Integrated Optimization of Procurement, Processing and Trade of Commodities in a Network Environment

We consider the integrated optimization problem of procurement, processing and trade of commodities over a network in a multiperiod setting. Motivated by the operations of a prominent commodity processing firm, we model a firm that operates a star network with multiple locations at which it can procure an input commodity and has processing capacity at a central location to convert the input into a processed commodity. The processed commodity is sold using forward contracts, while the input itself can be traded at the end of the horizon. We show that the single-node version of this problem can be solved optimally when the procurement cost for the input is piecewise linear and convex, and derive closed form expressions for the marginal value of input and output inventory. However, these marginal values are hard to compute because of high dimensionality of the state space and we develop an efficient heuristic to compute approximate marginal values. We also show that the star network problem can be approximated as an equivalent single node problem and propose heuristics for solving the network problem. We conduct numerical studies to evaluate the performance of both the single node and network heuristics. We find that the single node heuristics are near-optimal, capturing close to 90% of the value of an upper bound on the optimal expected profits. Approximating the star network by a single node is effective, with the gap between the heuristic and upper bound ranging from 7% to 14% for longer planning horizonshttp://deepblue.lib.umich.edu/bitstream/2027.42/55417/1/1095-Anupindi.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/55417/4/1095-Anupindi_2010.pd

Computational Fluid Dynamic Studies of Chemical Looping Combustion Systems

Responsible carbon management will be required for the future utilization of fossil fuels for power generation. One technology that is showing tremendous potential for carbon capture is the chemical looping combustion (CLC). CLC involves combustion of fuels by heterogeneous chemical reactions with an oxygen carrier, usually a granular metal oxide, exchanged between two fluidized beds. In any regular combustion process the oxidizer for the fuel is air which essentially is a mixture of oxygen and nitrogen. This results in a flue gas stream which consists of primarily of relatively dilute CO 2 (15 -- 20%), mixed with steam and nitrogen. In CLC, CO2 separation is easily achieved because the oxygen for the reaction is supplied by the carrier (e.g. a metal oxide), resulting in a flue gas stream consisting almost entirely of carbon dioxide and steam. The steam can be easily condensed to give pure CO2 which can then be easily sequestrated. Thus the CLC process for power generation provides a sequestration ready CO2 stream without the need for using costly gas separation techniques. The only operational penalty for CLC is then the slight pressure losses required to circulate the carrier between reactors and the carrier make-up costs. CLC requires many unit operations involving gas-solid or granular flow. Herein a computational fluid dynamic study is presented to analyze the performance of CLC systems utilizing both gaseous and solid fuels. There have been extensive experimental studies in CLC, however CFD simulations of this concept to date are quite limited. The present simulations were performed using the interpenetrating fluid representation of dense multiphase flow. The ANSYS-FLUENT(TM) CFD solver was used in the present study. The granular phases are represented as continua whose dynamics are governed by Navier-Stokes like equations, coupled to the N-S equations describing the fluid flow. Detailed sub-models to account for fluid-particle and particle-particle interaction forces have been included. Heat transfer is fully accounted for. Heterogeneous reactions are used to describe the coal conversion and the reactions of the gaseous fuel with the carrier. Global chemical reaction models of fuel and carrier were utilized. Capability of the model to simulate the segregation processes, depending on particle density and size differences between the carrier and the fuel, allows the design of a reactor with the desired behavior. The results obtained from CFD have been compared with available experimental information. The transient CFD simulations provided a reasonable agreement with the reported experimental data for batch reactors using gaseous as well as solid fuels, and for a full circulating fluid bed CLC using gaseous fuels.;The CFD models that were developed and validated using available experimental results have been applied for design evaluations of fuel reactor of CLC system utilizing char as fuel. It would be very desirable to utilize coal directly in the fuel reactor, which requires in situ gasification in either a moving or bubbling fluidized bed reactor. In such a design, H 2O (and CO2) must be recycled from the product stream as the fluidizing medium, which allows in-bed heat transfer and mediates chemical reactions between the two solid feeds (carrier and fuel), and gasifies the coal char. The solid coal fuel must be heated by the recycled metal oxide, driving off moisture and volatile material, and the remaining char must then be gasified to provide complete fuel utilization. The gaseous products of these reactions must then contact the hot, oxidized carrier before leaving the bed to obtain complete conversion of the fuel to H2O and CO 2. Further, the reduced carrier particles must be removed from the bed and returned as a pure stream to the air reactor for regeneration. It is critical that no unburned fuel, i.e., char, be returned with the spent carrier as this material will rapidly burn in the air reactor and the resulting CO2 will escape capture. Three designs have been developed and analyzed with CFD. Special attention is paid to Fe-based carriers (due to their low cost relative to other carriers), which is somewhat complicated due to the multiple oxidation states displayed by Fe. The non-linear interaction of factors such as multiphase hydrodynamics, heat transfer and chemical reaction is fully coupled in the numerical simulations allowing evaluation of design options for a full circulating CLC system using solid fuels

