Showing papers on "Beam (structure) published in 1995"

The 200-MeV proton therapy project at the Paul Scherrer Institute: conceptual design and practical realization.

Abstract: The new proton therapy facility is being assembled at the Paul Scherrer Institute (PSI). The beam delivered by the PSI sector cyclotron can be split and brought into a new hall where it is degraded from 590 MeV down to an energy in the range of 85-270 MeV. A new beam line following the degrader is used to clean the low-energetic beam in phase space and momentum band. The analyzed beam is then injected into a compact isocentric gantry, where it is applied to the patient using a new dynamic treatment modality, the so-called spot-scanning technique. This technique will permit full three-dimensional conformation of the dose to the target volume to be realized in a routine way without the need for individualized patient hardware like collimators and compensators. By combining the scanning of the focused pencil beam within the beam optics of the gantry and by mounting the patient table eccentrically on the gantry, the diameter of the rotating structure has been reduced to only 4 m. In the article the degrees of freedom available on the gantry to apply the beam to the patient (with two rotations for head treatments) are also discussed. The devices for the positioning of the patient on the gantry (x rays and proton radiography) and outside the treatment room (the patient transporter system and the modified mechanics of the computer tomograph unit) are briefly presented. The status of the facility and first experimental results are introduced for later reference.

Method for controlling configuration of laser induced breakdown and ablation

Abstract: In one aspect the invention provides a method for laser induced breakdown of a material with a pulsed laser beam where the material is characterized by a relationship of fluence breakdown threshold (Fth) versus laser beam pulse width (T) that exhibits an abrupt, rapid, and distinct change or at least a clearly detectable and distinct change in slope at a predetermined laser pulse width value. The method comprises generating a beam of laser pulses in which each pulse has a pulse width equal to or less than the predetermined laser pulse width value. The beam is focused to a point at or beneath the surface of a material where laser induced breakdown is desired. The beam may be used in combination with a mask in the beam path. The beam or mask may be moved in the X, Y and Z directions to produce desired features. The technique can produce features smaller than the spot size and Rayleigh range due to enhanced damage threshold accuracy in the short pulse regime.

Observation of two-dimensional spatial solitary waves in a quadratic medium.

Abstract: We report the first experimental demonstration of two-dimensional spatial solitary waves in second-order nonlinear optical material When an intense optical beam is focused into a phase-matchable second-order nonlinear material, the fundamental and generated second-harmonic fields are mutually trapped as a result of the strong nonlinear coupling which counteracts both diffraction and beam walkoff

Optical Particle Trapping with Higher-order Doughnut Beams Produced Using High Efficiency Computer Generated Holograms

Abstract: Laser beams containing higher-order phase singularities can be produced with high efficiency computer generated holograms made with very simple equipment. Using such holograms in an optical tweezers experiment we have successfully trapped reflective and absorptive particles in the dark central spot of a focused charge 3 singularity beam. Angular momentum absorbed from the beam can set particles into rotation.

Holographic storage using shift multiplexing

Abstract: The invention is embodied in a method of recording successive holograms in a recording medium, using at least a fan of M waves along at least a first axis with a separation angle between adjacent waves and directing the fan of M waves as a reference beam along a reference beam path onto the recording medium, successively modulating a wave with a succession of images to produce a succession of signal beams along a signal beam path lying at a propagation angle relative to the reference beam path so that the signal and reference beams intersect at a beam intersection lying within the medium, the beam intersection having a size corresponding to beam areas of the reference and signal beams, producing a succession of relative displacements in a direction parallel to the first axis between the recording medium and the beam intersection of the signal and reference beam paths in synchronism with the succession of signal beams, each of the displacements being less than the size of the intersection whereby to record successive holograms partially overlapped along a direction of the displacements.

Moving fibre/phase mask-scanning beam technique for enhanced flexibility in producing fibre gratings with uniform phase mask

Abstract: A new and flexible technique for producing photorefractive fibre gratings with a uniform phase mask is demonstrated. By slowly moving the fibre relative to the mask as the writing beam is scanned, wavelength shifts, pure apodisation and phase-shifted gratings can be achieved.

