Beam Area Research Articles

An Angular Radial Extended Interaction Amplifier at the W Band

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam-wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (-2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the -2° EIA can be improved by nearly 30% compared to the 0° EIA, and the -2° EIA has a greatly improved beam-wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed.

Numerical Study on the Effect of Interface Dynamic Damage of Steel–Concrete Composite Beam Bridge Caused by High–Frequency Impact Load

The group studs arrangement is applied to prefabricated composite beams to significantly improve construction speed. However, contact vibration exists in the unconstrained interface area of the high-speed railway composite beam during the operation period, which degrades the connecting performance of the composite beam and adversely affects the overall structure. In this study, finite element simulations of the vibration of concrete slabs and steel beams in the unconstrained interface area were carried out to obtain finite element models with damage. The effects of vibration damage on the degradation of the studs were investigated by push-out and pull-out tests using finite element simulation of the local specimen model. The macroscopic ontological models of the undamaged and previously damaged group studs were obtained. Compared with the specimen without damage, the ultimate bearing capacity of the pushed-out specimen with damage decreased by 24.8%; the ultimate slip decreased by 15%; and the stiffness decreased by 12.8%. The behavior of the pulled-out specimen with damage was almost the same as that of the specimen without damage. On this basis, a finite element model of the train–track–composite beam coupling system was established. The influence of the degradation of the connection on the coupling system with 300 km/h, 330 km/h, and 360 km/h train speeds was analyzed under the conditions of single-train driving and a two-train rendezvous. In the case of single-train travel, compared with the undamaged composite beam, the mid-span vertical displacements of the composite beams with damage increased by 13%, 8.38%, and 6.2% for train speeds of 360 km/h, 330 km/h, and 300 km/h, respectively; the transverse displacements increased by 24.2%, 15%, and 9.2%, respectively. In the case of a two-train rendezvous, the mid-span vertical displacements increased by 8.8%, 13.7%, and 12.8%, respectively; the transverse displacements increased by 26.4%, 53%, and 24.8%, respectively.

Engineering Multicolor Radiative Centers in hBN Flakes by Varying the Electron Beam Irradiation Parameters.

Recently, hBN has become an interesting platform for quantum optics due to the peculiar defect-related luminescence properties. In this work, multicolor radiative emissions are engineered and tailored by position-controlled low-energy electron irradiation. Varying the irradiation parameters, such as the electron beam energy and/or area dose, we are able to induce light emissions at different wavelengths in the green-red range. In particular, the 10 keV and 20 keV irradiation levels induce the appearance of broad emission in the orange-red range (600-660 nm), while 15 keV gives rise to a sharp emission in the green range (535 nm). The cumulative dose density increase demonstrates the presence of a threshold value. The overcoming of the threshold, which is different for each electron beam energy level, causes the generation of non-radiative recombination pathways.

CFD Analysis and Wind Tunnel Experiment for Ventilation Ducts with Structural Elements Inside

Ventilation ducts with a high cross-sectional area are frequently built as structural ducts that include inside transversal structural beams. In this way, the cross-sectional area requested is respected, but the transverse structural elements will have a big impact on the airflow, with eventually additional noise and vibration and a high amount of energy wasted across the beams. From this perspective, the aim of this study is to evaluate the impact of the transversal beams inside the ventilation ducts, to analyze different alternatives for airflow improvement using computational fluid dynamics (CFD) simulation, and to check the simulation results in the wind tunnel with an experimental model. The results of the experimental measurements have highlighted the high-pressure drop and, consequently, the high energy wasted across the transversal structural beams. It was found that the airflow downstream of the beam is changing the flow direction, and high turbulences and vortices are initiated in the shadow of the beam. According to the CFD analysis, the ventilation system can be improved by adding airflow deflectors in the beam area. In this way, the high turbulences are reduced, the vortices and backflow are canceled, and the pressure losses across the beam area of the ventilation duct are reduced by up to 90% compared with the beam without a deflector. Therefore, the energy wasted in the beam area can be reduced by up to 90%.

