Front Beam Research Articles

Solar Influences on the Return Direction of High‐Frequency Radar Backscatter

AbstractCoherent‐scatter, high‐frequency, phased‐array radars create narrow beams through the use of constructive and destructive interference patterns. This formation method leads to the creation of a secondary beam, or lobe, that is sent out behind the radar. This study investigates the relative importance of the beams in front of and behind the high‐frequency radar located in Hankasalmi, Finland, using observations taken over a solar cycle, as well as coincident observations from Hankasalmi and the Enhanced Polar Outflow Probe Radio Receiver Instrument. These observations show that the relative strength of the front and rear beams is frequency dependent, with the relative amount of power sent to the front lobe increasing with increasing frequency. At the range of frequencies used by Hankasalmi, both front and rear beams are always present, though the main beam is always stronger than the rear lobe. Because signals are always transmitted to the front and rear of the radar, it is always possible to receive backscatter from both return directions. Examining the return direction as a function of local time, season, and solar cycle shows that the dominant return direction depends primarily on the local ionospheric structure. Diurnal changes in plasma density typically cause an increase in the amount of groundscatter returning from the rear lobe at night, though the strength of this variation has a seasonal dependence. Solar cycle variations are also seen in the groundscatter return direction, modifying the existing local time and seasonal variations.

Numerical and experimental study on the design strategy of a new collapse zone structure for railway vehicles

ABSTRACTThis study proposes the design strategy of a new collapse zone structure for railway vehicles and explores its crashing performance through numerical simulation and experiments. Starting from the one-dimensional (1D) collision analysis of two train sets, the force–displacement characteristics of each vehicle-end can be expressed in the form of a non-linear spring and the energy absorption distribution for each vehicle interface was achieved. Then, the present paper moves on to the three-dimensional (3D) finite element analysis (FEA) for the detail design of the collapse zone structure which primarily consists of front beams, rolled hollow sections (RHSs), channels and collapse initiators. The 3D resultant force–displacement response matches well with 1D characteristics. Additionally, the energy absorption of 3D computation is larger than the required value. Finally, dynamic impact tests were conducted to validate the crashworthiness of the designed energy-absorbing structure. The results showed that all the critical indicators are within 10% of both methods, which satisfies the correlation requirements of EN15227. The deformed shapes are also comparable and with reasonable agreement between the test outcomes and FEA predictions. Therefore, the design strategy is well performed and the new designed collapse zone structure is recommended as a potential absorber of impact energy.

Specially profiled reflector for spherical front beams focusing

Focusing the power emitted from a source with spherical wave front by a specially profiled reflecting surface has been attempted using the simple ray tracing method. The reflector (mirror) surface profile that achieves such power redistribution is obtained from solving an ordinary first order differential equation using common numerical techniques. Furthermore, the proposed methodology can be useful to design complex reflectors for the electomagnatic and the acoustic systems, which finds broad engineering, industrial and biomedical applications.

2D theory of wakefield amplification by active medium

A train of microbunches generates in a passive dielectric-loaded waveguide an electromagnetic wake which propagates at the speed of the particles. This wake consists of propagating modes provided the electrons exceed the Cerenkov velocity. If the material is replaced with an active dielectric, identical to that of a laser, the wake is amplified. Another train of bunches, lagging many wavelengths behind, may be accelerated by this amplified wake. The gradient is limited by breakdown and saturation of the medium. Beam loading may be partially or even completely compensated by the gain along the trailing bunch. Preliminary results of a linear theory will be presented, assuming a 300MeV beam and high-pressure CO2 mixture as an active medium. In spite of many hundreds of modes excited by the front beam, the spectrum of the amplified field corresponds to a monochromatic wave determined primarily by the bandwidth of the medium. The analytic approach facilitates simple assessment of the effect of the various parameters on the accelerating gradient.

A model and comparison of 4-wheel-drive fixed-chassis tractor rollover during Phase I

A general model to predict quasi-static articulated tractor instability on a slope has been derived using kineto-static modelling. Under simplifying assumptions, it is possible to model fixed-chassis tractors and, in particular, include the effect of front axle-wheel mass. The model is therefore used in this paper to investigate the effect of front body mass on tractor stability and behaviour during Phase I rollover. The results are of particular relevance to four-wheel-drive (4WD) tractors. The change in potential energy for fixed-chassis tractors during Phase I rollover is also evaluated. The effects of mass partitioning are displayed graphically. It is shown that the stability of a tractor depends on the position of the centre of gravity (COG) of the main (posterior) body. For tractors with massive front wheels, tyres and beam axles, this COG is likely not to be the same as that found from the standard COG methods currently adopted. • Parametric model of tractor rollover initiation for tractors with front mass. • Mass partition properties of tractors important for stability calculation. • Model predicts effect of front mass is significant in terms of stability. • Application of brakes to all wheels potentially reduces full rollover likelihood.

