Beam Edge Research Articles

A State-of-the-Art Review: Side Near Surface Mounted (SNSM) Technique for Strengthening of RC Beams

Near surface mounted (NSM) technique with fiber reinforced polymer (FRP) worldwide is the most repairing systems for existing concrete structures. The use of NSM strengthening technique to RC members is an alternative method used for applying FRP flexural strengthening. Some limitations of applying the NSM to RC members such as; minimum value of groove to NSM bar diameter and minimum net distance between groove and the beam edge and between two adjacent grooves, which limits the use of NSM technique in RC beams with limited width, therefore many researcher introduce side near surface mounted (SNSM) technique by placing the FRP grooves at the sides of the beam. SNSM technique produced a significant enhancement in the flexural capacity of the RC beams. This paper reviews current research on RC members strengthening with SNSM technique. It focuses on the effect of NSM strengthening bar length, strengthening materials type, strengthening diameter, effect of filling material, effect of end anchorage, strengthening position, effect of spacing between NSM bars, prestress level of FRP, longitudinal reinforcement ratio and effect of pre-cracking of strengthened beams.

Finite Element Analysis of Graphene Oxide Hinge Structure-based RF NEM Switch

The modelling and simulation of nanoelectromechanical (NEM) switch is indispensable to get optimum device dimensions. The present work deals with the design and simulation of hinge structure-based Graphene oxide (GO) NEM switch. The Finite Element Modeling (FEM) of the NEM switch for different design parameters have performed in COMSOL Multiphysics. Moreover, the radio frequency (RF) performance of the switch structure with minimum pull-in voltage has also been investigated. The results state that pull-in voltage and von Mises stress exhibit a negative correlation with beam length and positive correlation with beam thickness and air gap. Furthermore, a long and thin suspended beam requires low pull-in voltage and undergoes less von Mises stress. The von Mises stress exhibits a strong effect at beam edges, perforation corners, and beam-top electrode interface due to edge termination effect. The present work facilitates optimisation of design parameters of a NEM switch that requires low pull-in voltage, undergoes less von Mises stress, and exhibits good RF performance.

Steel beam with web opening reinforced by induction heating

Induction heating (IH) is an advanced technology to increase the strength of the steel material up to 2 to 3 times. This research proposed an innovative reinforcement method on the steel beam with web opening, which made full and flexible use of the IH technology to partially strengthen the region around web opening. First, Vickers hardness tests were conducted to investigate the IH effect, and it showed that the hardness of induction-heated region (IH region) was improved to 1.88 times compared to the untreated normal-strength region. Then, the monotonic loading tests on four kinds of steel beams with normal section without web opening, non-reinforced section, plate-reinforced section, and IH-reinforced section were conducted to figure out the structural performance. The apparent reduction of the load resistance by 29% ~ 34% was observed on the non-reinforced beam compared to the normal beam. Plate and IH reinforcements were proved to be effective to ensure the load resistance, of which the ratios to the normal one were 1.19–1.28 and 0.85–0.86, respectively, and maintain the great deformation capacity. Although the lower ductility of the IH region eventually led to the cracking at the hole edge of IH-reinforced beam at relatively large displacement, the dispersion of the strain concentration around the web opening of IH-reinforced beam was successfully observed by the image data processing system. Last, several equations base on the SCI design method were proposed to capture the experimental results.

High-cadence observations and variable spin behaviour of magnetar Swift J1818.0−1607 after its outburst

ABSTRACT We report on multifrequency radio observations of the new magnetar Swift J1818.0−1607, following it for more than one month with high cadence. The observations commenced less than 35 h after its registered first outburst. We obtained timing, polarization, and spectral information. Swift J1818.0−1607 has an unusually steep spectrum for a radio emitting magnetar and also has a relatively narrow and simple pulse profile. The position angle swing of the polarization is flat over the pulse profile, possibly suggesting that our line of sight grazes the edge of the emission beam. This may also explain the steep spectrum. The spin evolution shows large variation in the spin-down rate, associated with four distinct timing events over the course of our observations. Those events may be related to the appearance and disappearance of a second pulse component. The first timing event coincides with our actual observations, while we did not detect significant changes in the emission properties that could reveal further magnetospheric changes. Characteristic ages inferred from the timing measurements over the course of months vary by nearly an order of magnitude. A longer-term spin-down measurement over approximately 100 d suggests a characteristic age of about 500 yr, larger than previously reported. Though Swift J1818.0−1607 could still be one of the youngest neutron stars (and magnetars) detected so far, we caution using the characteristic age as a true-age indicator given the caveats behind its calculation.

