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101.
In this paper, we show that self-similarity with respect to the existence of a (purely radial) homothetic Killing vector field for spherically symmetric spacetimes implies the separability of the spacetime metric in terms of the co-moving coordinates (and vice versa) and that the metric is, uniquely, the one recently reported in (Class. Quantam Grav. 18: 2147–2162; 2001). This spacetime, in general, has non-vanishing energy flux and shear. An interesting feature of this spacetime, in contrast to other self-similar spherically symmetric spacetimes (not reducible to our form) is that it has an arbitrary radial distribution of matter. 相似文献
102.
Christopher J. May Jeffrey C. Schank Sanjay Joshi Jonathan Tran R. J. Taylor I‐Esha Scott 《Complexity》2006,12(1):53-66
Biorobotic research continually demonstrates that behavior and cognition can be the emergent products of (1) embodied agents that are (2) dynamically embedded within an environment and (3) equipped with simple sensorimotor rules. Thigmotaxis is an orientation response to contact manifested in infant rats by wall following, corner burrowing, and group aggregation. Orientation responses have been long thought to be mediated only by sensory or central processes. Here we show that a random control architecture in a morphologically similar robot embedded in a scaled environment can reproduce thigmotaxic behaviors seen in infant rats. We conclude that (1) and (2) may play a larger role than previously thought in the generation of complex behaviors. © 2006 Wiley Periodicals, Inc. Complexity 12: 53–66, 2006 相似文献
103.
The case of a particle moving along a nonsmooth constraint under the action of uniform gravity is presented as an example
of indeterminancy in a classical situation. The indeterminacy arises from certain initial conditions having nonunique solutions
and is due to the failure of the Lipschitz condition at the corresponding points in the phase space of the equation of motion. 相似文献
104.
We demonstrate a kinetically-driven patterning scheme to selectively position arrays of Ge or Si nanoparticles within lithographically defined HfO2 windows. The surface reactions enabling patterning are revealed through temperature programmed desorption experiments and selectivity of the deposition is verified by X-ray photoelectron spectroscopy and scanning electron microscopy. Patterning is possible by exploiting the different reactivity of Ge and Si on HfO2 and SiO2 surfaces and employing a sacrificial SiO2 mask on which adatoms etch the SiO2 surface and do not accumulate to form nanocrystals. 相似文献
105.
We study the problem of finding a point in the relative interior of the optimal face of a linear program. We prove that in the worst case such a point can be obtained in O(n
3
L) arithmetic operations. This complexity is the same as the complexity for solving a linear program. We also show how to find such a point in practice. We report and discuss computational results obtained for the linear programming problems in the NETLIB test set.Research supported in part by NSF Grant CCR-8810107, CCR-9019469 and a grant from GTE Laboratories.Research supported in part by NSF Grant DDM-8922636 and NSF Coop. Agr. No. CCR-8809615 through Rice University. 相似文献
106.
A relaxed version of Karmarkar's method is developed. This method is proved to have the same polynomial time complexity as Karmarkar's method and its efficient implementation using inexact projections is discussed. Computational results obtained using a preliminary implementation of the method are presented which indicate that the method is practicable.This research was supported in part by NSF Grants CDR 84-21402 and DMS-85-12277 and ONR Contract N00014-87-K-0214. 相似文献
107.
Dutta S Abe H Aoyagi S Kibayashi C Gates KS 《Journal of the American Chemical Society》2005,127(43):15004-15005
Fasicularin is a structurally novel thiocyanate-containing alkaloid isolated from the ascidian Nephteis fasicularis. Early biological experiments suggested that this compound's cytotoxic properties may stem from its ability to damage cellular DNA. Sequence gel analysis reveals that treatment of a 5'-32P-labeled DNA duplex with fasicularin in pH 7.0 buffer causes strand cleavage selectively at guanine residues. Further experiments indicate that production of these base-labile lesions in DNA involves alkylation of guanine residues by a fasicularin-derived aziridinium ion. This work reveals fasicularin as the first natural product found to generate a DNA-alkylating aziridinium ion via a mechanism analogous to the clinically used anticancer drugs mechlorethamine, melphalan, and chlorambucil. 相似文献
108.
Lobinger P Jarzina H Roesky HW Singh S Kumar SS Schmidt HG Noltemeyer M Freyhardt HC 《Inorganic chemistry》2005,44(25):9192-9196
A novel synthetic approach is given for the preparation of a metal-organic lanthanide sol-gel precursor solution and its application for the production of coated conductors. Besides all other problems concerning the technical process itself, the key to a successful deposition of oxide layers is the choice of the precursor solution and the understanding of the mechanism of deposition. Moreover, the isolation and characterization of the species involved in the reaction is very important. Regarding the complex process occurring during the formation of the surface layer, it is obvious that the best choice should have a compound already containing the final composition of the layer. Two compounds of composition [Y(OAc)3(H2O)2]2 and [Y(OAc)3]2(H2O) were isolated from their precursor solution and characterized by X-ray structural analysis. A short outlook will give an insight into the possible bonding mechanisms of the surface layer. These experiments were made with the mixed metal-oxide system yttrium-stabilized zirconium oxide, which is widely used as a substrate for superconducting oxides. A study of the structure of hydrated yttrium acetates, by single-crystal X-ray diffraction, infrared spectra, and elemental analysis demonstrates that there are two separate structures for hydrated yttrium acetates, which play a role as an intermediate in the building of ceramic oxide layers for coated conductors. 相似文献
109.
Sanjay Pralhadrao Jadhav Bhagwan Ghanshamji Toksh Kamalakar Marutirao Jadhav Narayan Dadarao Shinde 《化学物理学报》2010,23(4):459-464
采用湿化学共沉淀法合成了Ni1-xCdxFe2O4 (0≤x≤0.5)的混合铁氧体,利用X射线衍射对其结构和晶相进行表征.结果表明:随着镉Cd浓度的增加晶格参数逐渐增大.扫描电子显微镜研究微观结构,TG/DTA研究了硫酸共沉淀物.揭示了在650 oC合成铁氧体同时进行分解.测量了纳米粒子的磁化强度和交流磁化率.结果表明,Ni1-xCdxFe2O4混合铁氧体的磁化率、居里温度和有效磁矩随着镉含量的增加下降。 相似文献
110.
Photophysical properties of cinchonine dication (C++) have been studied in protic and aprotic polymers by monitoring steady state and time resolved measurements. It is found to be sensitive towards the microenvironment of polymers. Edge excitation red shifted emission (EERS) is observed in all polymeric matrices. However, the magnitude of EERS is relatively high in protic as compared to aprotic polymer. Isobestic point in excitation spectra and three decay components in time resolved measurements indicate more than two trapped chemical species in the heterogeneous environment of the polymer. Solute-polymer interactions are found to produce the third decay channel, unlike in solution phase and may be useful to understand the polymer microenvironment. 相似文献