Enhanced Voidage Correlations for Packed Beds of Various Particle Shapes and Sizes

Mean voidage in packed beds of spherical, cylindrical, and nonconventional cylindrical particles has been accurately measured, and the data obtained were employed to develop predictive mean voidage correlations that were not only simpler to use and more accurate than existing correlations, but also helped in developing a single general voidage correlation incorporating a particle shape factor applicable to a variety of particle shapes. Such mean voidage correlations are highly sought in packed bed design for a multitude of applications and can also assist in minimizing pressure drop in such packed beds by guiding particle shape selection.     

荫罩板孔形尺寸的视觉检测算法研究

荫罩板是彩色显像管的重要元件,其质量的好坏直接决定显像管的质量,本文论述了采用计算机视觉检测技术实现荫罩板高精度,全自动检测的方法,发展了一个具有亚像素级精度的边缘提取及几何尺寸检测的算法,经试验证明检测精度优于1μm。     

Droplet‐Based Microreactors for Continuous Production of Palladium Nanocrystals with Controlled Sizes and Shapes

Droplet‐based microreactors are used for the continuous production of Pd nanocrystals. Specifically, commercially available polytetrafluoroethylene (PTFE) tube and silica capillaries are utilized to fabricate a fluidic device capable of generating water‐in‐oil droplets. In addition to the feasibility of using such droplets as microreactors for conducting a synthesis, the ability to control the composition and concentration of reagents by adjusting the flow rates is demonstrated; reagents are mixed by periodically pinching the PTFE tube, and nanocrystals are produced with uniform size distribution in a continuous fashion. The capability to tailor the size and shape of the resultant nanocrystals is further demonstrated by introducing the reducing agent and capping agent at different flow rates to control the nucleation and growth processes. The ability to transform a bulk synthesis into a droplet‐based system holds great potential for the development of a new route to the high‐volume production of nanocrystals.     

Determination of the Dynamic Characteristics of Measuring Transducers with Distributed Parameters

An algorithm is proposed for approximately determining the dynamic characteristics of measuring transducers with distributed parameters utilizing several test signals.     

The Role of Defects in the Formation of Mesoporous Silica Fibers,Films, and Curved Shapes

The main goal of this research news article is to describe how different kinds of topological defects that exist in a silicate liquid crystal seed can initiate and direct the growth of particular forms of mesoporous silica. This avenue of investigation emerged from the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and polarized optical microscopy (POM) studies of hexagonal mesoporous silica fibers, films, and curved shapes, which delineated the essential relations between synthesis conditions, morphology, bulk and surface mesostructure, and optical birefringence textures.^[1–3] While SEMs of faceted mesoporous silica first appeared in 1992,^[4] the recognition, understanding, and significance of morphogenesis of mesoporous silica with curved shapes emerged in a series of papers from our laboratory.     

Determination of Sheet Steel Formability Using Wide Band Electromagnetic-Acoustic Transducers

Abstract

An electromagnetic-acoustic transducer (EMAT) system was used in conjunction with a “sampled” CW signal-processing method to generate, receive, and process longitudinal and shear waves in thin steel sheets. Using the system, swept-frequency measurements were made up to 7.5 MHz. To relate the measurements to sheet steel formability, a dimensionless frequency ratio, K, was computed from the resonant frequencies. From theoretical considerations, K should be related to a measure of steel sheet formability, r . This parameter is traditionally measured by plastically deforming uniaxial tension specimens. Good correlation was found between K and r for a set of steel sheet representative of those typically used to produce automobile body parts.     

Estimate of the Ratio of the Data and Background Signals in Detecting the Magnetic Fields of Surface Defects by Magnetic Measurement Transducers

Measurement Techniques - The problems of identifying defective segments of the surface of monitored objects and estimating the parameters of the defects are examined. The use of magnetic...     

再生粗骨料的形态及缺陷对再生混凝土干燥收缩和力学性能的影响

本工作分析了三种不同工艺制备的再生粗骨料的形态、附着砂浆及界面区显微硬度,研究了骨料形态和缺陷对其干燥收缩和力学性能的影响,最后结合骨料的释水效应、显微硬度和断裂形态,探讨了不同工艺制备的再生骨料引起的缺陷差异及其对再生混凝土干燥收缩和力学性能的影响机理.结果表明:相对颚式破碎,反击式破碎制备的骨料的粒形较好,针片状较少,骨料表面附着的水泥浆体显著减少,采用圆盘整形工艺则可以进一步提高颗粒的粒形,减少骨料表面附着的砂浆.再生骨料中含有的砂浆导致其吸水率较高,具有一定的内养护作用,能够降低其早期收缩,但后期水分的蒸发仍会导致再生混凝土的干缩增大.反击式破碎制备的再生骨料(RA-C1)界面显微硬度高于颚式破碎制备的再生骨料(RA-E),且以其制备的混凝土的强度也大于RA-E组;反击式破碎+整形制备的再生骨料(RA-C2)虽然界面性能最好,但由于骨料强度不高导致其力学性能相对较低.     

Determination of Particle Sizes and Crystalline Phases on Colloidal Silicon Nanoparticle Suspensions

1.IDtroductionLightscatteringpropertiesofsphericalparticlescanbedescribedbyMietheoryl1]whichcanbeaP-pliedtocolloidalparticlessuspendedinthegasorliquidphase.Withsomecarethetheorycanevenbeap-pliedtodrypowdersorparticlesonasolidsupport[2]lthoughitisstrictlyvalidonlyforisolatedsphericalparticles.Informationonparticlesizer,sizedistribu-tionandnumberdensitiesN(r),andrefractiveindexhcanberetrievedbyexperimentaldata.Theex-tinctioncoefficient7ofacolloidalsuspension,forex-ample,canbedeterminedfromthea…     

A Procedure for Detecting Hidden Surface Defects in a Thin Plate by Means of Active Thermography

Let \(\varOmega _\epsilon \) be a metallic plate whose top inaccessible surface has been damaged by some chemical or mechanical agent. We heat the opposite side and collect a sequence of temperature maps \(u^\epsilon \). Here, we construct a formal explicit approximation of the damage \(\epsilon \theta \) by solving a nonlinear inverse problem for the heat equation in three steps: (i) smoothing of temperature maps, (ii) domain derivative of the temperature, (iii) thin plate approximation of the model and perturbation theory. Our inversion formula is tested with realistic synthetic data and used in a real laboratory experiment.     

Transducers for contactless induction inspections of underground pipelines

The block diagrams of digital and analog transducers used for frequency normalization of the amplitude of the electromotive force that the field of a pipeline induces in an induction pickup are described. Mathematical expressions are given for designing such transducers.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 52–55, April, 1995.