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991.
The mixture {yNH4Cl + (1 − y)MgCl2} (aq) has been studied using the hygrometric method at the temperature 298.15 K. The water activities are measured at total molalities from 0.30 mol kg−1 up to saturation for different ionic strength fractions y of NH4Cl with y = 0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. Experimental results are compared with the calculations using the models of Zdanovskii–Stokes–Robinson, Kusik and Meissner, Robinson and Stokes, Lietzke and Stoughton, Reilly–Wood and Robinson and Pitzer. Thermodynamic properties have been modeled using the Pitzer ion-interaction model with inclusion of an ionic strength dependence of the third virial coefficient for the binary systems. From these measurements and the obtained binary parameters β(0), β(1), C(0) and C(1), the mixing ionic parameters θNH4Mg and ψNH4MgCl are determined by the standard Pitzer model. The results show that a good accuracy is obtained with the standard Pitzer model using extended binary parameters. The parameters θNH4Mg and ψNH4MgCl were used for evaluation of activity coefficients in the mixture. The excess Gibbs energy is also determined. 相似文献
992.
Brasseur R Braun N El Kirat K Deleu M Mingeot-Leclercq MP Dufrêne YF 《Langmuir : the ACS journal of surfaces and colloids》2007,23(19):9769-9772
Under specific conditions, lipid membranes form ripple phases with intriguing nanoscale undulations. Here, we show using in situ atomic force microscopy (AFM) that the biologically important surfactin lipopeptide induces nanoripples of 30 nm periodicity in dipalmitoyl phosphatidylcholine (DPPC) bilayers at 25 degrees (i.e. well below the pretransition temperature of DPPC). Whereas most undulations formed the classical straight orientation with characteristic angle changes of 120 degrees , some of them also displayed unusual circular orientations. Strikingly, ripple structures were formed at 15% surfactin but were rarely or never observed at 5 and 30% surfactin, emphasizing the important role played by the surfactin concentration. Theoretical simulations corroborated the AFM data by revealing the formation of stable surfactin/lipid assemblies with positive curvature. 相似文献
993.
Soukaina Faarasse Nabil El Brahmi Grald Guillaumet Saïd El Kazzouli 《Molecules (Basel, Switzerland)》2021,26(19)
The regioselective C-H functionalization of the five-membered ring of the 6,5-fused heterocyclic systems is nowadays well documented due to its high reactivity compared to the six-membered ring. So, developing new procedures of C-H functionalization of the six-membered ring “by thinking out of the box” is extremely challenging, which explains the limited number of reports published to date. This review paper aims to highlight advances achieved in this emerging chemistry research and discusses recently reported methods. 相似文献
994.
Zahoor Ahmad Baba Basharat Hamid Tahir Ahmad Sheikh Saad H. Alotaibi Hesham A. El Enshasy Mohammad Javed Ansari Ali Tan Kee Zuan R. Z. Sayyed 《Molecules (Basel, Switzerland)》2021,26(19)
Soil potassium (K) supplement depends intensively on the application of chemical fertilizers, which have substantial harmful environmental effects. However, some bacteria can act as inoculants by converting unavailable and insoluble K forms into plant-accessible forms. Such bacteria are an eco-friendly approach for enhancing plant K absorption and consequently reducing utilization of chemical fertilization. Therefore, the present research was undertaken to isolate, screen, and characterize the K solubilizing bacteria (KSB) from the rhizosphere soils of northern India. Overall, 110 strains were isolated, but only 13 isolates showed significant K solubilizing ability by forming a halo zone on solid media. They were further screened for K solubilizing activity at 0 °C, 1 °C, 3 °C, 5 °C, 7 °C, 15 °C, and 20 °C for 5, 10, and 20 days. All the bacterial isolates showed mineral K solubilization activity at these different temperatures. However, the content of K solubilization increased with the upsurge in temperature and period of incubation. The isolate KSB (Grz) showed the highest K solubilization index of 462.28% after 48 h of incubation at 20 °C. The maximum of 23.38 µg K/mL broth was solubilized by the isolate KSB (Grz) at 20 °C after 20 days of incubation. Based on morphological, biochemical, and molecular characterization (through the 16S rDNA approach), the isolate KSB (Grz) was identified as Mesorhizobium sp. The majority of the strains produced HCN and ammonia. The maximum indole acetic acid (IAA) (31.54 µM/mL) and cellulase (390 µM/mL) were produced by the isolate KSB (Grz). In contrast, the highest protease (525.12 µM/mL) and chitinase (5.20 µM/mL) activities were shown by standard strain Bacillus mucilaginosus and KSB (Gmr) isolate, respectively. 相似文献
995.
Natural radioactivity and radon exhalation rates in building materials used in Egypt 总被引:2,自引:0,他引:2
Natural and fabricated building materials commonly used in Egypt were surveyed for both natural radionuclides content and radon exhalation rate. These include raw as well as construction products. Concentration of natural radionuclides in all samples were determined by γ-ray spectroscopy with HPGe detector. For Radon exhalation rate measurements of fabricated samples, the seal can-technique has been applied using CR-39 plastic track detectors. The radiation hazard indices of the total natural radioactivity in the studied samples were estimated. The results were compared with the corresponding results of different countries and were found to be lying within the average world values. Radon exhalation rate in the studied samples varied between 197 (cement brick) and 907 mBq m−2 h−1 (blast furnace slag cement). The results of this survey suggest that, using blast furnace slag cement for pre-coating the internal walls of buildings in the Urban region of Egypt is discouraged and the replacement of clay brick by cement brick will be more healthy for the public. 相似文献
996.