TPC Development by the LCTPC Collaboration for future Higgs factories

A future Higgs factory will impose demanding requirements on the detectors both in precision and in rate. To study the possibility of a time projection chamber as a central tracking detector at such a facility, the Linear Collider TPC (LCTPC) collaboration was founded in 2007. It is investigating various Micropattern Gaseous Detectors as a readout option for such a detector. A test setup was installed at the test beam area at DESY and many test beams campaigns have been performed since 2010. It was demonstrated that the required spatial resolutions could be reached.

Perovskite CsPbBr3 Single‐Crystal Detector Operating at 1010 Photons s−1 mm−2 for Ultra‐High Flux X‐ray Detection

AbstractSemiconductors for detecting hard radiation are confronted with considerable problems when operating at high photon fluxes. A perovskite CsPbBr3 single‐crystal detector capable of operating at X‐ray fluxes of up to 1010 photons s−1 mm−2 with beam area ≤ 0.25 mm2 at 58.61 keV for current‐mode X‐ray detection is reported. The spectrometer‐grade melt‐grown CsPbBr3 detectors show a gamma‐ray energy resolution of ~7.5% at 122 keV for 57Co and dark current as low as 4.3 nA (0.5 nA mm−2) at a reverse bias voltage of 200 V (118 V mm−1). The detector is tested at X‐ray energies of 8.2, 10, and 58.61 keV at a synchrotron light source under a reverse bias voltage of up to 1000 V (588 V mm−1). Under a sufficiently high bias voltage and within several hundreds of seconds X‐ray exposure, good photocurrent linearity (goodness of fit R2 > 0.99) and reproducibility are obtained up to a flux of ≈1010 photons s−1 mm−2 at beam area 0.25 mm2 with Lower Limit of Detection of ≈105 photons s−1 mm−2 and Charge Collection Efficiency of ≈100% for 58.61 keV X‐rays. Accordingly, wide application of CsPbBr3 detectors in high‐flux X‐ray detection is anticipated.

Posture and Dynamics Analysis of Hydraulic Support with Joint Clearance under Impact Load

A hydraulic support is one of the key pieces of equipment in a fully mechanized coal-mining face. The shaft is seriously worn due to repeated support shifting in coal-mining operations, and the hydraulic support bears a large amount of impact load in the support process, leading to a threat to its dynamic stability. In order to study the impact load on the posture and dynamics of a hydraulic support, and considering the joint clearance of the hydraulic-support hinge point, based on the dynamics software Adams, the equivalent variable-stiffness damping system is used to replace the column, and the impact analysis model of the hydraulic support with joint clearance is established. The roof pressure is vertically applied to the load balance area of the top beam by static load, and the impact load is vertically applied to the top beam downward. Based on the above model, considering the different distributions of joint clearance, research about the influence of joint clearance on the posture and dynamic characteristics of the hydraulic support is carried out. The results show that when there is joint clearance on both sides of the hydraulic support, when the top beam bears the impact load, the X-axis PMR (position movement ratio) at different positions of the top beam is more than 80%, and the forward-tilt posture is obvious. When the hydraulic support has only unilateral clearance, the front end of the top beam bears the impact load, and the front end of the top beam moves laterally, while the rear end of the top beam mainly moves longitudinally. When the end of the top beam bears the impact load, the vertical PMR of the top beam is less than 1%. When the impact load acts on the side with joint clearance, the top beam has a certain degree of lateral offset, and the offset directions on both sides of the top beam are inconsistent. At this time, the top beam presents a torsional-bearing posture. When the front end of the top beam is loaded, the mechanical curve of each hinge point is higher than the rear-end load. For the hinge point on the side without clearance, the maximum load-fluctuation coefficient reaches 1.04, while for the hinge point on the side with clearance, the minimum load is 0 kN, which will mean some hinge points cannot to play a supporting role. The analysis results will be helpful to research hydraulic supports considering joint clearance.

