The effect of various treatment conditions on natural zeolites: Ion exchange, acidic, thermal and steam treatments

Two different natural zeolites having different phase compositions were obtained from different regions of Turkey and modified by ion-exchange (0.5 M NH4NO3) and acid leaching using 1 M HCl. The natural and modified samples were treated at low temperature (LT), high temperature (HT) and steam (ST) conditions and characterised by XRF, XRD, BET, FTIR, DR-UV-Vis, NH3-TPD and TGA. Ion-exchange with NH4+ of natural zeolites results in the exchange of the Na+ and Ca2+ cations and the partial exchange of the Fe3+ and Mg2+ cations. However, steam and acidic treatments cause significant dealumination and decationisation, as well as loss of crystalline, sintering of phases and the formation of amorphous material. The presence of mordenite and quartz phases in the natural zeolites increases the stability towards acid treatment, whereas the structure of clinoptilolite-rich zeolites is mostly maintained after high temperature and steam treatments. The natural and modified zeolites treated at high temperature and in steam were found to be less stable compared with synthetic zeolites, resulting in a loss of crystallinity, a decrease in the surface area and pore volume, a decrease in the surface acidity as well as dealumination, and decationisation. (C) 2012 Elsevier Inc. All rights reserved.

Measurement of absolute charge-exchange cross sections for He2+ collisions with He and H-2

Reported are total, absolute charge-exchange cross sections for collisions of 3He(2+) ions with He and H-2. Measurements are reported at fixed energies between 0.33 and 4.67 keV/amu. Both the present results and earlier results of others are analyzed in terms of available experimental small-angle differential cross sections as a function of collision energy, and hence the geometry of the exit aperture of the gas-collision cells used by the various experimental groups. In addition, the effective length of gas-collision cells is studied using fluid dynamic and molecular flow simulations to address the density patterns near the cell entrance and exit apertures. When small acceptance-angle corrections were applied, the results of present and previous measurements for the single electron capture in these systems were brought into good accord in the relevant energy ranges. Taken in their entirety, the present data for 3He(2+) with He and H-2 lend themselves to new theoretical calculations of the multichannel charge-exchange cross sections.

The place(s) of student voice in 14-19 education policy reform: reflections on consultation and participation

Certain policy areas with considerable impact on young people's educational experiences and achievements, notably assessment and qualifications, do not involve consultation with young people to any meaningful extent. Findings from a national study, which included focus groups with 243 students in the 14-19 phase, are presented with respect to student consultation and participation in such policy areas. A lack of meaningful consultation regarding what students see as ‘higher level’ policy agendas was found (such as qualifications provision, choice or structure). Students are therefore ‘voiceless’ in relation to major qualifications reforms

Contribution of reverse Na+/Ca2+ exchange to spontaneous activity in interstitial cells of cajal in the rabbit urethra

Interstitial cells of Cajal (ICC) isolated from the rabbit urethra exhibit regular Ca2+ oscillations that are associated with spontaneous transient inward currents (STICs) recorded under voltage clamp. Their frequency is known to be very sensitive to external Ca2+ concentration but the mechanism of this has yet to be elucidated. In the present study experiments were performed to assess the role of Na+-Ca2+ exchange (NCX) in this process. Membrane currents were recorded using the patch clamp technique and measurements of intracellular Ca2+ were made using fast confocal microscopy. When reverse mode NCX was enhanced by decreasing the external Na+ concentration [Na+]o from 130 to 13 mM, the frequency of global Ca2+ oscillations and STICs increased. Conversely, inhibition of reverse mode NCX by KB-R7943 and SEA0400 decreased the frequency of Ca2+ oscillations and STICs. Application of caffeine (10 mM) and noradrenaline (10 microM) induced transient Ca2+-activated chloride currents (I(ClCa)) at -60 mV due to release of Ca2+ from ryanodine- and inositol trisphosphate (IP3)-sensitive Ca2+ stores, respectively, but these responses were not blocked by KB-R7943 or SEA0400 suggesting that neither drug blocked Ca2+-activated chloride channels or Ca2+ release from stores. Intact strips of rabbit urethra smooth muscle develop spontaneous myogenic tone. This tone was relaxed by application of SEA0400 in a concentration-dependent fashion. Finally, single cell RT-PCR experiments revealed that isolated ICC from the rabbit urethra only express the type 3 isoform of the Na+-Ca2+ exchanger (NCX3). These results suggest that frequency of spontaneous activity in urethral ICC can be modulated by Ca2+ entry via reverse NCX.

Na+/H+ exchange inhibitor cariporide attenuates skeletal muscle infarction when administered before ischemia or reperfusion

Administration of Na(+)/H(+) exchange isoform-1 (NHE-1) inhibitors before ischemia has been shown to attenuate myocardial infarction in several animal models of ischemia-reperfusion injury. However, controversy still exists as to the efficacy of NHE-1 inhibitors in protection of myocardial infarction when administered at the onset of reperfusion. Furthermore, the efficacy of NHE-1 inhibition in protection of skeletal muscle from infarction (necrosis) has not been studied. This information has potential clinical applications in prevention or salvage of skeletal muscle from ischemia-reperfusion injury in elective and trauma reconstructive surgery. The objective of this research project is to test our hypothesis that the NHE-1 inhibitor cariporide is effective in protection of skeletal muscle from infarction when administered at the onset of sustained ischemia or reperfusion and to study the mechanism of action of cariporide. In our studies, we observed that intravenous administration of cariporide 10 min before ischemia (1 or 3 mg/kg) or reperfusion (3 mg/kg) significantly reduced infarction in pig latissimus dorsi muscle flaps compared with the control, when these muscle flaps were subjected to 4 h of ischemia and 48 h of reperfusion (P <0.05; n = 5 pigs/group). Both preischemic and postischemic cariporide treatment (3 mg/kg) induced a significant decrease in muscle myeloperoxidase activity and mitochondrial-free Ca(2+) content and a significant increase in muscle ATP content within 2 h of reperfusion (P <0.05; n = 4 pigs/group). Preischemic and postischemic cariporide treatment (3 mg/kg) also significantly inhibited muscle NHE-1 protein expression within 2 h of reperfusion after 4 h of ischemia, compared with the control (P <0.05; n = 3 pigs/group). These observations support our hypothesis that cariporide attenuates skeletal muscle infarction when administered at the onset of ischemia or reperfusion, and the mechanism involves attenuation of neutrophil accumulation and mitochondrial-free Ca(2+) overload and preservation of ATP synthesis in the early stage of reperfusion.