Patterns in the solidification of a pure material are dealt with in this article. Results, deduced from a simple model based on heat conduction in the two phases and the effect of surface tension on the equilibrium temperature at the moving front, present a guide for experimental work. By introducing far-field conditions imitating what can be achieved in an experiment, we explain how the depths of the phases and the width of the container influence the patterns that can be seen if one advances the control variable to the critical point and then just beyond. Our new result is the existence of a third critical point. It occurs at small wave numbers and it is independent of surface tension. It appears because we take the depths of the phases into account. These depths are input values that offer the possibility of controlling crest-to-trough conduction, stabilizing in the solid, destabilizing in the liquid. The new critical point, and the patterns attending its appearance, can be found in cells of easily attainable widths. 相似文献
A cross-sectional study was carried out in rural areas of Jawan Block, District Aligarh, Uttar Pradesh, India, covering a total population of 3760 drawn from 11 villages. The total number of confirmed cases of rheumatic heart disease was 24 with a prevalence rate of 6.4 per 1000 of the general rural population. The prevalence of rheumatic heart disease increased with age until the age of 25 years. Females were more prone to rheumatic heart disease compared to males. Socio-economic class had a direct impact on the occurrence of rheumatic heart disease. 相似文献
A number of samples of thermally nitrided SiO2 with varying concentrations of electron traps were studied in an attempt to correlate the radiation-induced oxide charge with the number of electron traps. Also studied were the detrapping characteristics of irradiated devices. Etch-back experiments were performed to locate the centroid of the trapped charge. The results show that electron trapping does play a role in the improved radiation hardness of nitrided SiO2, but is not the sole cause of it 相似文献
Surrogate models have been widely applied to correlate design variables and performance parameters in turbomachinery optimization applications. With more design variables and uncertain factors taken into account in an optimization design problem, the mathematical relations between the design variables and the performance parameters might present linear, low-order nonlinear or even high-order nonlinear characteristics, and are usually analytically unknown. Therefore, it is required that surrogate models have high adaptability and prediction accuracy for both the linear and nonlinear characteristics. The paper mainly investigates the effectiveness of an adaptive region segmentation combining surrogate model based on support vector regression and kriging model applied to a transonic axial compressor to approximate the complicated relationships between geometrical variables and objective performance outputs with different sampling methods and sizes. The purpose is to explore the prediction accuracy and computational efficiency of this adaptive surrogate model in real turbomachinery applications. Three different sampling techniques are studied: (1) uniform design; (2) Latin hypercube sampling method; (3) Sobol quasi-random design. For the low dimensional case with five variables, the adaptive region segmentation combining surrogate model performs better (not worse) than the single component surrogate in terms of prediction accuracy and computational efficiency. In the meanwhile, it is also noted that the uniform design applied to the adaptive surrogate model has more advantages over the Latin hypercube sampling method especially for the small sample size cases, both performing better than the Sobol quasi-random design. Moreover, a high dimensional case with 12 variables is also utilized to further validate the prediction advantage of the adaptive region segmentation combining surrogate model over the single component surrogate, and the computational results favor it. Overall, the adaptive region segmentation combining surrogate model has produced acceptable to high prediction accuracy in presenting complex relationships between the geometrical variables and the objective performance outputs and performed robustly for a transonic axial compressor problem.
One strategy for alleviating excess latency (delay) in the Internet is the caching of web content at multiple locations. This
reduces the number of hops necessary to reach the desired content. This strategy is used for web content such as html pages,
images, streaming video, and Internet radio. The network of servers which store this content, and the collections of objects
stored on each server, is called a content distribution network (CDN). In order to optimally design a CDN, given a network
topology with available server storage capacity at various points in the network, one must decide which object collections
to place on each server in order to achieve performance or cost objectives. The placements must be within the storage limits
of the servers and must reflect the request patterns for each collection of objects to be cached. Researchers have suggested
formulations for the CDN problem which address performance by minimizing latency (the average number of hops is a commonly
accepted measure of latency) from client to content, or formulations that focus on minimizing cost of storage and/or bandwidth.
