N Value (n + value)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Quantum chemistry investigation of electronic structure and NMR spectral characteristics for fluorides of dialkylamidosulfoxylic acids and related compounds

MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2009
A. B. Rozhenko
Abstract The parent (H2NSF) and N,N -dialkyl-substituted fluorides of amidosulfoxylic acid (R2NSF, RMe or R2NMorph) as well as the related compounds XSF (XCH3, OH, F, SiH3, PH2, SH, Cl) have been investigated with quantum chemical calculations at the ab initio (MP2) level of approximation. The geometries, electronic structures, molecular orbital (MO) energies and NMR chemical shift values have been calculated to evaluate the role and extent of the polarization and delocalization effects in forming of the high-field fluorine NMR resonances within the series of interest. The ,F magnitudes for all investigated fluorides of amidosulfoxylic acid as well as the ,N value calculated for Me2NSF are in the good agreement with the 19F and 14N NMR chemical shift values measured experimentally. For the parent compounds, H2NSF and H2NSO2F, the orientation of principal axes of the magnetic shielding tensors and the corresponding principal ,ii values along these axes have been qualitatively interpreted basing on the analysis of the MO interactions in the presence of the rotating magnetic field. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Glass and Mineral Chemistry of Northern Central Indian Ridge Basalts: Compositional Diversity and Petrogenetic Significance

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2009
Dwijesh RAY
Abstract: The glass and mineral chemistry of basalts examined from the northern central Indian ridge (NCIR) provides an insight into magma genesis around the vicinity of two transform faults: Vityaz (VT) and Vema (VM). The studied mid-ocean ridge basalts (MORBs) from the outer ridge flank (VT area) and a near-ridge seamount (VM area) reveal that they are moderately phyric plagioclase basalts composed of plagioclase (phenocryst [An60,90] and groundmass [An35,79]), olivine (Fo81,88), diopside (Wo45,51, En25,37, Fs14,24), and titanomagnetite (FeOt,63.75 wt% and TiO2,22.69 wt%). The whole-rock composition of these basalts has similar Mg# [mole Mg/mole(Mg+Fe2+)] (VT basalt: ,0.56,0.58; VM basalt: ,0.57), but differ in their total alkali content (VT basalt: ,2.65; VM basalt: ,3.24). The bulk composition of the magma was gradually depleted in MgO and enriched in FeOt, TiO2, P2O5, and Na2O with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the ,REE of magma also increased with fractionation, without any change in the (La/Yb)N value. Glass from the VM seamount shows more fractionated characters (Mg#: 0.56,0.57) compared to the outer ridge flank lava of the VT area (Mg#: 0.63,0.65). This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure >10 kbar, followed by Fe-rich olivine at <10 kbar pressure. [source]


Origin, age and petrogenesis of Neoproterozoic composite dikes from the Arabian-Nubian Shield, SW Jordan

GEOLOGICAL JOURNAL, Issue 2 2004
G. Jarrar
Abstract The evolution of a Pan-African (c. 900,550,Ma) suite of composite dikes, with latite margins and rhyolite interiors, from southwest Jordan is discussed. The dikes cut the Neoproterozoic calc-alkaline granitoids and high-grade metamorphic rocks (c. 800,600,Ma) of the northern Arabian-Nubian Shield in Jordan and have been dated by the Rb-Sr isochron method at 566±7,Ma. The symmetrically distributed latite margins constitute less than one-quarter of the whole dike thickness. The rhyolite intruded a median fracture within the latite, while the latter was still hot but completely solidified. The dikes are alkaline and bimodal in composition with a gap in SiO2 between 61 and 74,wt%. Both end members display similar chondrite-normalized rare earth element patterns. The rhyolites display the compositional signature of A-type granites. The (La/Lu)N values are 6.02 and 4.91 for latites and rhyolites, respectively, and the rhyolites show a pronounced negative Eu anomaly, in contrast to the slight negative Eu anomaly of the latites. The chemical variability (e.g. Zr/Y, Zr/Nb, K/Rb) within and between latites and rhyolites does not support a fractional crystallization relationship between the felsic and mafic members of the dikes. We interpret the magma genesis of the composite dikes as the result of intrusion of mantle-derived mafic magma into the lower crust in an extensional tectonic regime. The mafic magma underwent extensive fractional crystallization, which supplied the necessary heat for melting of the lower crust. The products of the initial stages of partial melting (5,10%) mixed with the fractionating mafic magma and gave rise to the latite melts. Further partial melting of the lower crust (up to 30%) produced a felsic melt, which upon 50% fractional crystallization (hornblende 15%, biotite 5%, feldspars 60%, and quartz 20%) gave rise to the rhyolitic magma. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Subcritical crack growth behavior of Al2O3 -glass dental composites

