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  • 1
    Digitale Medien
    Digitale Medien
    Examination of dimethacrylate inhomogeneity by solvent swelling techniques (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1483-1492 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Dimethacrylate monomers polymerize to form highly crosslinked networks with an inhomogeneous distribution of regions of low and high crosslink density. The systems are probed in this work by observing the effects of solvents (nitrobenzene and water) on dynamic mechanical measurements, diffusion kinetics and fracture toughness experiments. Dynamic mechanical analysis showed that the addition of nitrobenzene is found to have little effect on the position of the glass transition or secondary relaxations for solvent levels of under 3.5 mass %. It is proposed that solvents initially diffuse into low crosslink density regions, impinging little on the methacrylate mainchains which reside largely in regions of high crosslink density. Only at higher solvent concentrations do these chains become plasticized. Confirmation of heterogeneity is provided by diffusion analysis of isothermal solvent uptake. This is also interpreted interpreted in terms of a two-stage diffusion process due to differential rates of sorption which occur in different microregions. Weighing of the water uptake of samples suspended in water indicated that some 30% of water absorbed at equilibrium exists within void regions. Addition of water causes the fracture mechanism to change from a ‘stick-slip’ mechanism characteristic of brittle polymers to stable crack growth with a lower fracture toughness. This is also attributed to differential swelling of the material causing internal stresses which aid material failure.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760312007
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  • 2
    Digitale Medien
    Digitale Medien
    Electron paramagnetic resonance study of the complex formed between copper and 1-[2(S)-3-mercapto-2-methylpropionyl]-L-proline (Captopril) in solid and aqueous solution (1989)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 227-232 
    Details
    ISSN: 0749-1581
    Schlagwort(e): EPR ; Copper complexes ; Captopril ; Anti-hypertensive agents ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: EPR spectroscopy was used to elucidate the nature of the interaction between copper and the antihypertensive agent 1-[2(S)-3-mercapto-2-methylpropionyl]-L-proline (Captopril) in both solid and aqueous solutions. The EPR spectra indicate that binding to copper(II) occurs via the ligand oxygens rather than the thiol moieties, and that the EPR-detectable copper is greatly reduced on complexation. The EPR parameters for the solid copper(II) complexes are in the range g∥ = 2.374-2.386, g⊥ = 2.076-2.086 and A∥Cu = 13.5 mT, and the parameters for the aqueous solutions are giso = 2.107-2.129 and A∥Cu = 7.1-8.6 mT.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260270306
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  • 3
    Digitale Medien
    Digitale Medien
    Tin in pharmacy and nutrition (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 6 (1992), S. 3-18 
    Details
    ISSN: 0268-2605
    Schlagwort(e): organotin ; tin ; toxicity ; essential elements ; radiopharmaceuticals ; dentifrices ; tinhaem ; antitumours ; antimalarials ; bactericidals ; antihelminthes ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The occurrence of tin in plants, animals and humans is discussed in relation to its abundance in the lithosphere and hydrosphere and the range of different tin(II) and tin(IV) complexes formed. A reasoned consideration of the essentiality or otherwise of tin for living species is given and it is concluded that tin is beneficial even if not yet proved to be an essential element.After reference to the chemistry of tin compounds, there is a detailed discussion of their toxicity in animals and humans. Feasible routes for tin intake and uptake into humans are described.The use of tin pharmaceuticals in previous and current times is reviewed and areas for which they are currently permitted for use in man as dentifrices and mouth washes, as radiopharmaceuticals and for the treatment of jaundiced newborns are described. A detailed review of tin-coating antitumour agents as representative tin pharmaceuticals is given.Finally, a range of tin compounds having other specific pharmaceutical applications and which are currently being investigated are listed.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aoc.590060103
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  • 4
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    Unbekannt
    The response and symmetry properties of a cylinder wake subjected to localized surface excitation (1992)
    Cambridge University Press
    Details
    Publikationsdatum: 1992-01-01
    Beschreibung: Symmetric and antisymmetric periodic disturbances introduced directly into the boundary layer on a circular cylinder at low Reynolds number are shown by experiment to be capable of modifying the vortex formation process and changing the vortex shedding frequency. Spectral measurements have shown that the antisymmetric vortex shedding mode is strongly coupled to the symmetric first harmonic mode. When symmetric excitation is applied, three different shapes of the mean velocity profiles can be identified as the forcing amplitude is increased. At low forcing amplitudes nonlinear interaction between the forcing field and the natural wake oscillator produces sum and difference modes. Symmetric forcing with intermediate-amplitude disturbances suppresses the natural shedding frequency, and the dominant vortex shedding energy appears as a sinuous mode at half the excitation frequency. At high symmetric forcing amplitudes a threshold is reached, above which the large-scale vortices do not form. The symmetries of the combination modes follow two simple rules based on the symmetries of the interacting modes. The symmetry rules provide an explanation for the fundamental difference in wake structure that occurs between symmetric forcing and antisymmetric forcing. © 1992, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Publiziert von Cambridge University Press
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  • 5
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    Quantitative measurements of three-dim ensional structures in the wake of a circular cylinder (1994)
    Cambridge University Press
    Details
    Publikationsdatum: 1994-07-10
