Hollow-beam focusing with electrostatic and periodic magnetic fields

A new method of focusing a hollow cylindrical electron beam is presented. The focusing system consists of a cylindrical center conductor inside the beam, a cylindrical outer conductor enclosing the beam, and a series of periodic magnets outside the tube. A radial electrostatic field between the conductors provides an outward force on the electrons. The periodic magnetic field produces an inward force on the electrons. The inward and outward forces can be adjusted to provide a balance of all the forces acting on the electrons at both boundaries of the beam by choosing the electric and magnetic fields properly. An approximate analysis has been made and is presented which gives necessary design information. A number of curves are presented which are useful in designing focusing systems of this type. Experimental results on a beam tester show that current transmission of over 90 per cent for perveance up to 11 micropervs can be obtained readily. The adjustments are not critical and the performance is very stable.     

The growth, structure, and magnetic properties of thin epitaxial films of GdMnO3 multiferroics

Thin epitaxial gadolinium manganite (GdMnO₃) films were manufactured on single-crystal substrates of neodymium gallate (001) (NdGaO₃) and strontium titanate (001) (SrTiO₃) by the high-frequency magnetron sputtering method. The RBS analysis demonstrated that the thickness of the obtained films was ??100 nm and the chemical composition corresponded to the stated stoichiometry. It was established by the X-ray diffraction analysis of the structure and phase composition of the obtained films that all films were single-phase but, depending on the temperature of the substrate during sputtering they have one or several types of orientations relative to the substrate. The X-ray diffraction analysis and high-resolution electron microscopy data on gadolinium manganite films on neodymium gallate substrates were verified. Features pointing to phase transitions in GdMnO₃ that were earlier discovered on bulk single-crystal samples were found in the temperature dependence of the magnetic susceptibility.     

Terahertz-radiation generation and detection in low-temperature-grown GaAs epitaxial films on GaAs (100) and (111)A substrates

The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity of the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.     

High intensity magnetic fields for the identification and study of donors in epitaxial gallium arsenide

High intensity magnetic fields are needed for the far infrared photoconductivity method to be used reliably in the identification of unitentional contaminants in ultra high purity epitaxial GaAs. We show experimental evidence that the inhomogeneous Stark broadening of the 1s→2p (m=?1) transition of the hydrogen-like donor almost disappears as the magnetic field is increased to 20 Tesla. Since the spectral lines also become narrower and the central cell correction (chemical shift) becomes larger, the “signature curve” method of identification permits positive identification of donor species. In particular, the donors Ge and Se have been identified in specimens that were reported to contain carbon and Sn respectively.     

Instability regions of an electron beam in superimposed periodic and uniform magnetic fields

The stability of an electron beam in a superimposed sinusoidal and uniform magnetic field is theoretically and experimentally investigated. The first instability region degenerates to a point within the first well-known passband for a zero uniform field component, whereas the second instability region coincides with the first stopband of the sinusoidal field. These considerations are of practical significance for periodic magnetically-focused electron beams.     

Thermodynamic stability of GaInSb,InAsSb, and GaInP epitaxial films

The miscibility gaps and the critical temperatures of spinodal decomposition of ternary semiconducting Ga-In-Sb, Ga-In-P, and In-As-Sb systems are calculated by taking into account the deformation energy and the effect of plastic relaxation caused by the misfit dislocations. It is shown that taking into consideration elastic energy narrows the ranges of spinodal decomposition and lowers its critical temperature. The introduction of the phenomenological parameter into Matthews-Blakeslee formula makes it possible to reach a satisfactory agreement between theoretically calculated values of critical thickness of epitaxial films and the experimental data.     

