects of type I collagen (Col I), fibronectin (Fn) and basic fibroblast growth factor (bFGF) on growth and proliferation of human MSCs (hMSCs) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphe-nyltetra-zolium bromide (MTT) assay. Our results show that low-dose bFGF (5–20 ng/ml) has a promotion effects for growth and proliferation of hMSCs. The proliferation, however, was back to the level similar to the control one (without bFGF treatment) after exposure to high-dose bFGF (40 ng/ml). Application of Col I, coating on the silicone surface or mixed with medium directly, yielded an obvious decrease in growth and proliferation of hMSCs. Moreover, the inhibitory effects exhibited a dose-dependence manner. On the other hand, Fn coating did not promote the growth and proliferation of hMSCs, and also did not inhibit proliferation, but enhanced the adhesion of hMSCs to silicone surface. These findings indicate that Col I decreases the growth and proliferation of hMSCs and is not suitable for encouraging expansion of hMSCs in vitro. Low-dose bFGF could be preferred as medium supplementation for hMSCs expansion and Fn is a better coating material for hMSCs adhesion. 相似文献