Showing papers on "Beam (structure) published in 1990"

Large-amplitude periodic oscillations in suspension bridges: some new connections with nonlinear analysis

Abstract: This paper surveys an area of nonlinear functional analysis and its applications. The main application is to the existence and multiplicity of periodic solutions of a possible mathematical models of nonlinearly supported bending beams, and their possible application to nonlinear behavior as observed in large-amplitude flexings in suspension bridges. A second area, periodic flexings in a floating beam, also nonlinearly supported, is covered at the end of the paper.

Generating radially polarized beams interferometrically.

Abstract: Two interferometric techniques for converting a linearly polarized laser beam into a radially polarized beam with uniform azimuthal intensity are described. The techniques are based on the linear combination of orthogonally polarized beams, which have tailored intensity and phase profiles. Linearly polarized beams with intensity profiles tailored using a modified laser or an apodization filter are combined in separate experiments to produce radially polarized light. A beam with an extinction ratio of −21.7 dB and azimuthal intensity variations of less than ±12% is produced using the modified laser output. The second technique uses circularly polarized light and a unique spiral phase delay plate to produce the required phase profile. When focused, a radially polarized beam has a net longitudinal field useful for particle acceleration and, perhaps, other unique applications.

Charged Particle Beams

Abstract: Phase Space Description of Charged Particle Beams Introduction to Beam Emittance Beam Emittance - Advanced Topics Introduction to Beam-Generated Forces Beam-Generated Forces - Advanced Topics Electron and Ion Guns High Power Pulsed Electron and Ion Diodes Paraxial Beam Transport with Space-Charge High Current Electron Beam Transport in Vacuum Ion Beam Neutralization Electron Beams in Plasmas Transverse Instabilities Longitudinal Instabilities Energy Extraction from Beams.

Ink-jet recording device

Abstract: PURPOSE: To make a beam member displaced by thermal energy of an exothermic body without allowing said body to make contact with recording liquid by providing the exothermic body to the beam member separately from the recording liquid, and by making the beam member bend by thermal energy of the exothermic body. CONSTITUTION: A cantilever deforms suddenly from its stationary state to a state of displacement in the direction marked with an arrow by bending moment produced by expansion that is brought about by supplying of electricity to a heater 7 of a cantilever-supporting member 10. The movement of the cantilever at this time make ink inside an ink chamber 8 be ejected in the form of ink drops 12 through nozzles of a nozzle plate 11, and recording is made therewith on recording paper. In the above-mentioned process, bending by effect of thermal stress is utilized by heating (by giving thermal shock) only the surface of the cantilever that is made in a single-layer structure. It is necessary to provide the device with better radiation characteristics for improvement of recording frequency. Therefore, it is desirable to arranged the heater 7 in a liquid chamber containing insulating cooling liquid that is provided separately from the liquid chamber 8, or to make the heater 7 to be air-cooled with a fan or the like. In the case where the structure is such that the beam is supported at the opposite ends, the two heaters 7 are arranged on the supporting members on the opposite ends. COPYRIGHT: (C)1992,JPO&Japio

Ultrasonic nondiffracting transducer for medical imaging

Abstract: The nondiffracting J/sub 0/ Bessel beam is evaluated, and its application to medical imaging is suggested. Computer simulations and experimental results for a ten-ring annular Bessel shaded transducer are described. Both continuous-wave (CW) and pulse-wave (PW) excitations are shown and compared to conventional Gaussian beams. The nondiffracting beam has about 1.27-nm radius main lobe with a 20-cm depth of field compared to the Gaussian transducer of the same size with a 1.27-mm radius main lobe at a focus of 12 cm and 2*4-cm depth of field. The side lobes of the nondiffracting beam are the same as the J/sub 0/ Bessel function. The effects of heterogeneity due to tissue on the nondiffracting beam and on the focused Gaussian beam are also reported. >

