Twin LC Resonator System for EPR Measurements Operating at Radio-Frequency

Two LC resonant circuits resonating at the same frequency (245 MHz) faced each other with reverse polarity (twin electron paramagnetic resonance (EPR) resonator). For the inductor of the LC circuit, a square single-turn one-loop coil (width, 38 mm) was fabricated. Each LC circuit was independently tuned using mechanical variable capacitors. A cylindrical phantom (diameter, 25 mm) including a 1 mM nitroxide radical physiological saline solution was located at the center of two coils (distance between these coils, 50 mm). Two resonant frequencies (the lower and the higher ones) were observed at each LC circuit of the twin EPR resonator with termination of the other LC circuit. The lower resonant frequency alone was observed when the powers from two LC circuits of the twin EPR resonator were combined by a 180° combiner. On the other hand, the higher frequency alone was observed when they were combined by a 0° combiner. EPR signals could be obtained using the 180° combiner (lower frequency) but not the 0° combiner (higher frequency).     

Charge transport in activated carbon electrodes: the behaviour of three electrolytes vis-à-vis their specific conductance

In this study, the electrochemical performances of different aqueous electrolytes (6 M KOH, 2 M KCl and 0.5 M K₂SO₄) in activated carbon electrodes are evaluated with regard to their use in electrochemical double layer capacitor (EDLC). The results from cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) were analysed. The lowest value of equivalent series resistance (ESR) and the highest values of specific capacitance and coulombic efficiency were observed, when KOH was the electrolyte. The impedance spectroscopy plots were fitted to an equivalent circuit of ladder type to evaluate the resistances to ion transport at different levels of hierarchies in the pore network. Also, the quality of the double layer capacitance at lower hierarchy that primarily contributes to the overall capacitance of the device was evaluated from the leakage resistance in the equivalent circuit. The fitted circuit parameters were further reviewed vis-à-vis the specific conductance of chosen electrolyte, and the number of successive charge–discharge cycles prior to the EIS measurements.     

SUNIST低环径比托卡马克的供电系统

介绍了SUNIST低环径比托卡马克的纵向场线圈、欧姆加热场线圈和平衡场线圈的电学参数。所用电容器组储能系统采用电容换流式准恒流充电回路。测量了这三组线圈中的放电电流,并将测量结果与回路计算结果作了比较。     

Oxidation state of vanadium in amorphous MnV2O6 formed during discharge–charge cycle and the improvement of its synthesis condition

Crystalline powders of anhydrous MnV₂O₆ were successfully synthesized at a temperature below 200 °C under autogenous hydrothermal condition. MnV₂O₆ powders, which were synthesized using high concentration solutions, more than 0.1 mol/L, gave a relatively high reversible capacity of 600 mA h/g and interesting cyclic performance, reversible capacity increasing to more than an initial charge capacity after the 3rd or 4th cycle of charge–discharge. The change in oxidation state of V ion on the course of the 1st discharge–charge process was investigated by different techniques, such as XAFS and XPS. During discharging, V⁵⁺ was found to change gradually to V⁴⁺, but it returned back completely to V⁵⁺ on charging process. The thinner particles of MnV₂O₆ crystals with rod-like morphology were synthesized at 135 °C, and much better anodic performance was achieved, much smaller irreversible capacity as about 300 mA h/g, stable reversible capacity as 600 mA h/g, and 100% Coulombic efficiency.     

Effect of carbon coating on the electrochemical performance of LiFePO<Subscript>4</Subscript>/C as cathode materials for aqueous electrolyte lithium-ion battery