TelePix – A fast region of interest trigger and timing layer for the EUDET Telescopes

Test beam facilities are essential to study the response of novel detectors to particles. At the DESY II Test Beam facility, users can test their detectors with an electron beam with a momentum from 1–6 GeV. To track the beam particles, EUDET-style telescopes are provided in each beam area. They provide excellent spatial resolution, but the time resolution is limited by the rolling shutter architecture to a precision of approximately 230 μs. Since the demand on particle rates – and hence track multiplicities – is increasing timing is becoming more relevant. DESY foresees several upgrades of the telescopes. TelePix is an upgrade project to provide track timestamping with a precision of better than 5 ns and a configurable region of interest to trigger the telescope readout. Small scale prototypes have been characterized in laboratory and test beam measurements. Laboratory tests with an injection corresponding to 2300 electrons show a S/N of above 20. Test beam characterization shows efficiencies of above 99% over a threshold range of more than 100 mV and time resolutions of 2.4 ns at low noise rates.

Using machine learning to predict gamma passing rate in volumetric-modulated arc therapy treatment plans.

This study aims to develop an algorithm to predict gamma passing rate (GPR) in the volumetric-modulated arc therapy (VMAT) technique. A total of 118 clinical VMAT plans, including 28 mediastina, 25 head and neck, 40 brains intensity-modulated radiosurgery, and 25 prostate cases, were created in RayStation treatment planning system for Edge and TrueBeam linacs. In-house scripts were developed to compute Modulation indices such as plan-averaged beam area (PA), plan-averaged beam irregularity (PI), total monitor unit (MU), leaf travel/arc length, mean dose rate variation, and mean gantry speed variation. Pretreatment verifications were performed on ArcCHECK phantom with SNC software. GPR was calculated with 3%/2mm and 10% threshold. The dataset was randomly split into a training (70%) and a test (30%) dataset. A random forest regression (RFR) model and support vector regression (SVR) with linear kernel were trained to predict GPR using the complexity metrics as input. The prediction performance was evaluated by calculating the mean absolute error (MAE), R2 , and root mean square error (RMSE). RMSEs at γ 3%/2mm for RFR and SVR were 1.407±0.103 and 1.447±0.121, respectively. MAE was 1.14±0.084 for RFR and 1.101±0.09 for SVR. R2 was equal to 0.703±0.027 and 0.689±0.053 for RFR and SVR, respectively. GPR of 3%/2mm with a 10% threshold can be predicted with an error smaller than 3% for 94% of plans using RFR and SVR models. The most important metrics that had the greatest impact on how accurately GPR can be predicted were determined to be the PA, PI, and total MU. In terms of its prediction values and errors, SVR (linear) appeared to be comparable with RFR for this dataset. Based on our results, the PA, PI, and total MU calculations may be useful in guiding VMAT plan evaluation and ultimately reducing uncertainties in planning and radiation delivery.

Tailored Surfaces on Biomedical Magnesium Alloys via Novel Beam and Friction Based Manufacturing Processes: A Review

Magnesium based alloys are attractive materials for biomedical applications as a result of their similar properties to the human bone and vital nature of the Mg ions during various functions of the human body. However, these materials suffer from poor corrosion resistance in chloride containing physiological environments. As a result, surface modification of biomedical alloys is needed to not only enhance the corrosion resistance but also biointegration characteristics. The current review article mainly focuses on beam and friction stir based techniques for surface processing of biomedical Mg alloys and composites. Each technique is further divided into sub-methods. Under the beam based processing, surface melting and bioceramic coating synthesis are discussed in detail. In the case of friction based methods, friction stir processing for grain refinement and techniques of surface modification to produce surface bioceramic composites are discussed. Furthermore, latest developments in the area of beam as well as friction stir additive manufacturing of biomedical Mg alloys and composites are elucidated. Lastly, possible directions for future progress and scaling up the lab level developments to actual applications in these materials processing areas for biomedical Mg alloys are provided.

