Facile synthesis and antimicrobial evaluations of some novel pyrazolo[3,4-b]selenolo[3,2-e]pyrazines and their related heterocycles

A new series of pyrazolopyrazinoselenolotriazolopyrimidines was synthesized by a facile method based on condensation of 5-amino-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]selenolo[3,2-e]pyrazine-6-carbonitrile ( 3 ) with triethyl orthoformate followed by intramolecular cyclization with hydrazine to afford 7-amino-8-imino-3-methyl-1-phenyl-1,8-dihydro-7H-pyrazolo[3″,4″:5′,6′]pyrazino[2′,3′:4,5] selenolo[3,2-d]pyrimidine ( 5 ). The latter compound was utilized as a multipurpose precursor for the construction of other new triazoles fused to the pyrazolopyrazino- selenolopyrimidine moiety. Alternatively, acetylation and chloro-acetylation of compound 3 using acetic anhydride and chloroacetyl chloride yielded the acetyl amino 11 and chloroacetamido 12 derivatives, respectively. Compound 12 underwent nucleophilic substitution upon reaction with morpholine to provide the morpholinyl acetamide 13 . Furthermore, the pyrazolopyridoselenolopyrazine ring system 14 was synthesized by the reaction of the o-amino-carbonitrile 3 with malononitrile. Assignment of the chemical structures for the new compounds was confirmed depending on elemental and spectral techniques. On the other hand, most of the synthesized compounds revealed promising results against various bacterial and fungal strains.     

A Semi-Supervised Learning Algorithm for Growing Neural Gas in Face Recognition

In many classification applications and face recognition tasks, there exist unlabelled data available for training along with labelled samples. The use of unlabelled data can improve the performance of a classifier. In this paper, a semi-supervised growing neural gas is proposed for learning with such partly labelled datasets in face recognition applications. The classifier is first trained on the labelled data and then gradually unlabelled data is classified and added to the training data. The classifier is retrained; and so on. The proposed iterative algorithm conforms to the EM framework and is demonstrated, on both artificial and real datasets, to significantly boost the classification rate with the use of unlabelled data. The improvement is particularly great when the labelled dataset is small. Comparison with support vector machine classifiers is also given. The algorithm is computationally efficient and easy to implement.     

Efficient way for detection of alcohols using hollow core photonic crystal fiber sensor

Optical Review - In this study, a simple hollow core hexagonal structured photonic crystal fiber is offered and analyzed to discern commonly used different type of alcohols in our daily life. The...     

Synthesis,reactions, and antioxidant activity of 3-(pyrrol-1-yl)-4,6-dimethyl selenolo[2,3-b]pyridine derivatives

Ethyl 4,6-dimethyl-3-(pyrrol-1-yl) selenolo[2,3-b]pyridine-2-carboxylate (2) was synthesized by the reaction of previously prepared ethyl 3-amino-4,6-dimethyl selenolo[2,3-b]pyridine-2-carboxylate (1) with 2,5-dimethoxytetrahydrofuran in acetic acid. The pyrrolyl ester (2) was converted into the corresponding carbohydrazide 3 which reacted with acetyl acetone, aromatic aldehydes, carbon disulfide in pyridine, and sodium nitrite to afford the corresponding dimethyl pyrazolyl 4, arylidene carbohydrazides 5a–d, oxadiazolyl thiole 6, and caboazide compound 8, respectively. The carboazide 8 reacted with different alcohols and amines to give the corresponding carbamates 9a–c and the aryl urea derivatives 10a–d. Heating of carboazide 8 in dry xylene afforded the pyridoselenolo-pyrrolopyrazinone 11. The latter compound was used as a versatile starting precursor for synthesis of other pyridoselenolo-pyrrolopyrazine compounds. The newly synthesized compounds and their derivatives were characterized by elemental analysis and spectroscopy (IR, ¹H-NMR, and mass spectra). Some of the newly synthesized pyrrolyl selenolopyridine compounds showed remarkable antioxidant activity compared to ascorbic acid.     

A 3D model of the cyclic thermomechanical behavior of shape memory alloys

The model in the first part of this paper is extended to account for SMA behavior under cyclic loading. To this end, three new state variables are introduced: internal stress B, residual strain ?_r and cumulated martensite volume fraction z_e. Several parameters of the extended model depend on z_e, making them evolve with cyclic phase change. Cyclic SMA effects including training and two-way shape memory are accounted for and several numerical simulations are provided and validated in the case of cyclic superelasticity.     

Kinetics of formation of barium tungstate in equimolar powder mixture of BaCO<Subscript>3</Subscript> and WO<Subscript>3</Subscript>

The formation of Barium monotungstate (BaWO₄) particles in equimolar powder mixtures of BaCO₃ and WO₃ was examined under isothermal and non-isothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO₂) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x–t and x–T data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600–1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO₃ species across the product layer (BaWO₄), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118–125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined non-isothermally.     

A nonlinear PSE method for two-fluid shear flows with complex interfacial topology

A nonlinear stability method is developed for laminar two-fluid shear flows which undergo changes in the interface topology. The method is based on the nonlinear parabolized stability equations (PSE) and incorporates a scalar-based interface capturing (IC) scheme in order to track complex deformations of the fluid interface. In doing so, the formulation retains the flexibility and physical insight of instability-wave based methods, while providing hydrodynamic modeling capabilities similar to direct numerical calculations: the new formulation, referred to as the IC-PSE, can capture the nonlinear physical mechanisms responsible for generating large-scale, two-fluid structures, without incurring heavy computational costs. This approach is valid for spatially developing, laminar two-fluid shear flows which are convectively unstable, and can naturally account for the growth of finite amplitude interfacial waves, along with changes to the interfacial topology. We demonstrate the accuracy of the IC-PSE against direct Navier–Stokes calculations for two-fluid mixing layers with density and viscosity stratification. The comparisons show that the IC-PSE can predict the dynamics of the instability waves and capture the formation of Kelvin–Helmholtz vortex rolls and large scale liquid structures, at an order of magnitude less computational cost than direct calculations. The role of surface tension in the IC-PSE formulation is shown to be valid for flows in which Re/We ? 1, and the method accurately predicts the formation and non-linear evolution of flow structures in this limit. This is demonstrated for spatially developing mixing layers which lead to vortex roll-up and ligaments, prior to droplet formation. The pinch-off process itself is a high surface tension phenomenon and in not considered herein. The method also accurately captures the effect of interfacial waves on the mean flow, and the topology changes during the non-linear evolution of the two-fluid structures.     

Spectral studies of Co substituted Ni-Zn ferrites

The spinel ferrites Zn_0.35Ni_0.65−xCo_xFe₂O₄, 0≤x≤1, have been prepared using the standard ceramic technique. Room temperature Mössbauer, X-ray and infrared IR spectra were used for carrying out this study. X-ray patterns reveal that all the samples have single-phase cubic spinel structure. The Mössbauer spectra of the samples show a paramagnetic phase for x=0 and a six-line magnetic pattern and a central paramagnetic phase for x≥0.1. They are analyzed and attributed to two magnetic subpatterns and two quadrupole doublets due to Fe³⁺ ions at the tetrahedral A-sites and octahedral B-sites. Four absorption bands are observed in IR spectra. They confirm the spinel structure of the samples and existence of Fe³⁺ ions in the sample sublattices. The deduced hyperfine interactions, lattice parameters, absorption band positions and intensities and force constant are found to be dependent on the substitution factor x, where the cation distribution is estimated. The hyperfine magnetic fields, magnetization and lattice resonant frequency are found to be dependent on the interionic distance.