Theoretische Betrachtungen über die Elektronenoptik einer Ringstrahl-Elektronenkanone

A ring beam electron gun consists of a circular cathode and of focusing and accelerating electrodes arranged concentrically in such a way that the electrons can be accelerated towards the centre of curvature of the ring-cathode. In this system the electron beam is brought to a focus in the centre of the gun in the plane of the circular cathode by cathode curvature, whilst in the perpendicular direction focusing is obtained by the geometry of the focusing electrodes. When the cathode is heated by a direct current the magnetic field of this circular current deflects the electron paths in the symmetry plane of the gun (plane of the ring-cathode) in such a manner that, neglecting the electron gas temperature, no electrons can reach a circular area of certain radius in the centre of the gun. The radius of this dead zone is calculated as a function of the relevant gun parameters according to the laminar theory and then the definition of the dead zone is modified with respect to the Maxwellian distribution of electron velocities and also for heating of the ring-cathode with a. c. If a second circular current concentric with the circular current of the cathode but flowing in the opposite direction is introduced, one can completely eliminate the electron deflection effect in the central part of the gun. The influence of this compensation current is calculated and represented in graphical form. Also some calculations of achievable current densities on a cylindrical object in the centre of the gun are reported both for compensated and partly compensated cases.     

Tiegelloses Zonenschmelzen hochschmelzender Metalle mit Hilfe von punktfokussierten Elektronenstrahlen

Summary In conventional systems for floating-zone melting with electron bombardment the use of ring-cathode electron guns is widely spread. However, little is known about the applicability of point-focus electron-beams for floating-zone melting. To study this type of process a floating-zone melting device with a horizontal specimen position and a single point-focus electron-beam has been constructed. The experiment showed that in spite of sagging of the molten zone due to gravity, it is possible to melt rods of all refractory metals with rod diameters up to 5 mm with well controllable operating characteristics. This method easily allows the growth of exactly oriented crystals of W, Ta, Mo and Nb using a goniometric holder with a seed crystal on one side. Some characteristics of this type of zone melting and some preliminary results of an investigation of the single crystals grown in this way are discussed.

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Gekürzte deutsche Fassung eines Vortrages, gehalten an «Second Internat. Conf. on Electron and Ion Beam Science and Technology», New York, April 1966.     

A boundary-value problem for the stationary vlasov-poisson equations: The plane diode

The stationary Vlasov-Poisson boundary value problem in a spatially one-dimensional domain is studied. The equations describe the flow of electrons in a plane diode. Existence is proved when the boundary condition (the cathode emission distribution) is a bounded function which decays super-linearly or a Dirac mass. Uniqueness is proved for (physically realistic) boundary conditions which are decreasing functions of the velocity variable. It is shown that uniqueness does not always hold for the Dirac mass boundary conditions.     

Hot electrons generated by ultra-short pulse laser interacting with solid targets

Hot electrons produced by ultra-short pulse laser interacting with solid targets were studied systematically. When 800 nm, 8 × 10¹⁵ W/cm² laser pulses interacted with solid targets, hot electron emission was found to be collimated in certain directions and the angular distribution of hot electrons depended on the energy absorption. The angular divergence of outgoing hot electrons was inversely proportional to the hot electron energy. The energy spectrum of hot electrons was found to be in a biMaxwellian distribution and the maximum energy was over 500 keV.     

Computational simulation of fluid and dilute particulate flows on spiral concentrators

Spiral separators are used globally in the fine coal and heavy mineral processing industries as gravity-concentration devices. Consisting of an open trough that spirals vertically downwards in helix configuration about a central axis, a slurry mix of particles and water is fed to the top of the concentrator. Particles are then separated radially on the basis of density and size as they gravitate downwards. To enhance performance, the geometric design has evolved historically by experimental trial-and-error investigations to develop a prototype suited to the given industrial application. This approach has proved somewhat prohibitive for design purposes however, and researchers have accordingly turned to numerical techniques in an attempt to develop a fully predictive and reliable model for use in the design process. Towards this end, the present paper uses Computational Fluid Dynamics (CFD) analysis to simulate fluid and dilute particulate flows on one operational spiral unit. The free-surface Volume-of-Fluid (VOF) algorithm, isotropic RNG k–ε turbulence model and Lagrangian method have been used for this purpose. Satisfactory predictions have been obtained with respect to a collaborative experimental program, and the model forms the basis for future examination of the two-way fluid-particle coupling processes and inter-particle effects.     