Organic electrolyte is widely used for lithium-ion rechargeable batteries but might cause flammable fumes or fire due to improper use such as overcharge or short circuit. That weakness encourages the development of tools and materials which are cheap and environmental friendly for rechargeable lithium-ion batteries with aqueous electrolyte. Lithium iron phosphate (LiFePO₄) with olivine structure is a potential candidate to be used as the cathode in aqueous electrolyte lithium-ion battery. However, LiFePO₄ has a low electronic conductivity compared to other cathodes. Conductive coating of LiFePO₄ was applied to improve the conductivity using sucrose as carbon source by heating to 600 °C for 3 h on an Argon atmosphere. The carbon-coated LiFePO₄ (LiFePO₄/C) was successfully prepared with three variations of the weight percentage of carbon. From the cyclic voltammetry, the addition of carbon coatings could improve the stability of cell battery in aqueous electrolyte. The result of galvanostatic charge/discharge shows that 9 % carbon exhibits the best result with the first specific discharge capacity of 13.3 mAh g^?1 and capacity fading by 2.2 % after 100 cycles. Although carbon coating enhances the conductivity of LiFePO₄, excessive addition of carbon could degrade the capacity of LiFePO₄.     

Investigation of intracavity third-harmonic generation at 1.06 μm in YCa4O(BO3)3 crystals

Intracavity sum-frequency mixing of 1.06 μm and 532 nm in YCa₄O(BO₃)₃ (YCOB) crystals cut for different type-I phase-matching directions of (θ,ϕ)=(106°,77.2°), (111°, 79.6°) and (65°, 82.8°) was investigated in a compact diode-end-pumped acousto-optical Q-switched Nd:YVO₄/KTP laser formed with a three-mirror folded resonator. The maximum 355-nm average output power of 124 mW was obtained in the phase-matching direction of (106°, 77.2°) with a pump-to-ultraviolet conversion efficiency of 3.3% at the repetition frequency of 20 kHz. Received: 17 September 2001 / Revised version: 27 November 2001 / Published online: 17 January 2002     

Effect of heptamethyldisilazane on the electrochemical performance of LiMn2O4/Li

The effect of heptamethyldisilazane as an electrolyte stabilizer on the cycling performance of a LiMn₂O₄/Li cell at different rates at 30 °C and the storage performance at 60 °C is investigated systematically based on conductivity test, linear sweep voltage, electrochemical impedance spectroscopy, scanning electron microscopy, X-ray diffraction, and charge–discharge measurements. The results show that heptamethyldisilazane added into the LiPF₆-based electrolyte can increase the stability of the original electrolyte; coulomb efficiency, the initial discharge capacity, and cycling performance at different rates in a sense, meanwhile, improve the storage performance at elevated temperature, although the C-rate performance of the cell is a little worse than that without heptamethyldisilazane in the electrolyte. When the LiMn₂O₄/Li cell with heptamethyldisilazane in the LiPF₆-based electrolyte stored at 60 °C for a week cycles 300 times, the capacity retention is up to 91.18 %, which is much higher than that (87.18 %) without the additive in the electrolyte. This is mainly due to the lower solid electrolyte interface resistance (R _f) in the cell, followed by the better morphology and structure of the cathode after storage at 60 °C for a week compared with the LiMn₂O₄/Li cell without heptamethyldisilazane.     

The kinetics of Cr layer coated on TiNi films for hydrogen absorption

The effect of hydrogen absorption on electrical resistance with temperature for TiNi and TiNi-Cr thin films was investigated. The TiNi thin films of thickness 800 Å were deposited at different angles (? = 0°, 30°, 45°, 60° and 75°) under 10^?5 Torr pressure by thermal evaporation on the glass substrate at room temperature. A layer of Cr of thickness 100 Å was coated on the TiNi thin films. The changing rate of hydrogen absorption increases after Cr layer coating because Cr enhances the catalytic properties of hydrogen absorption in thin films. The rate of hydrogen absorption increases with temperature at lower range but at higher range of temperature it was found to decrease and also it was found that the hydrogen absorption increases with angle of deposition.     

平板型感应耦合等离子体源的线圈配置对功率耦合效率的影响

基于感应耦合等离子体的变压器模型，分析了感应耦合等离子体的功率耦合效率与线圈配置(几何尺寸、电学参量)及等离子体基本参量(等离子体电子密度、电子-中性粒子有效碰撞频率)之间的关系；然后，改变平板型线圈的匝数从而改变了线圈的几何尺寸、电学参量，并且测量出了不同的线圈所对应的功率耦合效率.实验结果表明，线圈的电感量是能否实现放电的决定性因素；而功率耦合效率则与感应线圈的Q值、放电参量(气压、功率)等密切相关，射频输入功率的增加、放电气压的上升都会导致感应耦合等离子体耦合效率的提高，这与感应耦合等离子体的变压器模型预测结果是符合的. 然而，变压器模型给出的提高线圈Q值可导致耦合效率增强的预测结果仅适用于同等电感量的线圈条件. 本文对于单线圈的感应耦合等离子体源的研究为线圈的优化设计甚至大面积的多线圈感应耦合等离子体源研制提供了理论依据. 关键词： 感应耦合等离子体 功率耦合效率 变压器模型     