A theoretical analysis of the free vibrations of a clamped circular plate with damping

A theoretical analysis of the free vibrations of a clamped circular plate was undertaken. The effects of transverse shear were considered for application to relatively thick plates in which there exist sharp transients and frequencies corresponding to higher modes. The method adopted by R. D. Mindlin was used to develope [sic] the differential equation of motion for the plate. The damping effect due to the resistance of the medium in which the plate vibrates was also considered. This damping was assumed to be due to the generation of pressure waves caused by the displacement of the plate...Since the solution requires that the initial displacement function be known, the example presented is at best an approximation because the initial displacement function assumed did not include shear deformation. It should be emphasized that only one possibility of the roots of the frequency equation has been discussed in this investigation. Therefore, the solution presented is a particular solution. However, it is hoped that this is a significant first step in the study of the stated problem --Abstract, page ii-iii

Symbolic verification of timed asynchronous hardware protocols

pre-printCorrect interaction of asynchronous protocols re- quires verification. Timed asynchronous protocols add another layer of complexity to the verification challenge. A methodology and automated tool flow have been developed for verifying systems of timed asynchronous circuits through compositional model checking of formal models with symbolic methods. The approach uses relative timing constraints to model timing in asynchronous hardware protocols - a novel mapping of timing into the verification flow. Relative timing constraints are enforced at the interface external to the protocol component. SAT based and BDD based methods are explored employing both interleaving and simultaneous compositions. We present our representation of relative timing constraints, its mapping to a formal model, and results obtained using NuSMV on several moderate sized asynchronous protocol examples. The results show that the capability of previous methods is enhanced to enable the hierarchical verification of substantially larger timed systems

Gender differentials in adult mortality in India - with notes on rural-urban contrasts

This paper is a preliminary exploration of the trends and spatial variation in gender differentials in adult mortality in India, as also of the related rural-urban differentials. We pay particular attention of female mortality in the two prime reproductive age groups 15-29 and 30-44. The data for the study are taken from the Sample Registration System, available on an annual basis since 1970.

SCREENING OF SOME INDIAN HOUSEHOLD SPICES FOR COMPARATIVE STUDIES OF ANTIOXIDANT AND ANTIRADICAL ACTIVITIES BY USING IN-VITRO MODELS

 Background: India is endowed with enormous varieties of spices grown in the majority of the country and one of the largest exporters of spices in theworld. Many household spices are being used integrally in the Indian foods. Spices are normally added in the food to impart flavor. They are naturallyoccurring antioxidants, which have the potential capacity to counteract aging process in the body, to stabilize the cell membrane by scavenging freeradicals in small doses.Objectives: The current study was designed to determine antioxidant potential of some selected spices and their mixture based on the establishedscientific evidences and oxygen radical absorbance capacity values using different in vitro models and correlating.Methods: The powder of assigned spices and their mixture were alcoholically extracted by a simple maceration method. They were evaluated fortheir total phenolic and flavonoid contents. Antioxidative abilities of the extracts of spices individually and their mixtures extracts were analyzed byphosphomolybdenum assay, cupric ions reducing antioxidant capacity (CUPRAC) and ferric ions reducing ability power methods. The free radicalscavenging activities such as hydrogen peroxide, ABTS, anti-peroxidation like TBARS (thiobarbituric acid reactive substance), crocin bleaching andmetal chelation capacity were assayed through in vitro models.Results and Discussion: Antioxidant and antiradical effects of the selected spices extracts and spices mixture extract (SME) was ascertained throughdifferent in vitro models. Results of individual tests demonstrated good correlation among themselves. CUPRAC has strong correlation with all otherassays except to diphenyl-1-picrylhydrazyl (DPPH) and thiobarbituric acid reactive substances (TBARS). DPPH and TBARS were correlated with eachother however they demonstrated no relationship with other assays.Conclusion: Extracts of selected Indian spices extracts and SME have shown dissimilarity to each other. Study for the 1st time establishes aggregateindex for evaluation of Indian spices. On basis of aggregate index, nutmeg has highest value among the selected spices and no significant synergisticeffect has been found in SME. CUPRAC as antioxidant assay and hydroxyl free radical scavenging assay by using Smirnoff reagent are most appropriateassays to ascertain antioxidative and free scavenger properties of natural products.Keywords: Antioxidants, Antiradical, Oxygen Radical Absorbance Capacity, Spices, Spices Mixture Extract