Plasma environment during hot cathode direct current discharge plasma chemical vapor deposition of diamond films

The plasma characteristics have been investigatedin situ by using optical emission spectroscopy (OES) and the Langmuir probe during hot cathode direct current discharge plasma chemical vapor deposition of diamond films. The changes of atomic H and CH radical in the ground state have been calculated quantitatively according to the results of OES and the Langmuir probe measurement as discharge current density varied. It is shown that atomic H and CH radicals both in the ground state and in the excited state increase with the enhancement of the discharge current density in the plasma. The electron density and CH emission intensity increase linearly with the enhancement of discharge current densities. The generation of different carbon-containing radicals is related to the elevation of electron temperature. Combining the growth process of diamond films and the diagnostic results, it is shown that atomic H in the excited state may improve the diamond growth efficiently, and the increase of electron temperature and density plays an important role in the increase of the deposition rate of diamond films. Project supported by the National Natural Science Foundation of China (Grant Nos. 69493505, 19475039, 19835002).     

A population global optimization algorithm to solve the image alignment problem in electron crystallography

Knowledge of the structure of biological specimens is critical to understanding their function. Electron crystallography is an electron microscopy (EM) approach that derives the 3D structure of specimens at high-resolution, even at atomic detail. Prior to the tomographic reconstruction, the images taken from the microscope have to be properly aligned. Traditional alignment methods in electron crystallography are based on a phase residual function to be minimized by inefficient exhaustive search procedures. This work addresses this minimization problem from an evolutionary perspective. Universal Evolutionary Global Optimizer (UEGO), an evolutionary multimodal optimization algorithm, has been applied and evaluated for the task of image alignment in this field. UEGO has turned out to be a promising technique alternative to the standard methodology. The alignments found out by UEGO show high levels of accuracy, while reducing the number of function evaluations by a significant factor with respect to the standard method.     

Electron dynamical response in InP semiconductors driven by fluctuating electric fields

The complexity of electron dynamics in low-doped n-type InP crystals operating under fluctuating electric fields is deeply explored and discussed. In this study, we employ a multi-particle Monte Carlo approach to simulate the non-linear transport of electrons inside the semiconductor bulk. All possible scattering events of hot electrons in the medium, the main details of the band structure, as well as the heating effects, are taken into account. The results presented in this study derive from numerical simulations of the electron dynamical response to the application of a sub-Thz electric field, fluctuating for the superimposition of an external source of Gaussian correlated noise. The electronic noise features are statistically investigated by computing the correlation function of the velocity fluctuations, its spectral density and the variance, i.e. the total noise power, for different values of amplitude and frequency of the driving field. Our results show the presence of a cooperative non-linear behavior of electrons, whose dynamics is strongly affected by the field fluctuations. Moreover, the electrons self-organize among different valleys, giving rise to the reduction of the intrinsic noise. This counterintuitive effect critically depends on the relationship among the characteristic times of the external fluctuations and the temporal scales of complex phenomena involved in the electron dynamical response. In particular, the correlation time of the electric field fluctuations appears to be crucial both for the noise reduction effect and the appearance of an anomalous diffusion effect.     

The behavior of plasma with an arbitrary degree of degeneracy of electron gas in the conductive layer

We obtain an analytic solution of the boundary problem for the behavior (fluctuations) of an electron plasma with an arbitrary degree of degeneracy of the electron gas in the conductive layer in an external electric field. We use the kinetic Vlasov–Boltzmann equation with the Bhatnagar–Gross–Krook collision integral and the Maxwell equation for the electric field. We use the mirror boundary conditions for the reflections of electrons from the layer boundary. The boundary problem reduces to a one-dimensional problem with a single velocity. For this, we use the method of consecutive approximations, linearization of the equations with respect to the absolute distribution of the Fermi–Dirac electrons, and the conservation law for the number of particles. Separation of variables then helps reduce the problem equations to a characteristic system of equations. In the space of generalized functions, we find the eigensolutions of the initial system, which correspond to the continuous spectrum (Van Kampen mode). Solving the dispersion equation, we then find the eigensolutions corresponding to the adjoint and discrete spectra (Drude and Debye modes). We then construct the general solution of the boundary problem by decomposing it into the eigensolutions. The coefficients of the decomposition are given by the boundary conditions. This allows obtaining the decompositions of the distribution function and the electric field in explicit form.     