Simulating the process of steady-state thermoreflectance for measuring the thermal conductivity of materials

The measurement of thermal conductivity by the method of steady-state thermoreflectance is based on the effect of heating the sample by laser radiation. The power of reflected radiation from the sample is measured using an additional probe laser. The change in the reflection coefficient of the studied material due to the heating is proportional to the change of the sample temperature. The radiation power absorbed by the material acts as a volumetric heat source. The value of thermal conductivity is calculated according to the Fourier’s law of thermal conductivity. A steady-state thermoreflectance setup requires calibration, i.e., thermal conductivity measurement of reference samples. The value of the calibration coefficient, in turn, depends on the characteristics of the lasers used in the setup. In this work, a numerical model of sample heating is proposed which allows considering the shape and diameter of the incident radiation beam, the distribution of radiation power over the beam area, and the absorption and reflection coefficients of the material. A methodology for samples reflection and absorption coefficients determination, including measurements and calculations considering the Fabry-Perot effect, is proposed. The study was performed for the samples of germanium, silicon, gallium arsenide, and sitall. The irradiation was performed with a continuous wave single-mode diode laser with a wavelength of 980 nm. The incident radiation power distribution over the beam area was approximated according to the Gaussian function in the OriginPro software. The radiation power that passed through the samples and reflected from them was measured. The temperature of the samples during irradiation was measured with a thermal imager. The reflection and absorption coefficients of the samples were determined from the results of radiation power measurements using a mathematical model of the interaction of plane-polarized TE electromagnetic radiation with the material. Comparison of the calculation results with the literature data for germanium, silicon, and sitall samples showed their correspondence. For gallium arsenide there was a discrepancy between the calculation results and the literature data. For gallium arsenide samples, a model considering the Fabry-Perot effect was used, and the optical properties were determined numerically by searching for the minimum modules of the transfer functions of the transmitted and reflected radiation in the Matlab program. The model of electromagnetic heating of the investigated samples was implemented in the COMSOL Multiphysics software. A method for the determination of the reflection and absorption coefficients of materials investigated by the steady-state thermorflectance is proposed. The proposed model allows considering beam shape, width and distribution of the radiation power as well as the value of the absorbed radiation power for each sample. The difference between the calculated values of the sample temperature and the measurement results does not exceed 9 %. The model can be applied to measure the thermal conductivity of bulk and thin-film materials with unknown properties.

Photobiomodulation in the management of oral mucositis for adult head and neck cancer patients receiving irradiation: the LiTEFORM RCT.

