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101.
Traditionally evolution is seen as a process where from a pool of possible variations of a population (e.g. biological species or industrial goods) a few variations get selected which survive and proliferate, whereas the others vanish. Survival probabilities and proliferation rates are typically associated with the ‘fitness’ of particular variations. In this paper we argue that the notion of fitness is an a posteriori concept, in the sense that one can assign higher fitness to species that survive but one can generally not derive or predict fitness per se. Proliferation rates can be measured, whereas fitness landscapes, i.e. the inter-dependence of proliferation rates, cannot. For this reason we think that in a physical theory of evolution such notions should be avoided. In this spirit, here we propose a random matrix model of evolution where selection mechanisms are encoded in interaction matrices of species, thereby extending the previous work of ours by a control parameter describing suppressors in the system. We are able to recover some key facts of evolution dynamics endogenously, such as punctuated equilibrium, i.e. the existence of intrinsic large extinction events, and, at the same time, periods of dramatic diversification, as known e.g. from the fossil record. Further, we comment on two fundamental technical problems of a ‘physics of evolution’, the non-closedness of its phase space and the problem of co-evolving boundary conditions, apparent in all systems subject to evolution. 相似文献
102.
Rudolf Beran 《Annals of the Institute of Statistical Mathematics》1993,45(4):639-654
Linear regression models with random coefficients express the idea that each individual sampled may have a different linear response function. Technically speaking, random coefficient regression encompasses a rich variety of submodels. These include deconvolution or affine-mixture models as well as certain classical linear regression models that have heteroscedastic errors, or errors-in-variables, or random effects. This paper studies minimum distance estimates for the coefficient distributions in a general, semiparametric, random coefficient regression model. The analysis yields goodness-of-fit tests for the semiparametric model, prediction regions for future responses, and confidence regions for the distribution of the random coefficients.This research was supported in part by NSF Grant DMS 9001710. 相似文献
103.
Abstract An Equipement has been built for the generation of uniaxial pressure and of bending stress respectivety directly in the cavity of an X-band ESR spectrometer. Changes of the structure of paramagnetic centres (Fe3+ on Al3+ sites) could be detected in materials with a high content of corundum under the innuence of pressure and bending stress. The objects of investigation are not only suitable model system but also have practical relevance. The Fe3+-ions, incorporated in the materials react very sensitive on mechanically or thermally induced changes of the state of the matrix. They give insight into the materials at a microscopic level The interpretation of the observed intensity and shift effects is possible on the basis of an adequate spin-hamiltonian. 相似文献
104.
Polyaniline-modified tin oxide and tin oxide nanoparticles were synthesized using a solution route technique. The obtained
pristine products were characterized with X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and
optical absorption spectroscopy. Thermogravimetric analysis results showed that the polyaniline-modified SnO2 nanoparticles exhibit higher thermal stability than the SnO2 nanoparticles. Scanning electron microscopy analysis on the as-synthesized powders showed spherical particle in the range
of 50–100 nm. 相似文献
105.
Wehmschulte RJ Grigsby WJ Schiemenz B Bartlett RA Power PP 《Inorganic chemistry》1996,35(23):6694-6702
The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects. 相似文献
106.
The relation of the solution and bioactive conformation of sialyl Lewis x (sLe(x)) has been addressed by chemical means. To mimic the preferred solution conformation of sLe(x) 1, the more rigid analog 2 has been designed and synthesized. The sialic acid residue of 1 was replaced by a carboxylic acid function which is fixed in the equatorial position of a six membered ring acetal fused to galactose. Due to entropic considerations, an increased biological activity could be expected if the preferred solution conformation and bound form of sLe(x) were similar. Since mimic 2 was found to be inactive in an E-selectin binding assay, the bound form of sLe(x) most probably differs from the prevailing solution conformation. 相似文献
107.
