排序方式: 共有12条查询结果,搜索用时 31 毫秒
1.
In this paper we propose a new version of the Controlled Random Search(CRS) algorithm of Price. The new algorithmhas been tested on thirteen global optimization test problems. Numericalexperiments indicate that the resulting algorithm performs considerablybetter than the earlier versions of the CRS algorithms. The algorithm,therefore, could offer a reasonable alternative to many currently availablestochastic algorithms, especially for problems requiring direct searchtype methods. Also a classification of the CRS algorithms is made based onglobal technique – local technique and the relative performance ofclasses is numerically explored. 相似文献
2.
There is a lack of a representative set of test problems for comparing global optimization methods. To remedy this a classification of essentially unconstrained global optimization problems into unimodal, easy, moderately difficult, and difficult problems is proposed. The problem features giving this classification are the chance to miss the region of attraction of the global minimum, embeddedness of the global minimum, and the number of minimizers. The classification of some often used test problems are given and it is recognized that most of them are easy and some even unimodal. Global optimization solution techniques treated are global, local, and adaptive search and their use for tackling different classes of problems is discussed. The problem of fair comparison of methods is then adressed. Further possible components of a general global optimization tool based on the problem classes and solution techniques is presented. 相似文献
3.
Plane-wave reflection from interfaces with single and double wire media is considered. Such media exhibit strong spatial dispersion even at very low frequencies which causes appearance of additional waves. The problem of additional boundary conditions (ABC) in application to wire media is discussed and an ABC-free approach, known in solid state physics, is used. Expressions for the fields and Poynting vectors of refracted waves are derived. The directions and values of the power density flow of refracted waves are found and conservation of the power flow through the interface is checked. 相似文献
4.
Ari J. Viitanen Ismo V. Lindell 《International Journal of Infrared and Millimeter Waves》1993,14(10):1993-2010
Uniaxial bianisotropic medium is a generalization of the well-studied bi-isotropic and chiral media. It is obtained, for example, when microscopic helices with parallel axes are positioned in a host dielectric in random locations. Plane wave propagation in such a medium is studied and a simple solution for the dispersion equation and for the eigenwaves are found. As a numerical example, polarization properties of a transverse wave propagating in a uniaxial bianisotropic medium is considered. The results give a simple possibility to construct a polarization transformer with a transversely uniaxial chiral medium for changing the polarization of a propagating plane wave. 相似文献
5.
Steven E. Buchholz Charles A. Omer Paul V. Viitanen F. Slma Sariaslani Ralph G. Stahl 《Applied biochemistry and biotechnology》1992,32(1-3):149-158
Two recombinant strains ofStreptomyces griseus have been developed to report on the activation of promutagenic° chemicals. This activation is monitored by reversion of the bacterial test strains to a kana-mycin-resistant phenotype. Strain H69 detects point mutations and was reverted at an increased frequency by acetonitrile, 2-aminoanthracene, 1,2-benzanthracene, benzidine, benzo(a)pyrene, 9,10-dimethyl-1,2-benzanthracene, and glycine. The second strain, FS2, detects frame shift mutations and was reverted at an increased frequency by 1,2-benzanthracene, benzidine, and glycine. Compounds such as butylated hydroxytoluene, catechol, chlorobenzene, hydroquinone, potassium chloride, phenol,cis-stilbene,trans-stilbene, and toluene did not elicit positive responses in either strain. In addition, these strains are capable of detecting direct-acting mutagens such asN-methyl-N’-nitrosoguanidine and ICR-191, providing further evidence of their promise for detecting a wider range of mutagens. To our knowledge, this is the first report of bacterial strains capable of activating promutagenic compounds and detecting their mutagenic metabolites without the benefit of an exogenous activation system such as the rodent liver homogenate (S9). 相似文献
6.
7.
