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221.
Michelle Cutajar Robert A. Stockman Susan Braovac Calin Constantin Steindal Angeliki Zisi Stephen E. Harding 《Molecules (Basel, Switzerland)》2022,27(7)
Butvar B-98 and PDMS-OH both have a demonstrable ability as consolidants for archaeological wood. This makes them both potential treatment options for the Oseberg collection, which is one of the most important archaeological finds from the Viking era. Both Butvar B-98 and PDMS-OH are soluble in organic solvents, offering a useful alternative to aqueous-based consolidants. Extensive characterisation studies were carried out on both of these polymers, with the use of analytical ultracentrifugation and viscometry, for the benefit of conservators wanting to know more about the physical properties of these materials. Short column sedimentation equilibrium analysis using SEDFIT-MSTAR revealed a weight-average molar mass (weight-average molecular weight) Mw of (54.0 ± 1.5) kDa (kg · mol−1) for Butvar B-98, while four samples of PDMS-OH siloxanes (each with a different molar mass) had an Mw of (52.5 ± 3.0) kDa, (38.8 ± 1.5) kDa, (6.2 ± 0.7) kDa and (1.6 ± 0.1) kDa. Sedimentation velocity confirmed that all polymers were heterogeneous, with a wide range of molar masses. All molecular species showed considerable conformational asymmetry from measurements of intrinsic viscosity, which would facilitate networking interactions as consolidants. It is anticipated that the accumulated data on these two consolidants will enable conservators to make a more informed decision when it comes to choosing which treatment to administer to archaeological artefacts. 相似文献
222.
223.
Stefan Frunza Constantin Paul Ganea Irina Zgura Andreas Schönhals 《Liquid crystals》2020,47(6):908-917
ABSTRACTMolecular mobility of cyanophenyl alkylbenzoates (CPnBs) (n = 2, 3, 7 – number of carbon atoms in the alkyl chain) in the bulk and in composites with aerosil A380 is investigated by broadband dielectric spectroscopy, while thermal analysis and infrared spectroscopy were applied to characterise the molecular species. The work completes preliminary results obtained for the members with n = 4 … 6. An interaction by hydrogen bonding, between aerosil surface – OH groups and – CN or ester groups of the CPnB molecules takes place. It slows down the relaxation process as observed for related composites in comparison to the pure materials. The existence of two types of bonding might be the reason that Vogel temperature for the relaxation process in the surface layer does not show the odd-even effect. Temperature dependence of the relaxation rates for composites shows a crossover behaviour from a high to a low temperature regime. Moreover, the temperature dependence of the dielectric strength is unusual. As the loading degree is similar, comparison of the dielectric, spectroscopic and thermal data obtained here and with the results obtained for the composites with n = 4 … 6 can be directly done. Increasing the number of the members of the homologous series confirms and hardens the preliminary conclusions. 相似文献
224.
225.
Adrian Constantin 《Inventiones Mathematicae》2006,166(3):523-535
Analyzing a free boundary problem for harmonic functions we show that there are no closed particle paths in an irrotational inviscid traveling wave propagating at the surface of water over a flat bed: within a period each particle experiences a backward-forward motion with a slight forward drift. Mathematics Subject Classification (2000) 76B15, 35J67, 37J35 相似文献
226.
B. Frech L.F. Constantin A. Amy-Klein O. Phavorin C. Daussy C. Chardonnet M. Mürtz 《Applied physics. B, Lasers and optics》1998,67(2):217-221
4 frequency grid, to test the performance of the saturated fluorescence method for CO2 laser frequency stabilization. The Allan variance for the saturated-fluorescence-stabilized CO2 laser reached 60 Hz for an integration time of 300 s. We also performed three absolute measurements of CO2 laser frequencies stabilized by the saturated fluorescence method, with a sub-kHz accuracy. We obtained a 1.7 kHz redshift
of the CO2 saturated fluorescence lines, which we attribute essentially to pressure. This is in contradiction with the previous observation
of a blueshift [K.L. SooHoo, C. Freed, J.E. Thomas, H.A. Haus: Phys. Rev. Lett. 53, 1437 (1984)]. Furthermore, significant deviations of the measured frequencies from the data of Maki et al. [A.G. Maki, C.-C. Chou,
K. Evenson, L.R. Zink, J.T. Shy: J. Mol. Spec. 167, 211 (1994)] demonstrate the need for a new calibration of the CO2 frequency grid.
Received: 1 December 1997 相似文献
227.
Gabi Drochioiu Ionel Mangalagiu Ecaterina Avram Karin Popa Alin Constantin Dirtu Ioan Druta 《Analytical sciences》2004,20(10):1443-1447
A new sensitive spectrophotometric method has recently been developed for the trace determination of cyanide with ninhydrin. Cyanide ion was supposed to act as a specific base catalyst. Nevertheless, this paper demonstrates that the reported assay is based on a novel reaction of cyanide with 2,2-dihydroxy-1,3-indanedione, which affords purple or blue colored salts of 2-cyano-1,2,3-trihydroxy-2H indene. Hydrindantin is merely an intermediary of the reaction. The formation of a stable and isolable ninhydrin-cyanide compound has been confirmed by its preparation in crystalline form. Also, it is thoroughly characterized by elemental as well as MS, IR, UV/VIS and 1H NMR analyses. The Ruhemann's sequence of reactions of cyanide with ninhydrin has been reconsidered and an adequate mechanism of the reaction is proposed. As a consequence, the interference of oxidizers as well as copper, silver and mercury ions with the cyanide determination has been elucidated. 相似文献
228.
229.
We consider a model of quasigeostrophic turbulence that has proven useful in theoretical studies of large scale heat transport and coherent structure formation in planetary atmospheres and oceans. The model consists of a coupled pair of hyperbolic PDEs with a forcing which represents domain-scale thermal energy source. Although the use to which the model is typically put involves gathering information from very long numerical integrations, little of a rigorous nature is known about long-time properties of solutions to the equations. In this first paper we define a notion of weak solution, and show using Galerkin methods the long-time existence and uniqueness of such solutions. 相似文献
230.
Constantin P. Bachas 《Nuclear Physics B》1984,235(2):172-196
We construct an effective lattice action for a continuum theory, by fixing a set of collective coordinates which play the role of lattice variables. As opposed to Symanzik's improvement program our method involves no expansion in powers of the lattice spacing; in other words it simultaneously yields all “irrelevant” operators generated by the renormalization group to a given order in the continuum coupling constant. We are thus able to rigorously establish that the effective lattice action, for both smooth and singular collective coordinates, is local in the sense that long-range couplings decay exponentially over a distance independent of the mass gap of the theory; for asymtotically free theories this is interpreted as an existence proof of Wilson's infrared stable trajectories. Our methods are for convenience described in the context of dimensional φ4, but can be easily extended to any theory with a set of collective coordinates which (i) are renormalizable and (ii) provide an infrared cutoff. Application to the 2-dimensional O(N) σ-model is, in particular, discussed; the technical problems of renormalization posed by gauge invariance are, on the other hand, not dealt with in this paper, although our treatment of singular coordinates is meant as a prelude to them. A by-product of our proofs is the derivation of an interesting factorization property of Zimmermann-subtracted diagrams. 相似文献