Showing papers on "Beam (structure) published in 2005"

Bessel beams: Diffraction in a new light

Abstract: Diffraction is a cornerstone of optical physics and has implications for the design of all optical systems. The paper discusses the so-called 'non-diffracting' light field, commonly known as the Bessel beam. Approximations to such beams can be experimentally realized using a range of different means. The theoretical foundation of these beams is described and then various experiments that make use of Bessel beams are discussed: these cover a wide range of fields including non-linear optics, where the intense central core of the Bessel beam has attracted interest; short pulse non-diffracting fields; atom optics, where the narrow non-diffracting features of the Bessel beam are able to act as atomic guides and atomic confinement devices and optical manipulation, where the reconstruction properties of the beam enable new effects to be observed that cannot be seen with Gaussian beams. The intensity profile of the Bessel beam may offer routes to investigating statistical physics as well as new techniques for the...

Laser beam combining for high-power, high-radiance sources

Abstract: Beam combining of laser arrays with high efficiency and good beam quality for power and radiance (brightness) scaling is a long-standing problem in laser technology. Recently, significant progress has been made using wavelength (spectral) techniques and coherent (phased array) techniques, which has led to the demonstration of beam combining of a large semiconductor diode laser array (100 array elements) with near-diffraction-limited output (M/sup 2//spl sim/1.3) at significant power (35 W). This paper provides an overview of progress in beam combining and highlights some of the tradeoffs among beam-combining techniques.

Finite element prediction of wave motion in structural waveguides.

Abstract: A method is presented by which the wavenumbers for a one-dimensional waveguide can be predicted from a finite element (FE) model. The method involves postprocessing a conventional, but low order, FE model, the mass and stiffness matrices of which are typically found using a conventional FE package. This is in contrast to the most popular previous waveguide/FE approach, sometimes termed the spectral finite element approach, which requires new spectral element matrices to be developed. In the approach described here, a section of the waveguide is modeled using conventional FE software and the dynamic stiffness matrix formed. A periodicity condition is applied, the wavenumbers following from the eigensolution of the resulting transfer matrix. The method is described, estimation of wavenumbers, energy, and group velocity discussed, and numerical examples presented. These concern wave propagation in a beam and a simply supported plate strip, for which analytical solutions exist, and the more complex case of a viscoelastic laminate, which involves postprocessing an ANSYS FE model. The method is seen to yield accurate results for the wavenumbers and group velocities of both propagating and evanescent waves.

Identification of parameters of concrete damage plasticity constitutive model

Abstract: The paper presents a method and requiremens of the material parameters identification for concrete damage plasticity constitutive model. The laboratory tests, which are necessary to identify constitutive parameters of this model have been presented. Two standard applications have been shown that test the constitutive model of the concrete. The first one is the analysis of the three-point bending single-edge notched conrete beam specimen. The second presents the four-point bending single-edge notched conrete beam specimen under static loadings. In conclusion, the comparison of crack patterns in the numerical and laboratory [2,9] tests has been presented and discussed.

Beam manipulating by metallic nano-slits with variant widths

Abstract: A novel method is proposed to manipulate beam by modulating light phase through a metallic film with arrayed nano-slits, which have constant depth but variant widths. The slits transport electro-magnetic energy in the form of surface plasmon polaritons (SPPs) in nanometric waveguides and provide desired phase retardations of beam manipulating with variant phase propagation constant. Numerical simulation of an illustrative lens design example is performed through finite-difference time-domain (FDTD) method and shows agreement with theory analysis result. In addition, extraordinary optical transmission of SPPs through sub-wavelength metallic slits is observed in the simulation and helps to improve elements' energy using factor.

