Multiple-value inductance coils for working standards

The circuit and construction of new multiple-value toroidal inductance coils of 1 μH to 1 H for first- and second-class working inductance standards are described. Optimal relations between the dimensions of toroidal coils with different cross-section geometries providing the best Q factor for a given inductance and external coil diameter have been obtained. The results of experimental investigations are presented. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 21–24, October, 1997.     

Micromixer-based time-resolved NMR: applications to ubiquitin protein conformation

Time-resolved NMR spectroscopy is used to studychanges in protein conformation based on the elapsed time after a change in the solvent composition of a protein solution. The use of a micromixer and a continuous-flow method is described where the contents of two capillary flows are mixed rapidly, and then the NMR spectra of the combined flow are recorded at precise time points. The distance after mixing the two fluids and flow rates define the solvent-protein interaction time; this method allows the measurement of NMR spectra at precise mixing time points independent of spectral acquisition time. Integration of a micromixer and a microcoil NMR probe enables low-microliter volumes to be used without losing significant sensitivity in the NMR measurement. Ubiquitin, the model compound, changes its conformation from native to A-state at low pH and in 40% or higher methanol/water solvents. Proton NMR resonances of the His-68 and the Tyr-59 of ubiquitin are used to probe the conformational changes. Mixing ubiquitin and methanol solutions under low pH at microliter per minute flow rates yields both native and A-states. As the flow rate decreases, yielding longer reaction times, the population of the A-state increases. The micromixer-NMR system can probe reaction kinetics on a time scale of seconds.     

Use of Helmholtz coils for magnetic measurements

Helmholtz coils can be used for the measurement of open-circuit magnetization of most permanent magnet materials. The author describes the physics of the measurement, lists the materials that can be measured, derives the coil constant, and derives a correction factor for the measurement of arc magnets. A measurement is made by placing the magnet at the center of the coils, and zeroing the integrating voltmeter or fluxmeter. The magnet is then removed from the coil, parallel to the coil axis, to a distance such that the sample has no influence on the reading, typically 75 to 100 cm. The open-circuit magnetization of the sample is related to the time-integrated voltage     

Using Rogowski coils for transient current measurements

The Rogowski-coil method of measuring electric current has developed into a versatile measuring system with many applications throughout industry and in research. The technique possesses many features which offer an advantage over iron-cored current measuring devices and these are well illustrated by considering how it can be used for measuring transient currents. The authors describe the principle of operation of Rogowski coils and the practical aspects of using them and give several examples of their use in making transient measurements. The Rogowski coil is a conceptually simple device. Its theory of operation illustrates some basic principles of electromagnetism applied in a practical device. The coil itself provides a demonstration of Ampere's Law which is described by the authors     

Structured graphene devices for mass transport

The reversible atomic-mass transport along graphene devices has been achieved. The motion of Al and Au in the form of atoms or clusters is driven by applying an electric field between the metal electrodes that contact the graphene sheet. It is shown that Al moves in the direction of the applied electric field whereas Au tends to diffuse in all directions. The control of the motion of Al is further demonstrated by achieving a 90° turn, using a graphene device patterned in a crossroads configuration. The controlled motion of Al is attributed to the charge transfer from Al onto the graphene so that the Al is effectively charged and can be accelerated by the applied electric field. To get further insight into the actuation mechanism, theoretical simulations of individual Al and Au impurities on a perfect graphene sheet were performed. The direct (electrostatic) force was found to be ～1 pN and dominant over the wind force. These findings hold promise for practical use in future mass transport in complex circuits.     

部分编码结构光三维测量技术的研究

提出了一种部分编码结构光三维面形测量方法,将相位展开技术与条纹编码结合起来,既有效地减少了投影和拍摄的图像数量又提高了相位展开的可靠性.该方法利用部分编码技术对相邻的多根条纹进行整合,减小了条纹密度,然后再对整合后的条纹相位进行展开,最终得到整个图像的相位分布.实验证明,该方法可以较大程度地减少重建所需的画幅数,同时具有良好的精度和可靠性.     

Design of optimal measuring coils for magnetic measurements

Measurement Techniques -     

Quench detection system for twin coils HTS SMES

The quench detection and protection system is a critical element in superconducting magnets. After a short summary of the quench detection and protection issues in HTS magnets, an original detection system is presented. The main feature of this system is an active protection of the detection electronics during the discharges, making it possible to use standard electronics even if the discharge voltage is very high. The design of the detection system is therefore easier and it can be made very sensitive. An implementation example is presented for a twin coil HTS SMES prototype, showing the improvements when compared to classical detection systems during operation.     

