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1.
Dalila B. M. M. Fontes Eleni Hadjiconstantinou Nicos Christofides 《Journal of Global Optimization》2006,34(1):97-125
In this paper we obtain Lower Bounds (LBs) to concave cost network flow problems. The LBs are derived from state space relaxations
of a dynamic programming formulation, which involve the use of non-injective mapping functions guaranteing a reduction on
the cardinality of the state space. The general state space relaxation procedure is extended to address problems involving
transitions that go across several stages, as is the case of network flow problems. Applications for these LBs include: estimation
of the quality of heuristic solutions; local search methods that use information of the LB solution structure to find initial
solutions to restart the search (Fontes et al., 2003, Networks, 41, 221–228); and branch-and-bound (BB) methods having as
a bounding procedure a modified version of the LB algorithm developed here, (see Fontes et al., 2005a). These LBs are iteratively
improved by penalizing, in a Lagrangian fashion, customers not exactly satisfied or by performing state space modifications.
Both the penalties and the state space are updated by using the subgradient method. Additional constraints are developed to
improve further the LBs by reducing the searchable space. The computational results provided show that very good bounds can
be obtained for concave cost network flow problems, particularly for fixed-charge problems. 相似文献
2.
3.
The relationship between free radicals and acute or chronic inflammation has been well established. We have previously reported the significant antioxidant activity of the natural azulene derivatives chamazulene and guaiazulene. Furthermore, some synthetic azulene analogues have been found to possess anti-inflammatory activity. In this investigation we report the synthesis of five 3-alkyl or 3-(hydroxy)alkylazulene-1-carboxylic acids and esters, from tropolone, via the corresponding furanone. The synthesised compounds were tested for their effect on the peroxidation of rat hepatic microsomal membrane lipids, applying the 2-thiobarbituric acid test. Their anti-inflammatory activity was evaluated in vitro by the offered inhibition of soybean lipoxygenase. All the tested molecules were found to inhibit lipid peroxidation by 100% at 1 mM. They were also found to considerably inhibit lipoxygenase activity. The above results are discussed in relation to the structure and physicochemical properties of the examined azulene derivatives. 相似文献
4.
Andreadou I Tasouli A Bofilis E Chrysselis M Rekka E Tsantili-Kakoulidou A Iliodromitis E Siatra T Kremastinos DT 《Chemical & pharmaceutical bulletin》2002,50(2):165-168
Novel indole derivatives containing a triazole moiety (1a-d, 2a-c) were synthesized as lead compounds with interesting pharmacological profiles. Their antioxidant activity was investigated on in vitro non-enzymatic rat hepatic microsomal lipid peroxidation. All compounds showed significant effect in the above assay. The effect depended mainly on the attachment position of the triazole moiety on the indole nucleus. The most potent antioxidant derivatives la, 1c and 1d were tested for their protective ability against the oxidative damage of the myocardium after ischemia-reperfusion, in male rabbits which were subjected to 30 min regional ischemia followed by reperfusion. The tested antioxidant compounds 1a, 1c and 1d were continuously infused for 30 min starting at 10th min of ischemia and lasted at 10th min of reperfusion. The concentration of malondialdehyde (MDA, a marker of lipid peroxidation) and hemodynamic parameters (blood pressure and heart rate) were measured in the baseline, at 20th min of the sustained ischemia, 1st and 20th min of reperfusion. It was found that the examined compounds la, 1c and 1d reduced significantly the level of MDA in rabbits under ischemia-reperfusion and proved to be promising substances for further evaluation of anti-ischemic properties. 相似文献
5.
G. Vourlias N. Pistofidis D. Chaliambalias K. Chrissafis El. Pavlidou G. Stergioudis 《Journal of Thermal Analysis and Calorimetry》2007,87(2):401-409
Zinc coatings on ferrous substrates are possible to be applied with
thermal spraying. In the present work the corrosion behavior of zinc thermal
sprayed coatings deposited on low carbon steel St-37 was examined in a simulated
marine atmosphere (salt spray chamber-SSC) and in a dry atmosphere at elevated
temperature (400°C). The corrosion progress was examined by means of optical
microscopy, scanning electron microscopy, X-ray diffraction and thermogravimetric
analysis. From this investigation it was deduced that in the SSC the coating
is uniformly corroded, while the main corrosion products are hydrated zinc
oxides and chlorides. By contrast at 400°C only a thin, compact and continuous
film of ZnO is formed on top of the coating, which remains adherent to the
ferrous substrate. 相似文献
6.