Simulation Study on the Heavy Parts of Pipe Hydrostatic Tester and their Structures Optimization

The FE models of the front beam and the moving trolley of pipe hydrostatic tester are built with FE simulation software ABAQUS in the study. With the FE models, the force statuses of the two heavy parts of pipe hydrostatic tester are studied. It is found that the stress of the action field of the axial force and that of small field contacting with the pins of the front beam is higher and thicker middle cylinder can significantly improve the stress of the front beam. The stress of the middle cylinder and that of small field contacting with the pins of the moving trolley is higher. Thicker middle cylinder and optimizational ribs can significantly improve the stress of the moving trolley. The front beam and the moving trolley are optimized and the strength and the stiffness of the optimized front beam and moving trolley can be satisfied with the requirement of application. The results of the study are very useful to design the pipe hydrostatic tester.

Vehicle Ride Comfort Simulation under Pulse Road Surface Based on Multi-Body Dynamics

The shock absorber model and front beam model of a domestic car are built using UG according to the existing two-dimensional drawings. And they are assembled together with the rear beam model, steering knuckles model and arm model. The ADAMS software is used to build up an assembled vehicle model, which includes front and rear suspensions, chassis, steering, tires subsystems and so on. Response characteristics of vehicle ride comfort under pulse road surface are studied through simulation.

Study on Product Design and Process Simulation of Hydroformed Automobile Framework

To achieve smaller weight, stronger strength and higher stiffness, tube hydroforming is widely used in the industry. The front beam is analysed the front beam part is redesigned based on the technics, and automotive structural lightweight and integration are achieved under the precondition of ensuring vehicle performance and security. Then, the hydroforming process of front beam is analyzed by numerical simulation based upon the elastic-plastic finite element method, Belytschko-Tsay shell element theory and dynamic explicit solution, the internal pressure loading path as the main hydroforming process parameters is discussed in detail. The present analysis provide basis for its applications.

Spatio-temporal coherence of free electron laser pulses in the soft x-ray regime

The temporal coherence properties of soft x-ray free electron laser pulses at FLASH are measured at 23.9 nm by interfering two time-delayed partial beams directly on a CCD camera. The partial beams are obtained by wave front beam splitting in an autocorrelator operating at photon energies from h nu = 30 to 200 eV. At zero delay a visibility of (0.63+/- 0.04) is measured. The delay of one partial beam reveals a coherence time of 6 fs at 23.9 nm. The visibility further displays a non-monotonic decay, which can be rationalized by the presence of multiple pulse structure.

A Lumped-Circuit Model for a Triband Trapped Dipole Array-Part II: Stacked Arrays

Demands on emergency rf links have shown how important HF (330 MHz) communications can be for medium to long range. Efficient triband antennas have been developed and are quite popular for HF communications. In part 1, we described a lumped circuit model of the KLM 4-element KT-34A antenna. Here we consider its larger companion the 6-element KT-34XA and describe retuning the model for operation in the 10-, 15- and 20-m U.S. Army Military Affiliate Radio System (MARS) bands. We retune the parallel LC-circuits acting as traps and adjust the element lengths to obtain a MARSarray. A numerical model of this type of antenna is of interest to study antenna placement and the use of stacked arrays. We compare the radiation pattern of the 6-element KLM and MARS arrays and show examples for a stacked configuration over an imperfect ground plane. The model results for the individual arrays have the expected front and rear main beam angles but when stacked these angles change in a nonintuitive manner.

