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51.
We consider an approach for ex post evaluation of approximate solutions obtained by a well known simple greedy method for
set packing. A performance bound is derived that is a function of the highest average reward per item over subsets as well
as the number of allocated subsets and ground items. This a posterior bound can enable much revelation of optimality when
the solution is near optimal. One of the advantages of the ex post analysis is that it does not require computing the optimal
solution to the LP relaxation. The ex post bound will not be guaranteed to reveal substantial levels of optimality for all
problem instances but can be a useful tool that is complementary to other traditional methods for ex post evaluation for the
set packing problem. 相似文献
52.
It is shown that every properly embedded incompressible surface in a handlebody can be constructed by a canonical gluing process. A simple condition is given which asserts that the result of the gluing process is an incompressible surface. A new notion of isotopy is introduced in order to distinguish surfaces belonging to distinct isotopy classes. Several examples (known and new) are constructed. 相似文献
53.
Application of Complexity Theory to an Information Processing Model in Science Education 总被引:2,自引:0,他引:2
Dimitrios Stamovlasis Georgios Tsaparlis 《Nonlinear dynamics, psychology, and life sciences》2001,5(3):267-287
The current work examines the role of working-memory capacity in problem solving in science education. It treats an information-processing model with tools of complexity theory. Nonlinear methods are used to correlate the subjects' achievement scores with working-memory capacity. Data have been taken from the achievement scores in simple organic-synthesis chemical problems. The subjects (N = 319) were in grade twelve (age 17–18). Problems of various Z-demands (that is the number of steps needed to solve the problem) from two to eight were used. Rank-order sequences of the subjects, according to their scores, were generated, and each score was then replaced by the value of subject's working memory capacity measured by the digit backward span test. Then the sequences were mapped onto a one-dimensional random walk model and when treated as dynamic flows were found to possess fractal geometry with characteristics depending on the Z-demand of the problem. The findings were interpreted using concepts from complexity theory, such as correlation exponents, fractal dimensions and entropy. The null hypothesis was tested with surrogate data. 相似文献
54.
55.
The main objective of this paper is to develop an adaptive finite element method for computation of the values, and different sensitivity measures, of the Asian option with both fixed and floating strike. The pricing is based on Black–Scholes PDE-model and a method developed by Ve?e? where the resulting PDEs are of parabolic type in one spatial dimension and can be applied to both continuous and discrete Asian options. We propose using an adaptive finite element method which is based on a posteriori estimates of the error in desired quantities, which we derive using duality techniques. The a posteriori error estimates are tested and verified, and are used to calculate optimal meshes for each type of option. The use of adapted meshes gives superior accuracy and performance with less degrees of freedom than using uniform meshes. The suggested adaptive finite element method is stable, gives fast and accurate results, and can be applied to other types of options as well. 相似文献
56.
Georgios D. Samaras Nikolaos F. Matsatsinis Constantin Zopounidis 《European Journal of Operational Research》2008
The paper describes a multicriteria decision support system which aims at presenting an evaluation of the Athens Stock Exchange (ASE) stocks, on the basis of fundamental analysis. The system evaluates the stocks based on the method of fundamental analysis ratios, which is the most appropriate evaluation approach regarding investment decisions within a long term horizon. In addition to quantitative data deriving from fundamental analysis, the system uses qualitative data as well, in order to improve the reliability of the evaluation. The system introduced in this paper, utilises multicriteria analysis methodologies in order to rank the stocks by placing the best stock first and the worst last. Stock evaluation considers the specific characteristics of the potential investor, as well as his attitude towards undertaken risk. The final output of the system is four stock rankings which respond to four different criteria groups, depending on the type of accounting plan each listed company belongs to. The system incorporates a large volume of relevant information and operates in ‘real world conditions’ since its data are constantly updated. Finally, the system is intended for both institutional and private investors. 相似文献
57.
