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41.
Kostas Kleidis Apostolos Kuiroukidis Demetrios Papadopoulos Loukas Vlahos 《International Journal of Theoretical Physics》2007,46(9):2283-2298
We study the linear magnetohydrodynamic (MHD) equations, both in the Newtonian and the general-relativistic limit, as regards
a viscous magnetized fluid of finite conductivity and discuss instability criteria. In addition, we explore the excitation
of cosmological perturbations in anisotropic spacetimes, in the presence of an ambient magnetic field. Acoustic, electromagnetic
(e/m) and fast-magnetosonic modes, propagating normal to the magnetic field, can be excited, resulting in several implications
of cosmological significance. 相似文献
42.
The existence of the naphtho [9]annulenone 1 in two skeletally enantiomeric forms is demonstrated with the use of 1H? NMR. spectroscopy in conjunction with a chiral «shift» reagent. 相似文献
43.
Apostolos Hadjidimos 《Numerische Mathematik》1969,13(5):396-403
Summary Two well known high accuracy Alternating Direction Implicit difference schemes for solving Laplace's equation and the Biharmonic equation are considered. The set of iteration parameters of Douglas is used in both problems. More complete optimum values of the parameters involved are given. 相似文献
44.
Apostolos G. Bobos Emmanuel N. Protonotarios 《European Journal of Operational Research》1978,2(4):257-264
Deterioration of equipment is modeled as a multistate discrete time controlled Markov process. The states are classified according to the degree of deterioration. The problem of design of optimal systems for equipment maintenance and replacement is considered when the decision-maker may take, in each stage, one of many available maintenance actions, classified according to their “stochastic effectiveness”; no action and replacement are included as alternatives. It is assumed that the transition probabilities satisfy two conditions which effectively describe a trend for monotonically increasing expected deterioration and rate of deterioration. Under these assumptions it is proved in the paper that the optimal (cost minimizing) decision system in an infinite horizon is of the control limit rule type, rapidly obtained by policy improvement algorithms. A numerical example is presented for a specific practical application; detailed data are available from the authors on request. 相似文献
45.
Apostolos Hadjidimos 《Journal of Mathematical Analysis and Applications》1977,59(3):573-586
The purpose of this paper is to show the equivalence of Alternating Direction Preconditioning and Extrapolated Alternating Direction Implicit methods in the case of two-level one-parameter optimized schemes as far as convergence rates are concerned, and also to give optimum parameters for the numerical solution of the self-adjoint second-order elliptic partial differential equation and the biharmonic equation. 相似文献
46.
Iordanis Tzanidis Feidias Bairamis Dr. Lamprini Sygellou Dr. Konstantinos S. Andrikopoulos Prof. Apostolos Avgeropoulos Prof. Ioannis Konstantinou Prof. Dimitrios Tasis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(29):6643-6651
Nanoscale two-dimensional nanostructures have shown great potential as functional components in photocatalysis. Here, investigations on the synthesis of heterostructured hybrids, comprised of 0D CdS nanoparticles as semiconductor and 2D/2D graphene/MoSx as co-catalyst, are reported. The approach involves a rapid microwave-assisted reaction in autoclave conditions, by adopting either a one-step or a two-step protocol. The chemical speciation of the nanocomposites was found to depend strongly on the compounding conditions of the precursor substances. The photocatalytic activity was assessed by monitoring the photodegradation rate of 4-nitrophenol in solution using simulated solar light irradiation. The photocatalytic activity of the hybrids may be attributed to a combination of beneficial characteristics, strongly related to the chemical speciation of the composite components. Moreover, intimate contacts of the latter result in efficient heterojunctions. Overall, the present study provides valuable insight into the development of functional heterostructured photocatalysts comprised of two-dimensional nanomaterials. 相似文献
47.
Synthesis,characterization and self‐assembly of well‐defined linear heptablock quaterpolymers
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Christos Ntaras George Polymeropoulos George Zapsas Konstantinos Ntetsikas George Liontos Apostolos Karanastasis Dimitrios Moschovas Sofia Rangou Charlotte Stewart‐Sloan Nikos Hadjichristidis Edwin L. Thomas Apostolos Avgeropoulos 《Journal of Polymer Science.Polymer Physics》2016,54(15):1443-1449
Two well‐defined heptablock quaterpolymers of the ABCDCBA type [Α: polystyrene (PS), B: poly(butadiene) with ~90% 1,4‐microstructure (PB1,4), C: poly(isoprene) with ~55% 3,4‐microstructure (PI3,4) and D: poly(dimethylsiloxane) (PDMS)] were synthesized by combining anionic polymerization high vacuum techniques and hydrosilylation/chlorosilane chemistry. All intermediates and final products were characterized by size exclusion chromatography, membrane osmometry, and proton nuclear magnetic resonance spectroscopy. Fourier transform infrared spectroscopy was used to further verify the chemical modification reaction of the difunctional PDMS. The self‐assembly in bulk of these novel heptablock quarterpolymers, studied by transmission electron microscopy and small angle X‐ray scattering, revealed 3‐phase 4‐layer alternating lamellae morphology of PS, PB1,4, and mixed PI3,4/PDMS domains. Differential scanning calorimetry was used to further confirm the miscibility of PI3,4 and PDMS blocks. It is the first time that PDMS is the central segment in such multiblock polymers (≥3 chemically different blocks). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1443–1449 相似文献
48.
49.
I. Barandiaran D. Katsigiannopoulos E. Grana A. Avgeropoulos A. Eceiza G. Kortaberria 《Colloid and polymer science》2013,291(9):2173-2180
Poly(isoprene-block-methyl methacrylate) (PI-b-PMMA) block copolymers with different block ratios have been used to generate nanostructures both in thin films and by nanostructuring a thermosetting epoxy system. Obtained morphologies have been analyzed in terms of atomic force microscopy. The nanostructuring of thin films was carried out by thermal and solvent vapor annealing, in which the copolymer films were exposed to acetone vapors, selective solvent for methyl methacrylate (PMMA) block. By solvent vapor annealing thin films of both copolymers self-assembled into a hexagonally packed cylindrical morphology. Thermal annealing was carried out above the glass transition temperature of both blocks, obtaining worm-like and lamellar morphologies, depending on the block ratio. One of the copolymers has also been used for nanostructuring an epoxy thermosetting system. Morphologies consisting of spherical-shaped PI domains dispersed in a continuous epoxy matrix in which PMMA remained miscible were obtained, independently of the copolymer amount. 相似文献
50.
Polymer hydrogels have attracted much interest in recent years based on numerous applications mainly in biotechnology and medicine. For the knowledge‐based design and development of new materials for these and similar applications, it is essential to understand better the hydration properties of hydrogels and of polymers in general. With this term, we mean the particular organization of water in the hydrogel, which determines the properties of the water component, typically different than those of bulk water, and the impact of water on the properties of the polymer matrix itself. In this review, we focus on recent work with hydrogels based on poly(hydroxyethyl acrylate), mostly copolymers with a second hydrophobic polymer and silica nanocomposites. The combination of water sorption/diffusion, thermal and dielectric studies, by fully exploiting the capabilities of each individual technique, proves essential in providing significant information on particular aspects of hydration, such as water uptake, water organization, and diffusion coefficients; glass transition and plasticization; water and polymer dynamics; protonic conductivity, and in revealing interesting correlations between these particular aspects. In the outlook similarities and differences to other related systems, such as protein‐water and polymer solutions in non‐polar solvents, are stressed in the perspective of a broader study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献