Showing papers on "Beam (structure) published in 1973"

An augmented double cantilever beam model for studying crack propagation and arrest

Abstract: An improved analytical model for the double cantilever beam fracture specimen is developed by treating a finite length beam which is partly free and partly supported by an elastic foundation. The results obtained are shown to be in excellent agreement with established data for initial crack extension. Some preliminary computational results for unstable crack propagation are also presented.

Vibration analysis for electronic equipment

Abstract: Vibrations of simple electronic systems lumped masses for electronic assemblies beam structures for electronic subassemblies electronic components, frames, and rings printed-circuit boards and flat plates preventing sinusoidal vibration failures understanding random vibration designing for shock environments designing electronic boxes vibration fixtures and vibration testing fatigue in electronic structures.

Unified theory of Rayleigh-angle phenomena for acoustic beams at liquid-solid interfaces

Abstract: Various phenomena have been observed when a bounded acoustic beam is incident from a liquid onto the surface of a solid at or near the Rayleigh angle. These phenomena include: a shift of the reflected beam from the position predicted by geometrical acoustics, a null or minimum of intensity within the reflected beam, a 180° phase reversal of the field on either side of the null, a weak trailing field on only one side of the reflected beam and a frequency of least reflection when the solid is lossy. By carefully examining the reflection coefficient for angles in the vicinity of the Rayleight angle, and by taking into account the angular spectrum of plane waves that comprise a bounded beam, a model of the reflection process is developed that explains all of the observed phenomena. This model shows that the various critical-reflection effects result from the interference between a geometrically reflected field and the field of a leaky Rayleigh wave, which is excited by the incident beam. Moreover, this model resolves the conflict between various explanations made for these phenomena in the past; in particular, it is found that Schoch's classical description of a laterally displaced reflected beam is valid only for beams having a large width.

Reflection and Transmission of Beams at a Dielectric Interface

Abstract: When complex values are assigned to the source coordinates in the expressions for the fields radiated by a line or point source in a homogeneous medium, the resulting fields have the form of a two- or three-dimensional Gaussian beam. This fact may be utilized to develop results for beam propagation and scattering in inhomogeneous regions from corresponding results for point or line source fields. After justifying the analytic continuation procedure to derive rigorous integral solutions for the (two-dimensional) beam fields reflected by and transmitted through a plane dielectric interface, asymptotic results are obtained by the saddle point method; it is found that the analytic continuation to complex source coordinates can be performed directly on the asymptotic expressions for reflected, refracted and lateral wave constituents of ordinary line source fields. Interpretation of the reflected fields reveals that they incorporate directly the lateral beam shift, a phenomenon usually regarded as a diffraction...

Apparatus for heat treating a surface

Abstract: Apparatus using a high power laser beam for heat treating a surface, such as a metal surface to harden the surface scans the metal surface which has been coated with radiation absorbing material such as carbon, so that the scanned areas of the metal surface are rapidly heated to above the critical temperature of the metal. Since the heating is very shallow, the heated surface cools very rapidly and so the surface is hardened. The intensity profile of a typical high power laser beam is not flat and so as the beam scans the metal surface, heating of the surface across the width of the beam is not uniform. A flat beam intensity profile is obtained in the present invention by dithering (spacially oscillating) the beam continuously as it sweeps the metal surface. The cross-section area of the dithered beam is substantially greater than the cross-section area of the initial beam from the high power laser and the intensity profile across the dithered beam can be tailored and is dependent upon the initial beam intensity profile and the configuration of the dither. The intensity profile across the dithered beam can be further tailored by blocking portions of the dithered beam.

A Longitudinal Stability Criterion for Bunched Beams

Abstract: The unstable motion of a bunched beam consists of rigid-bunch (dipole) and higher bunch-shape oscillations of the individual bunches (individual-bunch modes), plus perhaps coupled motion of the different bunches (coupled-bunch modes). Stability is achieved either by decoupling the bunches or by a spread in synchrotron frequencies within a bunch. A stability criterion analogous to the Keil-Schnell criterion for coasting beams is given which includes the effect of a beam interacting with perfectly conducting walls, resistive walls, and resonant structures. Some examples for the CERN accelerators are included.

