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Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement 下载免费PDF全文
We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-T c superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (~10 μT-100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range (~1 kHz-10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils. 相似文献
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Liang Yan-li Yu Fei Yu Song-cheng Wu Yong-jun Zhang Hong-quan Qu Ling-bo 《Journal of luminescence》2012,132(4):1021-1024
The novel p-phenol derivatives, 4-(1-imidazolyl)-phenol, 4-hydroxybiphenyl, 4-hydroxy-4′-iodobiphenyl were employed as highly potent signal enhancers of luminol-hydrogen peroxide (H2O2)-horseradish peroxidase (HRP) chemiluminescence (CL) system. The CL reaction conditions were optimized, and the enhancement characteristics of these enhancers were compared with each other. The employment of these molecules greatly affected important assay parameters. Practically, the use of a novel enhancer, even a slightly change of the structure (or concentration) of 4-substituted phenol derivative, could affect assay properties quite dramatically. Furthermore, the use of different enhancers in the luminol–H2O2–HRP system can affect not only the intensity of the CL signal, which is well known, but also its kinetics. The experiment data indicated that the stronger intensity was combined with a more rapid decrease of the CL signal. 相似文献
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The connection between the field nonuniformity at an electrode and the distribution of discharge initiation sites over its surface is described. The results of experiments on the breakdown of transformer oil in the cone-plane system of electrodes is analyzed within the framework of a multifractal model of the charge distribution [1]. The conclusion given in [1] that the regions with the maximum local field strength are not always the most probable sites for initiation of a discharge was experimentally confirmed. We observed the theoretically predicted transition of the discharge initiation sites at sharp points on the surface of a cone. For electrodes of stainless steel and transformer oil a value of the index relates the probability of initiation of a discharge to the local field strength was determined.Scientific — Research Institute of High Voltages at Tomsk Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 32–35, April, 1995. 相似文献
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Y. Hamasaki T. Miyamoto Y. Kuhara M. Katoh K. Tada S. Takeuchi T. Nakahara 《Fiber and Integrated Optics》1981,3(4):383-389
An optical fiber sensor for measuring high electric field intensity and voltage, which utilizes the electro-optic effect of bismuth silicone oxide single crystal, has been developed successfully, and the fundamental characteristics have been evaluated. The electric field intensity distribution inside the coaxial electrodes has been measured with this sensor. The measured results are in agreement with the theoretical values. 相似文献
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V. D. Ovsiannikov V. V. Chernushkin 《Journal of Experimental and Theoretical Physics》2000,91(3):458-468
Under the conditions of the total Paschen-Back effect the diamagnetic interaction determines the dependence of the intensity of the Zeeman components of atomic radiation lines on a magnetic field. The change in the matrix elements of the radiative transitions is due to the magnetically induced corrections to the wavefunctions of the initial and final states, whose contributions are of the same order of magnitude for the head lines of the optical series. For the high-frequency lines the positive corrections to the matrix element from the wavefunction of the upper level dominate. A magnetic field also induces dipole radiative transitions with selection rules for the orbital angular momentum | Δl| ≥ 3. The matrix elements of such transitions increase rapidly with the energy of the upper level, making possible efficient single-photon population of the dipole-inaccessible Rydberg states in moderate magnetic fields. 相似文献
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Photoacoustic imaging is a hybrid biomedical imaging technique, combining rich optical contrasts and good acoustic resolution in deep tissues. As a noninvasive and nonionized imaging method, photoacoustic imaging has shown great potentials in biomedicine in the past decade. In this review, we give a brief introduction of the physical principle and three major implementations of photoacoustic imaging. Then, we present pictures of some recent progress about the extraction of new imaging parameters from photoacoustic radio-frequency signals. These parameters are highly associated with the tissue microstructure characteristics, including characteristic size, number density, and elasticity. This information could give us insight into various properties of tissue in-depth and be applied to tissue classification for basic research and clinical settings. 相似文献
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R. Vivek Sabaapathy N. Sankara Subramanian S. Vinoth Kumar S. Naveen Chandran G. Vimal Kumar 《Ionics》2007,13(5):311-317
The present work deals with the design, development, and implementation of an angle detector using n-ATO/p-PSi photovoltaic
sensor. Nanoporous structures have been developed over p-type porous silicon wafers by anodization technique under optimized
conditions. Photoluminescence studies of porous silicon show emission between 700 and 702 nm for the constant excitation at
350 nm, which illustrates that the band gap can be tuned according to the HF:H2O:C2H5OH ratio. n-ATO/p-PSi O heterojunction photovoltaic sensor has been developed by cost-effective Spray pyrolysis method. I–V
characteristics under dark and different illumination intensities have been investigated, and the results are discussed. The
fabricated sensor is employed for sensitive angle detection of a light source. The sensor is attached to a DC motor, which
rotates at 30 rpm. When the light is from the source incident on the light sensor, a dc voltage has been produced, which in
turn is amplified, and the signal has been used to stop the motor. The motor is coupled to a rotary transducer, which is calibrated
to read or display 0–3.60 V for 0–360°.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
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Yu. I. Golovin R. B. Morgunov A. A. Baskakov S. Z. Shmurak 《Physics of the Solid State》1999,41(11):1783-1785
After exposure of single-crystal ZnS with microscopic twinning to magnetic fields of 1–10 T, the integral electroluminescence
brightness is found to increase by several times. It is proposed that the magnetic field facilitates relaxation of a metastable
state of the structural defects.
