Solid-phase extraction of Mn(II), Co(II), Ni(II), Cu(II), Cd(II) and Pb(II) ions from environmental samples by flame atomic absorption spectrometry (FAAS)

A new method using a column packed with Amberlite XAD-2010 resin as a solid-phase extractant has been developed for the multi-element preconcentration of Mn(II), Co(II), Ni(II), Cu(II), Cd(II), and Pb(II) ions based on their complex formation with the sodium diethyldithiocarbamate (Na-DDTC) prior to flame atomic absorption spectrometric (FAAS) determinations. Metal complexes sorbed on the resin were eluted by 1 mol L(-1) HNO3 in acetone. Effects of the analytical conditions over the preconcentration yields of the metal ions, such as pH, quantity of Na-DDTC, eluent type, sample volume and flow rate, foreign ions etc. have been investigated. The limits of detection (LOD) of the analytes were found in the range 0.08-0.26 microg L(-1). The method was validated by analyzing three certified reference materials. The method has been applied for the determination of trace elements in some environmental samples.     

Expression of trkB and trkC mRNAs by adult midbrain dopamine neurons: a double-label in situ hybridization study

The documented trophic actions of the neurotrophins brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) upon ventral mesencephalic dopamine neurons in vitro and in vivo are presumed to be mediated through interactions with their high-affinity receptors TrkB (for BDNF and NT-4/5) and TrkC (for NT-3). Although both neurotrophin receptor mRNAs have been detected within the rat ventral midbrain, their specific association with mesencephalic dopaminergic cell bodies remains to be elucidated. The present study was performed to determine the precise organization of trkB and trkC mRNAs within rat ventral midbrain and to discern whether the neurotrophin receptor mRNAs are expressed specifically by dopaminergic neurons. In situ hybridization with isotopically labeled cRNA probes showed that trkB and trkC mRNAs were expressed in all mesencephalic dopamine cell groups, including all subdivisions of the substantia nigra and ventral tegmental area, and in the retrorubral field, rostral and caudal linear raphe nuclei, interfascicular nucleus, and supramammillary region. Combined isotopic/nonisotopic double-labeling in situ hybridization demonstrated that virtually all of the tyrosine hydroxylase (the catecholamine biosynthetic enzyme) mRNA-containing neurons in the ventral midbrain also expressed trkB or trkC mRNAs. Additional perikarya within these regions expressed the neurotrophin receptor mRNAs but were not dopaminergic. The present results demonstrate that essentially all mesencephalic dopaminergic neurons synthesize the neurotrophin receptors TrkB and TrkC and thus exhibit the capacity to respond directly to BDNF and NT-3 in the adult midbrain in vivo. Moreover, because BDNF and NT-3 are produced locally by subpopulations of the dopaminergic cells, the present data support the notion that the neurotrophins can influence the dopaminergic neurons through autocrine or paracrine mechanisms.     

Load transportation by dual arm robot using sliding mode control

In this study, a sliding mode controlled dual arm robotic system was designed. Such multi-arm, collaborative and synchronous robots typically are employed in hazardous situations such as radioactive materials transport explosives disposal and industrial applications. In the present study, a high performance, robust, non-chattering sliding mode controller (SMC) was developed for the purpose of safe load handling, transportation and trajectory realization. First, dynamic equations of robot/load interaction were derived. Then, the robust SMC was designed for the dual arm robotic system. In order to test the robustness of the proposed SMC, parameter variations and external disturbances were introduced to the system. Furthermore, for comparative purposes, the conventional and widely used, PID controller was also applied to the dual arm robot. Significantly, it was found that the SMC made smaller trajectory tracking errors than the PID controller. An overall analysis of the numerical results confirmed that the dual-arm robotic systems with the proposed SMC can safely and effectively be used in hazardous applications.     

Morphological and dielectric properties of barium chloride‐filled poly(vinylidene fluoride) films

Morphological characteristics of poly(vinylidene fluoride) (PVDF) films, filled with mass fractions (w ≤ 20%) of Barium Chloride (BaCl₂), were investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) absorption spectra and differential scanning calorimetry (DSC) measurements. The dielectric properties of films were measured from 250 Hz to 1 MHz range between 100 and 400 K as a function of frequency and temperature. Spectroscopic data revealed that the filled and unfilled films include α‐, β‐, and γ‐crystalline phases. By a 20% filling, 73% increase was obtained in the total degree of crystallinity. Since the BaCl₂ formed fluorine bridges over the chain segments on the crystal lamellar surface, the γ‐crystalline phase decreased, whereas the total degree of crystallinity increased. Dielectric measurements showed that maximum of the dielectric loss factor belonging to β‐relaxation transition decreased linearly with filling level. The filling process did not have any effect on the real dielectric constant till α‐relaxation transition region. However, in the α‐relaxation transition region, it was determined that the real dielectric constant increased linearly with filling level. POLYM. COMPOS., 31:1782–1789, 2010. © 2010 Society of Plastics Engineers.     

