Electrical switching properties of nanostructured multilayer superlattice Ge–Si…Cu…Si–Ge prepared by electron beam evaporation on glass

In this study, the fabrication of nanostructured multilayer superlattice Ge–Si…Cu…Si–Ge using electron beam evaporation on glass substrates at a temperature of 200 °C has been reported. The structural, optical and electrical characteristics of such films were then studied by means of DC polarization, powder X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), Rutherford backscattering (RBS) and UV–visible spectroscopic techniques. The XRD pattern obtained showed an amorphous state along with some reflected XRD signals from the Ge planes while there were no reflected signals from the Si and Cu layers. The average estimated grain size diameter (_Dav.)$\left(D_{av.}\right)$ is 30.13 nm as found from the XRD experiment using the Debye–Scherrer equation. The grain size as estimated from the AFM images was found to be within 28–31 nm, which is in good agreement with the XRD average value. RBS analysis confirmed the multilayer structure of the superlattice. The optical allowed indirect band gap of the superlattice obtained from the Tauc plot was found to be 1.19 eV, which is greater than that of bulk Ge semiconductor (0.66 eV). This fact indicates that the incorporation of a Cu layer instead of the Ge layer enables us to change the indirect to direct transitions in Ge/Si devices. Current density–voltage (J$J$–V$V$) characteristics of the nanodevice showed an electrical switching effect (VCNR) with the largest ON/OFF current ratio of the order of 10 ⁶ at 15 V.     

1H, 13C, NH, HH, CH COSY, HH NOESY NMR and UV-vis studies of Solophenyl red 3BL dye azo-hydrazone tautomerism in various solvents

Azo-hydrazone tautomeric behavior of polyazo Solophenyl red 3BL (C.I. Direct 80) dye in different solvents (water, methanol and DMSO) was investigated using 1H, 13C, NH, HH, CH COSY, HH NOESY NMR techniques and UV-vis spectroscopy. Two-dimensional NMR experiments were used to assign 1H, 13C and 15N NMR lines unambiguously. Results showed that the hydrazone-form proton NMR signal appeared in the weakest field with respect to tetramethylsilane, in comparison with the amide and phenolic proton NMR signals. UV-vis absorption spectroscopic evidences showed that azo-hydrazone mixture exists in water and DMSO solvents, but in methanol, only azo tautomer was dominant, which was in a good agreement with NMR spectroscopic results.     

Extending Time Profile of Morphine‐Induced Analgesia Using a Chitosan‐Based Molecular Imprinted Polymer Nanogel

Chitosan‐based molecular imprinted polymer (CS‐MIP) nanogel is prepared in the presence of morphine template, fully characterized and used as a new vehicle to extend duration of morphine analgesic effect in Naval Medical Research Institute mice. The CS‐MIP nanogel with ≈25 nm size range exhibits 98% loading efficiency, and in vitro release studies show an initial burst followed by an extended slow release of morphine. In order to study the feasibility of CS‐MIP nanogel as morphine carrier, 20 mice are divided into two groups randomly and received subcutaneous injection of morphine‐loaded CS‐MIP and morphine (10 mg kg^?1) dissolved in physiologic saline. Those received injection of morphine‐loaded CS‐MIP show slower and long lasting release of morphine with 193 min effective time of 50% (ET50) analgesia compared to 120 min ET50 in mice received morphine dissolved in physiologic saline. These results suggest that CS‐MIP nanogel can be a possible strategy as morphine carrier for controlled release and extension of its analgesic efficacy.

     

Stability of a fluid in a horizontal saturated porous layer: effect of non-linear concentration profile, initial, and boundary conditions

Carbon dioxide injected into saline aquifers dissolves in the resident brines increasing their density, which might lead to convective mixing. Understanding the factors that drive convection in aquifers is important for assessing geological CO₂ storage sites. A hydrodynamic stability analysis is performed for non-linear, transient concentration fields in a saturated, homogenous, porous medium under various boundary conditions. The onset of convection is predicted using linear stability analysis based on the amplification of the initial perturbations. The difficulty with such stability analysis is the choice of the initial conditions used to define the imposed perturbations. We use different noises to find the fastest growing noise as initial conditions for the stability analysis. The stability equations are solved using a Galerkin technique. The resulting coupled ordinary differential equations are integrated numerically using a fourth-order Runge–Kutta method. The upper and lower bounds of convection instabilities are obtained. We find that at high Rayleigh numbers, based on the fastest growing noise for all boundary conditions, both the instability time and the initial wavelength of the convective instabilities are independent of the porous layer thickness. The current analysis provides approximations that help in screening suitable candidates for homogenous geological CO₂ sequestration sites.     