Survival of by-catch from a beam trawl

Abstract: The passage of a beam trawl across the seabed leads to the direct mortality, or indirect mortality through subsequent predation, of some benthic species. In addition, animals retained in, or those that pass through, the cod end may also die as a result of the fishing process. The extent of this additional mortality needs to be quantified to calculate total mortality of non-target species associated with this type of fishery. Hence, we investigated the survival of animals caught by a 4 m beam trawl, in order to identify those species most sensitive to capture. Starfishes, hermit crabs and molluscs were highly resistent to the effects of capture (>60% survived in all cases). Fishes (except dogfish), sea urchins and swimming crabs suffered higher mortality after capture. Generally, the majority of the animals that passed through the meshes of the cod end survived. Experimental investigation of the cause of damage to certain species concluded that the chaln matrix fitted to the gear was largely responsible for the injuries sustained. The types of injuries and then extent were species-specific, and were related to the fragility and physical characteristics of each species. Our experiments revealed that whlle some species are highly sensitive to capture, others are capable of surviving the effects of capture

EMAT probe and technique for weld inspection

Abstract: A method and apparatus of inspecting for flaws in a specular reflector, where the flaws having an expected length and the reflector is electrically conductive. The method includes directing a beam of an electromagnetic acoustic transmitting transducer along a beam axis toward the specular reflector for producing a reflected electromagnetic acoustic beam. The transmitted beam has side lobes with zero points therebetween, at least some of the side lobes being major side lobes. The reflected beam is received using an electromagnetic acoustic receiving transmitter set at an angle to the beam axis, the angle being selected to be at one of the zero points and past all of the major lobes of the transmitted beam to eliminate root and crown signals of the weld, in the reflected signal.

Ultimate load behaviour of bamboo-reinforced lightweight concrete beams

Abstract: The classification of seven bamboos studied in accordance to their physical and mechanical properties, the type and method of application of water repellent treatment of bamboo splints and the bond strength between bamboo and lightweight concrete are described in this paper. The results of the experimental analysis of two simplysupported bamboo-reinforced lightweight concrete beams with an overall length of 340 cm and a cross-section of 12 cm by 30 cm width and height, respectively, subjected to two point loads up to collapse are presented. One beam of the same dimensions and concrete mix reinforced with steel was also tested for comparison of the results. Finally a recommendation based on the analysis of the results for the design of such beams is proposed.

Preisach modeling of piezoceramic and shape memory alloy hysteresis

Abstract: Smart materials such as piezoceramics and shape memory alloys (SMAs) exhibit significant hysteresis and in order to estimate the effect on open and closed loop control a suitable model is needed. One promising candidate is the Preisach independent domain hysteresis model that is characterized by the congruent minor loop and wiping out properties. Comparable minor loop and decaying oscillation test data for a multi-sheet piezoceramic actuator (made of lead zirconate titanate) attached to a flexible beam are presented and are seen to be very consistent with the two Preisach model properties. The commanded parameter is the sheet transverse electric field while the measured parameter is an approximately colocated strain induced in the beam. Equivalent data for a Nitinol SMA wire muscle, attached to the same beam, are also presented. The input and output parameters are the SMA current and a beam strain respectfully. The minor loop and wiping out evidence is less strong than that of the piezoceramic case, but encouraging. In all experiments the quasi-steady state responses were generated in order to avoid exciting beam flexible modes which would complicate the analysis.

Electromagnetic scattering from a multilayered sphere located in an arbitrary beam

Abstract: A solution is given for the problem of scattering of an arbitrary shaped beam by a multilayered sphere. Starting from Bromwich potentials and using the appropriate boundary conditions, we give expressions for the external and the internal fields. It is shown that the scattering coefficients can be generated from those established for a plane-wave illumination. Some numerical results that describe the scattering patterns and the radiation-pressure behavior when an incident Gaussian beam or a plane wave impinges on a multilayered sphere are presented.