Oral mucositis is a debilitating and painful complication of head and neck cancer irradiation that is characterised by inflammation of the mucous membranes, erythema and ulceration. Oral mucositis affects 6000 head and neck cancer patients per year in England and Wales. Current treatments have not proven to be effective. International studies suggest that low-level laser therapy may be an effective treatment. To assess the clinical effectiveness and cost-effectiveness of low-level laser therapy in the management of oral mucositis in head and neck cancer irradiation. To identify barriers to and facilitators of implementing low-level laser therapy in routine care. Placebo-controlled, individually randomised, multicentre Phase III superiority trial, with an internal pilot and health economic and qualitative process evaluations. The participants, outcome assessors and therapists were blinded. Nine NHS head and neck cancer sites in England and Wales. A total of 87 out of 380 participants were recruited who were aged ≥ 18 years and were undergoing head and neck cancer irradiation with ≥ 60 Gy. Random allocation (1 : 1 ratio) to either low-level laser therapy or sham low-level laser therapy three times per week for the duration of irradiation. The diode laser had the following specifications: wavelength 660 nm, power output 75 mW, beam area 1.5 cm2, irradiance 50 mW/cm2, exposure time 60 seconds and fluence 3 J/cm2. There were 20-30 spots per session. Sham low-level laser therapy was delivered in an identical manner. The mean Oral Mucositis Weekly Questionnaire-Head and Neck Cancer score at 6 weeks following the start of irradiation. Higher scores indicate a worse outcome. A total of 231 patients were screened and, of these, 87 were randomised (low-level laser therapy arm, n = 44; sham arm, n = 43). The mean age was 59.4 years (standard deviation 8.8 years) and 69 participants (79%) were male. The mean Oral Mucositis Weekly Questionnaire-Head and Neck Cancer score at 6 weeks was 33.2 (standard deviation 10) in the low-level laser therapy arm and 27.4 (standard deviation 13.8) in the sham arm. The trial lacked statistical power because it did not meet the recruitment target. Staff and patients willingly participated in the trial and worked hard to make the LiTEFORM trial succeed. However, the task of introducing, embedding and sustaining new low-level laser therapy services into a complex care pathway proved challenging. Sites could deliver low-level laser therapy to only a small number of patients at a time. The administration of low-level laser therapy was viewed as straightforward, but also time-consuming and sometimes uncomfortable for both patients and staff, particularly those staff who were not used to working in a patient's mouth. This trial had a robust design but lacked power to be definitive. Low-level laser therapy is relatively inexpensive. In contrast with previous trials, some patients found low-level laser therapy sessions to be difficult. The duration of low-level laser therapy sessions is, therefore, an important consideration. Clinicians experienced in oral cavity work most readily adapt to delivering low-level laser therapy, although other allied health professionals can be trained. Blinding the clinicians delivering low-level laser therapy is feasible. There are important human resource, real estate and logistical considerations for those setting up low-level laser therapy services. Further well-designed randomised controlled trials investigating low-level laser therapy in head and neck cancer irradiation are needed, with similar powered recruitment targets but addressing the recruitment challenges and logistical findings from this research. This trial is registered as ISRCTN14224600. This project was funded by the National Institute for Health and Care Research ( NIHR ) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 46. See the NIHR Journals Library website for further project information.

Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes

Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

Impact of Plan Quality and Complexity Metrics on Gamma Passing Rate SIMT SRS Technique

<h3>Purpose/Objective(s)</h3> Multiple studies have reported different outcomes regarding the effect of plan complexity and quality metrics on gamma passing rate. However, there is very little information in literature regarding a single isocenter multitarget (SIMT) SRS technique. This study aims to evaluate the effect of different plan complexity metrics and quality metrics on gamma passing rate (GPR). Moreover, we aim to analyze the impact of distance to isocenter (DIS) & target size on plan quality metrics for the SIMT SRS technique. <h3>Materials/Methods</h3> 40 previously treated patient scans with 4–11 targets, an average volume of 1.2 cc and DIS range of 1.45 to 8.75 cm were used to create SIMT SRS in a treatment planning system (TPS) for a Linac using 6MV-FFF beam energy. In-house programs were developed to compute complexity metrics such as Plan averaged beam Area (PA), Plan averaged beam Irregularity (PI), Total MU, Leaf Travel (LT), mean Dose Rate variation (DR), mean Gantry Speed (GS) variation. Also, target volume, DIS, Paddick Conformity (PCI), and RTOG Conformity (RTOG_CI) indices were calculated per target & per plan. Paddick Gradient index (PGI) only was computed per plan. Patient QAs were then performed on a 4-D detector phantom using SNC software for comparison between measurements and calculated dose with objectives of 3%2mm & 10% threshold as per AAPM TG-218 recommendation. Spearman correlation was used for correlation and T-test for determining whether there are any statistically significant differences between the means of calculation per target vs per plan for PCI and RTOG_CI. <h3>Results</h3> The following results were observed: no correlation between GPR and PGI/RTOG_CI/number of targets/ target size, a positive but weak correlation between PCI & GPR (0.322, p-value = 0.023) and a negative weak correlation between DIS & GPR (-0.38, p-value = 0.01). However, a strong correlation was observed between target size & PCI/RTOG_CI/PGI (0.793, 0.719 & 0.636 respectively (p-value<0.001)), but no correlation between plan quality metrics and DIS. There was a positive weak correlation between GPR & DR/PA and a negative weak correlation between PI & GPR (0.35, 0.302 & -0.33 respectively). A moderate correlation was observed between GS & GPR (0.46, p-value= 0.0025), while no correlation was found between GPR & LT/total MU. Moreover, there was significant difference in mean PCI, RTOG_CI between per target and per plan. <h3>Conclusion</h3> GPR of SRS/SRT using single-isocenter VMAT for multiple targets is not associated with DIS, LT, total MU, and plan quality metrics. Also, DIS does not have any impact on plan quality metrics. Instead, there is a strong correlation between tumor volume & plan quality metrics, indicating volume is an important predictor for plan quality metrics. Moreover, DIS has a moderate impact on GPR, showing that a larger distance between target location and isocenter can result in lower GPR. For plan quality evaluation, calculation of PCI & RTOG_CI should be done per tumor.