Fiz. Tverd. Tela (St. Petersburg) 41, 1944–1947 (November 1999) 相似文献
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It is widely held that Bohr has shown that the spin of a free electron is not measurable. We point out that Bohr's argument has some important ifs and buts. A concrete configuration is calculated to produce a clear spin separation. This is then shown not to contradict Bohr's reasoning. 相似文献
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研究了兼有电光效应和磁光效应的晶体内电光与磁光效应的互补特性及其传感应用. 在光强度调制条件下, 晶体中偏振光波的电光调制与磁光调制具有互相补偿的效果, 从而能够使输出光强度保持为一个固定值. 基于这种互补特性, 提出了一种利用单块闪烁锗酸铋(Bi4Ge3O12, BGO)晶体的电光补偿型光学电流(磁场)传感器, 其光学传感单元由两个偏振器和一块平行四边形BGO晶体组成. 该晶体自身能够产生π/2的光学相位偏置, 同时兼用作电流传感和电光补偿元件, 通过控制BGO晶体的外加电压, 能够实时补偿被测电流(磁场)变化引起的磁光旋转角和输出光强度的变化, 从而实现电流(磁场)的闭环光学测量. 实验测量了5.0 A范围内的工频交流电流, 所需要的电光补偿电压约为21.2 V/A, 补偿电压与被测电流之间具有良好的线性关系, 其非线性误差低于1.7%. 相似文献
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The effect of the optical excitation signal intensity on the impulse response of a photodetector based on a set of metal-semiconductor-metal
(MSM) rectifier contacts is studied. The response of the detector is better at a low optical excitation signal. When the energy
of an optical excitation pulse is high, the response can be improved by increasing the bias voltage. The advantages of a GaN-based
MSM diode in detecting high- energy radiation pulses are established. It is shown that the speed of the GaN-based MSM detector
may reach 25 ps for a 60-pJ optical excitation pulse at a wavelength of 290 nm. 相似文献
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A prototype RPC with position resolution less than 1 mm has been produced and studied. Based on this RPC detector, the effect of the width of the integrated FADC time window on the position resolution of a RPC has been studied experimentally and theoretically. The results of theoretical calculation and experimental measurement have shown good agreement. 相似文献
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西藏羊八井宇宙射线观测站的中子监测器主要探测宇宙射线次级粒子中能量在500 MeV—20 GeV的核子成分和少量的负μ子成分. 本文分析了2008—2010年观测站附近发生的62次雷暴期间中子监测器和大气平均电场仪的同步观测资料, 发现27次雷暴期间中子监测器计数率发生明显变化, 显著性S>5σ, 其中13次变化显著, 显著性S>10σ . 显著性S>10σ的13次个例信号变化百分比与地面电场场强幅值之间存在大体一致的变化趋势, 而显著性在5σ <S<10σ之间的14次个例信号变化百分比与地面电场场强幅值之间不存在相似的变化趋势. 较强雷暴当顶时中子监测器计数率变化一般不明显, 而中子监测器计数率变化明显的个例则多发生于雷暴云不当顶, 但探测器仍处于雷暴云下部正电荷层的控制范围之内时, 或者当顶雷暴处于形成或消散阶段. Dorman等把雷暴期间中子监测器计数率的变化归因于雷暴云内电场对宇宙射线次级粒子μ子的作用, 并建立了雷暴期间中子监测器计数率变化与雷暴地面电场相关联的理论. 本文分析发现雷暴期间羊八井中子监测器计数率变化与地面电场场强之间相关性较小或者没有相关性, 不支持Dorman的理论. 相似文献
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A prototype RPC with position resolution less than 1 mm has been produced and studied. Based on this RPC detector, the effect of the width of the integrated FADC time window on the position resolution of a RPC has been studied experimentally and theoretically. The results of theoretical calculation and experimental measurement have shown good agreement. 相似文献