Stable H and O isotope variations reveal sources of recharge in Dhofar,Sultanate of Oman

Due to the ability of stable water isotopes to characterize the origin of water and connected processes of groundwater recharge, we used the isotope variations of hydrogen and oxygen in different water sources for assessing the recharge process in the Dhofar region. δ¹⁸O and δ²H of precipitation, spring water, and groundwater cover a range from ?10 to +2 and from ?70 to +7?‰ (vs Vienna Standard Mean Ocean Water), respectively, and correlate in a linear relationship close to the Global Meteoric Water Line. No obvious evaporation processes are detected. A clear signal of the recent precipitation is given by the annual monsoon. The monsoon signal is confirmed by several springs existing in the south at the foot of the Dhofar mountains and sources at Gogub above 450?m and Tawi Atir at 650?m above sea level. They occur here first in the form of water intercepted by trees as stemflow and throughflow. The isotope signature of groundwater in the Dhofar mountains reflects the climatic conditions at the time of recharge and the lithological features of the limestone matrix. To the north, the isotope patterns of the groundwater are continuously depleted from the monsoon signal along the outcropping aquifer D (Lower Umm Er Radhuma). Here, a more negative signature towards the wells in the Najd desert region was observed. Cyclone water that flooded wadis in the Dhofar region occasionally, as observed in November 2011, falls isotopically into the same range as we observed in the fossil groundwater. Taking into account the different sources of precipitation and groundwater and thus a clear distinction of the isotopic composition of the water sources, we conclude a recharge process divided into a southward and a northward component in the Dhofar region.     

Improved performance of solar cell based on porous silicon surfaces

Porous silicon (PS) surfaces were fabricated by electrochemical etching for both sides of the Si wafer. The objective of the present study is to investigate the PS effect on performance of silicon solar cells. Moreover, enhancement of solar cell efficiency can be obtained by manipulating of the reflected mirrors, and the process is very promising for solar cells manufacturing due to its simplicity, lower cost and suitability for mass production. The surface of PS is observed to have been discrete pores with smooth walls, and with short branches pores for the polished wafer side. In contrast, the etched backside of the wafer was observed to have bigger pore size than the etched polished side, and pores on the surface are in random location. PS formed on the both sides has lower reflectivity value in comparison to the other researcher group. The increase in efficiency of solar cell fabricated with PS formed on both sides of the wafer were extremely observed in comparison to one side PS and bulk silicon solar cells respectively. Solar cell fabricated shows that the conversion efficiency increased to 14.5% in comparison to unetched sample. The porous surface texturing properties could enhance and increased the conversion efficiency of silicon solar cells, these results also showed that the efficiency with this procedure is more promising in comparison to other solar cells, which are fabricated under similar conditions.     

Polarization insensitive terahertz metamaterial absorber

We present the simulation, implementation, and measurement of a polarization insensitive resonant metamaterial absorber in the terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us to maximize absorption by varying the dielectric material and thickness and, hence, the effective electrical permittivity and magnetic permeability. Experimental absorption of 77% and 65% at 2.12 THz (in the operating frequency range of terahertz quantum cascade lasers) is observed for a spacer of polyimide or silicon dioxide respectively. These metamaterials are promising candidates as absorbing elements for thermally based terahertz imaging.     

Numerical Radius Inequalities for Certain 2 × 2 Operator Matrices

We prove several numerical radius inequalities for certain 2 × 2 operator matrices. Among other inequalities, it is shown that if X, Y, Z, and W are bounded linear operators on a Hilbert space, then

$$w\left( \left[\begin{array}{cc} X &; Y \\ Z &; W \end{array} \right] \right) \geq \max \left(w(X),w(W),\frac{w(Y+Z)}{2},\frac{w(Y-Z)}{2}\right) $$

and

$$w\left( \left[\begin{array}{cc}X &; Y \\ Z &; W\end{array} \right] \right) \leq \max \left( w(X), w(W)\right)+\frac{w(Y+Z)+w(Y-Z)}{2}. $$

As an application of a special case of the second inequality, it is shown that

$$\frac{\left\Vert X\right\Vert }{2}+\frac{\left\vert \left\Vert\operatorname{Re}{X}\right\Vert -\frac{\left\Vert X\right\Vert}{2}\right\vert }{4}+\frac{ \left\vert \left\Vert \operatorname{Im}{X}\right\Vert -\frac{\left\Vert X\right\Vert}{2}\right\vert }{4} \leq w(X), $$

which is a considerable improvement of the classical inequality \({\frac{ \left\Vert X\right\Vert }{2}\leq w(X)}\) . Here w(·) and || · || are the numerical radius and the usual operator norm, respectively.