Prediction of impedance components for eddy-current probe coils for standardization

Predictions are made with a view to standardizing the indications of eddy-current flaw detectors having finite-length air-cored surface probes. Excellent agreement with measurements has been obtained. Difficulties arising with the uses of ferrite-cored probes and the testing of ferrous metals are discussed.     

Quenching of superconducting coils

Although the speed of propagation of the boundary between normal and superconducting regions in a wire falls with decreasing current, different, and even opposite behaviour can be observed in a coil during a quench. It is suggested that this is due to the changing field causing hysterestic heating of the conductor.     

磁共振成像交替阻抗微带线射频线圈仿真分析

为研究改变交替阻抗微带线射频线圈的几何尺寸对感兴趣区内磁场分布的影响,保持微带线射频线圈总长度不变,改变宽带与窄带的长度比例和宽度比例,在HFSS中建立交替阻抗微带线射频线圈的仿真模型,与传统微带线射频线圈进行比较,利用ADS与HFSS的协同仿真实现线圈的调谐和匹配.仿真结果表明交替阻抗微带线射频线圈感兴趣区内的磁场均值比传统微带线射频线圈的提高了一倍以上.调整交替阻抗微带线射频线圈的宽带与窄带的长度比例和宽度比例,可以提高感兴趣区内的磁场强度,同时改善磁场分布的均匀性.     

Tilted toroidal coils for superconducting magnetic energy storage systems

Superconducting magnetic energy storage (SMES) systems can be used to improve power supply quality and reliability. In addition, large amounts of power can be drawn from a small stored energy supply. Nevertheless, the strong electromagnetic force caused by high magnetic fields and coil current is a serious problem for SMES. To cope with this problem, we propose a new coil design, the tilted toroidal coil (TTC). The TTC, obtained from the toroidal field coil (TFC) system by varying two pitching angles, allows the balancing of the electromagnetic force in the major radius direction, maintaining the same manufacturing simplicity of the TFC system. After determining balanced configurations through computer simulation, we built an experimental device to confirm the feasibility of the balancing effect.     

Analytical model for tilted coils in eddy-current nondestructive inspection

The electromagnetic field and impedance of a cylindrical eddy-current probe coil are calculated analytically for arbitrary coil orientation above a conductive half-space. The remarkably simple closed-form expressions are provided as a function of coil tilt angle. The effect of tilt on the impedance change produced by a long crack is also investigated by combining the analytical model with an existing thin-skin theory for surface crack inspections. Results for both cracked and uncracked conductors are expected to be useful for evaluation of movement-generated noise in eddy-current inspections.     

Amide proton back-exchange in deuterated peptides: applications to MS and NMR analyses

Deuterium for hydrogen exchange at amide sites in proteins is a well-established means of probing the stability of certain proteins and the effects of interactions with ligands and other proteins. When deuterium content is analyzed by mass spectrometry (MS) of digested peptides, corrections frequently need to be made for back-exchange that occurs during digestion, separation, and analysis. The back-exchange process is actually complex and deserving of analysis in a sequence-specific manner. Here an analysis of back-exchange in the decapeptide, angiotensin I, and a hexapeptide derived by digestion of a 15N-labeled carbohydrate-binding protein, galectin-3, is presented. Nuclear magnetic resonance (NMR) data are used to study back-exchange at specific sites in typical solvents used for separation and analysis, and the derived rates are found to be predictable using methods established for aqueous solvents. The predictability provides potentially new means of improving site specificity of MS analysis and new means of assigning NMR resonances for deuterium content analysis in peptides.     

Mathematical curls and toroidal coils

The author discusses magnetic vector potential giving an alternative view of whether a magnetic field exists outside a toroidal winding. The author discusses circulation in circular fields, the magnetic vector potential of a toroidal winding, the current transformer worked 'backwards', and short solenoids. An appendix discusses the rate of decline with radius on a circular field on its circulation     

Structured fluid theory

Summary The simplest case of structured fluid theory is shown to correspond to a type of Maxwell fluid which exhibits normal stress differences. A nonlinear problem related to the deformation of suspended liquid drops as induced by inertial effects is solved and the influence of structured fluid parameters investigated.

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Theorie strukturierter Flüssigkeiten

Zusammenfassung Es wird gezeigt, daß der einfachste Fall einer strukturierten Flüssigkeit einer Art Maxwellscher Flüssigkeit entspricht, welche Differenzen im Betrag der Normalspannungen aufweist. Ein nichtlineares Problem, welches mit der durch Trägheit verursachten Deformation eines Tropfens zusammenhängt, wird gelöst. Der Einfluß der Parameter der strukturierten Flüssigkeit wird untersucht.

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With 2 Figures