Cone-shaped Target Research Articles

Modeling simulation and experiment of micro-Doppler signature of precession

Spatial precession is a special micro-motion of the spinning-directional target, and the micro-Doppler signature of the cone-shaped target with precession is studied. The micro-motion model of precession is built first, and then the micro-Doppler model is developed based on the proposed concept of micro-motion matrix, by which the theoretical formula of micro-Doppler signature of precession is derived. In order to further approach to the actual case, the occlusion effect is firstly considered in micro-Doppler, and the simulated result with occlusion effect is well in accordance with the measured result in microwave anechoic chamber, which suggests that the micro-motion model and micro-Doppler model of precession are both valid.

Narrowband imaging method for spatial precession cone-shaped targets

The imaging method of the mid-course missile is the key technique of the missile defense system. Because of the special precession character of the ballistic missile warhead, the inverse synthetic aperture radar method cannot realize phase compensation with the constant phase offset function, which leads to blurring of the image. In this paper, we propose a new narrowband radar imaging method for the precession cone-shaped targets. The method acquires the Doppler modulation of the precession target’s scattering centers with high resolution time-frequency analysis method and extracts the Doppler parameter from the result of the time-frequency analysis with the general Radon transform, then reconstructs the scattering centers positions in the parameter domain. The experiment results with the anechoic chamber data of the representative cone-shaped object showed the effectiveness of the method.

Modeling Cytoskeletal Dynamics and Vesicle Movements in Growing Pollen Tubes

Intracellular cargo transport is a crucial process in growing plant cells. Since cellular expansion in walled cells entails the continuous assembly of new wall material, enormous amounts of polysaccharides need to be delivered to the growth site. In the rapidly elongating pollen tube the spatio-temporal movement pattern of exocytotic vesicles is precisely targeted and controlled by the continuously polymerizing actin cytoskeleton in the subapical region of the cell. Remarkably, the cone-shaped target region at the apical pole of the cylindrical cell does not contain much filamentous actin. We model the vesicular trafficking using as boundary conditions the expanding cell wall and the actin array forming the subapical actin fringe. Dynamic advancement of this actin fringe was obtained by imposing a steady shape and constant polymerization rate of the actin filaments. Letting vesicle flux into and out of the apical region be determined by the orientation of the actin microfilaments was sufficient to generate a flow that corresponds in magnitude and orientation to that observed experimentally. This model explains how the cytoplasmic streaming pattern in the apical region of the pollen tube can be generated without the presence of filamentous actin.View Large Image | View Hi-Res Image | Download PowerPoint Slide

High-quality MeV protons from laser interaction with umbrellalike cavity target

A scheme for producing high-intensity collimated MeV protons from laser interaction with an umbrellalike (cone cavity with an axial filament stemming from the apex) target back side is investigated by two- and three-dimensional particle-in-cell simulations. The process is based on target-normal sheath acceleration. The characteristics of the proton beam are analyzed and compared to that from the recently proposed cone-shaped back side target. It is found that instead of diverging after first focusing, as in the cone-shaped target, the protons produced from the umbrellalike target are well collimated. The large transverse sheath electric field at TV/m level and the self-generated quasistatic magnetic field at hundreds of megagauss level around the filament play important roles in the collimation of the protons.

Particle simulations of high-intensity laser interaction with cone targets

Hollow cone-shaped overdense plasma targets were used to investigate the generation and transport of fast particles in a high-intensity laser-matter interaction. Using 2d PIC simulations we examine cone, cone-wire and cone with an open tip target designs. Localization of electron jets and an angular spread are found in all cases of the laser-cone interaction. However, in the cone-wire geometry, at later times, the charge separation and radial electric fields around the wire collimate electron streams with an electron hot spot at the front end of the wire. The main mechanism of the electron transport in the targets is the reflection of electrons from the potential walls of the cone surface, and no significant surface electron transport is observed. Furthermore, the presence of harmonics in the reflected light suggests that the field intensity in the cone can be enhanced not only by simple multiple reflection but also by the field modulation due to harmonics generation. Moreover, it is found that the laser interaction with the open-tip cone can efficiently generate trains of short (<λ) attosecond electron sheets close to the laser axis.