Polarization behavior of Ni-YSZ cermet anodes in YSZ fuel cells running on methane under internal reforming conditions

The polarization characteristics of the Ni-YSZ cermet anode/YSZ interface were studied as a function of gas phase composition, temperature and anodic overpotential in methane fuelled internal reforming YSZ fuel cells. AC impedance measurements carried out under open circuit conditions in the temperature range 800 to 900°C showed the presence of at least two rate-limiting processes that were influenced by temperature and gas phase composition. The apparent polarization resistance, R_app, of the Ni-YSZ cermet anode/YSZ interface was found to increase with increasing methane partial pressure and decreasing H₂O partial pressure. The activation energy related to the apparent polarization conductance R _app ⁻¹ varied between 0.7 and 1.1 eV, mainly due to the variation of P_{H 2 O}. The order of magnitude of the apparent capacitance, C_app, values calculated from AC impedance data under open circuit conditions indicate that the observed capacitance corresponds to the double layer capacitance of the Ni/YSZ interface and/or a pseudo-capacitance related to adsorption of species on the Ni-YSZ cermet electrode accompanied by charge transfer. C_app was found to decrease with increasing methane partial pressure. AC impedance measurements carried out under closed circuit conditions at 900 °C and four different P_{H 2 O} showed the appearance of a low-frequency inductive loop at high anodic over-potentials, in addition to the features observed under open circuit conditions. The effect of gas phase composition on R_app was similar to the one observed under open circuit conditions. In addition an almost exponential decrease of R_app with increasing anodic overpotential was observed. The present results are compared with results presented in literature and discussed in the frame of the mechanism of the electrochemical and catalytic reactions taking place over the anode. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Intracavity second-harmonic generation of 1.06 μm in GdCa4O(BO3)3 crystals

The characteristics of intracavity second-harmonic generation (SHG) at 1.06 μm in GdCa₄O(BO₃)₃ (GdCOB) crystals cut for different type I phase-matching (PM) directions of (θ,φ)=(66.8°, 132.3°); (19.4°, 0°); (90°, 46°) have been investigated. It was found that the intracavity SHG was significantly efficient in the PM direction of (66.8°, 132.3°), and that the intrinsic lower effective nonlinear coefficient (d_eff) was responsible for the less-efficient SHG in the other two directions. A maximum CW SHG output power of 2.81 W was obtained with an optical conversion efficiency of 18.7%, while the corresponding effective intracavity SHG efficiency was determined to be 41.3%. The intracavity SHG efficiency of GdCOB has been found to reach two-thirds of that obtained with type II phase-matching KTiOPO₄ (KTP). Received: 26 April 2000 / Revised version: 3 July 2000 / Published online: 5 October 2000     

Frequency response of polycrystalline samples of α-Zr(HPO4)2·H2O with different relative densities

Polycrystalline samples of α-Zr(HPO₄)₂·H₂O with different relative densities were investigated by ac admittance measurements at 20°C and 75% relative humidity. The analysis of the frequency response allowed an equivalent circuit to be derived whose parameters were calculated by complex non-linear regression. It was found that the response of the polycrystalline samples was accurately modelled by a parallel combination of a resistance and a constant phase-angle element, both strongly dependent on relative density. The results are discussed on the basis of the present knowledge of the electrical properties of α-Zr(HPO₄)₂·H₂O.     