Klaus Müllen Siglinde Bender Eleni Kotzamani Hans Schmickler Bruno Frei Hans R. Wolf 《Tetrahedron letters》1981,22(36):3513-3516
The conformational mobility of a series of conjugated dienones is investigated by low-temperature NMR- and IR-spectroscopy and interpreted in terms of substituent effects. 相似文献
7.
M. Anastasiou Th. Hasapis T. Zorba E. Pavlidou K. Chrissafis K. M. Paraskevopoulos 《Journal of Thermal Analysis and Calorimetry》2006,84(1):27-32
Historic
plasters from wall paintings of Byzantine and post-Byzantine churches situated
in the Balkan region were studied. All wall paintings were made with fresco
technique and are dated from IX - XVI century. Plaster samples were followed
from room temperature to 1000°C by Thermogravimetric (TG) and Differential
Thermal Analysis (DTA), and one or two significant temperature regions, corresponding
to thermal decomposition mechanisms were observed. The analysis of the plaster
samples and the composition characterization was carried out using also, Fourier
Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM).
Although the main components are calcite and quartz (from sand) in different
proportions, there are differences between them such as the presence of gypsum
being either as a constituent element or due to environmental pollution. The
results are examined comparatively taking into account the creation time and
place of the paintings. 相似文献
8.
Yanna Milonaki Eleni Kaditi Stergios Pispas Costas Demetzos 《Journal of polymer science. Part A, Polymer chemistry》2012,50(6):1226-1237
Gradient (or pseudo‐diblock) copolymers were synthesized from 2‐methyl‐2‐oxazoline and 2‐phenyl‐2‐oxazoline monomer mixtures via cationic polymerization. The self‐assembling properties of these biocompatible gradient copolymers in aqueous solutions were investigated, in an effort to use the produced nanostructures as nanocarriers for hydrophobic pharmaceutical molecules. Dynamic and static light scattering as well as AFM measurements showed that the copolymers assemble in different supramolecular nanostructures (spherical micelles, vesicles and aggregates) depending on copolymer composition. Fluorescence spectroscopy studies revealed a microenvironment of unusually high polarity inside the nanostructures. This observation is related partly to the gradient structure of the copolymers. The polymeric nanostructures were stable with time. Their structural properties in different aqueous media—PBS buffer, RPMI solution—simulating conditions used in pharmacological/medicinal studies, have been also investigated and a composition dependent behavior was observed. Finally, the hydrophobic drug indomethacin was successfully encapsulated within the gradient copolymer nanostructures and the properties of the mixed aggregates were studied in respect to the initial copolymer assemblies. The produced aggregates encapsulating indomethacin showed a significant increase of their mass and size compared to original purely polymeric ones. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
9.
E. Fluck C. M. E. Pavlidou R. Janoschek 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):469-474
Abstract Experimental findings as well as quantum chemical calculations indicate that the P4 molecule has a remarkably low nucleophilicity. The P4H+ ion is predicted to have a ‘proton at apex’ configuration whereas a proton in the centre seems to be metastable. The influence of d orbitals on the stability of P4 against 2 P2 and 1/2 P8, the photoelectron spectrum, and the valence electron density is discussed. 相似文献
10.
Eleni G. Farmaki Constantinos E. Efstathiou 《International journal of environmental analytical chemistry》2013,93(2):85-105
Artificial Neural Networks (ANNs) have seen an explosion of interest over the last two decades and have been successfully applied in all fields of chemistry and particularly in analytical chemistry. Inspired from biological systems and originated from the perceptron, i.e. a program unit that learns concepts, ANNs are capable of gradual learning over time and modelling extremely complex functions. In addition to the traditional multivariate chemometric techniques, ANNs are often applied for prediction, clustering, classification, modelling of a property, process control, procedural optimisation and/or regression of the obtained data. This paper aims at presenting the most common network architectures such as Multi-layer Perceptrons (MLPs), Radial Basis Function (RBF) and Kohonen's self-organisations maps (SOM). Moreover, back-propagation (BP), the most widespread algorithm used today and its modifications, such as quick-propagation (QP) and Delta-bar-Delta, are also discussed. All architectures correlate input variables to output variables through non-linear, weighted, parameterised functions, called neurons. In addition, various training algorithms have been developed in order to minimise the prediction error made by the network. The applications of ANNs in water analysis and water quality assessment are also reviewed. Most of the ANNs works are focused on modelling and parameters prediction. In the case of water quality assessment, extended predictive models are constructed and optimised, while variables correlation and significance is usually estimated in the framework of the predictive or classifier models. On the contrary, ANNs models are not frequently used for clustering/classification purposes, although they seem to be an effective tool. ANNs proved to be a powerful, yet often complementary, tool for water quality assessment, prediction and classification. 相似文献