Adding Integers

<正>When am I ever going to use this?EARTH SCIENCE Thunderstorms are made of both positive and negative electrical charges.The negative charges(electrons)are at the bottom of a thundercloud,and positive charges(protons)are at the top.1.What is the charge at the top of a cloud where there are more protons     

Numerisch-theoretisch und experimentelle Untersuchung einer Hochstrom-Fernfokus-Elektronenkanone vom Tetroden-Typus

Starting from a earlier investigation of a telefocus-electron gun of the triode-type (Z. angew. Phys.11, 370 (1950) which however was unable to deliver high beam currents, a telefocus-gun of the tetrode-type for high beam currents was theoretically and experimentally investigated and the main results are presented in this paper. In the first part of this work a model-system has been investigated by numerical-theoretical methods to get an idea of the electron paths inside the gun as well as to estimate the highest obtainable perveance of the gun. In these investigations an analogy-resistance-network for the plotting of potential fields and an electronic computer for the electron path calculations have been used. These calculations showed that an electron-gun of small geometrical dimensions can be built which is able to focus high beam currents at long distances from the cathode. The relevant gung parameters are a short distance from cathode to first-anode and a high negative Wehnelt-potential. In the second part of the paper the results of some experimental investigations are reported. The experiments showed that by suitable dimensioning a 50 mA, 20 kV electron beam can be focussed in a crossover of some few tenths of mm diameter at a distance of 150–250 mm from the cathode. Some examples for the gun data are given. The aberrations of the electron gun are considerable at the higher currents: At 20 kV one can easily obtain a beam current of 150 mA with a cathode of 2 mm diameter. The aberrations influence infavourably the current density distribution in the crossover. The disturbance is especially noticeable for long cathode to focus distances as was the case in some reported experiments with a cathode to focus distance of 410 mm.The described telefocus-gun has been used for electron beam welding and some practical conclusions of these experiments are discussed in the paper.

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Leicht gekürzte Fassung eines Vortrages an der Second International Conference on Electron and Ion Beam Science and Technology, New York, April 17–20, 1966.     

Untersuchungen über Elektronenströmungen

Summary The laws of conservation of energy and charge are used in a perturbation theory for longitudinal controlled streams of electrons. Space charge, the electromagnetic field and the relativistic change of mass are taken into account. The relations in the classical field are found from a matrix form. Impedances of the streams are used. On terminals they are identical with the impedances of the electronic device. It is shown, howNyquist's noise formula can be derived from the shot noise, for a system in thermal equilibrium with potential minimum in the electron streams and high transit time angles. For a system not in thermal equilibrium some noise formulas are presented. A simplification of the calculation of the noise convection currents of the electrons coming at the electrodes can be made. When in all emission points the emission fluctuations are concentrated in the streams with maximal transit time the noise in the convection currents has the same value as the real noise. When a potential minimum is present, the current is important, which passes over the potential minimum. The noise of this current must be concentrated in the streams with maximal transit time beginning in the potential minimum.     

Identification of Viscoelastic Properties and Damaging Effects of Highly Extensible Polyurea

The present work aims particular at the experimental identification of the viscoelastic properties of polyurea as well as on the onset of the damage. For the viscoelastic part, several relaxation experiments are performed. From the measured data a general viscoelastic model is derived where we use two different approaches. At first we identify a general Maxwell model (combining spring and damping elements for finite deformations) to use a prony series with N elements, which requires the identification of 2N + 1 parameters. At second, a model of generalized fractional elements [3] is employed. Both approaches are studied in detail and are compared to data from literature; furthermore a comparison concerning the effort is presented. Damaging effects of Polyurea are investigated using tensile tests with and without cyclic loading. In particular we focus on the the onset of damage by cavitation. To this end the recovered specimens were analyzed using a laser microscope; the surfaces of the ruptured areas are compared in terms of quantity and size of voids. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

What does it mean for a student to understand the first-year calculus? Perspectives of 24 experts

This article presents the views of 24 nationally recognized authorities in the field of mathematics, and in particular the calculus, on student understanding of the first-year calculus. A framework emerged that includes four overarching end goals for understanding of the first-year calculus: (a) mastery of the fundamental concepts and-or skills of the first-year calculus, (b) construction of connections and relationships between and among concepts and skills, (c) the ability to use the ideas of the first-year calculus, and (d) a deep sense of the context and purpose of the calculus. Each end goal for student understanding is explored in detail and the potential for using the framework as an organizational tool is discussed.     

On the effect of electron-mass variation in numerical simulations of the Farley-Buneman instability

The Farley-Buneman instability is the plasma instability in the E region of the Earth’s ionosphere. Many studies on instability simulations use algorithms based on the particle method, which has many shortcomings. In particular, the solutions obtained with this method involve numerical noises owing to a finite number of the particles, since the electron mass is increased in order to reduce the computational complexity of the algorithm. In this study, the effect of an increase in the electron mass on the qualitative and quantitative characteristics of the instability development process are considered. For this purpose, a software package developed on the basis of a mathematical model consisting of the Poisson equation for the electric potential, the fluid equation for electrons, and the kinetic equation for ions is used. The equations are solved numerically, which makes it possible to avoid the problems inherent in the particle method. An important result obtained in this paper is that even a slight increase in the electron mass leads to a considerable variation of the instability development parameters. This variation manifests itself as an increase in the wavelength of plasma fluctuations and a decrease in the strength of the turbulent electric field.     

