Influence of dielectrics with light absorption on the photonic bandgap of porous alumina photonic crystals

In this work, the influences of dielectrics with light absorption on the photonic bandgaps (PBGs) of porous alumina photonic crystals (PCs) were studied. Transmittance spectra of porous alumina PCs adsorbing ethanol showed that all the PBGs positions red-shifted; however, the transmittance of the PBG bottom showed different trends when the PBGs were located in different wavelength regions. In the near infrared region, liquid ethanol has strong light absorption, and, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs first increased and then decreased. However, in the visible light region, liquid ethanol has little light absorption, and thus, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs increased gradually all the time. Simulated results were consistent with the experimental results. The capillary condensation of organic vapors in the pores of porous alumina accounted for the change in the PBG bottom transmittance. The nonnegligible light absorption of the organic vapors was the cause of the decrease in the transmittance. The results for porous alumina PC adsorbing methanol, acetone, and toluene further confirmed the influences of light absorption on the PBG bottomed transmittance.

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Assessment of Spatial Distribution of Porosity in Synthetic Quartz Cores Using Microfocus Computed Tomography (µCT)

The effects of particle sorting and compaction pressure on spatial distribution of porosity of synthetic quartz cores were investigated. A high-resolution X-ray computed tomography (CT) system with a microfocus X-ray source was used to acquire CT scans of 12 cores. The cores consist of a mixture of quartz powder and different proportions of quartz granulates (with a particle size range of 0.126 to 0.210 mm) that were compacted at 20.68 MPa (3,000 psi), 27.58 MPa (4,000 psi), and 34.47 MPa (5,000 psi) pressures. Calibration of core density was carried out according to the ASTM standard procedure. Computer algorithms were developed to calculate local porosity (φ) values, producing about 15 million φ values per core. The results of the analysis were represented by histograms and qualitatively compared with capillary pressure versus brine saturation measurements. As a result of changing the particle sorting (i.e., using a wider range of particle sizes), the standard deviation of the porosity distribution increases for the cores compacted under the same pressure. There were mixed trends of the effects of compaction pressure on porosity. However, they are qualitatively consistent with the capillary pressure measurements.     

铝熔体在多孔介财中的渗流过程

在流体流动相似原理的基础上,提出了铝熔体在多孔介南间隙中渗流模拟的原理和方法。设计建造了用于铝液和模拟液在外加压国下进行单向渗流的两套试验装置。     

Capillary Forces in Nanoparticle Adhesion: A Review of AFM Methods

This review focuses on the experimental determination and interpretation of capillary forces in the nanoparticle regime via atomic force microscopy (AFM), including an in-depth comparison of 28 AFM studies investigating the dependency of the capillary force between hydrophilic surfaces on the relative humidity of the system. Both colloidal probe experiments and experiments conducted with sharp AFM probes are considered. The dependence of the capillary forces on roughness, deformability, hydrophilicity, shape, and size, kinetics of meniscus formation and the relative humidity is discussed. These factors should be carefully considered in any experimental study in order to accurately determine the influence of capillary forces in nanoparticle adhesion.     

十二胺用量对正硅酸乙酯水解缩聚反应及其产物的影响

利用正硅酸乙酯为硅源,十二胺作为模板剂和催化剂,通过溶胶-凝胶法合成多孔SiO2微球,着重研究十二胺用量对正硅酸乙酯水解缩聚反应的速度及产物形貌和孔参数的影响。采用扫描电子显微镜、N2等温吸附、热重分析及小角度X射线衍射分析等对合成的多孔SiO2微球进行表征。结果表明:所有微球都具有双模微孔,随着十二胺用量的增加,合成的多孔SiO2微球的颗粒尺寸减小,比表面积减小,而孔的有序性提高。     

Microscopic studies of fluids in pores: Computer simulation and mean-field theory

The behavior of a simple model of a fluid confined to a single, infinitely long cylindrical pore is investigated by means of both a grand canonical Monte Carlo computer simulation and a mean-field theory. The theory is used to calculate the density profile of the fluid, as well as the grand potential of the system. The effect of the (size of the) pore radius as well as the temperature and pressure on the phase behavior of the fluid is studied in some detail, and the results are compared to those produced by related work in this field. The preliminary results from the simulation indicate that, in pores whose radii are a few molecular diameters in size, the fluid molecules tend to pack in cylindrically concentric shells about the axis of the pore.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

