Showing papers on "Beam (structure) published in 1989"

Theoretical determination of net radiation force and torque for a spherical particle illuminated by a focused laser beam

Abstract: Series expressions for the net radiation force and torque for a spherical particle illuminated by an arbitrarily defined monochromatic beam are derived utilizing the spherical‐particle/arbitrary‐beam interaction theory developed in an earlier paper. Calculations of net force and torque are presented for a 5‐μm‐diam water droplet in air optically levitated by a tightly focused (2 μm beam waist diameter) TEM00‐mode argon‐ion (λ=0.5145 μm) laser beam for on and off propagation axis, and on and off structural resonance conditions. Several features of these theoretical results are related to corresponding experimental observations.

The H-Mode of ASDEX

Abstract: The paper is a review of investigations of the H-mode on ASDEX performed since its discovery in 1982. The topics discussed are: (1) the development of the plasma profiles, with steep gradients in the edge region and flat profiles in the bulk plasma, (2) the MHD properties resulting from the profile changes, including an extensive stability analysis, (3) the impurity development, with special emphasis on the MHD aspects and on neoclassical impurity transport effects in quiescent H-phases, and (4) the properties of the edge plasma, including the evidence of threedimensional distortions at the edge. The part on confinement includes scaling studies and the results of transport analysis. The power threshold of the H-mode is found to depend weakly on the density, but there is probably no dependence on the toroidal field or the current. For the operational range of the H-mode, new results for the limiter H-mode on ASDEX and the development of the H-mode under beam current drive conditions are included. A number of experiments are described which demonstrate the crucial role of the edge electron temperature in the L-H transition. New results of magnetic and density fluctuation studies at the plasma edge within the edge transport barrier are presented. Finally, the findings on ASDEX are compared with results obtained on other machines and are used to test various H-mode theories.

Detailed models of piezoceramic actuation of beams

Abstract: In this paper, techniques for modeling induced strain actuation of beam-like components of intelligent structures are developed. Two analytical models and one numer ical model describing the detailed mechanics of induced strain actuators bonded to and embedded in one-dimensional structures are presented. The models illustrate the exten sion, bending, and localized shearing deformations induced. The range of parameters for which the simpler analytic models are valid is also established. The specific characteris tics of one type of induced strain actuator, piezoceramic materials, are discussed, and im plications for practical use of piezoceramic actuators are outlined. Experimental results are used to validate the beam actuation models presented.

Transverse localization of light.

Abstract: We study the propagation of light through a semi-infinite medium with transverse disorder (that is, disorder in two directions only). We show that such a system exhibits strong two-dimensional localization by demonstrating that on propagation a beam expands until the transverse localization length is reached.

A survey of the acoustic output of commercial extracorporeal shock wave lithotripters

Abstract: A survey of the pressures and intensities generated by different commercial extracorporeal shock wave (ESWL) lithotripters is reported. The lithotripters included in the survey are the Dornier HM3, Wolf Piezolith 2200 and 2300, Siemens Lithostar, Technomed Sonolith 2000 and 3000, and EDAP LT-01. Measurements were made using a polyvinylidene difluoride (PVdF) membrane hydrophone in water. The zero crossing frequency of one complete cycle of the focused pulse from ESWL equipment is in the range 0.1 to 1 MHz. Spatial-peak temporal-peak positive and negative pressures up to 114 MPa and 10 MPa, respectively, have been measured and the rise times of the positive pressure half cycle at maximum output settings are 30 ns or less. The mean spatial-peak temporal-average intensity of the lithotripters is 5.0 × 10 2 W m −2 when operated at a pulse repetition frequency of 1 Hz. The spatial-peak pulse-average intensity ranges from 6.6 × 10 7 to 1.24 × 10 9 W m −2 . The estimated acoustic energy in a single pulse (at the focus) at the maximum output setting of the lithotripters varies from 2.0 × 10 −3 J to about 9.0 × 10 −2 J. The beam area in the focal plane varies by a factor of 100 on different lithotripters and the temporal-peak pressure at the position of the skin at the entry point of the beam by a factor of 30. Measurement problems associated with hydrophone damage and the uncertainties in the hydrophone calibration at high pressures are discussed and an estimate of the total uncertainty in the absolute measurements of the spatial-peak temporal-peak positive pressure is given as ±36%.

