Linear Beam Research Articles

On modelling and adaptive control of a linear smart beam model interacting with fluid

This paper deals with modelling and control of Euler-Bernoulli smart beam interacting with a fluid medium. Several distributed piezo-patches (actuators and/or sensors) are bonded on the surface of the target beam. To model the vibrating beam properly, the effect of the piezo-patches and the hydrodynamic loads should be taken into account carefully. The partial differential equation PDE for the target oscillating beam is derived considering the piezo-actuators as input controls. Fluid forces are decomposed into two components: 1) hydrodynamic forces due to the beam oscillations, and 2) external (disturbance) hydrodynamic loads independent of beam motion. Then the PDE is discretized using the Galerkin approach to obtain standard multi-modal equations. An adaptive approximation control structure is proposed to suppress the beam vibration. The controller consists of a proportional-derivative PD control plus an adaptive approximation compensator AAC with guaranteed stability. A simply supported beam with 2 piezo-patches interacting with fluid is simulated. The disturbance hydrodynamic force that excites the beam vibration is assumed as a harmonic force with 50 Hz frequency and 1 N amplitude. The results prove the efficacy of the proposed control architecture.

FT-ICR mass spectrometry: Superconducting magnet, external ion source, ion-molecule reactions, and ion-ion traps.

The world of Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry has witnessed, especially in the last 30 years significant advances in many fields of science, such as electronics, magnets, new ICR cell designs, developed ICR event sequences, modern external ionization sources, and linear ion beam guides, as well as modern vacuum technology. In this review, a brief account is given focusing especially on the studies performed in Wanczek's group and ICR research laboratory at the University of Bremen. An FT-ICR mass spectrometer has been developed with a high magnetic field superconducting magnet, operating at 4.7 T. At this magnetic field, a trapping time of 13.5 h was obtained with 30% efficiency. For the tetrachloromethane molecular ion, m/z 166, a mass-resolving power m/Δm = 1.5 × 106 was measured at a pressure of 2 × 10-8 Torr. The transition from magnet sweep to frequency sweep and the application of Fourier-transform has greatly enhanced the ICR technology. External ion sources were invented and differential pumping schemes were developed for enabling ultrahigh vacuum condition for ICR detection, while guiding ions at relatively higher pressures, during their flight to the ICR cell. With the external ion source, a time-of-flight ICR tandem instrument is built. A method to measure the ion flight time and to trap the ions in the ICR cell is described. Many ICR cell characteristics such as z-axis ion ejection and coupling of radial and axial ion motions in a superposed homogeneous magnetic and inhomogeneous trapping electric field were extensively studied. Gas-phase ion-molecule reactions of several reactive inorganic compounds with a focus on phosphorous and sulfur as well as silicon chemistry were also studied in great detail. The gas-phase ion chemistry of several trifluoromethyl-reagents such as trifluoromethyltrimethylsilane and tris(trifluoromethyl)phosphine were also investigated in ICR. Dual polarities multisegmented ICR cells were invented and deeply characterized. Sophisticated ICR pulse event programs were developed to enable long-range ion-ion interactions between simultaneously trapped positive and negative ions.

Bend stiffener linear viscoelastic thermo-mechanical analysis. Part I — Experimental characterization and mathematical formulation

Bend stiffeners are subjected to cyclic loading during offshore operation or when subjected to a controlled full-scale qualification test. Due to the viscoelastic nature of the polyurethane, energy is dissipated within the material volume and the structure may experience a temperature increase, a phenomenon known as self-heating. The top connection is a flexible riser critical region in terms of fatigue, being the bend stiffener the main responsible for curvature control. As the curvature distribution is highly affected by the nonlinear time–temperature bend stiffener response, a detailed thermo-mechanical assessment may become relevant for riser lifetime and polyurethane material failure assessment, specially during accelerated full-scale tests. In the present paper (Part I), the polyurethane experimental characterization and steady-state thermo-mechanical mathematical formulation are presented for the bend stiffener self-heating assessment. A steady-state formulation is derived for a temperature dependent linear viscoelastic large deflection beam model to estimate the heat generation during harmonic tip loading. The temperature field distribution is calculated through a three-dimensional steady-state thermal model considering the viscoelastic heat calculated from the mechanical model with an iterative scheme. Stress relaxation tests are performed at different temperatures to determine the viscoelastic properties followed by thermal properties characterization through differential scanning calorimetry and by the Flash method to determine the specific heat, thermal conductivity and diffusivity, respectively. In a companion paper (Part II) the iterative numerical scheme is detailed and a case study presented.

