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  • 1
    ISSN: 1572-8927
    Keywords: Equilibrium constant ; enthalpy change ; entropy change ; heat capacity change ; capacity change ; flow calorimetry ; high temperature ; hydrochloric acid ; acetic acid ; sodium acetate ; isocoulombic reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The aqueous reactions, {ie865-1} were studied as a function of ionic strength at 275, 300, and 320°C using a flow calorimetric technique. Log K, ΔH and ΔS values were determined from the fits of the calculated and experimental heats while ΔCp values were calculated from the variation of ΔH values with temperature. The log K and ΔH values for the first two reactions agree well with literature values at these temperatures. No previous results have been reported for the third reaction. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the log K values determined in this study. The resulting plots of log K for the isocoulombic reactions vs. I/T were approximately linear, which demonstrates that the ΔCp values for these reactions are approximately zero.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-8927
    Keywords: Equilibrium constant ; enthalpy change ; entropy change ; heat ; capacity change ; flow calorimetry ; high temperature ; hydrogen sulfate ion and sodium sulfate ion formation ; isocoulombic effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The aqueous reactions, $$\begin{gathered} H^ + + SO_4^{2 - } = HSO_4^ - ,Na^ + + SO_4^{2 - } = NaSO_1^ - , \hfill \\ and H^ + + HSO_4^ - = H_2 SO_4 (aq) \hfill \\ \end{gathered} $$ were studied as a function of ionic strength(I) at 150, 175, 200, 250, 300 and 320°C using a flow calorimetric procedure. Log K, ΔH, ΔS and ΔC p values at I=0 were derived from the data at each temperature. Using these experimental values, equations describing log K, ΔH, ΔS and ΔC p at I=0 and temperatures from 150 to 320°C were derived for each system. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was evaluated as a technique for the extrapolation of log K values valid below 100°C to temperatures above 150°C. This evaluation indicated that the principle gives good estimates up to 320°C.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Computers and the humanities 6 (1972), S. 223-227 
    ISSN: 1572-8412
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Media Resources and Communication Sciences, Journalism
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 60 (1997), S. 538 -546 
    ISSN: 1432-0827
    Keywords: Key words: Nucleation — Magnesium — Growth — Biomineralization — Inhibition.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. The effects of magnesium ion on the formation of calcium-deficient hydroxyapatite [Ca9HPO4(PO4)5OH, CDHAp] from CaHPO4 and Ca4(PO4)2O dissolution were investigated using two magnesium sources: Mg3(PO4)2 (chemical system 1) or MgCl2· H2O (chemical system 2) solutions. Because chloroapatite does not form from aqueous solutions, the use of two magnesium sources facilitated the determination of magnesium's role during synthetic hydroxyapatite formation in vitro and possible related effects during biomineralization. Isothermal calorimetry determined the progress of reactions. Two peaks are observed as heat is evolved during the formation of CDHAp in water at 37.4°C. The nucleation and growth of CDHAp are the corresponding mechanisms. Although the time for complete reaction and total heat-of-reaction ΔHr remain constant, the height of the first peak is reduced as the concentration of magnesium ion approaches 4 mM in either chemical system. Magnesium does not substitute into CDHAp even though there are calcium vacancies available. Subsequent increases cause the remaining heat peak to broaden and the time required for complete reaction to approach 24 hours as the initial MgCl2 concentration reaches 100 mM. Supersaturation limits chemical system 1 to Mg3(PO4)2 concentrations below 10 mM. A MgCl2 concentration of 3.16 M precludes CDHAp from forming for over 3 months; rather newberyite, MgHPO4· 3H2O, precipitates. The morphology and surface area of the CDHAp formed in 100 mM MgCl2 solution are comparable to those of CDHAp formed in water. The surface areas are approximately 80 m2/g. Magnesium concentrations below 4 mM only inhibit nucleation whereas those above 4 mM inhibit growth as well. Magnesium phosphate complexes are more inhibitory than magnesium chloride complexes. Increasing the liquid-to-solids ratio or agitation significantly increases the induction period before reaction initiates. Increasing the liquid-to-solids ratio increases the time span for growth whereas increasing agitation decreases the time span for growth. The large inhibitory effect of agitation suggests quiescent systems are more suitable for determining the kinetics of HAp formation. A magnesium inorganic chemical activity (αMg=γMg[Mg2+]) many times greater than that in biological fluids is required before inhibition of hydroxyapatite formation is realized.