Effect Of Beam Size Research Articles

Beam-size effect and particle losses at SuperB factory developed in Italy

In the colliders, the macroscopically large impactparameters give a substantial contribution to the standard crosssection of the e+e−→ e+e−γ process. Theseimpact parameters may be much larger than the transverse sizes ofthe colliding bunches. It means that the standard cross section ofthis process has to be substantially modified. In the presentpaper such a beam-size effect is calculated for bremsstrahlung atSuperB factory developed in Italy. We find out that this effectreduces beam losses due to bremsstrahlung by about 40%. Weperform a critical comparison of our result with that presented inthe Conceptual Design Report of the Italian SuperBfactory [3].

Beam-size effects in electro-optic sampling of terahertz pulses

In electro-optic sampling of terahertz pulses with a finite diameter, the probe pulse is subject to a lensing effect. The altered diffraction leads to an additional phase shift Deltaeta in the far field compared to the case of a plane wave. It is demonstrated that Deltaeta is in the same order of magnitude as the direct electro-optic phase shift at the exit of the detection crystal and thus also gives a significant contribution to the measured amplitude.

Effective couple-stress continuum model of cellular solids and size effects analysis

The purpose of this paper is to develop a homogeneous, orthotropic couple-stress continuum model to take the place of the periodic heterogeneous cellular solids. Through generalizing the definition of the characteristic length for isotropic couple-stress continuum, four characteristic lengths are introduced as material engineering constants for such kind of continuum. In order to determine the effective moduli and the characteristic lengths of the effective couple-stress continuum, a Representative Volume Element (RVE) method is constructed. The effective properties are obtained based on the response of the RVE under prescribed boundary conditions, and our results agree with the analytical solutions in literature. In addition, the influences of the relative density, the topology, the size, and the properties of the solid material of cellular materials on the effective moduli as well as the characteristic lengths are discussed, respectively. Furthermore, the size effects in cellular solid beams are investigated using our effective couple-stress continuum model. The results show that the developed continuum model in this paper can precisely capture the size effects in cellular solids.

Influences of writing-beam size on the performances of dispersion-free multi-channel fiber Bragg grating

Analysis for the influences of writing-beam size on the performances of a dispersion-free multi-channel fiber Bragg grating (FBG) is presented. It is found that the writing-beam size strongly affects the response of this kind of grating and would make the grating spectrum considerably distorted once the beam size of the UV light is too large to form the complex index-modulation pattern within the fiber core. A novel design method has been proposed to compensate this beam-size effect and a nine-channel dispersion-free FBG with identical spectrum response has been obtained. This compensation method could decrease the tolerance for the demand of small writing-beam size and can be easily extended to the design and fabrication for most of the other complex FBGs.

Development of an LEFM dynamic crack criterion for correlated size and rate effects in concrete beams

The strength of concrete under severe dynamic loading depends on the specimen size and the loading rate. Although the size effect, under quasi-static loading, has been explained by the size-dependent strain energy rate, the main causes of the size and rate effects for dynamic loading cases have not been clarified. In this study, a linear elastic fracture mechanics (LEFM) dynamic crack criterion for a notched three-point bend specimen is developed to explain the size and rate effects, and the possible correlation of these effects. This was achieved by using energy balance, force equilibrium, and Griffith's crack model. From the proposed LEFM dynamic crack criterion, it was shown that (1) the kinetic energy rate seems to be the main cause of the rate effect, (2) the size and rate effects are not independent phenomena.

Effect of beam sizes on the amplitude and phase of photothermal deflection signals for both uniform and nonuniform heating

A detailed theoretical treatment of a one- (1D) and three-dimensional (3D) photothermal deflection (PTD) technique is presented. Important effects of the probe beam size occur in PTD experiments when the radius of this beam is of the order of magnitude of the thermal diffusion length. The calculation of this effect is checked by experiments in paraffin oil at low modulation frequency as well as for 1D and for 3D. In this last case, we have considered two kinds of deflection: normal and transverse, and we have studied their variation for different values of the pump beam radius. The coincidence between theoretical and experimental curves confirms the validity of our theoretical model.