Laser-Arc Hybrid Cladding of Al-Mg Alloy Coating on AZ80 Mg Alloy: Effect of Laser Beam Oscillations Amplitude.

The effect of beam oscillating amplitude on the microstructure and performance of AZ80 Mg alloy cladded with Al-Mg alloy coating by laser–arc hybrid welding was studied. The penetration depth decreases significantly while welds are widened because of the increase in the oscillating area of a laser beam. Alloy segregation and keyhole-induced porosity can be suppressed by the laser beam oscillation. With the increase in the oscillating amplitude, the Al distribution becomes uniform in the weld seam because of the rapid and fierce stirring by the oscillating laser. However, the diluting of the cladded Al alloy restrains the formation of the brittle Mg17Al12 phase, and then causes the weakening of hardness and wear resistance of the cladded layer. Considered comprehensively, the optimized oscillating amplitude was 1 mm, which can produce the weld seam with good appearance, fewer segregation and porosity defects, and acceptable hardness and wear resistance.

Dynamic MBSFN Beam Area Formation in 6G Multibeam Non-Terrestrial Networks

Providing innovative services and ensuring ubiquitous, ultrahigh-density, extreme-data-rate, and very low latency communications are essential for future sixth-generation systems, where the importance of non-terrestrial networks (NTNs) will incredibly rise. However, the management of both the capacity and the radio spectrum remains one of the main challenges, when a huge number of devices require access to dissimilar broadcast services at the same time. To cope with these issues, traditional single-beam satellite systems can be replaced with very high throughput satellite, where multibeam transmissions increase the capacity and improve the spectrum utilization while limiting interbeam interference. In this article, we propose a dynamic multicast/broadcast single-frequency network (MBSFN) beam area formation (D-MBAF) algorithm that dynamically groups beams into dedicated MBSFN beam areas (MBAs) to increase the aggregate data rate (ADR) of the multibeam NTN system and deliver a given video content to all the interested NTN terminals. D-MBAF leverages multicast subgrouping by clustering the NTN terminals into different MBAs that are simultaneously served with different data rates. Furthermore, the D-MBAF algorithm delivers the video content in different flows: the base layer with lower resolution and a set of enhancement layers with higher resolutions. Radio resources are efficiently allocated to avoid interference among the beams belonging to different MBAs. A simulation campaign is carried out under different scenarios to assess the effectiveness of the proposed D-MBAF algorithm in terms of mean throughput, ADR, resource block utilization, and number of sent layers. Obtained results confirm that the D-MBAF algorithm outperforms the single-frequency multibeam transmission and the multilayer video delivery schemes used as benchmarks.

The inclusion removal behavior during electron beam smelting of DD98M alloy

The DD98M alloy was prepared by electron beam smelting, and the effect of electron beam smelting parameters on the inclusion removal behavior was studied. The inclusion removal thermodynamics and kinetic mechanisms were analyzed. The results show that the O and N in the DD98M alloy can be reduced by 92.5% and 88.4% when smelted for 30 min with power of 12 kW, and no obvious inclusions are found in the microstructures. Increasing the smelting power or prolonging the smelting time will promote the removal of inclusion effectively. The inclusions are concentrated in the central area of the electron beam under the combined action of buoyancy and Marangoni effect. The inclusions in the near-surface area of the melt can be removed by dissolution, and the inclusion particles floating above the melt level can be decomposed under the action of electron beam bombardment.