Experimental characterization and physical modelling of the dose distribution of scanned proton pencil beams

Abstract: In this paper we present the pencil beam dose model used for treatment planning at the PSI proton gantry, the only system presently applying proton therapy with a beam scanning technique. The scope of the paper is to give a general overview on the various components of the dose model, on the related measurements and on the practical parametrization of the results. The physical model estimates from first physical principles absolute dose normalized to the number of incident protons. The proton beam flux is measured in practice by plane-parallel ionization chambers (ICs) normalized to protons via Faraday-cup measurements. It is therefore possible to predict and deliver absolute dose directly from this model without other means. The dose predicted in this way agrees very well with the results obtained with ICs calibrated in a cobalt beam. Emphasis is given in this paper to the characterization of nuclear interaction effects, which play a significant role in the model and are the major source of uncertainty in the direct estimation of the absolute dose. Nuclear interactions attenuate the primary proton flux, they modify the shape of the depth-dose curve and produce a faint beam halo of secondary dose around the primary proton pencil beam in water. A very simple beam halo model has been developed and used at PSI to eliminate the systematic dependences of the dose observed as a function of the size of the target volume. We show typical results for the relative (using a CCD system) and absolute (using calibrated ICs) dosimetry, routinely applied for the verification of patient plans. With the dose model including the nuclear beam halo we can predict quite precisely the dose directly from treatment planning without renormalization measurements, independently of the dose, shape and size of the dose fields. This applies also to the complex non-homogeneous dose distributions required for the delivery of range-intensity-modulated proton therapy, a novel therapy technique developed at PSI.

Flexural strengthening of concrete beams with CFRP laminates bonded into slits

Abstract: Near surface mounted (NSM) strengthening technique using carbon fibre reinforced polymer (CFRP) laminate strips was applied for doubling the load carrying capacity of concrete beams failing in bending. This objective was attained and the deformational capacity of the strengthened beams was similar to the corresponding reference beams. The NSM technique has provided a significant increment of the load at serviceability limit state, as well as, the stiffness after concrete cracking. The maximum strain in the CFRP laminates has attained values between 62% and 91% of its ultimate strain. A numerical strategy was developed to simulate the deformational behaviour of RC beams strengthened by NSM technique. Not only the load carrying capacity of the tested beams was well predicted, but also the corresponding deflection.

Laser Resonators and Beam Propagation 108

Abstract: The first € price and the £ and $ price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for Germany, the €(A) includes 10% for Austria. Prices indicated with ** include VAT for electronic products; 19% for Germany, 20% for Austria. All prices exclusive of carriage charges. Prices and other details are subject to change without notice. All errors and omissions excepted. N. Hodgson, H. Weber Laser Resonators and Beam Propagation

Reevaluation of Deflection Prediction for Concrete Beams Reinforced with Steel and Fiber Reinforced Polymer Bars

Abstract: This paper provides a critical evaluation of equations commonly used to compute short-term deflection for steel and fiber reinforced polymer (FRP) reinforced concrete beams Numerous proposals have been made for FRP in particular, and the different approaches are linked together by comparing the tension-stiffening component of each method Tension stiffening reflects the participation of concrete between cracks in stiffening the member response The Branson equation used in North America and other parts of the world is based on an empirically derived effective moment of inertia to calculate deflection The tension-stiffening component with this method is highly dependent on the applied level of loading relative to the cracking load as well as the ratio of uncracked-to-cracked transformed moment of inertia ( Ig ∕ Icr ) for the beam section Tension stiffening is overestimated for the high Ig ∕ Icr ratios typical with FRP concrete, leading to a much stiffer response and underprediction of member deflection

Approximate Floor Acceleration Demands in Multistory Buildings. I: Formulation

Abstract: An approximate method to estimate floor acceleration demands in multistory buildings responding elastically or practically elastic when subjected to earthquake ground motion is presented. The method can be used to estimate floor acceleration demands at any floor level for a given ground motion record. The dynamic characteristics of the building are approximated by using a simplified model based on equivalent continuum structure that consists of a combination of a flexural beam and a shear beam. Closed-form solutions for mode shapes, period ratios, and modal participation factors are presented. The effect of reduction of lateral stiffness along the height is investigated. It is shown that the effect of reduction in lateral stiffness on the dynamic characteristics of the structure is small in buildings that deflect laterally like flexural beams. For other buildings, approximate correction factors to the closed-form solutions of the uniform case are presented to take into account the effects of reduction of lateral stiffness. Approximate dynamic properties of the building are then used to estimate acceleration demands in the building using modal analysis.

