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161.
An extremely challenging problem of significant interest is to predict catastrophes in advance of their occurrences. We present a general approach to predicting catastrophes in nonlinear dynamical systems under the assumption that the system equations are completely unknown and only time series reflecting the evolution of the dynamical variables of the system are available. Our idea is to expand the vector field or map of the underlying system into a suitable function series and then to use the compressive-sensing technique to accurately estimate the various terms in the expansion. Examples using paradigmatic chaotic systems are provided to demonstrate our idea. 相似文献
162.
Antonios I. Arvanitakis Vassilios K. Kalpakides 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(12):1781-1792
The dynamics of a phase transition front in solids using the level set method is examined in this paper. Introducing an implicit
representation of singular surfaces, a regularized version of the sharp interface model arises. The interface transforms into
a thin transition layer of nonzero thickness where all quantities take inhomogeneous expressions within the body. It is proved
that the existence of an inhomogeneous energy of the material predicts inhomogeneity forces that drive the singularity. The
driving force is a material force entering the canonical momentum equation (pseudo-momentum) in a natural way. The evolution
problem requires a kinetic relation that determines the velocity of the phase transition as a function of the driving force.
Here, the kinetic relation is produced by invoking relations that can be considered as the regularized versions of the Rankine–Hugoniot
jump conditions. The effectiveness of the method is illustrated in a shape memory alloy bar. 相似文献
163.
Thevis M Sigmund G Gougoulidis V Beuck S Schlörer N Thomas A Kwiatkowska D Pokrywka A Schänzer W 《Analytical and bioanalytical chemistry》2011,401(2):543-551
Benfluorex [1-(m-trifluoromethylphenyl)-2-(β-benzoyloxyethyl)aminopropane] has been widely used for the treatment of atherogenic metabolic
disorders and impaired carbohydrate metabolism (particularly in obese type-II diabetic patients) as well as an anorectic drug.
Due to its potentially performance-enhancing properties, benfluorex has been added to the list of prohibited compounds and
methods of doping by the World Anti-Doping Agency (WADA) in 2010, necessitating the implementation of the drug as well as
its major metabolites into routine doping control procedures. In the present study, human urinary metabolites of benfluorex
were characterized by gas chromatography–electron ionization–mass spectrometry (GC-EI-MS) as well as liquid chromatography–electrospray
ionization–high resolution/high accuracy tandem mass spectrometry (LC-ESI-MS/MS). Commonly employed sports drug testing approaches
consisting of liquid–liquid extraction followed by GC-MS or urine dilution and immediate LC-MS/MS analysis were expanded and
validated with regard to specificity, recovery (48–54%, GC-MS only), intra- and interday precision (<25%), limits of detection
(5–8 ng/mL for LC-MS/MS and 80 ng/mL for GC-MS), and ion suppression (for LC-ESI-MS/MS only) to allow the detection of benfluorex
metabolites 1-(m-trifluoromethylphenyl)-2-(2-hydroxyethyl)aminopropane (M1), 1-(m-trifluoromethylphenyl)-2-(2-carboxymethyl)aminopropane (M2), and 1-(m-trifluoromethylphenyl)-2-aminopropane (M3) as well as the glucuronic acid conjugate of M1. 相似文献
164.
165.
Panagiota Georgantea Efstathia IoannouConstantinos Vagias Vassilios Roussis 《Tetrahedron letters》2013
Perezoperezone (1), curcuperezone (2), and diperezone (3), belonging to the rare class of bisabolane dimers, were isolated as minor constituents of the organic extract of the Caribbean soft coral, Pseudopterogorgia rigida. The structures of the new compounds 1 and 2 were established by detailed analyses of their NMR and MS data. 相似文献
166.
Dimitra G. Hela Vassilios D. Papadopoulos 《International journal of environmental analytical chemistry》2013,93(15):1676-1697
In this study, a detailed process of uncertainty estimation associated with matrix solid phase dispersion method (MSPD) for the extraction of organochlorinated compounds from fish coupled with gas chromatography is given. The evaluation of uncertainty arising from trueness using fully nested experimental designs is presented by estimating proportional bias, in terms of recovery. The uncertainty of measurements associated with the actual chromatographic process was also estimated. The methodology was applied for the determination of selected organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in real fish samples, from selected study locations in Western Greece (Mesologgi lagoon and Trichonida lake), based on chromatographic techniques. The sources of uncertainty are presented along with the calculated combined uncertainty terms derived from the analytical procedure and chromatographic process. The estimation of uncertainty was included in the presentation of final determinations. 相似文献
167.
George C. Bourantas Benjamin F. Zwick Theo Philippe Lavier Vassilios C. Loukopoulos Athanassios A. Dimas Adam Wittek Karol Miller 《国际流体数值方法杂志》2023,95(1):143-175
We present a strong form meshless solver for numerical solution of the nonstationary, incompressible, viscous Navier–Stokes equations in two (2D) and three dimensions (3D). We solve the flow equations in their stream function-vorticity (in 2D) and vector potential-vorticity (in 3D) formulation, by extending to 3D flows the boundary condition-enforced immersed boundary method, originally introduced in the literature for 2D problems. We use a Cartesian grid, uniform or locally refined, to discretize the spatial domain. We apply an explicit time integration scheme to update the transient vorticity equations, and we solve the Poisson type equation for the stream function or vector potential field using the meshless point collocation method. Spatial derivatives of the unknown field functions are computed using the discretization-corrected particle strength exchange method. We verify the accuracy of the proposed numerical scheme through commonly used benchmark and example problems. Excellent agreement with the data from the literature was achieved. The proposed method was shown to be very efficient, having relatively large critical time steps. 相似文献
168.
169.
Vassilios P. Papageorgiou Andreana N. Assimopoulou Elias A. Couladouros David Hepworth K. C. Nicolaou 《Angewandte Chemie (International ed. in English)》1999,38(3):270-301
Wound healing properties of plant extracts that contain the naphthoquinone natural products alkannin ( 1 ) and shikonin ( 2 ) have been known for many centuries. More recently, the biological properties of 1 , 2 , and related derivatives have been demonstrated experimentally, and their production both by cell cultures and chemical synthesis has been studied extensively. 相似文献
170.
Isothermal dielectric properties of poly(dimethylsiloxane) (PDMS) networks during cure were studied at room temperature with emphasis on the effect of catalyst concentration. The frequency range employed was 10−1 to 105 Hz. The dielectric response is sensitive to a change in catalyst levels as this was evidenced by the change in the values of the logarithm of the loss factor log ϵ”. We attribute these changes to dipolar and ionic contributions. A profile of the cure reaction of model elastomers may readily be obtained by using a combination of microsensors and time-domain dielectric spectroscopy. The results obtained show that the catalyst concentration affects both crosslinking and chain extension reactions. However, for the typical catalyst concentration at which typical networks are prepared, the crosslinking reaction is the dominant effect. 相似文献