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961.
Xu Runzhang 《Mathematical Methods in the Applied Sciences》2010,33(7):831-844
We study the Cauchy problem of nonlinear Klein–Gordon equation with dissipative term. By introducing a family of potential wells, we derive the invariant sets and prove the global existence, finite time blow up as well as the asymptotic behaviour of solutions. In particular, we show a sharp condition for global existence and finite time blow up of solutions. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
962.
Ruiz-Ángel MJ Torres-Lapasió JR Carda-Broch S García-Álvarez-Coque MC 《Journal of chromatography. A》2010,1217(45):7090-7099
Organic solvents are traditionally added to micellar mobile phases to achieve adequate retention times and peak profiles, in a chromatographic mode which has been called micellar liquid chromatography (MLC). The organic solvent content is limited to preserve the formation of micelles. However, at increasing organic solvent contents, the transition to a situation where micelles do not exist is gradual. Also, there is no reason to neglect the potentiality of mobile phases containing only surfactant monomers instead of micelles (high submicellar chromatography, HSC). This is demonstrated here for the analysis of β-blockers. The performance of four organic solvents (methanol, ethanol, 1-propanol, and acetonitrile) was compared in mobile phases containing the anionic surfactant sodium dodecyl sulphate in the MLC and HSC modes. The association of the organic solvent molecules with micelles gives rise to a significant loss in the elution strength of the organic solvent; whereas upon disruption of micelles, it tends to that observed in the hydro-organic mode. The elution behaviour of the β-blockers was modelled to predict the retention times. This allowed the detailed exploration of the selectivity and resolution of the chromatographic systems in relatively wide ranges of concentration of surfactant and organic solvent. The best performance in terms of resolution and analysis time was achieved using HSC with acetonitrile, being able to base-line resolve a mixture of eight β-blockers. Ethanol also provided a good separation performance, significantly improved with respect to methanol and 1-propanol. In contrast, the hydro-organic mode using acetonitrile or any of the short-chain alcohols could not succeed with the separation of the β-blockers, owing to the poorer selectivity and wider peaks. 相似文献
963.
Carbamoylferrocene (1) and ferrocenecarbonylhydrazide (2) were synthesised by modified literature procedures and studied by a combination of the conventional spectroscopic methods (IR, MS and NMR), X-ray crystallography and thermal analysis. The crystal structures of two new polymorphs of amide 1 and the structure of hydrazide 2 were determined, revealing extensive hydrogen bonding interactions of the polar ferrocene substituents and supportive π?π stacking interactions. Whereas the thermal behaviour of hydrazide 2 was relatively complicated, thermolysis of amide 1 in the presence of air oxygen led to a complete elimination of the organic constituents in a single step under mild conditions affording essentially pure hematite (α-Fe2O3). Mössbauer spectra, powder X-ray diffraction and high-resolution transmission electron microscopy indicated the pyrolytic hematite to result in the form of random aggregates of well crystalline nanoparticles. 相似文献
964.
Semi-interpenetrating polymer networks (SIPNs) of polyurethane (PU) and poly(methyl methacrylate) (PMMA) in different weight ratios viz., 90/10, 70/30, 60/40 and 50/50 were prepared. The SIPNs were characterized for physico-mechanical properties like density, tensile strength and elongation at break. Thermal stability of IPNs was measured using thermogravimetric analysis (TGA). From the TGA thermograms it was noticed that all IPNs are stable up to 325 °C and undergo three-step thermal degradation in the temperature ranges 251-400, 378-508 and 445-645 °C for first, second and third steps, respectively. Thermal degradation kinetic parameters like activation energy (Ea) were calculated using Broido, Coats-Redfern and Horowitz-Metzger models. The values obtained by Broido and Horowitz-Metzger methods showed concurrency, whereas Coats-Redfern method showed relatively lower values. Surface morphology measured using scanning electron microscope (SEM) showed two-phase morphology for all the IPNs. 相似文献
965.
Effect of chemical structure on combustion and thermal behaviour of polyurethane elastomer layered silicate nanocomposites 总被引:1,自引:0,他引:1
The effect of polyol molecular weight and functionality on nanodispersion of clay in PU/clay nanocomposites and the investigation of their thermal and combustion properties are reported and discussed. Lamellar elastomer polyurethane nanocomposites were synthesized using polyols with different molecular weight and functionality and according to these parameters they show several degrees of dispersion which affect their thermal and combustion behaviour. A barrier effect of clay layer is shown in TGA experiments by a delay of thermal degradation products release in nanocomposite materials compared to the virgin polymer; this barrier effect also leads to formation of char during combustion which lowers the peak of rate of heat release in cone calorimeter tests and eliminates fire-induced dripping of the nanocomposite sample during UL 94 test. However, in order to achieve non-burning behaviour nanocomposite technology must be combined with conventional flame retardant technology. 相似文献
966.
