Offset Beam Research Articles

A radiotherapy community data-driven approach to determine which complexity metrics best predict the impact of atypical TPS beam modeling on clinical dose calculation accuracy.

To quantify the impact of treatment planning system beam model parameters, based on the actual spread in radiotherapy community data, on clinical treatment plans and determine which complexity metrics best describe the impact beam modeling errors have on dose accuracy. Ten beam modeling parameters for a Varian accelerator were modified in RayStation to match radiotherapy community data at the 2.5, 25, 50, 75, and 97.5 percentile levels. These modifications were evaluated on 25 patient cases, including prostate, non-small cell lung, H&N, brain, and mesothelioma, generating 1,000 plan perturbations. Differences in the mean planned dose to clinical target volumes (CTV) and organs at risk (OAR) were evaluated with respect to the planned dose using the reference (50th-percentile) parameter values. Correlation between CTV dose differences, and 18 different complexity metrics were evaluated using linear regression; R-squared values were used to determine the best metric. Perturbations to MLC offset and transmission parameters demonstrated the greatest changes in dose: up to 5.7% in CTVs and 16.7% for OARs. More complex clinical plans showed greater dose perturbation with atypical beam model parameters. The mean MLC Gap and Tongue & Groove index (TGi) complexity metrics best described the impact of TPS beam modeling variations on clinical dose delivery across all anatomical sites; similar, though not identical, trends between complexity and dose perturbation were observed among all sites. Extreme values for MLC offset and MLC transmission beam modeling parameters were found to most substantially impact the dose distribution of clinical plans and careful attention should be given to these beam modeling parameters. The mean MLC Gap and TGi complexity metrics were best suited to identifying clinical plans most sensitive to beam modeling errors; this could help provide focus for clinical QA in identifying unacceptable plans.

Artificial neural network tools for predicting the functional response of ultrafast laser textured/structured surfaces

Artificial Neural Networks (ANNs) are well-established knowledge acquisition systems with proven capacity for learning and generalisation. Therefore, ANNs are widely applied to solve engineering problems and are often used in laser-based manufacturing applications. There are different pattern recognition and control problems where ANNs can be effectively applied, and one of them is laser structuring/texturing for surface functionalisation, e.g. in generating Laser-Induced Periodic Surface Structures (LIPSS). They are a particular type of sub-micron structures that are very sensitive to changes in laser processing conditions due to processing disturbances like varying Focal Offset Distance (FOD) and/or Beam Incident Angle (BIA) during the laser processing of 3D surfaces. As a result, the functional response of LIPSS-treated surfaces might be affected, too, and typically needs to be analysed with time-consuming experimental tests. Also, there is a lack of sufficient process monitoring and quality control tools available for LIPSS-treated surfaces that could identify processing patterns and interdependences. These tools are needed to determine whether the LIPSS generation process is in control and consequently whether the surface’s functional performance is still retained. In this research, an ANN-based approach is proposed for predicting the functional response of ultrafast laser structured/textured surfaces. It was demonstrated that the processing disturbances affecting the LIPSS treatments can be classified, and then, the surface response, namely wettability, of processed surfaces can be predicted with a very high accuracy using the developed ANN tools for pre- and post-processing of LIPSS topography data, i.e. their areal surface roughness parameters. A Generative Adversarial Network (GAN) was applied as a pre-processing tool to significantly reduce the number of required experimental data. The number of areal surface roughness parameters needed to fully characterise the functional response of a surface was minimised using a combination of feature selection methods. Based on statistical analysis and evolutionary optimisation, these methods narrowed down the initial set of 21 elements to a group of 10 and 6 elements, according to redundancy and relevance criteria, respectively. The validation of ANN tools, using the salient surface parameters, yielded accuracy close to 85% when applied for identification of processing disturbances, while the wettability was predicted within an r.m.s. error of 11 degrees, equivalent to the static water contact angle (CA) measurement uncertainty.

2-D Deformed Half Fisheye Lens as Beamforming Network to Excite Planar Arrays of Antennas for Multibeam Radiations

Multibeam (MB) radiations of antenna arrays rely on effective beamforming networks (BFNs). A 2-D fisheye lens-based BFN (FL-BFN) was developed using a half 2-D lens realizable on metal parallel-plate sandwiched substrates to excite a planar antenna array. This FL-BFN implemented the beam and antenna excitation ports on its half-circular circumference and straight boundaries. An optimization scheme was developed to minimize the ray propagation distortion due to an incomplete half-lens propagation path for an offset beam, which results in an aperiodic array of antennas for MB radiations. Excitations for periodic arrays can also be implemented by considering an aperiodic output port establishment. The rule to determine the positions of antenna elements is also shown for easy design. This FL-BFN performance is demonstrated using its output amplitudes and phases to excite a Vivaldi antenna array for MB radiation. Numerical simulations and measurements over a prototype were performed to validate its feasibility with distinguished agreements.