Preparation and Characterization of Novel Polyimides with Hydroxyl Groups

3,3′-diamino-4,4′-dihydroxybiphenyl (DADHBP) was synthesized and its chemical structure was confirmed by Fourier transform infrared (FT-IR) spectroscopy, ¹H-nuclear magnetic resonance (¹H-NMR), and differential scanning calorimetry (DSC). Then six poly(amic acid) (PAA) solutions were prepared by copolymerization of DADHBP, oxydiphthalicanhydride (ODPA), and 2,2-bis [4-(4-aminophenoxy)phenyl] propane (BAPOPP) in N,N-dimethylacetamide (DMAC) in different mole ratios. The polyimide (PI) films were obtained through thermal imidazation reactions of the thin layers of the above-mentioned precursor solutions. Chemical structures of all PI films were demonstrated by FT-IR. Thermal stabilities and decomposition behaviors of the PI films were tested by DSC and thermogravimetric analysis (TGA). Thermal measurements indicate that the polymers have high thermal stability and produce high char yields. The properties of the PI films were further studied by ultraviolet–visible spectroscopy, water absorption, surface energy, and mechanical measurements. Thermal analysis showed glass transition temperatures between 205.9°C and 276.7°C. Decomposition temperatures were higher than 360.2°C, with 10% weight losses in the range of 448.6°C～517.8°C. The prepared PI films also exhibited good UV absorption, low water absorption (<2%), low surface energy (<44.28 mJ/m²), and good mechanical properties.     

Investigation on the storage performance of LiMn2O4 at elevated temperature with the mixture of electrolyte stabilizer

In order to investigate the effect of different electrolytes of LiPF₆-based and LiPF₆-based with the mixed additives of ethanolamine and heptamethyldisilazane on the storage performance of LiMn₂O₄, the commercial LiMn₂O₄ are added into these different electrolytes for storing deliberately at 60 °C in air for 4 h. The results show that the electrolyte with additives can prevent LiMn₂O₄ from being eroded by HF to a certain extent, and improve the storage performance of the material. The initial discharge capacities are 97.7 and 88.4 mAh g^?1 at 0.1 and 1?C, respectively, which are much higher than that 84.4 and 63.6 mAh?g^?1 of LiMn₂O₄ stored in the electrolyte without additives. Moreover, the former LiMn₂O₄ retains 89.1 % of its initial discharge capacity at 1?C after 150 cycles, while this is not up to 84 % for the latter.     

合成聚肽嵌段共聚物PHEG-PBLG结构的核磁共振分析

通过L-谷氨酸苄酯和三光气反应制备谷氨酸苄酯的N-羧酸酐,以聚羟乙谷氨酸酰胺为大分子引发剂,投入不同配比的单体/引发剂（A/I）,共聚得到两亲性嵌段共聚物聚羟乙谷氨酰胺-聚谷氨酸苄酯（PHEG-PBLG）;通过核磁共振技术分析表征该合成聚肽的结构组成、分子量范围及螺旋结构;通过体外酶解实验研究了共聚物的降解情况. 研究结果表明：该合成聚肽化合物为两亲性嵌段聚合物：当聚合物中亲水链段PHEG分子量为9000,A/I为75∶1, 100∶1, 150∶1, 200∶1时,相应的共聚物的分子量分别为：1.27×10⁴,1.75×10⁴, 1.9×10⁴, 3.60×10⁴;该合成聚肽含有α-螺旋结构, 随着TFA的加入,该聚肽的结构由α-旋构象转化为随机盘绕构象.     

Resonator micro optic gyro with double phase modulation technique using an FPGA-based digital processor

Experiments on resonator micro-optic gyro (RMOG) with a digital proportional integral (PI) feedback scheme are performed. In this experimental setup, the key rotation sensing element is a polarization maintaining silica waveguide ring resonator (WRR) with a ring length of 7.9 cm and a diameter of 2.5 cm. A good linearity of 0.0015% over a wide range of ± 2 × 10⁴ °/s can be achieved for the RMOG theoretically. The optimal digital PI feedback scheme is adopted in the frequency servo loop to reduce the reciprocal frequency fluctuations due to the WRR resonance frequency and laser frequency drifts. Residual equivalent input fluctuation can be reduced as low as 0.03 °/s/√Hz based on the optimal digital PI feedback scheme, which is close to the shot noise limited spectral density 0.02 °/s/√Hz of the RMOG with the input optical power of 0.2 mW. Relationship between RMOG output signal and angular rate is obtained from ± 0.1 °/s to ± 5 °/s. The standard deviation of the residuals between RMOG output results and linear fit curve is 0.066 °/s. For an integration of the processing circuit, all the processing circuit is implemented by a field programmable gate array (FPGA) instead of instruments. The output of this digitalized RMOG is obtained over a range of ± 550 °/s. The linearity of this digitalized RMOG is 0.0169%.     