    Beschreibung: The fine scale three-dimensional structures usually associated with streamwise vortices in the near wake of a circular cylinder have been studied at Reynolds numbers ranging from 170 to 2200. Spatially continuous velocity measurements along lines parallel to the cylinder axis were obtained with a scanning laser anemometer. To detect the streamwise vortices in the amplitude modulated velocity field, it was necessary to develop a spatial decomposition technique to split the total flow into a primary flow component and a secondary flow component. The primary flow is comprised of the mean flow and Strouhal vortices, while the secondary flow is the result of the three-dimensional streamwise vortices that are the essence of transition to turbulence. The three-dimensional flow amplitude increases in the primary vortex formation region, then saturates shortly after the maximum amplitude in the primary flow is reached. In the near-wake region the wavelength decreases approximately like Re-05, but increases with downstream distance. A discontinuous increase in wavelength occurs below Re = 300 suggesting a fundamental change in the character of the three-dimensional flow. At downstream distances (x/D = 10–20), the spanwise wavelength decreases from 1.42D to 1.03D as the Reynolds number increases from 300 to 1200. © 1994, Cambridge University Press
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Publiziert von Cambridge University Press
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  • 6
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    Linear models for control of cavity flow oscillations (2006)
    Cambridge University Press
    Details
    Publikationsdatum: 2006-01-11
    Beschreibung: Models for understanding and controlling oscillations in the flow past a rectangular cavity are developed. These models may be used to guide control designs, to understand performance limits of feedback, and to interpret experimental results. Traditionally, cavity oscillations are assumed to be self-sustained: no external disturbances are necessary to maintain the oscillations, and amplitudes are limited by nonlinearities. We present experimental data which suggests that in some regimes, the oscillations may not be self-sustained, but lightly damped: oscillations are sustained by external forcing, such as boundary-layer turbulence. In these regimes, linear models suffice to describe the behaviour, and the final amplitude of oscillations depends on the characteristics of the external disturbances. These linear models are particularly appropriate for describing cavities in which feedback has been used for noise suppression, as the oscillations are small and nonlinearities are less likely to be important. It is shown that increasing the gain too much in such feedback control experiments can lead to a peak-splitting phenomenon, which is explained by the linear models. Fundamental performance limits indicate that peak splitting is likely to occur for narrow-bandwidth actuators and controllers. © 2006 Cambridge University Press.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Publiziert von Cambridge University Press
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  • 7
    facet.materialart.
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    Surging and plunging oscillations of an airfoil at low Reynolds number (2014)
    Cambridge University Press
    Details
    Publikationsdatum: 2014-12-15
    Beschreibung: We investigate the forces and unsteady flow structures associated with harmonic oscillations of an airfoil in the streamwise (surging) and transverse (plunging) directions in two-dimensional simulations at low Reynolds number. For the surging case, we show that there are specific frequencies where the wake instability synchronizes with the unsteady motion of the airfoil, leading to significant changes in the mean forces. Resonant behaviour of the time-averaged forces is observed near the vortex shedding frequency and its subharmonic; the behaviour is reminiscent of the dynamics of the generic nonlinear oscillator known as the Arnol'd tongue or the resonance horn. Below the wake instability frequency, there are two regimes where the fluctuating forces are amplified and attenuated, respectively. A detailed study of the flow structures associated with leading-edge vortex (LEV) growth and detachment are used to relate this behaviour with the LEV acting either in phase with the quasi-steady component of the forces for the amplification case, or out of phase for the attenuation case. Comparisons with wind tunnel measurements show that phenomenologically similar dynamics occur at higher Reynolds number. Finally, we show that qualitatively similar phenomena occur during both surging and plunging. © 2014 Cambridge University Press.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Publiziert von Cambridge University Press
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  • 8
    facet.materialart.
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    Reduced-order unsteady aerodynamic models at low Reynolds numbers (2013)
    Cambridge University Press
    Details
    Publikationsdatum: 2013-04-29
    Beschreibung: In this paper we develop reduced-order models for the unsteady lift on a pitching and plunging aerofoil over a range of angles of attack. In particular, we analyse the pitching and plunging dynamics for two cases: a two-dimensional flat plate at mathit{Re}= 100 using high-fidelity direct numerical simulations and a three-dimensional NACA 0006 aerofoil at mathit{Re}= 65hspace{0.167em} 000 using wind-tunnel measurements. Models are obtained at various angles of attack and they are verified against measurements using frequency response plots and large-amplitude manoeuvres. These models provide a low-dimensional balanced representation of the relevant unsteady fluid dynamics. In simulations, flow structures are visualized using finite-time Lyapunov exponents. A number of phenomenological trends are observed, both in the data and in the models. As the base angle of attack increases, the boundary layer begins to separate, resulting in a decreased quasi-steady lift coefficient slope and a delayed relaxation to steady state at low frequencies. This extends the low-frequency range of motions that excite unsteady effects, meaning that the quasi-steady approximation is not valid until lower frequencies than are predicted by Theodorsen's classical inviscid model. In addition, at small angles of attack, the lift coefficient rises to the steady-state value after a step in angle, while at larger angles of attack, the lift coefficient relaxes down to the steady-state after an initially high lift state. Flow visualization indicates that this coincides with the formation and convection of vortices at the leading edge and trailing edge. As the angle of attack approaches the critical angle for vortex shedding, the poles and zeros of the model approach the imaginary axis in the complex plane, and some zeros cross into the right half plane. This has significant implications for active flow control, which are discussed. These trends are observed in both simulations and wind-tunnel data. © 2013 Cambridge University Press.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Publiziert von Cambridge University Press
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