Influence of laser beam size on measurement sensitivity of thermophysical property gradients in layered structures using thermal-wave techniques

The influence of the photothermal laser source beam size on the measurement sensitivity of layered systems using photothermal radiometry (PTR) is presented. Based on an appropriate theoretical model, widely different behaviors of the photothermal amplitude and phase in terms of combinations of thermophysical properties (i.e., thermal conductivity and thermal diffusivity) between a thin coating and the substrate are observed. The beam size effect on PTR measurement sensitivity is theoretically examined and experimentally demonstrated using a carbonitrided C1018 steel sample. The experimental results of using a variable size laser beam for the carbonitrided C1018 sample validate the theoretical prediction, in which an expanded beam exhibits a much larger magnitude change in both amplitude and phase as a function of frequency than measurements with a focused beam. The fitted thermal conductivity and thermal diffusivity based on the assumed industrially relevant range of effective hardness case depth gives the approximate range of the change in thermal conductivity and thermal diffusivity of C1018 steels after the carbonitriding process.

Principles of free-space optical microelectromechanical systems

Optical microelectromechanical systems (MEMS) combine miniature optical components with precision fixtures, elastic suspensions, and microactuators, and allow complex functionality at low cost. However, the effect of the bounded nature of the beams propagating through the system on design is profound. The current paper reviews the fundamental consequences. Using a Gaussian beam formulation, models of guided modes in gradient index media, bounded beams and imaging components are constructed. Propagation algorithms are described. The alignment tolerances for common component trains such as fibre-to-fibre and beam-to-fibre connections are derived, limits on the curvature of reflecting surfaces are established, the scaling laws of free-space optical MEMS are presented and the effect of beam size on filter performance is clarified. Examples such as variable optical attenuators, optical cross-connect switches, filters and tunable lasers are discussed.

Effect of laser beam size on measurement contrast of thermophysical gradients in layered structures using thermal-wave techniques

The effect of the laser source spotsize on the measurement sensitivity of layered system using photothermal radiometry (PTR) technique is presented. The beam size effect on the PTR measurement sensitivity is theoretically examined and experimentally demonstrated using a carbo-nitrided C1018 steel sample. The experimental results using a focused beam and an expanded beam for a carbo-nitrided C1018 sample validated the theoretical prediction, according to which the expanded beam showed a much larger magnitude change (contrast) in both amplitude and phase than results with a focused beam.

Effect of Pulse Duration on Size and Character of the Lesion in Retinal Photocoagulation

To systematically evaluate the effects of laser beam size, power, and pulse duration of 1 to 100 milliseconds on the characteristics of ophthalmoscopically visible retinal coagulation lesions. A 532-nm Nd:YAG laser was used to irradiate 36 retinas in Dutch Belt rabbits with retinal beam sizes of 66, 132, and 330 mum. Lesions were clinically graded 1 minute after placement, their size measured by digital imaging, and their depth assessed histologically at different time points. Retinal lesion size increased linearly with laser power and logarithmically with pulse duration. The width of the therapeutic window, defined by the ratio of the threshold power for producing a rupture to that of a mild coagulation, decreased with decreasing pulse durations. For 132- and 330-mum retinal beam sizes, the therapeutic window declined from 3.9 to 3.0 and 5.4 to 3.7, respectively, as pulse duration decreased from 100 to 20 ms. At pulse durations of 1 millisecond, the therapeutic window decreased to unity, at which point rupture and a mild lesion were equally likely to occur. At shorter pulse durations, the width and axial extent of the retinal lesions are smaller and less dependent on variations in laser power than at longer durations. The width of the therapeutic window, a measure of relative safety, increases with the beam size. Pulse durations of approximately 20 milliseconds represent an optimal compromise between the favorable impact of speed, higher spatial localization, and reduced collateral damage on one hand, and sufficient width of the therapeutic window (> 3) on the other.