Multibeam Phased-Arrays Using Dual-Vector Distributed Beamforming: Architecture Overview and 28 GHz Transceiver Prototypes

This article presents a dual-vector distributed beamformer architecture that employs a series-feed network and is capable of supporting up to four simultaneous beams. The multibeam array uses scalar functions within each front end to create Cartesian-weighted signals needed for phase shifting. A dual-vector series-feed network combines/distributes these signals for the receiver/transmitter whereas a global quadrature interpolator is used to create two conjugate beams. By using an interpolator on either end of the series feed, a total of four beams can be obtained. Among these four beams, a first beam can be controlled independently, a second beam is formed as an image of the first, a third beam is offset from the first based on the amount of phase shift within the series-feed structure, and a fourth beam is an image of the offset beam. In this work, the theory of operation of the series-feed DVDB is presented and then two different four-element 28 GHz DVDB transceiver array prototypes in 120 nm SiGe BiCMOS technology are described. One uses a hybrid coupler for global interpolation at radio frequency (RF) and the other uses quadrature mixers for global interpolation at baseband. Measurement results for the array employing passive interpolation at RF show excellent phase-shifting performance, including < 1 dB root-mean-squared (RMS) gain error, < 2 degree RMS phase error, 24% 3 dB bandwidth, with 16–18.6 dBm saturated output power in transmit mode and 4.9–7.3 dB noise figure in receive mode. Measurement results for the array employing mixer-based interpolation likewise show excellent phase-shifting performance with similar RMS gain and phase errors and slightly degraded overall RF performance. Comparing the two, we conclude that the DVDB with passive interpolation at RF is better suited for partitioned systems where beamformers and transceivers are realized on separate chips to support larger, scalable arrays. In contrast, the DVDB with mixer-based interpolation is better suited for integrated systems where beamformers and frequency translation functions must be integrated together.

Experimental Study on the Effect of Offset Notch on Fracture Properties of Rock under Three‐Point Bending Beam

To investigate the effects of offset notch on the fracture properties of rock beam under bending load, granite beam specimens with “one single offset notch” and “central and offset double notches” are made. A series of three‐point bending beam tests on the specimens are carried out by controlling the displacement rate of central notch. The whole load‐displacement (P‐CMOD) curves are obtained. Experimental results show that the larger the distance between the offset notch and beam central is, the larger are the peak load and nominal strength of the specimen. The peak load and nominal strength for the “central and offset double notches” specimens are both larger than those for the “single central notch” specimen. A fracture model considering the effect of offset notch is developed, and the relationship between the offset notch parameter, tensile strength, and fracture toughness is established.

Optimisation of passenger ship structures in concept design stage

ABSTRACTThis paper presents an optimization method for concept design state of passenger ship with focus on utilisation of efficient Finite Element Modelling, evolutionary optimisation algorithm and indirect constraint relaxation. The response is analysed using 3D coarse mesh global finite element (FE) model, where stiffened panels are modelled using equivalent single layer (ESL) elements and the primary stiffeners are modelled with offset beam elements. The simplifications on stiffened panels and beams enable exploration of design space without changing the FE-mesh. The strength is defined based on classification society rules. Local stress peaks are allowed to exceed the rule-based strength limits, i.e. stress constraints are relaxed indirectly. Instead of increasing the allowed stress levels, the amount of material exceeding strength criteria is utilised. Optimization is based on Particle Swarm Optimization (PSO) algorithm with objective to reduce steel weight. The results show that stress relaxation has significant effect on the obtained total mass.

Absorption and secondary scattering of X-rays with an off-axis small beam for a cylindrical sample geometry.

Expressions for X-ray absorption and secondary scattering are developed for cylindrical sample geometries. The incident-beam size is assumed to be smaller than the sample and in general directed off-axis onto the cylindrical sample. It is shown that an offset beam has a non-negligible effect on both the absorption and multiple scattering terms, resulting in an asymmetric correction that must be applied to the measured scattering intensities. The integral forms of the corrections are first presented. A small-beam limit is then developed for easier computation.