Fractional Schrödinger equation in gravitational optics

This paper addresses issues surrounding the concept of fractional quantum mechanics, related to lights propagation in inhomogeneous nonlinear media, specifically restricted to a so-called gravitational optics. Besides Schrödinger–Newton equation, we have also concerned with linear and nonlinear Airy beam accelerations in flat and curved spaces and fractal photonics, related to nonlinear Schrödinger equation, where impact of the fractional Laplacian is discussed. Another important feature of the gravitational optics’ implementation is its geometry with the paraxial approximation, when quantum mechanics, in particular, fractional quantum mechanics, is an effective description of optical effects. In this case, fractional-time differentiation reflexes this geometry effect as well.

Immersed boundary simulations of fluid shear-induced deformation of a cantilever beam

A biofilm is a colony of microorganisms that adheres and grows on a surface typically in contact with a stagnant or flowing fluid environment. The hydrodynamic interaction between the fluid and the film structure plays a key role in the various phases of the biofilm life-cycle — formation, growth, detachment, and reestablishment. The fluid-flow conditions determine the shear stresses exerted upon the film structure causing it to deform up to a critical point, beyond which the biofilm is uprooted from the surface into a planktonic state in the flowing fluid. To develop a fundamental understanding of the effects of the fluid-flow parameters on the mechanics of the biofilm, this work considered an ideal 2D model scenario of ‘a rectangular cantilever beam immersed in a channel filled with viscous, incompressible fluid, where one end of the beam is fixed to the channel wall, bending in response to a shear flow.’ The Immersed boundary (IB) method was employed to simulate numerically the fluid–structure interaction. The effect of physical parameters of the problem — stiffness and height of the cantilever and flow velocity, along with the numerical parameters on the equilibrium structure of the elastic beam was investigated and the simulation results were qualitatively compared with respect to linear beam theory. A careful analysis of the “corner effects” — irregularities in beam shape near the free and fixed ends, has been presented. It was shown that this issue can be effectively eliminated by smoothing out the corners with a “fillet” or rounded shape. Finally, the IB formulation was extended to include porosity in the beam to investigate the effect of the resultant porous flow on the beam deflection.

Wide-fan-angle Flat-top Linear Laser Beam Generated by Long-pitch Diffraction Gratings

Wide-fan-angle Flat-top Linear Laser Beam Generated by Long-pitch Diffraction Gratings

Semi-analytical analysis of high-brightness microbunched beam dynamics with collective and intrabeam scattering effects

The studies of incoherent single-particle and collective multi-particle effects are, in general, separated in accelerator beam dynamics in that the two dynamical phenomena involve quite different time scales. Recent experimental measurements indicate that in some parameter regime, the small-angle, multiple scattering effects within a high-brightness electron beam can have a strong influence on microbunched beam dynamics. In this paper, we apply our recently developed semi-analytical kinetic analysis to investigate the collective phase space microbunched dynamics in the presence of incoherent single-particle effects. Particular emphasis will be placed on evaluation of the intrinsic or slice energy spread. An example of two linear beam transport lines, followed by two identical, interleaving bunch compressor chicanes, is then presented. The semi-analytical calculations are consistent with particle tracking simulations. Moreover, the threshold condition is derived, indicating the relation among relevant physical quantities. At threshold, the incoherent effect can be beneficial for effective suppression of the collective microbunching instability. We expect that this work could shed light on high-brightness electron transport beamline design to improve short-wavelength free-electron laser performance.

Проектирование легкой катерной надстройки из полимерных композиционных материалов

This paper discusses the design of lightweight polymeric-composite superstructure for a fast boat (displacement up to 1 t) with solar panels powering its propulsion motor. The superstructure is made up by composite beams with sufficient dynamic stiffness and strength to withstand operational loads. External load was defined as spectral, inertial, transmitted as accelerations or displacements from hull to the superstructure via bearing joints. The material was GFRP with foam filler. The simulation is performed as per finite-element method in linear spatial beam formulation, solving the problems of natural vibrations and maximum dangerous response to spectral kinematic effect as a superposition of modes weighed by spectral coefficients. The study presents calculation for the initial superstructure design and its variations, to analyse sensitivity of dynamic and spectral responses to design changes. The study implements a new technique of generating a model of composite binary profile on single mesh. The results of this analysis, further verified on a more detailed idealization and supplemented by a calculation of inertial disturbances due to pitching and rolling, will yield the methodology for more computer-efficient design of lightweight superstructures for small boats made of polymeric composite materials.

