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排序方式: 共有196条查询结果,搜索用时 109 毫秒
101.
Naoya Kishikawa Ayuko Ihara Masae Shirota Mitsuhiro Wada Yoshihito Ohba Nobuyuki Sera Kenichiro Nakashima Naotaka Kuroda 《Analytical sciences》2005,21(12):1467-1470
Thirteen polycyclic aromatic hydrocarbons (PAHs) and four nitropolycyclic aromatic hydrocarbons (NPAHs) on the surfaces of airborne particulates, which were collected at an industrial area of a western site of Japan during periods from 1976 to 1998, were retrospectively analyzed. PAHs and NPAHs were extracted from airborne particulates using hexane with ultrasonication, and then analyzed by HPLC systems with fluorescence detection and chemiluminescence detection, respectively. The total concentrations (mean +/- SD, n = 34) were 15.54 +/- 21.24 ng/m3 for PAHs and 5.85 +/- 8.16 pg/m3 for NPAHs. The concentrations of PAHs and NPAHs were found to be highest during the period between 1979 and 1982, and then reduced. The annual concentrations of PAHs and NPAHs were highly correlated with those of air pollutants from motor vehicle origin, such as carbon monoxide, suspended particulates and non-methane hydrocarbons. The results suggested that motor vehicle emissions were one of the predominant sources of atmospheric PAHs and NPAHs. 相似文献
102.
Tomoyuki Sugimoto Toshimitsu Hamasaki 《Annals of the Institute of Statistical Mathematics》2006,58(4):647-674
We consider a semiparametric cure model combining the Cox model with the logistic model. There are the two distinct methods
for estimating the nonparametric baseline hazard function of the model; one is based on a pseudo partial likelihood and the
other is to use an EM algorithm. In this paper, we discuss the consistency and the asymptotic normality of the estimators
from the two methods. Then, we show that the estimator from the pseudo partial likelihood can be characterized by the (forward)
Volterra integral equation, and the estimator from the EM algorithm by the Fredholm integral equation. These characterizations
reveal differences in the properties between the estimators from the two methods. In addition, a simulation study is performed
to numerically confirm the results in several finite samples. 相似文献
103.
Kishikawa N Ohkubo N Ohyama K Nakashima K Kuroda N 《Analytical and bioanalytical chemistry》2011,400(2):381-385
Ubiquinone is an important biologically active compound in the living body. The determination of ubiquinone in human plasma
is useful for the investigation of bioavailability of ubiquinone and for early diagnosis of several diseases. Therefore, we
developed a high-performance liquid chromatography (HPLC) with chemiluminescence detection method for the analysis of ubiquinone
in plasma samples. The method is based on luminol chemiluminescence detection of super oxide anion that is generated by the
redox cycle reaction between ubiquinone and dithiothreitol. The HPLC system involved an octyl column with a mobile phase of
methanol. Ubiquinone eluted from the column was mixed with dithiothreitol and luminol solutions simultaneously, and generated
chemiluminescence was monitored by chemiluminescence detector. The calibration curve for standard ubiquinone solution was
linear from 0.09 to 43.2 μg/mL (0.45–216 ng on column) with the correlation coefficient of 0.999, and the detection limit
(S/N = 3) was 26 ng/mL (130 pg on column). Using the proposed HPLC method, the peak of ubiquinone in human plasma could be
clearly detected on the chromatogram without any interference from plasma components. 相似文献
104.
Takuo Okuchi Masashi Yoshida Yoshiki Ohno Naotaka Tomioka Narangoo Purevjav Toyotaka Osakabe 《高压研究》2013,33(4):777-786
A new design of opposed anvil cell for time-of-flight neutron powder diffraction was prepared for use at advanced pulsed sources. A couple of single-crystal sapphire sphere anvils and a gasket of fully hardened Ti–Zr null alloy were combined to compress 35 mm3 of sample volume to 1 GPa and 11 mm3 to 2 GPa of pressures, respectively. A very high-quality powder diffraction pattern was obtained at Japan Proton Accelerator Research Complex for a controversial high pressure phase of methane hydrate. The counting statistics, resolution, absolute accuracy and d-value range of the pattern were all improved to be best suitable for precise structure refinement. The sample is optically accessible to be measured by Raman and fluorescence spectroscopy during and after compression. The current cell will be an alternative choice to study hydrogenous materials of complex structures that are stable at the described pressure regime. 相似文献
105.
Hiroto Oomae Joel T. Asubar Shinichi Nakamura Yoshio Jinbo Naotaka Uchitomi 《Journal of Crystal Growth》2012,338(1):129-133
We have directly grown zinc-blende (zb)-type MnAs thin films on InP (001) substrates without the aid of any buffer layer using molecular beam epitaxy (MBE). From the High-resolution X-ray diffraction (XRD) data, assuming face-centered cubic (fcc) MnAs structure, the average lattice constants values were calculated to be 6.068 and 6.060 Å for growth temperatures of 250 and 300 °C, respectively. High-resolution transmission electron microscopy (TEM) investigations and selected-area electron-diffraction (SAD) verified the successful growth of zb-type cubic MnAs coexisting with the NiAs-type hexagonal MnAs. The saturation magnetization was estimated to be 300 emu/cm3 determined from the magnetic field dependence of the magnetization curves. From the temperature dependence of magnetization, the Curie temperature was found to be approximately 308 K. Success in the growth of zb-type MnAs thin films could be reasonably explained by the existence of a monolayer of InAs at the interface between the MnAs and InP substrates. 相似文献
106.