Effect of growth and residual stress in AlN (0002) thin films on MEMS accelerometer design

This paper discusses the growth and evolution of residual stresses in (0002) preferentially oriented aluminum nitride (AlN) layers on Si (111) wafers by sputtering technique for the development of micro-electro-mechanical system (MEMS) accelerometer. The microstructure of the deposited films exhibited vertical columnar structures. Residual stresses in the sputtered AlN films are − 1.2 GPa, − 0.8 GPa, and − 0.25 GPa for the film thickness of 600 nm, 750 nm, and 900 nm respectively. The effect of the residual stress on the piezoelectric MEMS acceleration sensor structure is analyzed. The presence of residual stress reduced the resonant frequency (up to 14.72%) and bandwidth (up to 27.3%) of the accelerometer. The locations of the von-Mises stress maxima are shifted from the beam edges (adjoining to the proof-mass) to the whole proof-mass area. The normalized stress sensitivity (which defines the piezoelectric charge sensitivity) is reduced by two orders due to the residual stress in the AlN layers.

Ga-contamination-free scanning transmission electron microscope sample preparation by rectangular-shaped oxygen-ion-beam thinning using projection ion beam optical system

Rectangular-shaped oxygen O2+ ion beam thinning for scanning transmission electron microscope (STEM) sample preparation was investigated using a projection ion beam optical system equipped with a duoplasmatron gas ion source. The ion current can be increased by increasing the area of the rectangular-shaped oxygen ion beam and thereby overcome the low brightness of the ion source. Rectangular-shaped O2+ ion beams with different amounts of projection beam edge blur were formed in the X and Y directions by using a limiting mask between the ion source and projection mask. Gallium-contamination-free STEM sample preparation (rough, medium, and fine milling) was demonstrated using a projection ion beam optical system and three types of rectangular-shaped oxygen ion beams.

Measurement of the distribution of charge exchange ions in a Hall-effect thruster plume

Hall-effect thrusters (HET) are a stationary form of electric propulsion that have been widely used in space missions. However, the wide range of the divergence angle of the HET plasma plume and the high ion velocities can result in a large area where collisions and plume interactions occur. Of these, low-energy charge-exchange (CEX) ions typically originate from collisions, and can result in severe deposition and sputtering issues on spacecraft components. In this work, we propose a novel magnetic Faraday probe in coordination with a particle-in-cell (PIC) simulation code. This system is able to deflect CEX ions with a changing solenoid current, and can be used to obtain the ion density and energy levels of CEX ions through experimental measurements. In addition, a Faraday probe, a retarding potential analyzer (RPA), and a Langmuir probe were used to obtain the beam characteristics. The CEX ion density at the beam edge area was determined to be in the level of 2.54 × 1012 m−3 (the local ion density of the plasma plume is in the level of 1013 m−3), and the ion energy level at the beam edge area was found to be below 30.1 eV. Due to the difference in the vacuum levels between ground tests and in-space operation, CEX collisions will be more severe during ground tests, and can affect plume measurements and erosion of the thruster. Two different vacuum levels were tested experimentally here to study the relationship between CEX ions and the background neutrals. As a result, it was found that a high background neutral density can exacerbate CEX collisions at the beam edge area, which results in an increase in the CEX ion density and a decrease in the CEX ion energy. This study brings us new information on the CEX ion density and energy distribution at the beam edge area from an experimental point of view. Furthermore, data on CEX ions energy can be used as input data for future plume simulations.

