A Synthesis of Tactical Fleet Planning Models for the Car Rental Industry

Daily tactical planning of the vehicle fleet is critical for a car rental business. In this decision-making process planners have to address the conflicting concerns of field management, namely, assuring adequate vehicle availability to satisfy customer demand while maintaining a high degree of utilization for each car in the fleet; this is achieved by the appropriate fleet deployment among car rental locations. This work was inspired by a series of problems encountered by the decision-makers of a major US car rental company. We first present the formulation of the tactical fleet planning model. Based on its structure, we decompose the model into a fleet deployment model and a transportation model. We develop optimal conditions for both subproblems and then we present a heuristic to reduce the gap from optimality for the complete model. We further present the application of the entire solution methodology via a case analysis for the State of Florida. Finally, we develop three extensions to the fleet deployment model to capture the cost of unsatisfied demand and fleet surplus, the service level, and a general price-demand function. We provide optimal closed-form conditions for all the extensions.     

Identification of mechanical defects in MEMS using dynamic measurements for application in production monitoring

Investigations for non-destructive characterization of MEMS (Micro-Electro-Mechanical-Systems) are presented that can be applied in production monitoring in early stages. Different aspects and experimental results are shown for quadratic and circular silicon membrane structures with artificial structural defects. The quadratic membranes were manufactured with three variations of notches at the edges. The circular membranes had residues on the backside of the membrane resulting from the etching process. The dynamic properties of the structures were measured non-destructively by scanning laser-Doppler vibrometry. The consequences of the generated defects were investigated using the resonant frequencies and mode shapes of the membrane structures in comparison to the dynamic properties of accurate membranes. The results show that the generated defects lead to a variation of the dynamic properties depending on size and position of the defect.     

Persistent Photoconductivity,Nanoscale Topography,and Chemical Functionalization Can Collectively Influence the Behavior of PC12 Cells on Wide Bandgap Semiconductor Surfaces

Wide bandgap semiconductors such as gallium nitride (GaN) exhibit persistent photoconductivity properties. The incorporation of this asset into the fabrication of a unique biointerface is presented. Templates with lithographically defined regions with controlled roughness are generated during the semiconductor growth process. Template surface functional groups are varied using a benchtop surface functionalization procedure. The conductivity of the template is altered by exposure to UV light and the behavior of PC12 cells is mapped under different substrate conductivity. The pattern size and roughness are combined with surface chemistry to change the adhesion of PC12 cells when the GaN is made more conductive after UV light exposure. Furthermore, during neurite outgrowth, surface chemistry and initial conductivity difference are used to facilitate the extension to smoother areas on the GaN surface. These results can be utilized for unique bioelectronics interfaces to probe and control cellular behavior.     

Visible light-induced charge retention and photocatalysis with hybrid CdSe-Au nanodumbbells

Visible light photocatalysis is a promising route for harnessing of solar energy to perform useful chemical reactions and to convert light to chemical energy. Nanoscale photocatalytic systems used to date were based mostly on oxide semiconductors aided by metal deposition and were operational only under UV illumination. Additionally, the degree of control over particle size and shape was limited. We report visible light photocatalysis using highly controlled hybrid gold-tipped CdSe nanorods (nanodumbbells). Under visible light irradiation, charge separation takes place between the semiconductor and metal parts of the hybrid particles. The charge-separated state was then utilized for direct photoreduction of a model acceptor molecule, methylene blue, or alternatively, retained for later use to perform the reduction reaction in the dark.     

Strategies for oxidation catalyzed by polyoxometalates at the interface of homogeneous and heterogeneous catalysis

A basic premise behind the use of polyoxometalates in oxidation chemistry is the fact that polyoxometalates are oxidatively stable. This, a priori, leads to the conclusion that for practical purposes polyoxometalates would have distinct advantages over widely investigated organometallic compounds that are vulnerable to decomposition due to oxidation of the ligand bound to the metal center. Since polyoxometalate synthesis is normally carried out in water by mixing the stoichiometrically required amounts of monomeric metal salts and adjusting the pH to a specific acidic value many structure types are accessible by variation of the reaction stoichiometry, replacement of one or more addenda atoms with other transition or main group metals, and pH control. The structural variety available has enabled the use of polyoxometalates as catalysts for oxidation of hydrocarbons and functionalized organic substrates (alcohols, amines, sulfides, etc.) with a wide range of oxygen donors ranging from molecular oxygen, hydrogen peroxide, nitrous oxide, ozone, alkyl hydroperoxides, periodate, sulfoxide and others. The wide purview of oxidation reactions is enabled because the structural variety leads to oxidation through a number of different mechanistic motifs.From a synthetic organic point of view, the most applicable uses of polyoxometalates as catalysts involve the green oxygen donors – hydrogen peroxide and molecular oxygen. Since practical applications are in hand in this area, practical considerations concerned with catalyst recycle and/or recovery and the elimination of environmentally problematic solvents are also coming to the forefront. In this paper, we will present some of our activities in the area of catalyst engineering for catalytic synthetic applications by polyoxometalates including: (a) catalytic mesoporous solids from organic-polyoxometalate hybrid materials, (b) fluorous phase polyoxometalates with and without fluorous solvents and (c) the use of aqueous biphasic media for oxidation with hydrogen peroxide.     

Einfluss der Plattendicke auf die Kontaktzeit beim elastischen Stoßvorgang

Using a free fall apparatus, the coefficient of restitution and the contact time of steel spheres at impact on thin gold‐coated glass plates were measured experimentally. The influence of the impact velocity, the particle size, and the plate thickness has been investigated. The measurements were evaluated using the Zener model. However, since the model merely considers energy dissipation due to elastic flexural waves and ignores additional energy dissipation by friction and viscous damping, the experimental values remain slightly below the theoretical Zener curve.