THE THEORETICAL COST OF SEQUENTIAL AND PARALLEL ALGORITHMS FOR SOLVING LINEAR SYSTEMS OF EQUATIONS

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Void fraction measurement by X-ray absorption

An X-ray tube and scintillation detectors were mounted on test pipes containing static voids of air–water mixture. Due to fluctuations in the X-ray tube output, void fraction measurements were carried out by using two detectors, one as a reference and the other as a void monitor. The intensity of a narrow (30–100 kV) X-ray beam transmitted through test pipes of different I.D. was measured to obtain the void fraction. The uncertainty in measuring static void fraction, was found to decrease as the void fraction increases, and to increase as X-ray energy increases. It was found that for a certain test-section pipe diameter, there exist an optimum X-ray energy that gives a minimum uncertainty in void fraction measurement.     

Iterative approximation of fixed points of Prešić operators on partial metric spaces

We study the convergence of the Pre?i? type k‐step iterative method for a class of operators satisfying Pre?i? type contractive conditions on the setting of partial metric spaces. Some examples are presented to illustrate our obtained results. As applications of the presented convergence theorems, we derive global attractivity results for a class of matrix difference equations. Numerical experiments are also presented to illustrate the theoretical findings.     

Efficient Solvent‐Free Synthesis of Benzothiazine‐Fused Pyrrolo[3,4‐c]coumarins: Cycloaddition Reactions between Coumarin‐Based Dihydrobenzothiazoles and Isocyanides

A new and unusual synthesis of benzothiazine‐fused pyrrolo[3,4‐c]coumarins, involving the ring‐opening of coumarin‐based dihydrobenzothiazoles and subsequent [4+1] cycloaddition reaction with isocyanides, was described. Thus, simple heating of various 3‐(2,3‐dihydro‐2‐methylbenzo[d]thiazol‐2‐yl)coumarins with isocyanides produced the title compounds in good yields under solvent‐free conditions.     

DFT studies on the tetranuclear cubane complex [Ni4(ampd)4(Cl4)]·MeCN

Density functional theory (DFT) is used to investigate the structural properties of Ni(II) cubane [Ni₄(ampdH)₄Cl₄]·MeCN. The structural features and ground state geometry calculations are computed at the B3LYP/6-31G* (LANL2DZ) level of theory. We shed light on the highest occupied molecular orbital and lowest unoccupied molecular orbital. The absorption spectrum is calculated using time-dependent DFT. The absorption wavelengths are calculated using different functionals, i.e., pw91pw91, B3LYP, BHandHLYP, CAM-B3LYP, LC-BLYP, and M06. The LC-BLYP is in good agreement with the experimental data.     

Synthetic Approaches towards the Sulfonamide Substituted‐1,5‐Diarylimidazole‐2‐thiones as Selective Cyclooxygense‐2 inhibitors

A new series of sulfonamide substituted 1,5‐diarylimidazole, possessing C‐2 alkylthio moiety, were synthesized for their cyclooxygense‐2 (COX‐2) inhibitory activity starting from condensation of N,N‐dibenzylaminosulfonylphenacylamine hydrochloride ( 2 ) and corresponding isothiocyanate in the presence of Et₃N, followed by alkylation in the basic medium. In concomitant with these intermediates, 2‐arylamino‐5‐arylthiazole derivatives 5 were also produced. The ratio of these two products was variable with different isothiocyanates. Final debenzylation was achieved using concentrated sulfuric acid to give the title sulfonamides 8 .     

Heat-resistant and soluble fluorinated poly(amide imide)s based on non-coplanar ortho-linked diimide-dicarboxylic acid

A series of novel fluorinated heat-resistant poly(amide imide)s (PAIS) based on non-coplanar diimide-diacid monomer (DIDA) were synthesized and characterized. The poly(amide imide)s were obtained in high yields and possessed inherent viscosities in the range of 0.47-0.91 dL g⁻¹. All of the polymers were amorphous in nature, showed outstanding solubility and could be readily soluble in common organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinoned, dimethyl sulfoxide, N,N-dimethylformamide, pyridine and tetrahydrofuran. Glass transition temperatures were in the range of 221-263 °C, as determined by differential scanning calorimetry. Degradation temperatures for 10% weight loss occurred all above 520 °C and char yields was more than 50% at 700 °C in nitrogen atmosphere. Moreover, these PAIs possessed low refractive indexes (n = 1.58-1.59), birefringence (Δn = 0.008-0.013), and dielectric constants (? ≈ 2.5) due to the trifluoromethyl pendent groups and ortho-catenated aromatic rings that interrupt chain packing and increase free volume.     

Analysis of phospholipids using an open‐tubular capillary column with a monolithic layer of molecularly imprinted polymer in capillary electrochromatography‐electrospray ionization‐tandem mass spectrometry

In this study, an open‐tubular capillary electrochromatography (OT‐CEC) column with a monolithic layer of molecularly imprinted polymer (MIP) based on methacrylic acid, ethylene glycol dimethacrylate, and 4‐styrenesulfonic acid was utilized for the simultaneous separation and characterization of phospholipid (PL) molecular structures by interfacing with electrospray ionization‐tandem mass spectrometry (ESI‐MS‐MS). Introducing an MIP‐based monolith along with charged species at the OT column made it possible to separate PL molecules based on differences in head groups and acyl chain lengths in CEC. For the interface of OT‐CEC with ESI‐MS‐MS, a simple nanospray interface utilizing a sheath flow was developed and the resulting OT‐CEC‐ESI‐MS‐MS was able to separate PL standards (phosphatidylserines, phosphatidylethanolamines, phosphatidylglycerols, phosphatidic acid, and lysophosphatidylglycerols). The developed method was applied to human urinary lipid extracts, and resulted in the separation and structural identification of 18 molecules by data‐dependent collision‐induced dissociation.     

Rates of intra- and intermolecular electron transfers in hydrogenase deduced from steady-state activity measurements

Electrons are transferred over long distances along chains of FeS clusters in hydrogenases, mitochondrial complexes, and many other respiratory enzymes. It is usually presumed that electron transfer is fast in these systems, despite the fact that there has been no direct measurement of rates of FeS-to-FeS electron transfer in any respiratory enzyme. In this context, we propose and apply to NiFe hydrogenase an original strategy that consists of quantitatively interpreting the variations of steady-state activity that result from changing the nature of the FeS clusters which connect the active site to the redox partner, and/or the nature of the redox partner. Rates of intra- and intermolecular electron transfer are deduced from such large data sets. The mutation-induced variations of electron transfer rates cannot be explained by changes in intercenter distances and reduction potentials. This establishes that FeS-to-FeS rate constants are extremely sensitive to the nature and coordination of the centers.     

Melamine-(H_2SO_4)_3 and PVP-(H_2SO_4)_n as solid acids:Synthesis and application in the first mono-and di-nitration of bisphenol A and other phenols

Melamine and poly vinylpyrrolidone（PVP） reacted with neat sulfuric acid readily to form two new organic solid acids namely melamine-（H₂SO₄）₃ and PVP-（H₂SO₄）_n.These solid acids were used for the first nitration of bisphenol A as well as other phenols in the presence of NH₄NO₃.Mono- and di-nitro bisphenol A have been characterized with IR and ¹H NMR techniques.