Waveguides formed by quasi-steady-state photorefractive spatial solitons

Abstract: We show that a quasi-steady-state photorefractive spatial soliton forms a waveguide structure in the bulk of a photorefractive material. Although the optically induced waveguide is formed by a very low-power (microwatts) soliton beam, it can guide a powerful (watt) beam of a longer wavelength at which the medium is nonphotosensitive. Furthermore, the waveguide survives, either in the dark or when guiding the longer-wavelength beam, for a long time after the soliton beam is turned off. We take advantage of the solitons’ property of evolution from a relatively broad input beam into a narrow channel and show that the soliton induces a tapered waveguide (an optical funnel) that improves the coupling efficiency of light into the waveguiding structure.

Limitations of a pencil beam approach to photon dose calculations in lung tissue

Abstract: A common limitation in treatment planning systems for photon dose calculation is to ignore the impact on electron transport and photon scatter from patient heterogeneities. The heterogeneity correlation is often based on scaling operations along beam rays as for the method according to Batho or the more novel approach of 1D convolutions along beam paths applied in pencil-beam-based systems. The effects of the limitation have been studied in a mediastinum geometry for a wide range of beam qualities by comparing the results from a pencil-beam-based treatment planning system with the results from Monte Carlo calculations. As expected, the deviations within unit-density volumes are small while deviations in low-density volumes increase with increasing beam energy from approximately 3% for 4 MV to 14% for 18 MV x-rays as a result of increased electron disequilibrium.

A Triple Gaussian Pencil beam Model for Photon beam Treatment Planning

Abstract: The transverse profiles of pencil beams are often represented by Gaussian functions in order to speed up electron beam treatment planning algorithms, because convolutions of Gaussions with most beam fluence profiles can be performed analytically. We extend this approach to high-energy photon radiations. Monte-Carlo generated transverse profiles of photon pencil beams are adequately represented by a sum of three Gaussian functions, whose coefficients and parameters have been optimized using Fourier transform methods. The axial profile of the pencil beam is determined by the depth-dependent surface integral of the dose in the transverse plane. As a first application, the triple Gaussian pencil beam algorithm is used to demonstrate the field size dependence of the photon beam depth dose curve. Photon beams modified by wege filters or shielding blocks will be treated in a second communication.

Identifying Delamination in Composite Beams Using Built-In Piezoelectrics: Part I—Experiments and Analysis

Abstract: An investigation was performed on using piezoelectrics built into laminated composite structures to detect a delamination and estimate its size and location. Both experiments and analysis were conducted. In experiments, piezoceramics were attached to composite beams with and without an artificial delamination. Some of the piezoceramics were used as actuators to dynamically excite specimens while others were used as sensors to measure the beam responses. Tests showed that a delamination changed the measured piezo-induced dynamic forced response of beams. A delamination identification method is proposed which consists of a structural analysis, a response comparator, and a damage selector. The structural analysis was developed for predicting the output voltages of the sensors when a delaminated beam was excited by the actuators. The experimental results as well as the structural analysis are described in Part I of the study. In Part II, a response comparator and damage selector will be presented and will be ...

Laser beam delivery and eye tracking system

Abstract: A surface treatment laser beam delivery and tracking system. The laser (500) generates laser light (502) along a path at an energy level suitable for treating a surface. An optical translator (520) shifts the path onto a resulting beam path. An optical angle adjuster (310, 316, 320, 326) changes the angle of the resulting beam path relative to the original path such that the laser light is incident on the surface to be treated. A motion sensor (100) transmits light energy (101-T) to the surface and receives reflected light energy (101-R) from the surface via the optical angle adjuster. The light energy travels on a parallel path to the shifted beam through the optical angle adjuster. The motion sensor detects movement of the surface relative to the original path and generates error control signals indicative of the movement. The optical angle adjuster responds to the error control signals to change the angle of the resulting beam path.

