Use of o-phenylene dioxydiacetic acid impregnated in Amberlite XAD resin for separation and preconcentration of uranium(VI) and thorium(IV)

The impregnation of o-phenylene dioxydiacetic acid (OPDA) into a polymeric matrix, Amberlite XAD-2000, is reported and was characterized by infrared spectroscopy. The amount of attached OPDA to the polymer resin was found to be 1.77mmolg(-1) resin. The resin was used for the sorption of U(VI) and Th(IV) from aqueous solution. This sorbent was capable of preconcentrating U(VI) and Th(IV) from weakly acidic or neutral solution. The retained metals were eluted sequentially using 0.25molL(-1) HCl for U(VI) and 1molL(-1) HCl for Th(IV) and determined spectrophotometrically using arsenazo-(III). The capacity of the resin for U(VI) and Th(IV) was found to be 0.121 and 0.113mmolg(-1), respectively. The impregnated resin exhibits a high chemical stability, reusability and fast equilibration. The method was used for the determination of U(VI) and Th(IV) in synthetic samples and rock samples.     

2-D DOA estimation in case of unknown mutual coupling for multipath signals

In this paper, two dimensional (2-D) direction-of-arrival (DOA) estimation problem in case of unknown mutual coupling and multipath signals is investigated for antenna arrays. A new technique is proposed which uses a special array structure consisting of parallel uniform linear array (PULA). PULA structure is complemented with auxiliary antennas in order to have a structured mutual coupling matrix (MCM). MCM has a symmetric banded Toeplitz structure which allows the application of the ESPRIT algorithm for 2-D paired DOA estimation. The advantage of the PULA structure is exploited by dividing it into overlapping linear sub-arrays (triplets) and spatial smoothing is employed to mitigate multipath signals. Closed form expressions are presented for search-free, paired and unambiguous 2-D DOA estimation. Two algorithms PULA-1 and PULA-2 are proposed to effectively solve the problem. Several simulations are done and the accuracy of the proposed solution is shown.     

Rayleigh-maximum-likelihood filtering for speckle reduction of ultrasound images

Speckle is a multiplicative noise that degrades ultrasound images. Recent advancements in ultrasound instrumentation and portable ultrasound devices necessitate the need for more robust despeckling techniques, for both routine clinical practice and teleconsultation. Methods previously proposed for speckle reduction suffer from two major limitations: 1) noise attenuation is not sufficient, especially in the smooth and background areas; 2) existing methods do not sufficiently preserve or enhance edges--they only inhibit smoothing near edges. In this paper, we propose a novel technique that is capable of reducing the speckle more effectively than previous methods and jointly enhancing the edge information, rather than just inhibiting smoothing. The proposed method utilizes the Rayleigh distribution to model the speckle and adopts the robust maximum-likelihood estimation approach. The resulting estimator is statistically analyzed through first and second moment derivations. A tuning parameter that naturally evolves in the estimation equation is analyzed, and an adaptive method utilizing the instantaneous coefficient of variation is proposed to adjust this parameter. To further tailor performance, a weighted version of the proposed estimator is introduced to exploit varying statistics of input samples. Finally, the proposed method is evaluated and compared to well-accepted methods through simulations utilizing synthetic and real ultrasound data.     

Porous medium based burner for efficient and clean combustion of ammonia–hydrogen–air systems

Due to its high hydrogen density and extensive experience base, ammonia (NH₃) has been gaining special attention as a potential green energy carrier. This study focuses on premixed ammonia–hydrogen–air flames under standard temperature and pressure conditions using an inert silicon-carbide (SiC) porous block as a practical and effective medium for flame stabilization. Combustion experiments conducted using a lab scale burner resulted in stable combustion and high combustion efficiencies at very high ammonia concentration levels over a wide range of equivalence ratios. Noticeable power output densities have also been achieved. Preliminary results of NO_x emission measurements indicate NO_x concentrations as low as 35 ppm under rich conditions. The remarkable capability of this specific burner to operate efficiently and cleanly at high ammonia concentration levels, which can easily be achieved by partial cracking of NH₃, is believed to be a key accomplishment in the development of ammonia fired power generation systems.     