铝熔体在多孔介质中的渗流过程

在流体流动相似原理的基础上，提出了铝熔体在多孔介质间隙（简称多孔介质）中渗流模拟的原理和方法．设计建造了用于铝液和模拟液在外加压力下进行单向渗流的两套试验装置模拟试验揭示渗流时铝液在多孔介质中渗流的若干规律实践表明理论模型与试验吻合良好．     

The analysis of a two-phase zone with condensation in a porous medium

The one-dimensional steady-state heat and mass transfer in a two-phase zone of a water-saturated porous medium is studied. The system consists of a sand-water-vapour mixture in a tube that is heated from above and cooled from below. Under certain conditions, a two-phase zone of both vapour and water exists in the middle of the tube. A model problem for the temperature and the liquid saturation profiles within this two-phase zone is formulated by allowing for an explicit temperature dependence for the saturation vapour pressure together with an explicit saturation dependence for the capillary pressure. A boundary-layer analysis is performed on this model in the asymptotic limit of a large vapour-pressure gradient. This asymptotic limit is similar to the large-activation-energy limit commonly used in combustion problems. In this limit, and in the outer region away from any boundary layers, it is shown that the temperature profile is slowly varying and that the corresponding saturation profile agrees very well with that obtained in the previous model of Udell [J. Heat Transfer 105 (1983) p. 485] where strict isothermal conditions were assumed. The condensation and evaporation occurring within the boundary layers near the edges of the two-phase zone is examined. Finally, an iterative method is described that allows the temperature profile in the two-phase zone to be coupled to the temperature profiles in the two single-phase zones consisting of either water or vapour. This allows for the computation of the locations of the edges of the two-phase zone within the tube. Numerical computations are performed with realistic values of the parameters.     

超薄γ－Al_2O_3陶瓷膜的合成原位造粒成膜法

从无机铝盐出发，采用原位造粒技术，在自制的圆板状α－Ａｌ２Ｏ３载体表面上成膜，研究了原位造粒成膜的一些影响因素，并与溶胶－凝胶法以乙醇铝制备的载体γ－Ａｌ２Ｏ３膜进行了孔结构、表面状态和气体渗透性等性能和成膜机理的比较．结果表明：原位造粒法从无机铝盐出发可以制备具有微孔结构无针孔的γ－Ａｌ２Ｏ３膜．而且，具有如下优良品性：（１）膜的厚度薄而均匀、完好率大，膜厚度可控制在～１μｍ的水平，比乙醇铝水解溶胶－凝胶法制得的膜厚度～５μｍ薄得多；（２）具有良好的气体渗透性能，在保持基本相同的分离因子增量的情况下，其渗透率的减少量比乙醇铝水解溶胶－凝胶法的少得多；（３）在载体表面的微孔口原位造粒，粘着性好，不易脱落，而且粒径和孔径的大小可以通过浸渍时间及氨处理来调节等．     

A Note on the Micromechanics of Plastic Yield of Porous Solids

Experimental evidence suggests that, for materials exhibiting no appreciable work hardening and containing no more than approximately 20% volume fraction of pores, the macroscopic strain at which yield occurs is nearly constant, with a tendency to increase slightly as porosity increases. The present work shows that both observations - approximate constancy of strain at yield and its tendency to increase with porosity - have a relatively simple micromechanical explanation.     

First-order indicators for the estimation of discrete fractures in porous media

Faults and geological barriers can drastically affect the flow patterns in porous media. Such fractures can be modelled as interfaces that interact with the surrounding matrix. We propose a new technique for the estimation of the location and hydrogeological properties of a small number of large fractures in a porous medium from given distributed pressure or flow data. At each iteration, the algorithm builds a short list of candidates by comparing fracture indicators. These indicators quantify at the first order the decrease of a data misfit function; they are cheap to compute. Then, the best candidate is picked up by minimization of the objective function for each candidate. Optimally driven by the fit to the data, the approach has the great advantage of not requiring remeshing, nor shape derivation. The stability of the algorithm is shown on a series of numerical examples representative of typical situations.     

多孔介质中二氧化碳水合物生成的实验研究

以多孔介质为载体,将CO2以水合物的形式固定于海底,可以减缓温室效应.CO2水合物在多孔介质中与在纯水溶液中的生成条件有很大的不同,研究了在小型CO2气体水合物实验系统中,多孔介质中CO2水合物的生成特性,探讨了温度和压力对多孔介质中CO2水合物生成特性的影响.     

