共查询到20条相似文献,搜索用时 187 毫秒
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十分微弱的地磁场,转化为电信号的电流过于微弱,一般得不到比较准确的数据.为此,我们利用了实验室现有仪器和自制的运算放大器对地磁场的水平分量进行测量.此方法简便,实验仪器要求不高,易于普及. 相似文献
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1引言
大学物理实验中,“用霍尔效应法测量磁场”实验是工科各专业必做的实验之一,笔者已给学生上这个实验许多年,深感这个实验装置必须改进;因为在实验中,虽然笔者再三强调不要把励磁电流接至霍尔元件上,仍然有部分学生因接错线路而导致霍尔元件被烧毁.由于上大学物理实验课的学生多,仪器的使用率特别高,所以一个学期下来总有六七台甚至更多台霍尔效应实验仪中的霍尔元件被烧毁而需更换. 相似文献
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介绍了脉冲弦线磁场测量方法的基本原理和实验装置,研究了脉冲电流宽度对测量结果的影响,观测到双波叠加的新现象。该现象很好地解释了零信号的产生原因,并由此可以确定测量磁场二次积分时的脉冲电流宽度。 相似文献
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I. V. Kukushkin K. von Klitzing K. Eberl 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
The spin configuration of the ground state of a two-dimensional electron system is investigated for different FQHE states from an analysis of circular polarization of time-resolved luminescence. The method clearly distinguishes between fully spin polarized, partially spin polarized and spin unpolarized FQHE ground states. We demonstrate that FQHE states which are spin unpolarized or partially polarized at low magnetic fields become fully spin polarized at high fields. Temperature dependence of the spin polarization reveals a nonmonotonic behavior at
. At
and
the electron system is found to be fully spin polarized. This result does not indicate the existence of any skyrmionic excitations in high magnetic field limit. However, at
the observed spin depolarization of electron system at
and
becomes broader for lower magnetic fields, so that full spin polarization remains only in a small vicinity of
. Such a behavior could be considered as a precursor of skirmionic depolarization, which would dominate for smaller ratios between Zeeman and Coulomb energies.We demonstrate that the spin polarization of 2D-electron system at
and
can be strongly affected by hyperfine interaction between electrons and optically spin-oriented nuclears. This result is due to the fact that hyperfine interaction can both enhance and suppress effective Zeeman splitting in fixed external magnetic field. 相似文献
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In this work intentionally disordered two‐dimensional electron systems in modulation doped GaAs/GaAlAs heterostructures are studied by magnetotransport experiments. The disorder is provided by a δ‐doped layer of negatively charged beryllium acceptors. In low magnetic fields a strong negative magnetoresistance is observed that can be ascribed to magnetic‐field‐induced delocalization. At increased magnetic fields the quantum Hall effect exhibits broad Hall plateaus whose centers are shifted to higher magnetic fields, i.e. lower filling factors. This shift can be explained by an asymmetric density of states. Consistently, the transition into the insulating state of quantum Hall droplets in high magnetic fields occurs at critical filling factors around νc=0.4, i.e. well below the value 1/2 that is expected for symmetric disorder potentials. The insulator transition is characterized by the divergence of both the longitudinal resistance as well as the Hall resistance. This is contrary to other experiments which observe a finite Hall resistance in the insulating regime and has not been observed previously. According to recent theoretical studies the divergence of the Hall resistance points to quantum coherent transport via tunneling between quantum Hall droplets. The magnetotransport experiments are supplemented by simulations of potential landscapes for random and correlated distributions of repulsive scatterers, which enable the determination of percolation thresholds, densities of states, and oscillator strengths for far‐infrared excitations. These simulations reveal that the strong shift of the Hall plateaus and the observed critical filling factor for the insulator transition in high magnetic fields require an asymmetric density of states that can only be generated by a strongly correlated beryllium distribution. Cyclotron resonance on the same samples also indicates the possibility of correlations between the beryllium acceptors. 相似文献
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E. Krimmel 《Zeitschrift für Physik A Hadrons and Nuclei》1961,163(3):339-355
It is shown that a coherent superposition of parts of an electron wave field by magnetic fields is possible. The deflecting magnetic fields are formed by a quadrupole lens. The interference space in which the coherent superposition of three partial waves takes place is limited by a caustic surface. The interference phenomena in the neighbourhood of this surface can be described by means of an integral of the Airy type. A quadrupole lens with rectangular pole piece edges forms in great distance from its axis homogeneous magnetic fields of opposite direction. If a coherent irradiation of both these homogeneous fields can be achieved, they form a magnetic biprism if the paraxial part of the beam is stopped. The distance of interference fringes in such an interferogram would in first approximation be independent of the particle energy. 相似文献