Reflector antenna with improved scanning

Abstract: A Cassegrainian antenna system has a planar array as the feed. An intermediate reflector is positioned in the near field of the array for substantially collimated illumination with all array elements operating in phase. Accordingly, an on-axis main beam is radiated from the main reflector upon illumination by energy from the intermediate reflector. By impressing a linear phase gradient across the array, the main beam is controllably tilted off-axis.

Ion beam micromachining of integrated optics components.

Abstract: Thin film integrated optics components such as light guides, modulators, directional couplers, and polarizers demand high quality edge smoothness and high resolution pattern formation in dimensions down to submicrometer size. Fabrication techniques combining holographic and scanning electron beam lithography with ion beam micromachining have produced planar phase gratings with intervals as small as 2800 A, guiding channel couplers in GaAs, and also wire- grid polarizers for 10.6-µm radiation.

Ultrasonic reflection of a bounded beam at Rayleigh and critical angles for a plane liquid‐solid interface

Abstract: Limited beams of low MHz ultrasound are directed at plane interfaces between water and different solids. Reradiated energy is observed by means of schlieren visualization outside the region predicted by Schoch for incidence at the Rayleigh angle. Some of the solids have properties that would cause prediction of a beam displacement many times that for aluminum. Previous thoery would predict the reflected beam to emerge totally separated from the incident beam for several of the materials used, but no such separation is observed. It is concluded that the reradiated field is composed of specular reflection and Rayleigh‐wave radiation at and near the Rayleigh angle. These two radiations are out of phase at low MHz frequencies, and where they coexist and are of equal amplitude, which occurs within the specular region, a null strip occurs. This strip is sharply defined at exactly the Rayleigh angle. Surface waves (sometimes called pseudosurface waves) are also generated at the longitudinal and shear critical angles. These are also shown to radiate into the fluid but are generated to a much lesser degree and are difficult to demonstrate by schlieren visualization.

Large-Deflection Spatial Buckling of Thin-Walled Beams and Frames

Abstract: The potential energy expression and the (14 by 14) stiffness matrix of a straight thin-walled beam element of open asymmetric cross section, subjected to initial axial force, initial bending moments, and initial bimoment, are derived. The transformation matrix relating the forces and displacements (including bimoment and warping parameter) at the adjacent end cross section of two elements meeting at an angle is deduced as the limiting case of a transfer matrix of a curved beam. To cope with asymmetric cross sections, some element displacements and forces are referred to the shear center and others to the cross-sectional centroid and the matrix for transformation from shear center to centroid is set up. The incremental larger-displacement analysis is formulated using the Eulerian coordinate approach with updating of the local coordinate systems at each load increment. The deformed beams are imagined to be composed of straight elements. Results of lateral post-buckling analysis of various beams are presented.

Liquid crystal diffraction grating

Abstract: The device comprises at least one liquid-crystal cell placed on the path of the beam and constituted by a film of liquid crystals interposed between two walls provided with electrodes between which a potential difference can be applied by suitable means. The incidence of the light beam is oblique with respect to the first wall-liquid crystal interface which is encountered. Use is made of liquid crystals for which the direction of propagation of the light beam is dependent on the potential difference applied between the electrodes.

A beam-modulated time-of-flight mass spectrometer. I. Theoretical considerations

Abstract: The theory of a beam modulation technique, hitherto not used in time-of-flight mass spectrometry, is presented. Salient features of this technique are: firstly, resolution is independent of mass; secondly, resolution is independent of the location where the ions are initially formed; and thirdly, resolution is proportional to the square of the length of the drift space.

Light beam position encoder apparatus

Abstract: An improved sequentially scanned crossed light beam position encoder including means for detecting and transmitting the address of interrupted light beams, means for electrically detecting the subsequent status of an initially detected interrupted beam and means for inhibiting subsequent transfer of the address of the initially detected interrupted beam in the event the subsequent beam status at the address has not changed. The improvement includes means for continuously sequentially activating pairs of non-visible radiation sources and detectors to continuously scan the surface of a display device with respective crossing beams, and means responsive to the initial detection of an interrupted beam at an associated address and responsive to the subsequent absence of beam interruption at the same address on a subsequent scan to reset the system and prepare it for further detection of new beam interruptions.

