Effect of electron irradiation on the crystalline structure of hgte and hgl-xcdxte thin films

The influence of 8 MeV electrons on the crystalline structure of HgTe and Hg1-xCdxTe thin films was studied. HgTe and Hg1-xCdxTe layers were obtained by thermal evaporation and condensation in vacuum on optically flat silica glass substrates heated at different temperatures.

One finds that the results of irradiation of HgTe and Hg_1-xCd_xTe thin films with 8 MeV electrons depend on the preparation conditions of the samples, and therefore on the level of perfection of the crystalline structure and the quantity of nonstoichiometric atoms.     

1H and 13C NMR Determination of the Enantiomeric Purity of Substituted 4-Amino-3- (thien-2-Yl)-Butyric Acids and 4-Amino-3-(Benzo[b]Furan-2-yl)-Butyric Acids,Ligands of the GabaB Receptor.

The enantiomeric composition and absolute configuration of 4-Amino-3-(benzo[b]furan-2-yl)-Butanoic Acids and of 4-Amino-3-(thien-2-yl)-Butanoic Acids 1 may be accurately determined by ¹H and ¹³C nuclear magnetic resonance analysis of the corresponding derivatives 3 prepared by reaction with chiral reagents. Correlation with HPLC is signaled.     

Spectrophotometric Determination of Pyrithioxin in Pharmaceutical Preparations

Rapid direct and induced difference spectrophotometric methods for determination of pyrithioxin in single dosage forms (tablets and syrups) are reported. The direct methods depend upon measurement of the absorbance of pyrithioxin in different media at λ_max i-e at 296 nm in 0.1 M hydrochloric acid, at 328 nm in citric acid-phosphate buffer of pH 7 and at 314 nm in 0.1 M sodium hydroxide. The mean percentage recovery of the authentic samples were 100.55±0.43, 101.21±0.58 and 100.29±0.64 respectively (P=0.05). The absorbance difference methods are based upon either measurement of the difference between the acid and the alkaline solutions i-e. Δ A (Alk-Acid) at 318 nm with an accuracy of 100.72±0.88 or the absorbance difference between the acid and neutral solutions i-e Δ A (pH 7-acid) at 328 nm with an accuracy of 100.31±0.68.     

Coexistence and harvesting control policy in a food chain model with mutual defense of prey

A model is proposed to understand the dynamics in a food chain (one predator‐two prey). Unlike many approaches, we consider mutualism (for defense against predators) between the two groups of prey. We investigate the conditions for coexistence and exclusion. Unlike Elettreby's (2009) results, we show that prey can coexist in the absence of predators (as expected since there is no competition between prey). We also show the existence of Hopf bifurcation and limit cycle in the model, and numerically present bifurcation diagrams in terms of mutualism and harvesting. When the harvest is practiced for profit making, we provide the threshold effort value that determines the profitability of the harvest. We show that there is zero profit when the constant effort is applied. Below (resp. above) , there will always be gain (resp. loss). In the case of gain, we provide the optimal effort and optimal steady states that produce maximum profit and ensure coexistence. Recommendations for resource managers As a result of our investigation, we bring the following to the attention of management:

• 1. In the absence of predators, different groups of prey can coexist if they mutually help each other (no competition among them).
• 2. There is a maximal effort to invest in order to gain profit from the harvest. Above , the investment will result in a loss.
• 3. In the case of profit from harvest, policy makers should recommend the optimal effort to be applied and the optimal stock to harvest. This will guarantee maximum profit while ensuring sustainability of all species.

     

Identification of wild collected mosquito vectors of diseases using gas chromatography–mass spectrometry in Jazan Province,Saudi Arabia