Sound field calculation for rectangular sources

Abstract: A method is presented for calculation of the sound field from a rectangular continuous-wave source surrounded by a plane grid baffle. The approach is illustrated for square sources of 0.5, 1, 2, 5, 10, 20, and 100 lambda on a side. These results are compared to the sound fields produced by similarly sized circular sources. The beam widths and locations of on-axis minima are similar for the two sources, but the transverse pressure distribution is more uniform in the near-field of the square source. The effects of attenuation on the sound field of a square source are examined. >

Reflection of a beam of finite size from a corrugated waveguide

Abstract: The paper is concerned with the influence of the finite size of an incident beam upon both the anomalous-reflection spectrum and the shape of the energy distribution in a reflected beam. It is proved experimentally that the use of corrugated waveguides as a laser-resonator selective mirror improves the spatial coherence of radiation.

Effects of a Piezo-Actuator on a Finitely Deformed Beam Subjected to General Loading

Abstract: The deformation of a beam-column, the upper and lower surfaces of which are bonded in segments with piezo-ceramic liners, is studied for the purpose of obtaining appropriate expressions for the force transferred to the structural member by the piezo-actuator. This concept may be employed for the control of large dynamic deformations of a lattice-type flexible space-structure. The present model, which is based upon a static analysis, accounts for the effects of transverse shear and axial forces in addition to a bending moment on the beam in formulating the governing equilibrium equations. The present model provides more complete expressions for the force transmitted to the structural member than a model reported earlier in literature, in which the shear and axial forces are neglected.

The Non-Linear Response of a Slender Beam Carrying a Lumped Mass to a Principal Parametric Excitation: Theory and Experiment

Abstract: The non-linear response of a slender cantilever beam carrying a lumped mass to a principal parametric base excitation is investigated theoretically and experimentally. The Euler-Bernoulli theory for a slender beam is used to derive the governing non-linear partial differential equation for an arbitrary position of the lumped mass. The non-linear terms arising from inertia, curvature and axial displacement caused by large transverse deflections are retained up to third order. The linear eigenvalues and eigenfunctions are determined. The governing equation is discretized by Galerkin's method, and the coefficients of the temporal equation—comprised of integral representations of the eigenfunctions and their derivatives—are computed using the linear eigenfunctions. The method of multiple scales is used to determine an approximate solution of the temporal equation for the case of a single mode. Experiments were performed on metallic beams and later on composite beams because all of the metallic beams failed prematurely due to the very large response amplitudes. The results of the experiment show very good qualitative agreement with the theory.

System for, and method of, regulating the wavelength of a light beam

Abstract: A laser light beam is processed in a first optical path to produce light indications in a plurality of free spectral paths. These light indications are introduced through slits to produce signals at spaced positions at the opposite peripheries of a linear detector array. The distances between correlated pairs of energized detectors at the opposite peripheries of the array indicate the relative value of the laser wavelength in the free spectral ranges. The laser light beam is also processed in a second optical path, simultaneously with the processing of the laser light beam in the first optical path, to produce light in a single path. The second optical path is dependent upon the wavelength of the laser light beam. The light produced in the second optical path may be introduced through another slit to energize centrally disposed detectors in the array. The particular detectors energized are dependent upon the wavelength of the laser light. The detectors in the linear array may be scanned to produce signals related in time to the disposition of the detectors energized in the array. A data processing system processes these signals and produces a signal to adjust the wavelength of the laser beam to a particular value. When the laser is pulsed, the system described above may operate in real time after each pulse to adjust the laser before the next pulse to produce light at the particular wavelength.