Timoshenko Beam-Bending Solutions in Terms of Euler-Bernoulli Solutions

Abstract: The Timoshenko beam theory is an extension of the Euler-Bernoulli beam theory to allow for the effect of transverse shear deformation. This more refined beam theory relaxes the normality assumption of plane sections that remain plane and normal to the deformed centerline. The relaxation takes the form of allowing an additional rotation to the bending slope, and thus admits a nonzero shear strain. This paper pre-sents the deflection and stress resultants of single-span Timoshenko beams, with general loading and boundary conditions, in terms of the corresponding Euler-Bernoulli beam solutions. These exact relationships allow engineering designers to readily obtain the bending solutions of Timoshenko beams from the familiar Euler-Bernoulli solutions without having to perform the more complicated flexural–shear-deformation analysis.

Use of thickness-shear mode in adaptive sandwich structures

Abstract: A new adaptive sandwich structure is constructed using the shear mode of piezoelectric materials. A comparative study of the sandwich structure and the corresponding surface-mounted actuation structure is performed using finite-element analysis. The effects of actuator length and location on actuation performance of the structures are studied. The stress distributions under mechanical and electrical loads are investigated for both the sandwich beam and the surface-mounted actuation beam. It is shown that the stress level within the actuators is more severe for the surface-mounted actuation beam than for the sandwich. Also, the interface-stress distribution between actuator and host structure is analysed. It is shown that sandwich construction offers many advantages over conventional surface-mounted actuation constructions.

Beam-Photoelectron Interactions in Positron Storage Rings.

Abstract: The possibility of a coupled-bunch instability caused by beam-photoelectron interactions is discussed. Very many photoelectrons are produced in a storage ring when photons emitted by synchrotron radiation hit the beam chamber. Since electrons are not trapped by a positron beam in ion-trapping theory, they are not considered to affect the beam. However, it is possible that an enormous number of photoelectrons would have sufficient density to cause a coupled-bunch instability. A simulation has shown that such an instability may be serious for positron storage rings with high current and multibunches.

Impact Formulas for Vehicles Moving over Simple and Continuous Beams

Abstract: In this paper, a new set of impact formulas are developed for simple and continuous beams subjected to moving vehicle loads. By modeling a vehicle as sprung masses and a bridge structure by beam elements, a parametric study is performed for various simple and continuous beams traversed by five-axle trucks. Central to this study is the adoption of a nondimensional speed parameter s , which is defined as the ratio of the driving frequency of the vehicle, as represented by πv/L, with v denoting the velocity of the vehicle and L the characteristic length of the beam, to the fundamental frequency ω of the beam. From the numerical study, it is concluded that the impact factors for the deflections, bending moments, and shear forces at the midpoints of simple beams are linearly proportional to the speed parameter, and that these formulas can be multiplied by certain modification factors to yield results for continuous beams and support shears. Other parameters studied herein include the vehicle/bridge frequency r...

Method and apparatus for temporal and spatial beam integration

Abstract: A method and apparatus for providing sequential temporal and spatial integration of a collimated non-symmetrical excimer laser beam to optimize the temporal and spatial characteristics of the beam. The temporal integrator comprises a pair of cylindrical lenses spaced along the beam axis by a distance substantially equal to the sum of the focal length of both lenses, and a motor mechanism for rotating the two spaced cylindrical lenses about the beam axis. The spatial beam integrator includes a plurality of prisms distributed about a hollow center, the outlet face of each prism being angled with respect to the body axis of the spatial beam integrator so that portions of the laser beam passing through a given prism are refracted towards the center upon emergence from the outlet face. The spatial beam integrator is preferably rotated about the beam axis at twice the rotation rate of the cylindrical lenses so that the rotated beam emerging from the temporal beam integrator is stationary with respect to the spatial beam integrator. Alternatively, the spatial beam integrator may be rotated at the same rate as the cylindrical lenses, or may be maintained stationary, i.e., not rotated at all.

