A Parallel Projection for the Multicommodity Network Model

We present an application of parallel computing techniques to the solution of a quadratic programme that arises in the resource-directive decomposition method for multicommodity problems. A sequential algorithm for the quadratic programme is discussed, and its extension to a parallel implementation is given. Computational testing of the sequential and parallel algorithms was done on the Sequent Symmetry S81 parallel computer located in the Parallel Processing Laboratory at Southern Methodist University. On several large test problems the parallel version achieved a speed-up of 10 with 12 processors.     

Ethane oxidation and pyrolysis from 5 bar to 1000 bar: Experiments and simulation

An extensive experimental study of ethane oxidation and pyrolysis has been conducted in the high pressure shock tube at UIC covering reflected shock pressures from 5–1000 bar, reaction temperatures up to 1550 K and stoichiometric (Φ = 1), fuel rich (Φ = 5), and pyrolytic mixtures. The experimental data has been used to develop a single model that can simulate the whole dataset very well and is the first ethane model capable of simulating experimental results over such an extensive range of pressure, temperature, and stoichiometry. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 306–331, 2005     

Ene-sulfides as Reaction Partners of Organometallic Compounds

A comparison of the reactivity of ene-sulfides and en-ethers towards organometallic reagents reveals some remarkable differences. With the thio compounds metallation at the olefinic site next to the hetero atom dominates clearly over the alternative deprotonation of an allylic position. Only with propenyl phenyl sulfide both exchange modes were observed simultaneously, whereas with all higher homologues of it as well as vinyl phenyl sulfide the metal was exclusively attached to the olefinic α-carbon atom.     

Identification and determination of flavonoids,carotenoids and chlorophyll concentration in Cynodon dactylon (L.) by HPLC analysis

Cynodon dactylon (L.) is a potent medicinal plant in the traditional and current Indian medicinal systems. The objective of this research was to find out the levels of flavonoids, carotenoids and chlorophyll b in C. dactylon leaves by high-performance liquid chromatography (HPLC) equipped with a diode array detector. HPLC analysis revealed that total carotenoid and total flavonoid concentration were 62 mg/100 g and 249.1 μg/g, respectively. The mean chlorophyll b was 85.1 mg/100 g in C. dactylon. Among the flavonoids, quercetin (164.7 μg/g) was the major flavonoid followed by kaempferol (48.2 μg/g), rutin (18.4 μg/g), catechin (12.1 μg/g) and myricetin (5.7 μg/g). Of the carotenoids, β-carotene (35.2 mg/100 g) was predominant followed by lutein (17.0 mg/100 g), violaxanthin (5.8 mg/100 g) and zeaxanthin (4.2 mg/100 g). Chlorophyll b concentration was 85.1 mg/100 g in C. dactylon. The results of this investigation should be useful information for further pharmacological studies.     

Development of a reduced biodiesel surrogate model for compression ignition engine modeling

Methylbutanoate (MB), a C₄ methyl ester, represents the simplest surrogate that captures the chemical effects of the ester moiety in biodiesel and biodiesel surrogates. An updated chemical kinetic model has been developed to characterize the ignition and flame characteristics of MB. The mechanistic elements within this model that relate to the MB and smaller ester/oxygenate sub-mechanisms are drawn from the prototypical Fisher et al. model and from more recent theory and modeling efforts. The MB model development which is based on an iterative procedure involving global sensitivity analyses to identify elementary reactions that govern ignition and subsequent high level ab initio based theoretical updates to these reaction rates are presented. The MB model makes reasonable predictions of ignition delays and laminar flame speeds.The C₅–C₇ submechanisms from the LLNL n-heptane (NH) model were merged with the present MB model to obtain a detailed chemical kinetics model for a surrogate blend representing biodiesel. The detailed MB-NH model (661 species) was reduced using graph based techniques. The robust reduction techniques employed result in a reduced model (145 species) that is in good agreement with the detailed model over a wide range of conditions. 3-D compression ignition (CI) engine simulations utilizing this reduced chemistry model for MB-NH blends as a surrogate for biodiesel show good agreement with the experimental data suggesting the utility of this model for predictions of combustion and emission characteristics of biodiesel in realistic CI engine simulations.     