Pellet sublimation and expansion under runaway electron flux

This work provides a qualitative description of the pellet response to the ambient runaway electrons. For ITER-relevant parameters, our estimates suggest that the cryogenic pellets will be sublimated instantly at the edge of the runaway beam. The subsequent rapid expansion of the sublimated material spreads the impurities over the poloidal cross-section of a tokamak on a millisecond time scale prior to the complete ionization of the expanding cloud. The injected solid pellet turns into a rapidly expanding gas cloud before it reaches the core of the runaway beam. As a result, the pellet acts similar to the massive gas injection.

Quantitative Analysis of Nanorod Aggregation and Morphology from Scanning Electron Micrographs Using SEMseg.

General methods to achieve better physical insight about nanoparticle aggregation and assembly are needed because of the potential role of aggregation in a wide range of materials, environmental, and biological outcomes. Scanning electron microscopy (SEM) is fast and affordable compared to transmission electron microscopy, but SEM micrographs lack contrast and resolution due to lower beam energy, topographic contrast, edge effects, and charging. We present a new segmentation algorithm called SEMseg that is robust to the challenges inherent in SEM micrograph analysis and demonstrate its utility for analyzing gold (Au) nanorod aggregates. SEMseg not only supports nanoparticle size analysis for dispersed nanoparticles, but also discriminates between nanoparticles within an aggregate. We compare our algorithm to those incorporated into the commonly used software ImageJ and demonstrate improved segmentation of aggregate structures. New physical insight about aggregation is demonstrated by the introduction of an order parameter describing side-by-side structure in nanoparticle aggregates. We also present the segmentation and fitting algorithms included in SEMseg within a user-friendly graphical user interface. The resulting code is provided with an open-source interface to provide quantitative image processing tools for researchers to characterize both dispersed nanoparticles and nanoparticle assemblies in SEM micrographs with high throughput.

Characterization of Wedge Factors and Dose Distributions in Radiotherapy with Symmetric and Asymmetric Physical Wedged Beams of 6 MV Photon Beam

Introduction: Physical wedge by modify photon beam shape and intensity has been utilized in radiotherapy to obtain uniformly dose distribution in tumor site with reduced hot spots. Calculation of dosimetric parameters for both symmetric and asymmetric wedged fields is proved necessary during linear accelerator (Linac) commissioning. The present study aimed to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV beams. Material and Methods: The Siemens PRIMUS Linac head for 6 MV beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm2 field were obtained as a function of lateral distance as well for half beam wedged fields. Results: Based on the results of the present study, the calculated doses were in agreement with the measured data. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15˚, and 45˚ wedges. The total photon fluence of 15˚ and 45˚ physical wedged fields reduced to 71.6% and 27.7% of open field, respectively. Conclusion: The output factor for asymmetric wedged fields was found to be lower than corresponding symmetric open and wedged fields, particularly at field edges. Lack of scattering photons near the half beam edges resulted in dose fall-off in these regions possible to be overestimated by treatment planning system and consequently caused cold spots at target volume.

In-plane responses of multilayer FG-GPLRC curved beams in thermal environment under moving load

As a first attempt, the transient in-plane responses of multilayer functionally graded graphene platelet-reinforced composite (FG-GPLRC) curved beams in thermal environment under a concentrated moving load are investigated. The motion equations are derived based on the first-order shear deformation theory by considering the influences of the initial thermal stresses. The Chebyshev–Ritz method together with Newmark’s time integration scheme is employed to solve the equations of motion with different sets of boundary conditions. In this regard, the Chebyshev polynomials in conjunction with suitable boundary functions are used to construct the admissible functions of the field variables. Each layer is built up from an isotropic homogeneous polymer matrix reinforced by uniformly distributed and randomly oriented graphene platelets (GPLs). The multilayer FG-GPLRC curved beams are composed of a sufficient number of GPL-reinforced layers to create gradation without abrupt change in their material properties along the beam thickness direction. After validating the approach, the effects of moving load velocity, the GPL weight fraction and through-the-thickness distributions, total number of GPLRC curved beam layers, the curved beam geometric parameters, thermal environment and edge boundary conditions on the dynamic behavior of FG-GPLRC curved beams subjected to a moving load are studied.

