Search results for: Yahel Giat
Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 2

Search results for: Yahel Giat

2 Fill Rate Window as a Criterion for Spares Allocation

Authors: Michael Dreyfuss, Yahel Giat

Abstract:

Limited battery range and long recharging times are the greatest obstacles to the successful adoption of electric cars. One of the suggestions to overcome these problems is that carmakers retain ownership of batteries and provide battery swapping service so that customers exchange their depleted batteries for recharged batteries. Motivated by this example, we consider the problem of optimal spares allocation in an exchangeable-item, multi-location repair system. We generalize the standard service measures of fill rate and average waiting time to reflect the fact that customers penalize the service provider only if they have to wait more than a ‘tolerable’ time window. These measures are denoted as the window fill rate and the truncated waiting time, respectively. We find that the truncated waiting time is convex and therefore a greedy algorithm solves the spares allocation problem efficiently. We show that the window fill rate is generally S-shaped and describe an efficient algorithm to find a near-optimal solution and detail a priori and a posteriori upper bounds to the distance from optimum. The theory is complemented with a large scale numerical example demonstrating the spare battery allocation in battery swapping stations.

Keywords: convex-concave optimization, exchangeable item, M/G/infinity, multiple location, repair system, spares allocation, window fill rate

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1 Thorium-Doped PbS Thin Films for Radiation Damage Studies

Authors: Michael Shandalov, Tzvi Templeman, Michael Schmidt, Itzhak Kelson, Eyal Yahel

Abstract:

We present a new method to produce a model system for the study of radiation damage in non-radioactive materials. The method is based on homogeneously incorporating 228Th ions in PbS thin films using a small volume chemical bath deposition (CBD) technique. The common way to alloy metals with radioactive elements is by melting pure elements, which requires considerable amounts of radioactive material with its safety consequences such as high sample activity. Controlled doping of the thin films with (very) small amounts (100-200ppm) of radioactive elements such as thorium is expected to provide a unique path for studying radiation damage in materials due to decay processes without the need of sealed enclosure. As a first stage, we developed CBD process for controlled doping of PbS thin films (~100 nm thick) with the stable isotope (t1/2~106 years), 232Th. Next, we developed CBD process for controlled doping of PbS thin films with active 228Th isotope. This was achieved by altering deposition parameters such as temperature, pH, reagent concentrations and time. The 228Th-doped films were characterized using X-ray diffraction, which indicated a single phase material. Film morphology and thickness were determined using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) mapping in the analytical transmission electron microscope (A-TEM), X-ray photoelectron spectroscopy (XPS) depth profiles and autoradiography indicated that the Th ions were homogeneously distributed throughout the films, suggesting Pb substitution by Th ions in the crystal lattice. The properties of the PbS (228Th) film activity were investigated by using alpha-spectroscopy and gamma spectroscopy. The resulting films are applicable for isochronal annealing of resistivity measurements and currently under investigation. This work shows promise as a model system for the analysis of dilute defect systems in semiconductor thin films.

Keywords: thin films, doping, radiation damage, chemical bath deposition

Procedia PDF Downloads 351