Georgios M. Kontogeorgis Ioannis Tsivintzelis Nicolas von Solms Andreas Grenner David Bøgh Michael Frost Anders Knage-Rasmussen Ioannis G. Economou 《Fluid Phase Equilibria》2010
Association theories such as the CPA (cubic-plus-association), NRHB (non-random hydrogen bonding) equations of state and the various variants of SAFT (statistical associating fluid theory) have been extensively applied to phase equilibrium calculations. Such models can also be used for estimating the monomer fraction of hydrogen bonding compounds and their mixtures. Monomer fraction data are obtained from spectroscopic measurements and they are available for a few compounds such as pure water and alcohols as well as for some alcohol–alkane and similar mixtures. These data are useful for an understanding of the capabilities and limitations of association models. The purpose of this work is two-fold: (i) to compare the performance of three models, CPA, NRHB and sPC-SAFT, in predicting the monomer fraction of water, alcohols and mixtures of alcohol-inert compounds and (ii) to investigate whether “improved” model parameters can be obtained if monomer fraction data are included in the parameter estimation together with vapor pressures and liquid densities. The expression “improved” implies parameters which can represent several pure compound properties as well as monomer fraction data for pure compounds and mixtures. The accuracy of experimental monomer fraction data is discussed, as well as the role of monomer fraction data in clarifying which association scheme should be used in these equations of state. The results reveal that the investigated association models (CPA, sPC-SAFT and NRHB) can predict, at least qualitatively correct, monomer fractions of associating compounds and mixtures. Only, small differences are observed between the models. In addition, it has been shown that, using a suitable association scheme, a single set of parameters can describe satisfactorily vapor pressures, liquid densities and monomer fractions of water and alcohols. The 4C scheme is the best choice for water, while for methanol there is small difference between the 2B and 3B association schemes. 相似文献
58.
Absorption spectra of closed-shell Na(2), Na(3) (+), Na(4), Na(5) (+), Na(6), Na(7) (+), and Na(8) clusters are calculated using a complex Bethe-Salpeter equation derived using a conserving linear response method. In the framework of a quasiparticle approach, we determine electron-hole correlations in the presence of an external field. The calculated results are in excellent agreement with experimental spectra, and some possible cluster geometries that occur in experiments are analyzed. The position and the broadening of the resonances in the spectra arise from a consistent treatment of the scattering and dephasing contributions in the linear response calculation. Comparison between the experimental and the theoretical results yields information about the cluster geometry, which is not accessible experimentally. 相似文献
59.
Andromahi Tegou Sofia Papadimitriou Georgios Kokkinidis Sotirios Sotiropoulos 《Journal of Solid State Electrochemistry》2010,14(2):175-184
Platinized nickel and cobalt coatings, Pt(Ni) and Pt(Co), have been prepared on glassy carbon, GC, rotating disc electrode
substrates by a two-step room temperature procedure that involved the electrodeposition of nickel and cobalt layers and their
spontaneous partial replacement by platinum (“transmetalation”) when immersed into a chloroplatinic acid solution. By tuning
the quantity of initially deposited nickel and cobalt, Pt(Ni) and Pt(Co) bimetallic coatings having a 26% atom Ni and 30%
atom Co composition have been prepared. For both materials typical Pt surface electrochemistry was recorded during fast voltammetry
in deaerated acid, pointing to the existence of a continuous Pt skin over a Pt–Ni and Pt–Co core. Oxygen reduction at the
Pt(Ni)/GC and Pt(Co)/GC electrodes was studied by means of steady-state voltammetry at a rotating disc electrode and the construction
of Tafel plots from corresponding voltammetric data. It was found that, when the initial potential of the voltammetric sweep
allowed the formation of a complete Pt oxide monolayer, then oxygen reduction was hindered for low overpotentials at Pt(Ni)
and Pt(Co), compared to pure bulk Pt. On the other hand, when the initial potential was less positive (thus leading to the
formation of a fraction of surface oxide monolayer) the presence of Ni and Co enhanced the kinetics of oxygen reduction. The
former behaviour is attributed to a decrease in oxide reduction ability of Pt in the presence of Ni and Co, while the latter
to an increase in dissociative oxygen chemisorption due to Ni and Co. 相似文献
60.
The microstructure of water soluble nanoaggregates based on polyelectrolyte complex formed by the cationic comb-type copolymer
poly(acrylamide -co-[3- (methacryloyl-amino)propyl] trimethylammonium chloride)-graft- polyacrylamide [P(AM-co-MAPTAC)-g-PAM]
and the anionic linear polyelectrolyte sodium polyacrylate (NaPA) was investigated using the fluorescence probe technique.
The fluorescence probe were 1-anilinonaphthalene-8-sulfonic acid (ANS), pyrene (Py) and 1,10-bis(1-pyrene) decane (PD). The
fluorescence properties in polyelectrolyte complex solutions, which are sensitive to either micropolarity (ANS, Py) or microviscosity
(PD), were related to the quantities obtained in different pure or mixed solvents. Micropolarities were quantified utilizing
the polarity common index (Reichardt) E
T(30). ANS and Py showed a variation of the micropolarity with the charge ratio of the two polymers, with the lowest polarity
reached at the complex neutralization. The PD probe, by its excimer-to-monomer fluorescence intensities ratio, enabled us
to evidence the effect of the composition and the comb-type copolymer grafting density on the microviscosity of the interpolyelectrolytes
aggregates. It has been found that the microviscosity increased with the density of the grafting PAM chains. 相似文献