毛细管重力循环供冷装置的供冷性能研究

在同等条件测试空间内进行毛细管重力循环供冷方式（CGCC）和分体式空调器（PAC）的性能比较实验,并依据实验结果分析与评价毛细管重力循环供冷装置的供冷能力、舒适性和运行性能。其结果如下：重力循环供冷方式可以维持设计温度,并且不发生结露,由于此系统对地面结构具有蓄冷作用,因此其循环水泵和控制阀的开/关次数少于分体式空调器的开/关次数。另外,重力循环供冷方式可以有效缓解分体式空调器系统的吹风感现象。     

基于ANSYS软件对SiCp/A1(ZL102)复合材料铸造渗流过程多孔介质结构的有限元处理

采用统计平均的方法描述多孔介质微观结构的影响,根据多孔介质的连续介质模型及有限元方法对多孔介质内的铝液的渗流行为进行数值模拟,给出了可视化的瞬态温度场分布,并且初步预测了不同时刻的渗流有效高度.     

The effect of solid conversion on travelling combustion waves in porous media

A system of nonlinear partial differential equations, which describe the combustion of a gas passing through a porous medium, is examined. This model provides a bridge between recent porous-medium combustion studies and more classical combustion models. In particular, the effect of solid conversion on the downstream temperature is determined for travelling-wave solutions to the system. In cases for which the solid matrix is a perfect catalyst, solely enhancing the exothermic chemical reaction, with zero mass exchange, it is proved that the downstream temperature must always exceed the upstream temperature. However, when the solid is allowed to react with the gas, travelling-wave solutions for which the up- and down-stream temperatures are equal may be realised. A key result of this work is then the investigation of physical processes and related parameter ranges that give rise to travelling wave solutions with equal up- and down-stream temperatures. Specifically, two critical wavespeeds c_i with 0 < c₁ < c₂ are identified. For c < c₁ the downstream temperature always exceeds that upstream, whilst for c > c₂ no bounded travelling-wave solutions exist. Behaviour in the region c₁ < c < c₂ is new: here solutions having equal up- and down-stream temperatures are realised. The two factors upon which this result depends are the inclusion into the model of solid conversion effects and the distinction between solid and gas temperatures. Thus the inclusion of a new physical process, that of heat storage in the solid varying as the reaction proceeds, allows the existence of a new type of travelling-wave solution. Further phenomena studied include the appearance of nonunique solutions (which are of a type that may be related to ignition processes) and degenerate solutions which terminate precisely when all the solid and gaseous fuel is used up. Parameter regimes for the existence of these various types of solutions are found and the stability of such solutions discussed.     

Determination of the pore size distribution of correlated mesoporous networks

In the present work we study how the adsorption desorption hysteresis loop of a mesoporous disordered medium represented by a 3-dimensional Dual Site-Bond Model (DSBM) is affected by percolation. Site and bond distributions are assumed to be gaussians. The behavior of the threshold pressure for the evaporation processe suggests a method to determine the site and bond distributions from experimental adsorption-desorption hysteresis curves. Traditional methods developed for non-correlated networks are tested and evaluated against our simulation results showing the discrepancy mainly for highly correlated networks. Results of the prediction capability of our method are shown. Received: 30 March 2000     

正硅酸乙酯的水解缩聚反应及多孔SiO_2粉体的制备

详细描述了正硅酸乙酯的水解缩聚反应过程,简要介绍了影响反应过程的相关因素;综述了气凝胶和有序介孔SiO2材料这两种以该反应为基础的、具有代表性的多孔SiO2粉体的制备,特别是对多孔SiO2微球的制备进行了比较。指出以正硅酸乙酯的水解缩聚反应为基本过程制得的SiO2粉体中无序排列的孔是普遍存在的,如在反应过程中引入模板剂或采用其它手段,无序排列的孔可变为有序的。     

Studying Grout Propagation in Granular Soils by Image Processing Techniques

Abstract: This article presents two image‐processing techniques which allow studying grout propagation in granular soils. The first one deals with the evaluation of the cement grout concentration using UV spectrophotometry. The second is based on image segmentation processing: active contour model. We propose to develop the active contour model image analysis technique. This process, currently applied in the field of medicine, can be transposed to grout flow detection during soil injection. They are powerful image segmentation techniques that combine geometry, physics and approximation theory. Two distinct formulations exist to employ these techniques, parametric or geometric curves. These models have proven to be effective in segmenting and tracking non‐rigid structures. They exploit features derived from the image data together with a prior knowledge about the location, size and shape of these structures. We focus on a parametric approach for deformable models. They support highly intuitive interaction mechanisms. Those mechanisms allow, when necessary, researchers to bring their expertise to bear on the model‐based image interpretation task. In this paper, we show the development of the two different image analysis methods employed in our experiments for grout detection and grout concentration measurement.