Experimental studies of full-scale posttensioned steel connections

Abstract: Six full-scale interior connection subassemblies of posttensioned wide flange beam-to-column moment connections were subjected to inelastic cyclic loading up to 4% story drift to simulate earthquake loading effects. Bolted top and seat angles are used in the connection, along with posttensioned high strength strands that run parallel to the beam. These strands compress the beam flanges against the column flange to develop the resisting moment to service loading and to provide a restoring force that returns the structure to its initial position following an earthquake. The parameters studied in these experiments were the initial posttensioning force, the number of posttensioning strands, and the length of the reinforcing plates. The experimental results demonstrate that the posttensioned connection possesses good energy dissipation and ductility. Under drift levels of 4%, the beams and columns remain elastic, while only the top and seat angles are damaged and dissipate energy. The lack of damage to the beams, columns, and the posttensioning enable the system to return to its plumb position (i.e., it self-centers). Closed-form expressions are presented to predict the connection response and the results from these expressions compare well with the experimental results.

Seismic Performance of Post-tensioned Steel Moment Resisting Frames With Friction Devices

Abstract: A post-tensioned friction damped connection (PFDC) for earthquake resistant steel moment resisting frames (MRFs) is introduced. The connection includes friction devices on the beam flanges with post-tensioned high strength strands running parallel to the beam. The connection minimizes inelastic deformation to the components of the connection as well as the beams and columns, and requires no field welding. Inelastic analyses were performed on a six-story, four-bay steel MRF with PFDCs to study its response to strong ground motions. The PFDC–MRF was designed using a performance based design approach. Results show the MRF with PFDCs has good energy dissipation, self-centering capability, and strength. Variability in the maximum friction forces that develop in the friction devices was determined not to have a significant effect on the MRF performance. The analyses indicate that the seismic performance of a MRF with PFDCs can exceed that of a MRF with conventional moment resisting connections.

Helmholtz–Gauss waves

Abstract: A detailed study of the propagation of an arbitrary nondiffracting beam whose disturbance in the plane z=0 is modulated by a Gaussian envelope is presented. We call such a field a Helmholtz–Gauss (HzG) beam. A simple closed-form expression for the paraxial propagation of the HzG beams is written as the product of three factors: a complex amplitude depending on the z coordinate only, a Gaussian beam, and a complex scaled version of the transverse shape of the nondiffracting beam. The general expression for the angular spectrum of the HzG beams is also derived. We introduce for the first time closed-form expressions for the Mathieu–Gauss beams in elliptic coordinates and for the parabolic Gauss beams in parabolic coordinates. The properties of the considered beams are studied both analytically and numerically.

Present and future perspectives for high energy density physics with intense heavy ion and laser beams