Simulating fracture in rock using a micropolar peridynamic formulation

Mode I opening and mixed-mode I-II fracture experiments were performed with a homogeneous, fine grained sandstone using the three-point bending test. Specimens were notched at various lengths and positions of the beam edge to produce the desired loading condition. A micropolar peridynamic model was used to simulate the fracture initiation and propagation process. The analytical implicit formulation was derived by defining a specific macroelastic energy density function for micropolar non-local lattices, which depends on three deformation parameters: bond stretch, bond shear deformation accounting for the rotational degrees of freedom, and the particle’s relative rotation. The micropolar non-local lattice model is capable of handling a variable Poisson’s ratio, and is suitable for modelling the mechanical behavior of Cauchy isotropic solids subjected to non-homogeneous deformation fields and fracture. A preliminary analysis on a smooth boundary specimen was performed in order to validate the results obtained with the conceived peridynamic model adopting irregular discretizations. The failure process in notched sandstone specimens was simulated numerically in quasi-static conditions. Numerical results were compared with experimental data obtained from electronic speckle pattern interferometry (ESPI) tests, which were used to quantify and detect the fracture phenomena. Due to the intrinsic features of peridynamic theory, realistic crack patterns and crack initiation angles were obtained from the numerical simulations.

Stratigraphy of a layered structure utilizing XRF and scattered photons

A novel non-destructive method named Beam Edge Stratigraphy has been developed. This method targets the inspection of a layered structure deposited onto a massive substrate. The investigated object is irradiated by a planar, sharp X-ray beam passing over the surface at an acute angle. The scattered and XRF photons are recorded by a pinhole camera equipped with a semiconductor pixelated detector. Overall information about the layered structure is obtained for the area where this structure is fully enclosed within the planar beam, while measurement of the layer thicknesses with micrometric precision is obtained by analysing changes in the signal produced at the sharp edge of the beam. The technique presented primarily targets the investigation of medieval wooden panel paintings based on polychromy. Polychromy consists of several thin layers in a variety of colours and elemental composition. It is highly desirable to non-destructively investigate the current status of existing polychromy for various reasons, such as detecting possible deterioration and identifying previous restoration activities.

Contour Variability in Thyroid Eye Disease with Compressive Optic Neuropathy Treated with Radiation Therapy

PurposeFew studies have evaluated the methodology by which radiation therapy (RT) for thyroid eye disease and compressive optic neuropathy is performed. The objective of this study was to retrospectively review our experience from a radiation planning standpoint and to determine whether current treatment methods provide adequate dose to target and collateral structures. MethodsA retrospective review of 52 patients (104 orbits) with bilateral thyroid eye disease and compressive optic neuropathy treated with RT (20 Gy in 10 fractions) at our institution. RT plans were analyzed for target volumes and doses. Visual fields, color plates, and visual acuity were assessed pretreatment and at last available follow-up post RT. A standardized, anatomic contour of the retro-orbital space was applied to these retrospective plans to determine dose to the entire space, rather than the self-selected target structure. ResultsCompared with the anatomic retro-orbital space, the original contour overlapped by only 68%. Maximum and mean dose was 2134 cGy and 1910 cGy to the anatomic retro-orbital space. Consequently, 39.8% of the orbits had a mean dose <19 Gy (<17 Gy 16.4%, <18 Gy 27.6% <19 Gy 37.8%, <20 Gy 59.2%, 20-21 Gy 35.8%, >21 Gy 5%). There was no significant association of improvement in color plates (P = .07), visual fields (P = .77), and visual acuity (P = .62), based on these dose differences. When beam placement was retrospectively adjusted to include a space of 0.5 cm between the lens and the anterior beam edge, there was a 39.4% and 20.3% decrease in max and mean dose to the lens. ConclusionsWithout a standardized protocol for contouring in thyroid eye disease, target delineation was found to be rather varied, even among the same practitioner. Differences in dose to the anatomic retro-orbital space did not affect outcomes in the follow-up period. Although precise contouring of the retro-orbital space may be of little clinical consequence overall, a >0.5 cm space from the lens may significantly reduce or delay cataractogenesis.