Implementation of M-PFI method in design of steel plate walls

To demonstrate implementation of the modified-plate frame interaction (M-PFI) method in the design of a steel plate wall (SPW) system, three SPWs of different heights were designed for this paper using the M-PFI method. Evaluation of the M-PFI design methodology was performed using the finite element (FE) method to analyze each of the three SPWs under a pushover load to determine its load displacement diagram. FE results were then compared with M-PFI model results. Good agreement was observed for stiffness and strength of the SPW models obtained from both the M-PFI and FE methods. The FE method was used not only to evaluate the three SPW designs, but also to investigate the effects of beam size and material hardening on SPW design. This paper also presents a step-by-step M-PFI design procedure and a simplified flow chart to better illustrate the design process.

Size effect in RC deep beams: Experimental investigation and STM verification

An experimental program consisting of three groups of 11 specimens is carried out to investigate the possible causes of size effect, typically represented by a reduction in shear strength with an increase in the height of deep beams. It is well-known that deep beams behave very differently from shallow beams as arch action rather than flexure dominates the behaviour, after diagonal cracking has occurred. However, causes of size effect in deep beams remain unresolved. It is postulated that the factors influencing the strength of a compression member, i.e. the strut geometry and boundary conditions, govern the size effect. The experimental program provides experimental evidence for the hypotheses from strut-and-tie models. By properly configuring the loading and support plate dimensions, size effect in ultimate shear strength is significantly mitigated, even for beams with high h / b ratios and plain concrete web. Evenly-distributed web reinforcement is found to mitigate the size effect to some extent. Effects of out-of-plane actions on beam strength are also investigated and discussed. The modified STM incorporating the causes of size effect outperforms several other methods in accurately and consistently predicting the ultimate shear strengths.

Initial beam size study for passive scatter proton therapy. I. Monte Carlo verification

The purpose of this work was to provide an initial validation of a Monte Carlo (MC) model of the passive scattering treatment nozzle at the University of Texas M. D. Anderson Cancer Center Proton Therapy Center. The MC model included a detailed definition of each beam-modifying element in the nozzle, and calculations accounted for interactions of the beam with the rotating modulator wheel used to create the spread out Bragg peak. In this work we show comparisons of calculated dose and fluence profiles with measured data from the nozzle for the 250 and 180 MeV beam energies used for patient treatments. Agreement to within 1.5 mm of measured data was observed for all MC calculations. The high level of agreement between the measurements and the MC model for the two beam energies studied provides validation for use of the model in a study of the dosimetric effects of the proton beam size and shape at the nozzle entrance.

Monte Carlo analysis of tagged neutron beams for cargo container inspection

Fast neutrons produced via D+T reactions and tagged by the associated particle technique have been recently proposed to inspect cargo containers. The general characteristics of this technique are studied with Monte Carlo simulations by determining the properties of the tagged neutron beams as a function of the relevant design parameters (energy and size of the deuteron beam, geometry of the charged particle detector). Results from simulations, validated by experiments, show that the broadening of the correlation between the α-particle and the neutron, induced by kinematical as well as geometrical (beam and detector size) effects, is important and limits the dimension of the minimum voxel to be inspected. Moreover, the effect of the container filling is explored. The material filling produces a sizeable loss of correlation between α-particles and neutrons due to scattering and absorption. Conditions in inspecting cargo containers are discussed.

Mach–Zehnder Interferometric Switch Utilizing Faraday Rotation

An all-fiber interferometric switch based on Faraday rotation exhibited by magneto-optic materials in the presence of an external magnetic field is reported. The interferometer is Mach-Zehnder type and the related phase shift was obtained by the rotation of the state of polarization of a linearly polarized optical signal. The operation of the switch is demonstrated experimentally. The effect of the optical beam size on the achievable Faraday rotation is also investigated. Hysteresis is avoided as the magnetic field required for switching is much lower than the saturation field

Theoretical analysis of thermal damage in biological tissues caused by laser irradiation.