Deposition,post-deposition annealing,and characterization of epitaxial Ge films grown on Si(100) by pyrolysis of GeH4

As a first step towards developing heterostructures such as GaAs/Ge/Si entirely by chemical vapor deposition, Ge films have been deposited on (100) Si by the pyrolysis of GeH₄. The best films are grown at 700° C and are planar and specular, with RBS minimum channeling yields of ≈4.0% (near the theoretical value) and defect densities of 1.3 x 10⁸ cm⁻². Variations of in-situ cleaning conditions, which affect the nature of the Si substrate surface, greatly affect the ability to get good epitaxial growth at 700° C. The majority of the defects found in the Ge films are extrinsic stacking faults, formed by dissociation of misfit and thermal expansion accommodation dislocations. The stacking fault density is not significantly reduced by post-deposition annealing, as is the case for the dislocations observed in MBE Ge films. It is suggested that lowering the CVD growth temperature through the use of high vacuum deposition equipment would result in dislocation defects like those of MBE films which could then be annealed more effectively than stacking faults. Films with defect densities equivalent to MBE Ge films (~2 x 10⁷ cm⁻²) could then probably be produced.     

Electric and magnetic fields of a wave in proximity of aprogressively phased periodic structure

Unexpected waves have been observed that were localized in the region of, and propagating along, a progressively phased periodic structure. These waves are related to a dominant TM₀ mode associated with and bound to a thin dielectric layer covering a conducting plane     

On the growth,structure, and surface morphology of epitaxial CdTe films

The structure and surface morphology of epitaxial CdTe films grown on glassy substrates with and without compensation with an additional Te vapor source during growth are studied. The optimal conditions of the production of structurally perfect epitaxial films with a pure smooth surface with no inclusions of another phase (T _so = 1000–1100 K, T _su = 570–670 K) are determined. It is established that, on glassy substrates, the epitaxial films grow via the (111) plane of the face-centered cubic (fcc) lattice with the parameter a = 6.481 Å. By varying the temperature of the main and compensating sources, CdTe films with n- and p-type conductivity are produced.     

Different characteristics of high-temperature superconducting infrared detectors with granular and epitaxial films

We describe the measurements of infrared detection in granular and epitaxial films of YBa₂Cu₃O_7?δ . The experimental frequency response measurements stated that the response voltage of detector for epitaxial film decreased much more rapidly than that for granular film. Different relationship of infrared response and bias current for detectors from two types of films has been demonstrated. We attribute the descrapency to the characters of detectors associated with different types of film structures.     

3.2-5 Gb/s, 100 km error-free soliton transmission with erbiumamplifiers and repeaters

For the transmissions, the transform-limited soliton pulse source is a gain-switched distributed-feedback laser diode with a narrowband spectral filter and erbium amplifiers. A LiNbO₃ light intensity modulator is used for pulse switching. The preemphasis technique for sending solitons over a long distance, in which an erbium optical repeater is installed every 25 km as a lumped amplifier, is used     

Generation of spin waves in nonuniform magnetic fields, with application to magnetic delay lines

The theory of spin-wave generation in nonuniform magnetic fields is reviewed. Detailed theoretical results concerning the photon-magnon conversion, the magnon-phonon conversion, the frequency- and field-dependence of the delay time, and the insertion loss are presented. A general theory of the nonuniform demagnetizing field of nonellipsoidal samples is described. Experimental results concerning the field dependence of the delay time are presented both for the case in which the spin waves generated are exchange dominated and for the case in which they are dominated by the magnetostatic interaction. The insertion loss was found to vary with the applied magnetic field in an approximately periodic fashion showing two distinct periods of the order of 1 Oe and 100 Oe. The fast variation (period approximately 1 Oe) has been definitely identified as arising from the excitation of magnetoelastic resonances in the nonuniform magnetic field near the endfaces of the sample. The slow variation (period approrimately 100 Oe) is tentatively attributed to the interference of different partial waves arising from the reflection of the primary wave at the sidefaces of the sample.     

具有轴向磁场的自由电子激光器中的电子轨道、色散和增益

应用单粒子轨道理论讨论了存在轴向磁场的自由电子激光器中电子轨道的稳定性及辐射场的振幅变化、色散和增益;导出了辐射场变化和色散方程.     

