On Generalized Douglas–Weyl(α, β)-Metrics

In this paper, we study generalized Douglas–Weyl(α, β)-metrics. Suppose that a regular(α, β)-metric F is not of Randers type. We prove that F is a generalized Douglas–Weyl metric with vanishing S-curvature if and only if it is a Berwald metric. Moreover, by ignoring the regularity, if F is not a Berwald metric, then we find a family of almost regular Finsler metrics which is not Douglas nor Weyl. As its application, we show that generalized Douglas–Weyl square metric or Matsumoto metric with isotropic mean Berwald curvature are Berwald metrics.     

A simple,rapid and sensitive method based on modified multiwalled carbon nanotube for preconcentration and determination of lead ions in aqueous media in natural pHs

In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL^?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples.     

Embedding of Dynamical Symmetry Groups U(1, 1) and U(2) of a Free Particle on AdS 2 and S 2 into Parasupersymmetry Algebra

Using two different types of the laddering equations realized simultaneously by the associated Gegenbauer functions, we show that all quantum states corresponding to the motion of a free particle on AdS ₂ and S ² are splitted into infinite direct sums of infinite-and finite-dimensional Hilbert subspaces which represent Lie algebras u(1, 1) and u(2) with infinite- and finite-fold degeneracies, respectively. In addition, it is shown that the representation bases of Lie algebras with rank 1, i.e., gl(2, C), realize the representation of nonunitary parasupersymmetry algebra of arbitrary order. The realization of the representation of parasupersymmetry algebra by the Hilbert subspaces which describe the motion of a free particle on AdS ₂ and S ² with the dynamical symmetry groups U(1, 1) and U(2) are concluded as well.     

Modified carrageenan. 5. Preparation,swelling behavior,salt‐ and pH‐sensitivity of partially hydrolyzed crosslinked carrageenan‐graft‐polymethacrylamide superabsorbent hydrogel

The polysaccharide, kappa‐carrageenan (κC) was chemically modified to achieve a novel superabsorbent hydrogel via graft copolymerization of methacrylamide (MAM) onto the substrate followed by alkaline hydrolysis. Ammonium persulfate (APS) and N,N′‐methylene bisacrylamide (MBA) were used as a free‐radical initiator and a crosslinker, respectively. The saponification reaction was carried out using sodium hydroxide aqueous solution. Either κC‐g‐PMAM or hydrolyzed κC‐g‐PMAM (PMAM: polymethacrylamide) was characterized by FT‐IR spectroscopy. The effect of grafting variables (i.e. concentration of MBA, MAM, and APS) and alkaline hydrolysis conditions (i.e. NaOH concentration, hydrolysis time and temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The swelling capacity of these hydrogels was also measured in various salt solutions. Results indicated that the swelling ratios decreased with an increase in the ionic strength of the salt solutions. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Absorbency of superabsorbing hydrogels was examined in buffer solutions with pH range 1–13. Also, the pH reversibility and on–off switching behavior, at pH values 3.0 and 8.0, makes the synthesized hydrogels good candidates for controlled delivery of bioactive agents. Finally, swelling kinetics in distilled water and various salt solutions was preliminary investigated. Results showed that the swelling in water was faster than in saline solutions. Copyright © 2004 John Wiley & Sons, Ltd.     

Low-Field NMR Relaxation Analysis of High-Pressure Ethane Adsorption in Mesoporous Silicas

Understanding the behaviour of short-chain hydrocarbons confined to porous solids informs the targeted extraction of natural resources from geological features, and underpins rational developments in separation, storage and catalytic conversion processes. Herein, we report the application of low-field (12.7 MHz) ¹H nuclear magnetic resonance (NMR) relaxation measurements to characterise ethane dynamics within mesoporous silica materials exhibiting mean pore diameters between 6 and 50 nm. Our measurements provide NMR-based adsorption isotherms within the range 25–50 bar and at ambient temperature, incorporating the ethane condensation point (40.7 bar at our experimental temperature of 23.6 °C). The quantitative nature of the acquired data is validated via a direct comparison of NMR-derived excess adsorption capacities with ex situ gravimetric ethane adsorption measurements, which are demonstrated to agree to within 0.2 mmol g⁻¹ of the observed ethane capacity. NMR relaxation time distributions are further demonstrated as a means to decouple interparticle and mesopore dominated adsorption phenomena, with unexpectedly rapid relaxation rates associated with interparticle ethane gas confirmed via a direct comparison with NMR self-diffusion analysis.     

