The Dual-Reciprocity Boundary Element Analysis for Hydraulically Fractured Shale Gas Reservoirs Considering Diffusion and Sorption Kinetics

This work presents a new application of boundary element method (BEM) to model fluid transport in unconventional shale gas reservoirs with discrete hydraulic fractures considering diffusion, sorption kinetics and sorbed-phase surface diffusion. The fluid transport model consists of two governing partial differential equations (PDEs) written in terms of effective diffusivities for free and sorbed gases, respectively. Boundary integral formulations are analytically derived using the fundamental solution of the Laplace equation for the governing PDEs and Green’s second identity. The domain integrals arising due to the time-dependent function and nonlinear terms are transformed into boundary integrals employing the dual-reciprocity method. This transformation retains the domain-integral-free, boundary-integral-only character of standard BEM approaches. In the proposed solution, the free- and sorbed-gas flow in the shale matrix is solved simultaneously after coupling the fracture flow equation of free gas. Well production performance under the effect of relaxation phenomenon due to delayed responses of sorbed gas under nonequilibrium sorption condition is rigorously captured by imposing the zero-flux condition at fracture–matrix interface for the sorbed-gas transport equation. The validity of proposed solution is verified using several case studies through comparison against a commercial finite-element numerical simulator.

     

Analysis of Main Factors Determining the Prediction of Stabilization Energies of Halide-water Clusters

This work studies the main factors determining the stabilization energy [E _stab(n)] of a series of halide clusters, [X(H₂O) _n ]⁻ (X≡F, Br and I). This property measures the difference between the ionization process of the hydrated and isolated halide. In a previous paper [J. Chem. Phys., 121, 7269 (2004)], the E _stab(n) was studied for a large number of clusters (up to n = 60) by using classical computer simulations based on first-principles polarizable potentials to describe the halide–water interactions. In this work we analyze what features of the MCDHO-type model are necessary for a proper reproduction of the experimental E _stab. The role of the charge redistribution (polarizability) of the water molecule and halide anion, the geometrical relaxation of water molecule (flexibility), as well as the replacement of water clusters by a dielectric continuum of different dielectric permittivities are presented and discussed. The parallel behavior of the E _stab magnitude with the dielectric permittivity of the continuum and with the number of water molecules forming the cluster supports that the electrostatic interactions are the main responsible for the changes induced on the electron structures determining the energetics of the photodetachement process. The photodetachment process does not only occur without nuclear relaxation but also with a small electron redistribution of water molecules.     

Opposed-flow flame spread in microgravity-theoretical prediction of spread rate and flammability map

The spread rate formulas of de Ris in the thermal regime of opposed-flow flame spread are inarguably the most well-known formulas in the flame spread literature. Similar easy-to-use formulas are lacking in all other regimes of flame spread. This paper presents a simplified analysis leading to the development of closed-form expressions for spread rate for both thin and thick fuels in the microgravity regime of opposed-flow flame spread. The resulting formulas, expressed in terms of the thermal limit of spread rate and a radiation number that can be evaluated from the known parameters of the problem, are shown to reproduce the experimentally and numerically observed trends quite well at both limits of fuel thickness. These formulas are utilized to develop quantitative criterion to delineate thin and thick fuels in the microgravity and thermal regimes. The transition between the microgravity and thermal regimes is also explored. The flammability maps, derived from the spread rate expressions, are the first of their kind, establishing fuel thickness as one of the critical parameters.     

Separation of chlorophylls and their degradation products in marine phytoplankton by reversed-phase high-performance liquid chromatography

Summary An RP-HPLC procedure which separates chlorophylls and their degradation products is described. By employing an amonium acetate buffered mobile phase and a linear gradient elution, complex mixtures of chloroand phaeopigments are separated in less than 30 minutes. The method has been applied to the control of chlorophyll enzymatic degradation in cultures of two algal species, and has also been successfully used in the analysis of algal xanthophylls.     

A classical point charge model study of system size dependence of oxidation and reorganization free energies in aqueous solution

The response of water to a change of charge of a solvated ion is, to a good approximation, linear for the type of iron-like ions frequently used as a model system in classical force field studies of electron transfer. Free energies for such systems can be directly calculated from average vertical energy gaps. Exploiting this feature, we have computed the free energy and the reorganization energy of the M2+/M3+ and M1+/M2+ oxidations in a series of model systems all containing a single Mn+ ion and an increasing number of simple point charge water molecules. Long-range interactions are taken into account by Ewald summation methods. Our calculations confirm the observation made by Hummer, Pratt, and Garcia (J. Phys. Chem. 1996, 100, 1206) that the finite size correction to the estimate of solvation energy (and hence oxidation free energy) in such a setup is effectively proportional to the inverse third power (1/L3) of the length L of the periodic cell. The finite size correction to the reorganization energy is found to scale with 1/L. These simulation results are analyzed using a periodic generalization of the Born cavity model for solvation, yielding three different estimates of the cavity radius, namely, from the infinite system size extrapolation of oxidation free energy and reorganization energy, and from the slope of the linear dependence of oxidation free energy on 1/L3. The cavity radius for the reorganization energy is found to be significantly larger compared to the radius for the oxidation (solvation) free energy. The radius controlling the 1/L3 dependence of oxidation free energy is found to be comparable to the radius for reorganization. The implication of these results for density functional theory-based ab initio molecular dynamics calculation of redox potentials is discussed.     

