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1.
Melanie Parker 《School science and mathematics》1997,97(8):406-412
Percent is a standardized ratio comparison that is often used to describe relative amounts of increase and decrease. In this paper, the nonsymmetric relationship between percent of increase and percent of decrease is explored in several ways. Beginning with a simple graphical representation of the relationship, the functional relationship is developed, with relative decrease expressed as a function of relative increase. Once expressed in the form f(x) = 100x/(100 + x), an immediate connection is made to two other topics commonly found within the study of rates—the work problem and the harmonic mean. Finally, successive percents of increase or decrease are shown to be everyday applications of the geometric mean. This deeper look at a common mathematical concept has uncovered rich structural relationships between topics that are often isolated in the curriculum. 相似文献
2.
E. Schnell W. Kiesewetter Y. H. Kim E. Hayek 《Monatshefte für Chemie / Chemical Monthly》1971,102(5):1327-1336
Zusammenfassung Die für den Einbau in die Calciumphosphate der Knochensubstanz in Frage kommenden Strontiumphosphate wurden auf ihre Existenzbedingungen untersucht. Oktacalciumphosphat tauscht in verd. Lösungen einige Prozente des Calciums gegen Strontium aus. Obwohl der Struktur nach apatitartige Strontiumphosphate zwischen Sr/P=1.33 und 1.67 erhältlich sind, läßt sich ein röntgenoptisch reines Strontiumoktaphosphat nicht isolieren, jedoch ein solches mit kleinem Carbonatgehalt und — leicht — die den Calciumsalzen analogen Strontiumphosphatcarbonate verschiedener Zusammensetzung. Im Hydrothermalbereich (375o) sind je nach relativer Zusammensetzung des Strontiumphosphat-Systems SrHPO4, Sr2P2O7, Sr2(PO4)2 und Sr5(PO4)3OH stabil und gut kristallin erhältlich. Das Salz Sr6H3(PO4)5 läßt sich aus Lösungen von Strontiumphosphaten in Kohlensäure-Wasser, H2S-Wasser und in einem Barbiturat-Puffersystem rein darstellen.
Mit 2 Abbildungen
Herrn Prof. Dr. Dr. h. c.Hans Nowotny gewidmet. 相似文献
Ortho strontium phosphates
Strontium phosphates which possibly are being incorporated into the calcium phosphates of bony tissue were investigated. Octacalcium phosphate in dilute solutions exchanges a few percent of calcium against strontium. While strontium phosphates with apatite-like structures, and with ratios of Sr/P between 1.33 and 1.67 can be prepared, no pure strontium octaphosphate, as a distinctive X-ray phase can be isolated. Only preparations with small amounts of carbonate, as well as strontium phosphate carbonates analogous to the corresponding calcium salts can be obtained. At hydrothermal conditions (375o), the compounds SrHPO4, Sr2P2O7, Sr3(PO4)2 and Sr5(PO4)3OH are stable, and can be prepared in well cristallized form, depending on the relative composition of the strontium phosphate system. The salt Sr6H3(PO4)5 can be prepared in a pure state from solutions of strontium phosphates in aqueous solutions of carbonic acid, H2S and barbiturate buffer systems.
Mit 2 Abbildungen
Herrn Prof. Dr. Dr. h. c.Hans Nowotny gewidmet. 相似文献
3.
David M. Rogers Claire Wells Melanie Joseph Vanessa J. Boddington Joseph J.W. McDouall 《Journal of Molecular Structure》1998,434(1-3):239-245
We describe a procedure which may be used to aid selection of the active space in multiconfigurational self-consistent field (MCSCF) calculations for general chemical systems. Starting from a restricted Hartree-Fock calculation, we define a hierarchy of interacting virtual orbitals for every occupied orbital. The most strongly interacting orbitals are then taken to constitute the active space in a configuration interaction (CI) calculation. The natural orbital occupation numbers obtained from the CI calculation are then used to choose the active space to be used in a subsequent MCSCF calculation. We illustrate our method on a number of systems (Li2, B2, C2, carbonyl oxide and the transition state for oxidation of H2S by dioxirane). In all these cases, ‘intuitive’ active spaces are inadequate, as are active spaces derived from the natural orbitals of unrestricted Hartree-Fock calculations. 相似文献
4.