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A review of high operating temperature (HOT) infrared (IR) photon detector technology vis-a-vis material requirements, device design and state of the art achieved is presented in this article. The HOT photon detector concept offers the promise of operation at temperatures above 120 K to near room temperature. Advantages are reduction in system size, weight, cost and increase in system reliability. A theoretical study of the thermal generation–recombination (g–r) processes such as Auger and defect related Shockley Read Hall (SRH) recombination responsible for increasing dark current in HgCdTe detectors is presented. Results of theoretical analysis are used to evaluate performance of long wavelength (LW) and mid wavelength (MW) IR detectors at high operating temperatures. 相似文献
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Mössle M Han SI Myers WR Lee SK Kelso N Hatridge M Pines A Clarke J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,179(1):146-151
In magnetic resonance imaging performed at fields of 1 T and above, the presence of a metal insert can distort the image because of susceptibility differences within the sample and modification of the radiofrequency fields by screening currents. Furthermore, it is not feasible to perform nuclear magnetic resonance (NMR) spectroscopy or acquire a magnetic resonance image if the sample is enclosed in a metal container. Both problems can be overcome by substantially lowering the NMR frequency. Using a microtesla imaging system operating at 2.8 kHz, with a superconducting quantum interference device as the signal detector, we have obtained distortion-free images of a phantom containing a titanium bar and three-dimensional images of an object enclosed in an aluminum can; in both cases high-field images are inaccessible. 相似文献
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Differential algebraic method is of an effective technique in computer numerical analysis. It implements exactly differentiation up to arbitrary high order based on the nonstandard analysis. Some complicated nonlinear dynamics problems including high order aberrations of electron optics systems can be solved by mapping properties of differential algebraic quantities. However, the existing electron optical differential algebraic method can only be applied to those problems where the electric and/or magnetic fields are expressed in analytic forms. In this paper, the principle of differential algebraic method is applied to practical electron lenses whose electric/magnetic fields are in the forms of discrete arrays, for example, the files computed by FEM or FDM method. Thus the developed new differential algebraic method is applicable to engineering design. The programs were written for computing the high order aberrations of practical electron lenses. An example is given to show that the numerical results have good accuracy compared with the results computed by using the electric fields expressed in analytical form; the accuracy is limited only by the accuracy of the numerical computation of the fields and the arithmetic errors, and it is enough for engineering design. 相似文献
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Based on the model of the two calcium stores developed by Goldbeter, the influence of external magnetic field on the calcium concentration has been discussed. We believe that the cell membrane is a major site of interaction for extremely-low-frequency (ELF) electromagnetic fields, and the permeability of ions can be changed with the changing electromagnetic fields. It is shown that magnetic field initiatesintracellular calcium oscillation with a threshold in flux density, and that the calcium oscillations do not occur if the density of magnetic field is below the threshold. The results of theoretical calculation are consistent with that of the experiment. The intracellular free calcium concentrations of different cells exposed to the same magnetic fields are different from each other. It is indicated that the different behaviors such as oscillation, rise and invariability of calcium concentration are associated with the sort of cells. 相似文献
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This paper describes the structure and characteristics of a deflecting mirror using electromagnetic actuation. We used a moving
magnet structure for mirror actuation and focused on designing a mirror structure with effective magnetic force (for low-power
operation) and a simple fabrication process (to achieve low manufacturing cost). In this design, the magnetic forces of attraction
and repulsion are simultaneously used for mirror deflection, allowing the mirror to be operated with low current. Moreover,
the structures of the yoke core and magnet bar have been designed to further reduce the operating current. Such a mirror structure
is simple and can be easily fabricated with a small number of components. This structure can be used not only for a one-dimensionally
deflecting mirror but also for a two-dimensionally deflecting mirror by attaching a second yoke core. 相似文献