Physics Procedia最新文献

We propose here a novel device, called the Triassico, to microscopically study the entire surface of millimeter-sized spheres. The sphere dimensions can be as small as 1 mm, and the upper limit defined only by the power and by the mechanical characteristics of the motors used. Three motorized driving rods are arranged so an equilateral triangle is formed by the rod's axes, on such a triangle the sphere sits. Movement is achieved by rotating the rods with precise relative speeds and by exploiting the friction between the sphere and the rods surfaces. The sphere can be held in place by gravity or by an opposing trio of rods. By rotating the rods with specific relative angular velocities, a net torque can be exerted on the sphere which then rotates. No repositioning of the sphere or of the motors is needed to cover the full surface with the investigating tools. An algorithm was developed to position the sphere at any arbitrary polar and azimuthal angle. The algorithm minimizes the number of rotations needed by the rods, in order to efficiently select a particular position on the sphere surface. A prototype Triassico was developed for the National Ignition Facility, of the Lawrence Livermore National Laboratory (Livermore, California, USA), as a sphere manipulation apparatus for ion microbeam analysis at Sandia National Laboratories (Albuquerque, NM, USA) of Xe-doped DT inertial confinement fusion fuel spheres. Other applications span from samples orientation, ball bearing manufacturing, or jewelry.

Manufacturing of work pieces from stainless steel with laser additive manufacturing, known also as laser sintering or 3D printing may increase energy and material efficiency. The use of powder bed fusion offers advantages to make parts for dynamic applications of light weight and near-net-shape products. Due to these advantages among others, PBF may also reduce emissions and operational cost in various applications. However, there are only few life cycle assessment studies examining this subject despite its prospect to business opportunity. The application of Life Cycle Inventory (LCI) in Powder Bed Fusion (PBF) provides a distinct evaluation of material and energy consumption. LCI offers a possibility to improve knowledge of process efficiency. This study investigates effect of process sustainability in terms of raw material, energy and time consumption with PBF and CNC machining. The results of the experimental study indicated lower energy efficiency in the production process with PBF. This study revealed that specific energy consumption in PBF decreased when several components are built simultaneously than if they would be built individually. This is due to fact that energy consumption per part is lower. On the contrary, amount of energy needed to machine on part in case of CNC machining is lower when parts are done separately.

Realistic simulation of electromagnetic wave propagation in the actual human body can expedite the investigation of the phenomenon of harvesting implanted devices using wireless powering coupled from external sources. The parallel electromagnetics code suite ACE3P developed at SLAC National Accelerator Laboratory is based on the finite element method for high fidelity accelerator simulation, which can be enhanced to model electromagnetic wave propagation in the human body. Starting with a CAD model of a human phantom that is characterized by a number of tissues, a finite element mesh representing the complex geometries of the individual tissues is built for simulation. Employing an optimal power source with a specific pattern of field distribution, the propagation and focusing of electromagnetic waves in the phantom has been demonstrated. Substantial speedup of the simulation is achieved by using multiple compute cores on supercomputers.

Coded source imaging (CSI) technique could increase the utilization rate of neutron when high L/D required in neutron imaging. The images need to be reconstructed from the raw projections. The reconstruction would amplify the noise of the raw projection, which will affect the quality of reconstructed images. Study of Signal to Noise Ratio (SNR) in CSI shows image quality depends on geometry structure and neutron beam parameters. With analysis method based on correlation reconstruction arithmetic, SNR was detailed to assess the effects from different geometry factors. Numerical simulation as a further supplement proves the rationality of analysis method. The comparison of SNR between CSI and traditional neutron radiography (NR) shows that the SNR of CSI could be better than NR in some conditions.

Standard neutron imaging procedures are based on the “shadow” of the transmitted radiation, attenuated by the sample material. Under certain conditions significant deviations from pure transmission can be found in the form of enhancement or depression at the edges of the samples. These effects can limit the quantification process in the related regions. Otherwise, an enhancement and improvement of visibility can be achieved e.g. in defect analysis. In systematic studies we investigated the dependency of these effects on the specific material (mainly for common metals), such as the sample-to-detector distance, the beam collimation, the material thickness and the neutron energy. The beam lines ICON and BOA at PSI and ANTARES at TU München were used for these experiments due to their capability for neutron imaging with highest possible spatial resolution (6.5 to 13.5 micro-meter pixel size, respectively) and their cold beam spectrum. Next to the experimental data we used a McStas tool for the description of refraction and reflection features at edges for comparison. Even if minor contributions by coherent in-line propagation phase contrast are underlined, the major effect can be described by refraction of the neutrons at the sample-void interface. Ways to suppress and to magnify the edge effects can be derived from these findings.