Overview of Electron Cyclotron Heating and Electron Cyclotron Current Drive Launcher Development in Magnetic Fusion Devices

In any system designed for electron cyclotron (EC) heating (ECH) and EC current drive in fusion plasmas, the launcher is the matching element between the plasma and the transmission line. Only an appropriate launcher achieves efficient use of the gyrotron power for the many different high-power EC H&CD applications. The frontier is now set at ≈4 MW of launched power at 110 to 140 GHz for ≈10 s, to be further moved to ≈10 MW, 1000 s in the near future. ITER will push the limit to 20 MW, 170 GHz. The workhorse of the antenna system is the front steering setup consisting of a movable mirror, or a mirror array, in front of the hot plasma, which provides for full flexibility in the EC H&CD applications. However, because of the concern associated with cooled and movable parts in a hostile environment, an arrangement with movable mirrors positioned far from the vessel port, and connected to the plasma by imaging waveguides, is being developed as a remote steering backup solution. In a reactor, where flexibility is much less relevant than reliability, the situation could reverse. Techniques for a radial scan of the deposition layer different from front beam steering are discussed in this paper. The ideal goal would be a 100% coupling of the launched EC power, to occur within ≈2% of the plasma size and through pipes of size negligible with respect to the vessel, without negative impact on plasma periphery in spite of the high power densities transmitted through the edge.

Basic design of beamline and polarization control

The basic concept of synchrotron radiation beamlines for vacuum ultraviolet and X-ray experiments has been introduced to beginning users and designers of beamlines. The beamline defined here is composed of a front end, pre-mirrors, and a monochromator with refocusing mirrors, which are connected by beam pipes, providing monochromatic light for the experiments. Firstly, time characteristics of the synchrotron radiation are briefly reviewed. Secondly, the basic technology is introduced as the fundamental knowledge required to both users and designers. The topics are photoabsorption by air and solids, front ends and beam pipes, mirrors, monochromators, and filters. Thirdly, the design consideration is described mainly for the designers. The topics are design principle, principle of ray tracing, optical machinery and control, and vacuum. Fourthly, polarization control is considered. The topics are polarizers, polarization diagnosis of beamline, and circularly-polarized light generation. Finally, a brief summary is given introducing some references for further knowledge of the users and the designers.

Propagation of a dense relativistic electron beam through a gas

The ionization front induced by a relativistic high-density electron beam in a gas was studied in a one-dimensional (1D) approximation. The expression for the beam density corresponding to a steady front propagation was found in the limit of large (∼c) and small (⪡c) front velocities. The corresponding expression for front velocity was also found and the validity of the approximations used was verified. Finally, the values of front velocity and beam density were calculated for a wide range of beam energies and gas densities. The calculated values of the front velocity are in good agreement with the experimental data [D. Batani, S. D. Baton, M. Manclossi et al., Phys. Rev. Lett. 94, 055004 (2005).].

Improvement of the Joint Performance in Laser Welding of Aluminium Alloys

Considering the fuel consumption of cars, a light structure of aluminium alloys is desired for car bodies nowadays. However, fusion welding of aluminium alloys has some problems: reduction of joint efficiency, porosity formation, and hot cracking. In the present work, an investigation to improve the joint performance of laser welded joints has been carried out by the addition of Cu, Ni, and Zr to A6N01 alloy welds. An aluminium alloy plate of 2.0 mm in thickness with a filler metal bar was welded by a twin beam Nd: YAG laser facility (total power: 5 kW). The filler metals were prepared by changing the chemical compositions by adding elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 l/min was used. The defocusing distance was kept at 0 mm. At travel speeds of 3 to 9 m/min and at a laser power of 5 kW (front beam 2 kW, rear beam 3 kW), full penetration welds were obtained; whereas, at travel speeds of 12 to 18 m/min and the same power, partial penetration was observed. The joint efficiency of the laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining, and precipitation hardening. This type of hardening has been further considered by metallurgical examination.

Microscopy of biological sample through advanced diffractive optics from visible to x‐ray wavelength regime

The aim of this report is to demonstrate a unified version of microscopy through the use of advanced diffractive optics. The unified scheme derives from the technical possibility of realizing front wave engineering in a wide range of electromagnetic spectrum. The unified treatment is realized through the design and nanofabrication of phase diffractive elements (PDE) through which wave front beam shaping is obtained. In particular, we will show applications, by using biological samples, ranging from micromanipulation using optical tweezers to X-ray differential interference contrast (DIC) microscopy combined with X-ray fluorescence. We report some details on the design and physical implementation of diffractive elements that besides focusing also perform other optical functions: beam splitting, beam intensity, and phase redistribution or mode conversion. Laser beam splitting is used for multiple trapping and independent manipulation of micro-beads surrounding a cell as an array of tweezers and for arraying and sorting microscopic size biological samples. Another application is the Gauss to Laguerre-Gauss mode conversion, which allows for trapping and transfering orbital angular momentum of light to micro-particles immersed in a fluid. These experiments are performed in an inverted optical microscope coupled with an infrared laser beam and a spatial light modulator for diffractive optics implementation. High-resolution optics, fabricated by means of e-beam lithography, are demonstrated to control the intensity and the phase of the sheared beams in x-ray DIC microscopy. DIC experiments with phase objects reveal a dramatic increase in image contrast compared to bright-field x-ray microscopy. Besides the topographic information, fluorescence allows detection of certain chemical elements (Cl, P, Sc, K) in the same setup, by changing the photon energy of the x-ray beam.