Application of the Pulsed Nd: YAG Laser Welding to Investigate the Effect of Laser Beam Position on Weld Characteristics of AISI 420 Stainless Steel to Kovar Alloy

In the present study, dissimilar joining of AISI 420 Stainless Steel (SS 420) to Kovar alloy using a pulsed Nd:YAG laser welding was carried out. The effect of laser beam position with respect to the joint on the microstructure of dissimilar weldmetal was investigated through taking advantage of optical and scanning electron microscopy. Moreover, hardness measurement and fractography were performed to investigate the mechanical properties of weldmetal. A detailed effect of laser beam position on crack susceptibility of fusion zone is elaborated in this research work. The results showed promotion of susceptibility of fusion zone to cracking with offsetting laser beam position to SS 420 base metal. Also martensitic structure was formed in the weldmetal when off-set laser beam shifted 0.2 mm toward the SS 420 base metal. The microhardness test revealed that moving laser beam position toward SS 420 resulted in increasing weld hardness.

Single-Layer Wideband Circularly Polarized High-Efficiency Reflectarray for Satellite Communications

This paper presents a single-layer circularly polarized reflectarray which achieves large bandwidth (BW) in terms of axial ratio (AR), gain, aperture efficiency (AE) and radiation pattern. By using a novel wideband S-shaped phasing element, an offset-fed reflectarray with 20° offset beam is designed based on the element angular rotation method. Theoretical analysis is given to analyze the effect of angular rotated elements on the performance of the reflectarray, which indicates that the AR BW of the reflectarray can exceed the AR BW of the feed horn. Furthermore, the influence of the differential spatial phase delay is analyzed quantitatively, and the performance of S-element-based reflectarrays with different aperture sizes are investigated and discussed. To verify these concepts, a 180 mm $\times180$ mm prototype with $15 \times 15$ elements is fabricated and measured. The measured results confirm that the proposed reflectarray achieves a 68.5% 3-dB AR BW (7 to 14.3 GHz) and a 47.8% 3-dB gain BW (8.6 to 14 GHz). Moreover, the AE is larger than 50% in a 33% BW and larger than 30% in a 64% BW.

Curved drilling via inner hole laser reflection

In this paper, we describe curved hole drilling via the reflection of a laser beam off the sidewall of the drilled hole. A slightly offset laser beam forms a tilted surface at the bottom of the hole, controlling the angle of curvature. An ultraviolet laser beam operating at a wavelength of 266nm was used. To visualize the hole formation process, borosilicate glass was used as the laser workpiece. This method was able to drill a curved hole with an average angle of ∼3° with curvature beginning at a depth of 400–600μm. A curved hole with a diameter of <50μm was achieved. A branched hole was also demonstrated by using the reflection of the tilted sidewall. The curved hole formation process was recorded with a high speed camera. Once the ablated sidewall reached a certain depth, drilling ceased as the laser energy fell below the ablation threshold. Ultimately, judicious selection of an appropriate laser fluence and sidewall angle allow the formation of curved holes.

View-dependent geometric calibration for offset flat-panel cone beam computed tomography systems

Geometric parameters that define the geometry of imaging systems are crucial for image reconstruction and image quality in x-ray computed tomography (CT). The problem of determining geometric parameters for an offset flat-panel cone beam CT (CBCT) system, a recently introduced modality with a large field of view, with the assumption of an unstable mechanism and geometric parameters that vary in each view, is considered. To accurately and rapidly find the geometric parameters for each projection view, we use the projection matrix method and design a dedicated phantom that is partially visible in all projection views. The phantom consists of balls distributed symmetrically in a cylinder to ensure the inclusion of the phantom in all views, and a large portion of the phantom is covered in the projection image. To efficiently use calibrated geometric information in the reconstruction process and get rid of approximation errors, instead of decomposing the projection matrix into actual geometric parameters that are manually corrected before being used in reconstruction, as in conventional methods, we directly use the projection matrix and its pseudo-inverse in projection and backprojection operations of reconstruction algorithms. The experiments illustrate the efficacy of the proposed method with a real offset flat-panel CBCT system in dental imaging.