Spare parts for products that are at the end of their life cycles, but still under warranty, are logistically difficult because they are commonly not stored in the central warehouse. These uncommon spare parts occupy valuable space in smaller inventories and take a long time to be transported to the point of need, thus delaying the repair process. This paper proposes that storing the spare parts on a server and producing them with additive manufacturing (AM) on demand can shorten the repair cycle by simplifying the logistics. Introducing AM in the repair supply chain lowers the number of products that need to be reimbursed to the customer due to lengthy repairs, improves the repair statistics of the repair shops, and reduces the number of items that are held in stock. For this paper, the functionality of the concept was verified by reverse engineering a memory cover of a portable computer and laser sintering it from polyamide 12. The additively manufactured component fit well and the computer operated normally after the replacement. The current spare part supply chain model and models with AM machinery located at the repair shop, the centralized spare part provider, and the original equipment manufacturer were provided. The durations of the repair process in the models were compared by simulating two scenarios with the Monte Carlo method. As the biggest improvement, the model with the AM machine in the repair shop reduced the duration of the repair process from 14 days to three days. The result points to the conclusion that placing the machine as close to the need as possible is the best option, if there is enough demand. The spare parts currently compatible with AM are plastic components without strict surface roughness requirements, but more spare parts will become compatible with the development of AM.

Laser forming of sheet metal has the potential to add to the growing repertoire of laser processing. This is of particular interest for flexible manufacturing and rapid prototyping. A factor limiting the practical use is the planning of the process parameters, such as laser scan path, laser power, laser scan speed, laser spot size, dwell time, etc. This study presents a new method for calculating the error between the target shape and the current shape. The method is based on geometrical information and uses a projection of the second derivative of the target geometry unto the current geometry. By comparing the projected second derivative with the second derivative of the current geometry, the error can be calculated. Once the error has been found, a feedback control strategy can be used to update the process parameters. The new method entails that the error can be calculated without having to solve the large scale mechanical FEM as part of the planning process. This reduces the planning time and enables a simpler approach that, for the error calculation, is independent of material properties. The method is verified for a 2D feedback system for simple bends in sheet metal, using FEM simulations of the laser forming process.

An imaging facility (INUS) with thermal neutrons and γ radiations is in use at the tangential channel of the TRIGA Annular Core Pulsing Reactor (ACPR) from the Institute for Nuclear Research (INR). ACPR is a nuclear research reactor operated in steady state with a maximum power of 500 kW and in pulsing mode with a peak power of 20000 MW. ACPR was used for neutron imaging only by operation in steady state mode at a power of 100 kW. There are presented actual parameters of the facility after some beam port's and collimator's modifications, the last improvements in the remote control for different displacements with step by step motors to perform easier and faster experiments, the benefit of the using new lens, Xenon 0.95/25 mm, with low f-number (the ratio of the lens’ focal length (f) to the diameter of the aperture or iris diameter, written as f/#), that gathers more light than previously lens and the experiments for visualization of the first dynamic scenes with EM-CCD Hamamatsu C9100-02 camera. The experiments were made for static positions and movements of a pendulum with different contrast elements for thermal neutrons (captured by a ⁶Li-ZnS scintillator) and γ radiations (captured by a Lanex scintillator), with and without mono-crystal of bismuth filter in radiation beam. The effect of the bismuth filter at the formation of the image with each of the two scintillators is assessed. It is established the integration time on sensor to have the best images for static projections and minimum integration time on sensor for qualitatively analyzable images on monitor for real time imaging. Hamamatsu camera can be used now to acquire a sequence of more images with higher quality for tomography reconstructions in a given time as a consequence of the using of the new lens (because till now was not enough the maximum 10 s integration time on sensor for qualitative images) and of the control-command system with the new stepper motors that shortens the time to increment the position of the investigated object.

An experimental study of the use of graphene as an extractor (stripper) foil in the 11-MeV Siemens Eclipse Cyclotron is discussed in this paper. The main advantage of graphene is its high thermal conductivity compared to that of amorphous carbon films. Graphene also has significant mechanical strength. The lifetime of the graphene foils under proton bombardment exceeded 16,000 μAh. Graphene-based stripper foils demonstrated a significant increase in the transmission factor (defined as the ratio of the beam current on the target to the beam current on the stripper foil), which was approximately 90%. Fabrication of the graphene-based foils is discussed. The pros and cons of using the graphene material as a stripper foil in cyclotrons are analyzed.

Pulsed neutron transmission spectroscopy was applied to clarify a phase change phenomena of lead-bismuth eutectics (LBE). The melting and solidification behaviors of the LBE should be well understood to enhance the safety of an LBE-cooled accelerator driven system. In this study, the heating experiments were performed using a rectangular test section and LBE phase change process was visualized by the energy-resolved pulsed neutron imaging at BL22 RADEN facility in J-PARC and the solid/liquid interface was identified from the radiograph and Bragg edge information. The transient location of the interface was compared with measured temperature profiles and it would be useful to evaluate the LBE thermal properties.