Ultraviolet Radiation Exposure and its Impacts on Cutaneous Phosphorylation Signaling in Carcinogenesis: Focusing on Protein Tyrosine Phosphatases†

Sunlight exposure is a significant risk factor for UV-induced deteriorating transformations of epidermal homeostasis leading to skin carcinogenesis. The ability of UVB radiation to cause melanoma, as well as basal and squamous cell carcinomas, makes UVB the most harmful among the three known UV ranges. UVB-induced DNA mutations and dysregulation of signaling pathways contribute to skin cancer formation. Among various signaling pathways modulated by UVB, tyrosine phosphorylation signaling which is mediated by the action of protein tyrosine kinases (PTKs) on specific tyrosine residues is highly implicated in photocarcinogenesis. Following UVB irradiation, PTKs get activated and their downstream signaling pathways contribute to photocarcinogenesis by promoting the survival of damaged keratinocytes and increasing cell proliferation. While UVB activates oncogenic signaling pathways, it can also activate tumor suppressive signaling pathways as initial protective mechanisms to maintain epidermal homeostasis. Tyrosine dephosphorylation is one of the protective mechanisms and is mediated by the action of protein tyrosine phosphatases (PTPs). PTP can counteract UVB-mediated PTK activation and downregulate oncogenic signaling pathways. However, PTPs have not been studied extensively in photocarcinogenesis with previous studies regarding their inactivation induced by UVB. This current review will summarize the recent progress in the protective function of PTPs in epidermal photocarcinogenesis.     

Free Superoxide is an Intermediate in the Production of H2O2 by Copper(I)‐Aβ Peptide and O2

Oxidative stress is considered as an important factor and an early event in the etiology of Alzheimer's disease (AD). Cu bound to the peptide amyloid‐β (Aβ) is found in AD brains, and Cu‐Aβ could contribute to this oxidative stress, as it is able to produce in vitro H₂O₂ and HO^. in the presence of oxygen and biological reducing agents such as ascorbate. The mechanism of Cu‐Aβ‐catalyzed H₂O₂ production is however not known, although it was proposed that H₂O₂ is directly formed from O₂ via a 2‐electron process. Here, we implement an electrochemical setup and use the specificity of superoxide dismutase‐1 (SOD1) to show, for the first time, that H₂O₂ production by Cu‐Aβ in the presence of ascorbate occurs mainly via a free O₂^.? intermediate. This finding radically changes the view on the catalytic mechanism of H₂O₂ production by Cu‐Aβ, and opens the possibility that Cu‐Aβ‐catalyzed O₂^.? contributes to oxidative stress in AD, and hence may be of interest.     

The classification of homotopy classes of bounded curvature paths

A bounded curvature path is a continuously differentiable piecewise C² path with bounded absolute curvature that connects two points in the tangent bundle of a surface. In this note we give necessary and sufficient conditions for two bounded curvature paths, defined in the Euclidean plane, to be in the same connected component while keeping the curvature bounded at every stage of the deformation. Following our work in [3], [2] and [4] this work finishes a program started by Lester Dubins in [6] in 1961.     

Monitoring and Targeting the Initial Dimerization Stage of Amyloid Self‐Assembly

Amyloid deposits are pathological hallmark of a large group of human degenerative disorders of unrelated etiologies. While accumulating evidence suggests that early oligomers may account for tissue degeneration, most detection tools do not allow the monitoring of early association events. Here we exploit bimolecular fluorescence complementation analysis to detect and quantify the dimerization of three major amyloidogenic polypeptides; islet amyloid polypeptide, β‐amyloid and α‐synuclein. The constructed systems provided direct visualization of protein‐protein interactions in which only assembled dimers display strong fluorescent signal. Potential inhibitors that interfere with the initial intermolecular interactions of islet amyloid polypeptide were further identified using this system. Moreover, the identified compounds were able to inhibit the aggregation and cytotoxicity of islet amyloid polypeptide, demonstrating the importance of targeting amyloid dimer formation for future drug development.     

Effect of surface charge on the colloidal stability and in vitro uptake of carboxymethyl dextran-coated iron oxide nanoparticles

An easy and novel routine are reported for the preparation of metallic silver nanoparticles (AgNPs) with controlled morphology, using Na⁺–magadiite swelled with hexadecyltrimethylammonium bromide (CTA⁺–magadiite) and a layered aluminophosphate with kanemite-type structure modified with n-dodecylammonium and n-butylammonium (but,dod-AlPO-kan) as hosts. For the preparation of the metallic AgNPs (Ag⁰) in the interlamellar space, the CTA⁺–magadiite and but,dod-AlPO-kan hosts were dispersed in N,N-dimethylformamide (DMF) solution with different AgNO₃ concentrations. DMF acts as reducing agent of Ag⁺ ions leading to nanoparticles with disk-like morphology of magadiite silicate; these were characterized by TEM and UV–Vis spectroscopy. On the other hand, the AgNPs are intercalated in but,dod-AlPO-kan showing spherical-like morphology. The UV–Vis spectra of the nanocomposites based on Ag⁰ and magadiite silicate show bands at 565 nm that can be attributed to Ag⁰ nanodisks. The Ag-but,dod-AlPO-kan-based nanocomposites present a band at 422 nm attributed to the surface plasmon resonance of Ag⁰ nanospheres. The results of transmission electron microscopy agree very well with XRD and UV–Vis analysis, indicating the formation of AgNPs with different morphologies using the two kinds of lamellar materials. The magadiite host has an important role in the synthesis of Ag nanodisks, because it controls the growth of nanoparticles inside the interlayer region with disk-like morphology due the high interlayer interactions of the silicate, leading to the growth of nanoparticles in only two directions (xy plane). On the other hand, when but,dod-AlPO-kan is used a sphere-like morphology is preferred due the best accommodation of AgNPs between the layers of aluminophosphate host.