Electron beam producing system for very high acceleration voltages and beam powers

Abstract: An electron beam producing system for acceleration voltages in the order of magnitude of megavolts and beam powers in the order of magnitude of gigawatts, comprises a tubular housing of insulating material, in which adjacent to its one closed end a field emission cathode with a large surface area is arranged while at its other end, from which the electron beam emerges, an annular anode is arranged A device serves for collimating the electrons emitted by the cathode to form a collimated electron beam The device for collimating the electron consists of annular electrodes, which respectively comprise a part adjacent to their center opening and an outer part which is held on the housing and has a radial electrical passage extending towards the outside of the housing The inner part of the electrode lying closest to the cathode has at least approximately the shape of a frusto-conical surface which tapers towards the cathode; in that the inner part of the remaining electrodes is flat or at least approximately frusto-conical and respectively lies in an equipotential surface of an electric field, which collimates the electrons, emitted by the cathode, to form a parallel beam The housing is surrounded by a coaxial insulating casing with a clearance The intermediate space between the outer surface of the housing and the casing is surrounded with an electrically conducting liquid with a relatively high specific resistance and at the axial ends has a respective connection electrode, which makes contact with the liquid, for the operating voltage and that the outer parts of the electrodes are so shaped that the radial passages end at those sites of the liquid filled intermediate space at which the fraction, provided for the relevant electrode, of the operating voltage obtains when the operating voltage is applied to the connection electrodes

Problems associated with the injection of a high-energy neutral beam into a plasma

Abstract: Several problems associated with the heating of toroidal plasmas by high-energy neutral beams are discussed. The high-energy particles slow down classically on the background plasma and the distribution function of these particles is evaluated as a function of time by solving a simplified Fokker-Planck equation. The stability of this distribution is then examined both for times before and after it reaches its equilibrium configuration. It is found that in both cases the high energy distribution is unstable unless the angle of injection is almost parallel to the field lines. Finally, the problem of the electric field which is produced by an injected neutral beam is discussed.

Short-term average optical-beam spread in a turbulent medium

Abstract: On the basis of the extended Huygens–Fresnel principle, a general expression is derived for the short-term average optical-beam spread, as measured with respect to the instantaneous center of energy of the beam, of an initially coherent optical-beam wave propagating in a weakly inhomogeneous medium. The present analysis applies to the near field of the effective coherent transmitting aperture, where the beam wanders (dances) as a whole and does not break up into multiple patches or blobs. Central to the analysis is the short-term average mutual coherence function (MCF) of a spherical wave. This quantity is obtained from the corresponding long-term MCF by removing the random tilt of the wave front. Analytic expressions for the short-term beam spread are presented for the case of a Kolmogorov spectrum and the short-term average MCF derived by Fried. As expected, the short-term, turbulence-induced beam spread is always less than the corresponding long-term beam spread. Analytic and numerical results are given for the short-term average irradiance at focal range f, which is always greater than the corresponding long-term average irradiance.

The analysis of a time-of-flight neutron diffractometer for amorphous materials: the structure of a molecule in a liquid

Abstract: A comparison is made of the conventional method of using a continuous monochromatic slow neutron beam method of measuring the structure factor of an amorphous material (e.g. a liquid or a glass) and the method using a pulsed beam of heterochromatic neutrons and measurement of their time-of-flight. The Placzek [1] method has been adapted to the analysis of the time-of-flight experiment. The corrections required to convert the measured counting rates to static structure factors are explicitly evaluated for various detector laws and for any incident spectrum. It is shown that there is no particular virtue in equal-path time-of-flight arrangements. There is however a particular interest in a ‘1/v 2’ detector. The method of analysis is of particular value for the determination of the interference part of the structure factor at high momentum transfer. Some recent experiments on molecular liquids (Clarke and Dore [2 (a] are analysed and it is shown that certain features of the structure of a molecule in the liq...

Laser beam drill

Abstract: A method of drilling for subterranean fluid with a laser beam comprising positioning a laser beam generator in a wellhole electrically connected to an inhole voltage generator actuated by drilling mud or other liquid passing through a laser beam housing connected to the drill string. A reflecting crystal for the laser beam is positioned within the laser beam housing to reflect the beam preferably in elliptical pattern across the formation to be penetrated.

n‐Beam lattice images. IV. Computed two‐dimensional images

Abstract: The contrast in electron-microscope lattice images of crystals oriented with a zone axis parallel to the incident electron beam has been computed for several complex oxides with large unit cells. The effects of changes in crystal thickness, image defocus, objective aperture size (up to 100 contributing diffracted beams) and spherical aberration are considered, and it is shown that, under certain conditions, the appearance of the image resembles that of the crystal structure. The bounds of applicability of the simple charge-density approximation are investigated.