L. O. Wahlund G. Andersson-Lundman P. Julin M. Nordstr m M. Viitanen J. S f 《Magnetic resonance imaging》1992,10(6):859-865
Twenty-five elderly subjects were examined with brain magnetic resonance imaging (MRI). The subjects were divided into two groups: those with Mini-Mental State Examination (MMSE) scores above 25, and those subjects with MMSE scores between 18 and 24. The degree of white matter abnormalities (WMA) (expressed as relative volumes) as well as the presence of cerebrovascular risk factors were evaluated in the two groups. We found that a) subjects with low MMSE scores had significantly larger relative volumes of WMA than the subjects with higher scores, b) a significant correlation (rs = 0.53, p < 0.009) between MMSE scores and the relative volume of WMA was also established, and c) a weak significant correlation (rs = −0.51, p < 0.05) between arterial blood pressure and WMA was found in the subjects with high MMSE scores. Besides these findings no other correlations between the presence of cerebrovascular risk factors and WMA were found in any of the groups. 相似文献
8.
M. M. Viitanen R. G. v. Welzenis H. H. Brongersma F. P. F. van Berkel 《Solid State Ionics》2002,150(3-4):223-228
Perovskite oxide membranes (La0.6Sr0.4Co0.2Fe0.8O3) are used for the separation of oxygen from air. In oxygen permeation experiments these membranes showed a peculiar behavior. Besides poor performance, a characteristic coloring also appeared on the surface of the membranes. In order to understand what was happening to the surface of the membranes, they were analysed with Low-Energy Ion Spectroscopy (LEIS) and X-ray Photoelectron Spectroscopy (XPS). The analyses showed that the surface of the LSCF membrane was covered with a SiO2 layer, which obviously reduced the performance and caused the coloring. It was established that the source of the silicon was siloxane containing grease that was used in the manual valves of the setup. In a new improved permeation setup, where grease-free valves were used, the LSCF membranes showed remarkably better performance. The LEIS measurements showed also that the permeation experiment of 300 h did not affect the surface composition of the membranes. The contamination-free LSCF membranes only showed the presence of La, Sr and O in the outermost atomic layer. The observed absence of Co and Fe suggests that further improvement of the membrane performance is possible. 相似文献
9.
Pedersen CS Lauritsen FR Sysoev A Viitanen AK Mäkelä JM Adamov A Laakia J Mauriala T Kotiaho T 《Journal of the American Society for Mass Spectrometry》2008,19(9):1361-1366
Ionized acetates were used as model compounds to describe gas-phase behavior of oxygen containing compounds with respect to their formation of dimers in ion mobility spectrometry (IMS). The ions were created using corona discharge at atmospheric pressure and separated in a drift tube before analysis of the ions by mass spectrometry. At the ambient operational temperature and pressure used in our instrument, all acetates studied formed dimers. Using a homolog series of n-alkyl-acetates, we found that the collision cross section of a dimer was smaller than that of a monomer with the same reduced mass. Our experiments also showed that the reduced mobility of acetate dimers with different functional groups increased in the order n-alkyl = branched chain alkyl = cyclo alkyl < aromat. For mixed n-alkyl dimers we found that the reduced mobility of acetate dimers having the same number of carbons, for example a dimer of acetyl acetate and hexyl acetate has the same reduced mobility as a dimer composed of two butyl acetates. The fundamental behavior of acetate monomers and dimers described in this paper will assist in a better understanding of the influence of dimer formation in ion mobility spectrometry. 相似文献
10.
Scott DJ Manos S Coveney PV Rossiny JC Fearn S Kilner JA Pullar RC Alford NM Axelsson AK Zhang Y Chen L Yang S Evans JR Sebastian MT 《Journal of chemical information and modeling》2008,48(2):449-455
We present work on the creation of a ceramic materials database which contains data gleaned from literature data sets as well as new data obtained from combinatorial experiments on the London University Search Instrument. At the time of this writing, the database contains data related to two main groups of materials, mainly in the perovskite family. Permittivity measurements of electroceramic materials are the first area of interest, while ion diffusion measurements of oxygen ion conductors are the second. The nature of the database design does not restrict the type of measurements which can be stored; as the available data increase, the database may become a generic, publicly available ceramic materials resource. 相似文献