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 92 (1986), S. 57-70 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The igneous rocks of the Kialineq centre on the coast of East Greenland at 67°N include a number of quartz syenite and granite plutons intruded 35my BP. These are subvolcanic bodies emplaced by cauldron subsidence and with ring-dike and bell-jar form. Associated with the major intrusions is an extensive acid-basic mixed magma complex. Two-liquid structures, chilling of basic against acid magma, pillows of basic in acid, and net-veining of basic by acid magma, are superbly displayed. The basic magma was of a transitional or alkaline type and underwent varying degrees of fractionation in a regime of repeated intrusions and diverse chambers. Heterogeneous hybrid rocks intermediate between basalt and quartz syenite are strongly developed and were formed by repeated mechanical mixing of contrasting magmas. The energy for this mixing probably came in the main from cauldron-block subsidence. The quartz syenite magma, which itself fractionated towards granite, has initial 87Sr/86Sr ratios the same as the basic magma and is itself believed to be a fractionation product of alkali basalt magma.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 68 (1995), S. 223-245 
    ISSN: 1573-0794
    Keywords: meteoroids ; radio-meteors ; sporadic meteors ; meteor flux
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We have calculated the response functions for the Springhill (Ottawa) and Christchurch (New Zealand) radars. Using the sizes and locations of each of the six sporadic radio-meteor sources found in our previous study (Jones and Brown, 1993), we have determined the response of each radar to each of the sources. Then, using least-squares fit to data collected over several years, we have determined the strength of each source. Excellent agreement with the non-radar data is obtained for the total flux after application of a correction for the initial train radius. The results from the two radars show good consistency for the sources which are visible to both of them. For individual years the fits are good to between 5 and 10% but there does appear to be some variability from year to year which may be due to atmospheric effects.
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  • 7
    ISSN: 1359-5997
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract The hydration stoichiometry, products and kinetics of dicalcium silicate are summarized. Hydration takes a similar course to tricalcium silicate, but at a much slower rate. The differences and similarities between the two compounds are identified and discussed, and future research needs identified.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Zeitschrift für angewandte Mathematik und Physik 22 (1971), S. 855-864 
    ISSN: 1420-9039
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Résumé On sait qu'un semi-espace de terrain isotrope, élastique et incompressible — dont le module de cisaillement accroît linéairement avec la profondeur, partant de zéro à la surface — réagit à la charge superficielle exactement selon les hypothèses faites par Winkler dans sa théorie de la réaction du niveau de fondation. On examine ici jusqu'à quel point la validité de ce résultat s'applique à un milieu de profondeur limitée. On y démontre que, si la profondeur de la couche dépasse la largeur de la surface chargée, le tassement d'une charge répartie uniformément est aussi pratiquement uniforme. Cependant, au delà du sol chargé, la surface se souleve d'une manière sensible, même lorsque la couche est d'une épaisseur modérée.
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  • 9
    ISSN: 1359-5997
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Summary Evidence on the mechanism and products of tricalcium silicate hydration is summarized, and present-day interpretations of that evidence critically discussed, partly with a view to supplying a basis for mathematical modeling of the hydration process. There is general agreement on many, broad features of the reaction and its products, and it should be possible to express many of the proposed hypotheses in mathematical form. Uncertainties nevertheless remain about many questions that are of essential importance if kinetic equations based on an unequivocal understanding of the mechanism are to be formulated. The paper concludes with a list of these questions.
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  • 10
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Es wird über die Isolierung und Charakterisierung der Titelverbindung (Gly-l-Pro Lactam, I) aus dem SeesternLuidia clathrata berichtet. Die Kristallstruktur dieses Dioxopiperazinderivats wurde ermittelt. Der Piperazinring liegt in der Wannen-Konformation vor.
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