Construction of Third-Order Diagonal Implicit Runge-Kutta Methods for Stiff Problems

We presents a new third-order diagonally implicit Runge~Kutta integration formula for stiff initial value problems, designed to be A-stable methods. The stability of the methods is analyzed and numerical results are shown to verify the conclusions.     

On the invariant mean and statistical convergence

Two concepts - one of almost convergence and the other of statistical convergence - play a very active role in recent research on summability theory. The definition of almost convergence introduced by Lorentz [G.G. Lorentz, A contribution to theory of divergent sequences, Acta Math. 80 (1948) 167–190] originated from the concept of the Banach limit, while the statistical convergence introduced by Fast [H. Fast, Sur la convergence statistique, Colloq. Math. 2 (1951) 241–244] was defined through the concept of density. Both involve non-matrix methods of summability and they are incompatible. In this work we define two new kinds of summability methods by using these two mutually incompatible concepts of the Banach limit and of density to deal with those sequences which are statistically convergent but not almost convergent or vice versa.     

Revealing the ionization ability of binding site I of human serum albumin using 2-(2'-hydroxyphenyl)benzoxazole as a pH sensitive probe

The ability of site I of human serum albumin (HSA) to bind medium sized molecules is important for the distribution, metabolism, and efficacy of many drugs. Herein, we show that this binding site has the ionization ability that may alter the drug structure during the process of its delivery. We reveal this ability by employing 2-(2'-hydroxyphenyl)benzoxazole (HBO) as a pH sensitive probe. Binding of HBO in site I is studied here at physiological pH 7.2 using steady-state and lifetime spectroscopic measurements, molecular docking and molecular dynamics (MD) simulation methods. The complex photophysics of HBO and the unique fluorescence signature of its anionic form indicate that, upon binding with HSA, the molecule exists in equilibrium between the anionic and the syn-keto forms. The position of HBO inside the binding site was determined experimentally by measuring the fluorescence quenching of W214, the sole tryptophan residue in HSA. The ionization degree of HBO inside the binding site was estimated to be close to the ionization degree of HBO in an aqueous solution of pH 10. This was concluded by comparing the fluorescence behavior of bound HBO to that of HBO in different solvents and in aqueous solutions of different pH values. Molecular docking and MD simulations show that HBO binds in site I close to W214, confirming the experimental results, and pinpoint the dominant role of hydrophobic interactions in the binding site. The formation of the anionic form is proposed to be due to through-space interaction between the OH group of HBO and both R222 and I290 with a binding mode similar to that of warfarin in site I. Comparison of the results with those of HBO mixed with key amino acids in solution indicates the importance of through-space interaction in the formation of the anion, similar to enzymatic reactions.     

Latent ruthenium initiators containing fluoro aryloxide ligands

A new ligand, methyl 2,3,5,6-tetrafluoro-4-oxybenzoate (C₈H₃F₄O₃), combining an electron withdrawing group (C₆F₄) to tune the reactivity with an anchor group (CO₂Me) for immobilization on supports, was used to prepare four new ruthenium initiators, viz. Ru(C₈H₃F₄O₃)₂(CHPh)(3-Br-C₅H₅N)(H₂IMes) and Ru(C₈H₃F₄O₃)₂XL, where X = C,N-(CHCH₂CH₂-2-C₅H₄N) and L = PⁱPr₃, PCy₃ or H₂IMes. The new ligand greatly reduced the reactivity of the ruthenium centre at room temperature. The ¹H NMR and DSC investigation for the ROMP of norbornene dicarboximide monomers clearly demonstrated that the Ru(C₈H₃F₄O₃)₂XL initiators were inactive at room temperature and required elevated temperatures for their activation.     

GC-MS and LC-MS Identification of the Phenolic Compounds Present in the ethyl Acetate Fraction Obtained from Senna tora,L. Roxb. seeds

The aim of this work is to characterize the active constituents present in the ethyl acetate fraction of Senna tora, L. Roxb. seeds. Due to the fact that the main biological activity of S. tora, L seeds is attributed to its phenolic compounds which are mainly isolated from Ethyl acetate fraction, to avoid repetition of work and to save time, it was deemed necessary to confirm the identity of these phenolic compounds. This was done by GC-MS and LC-MS analysis of the ethyl acetate fraction where the structures of the isolated compounds were established on the basis of molecular ion peak and their fragmentation pattern. They were identified as Chrysophanol, Chrysarobin, 10-hydroxy-5-methoxy-2-methyl-1, 4-anthracenedione, Rubrofusarin, Parietin, Griseoxanthone-B, Isotorachrysone, and Cumbiasin B.

