Chronology and characteristics of groundwater along the United Arab Emirates-Oman arid region: a guide for regional sustainability

Journal of Radioanalytical and Nuclear Chemistry - Estimating groundwater recharge rate is essential for water sustainability of the arid region of the United Arab Emirates that receives most...     

Rapid determination of hydroflumethiazide in dosage forms by time-resolved chemiluminescence

Hydroflumethiazide was determined from the chemiluminescence produced in its reaction with Ce(IV) in acidic medium containing rhodamine 6G as a sensitizer using flow injection techniques (stopped flow mode). A straightforward automatic method based on measuring the peak height and peak area, which are directly proportional to the hydroflumethiazide concentration, was thus developed. The calibration graphs were linear over the concentration range of 1.0–30 μg mL⁻¹. The limit of detection as determined according to Clayton was 0.97 and 0.91 μg mL⁻¹ for peak height and peak area measurements, respectively. The relative standard deviation for ten samples was less than 3.0% with both types of measurements. The procedure was applied to the determination of hydroflumethiazide in pharmaceutical formulations, yielding excellent recoveries, since the determination is free of interference from common excipients and other drugs which are present in the formulation.     

Rational Improvement of Molar Absorptivity Guided by Oscillator Strength: A Case Study with Furoindolizine‐Based Core Skeleton

The rational improvement of photophysical properties can be highly valuable for the discovery of novel organic fluorophores. Using our new design strategy guided by the oscillator strength, we developed a series of full‐color‐tunable furoindolizine analogs with improved molar absorptivity through the fusion of a furan ring into the indolizine‐based Seoul fluorophore. The excellent correlation between the computable values (oscillator strength and theoretical S₀–S₁ energy gap) and photophysical properties (molar absorptivity and emission wavelength) confirmed the effectualness of our design strategy.     

Relative Permeability of Near-Miscible Fluids in Compositional Simulators

Miscible gas injection is one of the most effective enhanced oil recovery techniques. There are several challenges in accurately modeling this process, which occurs in the near-miscible region. The adjustment of relative permeability for near-miscible processes is the main focus of this work. The dependence of relative permeability on phase identification can lead to significant complications while simulating near-miscible displacements. We present an analysis of how existing methods incorporate compositional dependence in relative permeability functions. The sensitivity of the different methods to the choice of reference points is presented with guidelines to limit the modification of the relative permeabilities to physically reasonable values. We distinguish between the two objectives of reflecting near-miscible behavior and ensuring smooth transitions across phase changes. We highlight an important link that combines the two objectives in a more general framework. We make use of Gibbs free energy as a compositional indicator in the generalized framework. The new approach was implemented in an automatic differentiation general purpose research simulator and tested on a set of near-miscible gas-injection problems. We show that including compositional dependencies in the relative permeability near the critical point impacts the simulation results with significant improvements in nonlinear convergence.     

The causal boundary of product spacetimes

The new formulation of the causal completion of spacetimes suggested in Marolf and Ross (Class Quant Grav 20:4085, 2003), and modified later in Flores (Commun Math Phys 2007), is tested by computing the causal boundary for product spacetimes of a Lorentz interval and a Riemannian manifold. This is particularized for two important families of spacetimes, conformal to the previous ones: (standard) static spacetimes and Generalized Robertson-Walker spacetimes. As consequence, it is shown that this new approach essentially reproduces the structure of the conformal boundary for multiple classical spacetimes: Reissner–Nordström (including Schwarzschild), Anti-de Sitter, Taub and standard cosmological models as de Sitter and Einstein Universe.     

A normoxic acrylic acid polymer gel for dosimetery in radiation therapy

Journal of Radioanalytical and Nuclear Chemistry - A novel low toxic normoxic polymer gel dosimeter containing acrylic acid monomer is prepared and characterized for dosimetry in radiotherapy. Gel...     

Non-linear strain rate dependent micro-mechanical composite material model for finite element impact and crashworthiness simulation

The present study aims at implementation of a strain rate dependent, non-linear, micro-mechanics material model for laminated, unidirectional polymer matrix composites into the explicit finite element code LSDYNA. The objective is to develop an accurate and simple micro-mechanical, rate dependent material model, which is computationally efficient. Within the model a representative volume cell is assumed. The stress-strain relation including rate dependent effects for the micro-model is derived for both shell elements and solid elements. Micro-failure criterion is presented for each material constituent and failure mode. The implemented model can deal with problems such as impact, crashworthiness, and failure analysis under quasi-static loads. The developed material model has a wide range of applications such as jet engine jackets, armor plates, and structural crashworthiness simulation. The deformation response of two representative composite materials with varying fiber orientation is presented using the described technique. The predicted results compare favorably to experimental values.     

Uranium isotopes in carbonate aquifers of arid region setting

Groundwater in arid and semiarid regions is vital resource for many uses and therefore information about concentrations of uranium isotopes among other chemical parameters are necessary. In the study presented here, distribution of ²³⁸U and ²³⁵U in groundwater of four selected locations in the southern Arabian peninsula, namely at two locations within the United Arab Emirates (UAE) and two locations in Oman are discussed. The analyses of the uranium isotopes were performed using ICP-MS and the results indicated a range of concentrations for ²³⁵U and ²³⁸ U at 3–39 ng L^?1 (average: 18 ng L^?1) and 429–5,293 ng L^?1 (average: 2,508 ng L^?1) respectively. These uranium concentrations are below the higher permissible WHO limit for drinking water and also comparable to averages found in groundwater from similar aquifers in Florida and Tunisia. Negative correlation between rainfall and uranium concentrations suggests that in lithologically comparable aquifers, climate may influence the concentration of uranium in subtropical to arid regions.     

Ecosystems with mutually exclusive interactions self-organize to a state of high diversity

Ecological systems comprise an astonishing diversity of species that cooperate or compete with each other forming complex mutual dependencies. The minimum requirements to maintain a large species diversity on long time scales are in general unknown. Using lichen communities as an example, we propose a model for the evolution of mutually excluding organisms that compete for space. We suggest that chainlike or cyclic invasions open for creation of spatially separated subpopulations that subsequently can lead to increased diversity. In contrast to its nonspatial counterpart, our model predicts robust coexistence of a large number of species. It is demonstrated that large species diversity can be obtained on evolutionary time scales, provided that interactions between species have spatial constraints. In particular, a phase transition to a sustainable state of high diversity is identified.