Automated registration of sequential breath-hold dynamic contrast-enhanced MR images: a comparison of three techniques

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is increasingly in use as an investigational biomarker of response in cancer clinical studies. Proper registration of images acquired at different time points is essential for deriving diagnostic information from quantitative pharmacokinetic analysis of these data. Motion artifacts in the presence of time-varying intensity due to contrast enhancement make this registration problem challenging. DCE-MRI of chest and abdominal lesions is typically performed during sequential breath-holds, which introduces misregistration due to inconsistent diaphragm positions and also places constraints on temporal resolution vis-à-vis free-breathing. In this work, we have employed a computer-generated DCE-MRI phantom to compare the performance of two published methods, Progressive Principal Component Registration and Pharmacokinetic Model-Driven Registration, with Sequential Elastic Registration (SER) to register adjacent time-sample images using a published general-purpose elastic registration algorithm. In all three methods, a 3D rigid-body registration scheme with a mutual information similarity measure was used as a preprocessing step. The DCE-MRI phantom images were mathematically deformed to simulate misregistration, which was corrected using the three schemes. All three schemes were comparably successful in registering large regions of interest (ROIs) such as muscle, liver, and spleen. SER was superior in retaining tumor volume and shape, and in registering smaller but important ROIs such as tumor core and tumor rim. The performance of SER on clinical DCE-MRI data sets is also presented.     

Recovery of ammonium99Tc-pertechnetate from its reaction waste

A method is described for the recovery of NH₄ ⁹⁹TcO₄ from its reaction waste. From the collected waste solution⁹⁹Tc was precipitated as⁹⁹Tc₂S₇ which on digestion with ammoniacal hydrogen peroxide produced a mixture of NH₄ ⁹⁹TcO₄ and (NH₄)₂SO₄ from which the latter was removed by treatment with Ba(OH)₂. The solution fumished NH₄ ⁹⁹TcO₄ as a crystalline material in 54% overall yield and with 96–98% purity after chromatographic purification over Dowex 50W column. Recrystallisation of this material from aqueous ammoniacal ethanol gave the analytical material which compared well with a standard sample and with literature data in terms of its -counts/mg and its molar extinction co-efficients () at 244 and 286 nm.     

Isolation,Characterisation and Oxidation of Isomeric Ferrelactone Complexes.

Irradiation of 1,2-epoxy-l-vinylcyclopentane (1) in the presence of Fe(CO)₅ leads to the formation of isomeric $\text{syn}$-and $\text{anti}$- ferrelactones (2) and (3). The structures of these complexes were determined by X-ray crystallographic methods and on oxidation gave different ratios of β- and δ-lactones.     

Recovery of plutonium from phosphate containing aqueous analytical waste solutions using macroporous anion exchange resin

Distribution ratios of Pu(IV) between 7.5M HNO₃+0.75M H₃PO₄+0.3M H₂SO₄ media and a macroporous anion-exchange resin Amberlyst A-26 (MP) increased from 40 to 250 when 1M aluminium nitrate was added to the aqueous medium. When 1M ferric nitrate was used in place of aluminium nitrate the distribution ratio further increased to 850. The 10% Pu(IV) breakthrough capacities with a 5 ml bed resin column, using synthetic feed solutions containing 1M aluminium nitrate, were 1.4 g l^–1, 3.2 g l^–1 at flow rates of 30 ml per hour and 10 ml per hour, respectively. The corresponding 10% Pu(IV) breakthrough capacities in the presence of 1M ferric nitrate were 8.5 g l^–1 and 12.8 g l^–1. More than 97% of plutonium could be recovered from actual analytical phosphate waste solutions.     

A chemical model for redox regulation of protein tyrosine phosphatase 1B (PTP1B) activity

Growing evidence indicates that endogenously produced hydrogen peroxide acts as a cellular signaling molecule that (among other things) can regulate the activity of some protein phosphatases. Recent X-ray crystallographic studies revealed an unexpected chemical transformation underlying the redox regulation of protein tyrosine phosphatase 1B, in which oxidative inactivation of the enzyme yields an intrastrand protein cross-link between the catalytic cysteine residue and its neighboring amide nitrogen. This work describes a small organic molecule that serves as an effective model for the redox-sensing assembly of functional groups at the active site of PTP1B. Findings obtained using this model system suggest that the oxidative transformation of PTP1B to its "crosslinked" inactive form can proceed directly via oxidation of the active-site cysteine to a sulfenic acid (RSOH). The remarkably facile nature of this protein cross-link-forming reaction, along with the widespread cellular occurrence of protein sulfenic acids generated via oxidation of cysteine residues, suggests that the type of oxidative protein cross-link formation first seen in the context of PTP1B represents a potentially general mechanism for redox "switching" of protein function. Thus, the chemistry characterized here could have broad relevance to both redox-regulated signal transduction and the toxic effects of oxidative stress.