Thin-walled composite beams under bending, torsional, and extensional loads

Abstract: Symmetric and antisymmetric layup graphite-epoxy composite beams with thin-walled rectangular cross sections are fabricated using an autoclave molding technique and tested under bending, torsional, and extensional loads. The bending slope and elastic twist at a station are measured using an optical system, and the results correlated with predicted values from a simple beam analysis as well as a refined finite element analysis. A symmetric ply layup results in bending-twist coupling whereas an antisymmetric layup causes extension-twist coupling. Simple analytical results with plane-stress assumption agree better with measured data as well as finite element predictions than with plane-strain assumption. For symmetric layup beams, the bending-induced twist and torsion-induced bending slope are predicted satisfactorily using simple analytical solution. Correlations with measured data, however, are generally improved using a finite element solution. For antisymmetric beams, axial force-induced twist is predicted satisfactorily by both methods.

Method and apparatus for measuring thickness of thin films

Abstract: An apparatus (20) for measuring the thickness of a thin film layer (32) on substrate (28) includes a probe beam of radiation (24) focused substantially normal to the surface of the sample using a high numerical aperture lens (30). The high numerical aperture lens (30) provides a large spread of angles of incidence of the rays within the incident focused beam. A detector (50) measures the intensity across the reflected probe beam as a function of the angle of incidence with respect to the surface of the substrate (28) of various rays within the focused incident probe beam. A processor (52) functions to derive the thickness of the thin film layer based on these angular dependent intensity measurements. This result is achieved by using the angular dependent intensity measurements to solve the layer thickness using variations of the Fresnel equations. The invention is particularly suitable for measuring thin films, such as oxide layers, on silicon semiconductor samples.

Efficient beam propagation techniques

Abstract: It is shown that suitable modifications of the free-space-propagation operator in the standard fast-Fourier-transform beam propagation procedure yield a far more rapid code in the context of semiconductor rib waveguide calculations. The procedure curtails the diffraction experienced by the high-order Fourier components of the electric field and mirrors the structure of the recently introduced finite-difference beam propagation algorithm. It is used to investigate the propagation losses of a Y-junction composed of single-mode rib waveguides and illuminated by its normalized guided mode. >

Premature Failure of Externally Plated Reinforced Concrete Beams

Abstract: Reinforced concrete beams can be strengthened and stiffened by gluing mild steel plates to the tension face of the beam. However, experimental tests show that these externally bonded plates have a tendency to peel away after the formation of shear diagonal cracks or when the curvature in the beam is increased. Fifty‐seven plated reinforced concrete beams are tested to study peeling induced by increasing curvature; in these tests, the geometry and material properties of the beams are varied, and the reinforced concrete beams are subjected to pre‐cracking and pre‐cambering, as might occur in an existing structure. A method is derived for determining the moment at which peeling starts (serviceability limit) and the moment that causes complete separation of the plate (ultimate limit). This method, which depends on the flexural rigidity of the plated beam, the thickness of the plate, and the tensile strength of the concrete, can be used to adjust the size and extent of plating so that flexural peeling does not...

Composite tubular door beam reinforced with a syntactic foam core localized at the mid-span of the tube

Abstract: A lightweight, composite beams for reinforcing a vehicle door is provided. The reinforcing beam comprises a metal tube having a longitudinal cavity which is partially filled with a reinforcing polymeric core which in one aspect includes a thermoset or thermoplastic resin-based material. The core is friction fit or mechanically held within the metal tube at the mid-span of the tube. The composite beam includes end pieces which are adapted to be mounted to a vehicle door panel in a door cavity by spot-welds or the like. The horizontally mounted beam provides substantially increased resistance to side impacts to the vehicle door in the event of a collision.

Composite tubular door beam reinforced with a reacted core localized at the mid-span of the tube

Abstract: A lightweight, composite beam with a reacted core for reinforcing a vehicle door is provided. The reinforcing beam comprises a metal tube having a longitudinal cavity which is partially filled with either a reinforcing polymeric core which in one aspect includes a thermoset or thermoplastic resin-based material or a cementitious core which includes Portland cement and a filler. The reacted core is friction fit or mechanically held within the metal tube at the mid-span of the tube. The composite beam includes end pieces which are adapted to be mounted to a vehicle door panel in a door cavity by spot-welds or the like. The horizontally mounted beam provides substantially increased resistance to side impacts to the vehicle door in the event of a collision.