System and method for computer automated manufacturing using fluent material

Abstract: A system and method for constructing a three-dimensional object (10) from a design created on a CAD machine (14) is disclosed which includes a support (B) which may be indexed along two coordinate axes (X, Y) and a movable dispensing head (A) which indexes along a Z-axis. A fluent material (54) is dispensed or extruded from head (A) and as it is dispensed, the fluent material is subjected to a treatment by treatment sources (D) which cause the fluent material to transform into a fixed solidified state in the form of a three-dimensional object. Fluent material (54) may be a polymeric material which is solidified by an energy beam of ultraviolet light (56) upon dispensing. A shield (E) is provided to shield the dispensing head (A) and strand of material (54) so that the material is treated at the proper time and location to cause it to solidify properly to form the three-dimensional object. In accordance with the method, indexing takes place in desired steps so a dimensionally accurate object is formed.

Generation of high‐energy atomic beams in laser‐superconducting target interactions

Abstract: High‐energy atomic beams with Mach numbers as high as 5 were observed in excimer laser‐superconducting target interactions. The velocity distributions of the Y, Ba, Cu, and O atoms and ions could be described very well by a supersonic expansion‐type mechanism similar to a molecule beam. The physics of the atomic beam formation process is discussed.

New formulations of the matrix beam propagation method: application to rib waveguides

Abstract: A technique for the spectral analysis of strongly guided optical waveguiding media based on a variant of the recently introduced matrix beam propagation algorithm is discussed. In particular, it is shown that the lowest order modes of rib waveguides can be generated with a simple computer program using this method. The results are also obtained using a standard finite-element procedure. The relative efficiency of the two methods is considered. The propagating electric field and differential losses in a Y junction fabricated from rib waveguides are also evaluated. >

Penetration of energetic neutral beams into fusion plasmas

Abstract: The efficiency of neutral beam heating and current drive depends crucially on the deposition of the energy and momentum of the beam in the plasma. This deposition is determined by the atomic processes involved in the stopping (or effective ionization) of the neutral beam atoms. These processes have been studied in detail for the energy range from 10 keV/u to 10 MeV/u. The processes considered include both the ground state and the excited state of the beam atoms, thus allowing for the multistep ionization of the beam in collisions with the plasma constituents and impurities. The effective beam stopping cross-section has been calculated for a wide variety of beam and plasma parameters. The atomic database necessary for these calculations has been documented using the best data available at present. The stopping cross-section data are also given in terms of a convenient analytic fit, which can be used either in computer calculations or for simpler analytic estimates of neutral beam penetration.

Bessel beam ultrasonic transducer: Fabrication method and experimental results

Abstract: We report experimental results from a first‐of‐a‐kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric Bessel function pattern is ‘‘polarized into’’ a piezoelectric ceramic element. The resulting circular‐disk transducer has the usual full‐plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel function J0 (r), both in amplitude and in phase. The radiation field of a 1‐in.‐diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss‐Hermite model. Bessel transducers are of particular interest in attempts to achieve ‘‘diffractionless’’ beams.

Non-linear non-planar parametric responses of an inextensional beam☆

Abstract: The non-linear integro-differential equations of motion for an inextensional beam are used to investigate the planar and non-planar responses of a fixed-free beam to a principal parametric excitation. The beam is assumed to undergo flexure about two principal axes and torsion. The equations contain cubic non-linearities due to curvature and inertia. Two uniform beams with rectangular cross sections are considered: one has an aspect ratio near unity, and the other has an aspect ratio near 6.27. In both cases, the beam possesses a one-to-one internal resonance with one of the natural flexural frequencies in one plane being approximately equal to one of the natural flexural frequencies in the second plane. A combination of the Galerkin procedure and the method of multiple scales is used to construct a first-order uniform expansion for the interaction of the two resonant modes, yielding four first-order non-linear ordinary-differential equations governing the amplitudes and phases of the modes of vibration. The results show that the non-linear inertia terms produce a softening effect and play a significant role in the planar responses of high-frequency modes. On the other hand, the non-linear geometric terms produce a hardening effect and dominate the planar responses of low-frequency modes and non-planar responses for all modes. If the non-linear geometric terms were not included in the governing equations, then non-planar responses would not be predicted. For some range of parameters, Hopf bifurcations exist and the response consists of amplitude- and phase-modulated or chaotic motions.

