Substitution of Sr2+ by Eu3+ in Bi-2201 ceramics,effects on structure and physical properties

In this paper, we report the effects of the substitution of Sr by Eu on the properties of Bi-2201 ceramics. Samples with nominal compositions of Bi₂Sr_2?xEu_xCuO_y (x = 0–0.4) are elaborated in air by solid state reaction. They are characterized by means of X ray diffraction (XRD), scanning electron microscopy (SEM), magnetic and resistivity measurements. The undoped sample (x = 0) is monophasic and its structure belongs to phase A. No trace of superconductivity is observed down to 2 K for this sample and the variation of resistivity with temperature shows a semiconducting behaviour. As Eu is added and for x ≥ 0.2, the samples convert totally to B or Raveau phase and become superconducting. The highest T_c, obtained from both magnetic and resistivity measurements, is observed for x = 0.3. In the normal state, all the samples exhibit a semiconducting character which decreases as well as resistivity when the Eu content increases. The refinement of cell parameters is done with considering the structural modulation. The study shows that the substitution of Sr²⁺ by Eu³⁺ leads to an increase of a and b parameters, while c decreases similarly to those of the La doped phases. The a axis component of the modulation is observed to be independent of Eu content, while the c axis one increases slightly as this content increases. The XRD analysis has also revealed that the limit solubility of the used Eu₂O₃ oxide is situated between x = 0.3 and 0.4 of Eu content. The SEM micrographs show that the undoped sample consists of poorly connected grains with a random distribution. A quite different microstructure is obtained for the doped samples. The grains are more connected and have a flat shape which is characteristic of the Bi-based superconductors.     

Effect of fluorine doping on phase formation and properties of Bi(Pb)-2223 ceramics

Superconducting ceramics of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_yF_x (x = 0–0.6) are prepared in air by conventional solid state reaction and characterized. The study shows that the melting point of the samples decreases as fluorine content increases. As a consequence, the grain size increases with the doping level and for x = 0.6, the sample is completely deformed and presents a concave shape making impossible the measurements on it. The Vickers microhardness reaches its maximum for x = 0.2. The analysis of the X-ray diffraction results reveals that all the samples are composed of only Bi(Pb)-2212 and Bi(Pb)-2223 phases. The highest proportion of the high T_c phase (Bi(Pb)-2223) is also observed for x = 0.2 and is about 67.32%. The refinement of cell parameters is done by considering the structural modulation. The results show that the doping leads to a reduction of cell volume as well as the a axis component of modulation. From resistivity versus temperature measurements, it is shown that the doped phases exhibit higher onset critical transition temperatures than the undoped one. The residual resistivity increases with fluorine content suggesting that the doping introduces structural defects and disorder into the samples. The obtained critical current density at 77 K under zero magnetic field also increases with fluorine doping.     

A nonstandard finite difference method for solving a mathematical model of HIV-TB co-infection

We design and analyze an unconditionally convergent nonstandard finite-difference method to study transmission dynamics of a mathematical model of HIV-TB co-infection. The dynamics of this model are studied using the qualitative theory of dynamical systems. These qualitative features of the continuous model are preserved by the numerical method that we propose in this paper. This method also preserves positivity of the solution which is one of the essential requirements when modelling epidemic diseases. Furthermore, we show that the numerical method is unconditionally stable. Competitive numerical results confirming theoretical investigations are provided. Comparisons are also made with other conventional approaches that are routinely used to solve these types of problems.     

Static Subcategories of the Module Category of a Finite-Dimensional Hereditary Algebra

Let k be a field, Λ a finite-dimensional hereditary k-algebra, and modΛ the category of all finite-dimensional Λ-modules. We are going to characterize the representation type of Λ (tame or wild) in terms of the possible subcategories statM of all M-static modules, where M is an indecomposable Λ-module.     

Formation,characterization and stabilization of water-soluble colloidal MnO<Subscript>2</Subscript> in the oxidation of methionine,thiourea and thioacetamide by permanganate

Stabilization and characterisation of water soluble colloidal MnO₂ during the oxidation of sulphur-containing organic reductants “thiourea, thioactamide and methionine” by permanganate in aqueous neutral media are reported for the first time. Upon addition of permanganate to a solution of methionine, a transient species appears within the time of mixing, which is stable for several weeks. On the other hand, the transient species is unstable in the presence of thiourea and thioacetamide, respectively. The nature of manganese (IV) species present in the solution was characterized by spectrophotometric and coagulation measurements. On addition of HClO₄, there is a decrease in the absorbance of the reaction mixture. Under pseudo first-order conditions ([reductants] > []), the reduction rate was very fast up to the formation of water soluble colloidal MnO₂. The effect of various parameters, such as hydrogen ion concentration, amount of and concentration of reductants were investigated. Mechanisms consistent with the observed results have been proposed and discussed.     