Comparative measurements of plasma position using coils,hall probes,and bolometers on CASTOR tokamak

Plasma position on CASTOR tokamak is measured by several systems based on different experimental methods. Vertical and horizontal plasma displacements are deduced from data of 4 Mirnov coils spaced poloidaly by 45°. Output of the Mirnov coils is routinely used as an input for automatic feed-back control of plasma position on CASTOR. Independently, we used an array of 16 Hall sensors, which measure the required magnetic field directly. Additional information on plasma position is obtained from two arrays of bolometers that measure horizontal and vertical profile of plasma radiation. Principle design of the all used diagnostics is given. Comparison of horizontal and vertical displacements deduced using various experimental methods is presented.     

HL-2Aװ��ͬ��Բ��Ȧ�������ЧӦ

介绍了HL-2A装置上同心圆逆磁测量的原理以及同心圆系统的设计,包括线圈面积差的确定和积分电路的设计。对实验数据的分析表明,通过对杂散场的有效补偿,同心圆逆磁测量系统可获得较高的信噪比,能够在一些较复杂的放电条件下可靠地获取等离子体逆磁信号。     

����IGBT��SUNISTŷķ����Դϵͳ

为充分利用SUNIST球形托卡马克欧姆场的双向磁通,延长等离子体电流平顶时间,对欧姆场的电源系统进行了改造。提出了一种基于多个IGBT并联大电流低频开关的H桥双向放电电路,研发了该双向放电电路的核心元件——3kV/10kA级的IGBT并联大电流开关。对单相电容准恒流充电电路与三相桥式电容换流充电回路进行了研究,合理地确定了双向放电主回路中两组储能电容器C1和C2的充电系统。经过安装、调试以及初步试验,在欧姆场线圈中得到了从正10kA到负6kA的双向放电电流,等离子体电流波形也有明显改善。     

Brain Imaging with Slotted Hybridized Magnetic Metamaterial Hat at 7-T MRI

Study of human pathologies and acquisition of anatomical images without any surgical intervention inside human body is possible because of magnetic resonance imaging (MRI), which is the keystone technique to characterize the psychology and neurochemistry of human body. However, for clinical trials, the study and cure of human diseases are followed by medical investigations of different animal anatomies. By employing different imaging techniques to animal anatomical models during their clinical trials yielded in exceptional image acquisition without any surgical invasion in the model, which resulted in noninvasive technique as compared to surgical invasion and opened the possibility to study human pathologies more precisely. This work exploits the notable properties of unique combination of multi-circular hybridized surface coils which can be used as hybridized magnetic metamaterial hat (HMMH). HMMH not only strengthens the uniformity of radio frequency (RF) rotational symmetry around its axis but also improves the signal-to-noise ratio (SNR) for rat’s brain imaging at 7-T MRI. We analyzed a periodic array of strongly coupled circular copper coils attached on circular coil shaped printed circuit board (PCB) substrate. In the design, some copper coils were inspired by the slot cavity loaded with parametric elements (capacitor and inductor). In addition, coils in the form of HMMH exploited the advantages of the hybrid modes which exhibited better and deeper RF sensitivity into the region of interest (ROI) as compared to single loop RF coil by exciting two Eigen modes simultaneously which resulted in homogenized magnetic field (B-field) and enhanced SNR at ROI. At resonance, the value of relative negative permeability, μ _r  = ?7 + j11 was achieved at 300 MHz for 7-T MRI. Furthermore, image quality at ROI was optimized by varying rat’s head position under magnetic resonance (MR) coil of MRI apparatus and in the presence or absence of HMMH. Design configuration and circuit model analysis were also done.