The biosynthesis of several sesquiterpenes has been proposed to proceed via germacrene A. However, to date, the production of germacrene A has not been proven directly for any of the sesquiterpene synthases for which it was postulated as an intermediate. We demonstrate here for the first time that significant amounts of germacrene A (7.5% of the total amount of products) are indeed released from wild-type aristolochene synthase (AS) from Penicillium roqueforti. Germacrene A was identified through direct GC-MS comparison to an authentic sample and through production of beta-elemene in a thermal Cope rearrangement. AS also produced a small amount of valencene through deprotonation of C6 rather than C8 in the final step of the reaction. On the basis of the X-ray structure of AS, Tyr 92 was postulated to be the active-site acid responsible for protonation of germacrene A (Caruthers, J. M.; Kang, I.; Rynkiewicz, M. J.; Cane, D. E.; Christianson, D. W. J. Biol. Chem. 2000, 275, 25533-25539). The CD spectra of a mutant protein, ASY92F, in which Tyr 92 was replaced by Phe, and of AS were very similar. ASY92F was approximately 0.1% as active as nonmutated recombinant AS. The steady-state kinetic parameters were measured as 0.138 min(-1) and 0.189 mM for k(cat) and K(M), respectively. Similar to a mutant protein of 5-epi-aristolochene (Rising, K. A.; Starks, C. M.; Noel, J. P.; Chappell, J. J. Am. Chem. Soc. 2000, 122, 1861-1866), the mutant released significant amounts of germacrene A (approximately 29%). ASY92F also produced various amounts of a further five hydrocarbons of molecular weight 204, valencene, beta-(E)-farnesene, alpha- and beta-selinene, and selina-4,11-diene. 相似文献
5.
Potter CV Freshwater J Dean JL Kybett AP Kidd R James M Saxton H 《Chemical Society reviews》2004,33(9):567-572
In January 2003, the Royal Society of Chemistry launched Organic & Biomolecular Chemistry (OBC)--a journal promising to provide high quality research from all aspects of synthetic, physical and biomolecular organic chemistry. The journal was set to build upon the foundations laid down by its predecessor publications (J. Chem. Soc., Perkin Trans. 1 and J. Chem. Soc., Perkin Trans. 2) as well as complement the subject coverage already published in prestigious general chemistry journals such as Chemical Communications and Chemical Society Reviews. Nearly two years on, just how is the programme developing and what can the community expect to see from the Royal Society of Chemistry (RSC)? 相似文献
6.
E. Schnell 《Monatshefte für Chemie / Chemical Monthly》1962,93(5):1136-1141
Zusammenfassung Die Verbindung SiF4·N(CH3)3 ist in Benzol löslich und daraus in nadelförmigen Kristallen erhältlich, während SiF4·2 N(CH3)3 als in Petroläther schwer löslicher Niederschlag gewonnen werden kann. IR-Spektren beider Verbindungen werden mitgeteilt.Mit 2 Abbildungen 相似文献
7.
In solid-state NMR, deuteron (2H) spectroscopy can be performed in full analogy to1H spectroscopy, including2H chemical-shift resolution and2H-X dipolar correlation schemes, when the NMR experiments are conducted in a “rotor-synchronized” fashion under fast magic-angle
spinning. Here, 2H-X NMR experiments of this type, including2H-15N and2H-1H chemical-shift correlations and distance measurements, are introduced and demonstrated on cytosine monohydrate, whose acidic
protons can readily be replaced by deuterons by recrystallization from D2O. In this way,2H NMR spectroscopy provides information complementary to1H NMR data, which is particularly useful for studying hydrogen bonds in supra- or biomolecular systems.
Electronic supplementary material Supplementary material is available in the online versionof this article atand is accessible for authorized users. 相似文献
8.
An improved and efficient synthetic route to four functionalized bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) derivatives 2-5 is reported. Tetrathiolate 1 was readily prepared from 2,2'-bis(1,3,4,6-tetrathiapentalen-5-one) under carefully controlled conditions. Subsequent reaction of 1 with selected primary alkyl halides affords new functionalized BEDT-TTF derivatives in good yields. 相似文献
9.
Potter CV Thomas S Dean JL Kybett AP Kidd R James M Saxton H 《Chemical communications (Cambridge, England)》2004,(24):2781-2786
In January 2004, the Royal Society of Chemistry launched Organic & Biomolecular Chemistry (OBC) - a journal promising to provide high quality research from all aspects of synthetic, physical and biomolecular organic chemistry. The journal was set to build upon the foundations laid down by its predecessor publications (J. Chem. Soc., Perkin Trans. 1 and J. Chem. Soc., Perkin Trans. 2) as well as complement the subject coverage already published in prestigious general chemistry journals such as Chemical Communications and Chemical Society Reviews. Nearly two years on, just how is the programme developing and what can the community expect to see from the Royal Society of Chemistry (RSC)? 相似文献
10.
Multireference configuration interaction calculations are carried out for ground and excited states of dichloromethanol, Cl2CHOH, to investigate two important photofragmentation processes relevant to atmospheric chemistry. Five low-lying excited states (1(1)A", 2(1)A', 1(3)A", 2(3)A" and 1(3)A') in the energy range between 6.4 and 7.5 eV are found to be highly repulsive for C-Cl elongation, leading to ClCHOH (X2A) and Cl (X2P). Photodissociation along the C-O bond resulting in CHCl2 (X2A') and OH (X2II) has to overcome a barrier of about 0.5 eV because the low-lying excited states 1(1)A", 1(3)A' and 1(3)A" become repulsive only after the C-O bond is elongated by about 0.3 A. 相似文献