Study on rheological properties of silica nanofluids modified asphalt binder

Due to the existence of the nanoparticles (NPs) agglomeration phenomena in nanometer silica (SiO2) modified asphalt binder, solvent-free SiO2 nanofluids (NFs) were applied in asphalt modification to solve this issue in this research. The main objective is to investigate the rheological properties of SiO2 NFs modified asphalt binder. Solvent-free SiO2 NFs were manufactured based on SiO2 nanoparticles (NPs) by surface functionalization, and subsequently utilized to modify base asphalt binder with various dosages of 1 wt%, 3 wt% and 5 wt%. Fourier transform infrared spectrometer (FTIR), X-ray diffractometer (XRD), scanning electron microscope (SEM) and thermogravimetric analyzer (TGA) were conducted to investigate the microstructure characteristics and thermal stability of SiO2 NFs. The results prove that the successfully manufactured SiO2 NFs are suitable as a modifier to blend with asphalt binder. In addition, the compatibility between SiO2 NFs and base asphalt binder was also observed by SEM, indicating that the dispersion of SiO2 NFs and the compatibility with asphalt binder are much better than SiO2 NPs. Moreover, the tests of rheological property such as temperature sweep (TS), multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), frequency sweep (FS) and bending beam rheometer (BBR) were executed to analyze the rutting, fatigue and crack resistances of asphalt binder effected by the SiO2 NFs. A series of test results manifest that the addition of SiO2 NFs slightly reduces the rutting resistance at high temperatures, but is favorable to improving the fatigue life and low-temperature crack resistance of asphalt binder.

Modelling Adhesive Using Non-Linear Truss Elements in Mode I Delamination Problems

A fast and simple finite element model is presented in this paper to simulate the crack propagation in notched beam structures with two layers and one interface medium in Mode I delamination. The truss elements from FEAP element library are endowed with a user material law describing the bilinear cohesive zone model (CZM) with the material unloading path defined by embedding a history variable in the response. The layer is modelled with linear elastic Timoshenko beam elements. The method is used for damage growth and damage propagation simulations in interfaces with both ductile and brittle materials. The method is robust for ductile interfaces, but for brittle interfaces more specific numerical techniques are required. The results are evaluated using available analytical and numerical solutions and a good agreement is achieved.

Utjecaj izbora tehnike planiranja FiF/IMRT kod radioterapije operirane prostate

Introduction: Within the past two decades, we made significant progress in radiation therapy for prostate cancer. At UH Rijeka IMRT became the technique of choice for radiation therapy following radical prostatectomy since 2016. Previously, an advanced 3-DCRT technique using the field-in-field (FiF) method was used for dose distribution optimization around target volumes and organs-at-risk. This research has been performed to investigate the influence of planning technique choice (FiF or IMRT) on coverage of target volumes with prescribed dose and organs-at-risk sparing. Materials and methods: Comparison of dose distributions calculated using FiF and IMRT techniques was performed retrospectively for ten patients who underwent postoperative radiotherapy. The prescribed dose for all patients was delivered using IMRT, and for this research, we also calculated dose distributions using the FiF technique. For FiF and IMRT techniques, we used linear accelerator photon beams. To determine the influence of planning technique on dose distribution parameters related to target volumes (GTV, CTV, PTV1, PTV2) were analyzed. For organs-at-risk sparing evaluation (rectum, bladder, femoral heads), we used dose-volume constraints. Results and discussion: The analysis of parameters related to target volumes has shown that most of them had no statistically significant difference (V100%(GTV), V100%(CTV), V95%(PTV2), V95%(PTV1)). For both planning techniques, internationally set dose constraints were achieved. Statistically, we found a significant difference for V100%(PTV2), p=0,000534, and V100%(PTV1), p=0,042944 in favor of IMRT. A statistically significant difference (p=0,045966) was found for the volume of the rectum, which receives 40Gy, and for the volume of femoral heads, which receives 30Gy (p=0,000385), where the sparing is better for IMRT. For dose-volume constraints related to the bladder, no statistically significant differences were found. Conclusion: Results of this research show a statistically significant difference for V100% target volume coverage for PTV1 and PTV2, with better dose coverage accomplished by IMRT. Concerning organs-at-risk sparing, a statistically significant difference in favor of IMRT was found for rectum volume, which receives 40Gy. Expectedly, IMRT was superior to the FiF technique. However, differences between the two planning techniques were relatively small, which points to the fact that the FiF technique is viable as a technique of choice.

Computational Simulations for Infrared Laser Sealing and Cutting of Blood Vessels.