Influence of the satellite Io on Jupiter’s decametric radio emission

An analysis of the influence of the satellite Io on Jupiter’s decametric radio emission was carried out utilizing observations recorded at Kodaikanal and Boulder. The influence is found to be complicated and is different at the three sources. It is suggested that the Io related emission can be due to Cerenkov radiation by fast electrons acting as a well-separated stream.     

On a hyperbolic conservation law of electron transport in solid materials for electron probe microanalysis

The prediction of X-ray intensities based on the distribution of electrons throughout solid materials is essential to solve the inverse problem of quantifying the composition of materials in electron probe microanalysis (EPMA) [3]. We present a hyperbolic conservation law for electron transport in solid materials and investigate its validity under conditions typical for EPMA experiments. The conservation law is based on the time-stationary Boltzmann equation for binary electron-atom scattering. We model the energy loss of the electrons with a continuous slowing-down approximation. A first order moment approximation with respect to the angular variable is discussed. We propose to use a minimum entropy closure to derive a system of hyperbolic conservation laws, known as the M1 model [11]. A finite volume scheme for the numerical solution of the resulting equations is presented. Important numerical aspects of the scheme are discussed, such as bounds for the finite propagation speeds, as well as difficulties arising fromspatial discontinuities in thematerial coefficients and the scaling of the characteristic velocities with the stopping power of the electrons.We compare the accuracy and performance of the numerical solution of the hyperbolic conservation law to Monte Carlo simulations. The results indicate a reasonable accuracy of the proposed method and showthat compared to the MonteCarlo simulation the finite volume scheme is computationally less expensive.     

Feynman-diagramme als vektorsysteme invariantentheoretisch behandelt (compton-streuung,elektron-positron-vernichtung

Employing a special contact transformation devised by S. Lie, which takes spheres into lines, we interpret the Feynman diagrams of photon electron scattering in terms of vector systems. This gives a nice kinematic model of Compton scattering. We further compute in detail the transition probabilities of the Compton scattering process by making use of the calculus of chains of complexes from classical invariant theory rather than applying the usual Dirac-matrix technique. In the final paragraph of this paper an application of our calculations to the treatment of myon decay is indicated.     

Numerical study of the metal vapour transport in tungsten inert-gas welding in argon for stainless steel

Metal vapour emanating from the weld pool during tungsten-inert-gas (TIG) welding affects the arc welding process. To understand the transport mechanisms of metal vapour in a TIG arc, an axisymmetric computational model is developed that includes the tungsten cathode, stainless-steel anode workpiece and the arc plasma region self-consistently. The combined diffusion coefficient method, which calculates diffusion coefficients due to mole fraction gradients (ordinary diffusion), temperature gradients, pressure gradients and the electric field is used to treat iron–chromium–argon and iron–chromium–helium plasmas. It was found that in both cases, metal vapours can reach the cathode region. The effect of different diffusion coefficients on metal vapour transport was investigated. It was found that ordinary diffusion is the main driving force for upward metal vapour diffusion away from the anode workpiece in an argon arc. The diffusive transport carries the metal vapour into the recirculating convective flow, which then transports the metal vapour to the cathode region. Here the upward diffusion driven by the temperature gradient and electric field leads to the build of high concentrations of the metal vapours adjacent to the cathode. In the helium arc, in contrast, metal vapour is transported upwards from the workpiece by electric field diffusion, which is much stronger in this case. Spectroscopic measurements of atomic chromium emission show that metal vapour can reach the cathode region in an argon TIG arc, providing support for the predictions of the model. Only by taking into account all diffusion driving forces is it possible to predict the distribution of metal vapour in a TIG welding arc.     

A tiling and routing heuristic for the screening of cytological samples

In the screening of cytological samples, a slide is examined using a microscope. Since the area of the specimen is very large compared with the area of a microscope field of view (FOV), a large number of FOVs is needed to cover the entire specimen area. A heuristic reducing the number of FOVs has been developed to aid in screening these specimens on the automated microscopy workstation. A smear slide is prescreened on a computer-aided optimal microscope system and locations of diagnostically significant material are stored. The heuristic computes a set of FOVs that covers this material and a route between them. As the problem is of large scale and must be solved repeatedly in real time any heuristic must be very fast. Our heuristic solves a set partitioning problem, followed by a traveling salesman problem. It produces a good solution within a very short computing time.