     

Determination of oxolinic acid in cow's milk and human urine by means of a single-use phosphorimetric sensor

A single-use phosphorimetric drop plane sensor for the determination of oxolinic acid (OXA) is proposed. The sensor was formed by a 30x16 mm(2) rectangular strip of Mylar type polyester as solid support that contained a circular sensing zone, 6 mm in diameter and 20 mum in thickness, formed by PVC plasticized with tributylphosphate adhered to its surface. When the strip was introduced for 1 hour into a sample solution, the analyte was retained in the sensing zone, making it possible to directly measure the phosphorescence intensity emitted by the OXA in the solid phase, at lambda(exc)=330 nm and lambda(em)=449 nm. The variables that affect the construction of the sensor have been studied, along with the experimental variables that influence the fixation of the analyte in the sensor. The method's detection limit was 0.01 mg l(-1) with an applicable concentration range from 0.04 to 1.50 mg l(-1) and a repeatability of 2.6% at the concentration range of 0.8 mg l(-1). The method was applied to samples of human urine and cows' milk, with recovery percentages ranging between 97.6 and 108.7%.     

Synthesis of 4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-N-methylhydrazino-2,1,3-benzoxadiazole (DAABD-MHz) as a derivatization reagent for aldehydes in liquid chromatography/electrospray ionization-tandem mass spectrometry

Benzofurazan derivatization reagent, 4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-N-methylhydrazino-2,1,3-benzoxadiazole (DAABD-MHz), for aldehydes in liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS), was synthesized. DAABD-MHz reacted with aliphatic aldehydes under mild conditions. The generated derivatives were separated on a reversed-phase column and detected by ESI-MS/MS with detection limits of 30-60 fmol on-column. Upon collision-induced dissociation, a single and intense fragment ion at m/z 151 was observed. These results suggested that DAABD-MHz was suitable as a derivatization reagent in LC/ESI-MS/MS.     

Ensemble of a subset of <Emphasis Type="Italic">k</Emphasis>NN classifiers

Combining multiple classifiers, known as ensemble methods, can give substantial improvement in prediction performance of learning algorithms especially in the presence of non-informative features in the data sets. We propose an ensemble of subset of kNN classifiers, ESkNN, for classification task in two steps. Firstly, we choose classifiers based upon their individual performance using the out-of-sample accuracy. The selected classifiers are then combined sequentially starting from the best model and assessed for collective performance on a validation data set. We use bench mark data sets with their original and some added non-informative features for the evaluation of our method. The results are compared with usual kNN, bagged kNN, random kNN, multiple feature subset method, random forest and support vector machines. Our experimental comparisons on benchmark classification problems and simulated data sets reveal that the proposed ensemble gives better classification performance than the usual kNN and its ensembles, and performs comparable to random forest and support vector machines.     

Design and numerical analysis of a photonic crystal fiber (PCF)-based flattened dispersion THz waveguide

Optical Review - We present the modeling of a porous core dispersion flatten photonic crystal fiber (PCF) for the fruitful transmission of THz signals. The model comprises only rectangular holes in...     

Characterization of the flow over a cylinder moving harmonically in the cross-flow direction

The flow over a stationary cylinder is self-excited with a specific natural frequency f_N. When the cylinder is moved harmonically in the cross-flow direction, the response of the flow (in terms of the lift force) will contain two frequencies, namely, the natural frequency f_N and the excitation frequency f_E. When f_E is close to f_N, the natural flow response will be entrained by the excitation, and the response will be periodic with frequency f_E, and dynamicists refer to this phenomenon as lock-in or synchronization. When f_E is away from f_N, the flow will be either periodic with a period that is multiple of the excitation period (i.e., period-n) and dynamicists refer to this phenomenon as secondary synchronization or quasiperiodic consisting of two incommensurate frequencies, or chaotic. We use modern methods of non-linear dynamics to characterize these responses and show that the route to chaos is torus breakdown.