In this research, we develop a model which allows for the simultaneous treatment of performance and cost, present examples
to illustrate the application of the model and perform a detailed designed experiment to gain insights into cost/hops tradeoff
for a variety of network parameters. 相似文献
Measurements of the Hall coefficient, dc electrical conductivity, and magnetoresistance have been made on two highly compensated, plastically bent,n-type InSb samples from liquid helium to room temperature. The number and Hall mobility of charge carriers and the electrical conductivity are greatly affected by plastic bending. The mobility decreases appreciably and the number of charge carriers increases in both the deformed samples. This increase of effective charge carriers can be attributed to the introduction of effective donor centers due to plastic bending. The electrical conductivity in one of the deformed samples increases between the temperature ranges 4.2–15 K and 125–190 K compared to that of the undeformed state of the sample. This unusual increase in is attributed to the large increase inn value. The magnetoresistance at 4.2 K is due to impurity-band conduction and is found to be positive. It shows approximately a linear variation with magnetic field in both the deformed samples. The observed behavior of the magnetoresistance at 300 K is consistent with the behavior expected for free electrons. The observed / at 77.4 K is found to be less than that at 300 K and is explained in terms of the Hall mobility values at these two temperatures. 相似文献
A thermodynamic equilibrium model is developed for the distribution of iron(III) between phases of the system ferric sulfate-sulfuric
acid/β-alkenyl-8-hydroxyquinoline in xylene. Equilibrium data are obtained in the range [Fe]T (0.01 to 0.20 mol/dm3), pH (0.2 to 2.0), [HR] (0.02 to 0.06 mol/dm3) and temperatureT(298 to 323 K). The best fit of the data from a linear regression results in the following equation: % MathType!MTEF!2!1!+-%
feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0x%
Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaO% qaaiGacYgacaGGUbWaaSaaaeaadaWadaqaamaanaaabaGaamOraiaa
The regression analysis employs the aqueous phase ionic concentration of [Fe+3] and [H+], which are obtained by consideration of pertinent aqueous phase species equilibria. This model includes the effects of ionic
strength on the aqueous phase equilibrium concentration. The stoichiometry of the given reaction is established using the
method of continuous variation. Presence of only one species in the organic phase is also determined by the method of continuous
variation. The results indicate that the enthalpy of the reaction and the entropy change are −21.8 kJ/mole and −0.05 J/mole
K, respectively. 相似文献
In order to explore the effects of chemical composition on the rheological behavior o filled polymeric systems, we prepared polystyrene (9PS) and poly(methyl methacrylate) (PMMA) particles crosslinked with either ethylene glycol dimethacrylate (EGDMA) or divinyl benzene (DVB), and mixed these particles in a PMMA matrix. PS particles crosslinked with 10% EGDMA are better dispersed in a PMMA matrix, compared to PS particles, crosslinked with 10% DVB, due to the compatibilizing effect of EGDMA. For PMMA particles crosslinked with DVB, particle-matrix interactions in a PMMA matrix are smaller than in EGDMA-PMMA filled PMMA. Therefore, particles tend to agglomerate in PMMA composites filled with DVB-PMMA particles, especially in a low molecular weight matrix. We compared PMMA matrices of molecular weights 35,000 and 75,000. Higher particle-matrix interaction in the higher molecular weight matrix resulted in lower relative viscosities for DVB-PS filled systems, due to better dispersion of the particles. Composites filled with EGDMA-PS particles behave similarly to those filled with DVB-PS particles. PMMA composites filled with DVB-PMMA particles have a lower relative viscosity in the higher molecular weight PMMA matrix at low shear rates, due to better dispersion in the higher molecular weight matrix. However at high shear rates, particles are well dispersed in both PMMA matrices and, then, the relative viscosity is higher due to better bonding in the higher molecular weight matrix. 相似文献