Blood vessel burst pressures were simulated and predicted for sealing and cutting of vessels in a two-step process, using low (<25 W), medium (~100 W), and high (200 W) power lasers at a wavelength of 1470 nm. Monte Carlo optical transport, heat transfer, Arrhenius integral tissue damage simulations, and vessel pressure equations were utilized. The purpose of these studies was to first validate the numerical model by comparison with experimental results (for low and medium power) and then to use the model to simulate parameters that could not be experimentally tested (for high power). The goal was to reduce the large range of parameters (power, irradiation time, and linear beam dimensions) to be tested in future experiments, for achieving short vessel sealing/cutting times, minimal bifurcated seal zones (BSZ), and high vessel burst pressures. Blood vessels were compressed to 400 μm thickness. A wide range of linear beam profiles (1-5 mm widths and 8-9.5 mm lengths), incident powers (20-200 W) and clinically relevant irradiation times (0.5-5.0 s) were simulated and peak seal and cut temperatures as well as thermal seal zones, ablation zones, and BSZ computed. A simplistic mathematical expression was used to estimate vessel burst pressures based on seal width. Optimal low-power parameters were: 24W/5s/8×2mm (sealing) and 24W/5s/8×1mm (cutting), yielding a BSZ of 0.4 mm, corresponding to experimental burst pressures of ~450 mmHg. Optimal medium-power parameters were: 90W/1s/9.5×3mm (sealing) and 90W/1s/9.5×1mm (cutting), yielding a BSZ of 0.9 mm for burst pressures of ~1300 mmHg. Simulated only optimal high-power parameters were: 200W/0.5s/9×3 mm (sealing) and 200W/0.5s/9×1mm (cutting), yielding a BSZ of 0.9 mm and extrapolated to predict a seal strength of ~1300 mmHg. All lasers produced seal zones between 0.4-1.5 mm, corresponding to high vessel burst pressures of 300-1300 mmHg (well above normal systolic blood pressure of 120 mmHg). Higher laser powers enable shorter sealing/cutting times and higher vessel strengths.

Growth of Nanostructured Silver Flowers by Metal-Mediated Catalysis for Surface-Enhanced Raman Spectroscopy Application.

Metallic flowers with nanoscale surface roughness can provide a platform for highly sensitive and reproductive surface-enhanced Raman spectroscopy (SERS). Here, we present a method to grow a nanostructured silver flower (NSF) at the apex of a plasmonic tip based on metal-mediated catalysis, where the NSF was rapidly generated in no more than 1 min. The NSF was used as the SERS substrate under linear polarization beam (LPB) excitation to achieve a 10–9 M detection sensitivity for the malachite green analyte. The reproducibility for SERS is examined to have been guaranteed by comparing Raman intensity enhanced by different NSFs. Compared with the LPB, the azimuthal vector beam (AVB) excitation can further improve the SERS activity of the NSF, which is consistent with the simulation result that the gap mode can be effectively generated between two adjacent Ag nanoparticles (NPs) and between the NPs and the Ag pyramids on the surface of the NSF under AVB illumination. This work makes it promising for plasmonic tip-mediated catalysis to be applied in nanofabrication, the products of which can be further exploited in nanostructure-based ultrasensitive detection.

A micromechanical model of fiber bridging including effects of large deflections of the bridging fibers

A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscopic mixed-mode bridging laws (traction-separation laws). The model is based on non-linear beam theory and takes into account debonding between fiber and matrix as well as buckling of fibers in compression. Further, it is shown how failure of the bridging fibers can be taken into account through a Weibull distributed failure strain. Predictions made by the proposed model are compared with predictions made by detailed 3D finite element models, and a very good agreement was observed. It is shown that models based on linear beam theory are only valid for small transverse deflections of the bridging ligament and greatly underestimate the force transferred by ligaments subjected to moderately large deflections. The novel model, on the other hand, is applicable in the entire range where the bridging problem transitions from a beam bending problem to a bar-like problem. Finally, an example of how the proposed model can be used for parameter/sensitivity studies is given. A conclusion from this study is that reducing the fracture toughness, Gc, of the interface between fibers and matrix may lead to increased energy dissipation through cross-over fiber bridging as more fibres remain intact longer.

Geometrically Non-Linear Vibration of a Cantilever Interacting with Rarefied Gas Flow

Abstract The work is devoted to study 2D pressure driven rarefied gas flow in a microchannel having an elastic obstacle. The elastic obstacle is clamped at the bottom channel wall and its length is half of the channel height. The gas flow is simulated by Direct Simulation Monte Carlo (DSMC) method applying the advanced Simplified Bernoulli Trial (SBT) collision scheme. The elastic obstacle is modelled as geometrically nonlinear Euler Bernoulli beam. A reduced 3 modes reduction model of the beam is created. The influence of the gas flow on the beam vibration is studied, considering the linear and nonlinear beam theories.

Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications.

Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.