Abstract: Intense heavy ion beams from the Gesellschaft fur Schwerionenforschung ~GSI, Darmstadt, Germany! accelerator facilities, together with two high energy laser systems: petawatt high energy laser for ion experiments ~PHELIX! and nanosecond high energy laser for ion experiments ~NHELIX! are a unique combination to facilitate pioneering beam-plasma interaction experiments, to generate and probe high-energy-density ~HED! matter and to address basic physics issues associated with heavy ion driven inertial confinement fusion. In one class of experiments, the laser will be used to generate plasma and the ion beam will be used to study the energy loss of energetic ions in ionized matter, and to probe the physical state of the laser-generated plasma. In another class of experiments, the intense heavy ion beam will be employed to create a sample of HED matter and the laser beam, together with other diagnostic tools, will be used to explore the properties of these exotic states of matter. The existing heavy ion synchrotron facility, SIS18, deliver an intense uranium beam that deposit about 1 kJ0g specific energy in solid matter. Using this beam, experiments have recently been performed where solid lead foils had been heated and a brightness temperature on the order of 5000 K was measured, using a fast multi-channel pyrometer that has been developed jointly by GSI and IPCP Chernogolovka. It is expected that the future heavy ion facility, facility for antiprotons and ion research ~FAIR! will provide compressed beam pulses with an intensity that exceeds the current beam intensities by three orders of magnitude. This will open up the possibility to explore the thermophysical and transport properties of HED matter in a regime that is very difficult to access using the traditional methods of shock compression. Beam plasma interaction experiments using dense plasmas with a G-parameter between 0.5 and 1.5 have also been carried out. This dense Ar-plasma was generated by explosively driven shockwaves and showed enhanced energy loss for Xe and Ar ions in the energy range between 5.9 to 11.4 MeV.

A 3D photon superposition/convolution algorithm and its foundation on results of Monte Carlo calculations

Abstract: Based on previous publications on a triple Gaussian analytical pencil beam model and on Monte Carlo calculations using Monte Carlo codes GEANT-Fluka, versions 95, 98, 2002, and BEAMnrc/EGSnrc, a three-dimensional (3D) superposition/convolution algorithm for photon beams (6 MV, 18 MV) is presented. Tissue heterogeneity is taken into account by electron density information of CT images. A clinical beam consists of a superposition of divergent pencil beams. A slab-geometry was used as a phantom model to test computed results by measurements. An essential result is the existence of further dose build-up and build-down effects in the domain of density discontinuities. These effects have increasing magnitude for field sizes < or =5.5 cm(2) and densities < or = 0.25 g cm(-3), in particular with regard to field sizes considered in stereotaxy. They could be confirmed by measurements (mean standard deviation 2%). A practical impact is the dose distribution at transitions from bone to soft tissue, lung or cavities.

Fractional optical vortex beam induced rotation of particles

Abstract: We experimentally demonstrate optical rotation and manipulation of microscopic particles by use of optical vortex beams with fractional topological charges, namely fractional optical vortex beams, which are coupled in an optical tweezers system. Like the vortex beams with integer topological charges, the fractional optical vortex beams are also capable of rotating particles induced by the transfer of orbital angular momentum. However, the unique radial opening (low-intensity gap) in the intensity ring encompassing the dark core, due to the fractional nature of the beam, hinders the rotation significantly. The fractional vortex beam’s orbital angular momentum and radial opening are exploited to guide and transport microscopic particles.

Beam Size, Shape and Efficiencies for the ATNF Mopra Radio Telescope at 86-115 GHz

Abstract: We present data characterising the performance of the Mopra Radio Telescope during the period 2000-2004, including measurements of the beam size and shape, as well as the overall beam efficiency of the telescope. In 2004 the full width half maximum of the beam was measured to be 36 ± 3 �� at 86 GHz, falling to 33 ± 2 �� at 115 GHz. Based on our observations of Jupiter we measured the beam efficiency of the Gaussian main beam to be 0.49 ± 0.03 at 86 GHz and 0.42 ± 0.02 at 115 GHz. Sources with angular sizes of ∼80 �� couple well to the main beam, while sources with angular sizes between ∼80 �� and ∼160 �� couple to the both the main beam and inner error beam. Measurements indicate that the inner error beam contains approximately one-third the power of the main beam. We also compare efficiency corrected spectra to measurements made at similar facilities and present standard spectra taken towards the molecular clouds Orion-KL and M17-SW.