Transient electric and magnetic fields associated with establishinga finite electrostatic dipole, revisited

The authors reexamine the analysis of M.J. Master and M.A. Uman (1983), who derived and plotted the electromagnetic field waveforms generated by a square wave of current propagating with constant speed along a finite linear path, resulting in the formation of a finite electrostatic dipole. It was concluded that such a square pulse of current had charge only at its front and rear. The authors argue that errors were made in that analysis, correct these errors, and extend the overall analysis: (1) to show that the decomposition of the electromagnetic fields into electrostatic, induction, and radiation components on the basis of distance dependence is not general; (2) to demonstrate the use of the continuity equation in finding the charge distribution along a current path when the current distribution is known; and (3) to show how a seemingly simple analytical technique, the treatment of an abrupt step of current as a linearly rising current in the limit that the risetime goes to zero, can lead to erroneous results if there is not a good physical and mathematical understanding of all the variables involved     

激光共聚焦显微镜观察光敏剂ALA和HMME在肿瘤细胞的胞内分布

目的：研究不同光敏剂在肿瘤细胞的胞内分布,观察光敏剂的亚细胞光化学作用位点。方法：使用激光共聚焦显微镜观察光敏剂5-ALA和HMME在结肠癌SW480细胞及红白血病K562细胞的胞内分布。结果：5-ALA及HMME在进入肿瘤细胞早期主要分布于胞膜。而在后期主要以颗粒状荧光分布于胞质,5-ALA分布相对弥散,HMME分布相对集中,核内分布极少。结论：光敏剂5-ALA和HMME主要分布于肿瘤细胞的胞质,这表明它们的光化学作用位点首先在胞质内细胞器,而不是细胞核。     

Interaction of low-frequency electric and magnetic fields with thehuman body

Interactions of electric and magnetic fields at power line frequencies (50 and 60 Hz) in humans have been the subject of intensive scientific inquiry and considerable public concern during the last two decades. As a part of the scientific effort, extensive evaluations of induced electric field and current density in the human body have been performed. Realistic, heterogeneous, high-resolution models of the body have been analyzed using various numerical methods. Exposures to uniform and nonuniform electric and magnetic fields are considered, thus accounting for typical environmental and occupational scenarios. Numerical values of the average and maximum induced electric field and current density are given for various organs and tissues. Effects on the dosimetric measures of changes in the tissue conductivity, model resolution and organ modeling in situ, and isolation are discussed. It is shown that results from various laboratories agree reasonably well. It is also shown how the macroscopic numerical evaluation of induced fields can be further extended to model more refined cellular systems. This is demonstrated for gap junction connected cells     

Formation of a periodic magnetic field by a sequence of rings with different magnetic and electric properties

The electrodynamic analysis of the topography of magnetic fields generated in a spatially periodic structure is performed. The structure is a solenoid containing periodically spaced rings made from materials with different electric and magnetic properties. The system of equations relating the amplitudes of spatial harmonics of the magnetic field is derived and numerically analyzed. Dependences of the amplitudes of longitudinal and transverse components of the modulated magnetic field on the ring dimensions, the current frequency, and the magnetic and electric properties of the ring materials are investigated. The field amplitudes obtained during the complete electrodynamic analysis are compared with the amplitudes of a periodic magnetic field obtained in the impedance approximation.     

Magneto-optical visualization of magnetic processes in superconducting strip with the application of magnetic fields and currents

The magneto-optical imaging (MOI) technique is widely employed to characterize the magnetic properties of superconductors and other magnetic materials because it can easily show the variation of flux density over a plane with relatively high resolution. In this paper, flux profiles visualized by the MOI technique will be presented for different experimental conditions. The sample investigated is a high-temperature superconducting single strip. Three cases are investigated: 1) application of external currents; 2) application of external magnetic fields; and 3) simultaneous application of external magnetic field and current. The behavior of complicated vortex penetration into the samples for different conditions will be discussed in detail. The magnetic flux profiles are calculated taking into account the sample thickness, as well as the interval between the sample and the MOI indicator film. The calculated and the experimental results are compared and discussed.