The N-terminal His-tag affects the enantioselectivity of staphylococcal lipases: a monolayer study

In order to check the influence of the polyhistidine tag at the N-terminus of recombinant lipases, a comparative study on the interfacial properties of native and recombinant Staphylococcus simulans (SSL and rSSL) or Staphylococcus xylosus lipase (SXL and rSXL) was investigated using the monomolecular film technique. No phospholipase activity was detected with rSSL or rSXL when using different phospholipids spread as monomolecular films maintained at various surface pressures, suggesting that the His-tag in the N-terminus of the recombinant proteins, do not affect the substrate recognition. The critical surface pressure measured with monomolecular films of egg-PC was slightly lowered with the two recombinant proteins compared to the native SSL or SXL one. A kinetic study on the surface pressure dependency, stereoselectivity and regioselectivity of native and recombinant SSL or SXL was performed using three dicaprin isomers spread as monomolecular films at the air-water interface. Our results show clearly that the presence of polyhistidine tag at the N-terminus of SSL or SXL changes their stereo- and regioselectivity.     

Studies on the kinetics of growth of silver nanoparticles in different surfactant solutions

We produced gels using electrolytic-reduction ion water and magnesium aluminum silicates (smectone^®), and evaluated in detail gel properties in the presence of various types of salt (NaCl, KCl, CaCl₂, MgCl₂, and AlCl₃). Each salt was added to deionized-distilled water or electrolytic-reduction ion water, and phase diagrams for the smectone^® concentration (2.0–4.0%) were produced. The areas of the three phases of smectone^® (gel, sol, and separation) at each salt concentration were expressed as percentages of the total area. As a result, uni- and polyvalent cations (excluding Ca²⁺ ions) affected the stability of gels produced using electrolytic-reduction ion water, and, particularly, univalent cations (Na⁺, K⁺) markedly improved gel stability.Using electrolytic-reduction ion water as a dispersal medium, drug delivery systems (DDS) that can maintain the gelling state can be prepared. Thus, gel preparations with maintained functions or controlled-release transdermal drugs can be obtained.     

Anticancer and anti-inflammatory sulfur-containing semisynthetic derivatives of sarcophine

Sarcophine (1), a cembranoid diterpene is known to inhibit the process of tumorigenesis. Sarcophine can be isolated in large amounts from the Red Sea soft coral Sarcophyton glaucum and hence is an ideal target for semisynthetic or biocatalytic modifications. Hydroxylated derivatives of 1 were reported to improve its anticancer activity. Despite the promising results and ready availability, there are limited attempts towards further diversifying the library of sarcophine derivatives. Hence, the current study targets the epoxide ring to generate sulfur-containing derivatives of sarcophine by reacting it with ammonium thiocyanate and Lawesson's reagent. Structure elucidation of the products was based on extensive 1D and 2D NMR and high resolution mass spectrometry, in addition to mechanistic considerations. The effect of these derivatives on highly malignant +SA mammary epithialial cell proliferation is reported. Anti-inflammatory potential of sarcophine and its derivatives is also demonstrated.     

Preparation of chemically deposited thin films of CdS/PbS solar cell

The present paper reports the preparation of a solar cell which has a cross-sectional scheme: ITO/CdS/PbS, containing a commercially transparent conductive ITO; chemically deposited n-type CdS (340 nm) and absorbed layer of p-type PbS (1400 nm). The structural and optical properties of the constituent films are presented. X-ray diffraction showed that all of the thin films are polycrystalline. Using scanning electron microscopy, the present study revealed that the films have uniform surface morphology over the substrate. The solar cell was characterized by determining the open circuit voltage, short-circuit current density, and J–V under 40 mW/cm² solar radiation. The efficiency of the solar cells was 1.35%, which is much higher (0.041, 0.5 and 0.1–0.4%) and slightly smaller (1.65%) than some solar cells reported in the literature.