Analysis and performance assessment of a combined geothermal power-based hydrogen production and liquefaction system

In this paper, the thermodynamic study of a combined geothermal power-based hydrogen generation and liquefaction system is investigated for performance assessment. Because hydrogen is the energy of future, the purpose of this study is to produce hydrogen in a clear way. The results of study can be helpful for decision makers in terms of the integrated system efficiency. The presented integrated hydrogen production and liquefaction system consists of a combined geothermal power system, a PEM electrolyzer, and a hydrogen liquefaction and storage system. The exergy destruction rates, exergy destruction ratios and exergetic performance values of presented integrated system and its subsystems are determined by using the balance equations for mass, energy, entropy, energy and exergy and evaluated their performances by means of energetic and exergetic efficiencies. In this regard, the impact of some design parameters and operating conditions on the hydrogen production and liquefaction and its exergy destruction rates and exergetic performances are investigated parametrically. According to these parametric analysis results, the most influential parameter affecting system exergy efficiency is found to be geothermal source temperature in such a way that as geothermal fluid temperature increases from 130 °C to 200 °C which results in an increase of exergy efficiency from 38% to 64%. Results also show that, PEM electrolyzer temperature is more effective than reference temperature. As PEM electrolyzer temperature increases from 60 °C to 85 °C, the hydrogen production efficiency increases from nearly 39% to 44%.     

Preparation and optimization of superabsorbent hydrogel micromatrices based on poly(acrylic acid), partly sodium salt-g-poly(ethylene oxide) for modified release of indomethacin

The purpose of this study was to prepare modified-release dosage of indomethacin (IND) in the form of micromatrices based on a superabsorbent hydrogel (SAH), poly(acrylic acid), partly sodium salt-g-poly(ethylene oxide) (PAAc-Na-g-PEO). A soaking procedure was used for the preparation of drug-loaded hydrogel micromatrices. The amount of IND, volume of drug-loading solution, and amount of PAAc-Na-g-PEO granules used for preparing micromatrices were the independent factors. The dependent factors were the measured responses from micromatrices, that is, percent recovery, percent entrapment efficiency, and the time at which 63.2% of the drug was released (T_d, minutes). A three-factor, three-level full factorial design (33) was created to optimize formulations. Nonlinear regression analysis indicated a good correlation between the measured responses and the independent factors. Optimum responses were obtained from medium levels of IND and SAH and low level of drug-loading solution. Differential scanning calorimetry, X-ray diffraction analysis, and scanning electron micrography indicated that IND crystals are physically adsorbed into the pores and irregular spaces of the hydrogel.     

Comparison of the structural and magnetic properties of submicron barium hexaferrite powders prepared by molten salt and solid state calcination routes

The effect of crystallinity and particle morphology of the submicron barium hexaferrite (BaFe₁₂O₁₉) powders on the magnetic properties was investigated on powders synthesized by solid-state calcination (BHF-c) and molten salt synthesis (BHF-m) methods. Solid-state calcination route was found to yield agglomerated powders with poor crystallinity, whereas molten salt synthesis resulted in well crystallized powders with an anisometric morphology. The saturation magnetization of the BHF-m and BHF-c samples is 59 emu/g, and 56 emu/g at 300 K, and 90 emu/g, and 86 emu/g at 10 K. The temperature dependence of magnetization of the BHF-m is higher and the increase in magnetocrystal anisotropy with decreasing temperature is also steeper than that of the BHF-c due to the higher crystallinity. The magnetocrystalline anisotropy constant, K, calculated from the Stoner–Wohlfarth theory, of the BHF-m and BHF-c powders is 14.24 and 10.14 HA²/kg, respectively. The higher effective anisotropy, K_eff of the BHF-m is also confirmed through ferromagnetic resonance measurements. In conclusion, the higher crystallinity, slightly higher particle size and anisometric morphology of the BHF-m particles translated into higher magnetic properties and magnetocrystalline anisotropy.     

Electronic structure, spectra and photophysical properties of N-triazinylderivatives of 1-aminopyrene. Semi-empirical theoretical study

The geometry and excited state characteristics of five N-triazinyl derivatives of 1-aminopyrene were calculated using AM1, CNDO/S and ZINDO/S methods. For the optimized structures of the studied molecules, L_b, L_a and B_b transitions (localized on the amino pyrene moiety) were found, as well as charge-transfer states characterized by a charge transfer from the amino pyrene to the triazinyl ring. The energy of such strongly polar charge-transfer states depends on the chemical structure of the compound and on the solvent polarity. The relationships among each charge-transfer-to-emitting state energy gap, solvent polarity and fluorescence quantum yield of the studied compounds are discussed.