Propagation of electromagnetic waves through turbulent plasma using transport theory

Abstract: Transport methods have been employed to study the propagation of a narrow-angle electromagnetic beam through a turbulent plasma. Results are presented for the mean-square angular divergence of the beam, the beam cross section, and the power received by a planar aperture in the medium and the mutual coherence function. The problem of backscattered radiation is also considered and results are obtained which reduce, in the limit of zero true absorption, to previous results.

Electron beam electrical power transmission system

Abstract: Electrical power is transmitted from a transmitting location to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting location and the receiving location. The beam is magnetically focused within the evacuated pipe. Electrical power to be transmitted is put into the beam in the form of kinetic energy by accelerating the beam to a high kinetic energy. The kinetic energy is extracted from the beam at the receiving location and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is extracted from the beam by collecting the beam current at a potential substantially equal to the potential of the source of the electrons, i.e. cathode potential, and causing the collected beam current to flow through the load to develop the depressed collector potential. In another embodiment, radio frequency accelerator means are utilized for r.f. current density modulating and accelerating the beam. The radio frequency current modulation on the beam is extracted at the receiving end by means of radio frequency circuits coupled to the beam. The extracted radio frequency energy is rectified for application to the load. In another embodiment, AC power at conventional AC power frequencies, as of 60 Hertz, is extracted from the beam by sequentially directing the beam into a plurality of depressed collectors coupled to respective primary windings of power transformers for deriving AC output power for application to a load.

Laser device with articulated arm

Abstract: Apparatus for conducting a laser beam from a laser, through an articulated arm, to an output device, said apparatus being constructed so that the output device is easily maneuvered. In one embodiment, a beam from a laser mounted on an optical bench is directed to a first mirror that reflects the beam upward along the axis of a vertical shaft. At the top of the shaft, a second mirror, mounted on a conical bearing and rotatable about the axis of the vertical shaft, reflects the laser beam along the axis of a horizontal sleeve to a third mirror that is mounted on a sleeve bearing so that it is rotatable about the horizontal axis. In like fashion, the beam from the third mirror is successively incident on fourth, fifth, sixth, seventh, and eighth mirrors all of which are rotatable about the axis of the shaft down which the incident beam propagates. Finally, the beam from the eighth mirror enters the output device. The second through eighth mirrors are all mounted in the articulated arm and are interconnected by sleeve bearings and, in some cases, hollow tubes. The arm is supported by a counterbalancing system that is connected to the arm at a point between the third and fourth mirrors.

Fabrication of glass fibers from preform by lasers

Abstract: Method and apparatus for drawing both clad and unclad fibers of indefinite length from glass preforms are described. A laser beam, generated by a laser operating in the far infrared, is used as a source of heat. In a particular embodiment, a beam of annular cross section is formed and directed substantially around the periphery of the preform.

Structure of water and carbon dioxide clusters formed via homogeneous nucleation in nozzle beams

Abstract: A nozzle molecular beam is operated so as to optimize the molecular clustering in the free jet expansion. Continuous beams of carbon dioxide and water are sampled with an ionization gauge detector. The increased beam intensity under some operating conditions can only be attributed to clustering. A high energy electron beam of 39.5 keV is used to obtain Debye‐Scherrer diffraction patterns from carbon dioxide and water clusters. The largest size clusters produced are solid and have the structure of the bulk material which is simple cubic for CO2 and diamond cubic for H2O. The average diameters for CO2 and H2O are 52±5 and 54±5 A, respectively, corresponding to 1600 and 2600 molecules per cluster. The CO2 data are in agreement with other beam results and, to the authors' knowledge, these are the first data published on the structure of water clusters formed from the vapor phase via homogeneous nucleation. Based on the diffraction data the structure of clusters down to average sizes in the range of 300–450 molecules per cluster can be treated as bulk phase.

Destructive Instabilities in Hollow Intense Relativistic Electron Beams

Abstract: BS>It is found that a 400-keV, 10-40-kA, 50-nsec duration hollow relativistic electron beam suffers from a severe instability when injected into neutral gas along a magnetic field. The dependence of beam distortion on beam thickness, magnetic field strength, beam current, and proximity of the surrounding conducting walls is experimentally studied. The experimental observations are consistent with the diocotron instability occurring during the first several nanoseconds of the beam pulse. (auth)