Laser apparatus for concurrent analysis and treatment

Abstract: The present invention discloses an apparatus in which two laser beams are concurrently scanned across a region of tissue to be treated by laser therapy. A first "analysis" beam is used to excite characteristic light emission or reflection from the surface. This scattered light is detected and analyzed to determine the properties of the small portion of the surface under illumination and at that instant by the analysis beam. A second "treatment" beam is scanned concurrently with the analysis beam. The properties of the surface at each small region (as determined by the analysis beam) are used to adjust the power and other properties of the treatment beam such that each small region of the surface receives optimal exposure. Automatic controlled scanning of both beams allows very rapid treatment of large areas of tissue, while adjusting in real-time the power levels of the lasers to achieve optimal treatment at each point treated.

A comparative study of performances of various base isolation systems, part I: Shear beam structures

Abstract: A comparative study of performances of different base isolators for shear beam type structures is carried out. Several leading base isolation systems, including the laminated rubber bearing with and without lead plug, the resilient-friction base isolator with and without sliding upper plate, and the EDF system are considered. Displacement and acceleration response spectra for a shear beam structure subject to the accelerograms of the N00W component of El Centro 1940 and the N90W component of Mexico City 1985 earthquakes and their magnified forms are evaluated. A series of parametric studies is carried out and advantages and disadvantages of various base isolation systems are identified. Comparisons of the results with the response spectra of a fixed-base structure show that the base isolation systems are, in general, highly effective in reducing the peak acceleration transmitted to the superstructure. Thus, the deflections and stresses generated in a base-isolated structure are significantly lower than those of a fixed-base one. Furthermore, the results of the study also show that the friction-type base isolators are less sensitive to severe variations in frequency content and amplitude of the ground acceleration.

Optical head with flying lens

Abstract: A micro-objective lens is carried on an air bearing slider (30) with an optical passage through which the lens focuses an energy beam onto a spot on an optical data storage medium (10). The slider accomplishes automatic focusing. An RF coil is affixed to the slider facing the storage medium and surrounding the beam axis. The proximity of the coil lowers power switching requirements.

Flexural and shear moduli of full-section fiber reinforced plastic (FRP) pultruded beams

Abstract: An experimental methodology is presented for the simutaneous determination of the section flexural modulus and the section shear modulus of thin-walled fiber reinforced polyester and vinylester pultruded beams. A pilot test program, involving four different fiber reinforced plastic (FRP) beams, is described and results are discussed. A slenderness ratio is introduced to characterize the shape of the thin-walled beam, and recommended values of this ratio are suggested for design purposes. With available values of the section moduli the designer has the option of using the Timoshenko beam theory instead of the Euler-Bernoulli beam theory.

Beam-Column Moment Connections for Composite Frames: Part 1

Abstract: Increasingly, engineers are designing composite and mixed building system of structural steel and reinforced concrete to produce more efficient structures than realized using either material alone. Recent literature has pointed out a need for greater understanding of the interaction of structural steel and reinforced concrete in such systems. In this paper, the behavior of composite beam-column connections is examined through results of an experimental research program where 15 two-thirds scale joint specimens were tested under monotonic and cyclic loading. Such connections are typically employed in composite framed structures consisting of steel beams and reinforced concrete or composite columns. Significant strength increases were achieved using straightforward details to enhance concrete participation in the joint region. Details considered include the following attachments to the steel beam: vertical stiffener plates, steel columns, welded shear studs, and Dywidag reinforcing bars. The results and discussion presented in this paper provide background for a companion paper that includes a design model for calculating the joint strength.