A converse of Baer’s theorem

Schur’s classical theorem states that for a group $G$ , if $G/Z(G)$ is finite, then $G'$ is finite. Baer extended this theorem for the factor group $G/Z_n(G)$ , in which $Z_n(G)$ is the $n$ -th term of the upper central series of $G$ . Hekster proved a converse of Baer’s theorem as follows: If $G$ is a finitely generated group such that $\gamma _{n+1}(G)$ is finite, then $G/Z_n(G)$ is finite where $\gamma _{n+1}(G)$ denotes the $(n+1)$ st term of the lower central series of $G$ . In this paper, we generalize this result by obtaining the same conclusion under the weaker hypothesis that $G/Z_n(G)$ is finitely generated. Furthermore, we show that the index of the subgroup $Z_n(G)$ is bounded by a precisely determined function of the order of $\gamma _{n+1}(G)$ . Moreover, we prove that the mentioned theorem of Hekster is also valid under a weaker condition that $Z_{2n}(G)/Z_{n}(G)$ is finitely generated. Although in this case the bound for the order of $\gamma _{n+1}(G)$ is not achieved.     

Mechanism for the degradation of erythromycin A and erythromycin A 2'-ethyl succinate in acidic aqueous solution

A major drawback of the antibiotic erythromycin A is its extreme acid sensitivity, leading to rapid inactivation in the stomach. The accepted model for degradation in aqueous acidic solution has erythromycin A in equilibrium with erythromycin A enol ether and degrading to anhydroerythromycin A. We report a detailed kinetic study of the acidic degradation of erythromycin A and of erythromycin A 2'-ethyl succinate (the market-leading pediatric prodrug), investigating the reaction rates and degradation products via NMR. This reveals that the accepted mechanism is incorrect and that both the enol ether and the anhydride are in equilibrium with the parent erythromycin. By implication, both the anhydride and enol ether are antibacterially inactive reservoirs for the parent erythromycin. The actual degradation pathway is the slow loss of cladinose from erythromycin A (or erythromycin A 2'-ethyl succinate), which is reported here for the first time in a kinetic study. The kinetic analysis is based on global, nonlinear, simultaneous least-squares fitting of time course concentrations for all species across multiple datasets to integrated rate expressions, to provide robust estimates of the rate constants.     

A new insight to the role of bubble properties on inertial effect in particle–bubble interaction

In this study the impact of bubble surface characterization (mobility or immobility), its diameter and velocity is investigated on inertial forces in particle–bubble collision efficiency (E_C). Three models including Sutherland (E_C-SU), Schulze (E_C-SC), and generalized Sutherland Equation (E_C-GSE) were taken into account with regard to their differences from the inertial point of view in the particle size range of 1–100?µm. Bubble diameters of 0.08, 0.12, and 0.15?cm and bubble velocities of 10, 20 and 30?cm/s were selected to study the flotation of chalcopyrite. Weber and Paddock collision model (E_C-W&P) was taken for evaluation of the effect of bubble surface mobility on E_C. It was found that when the bubble diameter is 0.12?cm, reducing bubble velocity from 30 to 20?cm/s, the inertia force can be ignored for wider range of particle size. Corresponding particle size in cross-sectional point between GSE and Schulze collision models was introduced for better evaluation of the positive and negative particle inertial effects. The best agreement between them was taken for bubble diameter of 0.12?cm and velocity of 20?cm/s. It was concluded that the influence of bubble velocity is more effective than bubble diameter regarding its role on particle inertial forces in particle–bubble interaction.     

Hartree-Fock, Møller-Plesset calculations and dynamic NMR study of 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one

The experimental (1)H, (13)C NMR spectra of 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one were recorded in CDCl(3) at temperature range 213-323 K. The variable temperature spectra revealed a dynamic NMR effect which is attributed to restricted rotation around the C=C double bond. Fast exchange processes of deuterium atoms between CDCl(3) and 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one or fast exchange of proton between nitrogen and oxygen atoms of carbonyl group is also revealed by broadening of N-H (singlet) proton NMR signals. Proton and carbon theoretical chemical shifts of the title molecule were calculated by using RHF and MP2-GIAO levels and different basis sets in gas phase at 298 K. The calculated proton chemical shifts show that the experimental values have no agreement with theoretical values, but for carbon chemical shifts a good agreement achieved by using RHF with 6-31G basis set and MP2/3-21G, 6-31G basis sets. Discrepancies are attributed to either the limitations of calculating program, because the change of the structure while rotation are not considered. The results showed that to select of basis set has more important rule, because RHF-GIAO level calculation with 6-31G basis set in gas phase can excellently reproduce the (13)C NMR spectrum. Moreover, MP2/3-21G, 6-31G calculation has not significant influence on (13)C NMR chemical shifts with respect to RHF-6-31G.     

Heat transfer simulation in a helically coiled tube steam generator

A symmetric helically coiled tube steam generator that operates by methane has been simulated analytically and numerically. In the analytical method, the furnace has been divided into five zones. The numerical method computes the total heat absorbed in the furnace, while the existing analytical methods compute only the radiation heat transfer. In addition, according to the numerical results, a correlation is proposed for the Nusselt number in the furnace.