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1.
M. Zakrzewski D. D. Klug J. A. Ripmeester 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(3):237-247
A high-pressure phase of the clathrate hydrate of tetrahydrofuran was prepared by freezing a liquid phase of overall composition THF · 7 H2O under a pressure of 3.0 kbar, or by pressurizing the solid structure II THF hydrate of 255K to 3.4 kbar. Unfortunately, the products recovered at 77K were always mixed phase materials as shown by X-ray powder diffraction. A number of diffraction lines could be indexed in terms of the cubic structure I hydrate with a slightly expanded lattice parameter, 12.08 Å, giving some support to Dyadin's idea that the high pressure phase transition involves a conversion of Structure II to Structure I. Other phases observed in the recovered product include Ice IX and amorphous materials. The reversion of the high pressure sample to the structure II hydrate was followed by differential scanning calorimetry. At ambient pressure, the high pressure sample converts slowly back to Structure II hydrate event at 77K.NRCC No. 35786. 相似文献
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Athos Bellomo und Otto Klug 《Fresenius' Journal of Analytical Chemistry》1965,207(2):93-98
Zusammenfassung Die Messung der Elektrolytkonzentration in fließenden Lösungen, auch bei solchen, die Niederschläge oder Suspensionen enthalten, wird auf Grund der Veränderung des Dielektrikums einer Zelle, welche von einem elektrischen Hochfrequenzstrom durchflossen wird, durchgeführt. Auf diesem Wege ist die quantitative Bestimmung der Konzentration der gelösten Substanz oder die der durchlaufenden Menge beträchtlich vereinfacht und automatisiert. Dabei werden subjektive und Manipulationsfehler weitgehend ausgeschlossen. Die untersuchte Probe erleidet keinerlei Veränderungen.
Summary The electrolyte concentration of flowing solutions and of suspensions or solutions containing precipitates can be measured by the variation of the dielectrics in a cell, which is coupled with a high-frequency circuit. By means of this method the quantitative determination of the concentration of solutions or the determination of the quantity of ions passed through the tube can be simplified. The method makes possible an automatization and it precludes the possibility of subjective and manipulation errors. During the measurement the sample remains unchanged.相似文献
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Manoj K. Kolel‐Veetil Kenan P. Fears Syed B. Qadri Christopher A. Klug Teddy M. Keller 《Journal of polymer science. Part A, Polymer chemistry》2012,50(15):3158-3170
A semicrystalline inorganic–organic hybrid crosslinked network containing polyhedral oligomeric silsesquioxane (POSS) cores was constructed by the unusual hydrosilylation of the terminal vinyl groups of an internal acetylene‐containing silane linker by a POSS monomer. Products from the thermal treatments of this network in either argon or air at 250, 550, and 1000 °C, respectively, were characterized by Fourier transform infrared, Solid‐state 13C and 29Si magic angle spinning NMR, X‐ray diffraction and XPS analyses. The highly symmetrically functionalized POSS silica clusters, in the fluorite silica phase, in the network were found to remain unchanged on thermal treatment possibly due to the shielding of the silica core by the functionalities and a cancellation of thermal stresses on the silica core. Stabilization of the metastable α‐cristobalite phase, which is typically formed on cooling by a β‐ to α‐transition of the β‐cristobalite phase formed above 1400 °C, was observed in the amorphous regions in the network sample treated only to 1000 °C in air. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
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Manoj K. Kolel‐Veetil Dawn D. Dominguez Christopher A. Klug Kenan P. Fears Syed B. Qadri Daniel Fragiadakis Teddy M. Keller 《Journal of polymer science. Part A, Polymer chemistry》2013,51(12):2638-2650
Structural isomers of thermo‐oxidatively stable poly(carborane‐siloxane‐arylacetylene) (PCSAA), namely, m‐PCSAA and p‐PCSAA, were synthesized by the reaction of the dimagnesium salts of m‐diethynylbenzene or p‐diethynylbenzene with 1,7‐bis(chlorotetramethyldisiloxyl)‐m‐carborane. The developed polymers have exceptional thermo‐oxidative properties similar to their diacetylene counterpart poly(carborane‐siloxane‐acetylene), PCSA. Thermal treatment of either of the PCSAAs results in a fully crosslinked thermoset by 500 °C resulting from the cycloaddition reactions involving the acetylene and aryl functionalities and subsequent formation of bridging disilylmethylene entities as discerned from Fourier transform infrared, 13C and 29Si solid‐state NMR, and XPS studies. X‐ray diffraction analysis revealed that the thermosets obtained from p‐PCSAA possess enhanced crystallinity when compared to that obtained from m‐PCSAA possibly due to more efficient packing interactions of the p‐diethynylbenzene groups during thermoset formation. The presence of the aryl groups in the backbone of the PCSAAs' chains appeared to have enhanced the storage and bulk moduli of their thermosets when compared to the thermoset of PCSA. Dielectric studies of m‐PCSAA and p‐PCSAA revealed segmental relaxation peaks, α, above their glass transition temperatures with p‐PCSAA exhibiting a broader peak with a slower relaxation rate than m‐PCSAA. © 2013 Wiley Periodicals, Inc.? J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2638–2650 相似文献
7.
A combination of reverse Monte Carlo, molecular dynamics, and lattice dynamics simulations were used to obtain structural and thermodynamic data for low-density amorphous ice. A thermodynamically discontinuous transformation to a phase with properties and a structure consistent with supercooled liquid water is found to occur at approximately 130 K. Quantum corrections have a profound effect on thermodynamic properties and the location of important thermodynamic points in the water phase diagram. 相似文献
8.
Haines J Chateau C Léger JM Bogicevic C Hull S Klug DD Tse JS 《Physical review letters》2003,91(1):015503
The cristobalitelike forms of the ternary silica analogues BPO4 and BAsO4 were investigated at high pressure by x-ray diffraction and theoretical methods. The behavior of these compounds represents an extreme case in which the tilt angle of the constituent tetrahedra increases in a spectacular way at high pressure resulting in a major change in topology from a cristobalitelike framework towards a "collapsed cristobalite" structure. These compounds provide the first examples of the collapse of a framework structure to a close-packed form in a continuous manner without an intervening phase transition. 相似文献
9.
Trent D Lund Timothy W West Lilyan Y Tian Lihong H Bu Daniel L Simmons Kenneth DR Setchell Herman Adlercreutz Edwin D Lephart 《BMC neuroscience》2001,2(1):20-13
Background
In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined. 相似文献10.
The high-pressure structural transformation of elemental Sn is studied using an ab initio density functional theory implementation of the metadynamics method that predicts with sufficient compression, Sn will transform from the bcc structure into an hcp structure. The low-free-energy pathway associated with this phase transition is characterized as the Burgers transition mechanism. The superconducting properties of Sn under pressure are also investigated. Both bcc and hcp structures of Sn exhibit very weak electron-phonon coupling and therefore would not sustain superconductivity at high pressure. 相似文献