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141.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
142.
E.D. Aydin C.R.E. de Oliveira 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(3):247-260
In this paper, we solve the steady-state form of the Boltzmann transport equation in homogeneous and heterogeneous tissue-like media with a finite element-spherical harmonics (FE-PN) radiation transport method. We compare FE-transport and diffusion solutions in terms of the ratio of absorption to reduced scattering coefficient, (μa/μs′) and the anisotropy factor g. Two different scattering phase function formulas are employed to model anisotropic scattering in the slab media with high g-value. Influence of void-like heterogeneities, and of their boundaries with the surrounding medium on the transport of photons are also examined. 相似文献
143.
We show that reductions of KP hierarchies related to the loop algebra of SLn with homogeneous gradation give solutions of the Darboux-Egoroff system of PDE's. Using explicit dressing matrices of the Riemann-Hilbert problem generalized to include a set of commuting additional symmetries, we construct solutions of the Witten– Dijkgraaf–E. Verlinde–H. Verlinde equations. 相似文献
144.
报道Ar^q Ne(q=8,9,11,12)碰撞体系中多电子转移过程,得到了多组实验测量电荷交换截面数据,讨论入射离子电荷交换截面、反冲离子产生截面与入射离子电荷态、能量以及散射离子电荷态的关系,并且将实验结果与Ar^q Ar碰撞体系进行对比研究。在修正分子库仑过垒模型的基础上,对实验现象做了合理的解释。 相似文献
145.
146.
Marcos Almeida Bezerra Sérgio Mitihiro do Nascimento Maêda Eliane Padua Oliveira Maria de Fátima Batista de Carvalho Ricardo Erthal Santelli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
In the present paper a procedure is proposed for the determination of traces of Cd, Co, Mn and Cr in petroleum industry produced water by inductively coupled plasma optical emission spectrometry. The procedure is based on cloud point extraction of these metals, as their dithizonate complexes, into the surfactant-rich phase of octylphenoxypolyethoxyethanol surfactant (Triton X-114). Extractions were carried out in solutions with salinities between 10‰ and 70‰. Since residual salinity in the surfactant-rich phase caused differences in its transport to the plasma, yttrium was used as an internal standard to correct for this effect. The simultaneous metal extraction procedure was optimized by response surface methodology using a Doehlert design and desirability function. Enhancement factors of 21, 21, 9 and 19, along with limits of quantification of 0.093, 0.20, 0.73 and 1.2 μg L− 1, and precision expressed as relative standard deviation (n = 8, 20.0 μg L− 1) of 5.8, 1.2, 1.7 and 5.7% were obtained for Cd, Co, Mn and Cr, respectively. The accuracy was evaluated by spike recovery tests on the high salinity water samples with salinity of 40 and 63‰. 相似文献
147.
C.P. Paul P. Ganesh S.K. Mishra P. Bhargava J. Negi A.K. Nath 《Optics & Laser Technology》2007,39(4):800-805
This paper presents an investigation of laser rapid manufacturing (LRM) for Inconel-625 components. LRM is an upcoming rapid manufacturing technology, it is similar to laser cladding at process level with different end applications. In general, laser-cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near-net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high-power continuous wave (CW) CO2 laser system, integrated with a co-axial powder-feeding system and a three-axis workstation were used. The effect of processing parameters during LRM of Inconel-625 was studied and the optimum set of parameters for the maximum deposition rate was established employing Orthogonal L9 array of Taguchi technique. Results indicated that the powder feed rate and the scan speed contributed about 56% and 26%, respectively to the deposition rate, while the influence of laser power was limited to 10% only. Fabricated components were subjected to non-destructive testing (like—ultrasonic testing, dye-penetrant testing), tensile testing, impact testing, metallographic examinations and micro-hardness measurement. The test results revealed defect-free material deposition with improved mechanical strength without sacrificing the ductility. 相似文献
148.
M. C. Caracoche J. A. Martínez P. C. Rivas M. A. Taylor A. F. Pasquevich S. Barolin O. A. de Sanctis 《Hyperfine Interactions》2007,179(1-3):87-93
The hyperfine quadrupole interaction at Hf sites in films and powders of 14 mol% CaO–HfO2 and 20 mol% CaO–HfO2 has been determined as a function of temperature. Results indicate the formation of a cubic solid solution and other microstructures assigned to the ?1 (CaHf4O9) and ?2 (Ca6Hf19O44) phases. Dynamical effects on the electric field gradient reveal the existence of oxygen vacancies movements in the solid solution. The thermal behavior of the relaxation constant observed in films allowed the determination of activation energies of 0.54 eV and 0.70 eV for the 14 mol% and 20 mol% CaO doped hafnias, respectively. The influence of the microdomains and the stability of the cubic solid solution are discussed. 相似文献
149.
Helga Fetter Berta Gamboa de Buen Jesús García-Falset 《Journal of Mathematical Analysis and Applications》2003,285(2):444-455
We consider a family of spaces wider than r-UNC spaces and we give some fixed point results in the setting of these spaces. 相似文献
150.
E. de A. Gonçalves V. M. de Oliveira A. Rosas P. R.A. Campos 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):127-132
Adaptation of populations takes place with the occurrence and subsequent fixation of mutations that confer some selective
advantage
to the individuals which acquire it. For this reason, the study of the process of fixation of advantageous mutations has a
long history
in the population genetics literature. Particularly, the previous investigations aimed to find out the main evolutionary forces
affecting the strength of natural selection in the populations.
In the current work, we investigate the dynamics of fixation of beneficial mutations in a subdivided population. The subpopulations
(demes)
can exchange migrants
among their neighbors, in a migration network which is assumed to have either a random graph or a scale-free topology. We
have observed that the migration rate
drastically affects the dynamics of mutation fixation, despite of the fact that the probability of fixation is invariant on
the
migration rate, accordingly to
Maruyama's conjecture. In addition, we have noticed a topological dependence of the adaptive evolution of the population when
clonal interference
becomes effective. 相似文献