Combining a Magnetic Field Modulation Coil with a Surface-Coil-Type EPR Resonator

It is thought that the design of magnetic field modulation coils is one of the factors limiting enlargement of the sample size in electron paramagnetic resonance (EPR) measurements. In this study, we miniaturized the magnetic field modulation coil and combined it with a surface-coil-type resonator (SCR). The inductor of the SCR was a circular single-turn one-loop coil (diameter, 1 mm), and the magnetic field modulation coil was a twin-loop coil consisting of two solenoid coils each made of 15 turns of copper wire on a cylindrical bobbin with an axial length of 3 mm and an elliptical cross section (major axis, 7 mm; minor axis, 3 mm). The former was located on the latter via a spacer (thickness, 3 mm) in such a way that the directions of their axes coincided. Their combined size was about 10 mm wide, 10 mm deep, and 6 mm high. The transmission lines of the SCR were set on resonance at about 700 MHz. EPR measurements of a phantom (comprising agar that included a nitroxide radical and physiological saline solution), made with a miniaturized modulation coil combined with the SCR, exhibited a sensitivity similar to that for the conventional method. Authors' address: Hidekatsu Yokoyama, Department of Pharmaceutical Sciences, International University of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara 324-8501, Japan     

A low-cost implementation of EPR detection in a dissolution DNP setup

The implementation of electron paramagnetic resonance (EPR) detection in a low-temperature dissolution dynamic nuclear polarization (DNP) setup is presented. Using a coil oriented parallel to the static magnetic field, the change of the longitudinal magnetization of free radicals is measured upon resonant irradiation of an amplitude or frequency modulated microwave (mw) field. The absorption EPR spectrum is measured if the amplitude of the mw field is modulated, whilst the first derivative of the spectrum is obtained with frequency modulation. Using a burst of pulses, it is also possible to perform pump-probe experiments such as saturation-recovery or electron-electron double resonance experiments. Furthermore, the magnetization could be monitored in a time-resolved manner during amplitude modulation, thus making it possible to record its transient as it is approaching an equilibrium value. Experimental examples are shown with frozen solutions of trityl radical and TEMPO, two commonly used radicals for dissolution DNP experiments.     

EPR Spectroscopy Using Magnetic Field Gradient Modulated by a Triangular Wave

Magnetic field gradient modulation is one of the techniques to obtain an electron paramagnetic resonance (EPR) spectrum in a selected region of the sample. In this study, the magnetic field gradient modulation using a triangular wave was performed to overcome a problem during the sine wave modulation. Plastic materials were used for the bobbins and cases of the electromagnet to reduce the eddy current loss and drive the gradient coils in three-dimensional directions at a frequency of over 160 Hz. While the EPR signal splitting in a nonselected region, which is a problem in spectral analysis, was observed during the simulation and the actual measurement with the sine wave gradient modulation, the EPR signal broadening without splitting was observed in those with the triangular wave modulation. Thus, it is postulated that the triangular wave is more suitable than the sine one for the field gradient modulation. The spatial resolution was determined to be about 4 or 2 mm at the field gradient of 1 or 2 mT/cm, respectively. The separation of the EPR spectra of two types of radicals was also made by the triangular wave gradient modulation. Authors' address: Hidekatsu Yokoyama, Department of Pharmaceutical Sciences, International University of Health and Welfare, 2600-1, Kitakanemaru, Ohtawara 324-8501, Japan     

EPR在体测量专用调制磁场驱动装置

利用电子顺磁共振（electron paramagnetic resonance,EPR）在体测量人牙齿可以实现无损伤地快速评估人体辐射剂量,具有实际应用价值.本文针对EPR在体测量牙齿剂量的应用特点,研制了专用调制磁场驱动装置,包括功率放大器、调制磁场激励线圈、调制频率设定模块、感应型调制幅度显示模块等.功率放大器采用脉冲功率放大方式取代传统的线性放大方式,用多N-MOSFET管H桥电路,功率容量大、效率高、结构简单,且调制频率设定自如.实验结果表明：（1）此装置可在大于9 cm磁极间距的中心样品位置产生调制幅度为0~0.9 mT的调制磁场,调制频率为10~100 kHz;（2）用该装置与EPR在体测量谱仪配合使用,可以明显观测到1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）样品谱线调制增宽过程以及辐射诱发的整体牙齿中的自由基信号,验证了该装置的高调制效率和实用性.     

The Sound Field in a Marine Waveguide with a Cylindrical Inhomogeneity

Acoustical Physics - A three-dimensional analytical solution is constructed for the model of an inhomogeneous hydroacoustic waveguide with a cylindrical inhomogeneity within the sedimentary layer....     

