Analytical models for supplier selection and order quantity allocation

In the literature, decision models and techniques for supplier selection do not often consider inventory management of the items being purchased as part of the analysis. In this article, two mixed integer nonlinear programming models are proposed to select the best set of suppliers and determine the proper allocation of order quantities while minimizing the annual ordering, inventory holding, and purchasing costs under suppliers’ capacity and quality constraints. The first model allows independent order quantities for each supplier while the second model restricts all order quantities to be of equal size, as it would be required in a multi-stage (supply chain) inventory model. Illustrative examples are used to highlight the advantages of the proposed models over a previous model introduced in the literature.     

Formation of simple organic molecules in the interstellar medium

In this work we present a methodology for the synthesis of simple molecules from basic formaldehyde (H₂CO) precursors. We have approached this challenging problem by considering a basic dimerization scheme that eventually leads to diose and methyl formate, using an HCO⁺ proton source. This species was chosen due to its ample abundance in the atmosphere. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A modular approach to a new class of phosphinohydrazones and their use in asymmetric allylic alkylation reactions

A group of five phosphino hydrazones with a pendant binaphthyl unit as a chiral modifier has been synthesized from non-racemic 2,2′-bis(bromomethyl)-1,1′-binaphthyl and 3,3′-diiodo-2,2′-bis(bromomethyl)-1,1′-binaphthyl as the key intermediates. Their efficiency as chiral ligands in palladium-catalyzed allylic alkylation reactions has been investigated showing up to 95% ee under optimized conditions. X-ray diffraction structures of mono- and dimeric Pd complexes are also reported.     

Electron paramagnetic resonance of some lanthanide ions in yttrium and lutetium vanadate

The electron paramagnetic resonance (EPR) parameters have been determined for the trivalent ions neodymium, erbium and ytterbium, at low abundance in lutetium vanadate. Crystal field splittings produce ground states which are Kramers doublets, and measurements were made of theg-values both parallel and perpendicular to the tetragonal axis; they are compared with previous measurements in yttrium vanadate. Two of the crystal field splitting parameters of the trivalent gadolinium ion (S = 7/2) in LuVO₄ show noticeable difference from those in YVO₄.     

Control limits for two-state partially observable Markov decision processes

A production process can be in either a GOOD or a BAD state. The true state is unknown and can only be inferred from observations. If the state is good during one period it may deteriorate and become bad during the next period. Two actions are available: CONTINUE or REPLACE (for a fixed cost). The objective is to maximize the expected discounted value of the total future profits.     

Biodegradable polycaprolactone–polyanhydrides blends

Biodegradable polymers based on a blend of polycaprolactone (PCL) and aliphatic polyanhydrides with various monomer lengths were prepared to obtain desired polymer blends for use as drug carriers. The physicochemical, mechanical, and drug‐release properties of these blends were investigated by various techniques to evaluate the uniformity degree of the polymer blends to establish their potential applications in drug delivery. The results demonstrated that the heat of fusion (ΔH) of the polyanhydride or the blend is increased in relation to the length of the aliphatic chain. However, the blends had different properties than pure polyanhydride, and the crystallization degree of the blends, as expressed by the ΔH, decreased in relation to the ΔH of the pure polyanhydride. Drug‐release studies from blends of PCL and aliphatic polyanhydrides demonstrated first‐order kinetics of the release rate. Polymer degradation was independent at the polyanhydride monomer length. On the basis of theoretical calculation of the interaction factor, a blend of PCL and poly(dodecanedeoic anhydride) was chosen for further elucidation of its thermal, mechanical, and degradation properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3781–3787, 2003     

Long-range acoustic scattering from a shallow-water mud-volcano cluster

Analysis of reverberation measurements in the Straits of Sicily shows high intensity, discrete, scattered returns 10-20 dB above background reverberation. These returns are due to scattering from mud volcanoes. The reverberation from the mud volcanoes at ranges of 15-22 km is reasonably consistent over these spatial scales (i.e., kilometers) and temporal scales of several hours; measurements separated by 4 years are also similar. Statistical characterization indicates that the reverberation associated with a mud-volcano cluster is strongly non-Rayleigh and that the reverberation can be characterized by a single (shape) parameter, roughly independent of frequency. The non-Rayleigh statistics, with a concomitant increase in the probability of false alarm, indicate that mud volcanoes are a likely source of clutter. Mean target strengths were estimated at 1-11 dB over 160-1400 Hz and are consistent with target strengths measured during a different year at short (direct-path) ranges. Accumulated evidence points to small (order 10 m diameter and several meters high) carbonate chimneys on the mud-volcano edifice as the scattering mechanism as opposed to the edifice itself or scattering from gas bubbles in the water column. Thus, the results represent acoustic scattering from mud volcanoes in a quiescent state.     

Influence of root resistivity on plant water uptake mechanism,Part II: analytical solutions for low/moderate soil-root conductivity ratio

A one-dimensional approximate analytical model, which preserves the main features of soil-crop-atmospheric hydrodynamics, has been suggested for plant roots of low soil-root conductivity ratio (SRCR). The proposed approach involves physically based concepts, such as mass balance equation, Darcy’s law, and related water uptake and plant transpiration functions. Two main assumptions have been made to derive the analytical solution: (1) gravitational flow is adopted and (2) the uniform soil moisture distribution within the root water activity zone is supposed. The mass balance equation in its integral form is solved by the method of characteristics. This leads to the two functional equations for soil pressure head and root potential, which can be solved simultaneously by using common software. The model has been further verified against the numerical one. The model represents a reasonable compromise between the complicated mechanism of unsaturated water flow with root water uptake (RWU) and still insufficient knowledge of the soil-plant-atmospheric continuum. It is able to account for temporal fluctuations in root activity zone and provides a relatively simple algorithm for investigation of RWU-mechanism. Besides the theoretical and applicative importance, this flow model yields water and velocity distributions within soil profile, and, thereby, constitutes a preliminary step toward solution of contaminant transport problems in vadose zone. Deceased