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1.
《Journal of Magnetic Resonance (1969)》1985,61(1):52-58
A conventional, high-resolution NMR spectrometer has been adapted for measurement of the two-dimensional spatial distribution of spin-lattice relaxation rates using the inversion-recovery pulse sequence incorporated into the two-dimensional “spin-warp” imaging method. The approach is illustrated using a phantom made of capillary tubes containing aqueous manganese ethylenediaminetetracetic acid. 相似文献
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The hydrocarbon contamination of an AEI ES 100 spectrometer has been studied in order to determine the reliability of the C 1s line as a standard in X-ray photoelectron spectra of non conducting solids. With alumina samples, it is shown that the contamination layer of this non ultra-high vacuum spectrometer is a suitable standard of energy for the correction of the charging effect and that it gives relative measurements with an accuracy of ± 0.2 eV when the sample temperature is varied from ?180°C to 200dgC or the sample holder is biased between ?10 and 10 V. About 75 spectra were recorded with powdered alumina compressed into a copper grid and the standard deviations of the corrected kinetic energies of the Al 2p and O 1s photoelectrons are respectively 0.09 and 0.06 eV.No effects of the X-ray tube current and the irradiation time are detected. The charging effect increases with the sample temperature (+0.6 eV from ?180 to 200°C). 相似文献
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Concentration by centrifugation for gas exchange EPR oximetry measurements with loop-gap resonators 总被引:1,自引:0,他引:1
Subczynski WK Felix CC Klug CS Hyde JS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,176(2):244-248
Measurement of the bimolecular collision rate between a spin label and oxygen is conveniently carried out using a gas permeable plastic sample tube of small diameter that fits a loop-gap resonator. It is often desirable to concentrate the sample by centrifugation in order to improve the signal-to-noise ratio (SNR), but the deformable nature of small plastic sample tubes presents technical problems. Solutions to these problems are described. Two geometries were considered: (i) a methylpentene polymer, TPX, from Mitsui Chemicals, at X-band and (ii) Teflon tubing with 0.075 mm wall thickness at Q-band. Sample holders were fabricated from Delrin that fit the Eppendorf microcentrifuge tubes and support the sample capillaries. For TPX, pressure of the sealant at the end of the sample tube against the Delrin sample holder provided an adequate seal. For Teflon, the holder permitted introduction of water around the tube in order to equalize pressures across the sealant during centrifugation. Typically, the SNR was improved by a factor of five to eight. Oxygen accessibility applications in site-directed spin labeling studies are discussed. 相似文献
4.
利用落塔设施创造的短时间微重力条件, 研究了不同尺寸的正方形和三角形截面的毛细管中的流体在微重力条件下的流动行为, 并与圆形毛细管中的毛细流动进行了对比, 总结出了毛细管尺寸和截面形状对界面张力主导的毛细流动行为的影响规律. 结果显示, 对于同样形状的毛细管, 其尺寸对于毛细流动的影响规律基本相同; 而对于不同的截面形状, 方形管和三角形管都与截面积小得多的圆形管有一定的类似性. 相关结果对于深入理解不同条件下的界面张力主导的毛细流动特性, 以及在空间微重力条件下通过改变毛细管的形状来实现流速和流量的独 立控制等方面都具有明显的现实意义.
关键词:
微重力
毛细流动
毛细管形状 相似文献
5.