Plasma fluctuation measurements in tokamaks using beam‐plasma interactions

Abstract: High‐frequency observations of light emitted from the interactions between plasma ions and injected neutral beam atoms allow the measurement of moderate‐wavelength fluctuations in plasma and impurity ion densities. To detect turbulence in the local plasma ion density, the collisionally excited fluorescence from a neutral beam is measured either separately at several spatial points or with a multichannel imaging detector. Similarly, the role of impurity ion density fluctuations is measured using charge exchange recombination excited transitions emitted by the ion species of interest. This technique can access the relatively unexplored region of long‐wavelength plasma turbulence with k⊥ρi≪1, and hence complements measurements from scattering experiments. Optimization of neutral beam geometry and optical sightlines can result in very good localization and resolution (Δx≤1 cm) in the hot plasma core region. The detectable fluctuation level is determined by photon statistics, atomic excitation processes, and b...

Bending of sandwich beams with transversely flexible core

Abstract: The bending behavior of a sandwich beam with a foam core is analytically investigated. The beam consists of upper and lower skins, metallic or composite laminated, and a soft core. The loading pattern consists of concentrated as well as distributed loads exerted at the upper or the lower skin or a combination of the two. The analysis includes the effects of the flexibility of the core in the vertical direction on the overall bending behavior. The main parameters affecting the overall behavior and particularly the peeling and the shear stresses between the skins and the core are studied. ANDWICH beams have been used in various industries for many years. A typical beam consists of two skins made of metal or laminated composite and a core. The core is usually made of honeycomb, metallic or nonmetallic, which is stiff in the vertical direction and flexible in the horizontal one. In recent years, plastic foams are used for cores in sandwich structures. In this case, the effect of the transverse flexibility of the core on the mechanical behavior of the beam should be taken into account. This flexibility affects the transverse bend- ing behavior of the beam and leads to unequal deflections of the upper and lower symmetrical skins (see Fig. 1). Sandwich beams with honeycomb cores were considered by many researchers. Reissner1'2 included the shear strain effect on the bending, but only the average bending behavior of the composite beam is considered. Many researchers3'5 dealt with the analysis of beams with an antiplane core, i.e., a core with shear rigidity only. The Hexcel designer manual6 outlines the design procedures for beams with honeycomb cores only. An antiplane-cor e approach with anisotropic and composite skin appears in Refs. 7-9. Ojalvo10 assumed different deflec- tions to the two skins, but neglected the peeling stresses. Ogorkiewicz and Sayigh11 dealt with a foam core by replacing it with an ordinary beam with equivalent properties. In this paper, the proposed analysis includes the effects of the transverse flexibility of the core and the peeling stresses between the skin face and the core on the overall bending behavior. The analysis is general and applicable to metallic or com- posite laminated identical skins. The behavior is described in terms of the deflections, the peeling, and the shear stresses in the adhesive layers. The effect of the variables that govern the behavior is incorporated through a parametric study. The mathematical formulation and the boundary conditions are discussed. The analytical solution for the various types of loading with different boundary conditions is presented.

The geometric transfer function for cone and fan beam collimators

Abstract: Geometric response functions are derived for both cone and fan beam collimators for the scintillation camera. The formulation is based on an effective response function which is determined by the geometric response of a single hole. The technique provides an accurate description of the spatial resolution by characterising the complete geometric response function which includes the effects of the shape and orientation of the collimator holes. The theoretical formulation was used to design a fan beam collimator for SPECT imaging and was shown to agree well with the experimental results.