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2003
Qingshan Zhu
Abstract The purpose of this study is to investigate the subcritical crack growth (SCG) behavior of alumina-glass dental composites. Alumina-glass composites were fabricated by infiltrating molten glass to porous alumina preforms. Rectangular bars of the composite were subject to dynamic loading in air, with stressing rates ranging from 0.01 MPa/s to 2 MPa/s. The SCG parameter n was determined to be 22.1 for the composite, which is substantially lower than those of high-purity dense alumina. Investigations showed that glass phases are responsible for the low n value as cracks propagate preferentially within glass phases or along the interface between glass phases and alumina phases, due to the fact that glasses are more vulnerable to chemical attacks by water molecules under stress corrosion conditions. The SCG behavior of the infiltration glass was also investigated and the SCG parameter n was determined to be 18.7. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 65B: 233,238, 2003 [source]


Resistance Variation of Salmonella enterica Serovars to Pulsed Electric Fields Treatments

JOURNAL OF FOOD SCIENCE, Issue 7 2003
I. ÁLvarez
ABSTRACT: Inactivation of Salmonella serovar Enteritidis and Salmonella serovar Typhimurium by pulsed electric fields has been investigated. A tertiary model based on the Weibull distribution (n= 0.262) and on a new parameter (ZPEF), accurately described the kinetics of inactivation of these microorganisms among 15 and 28 kV/cm. In the range of 19 to 28 kV/cm, this model also described previously published data of inactivation of serovar Senftenberg when the n value was set at 0.437. The ZPEF value for the 3 Salmonella serovars was 15.787 kV/cm. From 19 to 28 kV/cm, the time to inactivate 5 Log10 cycles of the population of serovar Enteritidis was 2.06 and 2.66 times lower than that to inactivate serovar Typhimurium and serovar Senftenberg, respectively. [source]


Synthesis and characterization of multiblock copolymers composed of poly(5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one) outer blocks and poly(L -lactide) inner blocks

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2006
Jamie M. Messman
Abstract Ethylene glycol (EG) initiated, hydroxyl-telechelic poly(L -lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring-opening polymerization of 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) with the goal of creating A,B,A-type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A,(B,A)n,B,A type were actually obtained, where A is poly(5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one), B is PLLA, and n is greater than 0. 1H and 13C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number-average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C6H8O4 units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number-average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide-angle X-ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high-conversion L -lactide polymerizations resulted in excessive randomization, presumably because of residual L -lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817,6835, 2006 [source]


Structural elucidation of the Bi2(n,+,2)MonO6(n,+,1) (n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopy

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009
Ángel R. Landa-Cánovas
The cationic framework structure of a whole new family of compounds with the general formula Bi2(n,+,2)MonO6(n,+,1) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi10Mo3O24. These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all show fluorite superstructures. They consist of a common ,-Bi2O3 fluorite-type framework, inside of which are distributed ribbons of {MoO4} tetrahedra which are infinite along b, one tetrahedron thick along c, and of variable widths of 3, 4, 5 or 6 {MoO4} tetrahedra along a depending on the family member (n value). These {MoO4} tetrahedra are isolated, i.e. without sharing any corner as in the [Bi12O14] columnar structural-type phase Bi[Bi12O14][MoO4]4[VO4]. The structure of all these family members can be described as crystallographic shear derivatives from Aurivillius-type phases such as Bi2MoO6, the n = , end member. All these compounds are good oxygen-ion conductors. [source]