All-MEMS Lidar Using Hybrid Optical Architecture with Digital Micromirror Devices and a 2D-MEMS Mirror.

In a lidar system, replacing moving components with solid-state devices is highly anticipated to make a reliable and compact lidar system, provided that a substantially large beam area with a large angular extent as well as high angular resolution is assured for the lidar transmitter and receiver. A new quasi-solid-state lidar optical architecture employs a transmitter with a two-dimensional MEMS mirror for fine beam steering at a fraction of the degree of the angular resolution and is combined with a digital micromirror device for wide FOV scanning over 37 degree while sustaining a large aperture area of 140 mm squared. In the receiver, a second digital micromirror device is synchronized to the transmitter DMD, which enables a large FOV receiver. An angular resolution of by was achieved with 0.588 fps for scanning 1344 points within the field of view.

Radial spin echo small-angle neutron scattering method: concept and performance.

A novel spin echo small-angle neutron scattering (SESANS) concept based on a rotationally symmetric magnetic field geometry is introduced. The proposed method is similar to the conventional linear SESANS technique but uses longitudinal precession fields and field gradients in a radial direction, as typically found in neutron spin echo (NSE) spectrometers. Radial SESANS could thus be implemented as an add-on to NSE setups. The neutron trajectory through the instrument is encoded with the help of radial gradients generated by radial shifters, which are coils placed in the beam area similar to Fresnel coils. The present work introduces the setup of the instrument and explores its performance and the relationship between the encoded momentum transfer and the precession angle. The results indicate that radial SESANS is only sensitive to scattering along the radial direction and thus measures the projected correlation function along this direction as a function of the spin echo length, defined similarly to linear SESANS. For an evaluation of the performance of the setup, the case of scattering from solid spheres is considered and the results calculated for the radial and linear SESANS cases are compared. Also discussed is the implementation of the radial magnetic field geometry in spin echo modulated small-angle neutron scattering.

Prediction of VMAT delivery accuracy using plan modulation complexity score and log-files analysis

The purpose of this study was to develop a predictive model based on plan complexity metrics and linac log-files analysis to classify the dosimetric accuracy of VMAT plans. A total of 612 VMAT plans, corresponding to 1224 arcs, were analyzed. All VMAT arcs underwent pre-treatment verification that was performed by means of the dynamic log-files generated by the linac. The comparison of predicted (by TPS) and measured (by log-files) integral fluences was performed using γ-analysis in terms of the percentage of points with γ-value smaller than one (γ%) and using a stringent 2%(local)/2 mm criteria. This γ-analysis was performed by a commercial software LinacWatch. The action limits (AL) were derived from the mean values, standard deviations and the confidence limit (CL) of the γ% distribution. A plan complexity metric, the modulation complexity score (MCS), based on the aperture beam area variability and leaf sequence variability was used as input variable of the model. A binary logistic regression (LR) model was developed to classify QA results as ‘pass’ (γ% ≥ AL) or ‘fail’ (γ% < AL). Receiver operator characteristics (ROC) curves were used to determine the optimal MCS threshold to flag ‘failed’ plans that need to be re-optimized. The model reliability was evaluated stratifying the plans in training, validation and testing groups. The confidence and action limits for γ% were found 20.1% and 79.9%, respectively. The accuracy of the model for the training and testing dataset was 97.4% and 98.0%, respectively. The optimal MCS threshold value for the identification of failed plans was 0.142, providing a true positive rate able to flag the plans failing QA of 91%. In clinical routine, the use of this MCS threshold may allow the prompt identification of overly modulated plans, then reducing the number of QA failures and improving the quality of VMAT plans used for treatment.