Measurement of a time dependent spatial beam profile of an RF-driven H- ion source.

The AC component of a beam current extracted from a negative hydrogen (H-) ion source was detected through a 0.1 mm wide, 66.5 mm long entrance slit to observe the spatial distribution. An internal antenna type multicusp source driven by a 2 MHz radio frequency (RF) power delivered beams to an electrostatic accelerator coupled to a pair of magnetic lenses. The local beam intensity measured by a Faraday cup after the entrance slit exhibited an oscillation showing two main frequency components: the RF power supply frequency and the frequency two times the driving RF. The frequency spectrum of the detected signal showed sharp peaks at 2 MHz, 4 MHz, and 6 MHz as well as at 3 MHz and 5 MHz. A 1 mm displacement of the Faraday cup slit position from the center of the beam axis increased the oscillation amplitude, corresponding to a larger amplitude of the AC component at the beam edge.

Beam penumbra reduction of Gamma Knife machine model 4C using Monte Carlo simulation

Background and objectiveIn small radiation fields used in stereotactic radiosurgery penumbra is an important portion of the field size especially when critical organs at risk are located near the treatment sites. This study was aimed to reduce penumbra width (90%–50% isodose lines) of Gamma Knife (GK) machine by investigating of source to diaphragm distance (SDD) and designing compensating filter. MethodsCompensating filters at the end of the helmet collimators with the aim of reducing penumbra as well as reducing hot spots appeared near the edge of beam were modeled using Monte Carlo simulation code. Moreover, the SDD parameter was increased as one of the effective factors on penumbra width. ResultsResults showed that single beam penumbra width using optimal design of filters was decreased by 59.49%, 42.50%, 39.02% and 34.44% with attenuation of 30.53%, 13.67%, 11.43% and 9.82% for 4, 8, 14 and 18 mm field sizes, respectively. ConclusionsThe designed filters lead to considerable reductions in single beams penumbra width as well as a noticeable reduction in maximum dose emerged near the beam edge due to the curved lateral surface of filters.

On the beam properties of radio pulsars with interpulse emission

ABSTRACT In the canonical picture of pulsars, radio emission arises from a narrow cone centred on the star’s magnetic axis but many basic details remain unclear. We use high-quality polarization data taken with the Parkes radio telescope to constrain the geometry and emission heights of pulsars showing interpulse emission, and include the possibility that emission heights in the main and interpulse may be different. We show that emission heights are low in the centre of the beam, typically less than 3 per cent of the light cylinder radius. The emission beams are underfilled in longitude, with an average profile width only 60 per cent of the maximal beamwidth and there is a strong preference for the visible emission to be located on the trailing part of the beam. We show substantial evidence that the emission heights are larger at the beam edges than in the beam centre. There is some indication that a fan-like emission beam explains the data better than conal structures. Finally, there is a strong correlation between handedness of circular polarization in the main and interpulse profiles, which implies that the hand of circular polarization is determined by the hemisphere of the visible emission.

Radiation-Induced Brain Injury after Proton Radiotherapy Is Linked to Increased Distal Edge Linear Energy Transfer (LET) and Anatomically Variable Radiation Sensitivity