Electrical Properties of Nanostructured Magnetic Colloid and Influence of Magnetic Field

We investigate the electrical properties of the nanostructured magnetic colloid without and with magnetic field. The competition between the directional motion of the charged magnetic nanoparticles and other minor nonmagnetic impurities （also small amount of ions） under applied voltage and their random orientation due to thermal activation is implemented to elaborate the electrically conduction mechanism under zero magnetic field. Two equivalent electric circuits are employed for explaining the charging and discharging processes. The tunnelling conduction mechanism upon application of externally magnetic field may exist in the nanostructured magnetic colloid. The alternation of the two conduction mechanisms accounts for the current spikes when the magnetic field is switched on or off. This work presents the peculiar electrical phenomena of the magnetically colloidal system.     

Comparison of Overhauser DNP at 0.34 and 3.4?T with Frémy’s Salt

Dynamic nuclear polarization (DNP) is investigated in the liquid state using a model system of Frémy's salt dissolved in water. Nuclear magnetic resonance signal enhancements at 0.34 and 3.4?T of the bulk water protons are recorded as a function of the irradiation time and the polarizer concentration. The build-up rates are consistent with the T(1n) of the observed water protons at room temperature (for 9?GHz/0.34?T) and for about 50?±?10?°C at 94?GHz/3.4?T. At 94?GHz/3.4?T, we observe in our setup a maximal enhancement of -50 at 25?mM polarizer concentration. The use of Frémy's salt allows the determination of the saturation factors at 94?GHz by pulsed ELDOR experiments. The results are well consistent with the Overhauser DNP mechanism and indicate that higher enhancements at this intermediate frequency require higher sample temperatures.     

Viscosity of a Magnetic Fluid in a Strong Magnetic Field

Acoustical Physics - The paper presents an estimate for the viscosity and its increment (“magneto-viscous” effect) in a thin wall layer of a magnetic fluid column oscillating in a tube...     

Influence of a Constant Magnetic Field on Some Properties of Water Solutions

Doklady Physics - The effect of a static magnetic field with induction up to 7 T on the concentration of dissolved molecular oxygen, the concentration of hydrogen peroxide, the redox potential, and...     

在自由空间里的运动磁场和时变磁场都没有产生电场

在自由空间里,磁场运动时没有产生电场、时变磁场的辐射运动也没有产生电场.故,“磁生电”的真实原因是：金属电子在广义洛伦兹磁力的作用下的流动而形成Ic,却不是法拉第-麦克斯韦-爱因斯坦在自由空间里虚构的位移电流Id.基于唯物主义自然观,联系电磁感应的物质是洛伦兹的金属电子,却不是法拉第-麦克斯韦-爱因斯坦的真空以太.     

Small Mass Asymptotics for a Charged Particle in a Magnetic Field and Long-Time Influence of Small Perturbations

We consider small mass asymptotics of the motion of a charged particle in a potential combined with a magnetic field. After an appropriate regularization, a Smoluchowski-Kramers type approximation is established. This approximation allows to study long-time influence on the motion of various perturbations, deterministic and stochastic. In particular, even in the case of pure deterministic perturbations, the long-time evolution of the perturbed system can be stochastic.     

Wave Packets in a Magnetic Field

A Gaussian wave packet confined to move on a plane perpendicular to a magnetic field remains a Gaussian wave packet in its time evolution. The average position and momentum follow the Ehrenfest equations which are identical to the classical Hamilton equations. A set of nonlinear equations decoupled from the Ehrenfest equation is derived for the parameters describing the time evolution of the density distribution and phases of a wave packet. Explicit solutions are then obtained when the "internal" angular momentum of the wave packet vanishes. In this case it is shown that the motion of the wave packet is a superposition of a translational motion, a rotation and a vibration.     

耦合强度和磁场对极化子基态的影响

利用线性组合算符和幺正变换相结合的方法,推导出极化子基态与耦合强度和磁场强度的关系。数值计算表明:当磁场强度给定时,随着耦合常数α的增加,振动频率λ先减小后增大;基态能量E₀单调下降;自陷能E_0tr单调增大;Landau能E_0L先增大,达到最大值后又下降。当耦合强度给定时,随着磁场强度的增大,λ单调增大,且α愈小,λ增加愈快;基态能量E₀随磁场强度的增大而增大;自陷能E_0tr随着磁场强度的增大而略有增加;Landau能E_0L随着磁场强度的增大先增大,达到最大值后,又开始下降。     

Ising Field Theory in a Magnetic Field: Analytic Properties of the Free Energy

We study the analytic properties of the scaling function associated with the 2D Ising model free energy in the critical domain TT _c , H0. The analysis is based on numerical data obtained through the Truncated Free Fermion Space Approach. We determine the discontinuities across the Yang–Lee and Langer branch cuts. We confirm the standard analyticity assumptions and propose extended analyticity; roughly speaking, the latter states that the Yang–Lee branching point is the nearest singularity under Langer's branch cut. We support the extended analyticity by evaluating numerically the associated extended dispersion relation.     

Influence of a Pulsed Axial Magnetic Field on a High-Current Arc of a Vacuum Circuit Breaker

Russian Physics Journal - The effect of a relatively short external axial magnetic field on the characteristics of a vacuum arc discharge in a vacuum circuit breaker is studied. A pulsed magnetic...