Communication—Electron-Beam Stimulated Release of Dislocations from Pinning Sites in GaN

To achieve low leakage in GaN-based power devices and improve reliability in optoelectronic devices such as laser diodes, it is necessary to reduce dislocation density in epitaxial layers and control their introduction during processing. We have previously shown that dislocations can be introduced at room temperature in GaN. The effect of electron-beam irradiation at fixed points on the shift of such freshly introduced dislocations in GaN is reported. Dislocations can be displaced up to 10-15 µm from the beam position. We conclude the main reason limiting the dislocation travelling distance is the existence of a high number of pinning sites.

Preliminary Design of the Support Structure for a Rotating Carbon-ion Transfer Line for Medical Applications

The development of new bent superconducting magnets together with the optimization of the support structure open the way to a considerable reduction in the weight and complexity of rotating gantries for medical applications. The magnets, which define the transfer line to deliver carbon ions to the patients from different angles, are supported by a rotating structure that should be as rigid and as lightweight as possible. Relative displacements of the magnets due to deformations cause incorrect beam position and consequent errors in hitting the target tissues. This paper describes a possible rotating structure which is considerably lighter than the previous designs. A method to compensate part of the deformation by complementary rotations of the driving motor is proposed. The influence of the construction tolerances and deformations of the supports is also analyzed and alignment and adjustment possibilities are discussed.

HOTCAP: a new software package for high-speed oscilloscope-based three-dimensional bunch charge and position measurement

A software package to be used in high-speed oscilloscope-based three-dimensional bunch-by-bunch charge and position measurement is presented. The software package takes the pick-up electrode signal waveform recorded by the high-speed oscilloscope as input, and it calculates and outputs the bunch-by-bunch charge and position. In addition to enabling a three-dimensional observation of the motion of each passing bunch on all beam position monitor pick-up electrodes, it offers many additional features such as injection analysis, bunch response function reconstruction, and turn-by-turn beam analysis. The software package has an easy-to-understand graphical user interface and convenient interactive operation, which has been verified on the Windows 10 system.

Study of the Peak to Background (P/B) Method Behavior as a Function of Take-Off Angle, Tilt Angle, Particle Size, and Beam Energy

Monte Carlo simulations were performed to investigate the behavior of the peak to background ratio (P/B) of particles on a substrate as a function of different variables such as take-off angle, tilt angle, particle size, and beam energy. The results showed that the P/B highly depends on the beam energy, the size of particles, and the composition of the substrates. Results showed that the rate of intensity reduction of the peak is less than the background for a high tilt angle (60 degrees), and thereby, the P/B increases at a high tilt angle. It was shown that by increasing the take-off angle, the P/B initially reduces and then reaches a plateau. Results showed that the P/B highly depends on the size of particles. Analyses showed that by moving the electron beam from the center to the side of the particle, the P/B increases. Finally, the spherical particles have higher sensitivity of the P/B to the beam position than the cubical particles.

Study of the steering of a wide span vehicle controlled by a local positioning system

Controlled traffic farming allows to minimize traffic-induced soil compaction by a permanent separation of the crop zone from the traffic lanes used by wide span tractors. The Authors developed an agricultural wide span vehicle equipped with a skid equipment for turning and an automatic driving system prototype based on a laser beam. The aim of this work was to study the kinematic conditions that control the steering of this machine. Furthermore, the accuracy and the maximum delay time of the signal transmission by the automatic driving system of the set-up was also assessed. In comparison with crawler tractors, the turning of the agricultural wide span vehicle needs a smaller difference in the moments applied to its right- and left-side wheels. For the predetermined accuracy of the beam position relative to the plant rows, ±ds = ±0.025 m, the accuracy of the direction of the laser beam at a distance S=200 m should not be more than ±0.07° and ±0.0014°, considering a run length of 1000 m. Furthermore, at a speed V=2.5 m s–1 a trajectory deviation φ≤5° requires a topmost delay time of the control signal of Δtmax=0.11 s is required.

Beam and sample movement compensation for robust spectro-microscopy measurements on a hard X-ray nanoprobe

Static and in situ nanoscale spectro-microscopy is now routinely performed on the Hard X-ray Nanoprobe beamline at Diamond and the solutions implemented to provide robust energy scanning and experimental operation are described. A software-based scheme for active feedback stabilization of X-ray beam position and monochromatic beam flux across the operating energy range of the beamline is reported, consisting of two linked feedback loops using extremum seeking and position control. Multimodal registration methods have been implemented for active compensation of drift during an experiment to compensate for sample movement during in situ experiments or from beam-induced effects.

MATHEMATICAL MODELING OF THE COVERING OPTIMIZATION OF THE ROUND BUILDINGS IN A PLAN WITH A RADIAL BEAM POSITION

The article presents the results of optimization of the angle between radial beams in the floor of a circular building in the plan. On the one hand, they rest on the central post, and on the other, on vertical supporting structures along the circle. Steel decking is laid on the beams. The angle between the beams is determined so that the mass of the beam and the deck is minimal. This angle is considered optimal. To solve the problem, the target function of the cost of flooring and radial beams per unit floor area is used. This function depends on the angle between the beams. Using mathematical methods of differentiation, the minimum of the objective function and the corresponding value of the optimal angle were found. The thickness of the flooring was determined on the basis of ensuring its rigidity. It is assumed that composite welded radial beams have I-beams with two axes of symmetry. The height of the beam corresponds to the equality of the areas of the shelves and the wall. The problem of determining the optimal angle between the beams was solved on the basis of ensuring the strength of the beams under normal stresses. In the design diagram of the beam, a triangular distributed load is adopted. The dimensions of the cross-section of the beam were determined based on the equality of the required and actual moments of resistance, and were included in the target cost function. The study took into account that the deflection of the beam at the optimal angle between them can exceed the limiting standard value. Based on the solution of the system of equations of strength and stiffness, a formula is obtained for the minimum angle between the beams from the stiffness condition. The carried out mathematical studies have shown that at the optimal angle between the beams, it is possible to ensure its rigidity. This is possible when the flexibility of the beam wall exceeds a certain minimum value. Analysis of the formula for the minimum value of the wall flexibility showed that it is proportional to the design steel resistance to the sixth power. Therefore, to ensure that the deflection of the beam does not exceed the limiting value at the optimum angle, it is necessary to use low strength steel. To confirm the practical feasibility of using the proposed method, the problem was solved with certain numerical data. The results obtained have confirmed that the problem has a practical meaning at a relatively low steel strength. In addition, it turned out that the optimal angle between the beams does not depend on its span.