The incidence of radiation necrosis (RN) after proton beam therapy (PBT) has been discussed particularly in the context of a potentially enhanced biological effectiveness (RBE) towards the distal field edge. RN is commonly identified as radiation-induced contrast enhancing (RI-CE) lesions in magnetic resonance images (MRI), which need to be distinguished from post-operative changes and gliosis. We set out to (i) determine the safety of PBT by evaluating the incidence of RI-CE lesions and (ii) investigate the possibility of spatially variable radiation sensitivity, either caused by enhanced distal RBE or engrained in the anatomy of the brain. We reviewed 110 patients (median age 35 years) who had received actively scanned proton radiotherapy between 2010 and 2015 for histologically proven low grade glioma. Median dose was 54 Gy (RBE = 1.1) (range 50.4 – 60 Gy RBE). Every treatment plan was re-calculated with Monte Carlo (Fluka) to yield a dose and dose-averaged linear energy transfer (LETD) distribution. Regular follow-up amounted to more than 1200 MRI examinations (median follow up 39 months), on which RI-CE lesions were delineated. Every volume element of 1 mm3 in the brain receiving a dose of more than 40 Gy(RBE) was tagged with (i) the proximity to the ventricular system (PVS) and (ii) the LETD. The relative risks for RI-CE lesions were assessed by logistic regression with these parameters, without further biological model assumptions. To account for the growth dynamics of lesions between MRI scans, voxel weights were modified to avoid statistical bias of large lesions at the time of discovery. PBT for low grade glioma results in overall survival of 95 % after two years and 90 % after seven years. Median progression free survival has not yet been reached with surviving fractions of 85 % after two years and 54 % after seven years. The incidence of temporary or clinically silent radiation induced brain injury was significantly higher than previously assumed and was observed in 31 (28 %) patients with a median latency of 15 months. RI-CE lesions with clinical symptoms ≥ CTCAE °II were observed in seven (6.3 %) patients. Of all RI-CE lesions, 26 (51 %) were in a high LETD (LETD >= 5.0 keV/mum) volume and 32 (63 %) were in proximity to the ventricular system (distance voxel-ventricle <= 4mm). Consequentially, both high LETD: OR = 2.6 (95% CI: 1.4–4.8, p = 0.003) and PVS: OR = 8.7 (95% CI: 5.0–15.4, p < 0.001) are highly predictive risk factors. PBT is a safe and efficacious option for patients with low grade glioma. Clinically relevant and symptomatic radiation necrosis was as rare as known from conventional photon treatment. The spatial analysis of the lesion occurrence pattern hints at a moderately increased RBE at the distal edge of the proton beam. Surprisingly, a dose > 40 Gy(RBE) in proximity to the ventricles increases the risk of a lesion 3-fold more than LETD, which hints at a narrowly defined region of elevated radiation sensitivity.

Buckling of a Timoshenko beam bonded to an elastic half-plane: Effects of sharp and smooth beam edges

The problem of a compressed Timoshenko beam of finite length in frictionless and bilateral contact with an elastic half-plane is investigated here. The problem formulation leads to an integro-differential equation which can be transformed into an algebraic system by expanding the rotation of the beam cross sections in series of Chebyshev polynomials. An eigenvalue problem is then obtained, whose solution provides the buckling loads of the beam and, in turn, the corresponding buckling mode shapes. Beams with sharp or smooth edges are considered in detail, founding relevant differences. In particular, it is shown that beams with smooth edges cannot exhibit a rigid-body buckling mode. A limit value of the soil compliance is found for beam with sharp edges, below which an analytic buckling load formula is provided without loss of reliability. Finally, in agreement with the Galin solution for the rigid flat punch on a half-plane, a simple relation between the half-plane elastic modulus and the Winkler soil constant is found. Thus, a straightforward formula predicting the buckling loads of stiff beams resting on compliant substrates is proposed.

An analytical capacitance modeling of step structured perforated RF MEMS switch

In this paper, we have developed an analytical model for capacitance measurement of step structure perforated RF MEMS Switch. Capacitance model plays an important role to design and fabricate a high-performance of RF MEMS switches. Modelling signifies the validation of the proposed switch to design before fabrication by comparing the analytical and simulated results. Here, an analytical capacitance model for step structure perforated RF MEMS Switch is proposed based on ligament efficiency. The total capacitance of the switch is formulated with the parallel-plate capacitance developed by the total surface area of the electrodes and fringing field capacitance developed by sidewalls of the beam edges and perforations. The percentage of error is calculated to analyse the accuracy of the proposed model. The proposed capacitance model is verified by varying the switch design parameters such as dielectric thickness, the gap between electrodes, beam thickness and ligament efficiency. The percentage of error by the proposed model is compared with the two benchmark models and the obtained results shows good agreement than the benchmark models.