Cros B. Courtois C. Malka G. Matthieussent G. Marques J.R. Dorchies F. Amiranoff F. Rebibo S. Hamoniaux G. Blanchot N. Miquel J.L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(4):1071-1077
In order to extend plasma accelerators, the laser beam has to be guided inside gas or plasma over a distance of the order of the dephasing length, which is typically much larger than the diffraction length zR of the laser. A capillary tube can be used as a waveguide for high-intensity laser pulses over distances well in excess of zR. Experimental demonstration of monomode guiding over 100 zR of 1016 W/cm2 pulses has been obtained in evacuated capillary tubes (45-70-μm inner diameter). A drop of transmission has been observed when the intensity of the amplified spontaneous emission (ASE) is high enough to ionize the capillary tube entrance. Propagation in helium gas-filled (10-40 mbar) capillary tubes has been studied at intensities up to 1016 W/cm2; a plasma column with on-axis density of the order of 1017 cm-3 has been created on a length of the order of 4 cm. The use of a capillary tube for an extended accelerator is discussed for the ease of linear, resonant excitation of plasma waves by laser wakefield 相似文献
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In the present work, an appliance for the measurement of the radiothermoluminescence of thin polymer layers irradiated at a temperature T = 80 K is described. The design of the electron beam source used for the irradiation as well as of both the cooling and the healing systems is presented in detail. An electrode system of oscillograph tubes is used as an election source yielding flux density I ≥ 10?6 A/cm2 with electron energy being variable from 5 keV to 25 keV. The appliance offers particular advantage by the aggregation of irradiation source, sample holder and SEV, rendering possible measurement of isothermal luminescence at low temperature immediately after irradiation. 相似文献
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A high-resolution gamma-ray spectrometer with a Ge(Li)-detector is described. The spectrometer is used as a single crystal spectrometer as well as a three crystal pair spectrometer with a Ge(Li) central detector and two NaJ-crystals for the detection of the annihilation quanta. Measurements were made of214Po. The sources were222Rn in small glass tubes. 66 gamma-rays, 10 of which hitherto unknown, were observed. An improved level scheme of214Po is given. 相似文献
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《International Journal of Mass Spectrometry and Ion Physics》1978,26(2):149-154
Thermal studies may conveniently be carried out in a programmable-temperature direct insertion probe for a mass spectrometer. If the substance is volatile, little information is gained concerning its decomposition. This problem is overcome by decomposing the material in an inert atmosphere. Helium may be used for this purpose, the output gases being sampled by the mass spectrometer. This is normally achieved by way of a capillary leak but can also be done using a GC-MS interface in which the helium is preferentially removed from the gas flow. An increase in sensitivity is thus realised. The two techniques are compared and shown to be complementary in some circumstances. 相似文献
13.
Modification of spontaneous emission rate of micrometer-sized light sources using hollow-core photonic crystal fibers
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We investigate numerically and experimentally the modification of
the spontaneous emission rate for micrometer-sized light sources
embedded in a hollow-core photonic crystal fiber (HCPCF). The
diameter of the light source is deliberately chosen such that they
could be easily introduced into the central hole of the hollow-core
photonic crystal fiber by capillary force. The photoluminescence
from the microparticles is measured by using an inverted microscope
in combination with a spectrometer. The modification of the spontaneous
emission rate is observed in a wavelength region where there is no
band gap. The experimental observations are consistent with
the simulation results obtained by the plane wave expansion and
finite-difference time-domain techniques. 相似文献
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《X射线光谱测定》2004,33(4):312-316
In recent years, new components for x‐ray analysis have been developed: capillary optics, microfocus x‐ray tubes and compact detectors, e.g. energy‐dispersive detectors without liquid nitrogen cooling. Microfocus tubes have a relatively low power but their brightness is up to 100 times higher than for normal x‐ray tubes which are used in diffractometry. A combination of these tubes with highly efficient capillary optical elements allows one to obtain parallel or focused beams of high intensity. Combining such a special source with detectors of different kinds, a compact system can be realized which may be successfully used in micro‐XRF, in diffraction and microdiffraction, etc. The system presented is designed in a modular way so that the components may be replaced by each other. Some examples of applications of such systems are reported. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
G. Genoud K. Cassou F. Wojda H. E. Ferrari C. Kamperidis M. Burza A. Persson J. Uhlig S. Kneip S. P. D. Mangles A. Lifschitz B. Cros C.-G. Wahlstr?m 《Applied physics. B, Lasers and optics》2011,105(2):309-316
Electron beams and betatron X-ray radiation generated by laser wakefield acceleration in long plasma targets are studied. The targets consist of hydrogen filled dielectric capillary tubes of diameter 150 to 200 microns and length 6 to 20?mm. Electron beams are observed for peak laser intensities as low as 5×1017?W/cm2. It is found that the capillary collects energy outside the main peak of the focal spot and contributes to keep the beam self-focused over a distance longer than in a gas jet of similar density. This enables the pulse to evolve enough to reach the threshold for wavebreaking, and thus trap and accelerate electrons. No electrons were observed for capillaries of large diameter (250???m), confirming that the capillary influences the interaction and does not have the same behaviour as a gas cell. Finally, X-rays are used as a diagnostic of the interaction and, in particular, to estimate the position of the electrons trapping point inside the capillary. 相似文献
17.
K. Nowakowska-Langier L. Jakubowski E. O. Baronova K. Czaus M. Rabinski M. J. Jakubowski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):377-382
This study reports the results of a pilot experiment concerning observations of extreme ultraviolet emission from plasma produced
by the capillary discharges. A few kA current was applied across the gas-filled alumina capillary (1 mm diameter and 8 mm
long) to generate radiation in the EUV region (12–63 nm). Spectroscopic studies were carried out by means of a XEUV spectrometer
which was upgraded for special lithography purposes. The results obtained from the EUV spectroscopic measurements provided
information about the radiation processes from xenon and argon plasma and testifies that given capillary is an effective source
of EUV emission. Additionally we showed a simulation which describes plasma dynamics parameters and dynamics of various ionization
stages in capillary discharge. Our computer simulation confirmed the presence of ions, which spectra was registered in the
experiment. 相似文献
18.