Design and characterization of telecentric f-θ scanning lenses for broadband terahertz frequency systems.

Telecentric beam scanning using f-θ lenses offers nearly uniform spot size, linear beam displacement, and normal incidence angle over a planar surface. These unique properties allow for the minimization of imaging distortion over a wide field-of-view. In this article, we present a numerical method for designing custom f-θ lenses in the THz regime. We fabricated three lenses made from different commonly used polymer materials in the THz optics. We demonstrated their optical performance metrics compared to a conventional plano-convex lens over the broadband 0.3 THz–1 THz range. We find that the f-θ lens designed using the optical properties of high-density polyethylene achieved superior performance by maintaining a constant phase over a wide field of view of about 34°. We demonstrate this isophase property by measuring a constant time of arrival of the THz time-domain pulses over a reference mirror with a standard deviation of ∼19 fs, in excellent agreement with simulation predictions. This work will pave the way for the design and implementation of highly precise and fast telecentric imaging systems in the THz frequencies.

ANALISIS KUALITAS DATA KELUARAN HARIAN ELEKTRON AKSELERATOR LINIER

Linac radiotherapy measurentoften experience instability. One of the irradiation errors with Linac can occur because the radiation beam that comes out is not expected properly. Determination of the correction factor and linearity is important to analyze the charge output of the electron energy emitted by Linac's modality to see the stability of the emitted charge. This study uses Electron Linear Accelerator Electron beam daily output data with a 10 cm × 10 cm applicator, 100 cm SSD, 0.125 cc cylindrical ionization detector PTW type 31010 Semiflek and uses a slab solid phantom with energy variations of 6 MeV, 8 MeV, 10 MeV, 12 MeV and 15 MeV. The measurement results are calculated using the IAEA TRS 398 protocol. The result of linearity correction factor of 96.87% which shows the stability value of the electron beam load output is very good, and the results of the correction factor show the enumeration values of each energy 6 MeV, 8 MeV, 10 MeV, 12 MeV and 15 MeV namely 0.030342129 nC, 0.03034 nC, 0.03034 nC, 0.03034 nC and 0.03034 nC values respectively still within the tolerance range of measurement ± 1. The correction factor that has been obtained is used as a parameter in calculating the absorbance dose to the maximum depth.

Evaluation of ionization chamber stability checks using various sources.

It is important to check stability of ionization chambers in between regular calibration cycles. Stability checks can include individual 60Co irradiations, use of a beta-emitting check source, or redundant measurements in megavoltage photon beams. While 60Co irradiators are considered stable, they are rarely found in the clinical setting. Thus, this study seeks to compare the precision and efficiency in monitoring chamber stability using 90Sr check sources and linear accelerator beams which are both commonly found in the clinical setting, and compare these sources to 60Co. Measurements were made with a 90Sr beta-emitting check source and a 6 MV photon beam using a Constancy Check Phantom with three custom inserts to hold the ionization chambers. A comparison of both methods was performed with an Exradin A28 scanning chamber, Wellhofer IC69 Farmer-type chamber, and Exradin A12 Farmer-type chamber. Chamber stability was evaluated with individual charge readings and charge ratios among the three chambers. Results were compared to measurements taken in 60Co with three Farmer-type chambers: the NEL 2571, PTW N30001G, and Exradin A12. Stability of individual charge reading was found to be within ±1.0% for 90Sr source measurements and ±0.5% for external beam measurements, including the 60Co comparison. Additionally, the standard deviation of the mean charge ratios ranged from 0.15% to 0.40% for 90Sr measurements and from 0.10% to 0.30% for the external beam measurements. This work provides a comparison of techniques used to assess stability of ionization chambers in order to better inform the clinical physicist.

Operating a graphite calorimeter in quasi-isothermal mode under high-energy x-ray beams

In this study, we developed a semi-active method to run a graphite calorimeter in the quasi-isothermal mode under high-energy x-ray beams. The rate of energy imparted by the beam during irradiation was compensated mainly by removing the electrical heating power based on the pre-calculation and in part by an active automated algorithm, as well, while the temperature of the calorimeter core was kept constant. Irradiations were performed under the linear electron accelerator x-ray beams at 6, 8, 10, 15, and 18 MV. A simple model was applied to analyze the results. The energy imparted to the core was determined with an uncertainty level of 0.2%–0.3%, and the results were reaffirmed by comparing it with that obtained by the quasi-adiabatic mode. The normalized root-mean-square deviation to the mean from the quasi-adiabatic mode was 0.11%, and the associated uncertainty was 0.16% taking into account the correlation of the uncertainty components. This level of agreement showed that the present method is practical for the high-energy x-ray dosimetry.