Takuya Kochi Kazuya Ichinose Masayuki Shigekane Taro Hamasaki Fumitoshi Kakiuchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(16):5315-5319
Sequential formation of distant bonds in organic molecules was achieved for the palladium‐catalyzed hydrosilylation/cyclization of various 1,n‐dienes by chain walking of the metal catalyst. The reaction was applicable to various 1,n‐dienes, including a 1,13‐diene, to form a cyclopentane ring as well as a carbon–silicon bond at a remote site. The use of “nondissociative” chain walking provides a fascinating strategy in organic synthesis to functionalize distant parts of organic molecules, in a particular order, within a catalytic cycle by effectively moving the reactive center from a remote position. 相似文献
107.
Michio Sakakihara Munenori Morimoto Hiroshi Niki Naotaka Okamoto 《International Journal of Computational Fluid Dynamics》2013,27(8):625-630
A precondition for the Gauss–Seidel iterative method to solve a linear system of equations arising from the boundary element method for the Laplace and convective diffusion with first-order reaction problems is presented in this paper. The present precondition is based on the elementary matrix operation. We discuss the effect of the precondition in comparison with the Gauss elimination (GE) method in some numerical experiments. 相似文献
108.
Naoya Kishikawa Kimiko Kubo Sherin Farouk Hammad Mokhtar Mohamed Mabrouk Ahmed Habib Hamed Elfatatry Kaname Ohyama Kenichiro Nakashima Naotaka Kuroda 《Journal of chromatography. A》2009,1216(40):6873-6876
The fluorogenic derivatization method for aryl halide was developed for the first time. This method was based on the formation of fluorescent biphenyl structure by Suzuki coupling reaction between aryl halides and non-fluorescent phenylboronic acid (PBA). We measured the fluorescence spectra of the products obtained by the reaction of p-substituted aryl bromides (i.e., 4-bromobenzonitrile, 4-bromoanisole, 4-bromobenzoic acid ethyl ester and 4-bromotoluene) with PBA in the presence of palladium (II) acetate as a catalyst. The significant fluorescence at excitation maximum wavelength of 275–290 nm and emission maximum wavelength of 315–350 nm was detected in all the tested aryl bromides. This result demonstrated that non-fluorescent aryl bromides could be converted to the fluorescent biphenyl derivatives by the coupling reaction with non-fluorescent PBA. We tried to determine these aryl bromides by HPLC-fluorescence detection with pre-column derivatization. The aryl bromide derivatives were detected on the chromatogram within 30 min without any interfering peak derived from the reagent blank. The detection limits (S/N = 3) for aryl bromides were 13–157 fmol/injection. 相似文献
109.
Amponsaa-Karikari A Kishikawa N Ohba Y Nakashima K Kuroda N 《Biomedical chromatography : BMC》2006,20(11):1157-1162
Artemisinin is an antimalarial drug containing an internal endoperoxide linkage in its structure. A simple, selective and sensitive high-performance liquid chromatography (HPLC)-peroxyoxalate chemiluminescence (PO-CL) method for the determination of artemisinin was developed. This method is based on the fact that endoperoxide in artemisinin structure can be converted to hydrogen peroxide (H(2)O(2)) under ultraviolet (UV) irradiation and the generated hydrogen peroxide can be measured using PO-CL detection. The HPLC-PO-CL system was optimized on a mobile phase, post column chemiluminescence reagent, UV source and irradiation time. In addition, the system was combined with simple liquid-liquid extraction using n-hexane that allowed selective and sensitive determination of artemisinin in serum. The limit of detection using 0.5 mL of blood was 0.062 micromol/L (17.5 ng/mL) at a signal-to-noise ratio of 3. Calibration curve obtained for artemisinin in human serum 4-80 micromol/L (1.1-22.6 microg/mL) showed a good linearity (r = 0.999). 相似文献
110.
Hikishima K Yagi K Numano T Homma K Nitta N Nakatani T Hyodo K 《Magnetic resonance imaging》2008,26(4):437-445
High b-value diffusion magnetic resonance imaging (MRI) enables us to detect far smaller architectures, by using q-space analysis, than the resolution in conventional MRI. Average displacement, one of the q-space parameters, quantitatively reflects architecture size and is very useful in observing small changes in microstructures in vivo (e.g., neurodegeneration, tumor heterogeneity, and others). Diffusion-weighted imaging (DWI) is performed by a two-dimensional (2D) multislice method; however, due to finite slice thickness and slice gap, there is a partial-volume effect that makes it difficult to detect the net q-space signal. On the other hand, three-dimensional (3D) MRI, having the advantages of very thin slice thickness and no slice gap (contiguous slices), allows volumetric evaluation acquired in a small isotropic voxel, as compared to 2D multislice imaging. Little is known about the isotropic high-resolution 3D DWI application to q-space analysis. In this study, we have developed and implemented a high b-value 3D DWI sequence, applied q-space analysis to study the reliability of high b-value 3D DWI and obtained a microscopic analytical map with isotropic high resolution and less contamination. 相似文献