Solid phase extraction of gold by sorption on octadecyl silica membrane disks modified with pentathia-15-crown-5 and determination by AAS

A simple and selective method for rapid and efficient concentration and determination of μg l⁻¹ levels of Au(III) ions in aqueous solution using octadecyl silica membrane disks modified by pentathia-15-crown-5 and flame atomic absorption spectrometry is presented. The influence of flow rates of eluent and sample solution, amount of ligand, types and least amount of eluent for elution of Au from disks were investigated. Break through volume and limit of detection of the membrane disks modified by 5 mg of the thiacrown ether was found to be 2.0 l and 1.0 μg l⁻¹, respectively. The effects of various cationic interferences on percent recovery of gold were studied. The method was successfully applied for the determinations of gold in some pharmaceutical samples and for the recovery of trace Au³⁺ ions from synthetic and water samples.     

Thermal stability and degradation mechanisms of poly(acrylic acid) and its salts: Part 3—Magnesium and calcium salts

The magnesium and calcium salts of acrylic acid have been polymerised in aqueous solution using ammonium persulphate as initiator. Both polymers were also prepared by the neutralisation of poly(acrylic acid) with metal oxide in the same medium.

The thermal degradation behaviour of magnesium and calcium polyacrylate was studied using thermogravimetry (TG), differential thermal analysis (DTA) and thermal volatilisation analysis (TVA). Degradation products were investigated by IR spectroscopy, mass spectrometry and GC-MS techniques, the volatile product fraction having first been separated by subambient TVA.

The decompositions of these materials show some similarities to the behaviour of the alkali metal salts of poly(acrylic acid) and to that of the alkaline earth metal salts of poly(methacrylic acid), but there are also important differences. Acetone and carbon dioxide are the most important volatile products and, in addition, there are various other carbonyl containing products. More carbon dioxide, resulting from side group scission, is evolved from magnesium polyacrylate than from calcium polyacrylate, because of the lower thermal stability of magnesium carbonate.     

Synthesis of novel fluorene-functionalised nanoporous silica and its luminescence behaviour in acidic media

Fluorene-functionalised nanoporous silica (FL-NH₂-SBA-15) was prepared using the post-synthesis grafting method of SBA-15. The material thus obtained was characterised by means of small- and wide-angle X-ray diffraction, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and elemental analysis. The results showed that the organised structure is preserved after the post-grafting procedure. Surface area and pore-size decreased by attaching functional groups to the pore surface. In addition, the pore volume was reduced with functionalisation. The amount of fluorene grafted onto the surface of SBA-15 was 0.55 mmol with a yield of approximately 46 %. The emission spectra of FL-NH₂-SBA-15 in acidic media were studied and are discussed in detail. The structural change between FL-NH₂-SBA-15 and the protonated form might be an effective candidate for acid-dependent molecular-sensor models for advanced application in molecular sensors in the future.     

The knockout reaction of <Superscript>15</Superscript>C on a <Superscript>9</Superscript>Be target at intermediate energies

In this work, neutron knockout reactions of ¹⁵C on a ⁹Be target at energy 103 and 250 MeV/nucleon are studied. Using the Eikonal approximation of the Glauber model, total neutron removal cross sections, the stripping and diffractive cross sections as well as ¹⁴C longitudinal momentum distributions are determined in both ¹⁵C ground state and exited states of the wave function. We compared the results of our calculations with the available experimental data obtained recently. The calculated cross sections of ¹⁵C and ¹⁴C reactions, as well as the momentum distribution are in relatively good agreement with available data.