Holographic shift multiplexing in thin volumetric media

We describe a three-dimensional theoretical model of holographic shift multiplexing in thin volumetric media in paraxial approximation. In the case of shift multiplexing with three-dimensional beams, additional cross talk is found and its origin is attributed to Bragg-matching synchronism which occurs when shift in both transverse dimensions (x and y) is considered. The origin of this cross talk is attributed to three-dimensional Bragg degeneracy. The experimental results obtained for the case of two spherical wave front beams are in excellent agreement with the theoretical predictions. We propose theoretically that the cross talk in spherical multiplexing can be minimized if reference and signal waves have the same radius of curvature.

Strain-rate effects on the energy absorption capability of crash boxes with different geometry

The front beam of vehicle body is the most important component for energy dissipation during frontal crash. It must dissipate most of the kinetic energy of the vehicle in a stable, controlled and uniform crushing process. The optimal design of a front beam, always represented by a simple thin shell prismatic column, must keep into account various design parameters such as column section, sheet thickness, and material properties including the strain rate effect. The proposed work is about the analysis of strain-rate effects on the axial crush of simple spot-welded columns having different geometric configurations. Materials are steels used in the automotive industry. Axial impact is analysed in a speed range from 0.5 mm/s up to 10 m/s, with axial loads up to 100 kN. Measured loads during crush are used to evaluate the influencing parameters, together with energy absorption indicators. Strain-rate effects on components are then evaluated comparing strain-rate influence on the material as examined in previous works.

Beam configurations for 3D tomographic intensity modulated radiation therapy

We extend the theory of three-dimensional (3D) tomographic intensity modulated radiation therapy (IMRT). The geometry consists of two-dimensional modulated beams on a sphere centred in the tumour. The theory provides an efficient algorithm for computing beam modulation patterns that approximately ‘reconstruct’ the prescribed dose function. In this paper optimum beam numbers are estimated from dose function spherical harmonics using the 3D projection-slice theorem. An extension to three dimensions of the ‘Bow Tie’ criterion for beam numbers is derived. The effects of insufficient beam front sampling and beam numbers are characterized with a configuration-dependent matrix. Factors that independently increase beam numbers, such as tumour size and shape, are related to the spherical harmonic content in the dose function. Examples of tomographic IMRT reconstruction with a 3D concave tumour are given.

Investigation of light emitting diodes using nuclear microprobes

The quality of semiconductor p–n junctions and substrates is essential for a reliable performance of microelectronic devices. The imaging techniques of ion beam induced charge (IBIC) and ionoluminescence (IL) are applied to image and analyze light emitting diodes (LEDs). The LEDs have been imaged both from the front (beam normal to p–n junction plane) and from the transverse direction (beam parallel to p–n junction plane). The imaging techniques provide details on the structural uniformity of the p–n junction and the light emitting properties, as stimulated by proton irradiation. Following IBIC and IL analysis, PIXE and RBS provide elemental distribution information on the metal layers and other components in the LEDs. The techniques which can be utilized by the nuclear microprobe potentially provide powerful tools for the failure analysis and quality control of the fabrication of microelectronic devices.

The computer construction of weaving designs

Weaving is the art of forming a fabric by interlacing threads at right angles and is performed on a frame called a loom. The threads at right angles to the weaver are the warp threads, and the threads parallel to the weaver and which are inserted between the warp threads are the weft threads. The warp threads are alternately raised and lowered to create a shed through which the weft thread is inserted. They are fastened to a warp roller at the back of the loom, pass over a back beam and through the eyes of vertical wires called heddles, and then through reeds which help keep them parallel and in the proper sequence. The woven cloth passes over a front beam and is then wound onto a cloth roller. Each row of heddles is attached to a harness, and there may be two, four, eight or more harnesses. Each warp thread passes through a heddle on any one of the harnesses. The harnesses are raised and lowered by treadles which are worked by the fingers on a table loom and by the feet on a foot loom. Harnesses may be tied together so that more than one may be operated by the same treadle. As a group of warp threads is raised or lowered by the treddles, the shuttle with the weft thread is inserted into the shed between the two groups of threads.