Исследование отклонения диаграммы направленности офсетной антенны эллиптической поляризации

Исследование отклонения диаграммы направленности офсетной антенны эллиптической поляризации

A numerical model for simulation of RC beam-column connections

Beam to column connections in reinforced concrete (RC) frames are among the elements having essential effects in determining the performance and behavior of structure under different loads. Role of these connections against the lateral loads especially strong earthquakes is such important that experience of past earthquakes confirm their effect in defining value and extent of structural damages. Therefore, to appropriately address the seismic performance of new or existing RC frames, engineers need models able to predict the connection behavior with an acceptable accuracy and enough simplicity. In this research, a numerical model for simulating the elastic and inelastic behavior of RC beam-column connections is presented. This model consists of a rigid offset element and beam and column elements with concentrated plasticity. The rigid offset element is calibrated to give a good estimation of the initial stiffness based on the shear demand ratio of the connection. Each of the beam and column elements with concentrated plasticity includes two rotational springs in series. One spring represents the nonlinear behavior of beam and column and the other contains the nonlinear behavior of the connection. Each one of the rotational springs possesses its own moment-rotation response curve. Comparison of the simulated response with that of the existing experimental results confirms that the suggested model follows the seismic response of beam-column connections with a very good accuracy.

1-D Large Signal Model of Folded-Waveguide Traveling Wave Tubes

A recently published hybrid circuit model for folded-waveguide slow wave structures has been implemented in the 1-D large signal code CHRISTINE. The resulting code is applied to a design for a G-band (220 GHz) folded-waveguide traveling wave tube. Results of small and large signal gain are compared with those from TESLA, a 2-D code using the same circuit model. Conditions for accuracy of the 1-D model are illustrated and explained. The effects of an offset beam tunnel on circuit dispersion and amplifier stability are illustrated using the CHRISTINE code.

Parametric effects of bubble-microcantilever impacts in a confined channel

In this study, we have investigated the impact of bubbles with microcantilever obstacles in a confined channel. Static cantilevers of thickness 100μm were considered. Cantilevers were mounted perpendicular to the mean flow in a vertically oriented channel with width of 2mm, span of 10mm, and length of 585mm. Steady, fully developed upward flows with channel Reynolds numbers based on mean fluid velocity and hydraulic diameter of 800–2400 were considered. Bubbles of diameter of 400–2000μm were introduced upstream of the test section, and impacts were observed by using a microscope equipped with a high frame rate camera. Observations were made in planes normal to the length of cantilevers backlit by using white light. Liquid density (ρ), interfacial surface tension (σ), bubble velocity immediately prior to impact (Ububble), bubble diameter (D), obstacle thickness (t), impact offset distance (d), channel width (w), and beam location are all potential influences on the result of bubble-beam impacts. Five dimensionless combinations of these quantities: Weber number (We=ρUbubble2D∕σ), impact offset (B=2d∕D where d is the impact offset distance), bubble diameter relative to beam thickness (D∕t), bubble diameter relative to channel width (D∕w), and beam offset from channel centerline relative to channel size (O=offset∕w, where offset is the distance the beam is displaced from the channel centerline), were considered in the following ranges: 0≤We≤12, 8≤D∕t≤90, B≤1, D∕w≤1, and 0≤O≤0.1. Multiple types of interactions ranging from bouncing with little deformation to wrapping with substantial deformation to splitting into two were observed. Splitting required a minimum Weber number to occur, which was observed to be independent of D∕t for all cases considered. Impact offset B and D∕w combined to affect impact outcome. For D∕w≤0.6, the Weber number required for splitting was observed to increase with offset B. As bubble diameter D approached the channel width w (0.6≤D∕w≤0.75) under laminar flow conditions, channel gradient effects could generate a substantial lift force toward the center of the channel for bubbles approaching offset from the channel centerline. This lift force caused bubbles to cross from one side of the beam to the other; this type of interaction increased the likelihood of splitting and resulted in a number of low-We, high B splitting cases. Bubble impacts with channel walls reduced this phenomenon for D∕w≥0.75.

Generation of Multiple Beam Patterns Using a Mechanically Reconfigurable Smart Reflector Antenna System

In this research, a novel computational design and operation methodology for a reconfigurable dual offset contour beam reflector antenna (DCBRA) using a mechanically adjustable subreflector is presented. The subreflector is made with a thin flexible material such that it deforms by movement of a set of linear point actuators attached on its back surface. The deformable subreflector allows the electromagnetic field illuminating the main reflector to be changed leading to a different far-field radiation pattern. For the analysis, the Finite Element Method (FEM) is applied to calculate the deformed shape of the subreflector from a given configuration and movement of actuators and Physical Optics (PO) is utilized to calculate radiation patterns for both the main reflector and the subreflector. Finally a unified computation tool is developed which employs optimization techniques to synergistically combine the PO routine and the FEM code. The overall goal of the combination is to find the optimal actuation values of the actuators needed to generate a specific far-field radiation pattern related to a desired geographical footprint. Simulation results on the generation of contour beams for four different geographic regions—CONUS, Australia, Brazil, and Afghanistan—are presented.