Effect of pH,ionic strength,and temperature on uranyl ion adsorption by poly(N‐vinyl 2‐pyrrolidone‐g‐tartaric acid) hydrogels

Poly‐electrolyte N‐vinyl 2‐pyrrolidone‐g‐tartaric acid (PVP‐g‐TA) hydrogels with varying compositions were prepared in the form of rods from ternary mixtures of N‐vinyl 2‐pyrrolidone/tartaric acid/water. The effect of external stimuli, such as the solution pH, ionic strength, and temperature, on uranyl adsorption by these hydrogels was investigated. Uranyl adsorption capacities of the hydrogels were determined to be 53.2–72.2 (mg UO/g dry gel) at pH 1.8, and 35.3–60.7 (mg UO/g dry gel) at pH 3.8, depending on the amount of TA in the hydrogel. The adsorption studies have shown that the temperature and the ionic strength of the swelling solution also influence uranyl ion adsorption by PVP‐g‐TA hydrogels. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2219–2226, 2000     

Mechanical properties and water vapor permeation of vinyltriethoxysilane/methyl methacrylate copolymers

Methyl methacrylate (MMA) was copolymerized with vinyltriethoxysilane (VTES) using ⁶⁰Co-γ-radiation at varying volume fractions of the liquid monomers in the feed. Thin copolymer films were prepared by casting tetrahydrofuran solutions of the copolymers on a mercury surface. The effect of the mole fraction of VTES in the copolymer on the glass transition temperatures, mechanical properties and water vapor permeabilities were investigated. Glass transition temperatures and mechanical properties decreased with increasing VTES content in the copolymer. However, the water vapor permeabilities were found to increase with the VTES content. The increased water vapor permeation was attributed to increased water solubility in the copolymers due to the presence of Si-O-bonds.     

New metal chelate sorbent for albumin adsorption: Cibacron Blue F3GA-Zn(II) attached microporous poly(HEMA) membranes

Poly(2-hydroxyethyl methacrylate) [poly(HEMA)] membranes were prepared by UV-initiated photopolymerization of HEMA in the presence of an initiator (α-α′-azobis-isobutyronitrile, AIBN). The triazine dye Cibacron Blue F3GA was attached as an affinity ligand to poly(HEMA) membranes, covalently. These affinity membranes with a swelling ratio of 58% and containing 10.7 mmol Cibacron Blue F3GA/m² were used in the albumin adsorption studies. After dye-attachment, Zn(II) ions were chelated within the membranes via attached-dye molecules. Different amounts of Zn(II) ions [650–1440 mg Zn(II)/m²] were loaded on the membranes by changing the initial concentration of Zn(II) ions and pH. Bovine serum albumin (BSA) adsorption on these membranes from aqueous solutions containing different amounts of BSA at different pH was investigated in batch reactors. The nonspecific adsorption of BSA on the poly(HEMA) membranes was negligible. Cibacron Blue F3GA attachment significantly increased the BSA adsorption up to 92.1 mg BSA/m². Adsorption capacity was further increased when Zn(II) ions were attached (up to 144.8 mg BSA m²). More than 90% of the adsorbed BSA was desorbed in 1 h in the desorption medium containing 0.5M NaSCN at pH 8.0 and 0.025M EDTA at pH 4.9. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 657–664, 1998     

Gamma‐rays induced copolymerization of vinyl triethoxy silane and methyl methacrylate: Their spectroscopic characterization

The γ‐ray–induced copolymerization of vinyl triethoxy silane (VTES) with methyl methacrylate (MMA) was developed to be used in the simultaneous preservation and consolidation of archeological artifacts. A detailed analysis was performed to characterize the copolymerization reaction and conversion. The copolymers were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), and elemental analysis techniques. The mol fraction of VTES units in the synthesized copolymers were determined by elemental analysis of silicone pertaining to VTES segments using inductive coupling plasma spectroscopy (ICP). The effect of VTES mol fraction in the initial feed and the irradiation dose (6.5, 8.5, 10.0 kGy) on the yield of copolymerization was investigated. The yield of the copolymerization was found to decrease with increasing the VTES mol fraction in the monomer feed, and to increase with increasing the irradiation dose at each monomer composition. However, using the data obtained from the ICP measurements, the mol fraction of the VTES units in synthesized copolymers was determined to increase with increasing the VTES concentration in the initial monomer feed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 141–147, 1999     

Renewable hydrogen energy regulations,codes and standards: Challenges faced by an EU candidate country

The European Union is one of the most important players in the field of world energy with an integrated and well-organized energy market. However, energy policies in the EU are not sustainable. The EU is the world’s largest importer of fossil fuels and is leading global action in accelerating the transition to renewable energy and low-carbon economy at present. Renewables make the second-largest contribution to domestic energy production after coal.