The rosetta experiment: atmospheric soft error rate testing in differing technology FPGAs

Abstract: Results are presented from real-time experiments that evaluated large field programmable gate arrays (FPGAs) fabricated in different CMOS technologies (0.15 /spl mu/m, 0.13 /spl mu/m, and 90 nm) for their sensitivity to radiation-induced single-event upsets (SEUs). These results are compared to circuit simulation (Qcrit) studies as well as to Los Alamos Neutron Science Center (LANSCE) neutron beam results and Crocker Nuclear Laboratory (University of California, Davis) cyclotron proton beam results.

Distribution of steel fibres in rectangular sections

Abstract: In this paper a calculation method is explained to predict the total number of fibres crossing a rectangular section. The largest part of the paper deals with the theoretical calculation of an orientation factor. The orientation factor is defined here as the average length of the projection on the longitudinal axis of all fibres crossing a section, divided by the fibre length. Once the orientation factor is found, a simple calculation gives the number of fibres crossing a crack. Since the proposed approach is to a large extent new, there is a need for verification with test results. For this reason a fibre counting was done on 107 Rilem beam specimens, involving different fibre types. The comparison with the calculated number of fibres shows that the model provides good predictions of the number of fibres crossing a section.

FAME: a new beamline for x-ray absorption investigations of very-diluted systems of environmental, material and biological interests

Abstract: FAME is the French Absorption spectroscopy beamline in Material and Environmental sciences at the ESRF (France), operational since September 2002. Technically speaking, the source is a 0.85 T bending magnet and the main optical element is a two-crystals monochromator using either Si(111) or Si(220) monocrystals so that the available energy ranges from 4 to 40 keV. The first crystal is liquid nitrogen cooled in order to avoid a thermal bump and thus preserve the energy resolution. The second crystal is dynamically bent during the energy scan in order to focus the beam in the horizontal plane. Two bendable mirrors are located before and after the monochromator, for beam-collimation (to optimize the energy resolution) and vertical focalization, respectively. During scans, the beam on the sample is kept constant in position and size (around 150 × 200 μm2, V × H). The high flux on the sample combined with the sensitivity of our 30-elements fluorescence detector allow to decrease the detection limit down to 10 ppm or around less than a monolayer. Moreover, quick-EXAFS acquisition is operational: the acquisition time may be reduced down to 30s.

Long-Term Performance of Corrosion-Damaged Reinforced Concrete Beams

Abstract: Research is needed to clarify the interaction between the degree of corrosion, the corrosion crack width, and the load carrying capacity in the presence of a sustained load in reinforced concrete (RC) beams having well-anchored steel reinforcement. This article reports on a study that investigated the combined effect of corrosion and sustained loads on the structural performance of nine RC beams (each measuring 152 x 254 x 3200 mm). One beam was tested as a virgin while eight beams were exposed to accelerated corrosion for up to 310 days using an impressed current technique. Four beams were corroded under a sustained load that corresponded to approximately 60% of the yield load of the virgin beam. The four remaining beams were kept unloaded during the corrosion exposure. Test results showed that the presence of a sustained load and associated flexural cracks during corrosion exposure significantly reduced the time to corrosion cracking and slightly increased the corrosion crack width. The presence of flexural cracks during corrosion exposure initially increased the steel mass loss rate and, consequently, the reduction in the beam strength. As time progressed, no correlation between the reduction in the beam strength and the presence of flexural cracks was observed.

Design, Modeling, Optimization, and Experimental Tests of a Particle Beam Width Probe for the Aerodyne Aerosol Mass Spectrometer

Abstract: Aerodynamic lens inlets have revolutionized aerosol mass spectrometry by allowing the introduction of a very narrow particle beam into a vacuum chamber for subsequent analysis. The real-time measurement of particle beam width after an aerodynamic lens is of interest for two reasons: (1) it allows a correction to be made to the measured particle concentration if the beam is so broad, due to poor focusing by non-spherical particles, that some particles miss the detection system; and (2) under constant lens pressure it can provide a surrogate particle non-sphericity measurement. For these reasons, a beam width probe (BWP) has been designed and implemented for the Aerodyne Aerosol Mass Spectrometer (AMS), although this approach is also applicable to other instruments that use aerodynamic lens inlets. The probe implemented here consists of a thin vertical wire that can be precisely positioned to partially block the particle beam at fixed horizontal locations in order to map out the width of the particle beam. ...