A study on the mixture formation process of evaporating diesel spray by offset incidence laser beam

This paper analyzes heterogeneous distribution of branch-like structure at the downstream region of the spray. The liquid and vapor phase of the spray are obtained using a 35mm still camera and CCD camera in order to investigate spray structure of evaporating diesel spray. There have been many studies conducted on diesel spray structure but have yet only focused on the analyses of 2-D structure. There are a few information which is concerned with 3-D structure analysis of evaporating spray. The heterogeneous distribution of droplets in inner spray affects the mixture formation of diesel spray and the combustion characteristics of the diesel engines. In this study, the laser beam of 2-D plane was used in order to investigate 3-D structure of evaporating spray. The incident laser beam was offset on the central axis of the spray. From the analysis of images taken by offset laser beam, we will examine the formation mechanism of heterogeneous distribution of the diesel spray by vortex flow at the downstream of the spray. The images of liquid and vapor phase of free spray are simultaneously taken through an exciplex fluorescence method. Through this, the branch-like structure consisting of heterogeneous distribution of the droplets forms high concentrated vapor phase at the periphery of droplets and at the spray tip.

Calibrating short‐timescale tropospheric phase fluctuations seen by a radio telescope: Limits from subreflector and Cassegrain feed ring radiometer placement

Water vapor radiometers (WVRs) measure tropospheric brightness temperatures and use those measurements to infer path delay. Calibration of short‐timescale phase fluctuations at a radio telescope requires that the WVR and radio telescope sample a similar volume of the troposphere. Using a statistical (Kolmogorov frozen flow) model of tropospheric fluctuations, the short‐timescale calibration capability of two WVR configurations has been quantified. The first configuration is a WVR mounted, with its own antenna, on the back side of the main radio telescope subreflector, giving a conical beam that is coaxial with the main cylindrical near‐field beam of the large telescope. The second configuration uses a Cassegrain feed ring, with the WVR and radio astronomy feeds at different positions on the ring. This second configuration gives a cylindrical calibration near‐field beam, offset in angle to the main cylindrical beam. An important application of short‐timescale phase calibration is improving the coherence of high‐frequency interferometric observations. For two cases of current/near future interest (86 GHz very long baseline interferometry with the Very Long Baseline Array; 350 GHz observations with the Atacama Large Millimeter Array, ALMA), useful calibration could be achieved with either geometry (coaxial conical beam or offset cylindrical beam). For a coaxial conical beam, a 2° WVR beam width would allow significant coherence improvement, but a beam width ≤1° (full width at half maximum) is needed for optimum performance. For an offset cylindrical beam, the desired angular offset (on the sky) is ≤1° for 43 GHz Very Large Array observations, or ≤0.3° for 350 GHz ALMA observations.

720 オフセット圧縮はりの大たわみ変形解析 : 両端回転支持はりの場合

720 オフセット圧縮はりの大たわみ変形解析 : 両端回転支持はりの場合

High-aperture diffraction of a scalar, off-axis Gaussian beam

A scalar treatment for Gaussian beams offset from the optic axis and then focused by a high-numerical-aperture lens is presented. Such a theory is required for describing certain types of Doppler microscopes, i.e., when the measurement is simultaneously performed by more than a single beam axially offset and then focused by a lens. Analytic expressions for the intensity in the focal region of the high-aperture lens are derived. From these expressions we calculate the intensity in the focal region with parameters of beam size, beam offset, and the numerical aperture of the lens. The relative location and variation of the intensity around the focal region are discussed in detail. We show that for small-diameter Gaussian beams the Strehl ratio increases above unity as the beam is offset from the optic axis. This is explained by the increase in the effective numerical aperture of the offset beam compared with the one collinear with the optic axis. From examining the focal distribution, we conclude that it rotates for small beam size and that increasing beam diameter causes the focused distribution to rotate and shear, i.e., to distort. We also show that the distortion of the distribution increases with increasing numerical aperture.