P. Możejko G. Kasperski Cz. Szmytkowski A. Zecca G.P. Karwasz L. Del Longo R.S. Brusa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):481-485
The absolute total cross-sections for electron scattering on SiCl4 molecules have been measured in two distinct electron-transmission experiments, in Gdansk and in Trento laboratory, for impact energy ranging from 0.3 to 250 eV and from 75 to 4000 eV, respectively. The e--SiCl4 total cross-section function shows two very distinct resonant-like features: the strong peak at 1.9 eV and much broader main maximum centered near 10 eV with some additional substructure close to 5 eV. The present results are compared with low-energy total experimental data and elastic theoretical calculations for electron collisions with silicon tetrachloride molecules. 相似文献
997.
C. Wiele F. Haake K. Rzażewski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(3):405-409
We solve the superradiant laser model in two limiting cases. First the stationary low-pumping regime is considered where a
first-order phase transition in the semiclassical solution occurs. This discontinuity is smeared out in the quantum regime.
Second, we solve the model in the non-stationary regime where we find a temporally periodic solution. For a certain parameter
range well-separated pulses may occur.
Received: 19 June 1998 / Accepted: 19 October 1998 相似文献
998.
H. El‐Shall Jin‐hwan Jeon E. A. Abdel‐Aal S. Khan L. Gower Y. Rabinovich 《Crystal Research and Technology》2004,39(3):214-221
There are various organic and inorganic constituents in kidney stones. Among them, calcium oxalate monohydrate (COM) is the primary inorganic constituent of kidney stones. However, the mechanisms of formation of kidney stones are not well understood. In this regard, a basic study is carried out for better understanding of nucleation, crystal growth and/or aggregation of formed COM crystals. The primary nucleation of calcium oxalate monohydrate is studied at the laboratory scale using turbidity measurements. Calcium chloride and potassium oxalate solutions are mixed and then added to a Turbidimeter tube for continuous recording of turbidity. Induction time (time to induce formation of detectable crystals) is estimated from time‐turbidity graphs. The effect of some urinary species, such as oxalate and calcium, on nucleation and crystallization characteristics of COM is determined by particle size distribution analysis, measuring weight of crystals and calculation of relative supersaturation. The classical nucleation theory is applied at high supersaturation ratios (SR) ranging from 1.6 to 2.2. The results indicate that nucleation rate increases with increasing supersaturation ratio from 0.81 × 1028 nuclei/cm3.sec at 1.6 SR, to 18.02 × 1028 nuclei/cm3.sec at 2.2 SR. On the other hand, free energy change and radius of critical nucleus are decreased as supersaturation ratio is increased. The nucleation rates are higher than those reported in literature. Such discrepancy is discussed on the bases of differences in experimental techniques. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
We have studied the effect of subsequent gamma (γ) irradiation on the absorption spectra and the optical energy gap of ZnO thin films doped with Li (ZnO:Li). The optical transmission (T) and optical reflection (R) in the wavelength range 190∼800 nm of films deposited at 300 °C on sapphire, MgO or quartz substrates were measured. The dependence of the absorption coefficient α on photon energy hν was determined as a function of γ‐doses. The films show direct allowed interband transition that influenced by the gamma doses. Both the optical energy gap Eoptg and the absorption coefficient (α) were found to be γ‐dose dependent. The results can be discussed on the basis of γ‐irradiation‐induced defects in the film and on the film structure. The absorption coefficient exhibits exponential dependence on photon energy obeying Urbach's rule in the absorption edge. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
Free Sulfate is a major parameter affecting gypsum crystallization during phosphoric acid production. Gypsum crystal size, shape and filtration rate are significantly affected by the concentration of free sulfate. It is, therefore, important to evaluate the effectiveness of different sulfate levels from 1.5% to 3.5% on induction time and gypsum morphology. The crystallization of gypsum was carried out under simulated conditions of phosphoric acid production by the dihydrate process. Calcium hydrogen phosphate and sulfuric acid were mixed with dilute phosphoric acid at 80 °C, and the turbidity of the reaction mixture was measured at different time periods to calculate the induction time of gypsum crystals formation. With increasing free sulfate concentration, the induction time was significantly decreased. Chemical processing of Central and South Florida phosphate concentrates under different concentrations of free sulfate from 1.5% to 5.5% was carried out. The change on crystal size distribution and filtration rate were traced with free sulfate concentrations. The results show that, filtration rate of phosphogypsum was correlated to the mean diameter of crystals. In addition, induction time and co‐crystallized (lattice) P2O5 % in gypsum are decreased with increasing free sulfate content from 1.5% to 3.5%. Morphology of formed gypsum crystals at different sulfate contents and different supersaturation ratios are investigated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献