The photogalvanic effect of Fe(II)-β-diketonate/thionine systems in aqueous acetonitrile

Summary The photogalvanic effect of ferrousbis-(acetylacetonate) (Fe(II)(acac)₂) and ferrousbis-(trifluoroacetylacetonate) (Fe(II)(tfac)₂) complexes in aqueous acetonitrile thionine dye solutions has been studied in a photogalvanic cell of 70 cm³ capacity with identical platinum electrodes (area: 0.25 cm²) using visible light (80 mW/cm²) at 25°C. The theoretical Sunlight Engineering Efficiency (SEE) was determined for both complexes and it was found that the best SEE was obtained when Fe(II)(tfac)₂ was used at a concentration of 1.5×10^–4 mol/dm³ with a thionine concentration of 1×10^–4 mol/dm³ atpH=4 in 40% aqueous acetonitrile. Effects of incident light intensity and temperature on the photogalvanic performance and the action spectrum of the present system were also investigated. A mechanism of the photoredox reaction between the Fe(II)-complex and the dye molecule is proposed.

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Der photogalvanische Effekt von Fe(II)--Diketonat/Thionin-Systemen in wäßrigem Acetonitril

Zusammenfassung Der photogalvanische Effekt von Eisen(II)-bis-(acetonylacetonat) (Fe(II)(acac)₂) und Eisen(II)-bis-(trifluoracetylacetonat) (Fe(II)(tfac)₂ in wäßriger acetonitrilischer Thioninlösung wurde in einer photogalvanischen Zelle (70 cm³) mit identischen Platinelektroden (Fläche: 0.25 cm²) mit sichtbarem Licht (80 mW/cm²) bei 25°C untersucht. Für beide Komplexe wurde die theoretische Sunlight Engineering Efficiency (SEE) bestimmt; der beste SEE-Wert wurde für Fe(II)(tfac)₂ bei einer Konzentration von 1.5×10^–4 mol/dm³ beipH=4 in 40%igem Acetonitril gefunden (Thioninkonzentration: 1.0×10^–4 mol/dm³). Effekte, die durch Änderung der Lichtintensität und der Temperatur hervorgerufen werden, werden diskutiert. Ein Mechanismus für die Photoredoxreaktion zwischen dem Fe(II)-Komplex und dem Farbstoffmolekül wird vorgeschlagen.

     

Matrix Heterogeneity Effects on Gas Transport and Adsorption in Coalbed and Shale Gas Reservoirs

In coalbeds and shales, gas transport and storage are important for accurate prediction of production rates and for the consideration of subsurface greenhouse gas sequestration. They involve coupled fluid phenomena in porous medium including viscous flow, diffusive transport, and adsorption. Standard approach to describe gas–matrix interactions is deterministic and neglects the effects of local spatial heterogeneities in porosity and material content of the matrix. In this study, adopting weak-noise and mean-field approximations and using a statistical approach in spectral domain, matrix heterogeneity effects are investigated in the presence of non-equilibrium adsorption with random partition coefficient. It is found that the local heterogeneities can generate non-trivial transport and kinetic effects which retard gas release from the matrix and influence the ultimate gas recovery adversely. Macro-transport shows 1/[1 + N _Pe /(1 + N _Pe )] dependence on the Péclet number, and persists at the diffusive ultra-low permeability limit. Macro-kinetics is directly related to Thiele modulus by the following expression: N _Th /(1 + 2N _Pe ). It leads to trapping of gas in the adsorbed phase during its release from the matrix, and to an adsorption threshold during the gas uptake by the matrix. Both effects are proportional to the initially available adsorbed gas amount and becomes more pronounced with the increasing variance of the porosity field. Consequently, a new upscaled deterministic gas mass balance is proposed for practical purposes. Numerical results are presented showing free and adsorbed gas distributions and fractional gas sorption curves for unipore coal matrix exhibiting Gaussian porosity distribution. This study is a unique approach for our further understanding of the coalbeds and gas shales, and it is important for the development of sound numerical gas production and sequestration models.     

New macrocyclic complexes containing amide,imine and secondary amine functions

New double-ring octa-aza macrocyclic complexes, synthesized by condensation of oxamide-N,N-diethanoic acid with diethylenetriamine in 1:2 ratio in the presence of CuII, NiII or CoII, have been characterized by elemental analyses, i.r., u.v., magnetic susceptibility and conductivity measurements. The complexes are non-electrolytes, in which each metal ion is in a spin-free state in a pseudo- octahedral geometry. The high magnetic moments are attributed to a ferromagnetic effect.     

Conductometric study of calcium carbonate prenucleation stage: underlining the role of CaCO3o ion pairs

Calcium carbonate crystallization process, especially the prenucleation stage, has increasingly been the subject of several works. In the present work, a simple method based on electrical conductivity modeling applied to the FCP (Fast Controlled Precipitation) method data is used to highlight the role of CaCO₃^o ion pairs on calcium carbonate prenucleation stage. A good agreement was obtained between the resistivity vs pH curves estimated by the McCleskey model equation and obtained experimentally in a FCP test. Results showed that the nucleation process begins with the formation of CaCO₃^o ion pairs as pre‐nuclei as soon as the calcite‐equilibrium pH is reached. Additionally CaCO₃^o content increases with pH to form aggregates, which depend on the saturation state of the solution. Basing on our thermodynamic data, these aggregates do not form amorphous calcium carbonate ACC as an intermediate phase. They lead to the formation of stable calcium carbonate nuclei which will further evolve to crystallize. Furthermore we demonstrate that in addition to their inhibitory effect on the Ca²⁺ and CO₃²⁻ association to form ion pairs, the two scale inhibitors sodium triphosphate (STP) and sodium polyacrylate (RPI) reduce ion pairs aggregation rate.     

Modified grating-based external cavity diode laser for simultaneous dual-wavelengths operation

We have reported a modified V-shaped external cavity, which is constructed around a commercial diode laser operating at a center wavelength of λ=785 nm by adding a new coated glass plate with about 50% reflectivity to the cavity. This allows simultaneous dual-wavelengths operation in the vicinity of Δν_min=0.18 THz to Δν_max=0.22 THz, which can be used as laser source for terahertz generation either for semiconductor devices or nonlinear schemes.     

A new model for deformed carbon nanotubes using Green’s function

A new method for modeling and analysis of deformed carbon nanotubes (CNTs) using Green’s function, is presented in this paper, for the first time. Using the proposed method, a new circuit model is obtained for the deformation region of a deformed single-walled CNT (SWCNT), which the values of its elements depend on the type of deformation and also the deformation parameters such as the coupling matrices and the energy variations of deformation region. The comparison between the obtained results from the analysis of proposed model and the literature gives a good match which approves the accuracy and correctness of the proposed model.     

The large time behavior of solutions of a diffusion equation involving a nonlocal convection term

We study the existence, uniqueness, and asymtotic behaviour of non-negative solutions to a parabolic diffusion equation involving a nonlocal con-vective term on a bounded domain ? contained in Rⁿ. We apply the In variance Principle of LaSalle and Hale to prove that the solution tends to zero as t → ∞     

Testing instantaneous linear Granger causality in presence of nonlinear dynamics

This Note is devoted to the test of instantaneous linear Granger causality when the errors are dependent but uncorrelated. The assumptions are weak and include a large set of dynamics as for instance the GARCH processes. We show that the standard Wald test for testing instantaneous linear Granger causality is not valid in our framework. As a consequence Wald tests which are valid in our framework are proposed.