Gentilini C Evangelista F Rudolf P Franchi P Lucarini M Pasquato L 《Journal of the American Chemical Society》2008,130(46):15678-15682
The preparation and the properties of gold nanoparticles (Au NPs) protected by perfluorinated amphiphiles are described. The thiols were devised to form a perfluorinated region close to the gold surface and to have a hydrophilic portion in contact with the bulk solvent to impart solubility in water. The monolayer protected clusters were prepared, in an homogeneous phase using sodium thiolates because of the low nucleophilicity of the alpha-perfluorinated thiols, and fully characterized with (1)H, (19)F NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Au NPs with core diameters ranging from 1.6 to 2.9 nm, depending on the reaction conditions, were obtained. Water-soluble NPs (MPC-F8-PEGs) were obtained with the thiol HS-F8-PEG ending with a short poly(ethylene glycol) unit (PEG-OMe 550), whereas thiols with shorter PEG chains give rise to NPs insoluble in water. MPC-F8-PEGs undergo an exchange reaction with amphiphilic alkyl thiols. ESR investigations, using a hydrophobic radical probe, indicate that the MPC-F8-PEG monolayer shows a greater hydrophobicity compared to the analogous hydrogenated monolayer. 相似文献
108.
Theodosis Giousis Georgia Potsi Antonios Kouloumpis Konstantinos Spyrou Yiannis Georgantas Nikolaos Chalmpes Konstantinos Dimos Myrsini‐Kiriaki Antoniou Georgios Papavassiliou Athanasios B. Bourlinos Hae Jin Kim Vijay Kumar Shankarayya Wadi Saeed Alhassan Majid Ahmadi Bart J. Kooi Graeme Blake Daniel M. Balazs Maria A. Loi Dimitrios Gournis Petra Rudolf 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2021,133(1):364-369
Germanane (GeH), a germanium analogue of graphane, has recently attracted considerable interest because its remarkable combination of properties makes it an extremely suitable candidate to be used as 2D material for field effect devices, photovoltaics, and photocatalysis. Up to now, the synthesis of GeH has been conducted by substituting Ca by H in a β‐CaGe2 layered Zintl phase through topochemical deintercalation in aqueous HCl. This reaction is generally slow and takes place over 6 to 14 days. The new and facile protocol presented here allows to synthesize GeH at room temperature in a significantly shorter time (a few minutes), which renders this method highly attractive for technological applications. The GeH produced with this method is highly pure and has a band gap (Eg) close to 1.4 eV, a lower value than that reported for germanane synthesized using HCl, which is promising for incorporation of GeH in solar cells. 相似文献
109.
110.
The effect of chloride concentration and pH on pitting corrosion of AA7075 aluminum alloy coated with phenyltrimethoxysilane 总被引:1,自引:0,他引:1
A. A. Younis M. M. B. El-Sabbah Rudolf Holze 《Journal of Solid State Electrochemistry》2012,16(3):1033-1040
The effect of chloride ion concentration and pH of solution on the corrosion behavior of aluminum alloy AA7075 coated with
phenyltrimethoxysilane (PTMS) immersed in aqueous solutions of NaCl is reported. Potentiodynamic polarization, linear polarization,
open circuit potential, and weight loss measurements were performed. The surface of samples was examined using SEM and optical
microscopy. Elemental characterization of the coating by secondary ion mass spectrometry indicates an intermediate layer between
coating and aluminum alloy surface. The corrosion behavior of the aluminum alloy AA7075 depends on chloride concentration
and pH of solution. In acidic or neutral solutions, general and pitting corrosion occur simultaneously. On the contrary, exposure
to alkaline solutions results in general corrosion only. Results further reveal that aluminum alloy AA7075 is susceptible
to pitting corrosion in all chloride solutions with concentrations between 0.05 M and 2 M NaCl; an increase in the chloride
concentration slightly shifted both the pitting and corrosion potentials to more active values. Linear polarization resistance
measurements show a substantially improved corrosion resistance value in case of samples coated with PTMS as compared to uncoated
samples in both neutral (pH = 7), acidic (pH = 0.85 and 3), and alkaline chloride solutions (pH = 10 and 12.85). The higher
corrosion resistance of the aluminum alloy coated with PTMS can be attributed to the hydrophobic coating which acts as a barrier
and prevents chloride ion penetration and subsequent reaction with the aluminum alloy. 相似文献