Matthias?WeilEmail author Berthold?St?ger Erich?Zobetz Enrique J.?Baran 《Monatshefte für Chemie / Chemical Monthly》2006,137(8):987-996
Summary. Dark-red single crystals of HgCr2O7 were grown by reacting HgO and CrO3 in excess at 200°C for four days. The crystal structure (space group P32, Z = 3, a = 7.2389(10), c = 9.461(2) ?, 1363 structure factors, 57 parameters, R[F
2>2σ(F
2)] = 0.0369, wR(F
2 all) = 0.0693) was determined from a crystal twinned by merohedry according to (110). It consists of nearly linear HgO2 units (
(Hg–O) = 2.02 ?) and dichromate units that are linked into infinite chains ‘O3Cr–O–CrO3–Hg–O3Cr–O–CrO3’ running parallel to the c-axis. Six additional Hg–O contacts between 2.73 and 2.96 ? stabilise the structural arrangement. The dichromate anion exhibits
a staggered conformation with a bent Cr–O–Cr bridging angle of 140.7(6)°. Upon heating above 300°C, HgCr2O7 decomposes in a two-step mechanism to Cr2O3. The title compound was additionally characterised by vibrational spectroscopy. 相似文献
967.
W. Hermel 《Isotopes in environmental and health studies》2013,49(4):140-143
Ausgehend von der Bedeutung der Kenngröβe “Oberfläche” fur die Charakterisierung des dispersiven Zustandes wird ein Verfahren zur Bestimmung kleiner spezifischer Oberflächen beschrieben. Es wurde auf der Basis bekannter Arbeiten zur tritiummarkierten Wasserdampfsorption entwickelt und beruht auf den Voraussetzungen der traditionellen BET-Adsorptionsmethoden. Über die Anwendung des Verfahrens bei der Untersuchung wesentlicher die Sinterwerkstoffherstellung beeinflussender Zusammenhänge ivird berichtet. 相似文献
968.
The Peter Principle is a theory that provides a paradoxical explanation for job incompetence in a hierarchical organisation. It argues that should staff be competent at a given level, their competence may not be implicit at higher levels due to the differences in the skill set required. Furthering the work of a recent investigation into the Peter Principle utilising agent based simulation, this paper explores external factors upon varying promotion strategies to assess efficiency. Through additional elements of social networks and organisational thought, a more representative view of workplace interaction is presented. Results of the simulation found that although the Peter Principle affects efficiency, it may not be to the levels previously suggested. Furthermore promotion on merit provided the most favourable maximum and minimum efficiency margins, given the absence of clear evidence pertaining to the existence of the Peter Principle. 相似文献
969.
A cross-linkable comonomer containing a diacetylene group, named dimethyl 4,4'-(buta-1,3-diyne-1,4-diyl)dibenzoate (DA) was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol to prepare a series of slightly cross-linked PBS copolyesters (PBDASx). The chemical structure, crystallization and rheological behaviours of PBDASx were well investigated. Compared to neat PBS, PBDASx showed the greatly increased crystallization rate because of the promoting nucleation of the cross-linking domains, and the XRD results indicated that it had no influence on crystallization structure of PBS. The rheological behaviours indicate that PBDASx possessed higher viscosity than neat PBS even at high shear rate and temperature. PBDAS0.3 exhibited better comprehensive properties than neat PBS, which will widen applications of PBS. 相似文献
970.
This paper provides details of a new test rig design and methodology intended for, and successfully applied to, measuring the gear wear rate and performance of polymer composite gears under both dry and lubricated conditions. One of its unique contributions is that it continuously measures the gear wear rate, a feature essential for understanding polymer gear behaviour. While sharing some concepts with the traditional back-to-back test configuration used for steel gears, the new method introduces a rotary freedom to the block supporting the polymer gears under test. This block rotates if the gear tooth thickness is reduced, which aids control of the test load. The gear surface wear rate is recorded continuously by using a capacitance transducer to measure the pivot block motion. A second unique contribution of the new test method involves splitting the support block so that controlled misaligned gear engagements (not reported in other designs) can be introduced and subsequent changes to wear behaviour studied. The paper first outlines the test rig concepts and design before discussing in more detail the gear wear rate measuring principles, the methods of centre distance adjustment and the achievement of virtually constant gear loading. Finally, a selection test results are presented in summary to further validate the new test method and illustrate potential applications. 相似文献