Acoustic radiation force on a small compressible sphere in a focused beam

Abstract: A general expression for the acoustic radiation force on a small compressible sphere has been derived and expressed in terms of the time‐averaged densities Ti and Vi of kinetic and potential energies, respectively, in the incident sound field. The results have been applied to two focused beams: Gaussian beams and piston beams. For both cases, the analytical expressions of the radiation forces on a small compressible sphere placed on the axis of the beams are calculated. The pertinent applications in acoustic levitation and bubble dynamics are discussed.

Atomic force microscope

Abstract: An atomic force microscope comprises a probe having a sharply-pointed tip end. The probe is supported on the free end portion of a cantilever and is close to the surface of a specimen. When an interatomic force is produced, the cantilever is deformed, and the probe is displaced. The displacement of the probe is detected by an optical system. A light beam emitted from a light source is collimated by a lens, and reflected by a polarized beam-splitter, and also by a half-mirror. Then, the light beam passes through a quarter wavelength plate and an objective lens, such that the light is converged on the cantilever. The reflected light beam from the cantilever returns along the same optical path and passes through the splitter. The light beam is divided into two light beams at the splitter. These two light beams are reflected by respective prisms and are then incident on respective photodetectors. These photodetectors detect the displacement of the probe.

Nonparaxial Gaussian beams

Abstract: When the waist size of a Gaussian beam becomes of the order of the wavelength of light, the beam does not satisfy the paraxial condition in which it is derived. In this paper, we define the lower bound to the waist size by showing that a Gaussian beam whose waist size is larger than this bound safely satisfies the paraxial condition. A beam which is Gaussian in form but violates the paraxial condition is called a nonparaxial Gaussian beam. We clarify the range of the waist size for which the first-order correction to this beam is effective. It is shown that a distinct value of the waist size exists for which the paraxial approximation completely fails and the first-order correction never works.

Wander of an optical beam in the turbulent atmosphere.

Abstract: A simple, analytic, geometrical optics expression for the variance of the beam displacements caused by propagation through weak refractive turbulence described by the Kolmogorov spectrum is presented. The analytical formula includes the effect of the divergence or convergence of the initial beam. The formula is compared with numerical results obtained from a more complicated expression including effects of diffraction and strong path-integrated turbulence. The simple geometrical optics expression holds for apertures larger than the Fresnel zone size and larger than the ratio of the square of the Fresnel zone to the phase coherence length.

Current measurement on MeV energy ion beams

Abstract: It is a crucial problem to obtain the number of incident particles in MeV energy ion beam techniques. To solve this problem a simple but powerful method, the transmission Faraday cup is suggested. A rotating beam chopper periodically detects the beam current. To eliminate the disturbing current of the secondary electrons it is surrounded on both sides by a Faraday cup. Additional mechanical shields as well as electrostatic and magnetic fields keep away the charged particles different from the ions of the incident beam. The (p, γ) reaction and He RBS test measurements show that the particle number reproducibility is better than 1% and 2%, respectively. The reproducibility in the charge measurement was found to be ~ 0.6%.

Daytime running light system

Abstract: A daytime running light system employs level sensing comparators to effect reduced illuminating the high beam filaments of headlamps of a vehicle and short circuit protection to the circuit as well as to a high beam indicator circuit which only operates when the high beam filaments operate at full intensity

Apparatus for measuring the mode quality of a laser beam

Abstract: A method and apparatus for determining the quality of a multimode laser beam (10). In the preferred embodiment, the apparatus includes a lens (32) for creating a transformed or imaged waist from the input beam. The location of the transformed beam waist and its diameter are then determined. These steps can be carried out by chopping the beam using a rotating hub (34) having apertures (36,38) for selectively passing the beam. Preferably, one of the apertures has a pair of 45° knife edges (40,42). The transmission of the beam past the knife edge is monitored by a detector (30). In operation, the lens focal position is varied while the transmission of the beam past the knife edge is monitored in order to locate and measure the diameter of the transformed waist. The diameter of the beam at one other known location is measured. A processor then calculates beam quality by fitting these measurements to a mathematical model. Once the quality of the beam is calculated, the location of the original beam waist and its diameter can be derived. Once all of the beam parameters are derived, the propagation characteristics of the beam can be predicted.