Xing Gao Songqi Gu Qian Gao Yang Zou Zheng Jiang Shuo Zhang Xiangjun Wei Haisheng Yu Guodong Sheng Peiquan Duan Yuying Huang 《X射线光谱测定》2013,42(6):502-507
A high‐resolution X‐ray fluorescence spectrometer based on Rowland circle geometry was developed and installed at BL14W1 XAFS beamline of Shanghai Synchrotron Radiation Facility. The spectrometer mainly consists of three parts: a sample holder, a spherically curved Si crystal, and an avalanche photodiode detector. The simplicity of the spectrometer makes it easily assembled on the general purpose X‐ray absorption beamline. X‐ray emission spectroscopy and high‐resolution X‐ray absorption near edge spectroscopy can be carried out by using this spectrometer. X‐ray emission preliminary results with high‐resolution about 3 eV of Mn compounds were obtained, which confirmed the feasibility of the spectrometer. The application about Eu (III) retention on manganese dioxide was also studied using this spectrometer. Compared with conventional X‐ray absorption fine structure spectroscopy technique, the fluorescence peak of probed element [Eu (III) Lα] and matrix constituents (Mn Kα) were discriminated using this technique, indicating its superiority in fluorescence detection. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
V. T. Kogan A. K. Pavlov Yu. V. Chichagov Yu. V. Tubol’tsev M. I. Savchenko O. B. Smirnov O. S. Viktorova I. V. Viktorov S. A. Vlasov B. M. Dubenskiĭ V. Nedvigin Ya. Gao 《Technical Physics》2007,52(12):1604-1610
A prototype mobile mass spectrometer for direct detection of heavy metal traces in water is proposed. The instrument allows automated dosed injection of liquid samples (2.5–20.0 μl) into the lock vacuum chamber of the instrument, extraction of salts containing target components for their following introduction into the high-vacuum chamber of the instrument, and determination of the component concentrations in the initial sample by means of a portable magnetic mass spectrometer equipped with an original electron-impact ion source. Experimental testing of the spectrometer using aqueous solutions containing Zn, Fe, Cu, As, and Cd shows that the instrument can detect heavy metals in water, including salt water, at concentrations ranging from 1 mg/l to 10 μg/l. The experimental results are discussed. 相似文献
20.
基于遗传算法的近红外光谱定性分析特征波长提取方法研究 总被引:1,自引:0,他引:1
近红外光谱分析技术虽在多领域获得广泛应用,但应用时仍以实验室仪器为主,目前光谱仪存在体积大、功耗高、价格贵等问题,有能力购买与使用此类仪器的主要是高校、科研院所、大型企业等,常用的基于傅里叶变换或光栅原理的光谱仪价格通常高达几十万元,超出中小企业、普通百姓的经济承受能力,因此近红外光谱仪的进一步推广应用仍有难度。降低仪器造价并实现微型化,是推广近红外光谱技术应用的一个重要方向,近红外光谱仪小型化的努力方向有CT正交型光栅技术以及微机电系统技术,但这两种技术方案对光谱仪体积缩小幅度有限,仍存在价格高、内部有移动部件等问题,难以做到真正微型化。据光谱仪的工作原理可知,其价格高低及微型化难度与仪器所能检测波段以及分辨率密切相关,以线性渐变滤光片与InGaAs探测器为例,分辨率越高,检测的波长点越多,其价格越高,制造难度越大。针对某一特定的定性分析任务,若能从大量波长点中挑选出少量特征波长点,并利用挑选得到的少量特征波长点完成对被测样本的定性分析任务,则可降低仪器制造成本,并降低光谱仪微型化难度,从而有利于近红外光谱分析技术的推广与应用。以玉米单倍体和多倍体籽粒作为研究对象,针对两类籽粒分类任务,分多天以漫透射方式采集被研究对象的近红外光谱,按时间顺序将所采数据分为5个数据集,对第1个数据集使用遗传算法提取出10个特征波长点,再将提取得到10个特征波长点,用于剩余4个数据集的单倍体、二倍体鉴别,以检验方法的有效性。实验结果表明使用10个特征波长点能够获得与全光谱基本一致的鉴别效果,说明使用少量特征波长点上的吸光度值也能够有效鉴别单倍体,可为其他领域某特定任务开发低成本便携式微型近红外光谱仪提供借鉴。 相似文献