A bioheat transfer approach is proposed to study thermal damage in biological tissues caused by laser radiation. The laser light propagation in the tissue is first solved by using a robust seven-flux model in cylindrical coordinate system. The resulting spatial distribution of the absorbed laser energy is incorporated into the bioheat transfer equation for solving temperature response. Thermal damage to the tissue is assessed by the extent of denatured protein using a rate process equation. It is found that for the tissue studied, a significant protein denaturation process would take place when temperature exceeds about 53 degrees C. The effects of laser power, exposure time and beam size as well as the tissue absorption and scattering coefficients on the thermal damage process are examined and discussed. The laser conditions that cause irreversible damage to the tissue are also identified.

A parallel tracking method for acoustic radiation force impulse imaging

Radiation force-based techniques have been developed by several groups for imaging the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one such method that uses commercially available scanners to generate localized radiation forces in tissue. The response of the tissue to the radiation force is determined using conventional B-mode imaging pulses to track micron-scale displacements in tissue. Current research in ARFI imaging is focused on producing real-time images of tissue displacements and related mechanical properties. Obstacles to producing a real-time ARFI imaging modality include data acquisition, processing power, data transfer rates, heating of the transducer, and patient safety concerns. We propose a parallel receive beamforming technique to reduce transducer heating and patient acoustic exposure, and to facilitate data acquisition for real-time ARFI imaging. Custom beam sequencing was used with a commercially available scanner to track tissue displacements with parallel-receive beamforming in tissue-mimicking phantoms. Using simulations, the effects of material properties on parallel tracking are observed. Transducer and tissue heating for parallel tracking are compared to standard ARFI beam sequencing. The effects of tracking beam position and size of the tracked region are also discussed in relation to the size and temporal response of the region of applied force, and the impact on ARFI image contrast and signal-to-noise ratio are quantified.

Size effect of glulam beams in tension perpendicular to grain

The strength of wood is reduced when the stressed volume is increased. The phenomenon is termed size effect and is often explained as being stochastic in the sense that the probability of weak locations occurring in the wood increases with increased volume. This paper presents the hypothesis that the lower strength is caused by stress concentrations. The stress concentrations arise from the anisotropic structure of wood, and are therefore deterministic. The hypothesis is substantiated through extensive FEM-calculations and experiments. A reasonable agreement between ultimate stresses determined experimentally and in FEM-computations was found.

The effect of beam size on real-time determination of powder blend homogeneity by an online near infrared sensor

Online blend uniformity study was conducted with a near infrared (NIR) sensor and a simulated formulation consisting of acetaminophen and four excipients. Quantitative calibration models were developed and validated for the sensor and assay results were obtained in real time for acetaminophen and three excipients. Mechanical thief samples were also collected during the study. The samples were analyzed offline by a bench-top near infrared spectrometer and used as reference. Comparison of the online and offline data shows a significant difference in standard deviation for acetaminophen and excipients. R.S.D. data calculated from the real-time assay values for acetaminophen was 3.5–13.2-fold lower than those from the offline results. The cause for the discrepancy is believed to be the large beam size of the online sensor. A simple complete-random-mixture model was used to explain the discrepancy. It is concluded that beam size is an important factor in quantitative online blending uniformity studies.

Probe beam size effect on the measurement of the distance between the probe beam and the sample in photothermal deflection

A distance-scan method to determine the distance between the probe beam and sample, which is not easily measured exactly, in photothermal deflection (PD) was reported, with which the distance and thermal diffusivity of the deflecting medium can be simultaneously measured. Probe beam size effect (PBSE) on PD phase signal was quantitatively analyzed to clearly show its physical meaning. The measured distance was experimentally verified as correct and reliable, and the measured thermal diffusivities of N2 and CO2 are in good agreement with the literature values. They could not be precisely measured by phase signal without considering the PBSE.