Thirty‐three species of mosquitoes have been reported from the Kingdom of Saudi Arabia. Several of these mosquitoes, Anopheles gambiae Giles s.l., Anopheles stephensi Liston, Culex pipiens Linnaeus, Culex quinquefasciatus Say, Culex tritaeniorhynchus Giles, Stegomyia aegypti (Linnaeus) and Aedimorphus vexans arabiensis (Patton) are known vectors of human and animal diseases. In this study, the cuticular hydrocarbon profiles of eight mosquito species using gas chromatography–mass spectrometry were analyzed. Wild collected fourth‐instar larvae were reared, and single, newly emerged, unfed adult females were used for the analysis. A total of 146–160 peaks were detected from the cuticular extracts by gas chromatography. Repeated analysis of variance (ANOVA) and Tukey HSD Post Hoc test was used to test for quantitative differences in relative hydrocarbon quantity. In addition, a linear regression model was applied using Enter method to determine the diagnostic peaks for the eight mosquito specimens. The ANOVA test indicated that relative peaks were significant (P < 0.05) when selected pairs of peaks were compared. Also, seven compounds showed qualitative differences among the five mosquito vectors tested. The classes of constituents present were n‐alkanes, monomethylalkanes, dimethylalkanes, trimethylalkanes, alkenes, branched aromatic hydrocarbons, aldehydes and esters. These compounds have a carbon chain length ranging from 8 to 18 carbons. The most abundant compound in all adult mosquito specimens was n‐hexylacrylate [retention time (RT) 6.73 min], which was not detected in Cx. pipiens. In Cx. pipiens, the most abundant peak was benzaldehyde (RT 2.98 min). Gas chromatography–mass spectrometry is a suitable method to identify adult mosquitoes, especially from focal areas of public health concern such as Jazan Province, Saudi Arabia. This method allows a wide range of adult collected material to be identified with high accuracy. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis, characterization, and thermal investigation of some transition metal complexes of benzopyran-4-one Schiff base as thermal stabilizers for rigid poly(vinyl chloride) (PVC)

New metal complexes of Schiff base (PB) prepared from condensation reaction of 2-aminopyridine and 6-formyl-5,7-dihydroxy-2-methylbenzopyran-4-one with metal ions; Mn(II), Co(II), Ni(II), and Cu(II) are prepared. Different analysis tools like elemental analyses, FTIR, thermal analysis, conductivity, electronic spectra, and magnetic susceptibility measurements are all used to elucidate the structures of the newly prepared metal complexes. The free Schiff base (PB) has been examined as thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high induction period value (T _s) when compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate and calcium–zinc stearate (Ca–Zn soap). Blending Schiff base or its metal complexes with Mn(II), Co(II), Ni(II), and Cu(II) ions with the reference stabilizers in different ratios had a synergistic effect on the induction period (thermal stability). The stabilizing efficiency is attributed at least partially to the ability of the stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation process.     

α‐Cyanodithioic Acids and Their Corresponding Mono‐ and Dithiolate Salts as Building Blocks for the Synthesis of Novel Mercaptothiophenes

A novel and efficient method for the synthesis of mercaptothiophenes using cyanodithioic acids and their corresponding mono‐ and dithiolate salts as starting components is described.     

Stability Constants for the Equilibrium Models of Iron(III) with Several Biological Buffers in Aqueous Solutions

The complexation equilibria of Fe(III) with two buffer families, which are ubiquitous in biological system studies, were studied by potentiometric measurements at a constant ionic strength of I = 0.1 mol·dm^?3 NaNO₃ in aqueous solutions at 298.15 K. The members of TRIS family are tris(hydroxymethyl)aminomethane (TRIS), N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid (TES), N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS), N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO), and N-tris(hydroxymethyl)methyl-4-aminobutanesulfonic acid (TABS) buffers. The members of morpholine family are 4-morpholineethanesulfonic acid (MES), 4-morpholinepropanesulfonic acid (MOPS), 3-morpholino-2-hydroxypropanesulfonic acid (MOPSO), and 4-(N-morpholino) butanesulfonic acid (MOBS) buffers. The overall stability constants were determined from pH-metric data using the least-squares curve-fitting program HYPERQUAD 2008. Based on the best-fit results, the species formed at equilibrium are ML, ML₂, ML₂H_?1, and ML₃ in the systems with TRIS family buffers. The complex species ML, ML₂, ML₂H_?1, and MLH_?1 are formed in the MOPSO-containing system, while ML, ML₂, and ML₂H_?1 are formed in the systems with MES, MOPS, and MOBS. The stabilities of the complexes fall in the order TABS > TRIS > TAPS > TAPSO > TES and MOBS > MOPS > MOPSO > MES for the TRIS family and morpholine families, respectively.     

A one-pot tandem synthesis of various 1,2-disubstituted benzimidazoles

A facile method to synthesize various 1,2-disubstituted benzimidazoles is developed. It is suggested that formation of a Meisenheimer adduct between the substrate, amine, and solvent aids the N-arylation process. The generality of the protocol is demonstrated by the efficient reactions involving numerous substituents ranging from electron-withdrawing groups to electron-donating groups.