     

Existence results for a nonlinear version of Rotenberg model with infinite maturation velocities

In this paper, we present some existence results on L¹ spaces of a nonlinear boundary value problem derived from a model introduced by Rotenberg (1983) describing the growth of a cell population. Each cell of this population is distinguished by its degree of maturity μ ∈ [0,1] and its maturation velocity v. The biological boundary at μ = 0 and μ = 1 are fixed and tightly coupled through the mitosis. At mitosis, daughter cells and mother cells are related by a general reproduction rule, which covers all known biological ones. In this work, the maturation velocity is allowed to be infinite, that is, v ∈ [0, + ∞ ). This hypothesis introduce some mathematical difficulties, which are overcomed by using a measure of weak noncompactness adapted to the problem and a recent fixed point theorem (Theorem 3.2) involving weakly compact operators on nonreflexive Banach spaces. Copyright © 2014 John Wiley & Sons, Ltd.     

Interactions of Ionic Surfactants With PEO-PBO-PEO Triblock Copolymers in Aqueous Solutions

The interactions of triblock copolymers (TBP) with ionic surfactants were studied employing surface tensiometry, electrical conductivity, steady-state fluorescence (SSF), and dynamic light scattering (DLS) techniques. An increasing trend in the critical micelle concentration (CMC) of SDS/CTAB in the presence of triblock copolymers was observed especially at higher polymer to surfactant ratio. The delay in the CMC of surfactants was more pronounced in the presence of E₄₈B₁₀E₄₈ possibly due to its less hydrophobic nature. The negative values of free energy of micellization (ΔG_m) both in case of SDS and CTAB confirmed the spontaneity of the processes. The aggregation number (N_agg) and hydrodynamic radius (R_h) of polymer/surfactant mixed systems were determined by SSF and DLS. The suppression of the surfactant micelle size in the presence of TBP was confirmed by SSF and DLS studies.     

Environmental Application of Chitosan Resins for the Treatment of Water and Wastewater: A Review

Chitosan is a polysaccharide formed mainly from repeating residues of D-glucosamine, having primary amino groups. It is of great interest not only as an underutilized resource, but also as a new functional material of high potential in various fields, and recent progress in chitin chemistry is quite noteworthy. The purpose of this review is to take a closer look at chitosan application in water technology based on (a) its ability to bind toxic pollutants, (b) the mod of chitosan modification, (c) the nature of the interaction of chitosan with different pollutants, and (d) chitosan regeneration and recycling.     

Solvent-exfoliated graphene at extremely high concentration

We describe three related methods to disperse graphene in solvents with concentrations from 2 to 63 mg/mL. Simply sonicating graphite in N-methyl-2-pyrrolidinone, followed by centrifugation, gives dispersed graphene at concentrations of up to 2 mg/mL. Filtration of a sonicated but uncentrifuged dispersion gives a partially exfoliated powder that can be redispersed at concentrations of up to 20 mg/mL. However, this process can be significantly improved by removing any unexfolaited graphite from the starting dispersion by centrifugation. The centrifuged dispersion can be filtered to give a powder of exfoliated few-layer graphene. This powder can be redispersed at concentrations of at least 63 mg/mL. The dispersed flakes are ~1 μm long and ~3 to 4 layers thick on average. Although some sedimentation occurs, ~26-28 mg/mL of the dispersed graphene appears to be indefinitely stable.     

Development of a molecularly imprinted polymer for selective extraction followed by liquid chromatographic determination of sitagliptin in rat plasma and urine

A novel water-compatible molecularly imprinted solid-phase extraction (MISPE) combined with zwitterionic hydrophilic interaction liquid chromatography (ZIC-HILIC) method for selective extraction and determination of sitagliptin in rat serum and urine was developed and validated. The effects of progenic solvents, pH, cross linker and amount of monomer were studied to optimize the efficiency and selectivity. The adsorption kinetics and isotherms were measured. The molecularly imprinted polymer (MIP) showed good specific adsorption capacity with an optimum of 180 mg/g at pH 7.5 and selective extraction of sitagliptin from rat plasma and urine. The recovery of sitagliptin from rat urine and plasma was >98%. The limits of detection (LOD) and quantification (LOQ) were 0.03 and 0.10 μg/L respectively. The proposed method overcomes the matrix effects of phospholipids generally encountered while preparation of plasma samples by precipitation of proteins.