Parallel-beam coupling into channel-cut monochromators using curved graded multilayers

Abstract: Parabolically bent multilayers with laterally graded period were applied as condensing reflectors to convert divergent X-rays from laboratory X-ray sources into a parallel beam. Two different modes of coupling such a collimated beam into multi-reflection channel-cut monochromators for high-resolution X-ray diffractometry were tested. (i) Parallel coupling (the scattering vector of the mirror reflection is in the plane of the scattering vectors of the monochromator and the sample) enables one to exploit a wider solid angle range of the X-ray source and to gain nearly two orders of magnitude in intensity. (ii) Crossed coupling (the scattering vector of the mirror reflection is perpendicular to the scattering vectors of the monochromator and the sample) delivers a beam with much reduced vertical divergence. This eliminates the line broadening in rocking curve measurements even for strongly tilted samples.

A Monte Carlo model of photon beams used in radiation therapy.

Abstract: A generic Monte Carlo model of a photon therapy machine is described. The model, known as McRad, is based on EGS4 and has been in use since 1991. Its primary function has been the characterization of the incident photon fluence for use by dose calculation algorithms. The accuracy of McRad is examined by comparing the dose distributions in a water phantom generated using only the Monte Carlo data with measured dose distributions for two machines in our clinic; a 6 MV Varian Clinac 600C and the 15 MV beam from a Clinac 2100C. The Monte Carlo generated dose distributions are computed using a dose calculation algorithm based on the use of differential pencil beam kernels. It was found that the match to measured data could be improved if the model is tuned by adjusting the energy of the electron beam incident on the target. The beam profiles were found to be more sensitive indicators of the electron beam energy than the depth dose curves. Beyond the depths reached by contaminant electrons, the computed and measured depth dose curves agree to better than 1%. The comparison of beam profiles indicate that in regions up to within 1 cm of the field edge, the measured and computed doses generally agree to within 2%–3%.

Optics and interferometry with Na2 molecules.

Abstract: We have produced an intense, pure beam of sodium molecules (Na2) by using light forces to separate the atomic and molecular species in a seeded supersonic beam. We used diffraction from a microfabricated grating to study the atomic and molecular sodium in the beam. Using three of these gratings, we constructed a molecule interferometer with fully separated beams and high contrast fringes. We measured both the real and imaginary parts of the index of refraction of neon gas for Na2 molecule de Broglie waves by inserting a gas cell in one arm of the interferometer. PACS numbers: 03.75.‐b, 07.77.Gx, 34.20.Gj Quantum mechanical treatment of the center-of-mass motion of increasingly complex systems is an important theme in modern physics. This issue is manifest theoretically in studies of the transition from quantum through mesoscopic to classical regimes and experimentally in efforts to coherently control and manipulate the external spatial coordinates of complex systems (e.g., matter wave optics and interferometry). Recently, matter wave optics and interferometry have been extended to atoms with the many techniques for the coherent manipulation of the external degrees of freedom of atoms constituting a new

The modeling of piezoceramic patch interactions with shells, plates, and beams

Abstract: General models describing the interactions between a pair of piezoceramic patches and elastic substructures consisting of a cylindrical shell, plate and beam are presented. In each case, the manner in which the patch loads enter both the strong and weak forms of the time-dependent structural equations of motion is described. Through force and moment balancing, these loads are then determined in terms of material properties of the patch and substructure (thickness, elastic properties, Poisson ratios), the geometry of the patch placement, and the voltages into the patches. In the case of the shell, the coupling between banding and inplane deformations, which is due to the curvature, is retained. These models are sufficiently general to allow for potentially different patch voltages which implies that they can be suitably employed when using piezoceramic patches for controlling system dynamics when both extensional and bending vibrations are present.

Method and apparatus for conformal radiation therapy

Abstract: A method and apparatus for conformal radiation therapy, with a radiation beam having a pre-determined, constant beam intensity, treats the entire tumor volume of a patient's tumor, and the beam intensity of the radiation beam is spatially modulated across the tumor, by separating the radiation into a plurality of treatment beam segments and independently modulating the beam intensity of the plurality of radiation beam segments. The independent modulation of the beam intensities may be accomplished by selectively and independently filling, or removing, a flowable, radiation blocking material from a compartment associated with each radiation beam segment.