Proton Acceleration in the Interaction of an Intense Laser Light with a Cone Plasma Target and Coated Proton Layer

To increase the acceleration rate for producing highly energetic protons, a scheme using a cone-shaped target with a coated proton layer is proposed and demonstrated by 2D particle-in-cell (PIC) simulation. The simulation results show that because the laser light and electrons are guided along the cone wall, the energy and density of hot electrons are enhanced in the cone target. Thus, the amplitude of the sheath field on the target's rear surface is enhanced, since it is proportional to the hot electrons' temperature and the logarithm of their density. Therefore, protons are accelerated strongly by this sheath field.

Converging shock waves in porous media

We have numerically solved several problems related to converging shock waves, including (i) one-dimensional spherical and cylindrical waves with cumulation limited to a ball or cylinder of small radius and (ii) shock-wave flow in a cone-shaped solid target. The passage from a continuous loaded substance to a porous medium in these problems leads to a significant increase in both temperature and pressure in the sample. This character of pressure variation depending on the porosity qualitatively differs from the case of plane waves of constant intensity, for which an increase in the sample porosity under otherwise equal conditions of loading always leads to a decrease in the pressure.

Path Reproduction Tests Using a Torus Treadmill

This paper describes experiments regarding navigation performance using a new locomotion interface for walking through virtual space. Although traveling on foot is the most intuitive style of locomotion, proprioceptive feedback from walking is not provided in most applications of virtual environments. We developed an infinite surface driven by actuators for enabling a sense of walking. Torus-shaped surfaces are selected to realize the locomotion interface. The device employs twelve sets of treadmills, connected side by side and driven in perpendicular directions. The virtual infinite surface is generated by the motion of the treadmills. A walker can go in any direction while his/her position is fixed in the real world. The device is called a Torus Treadmill. Navigation performance was measured by path-reproduction tests. Subjects were immersed in a virtual grass-covered plain on which a cone-shaped target object was placed. The subjects first traveled to the target object. After they reached it, the target object disappeared and the rehomed subjects were asked to return to the place where the target object was placed. We also set two target objects, and the subject traveled along a bent path. We compared two locomotion modes: walking on the Torus Treadmill and moving purely by joystick operation. The results of the bent-path experiment showed that the accuracy of the path reproduction in the Torus Treadmill mode is better than that of joystick mode.

The haefely-gfk fast-neutron generator

The radiation source of the Haefely generator is a compact, sealed neutron tube, invented by K. A. Schmidt at the German Institute for Applied Nuclear Physics of the Gesellschaft fur Kernforschung (Nuclear Research Center) in Karlsruhe. Under the terms of an exclusive worldwide agreement, Haefely is licensed to manufacture and market the Karlsruhe Intense Neutron (KARIN) generator tube. The tube has axial symmetry with a concentric 250-kV accelerating structure. A mixed beam of deuterium and tritium ions impinges radially on a cone-shaped target electrode where 14MeV neutrons of the D-T fusion reaction are generated. Integral with the tube is a tritium reservoir. The only external connections required are the power supplies and the cooling water. The KARIN generator tube is enclosed in a shielded source head to suppress all emitted neutrons not directed at the patient. The protective shield consists of layers of steel, moderating material mixed with boron, and lead. The rotating gantry that positions the source head provides isocentric source motion for multi-port treatment or arc therapy. Dose level from the source is 20 rad/min at a source-to-skin distance of 85 em, or 15 rad/min at a source-to-skin distance of 100 cm. Laboratory models of the neutron tube have provided data on tube life and performance characteristics. The prototype of a clinical fast-neutron generator for cancer therapy was installed at the Deutsches Krebsforschungszentrum (German Cancer Research Center) in Heidelberg and became operational in August 1976. Initial tests with this clinical unit will include dosimetry and neutron-field mapping, followed shortly by clinical research on fast-neutron cancer therapy. Based upon the present experience, the mean lifetime of the tube is approximately 700 hr if operated at nominal neutron yield. The Haefely fast-neutron gererator will be marketed worldwide when the prototype at the German Cancer Research Center is fully operational and has proven the claimed performance.