Beam-combining laser beam source device

Abstract: A beam-combining laser beam source device comprising an airtight housing and a laser beam source unit housed in the housing. The laser beam source unit comprises laser beam sources and collimator optical systems respectively positioned in optical paths of laser beams, which are radiated from the laser beam sources, in order to collimate the laser beams. Optical path adjusting elements are respectively positioned in the optical paths of the laser beams in order to radiate the laser beams along optical paths parallel and close to one another. The laser beam sources, the collimator optical systems, and the optical path adjusting elements are supported on a single support. The housing is provided with a temperature sensor, which detects the temperature in the housing, and temperature adjusting elements which heat or chill the housing on the basis of control of the temperature sensor so that the temperature in the housing is kept constant.

Method of and arrangement for measuring vibrations

Abstract: The movement of a predetermined zone of a surface of a vibrating object is measured by separating a laser beam (12) having a predetermined coherence length into a probe beam (14) and a reference beam (15). The reference beam (15) is then delayed relative to the probe beam (14) by a predetermined time interval sufficient for the probe beam (14) to travel through a predetermined distance at least corresponding to the coherence length, before being combined with the probe beam (14) to form a combination beam (24). The combination beam is then subdivided into a plurality of substantially equal component beams each (25,26,27) of which is conducted along a separate path to a location spaced from the predetermined zone substantially by one-half of the distance traveled by light in the predetermined time interval between the above location and the predetermined zone. A predetermined portion of each component beam is reflected at the respective location back into the respective path, while the remainder of each component beam is directed to the predetermined zone (35) for return therefrom at least predominantly back toward the respective location and into the respective path with attendant coherent interference of the returned probe beam part with the reflected reference beam part of the same component beam. The return light beams (50) are demodulated to obtain an indication of the movement of the predetermined zone.

Fiber output coupler with beam shaping optics for laser materials processing system

Abstract: A coupler apparatus for supporting an output end of an optical fiber is described. In one embodiment, the coupler apparatus includes a first lens for collimating as a first collimated beam a portion of a high power laser beam emitted from the output end of the fiber. The beam, as it is transmitted through the coupler, is expanded and shaped into a materials processing beam portion which is focused onto a workpiece surface.

Internal fields of a spherical particle illuminated by a tightly focused laser beam: Focal point positioning effects at resonance

Abstract: The spherical particle/arbitrary beam interaction theory developed in an earlier paper is used to investigate the dependence of structural resonance behavior on focal point positioning for a spherical particle illuminated by a tightly focused (beam diameter less than sphere diameter), linearly polarized, Gaussian‐profiled laser beam. Calculations of absorption efficiency and distributions of normalized source function (electric field magnitude) are presented as a function of focal point positioning for a particle with a complex relative index of refraction of n=1.33+5.0×10−6i and a size parameter of α≊29.5 at both nonresonance and resonance conditions. The results of the calculations indicate that structural resonances are not excited during the on‐center focal point positioning of such a tightly focused beam but structural resonances can be excited by proper on‐edge focal point positioning. Electric wave resonances were found to be excited by moving the focal point from on‐center towards the edge of the sphere parallel to the direction of the incident beam electric field polarization. Magnetic wave resonances were found to be excited by moving the focal point from on‐center towards the edge of the sphere perpendicular to the direction of the incident beam electric field polarization.

Local bond of deformed bars with different diameters in confined concrete

Abstract: Slippage of the beam reinforcement crossing the interior joints in reinforced concrete frames can lead to large fixed-end rotations and overall beam deformations, causing major structural damage under severe seismic excitations. It is thus important to anchor adequately deformed bars inside the confined core of earthquake-resistant joints. The key factor governing the anchored-bar behavior in confined concrete is the local bond stress-slip relationship. This investigation addreses the effects of bar diameter on this relationship. Experimental data have been generated on the local bond behaviour for deformed bars of different diameters partially embedded in confined concrete. The results are used to assess the anchored bar-diameter effects of the ultimate local bond strenth and local bond stress-slip relationship in confined concrete. Based on the test data, an empirical local bond constitutive model has been generated that accounts for the bar diameter effects.