High-flux beam source for cold, slow atoms or molecules.

Abstract: We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applications.

Development of a Single-Edge Notched Beam Test for Asphalt Concrete Mixtures

Abstract: This paper describes the development of a fracture test for determining the fracture energy of asphalt concrete. The test will be used in combination with numerical analysis and field studies to obtain a better understanding of the mechanisms of reflective cracking in asphalt concrete overlays. A review of the literature revealed that a single-edge notched beam (SE(B)) test specimen was the most promising fracture test for the objectives of the reflective cracking study. Existing servohydraulic testing equipment was modified to perform the SE(B) test along with new loading fixtures, sensors, data collection, and analysis procedures. Preliminary tests were conducted to develop test procedures, to obtain a better understanding of crack-front characteristics, to investigate test repeatability, to examine variations of fracture energy with temperature, and to investigate mixed-mode fracture. The results from the tests follow expected trends and test variability appears to be within a range typical for asphalt concrete fracture testing.

Laser irradiation apparatus and laser irradiation method

Abstract: It is an object of the present invention to provide a laser irradiation apparatus which can manufacture a homogenously crystallized film by varying the energy intensity of an irradiation beam in forward and backward directions of the irradiation. A laser irradiation apparatus of the present invention comprises a laser oscillator and means for varying beam intensity wherein a laser beam is obliquely incident into the irradiation surface, the laser beam is scanned relative to the irradiation surface, and the beam intensity is varied in accordance with the scanning direction. Further, the laser oscillator is a continuous wave solid-state laser, gas laser, or metal laser. A pulsed laser having a repetition frequency of 10 MHz or more can also be used.

Shear Strengthening of Reinforced Concrete Beams Using Carbon-Fiber-Reinforced Polymer Laminates

Abstract: Shear failure is catastrophic and occurs usually without advance warning; thus it is desirable that the beam fails in flexure rather than in shear. Many existing reinforced concrete (RC) members are found to be deficient in shear strength and need to be repaired. Externally bonded reinforcement such as carbon-fiber-reinforced polymer (CFRP) provides an excellent solution in these situations. To investigate the shear behavior of RC beams with externally bonded CFRP shear reinforcement, 11 RC beams without steel shear reinforcement were cast at the concrete laboratory of the New Jersey Institute of Technology. After the beams were kept in the curing room for 28 days , carbon-fiber strips and fabrics made by Sika Corp. were applied on both sides of the beams at various orientations with respect to the axis of the beam. All beams were tested on a 979 kN (220 kips) MTS testing machine. Results of the test demonstrate the feasibility of using an externally applied, epoxy-bonded CFRP system to restore or increas...

Fast microtomography using high energy synchrotron radiation

Abstract: At the High Energy Beamline ID15A at the European Synchrotron Radiation Facility we have developed a fast three-dimensional x-ray microtomography system, which acquires a complete dataset in typically less than 10s. This unprecedented speed is achieved by combining a high efficiency phosphor screen, a reflecting microscope objective and a fast charge coupled device detector with the very intense high-energy white beam radiation provided by a wiggler source. The achieved spatial resolution is 2μm. The available x-ray energy spectrum spans from 20to250keV and can therefore be used for low and high Z materials. The spectrum can be modified by inserting different filters into the x-ray beam in order to optimize the signal-to-noise ratio and to avoid beam-hardening artifacts. Different phosphors with different energy sensitivity can be used. The very high speed allows in situ studies of systems evolving on the time scale of a few seconds or minutes. Three examples are given on sintering of metallic powders, so...