Electrochemical Reduction of 4,4,-(2,2,2-Trichloroethane-1,1-diyl)- bis(chlorobenzene) (DDT) and 4,4,-(2,2-Dichloroethane-1,1-diyl)- bis(chlorobenzene) (DDD) at Carbon Cathodes in Dimethylformamide

ELECTROANALYSIS, Issue 4 2006
Mohammad
Abstract In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4,-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4,-(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4,-(ethene-1,1-diyl)bis(chlorobenzene) (DDNU) as principal product (67,94%), together with 4,4,-(2-chloroethene-1,1-diyl)bis(chlorobenzene) (DDMU), 1-chloro-4-styrylbenzene, and traces of both 1,1-diphenylethane and 4,4,-(ethane-1,1-diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D2O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon,chlorine bonds of DDT is a two-electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products. [source]


Comparative theoretical study of small Rhn nanoparticles (2 , n , 8) using DFT methods

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2010
V. Bertin
Abstract This work is aimed at identifying some key characteristics (energy, geometry, and spin) concerning Rhn particles (2 = n , 8) to perform further studies on adsorption and coadsorption sites of pollutants (CO and NO). The DFT methods of the Gaussian 03 program with the LANL2DZ basis set and the LANL2 potential are used. With the purpose to obtain a better nanoparticles definition, five different functionals were tested: B3LYP, O3LYP, BPW91, BP86, and HCTH; and the corresponding results are used to determine which of them best describes distances, spin, and gives acceptable highest vibration frequency and binding energy values, by comparing these results with values measured or calculated by many other authors. For the structure optimization process of the particles, the initial geometric shape was taken mainly from the literature, using the Rh,Rh distance: 2.67 Å, known for the bulk; and doing a complete optimization. We also considered flat nanoparticles structures, which most of them display three-dimensional structures after the optimization process. The few flat shapes are mainly higher in energy than those of three-dimensional structure. For some Rhn particles for different n values, the spin of the ground state present degeneration. In some cases, the optimization process changes the initial geometry, but in most cases, there are only minor changes in bonds and geometry. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]


In situ ellipsometric studies of formation kinetics of rare earth metal conversion coatings on magnesium alloy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008
Lingjie Li
Abstract In situ spectroscopic ellipsometry was employed to investigate the initial regime of rare earth metal (REM) conversion coatings formation on AZ31 magnesium alloy. Three REM salts solutions, 0.05 mol·dm -3 Ce(NO3)3, La(NO)3 and Sm(NO)3 solutions, were used for REM conversion coatings preparation. By deconvoluting the ellipsometric data, the surface of the fresh well-polished AZ31 magnesium alloy was found to be covered with 15.80 nm thick native (hydr)oxide film; the refractive indices and the thickness of Ce, La and Sm conversion coatings were obtained. The formation kinetics of three REM coatings follows different exponential functions and the coatings exhibit different optical properties. La conversion coating has the largest n values and the lowest k values while Sm conversion coating is just opposite. Moreover, the pH variation of the bulk conversion solutions upon the coatings formation was recorded. It is confirmed that the reduction of protons leads to the interfacial pH increasing and further results in the precipitation of REM hydroxide gel, which is critical for the REM conversion coatings formation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Rheological behaviour of weaning food formulations as affected by addition of malt

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 10 2006
Mamudu Halidu Badau
Summary Eight weaning food formulations were prepared from the mixture of pearl millet, cowpea and groundnut in the ratio of 70:20:10. The viscosities of gruels from the eight weaning food formulations were determined at eight shear rates and five temperatures, and data obtained were subjected to power-law and Arrhenius equations. The viscosity of the weaning food gruels decreased with increase in shear rate and temperature. The gruels from the eight weaning food formulations exhibited pseudoplastic behaviour. The power-law indices (,n' values) were significantly (P < 0.05) affected by the formulations and changes in temperature. Weaning food formulations that had no malt showed the least sensitivity to temperature, while the one that had 5% ICMV-IS 94206 malt showed the highest. The correlation coefficient ranged from ,0.9993 to ,0.9524, showing that the power-law model adequately described the viscosity and shear rate characteristics of the weaning food gruels. [source]