Performance of concrete coating under varying exposure conditions

This paper reports the results of a study conducted to evaluate the performance of ten concrete coatings, representative of five generic types, under varying exposure conditions. The performance of selected coatings was assessed on laboratory specimens by testing their adhesion to concrete, crack-bridging ability, chloride permeability and resistance to moisture and thermal variations. The data indicate that the overall performance of epoxy resin and polyurethane coatings was better than that of other generic types of coatings depending on chemical formulations. Further, a variation in the performance of coatings of similar generic type was noted. The selected coating needs to be tested under conditions similar to the exposure environment. Guidelines for the selection of concrete coatings appropriate for the service conditions are presented along with the performance criteria.

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Résumé Ce papier rapporte les résultats d'une étude qui a été conduite afin d'évaluer la performance d'une dizaine de revêtements en béton représentant cinq types génériques sous des conditions d'exposition variables. La performance des revêtements sélectionnés a été évaluée sur des échantillons de laboratoire en testant leur adhérence au béton, leur aptitude à émousser les fissures, la perméabilité des chlorures et la résistance à l'humidité et aux variations thermiques. Les données indiquent que la performance globale de la résine époxyde et des revêtements de polyuréthanne était meilleure que celle des autres types de revêtements en fonction de leurs formulations chimiques. De plus, une variation de la performance des revêtements de type générique similaire a été notée. Les revêtements sélectionnés doivent être testés sous des conditions similaires à celles de l'environnement d'exposition. Les règles de sélection des revêtements de béton approriés pour les conditions de service sont présentées ainsi que les critères de performance.

     

Performance evaluation of repair systems under varying exposure conditions

This paper reports results of a study conducted to assess the performance of commonly utilized repair systems when exposed to some selected exposure conditions, such as marine, belowground, fire, acid, and sulfur fumes. The performance of the selected repair systems was assessed by exposing large-sized repaired concrete specimens to the selected exposure conditions in addition to thermal variations. After the completion of the exposure, the repaired specimens were visually examined for damage to the surface coating and presence of rust stains, salt scaling, etc. The bond of the coating with the substrate was evaluated and then the specimens were crushed to retrieve reinforcing steel bars that were examined for the extent of corrosion, if any. The data developed in this study were utilized to recommend repair systems suitable for the selected exposure conditions.     

Modeling the performance of direct-detection Doppler lidar systems including cloud and solar background variability

Previous modeling of the performance of spaceborne direct-detection Doppler lidar systems assumed extremely idealized atmospheric models. Here we develop a technique for modeling the performance of these systems in a more realistic atmosphere, based on actual airborne lidar observations. The resulting atmospheric model contains cloud and aerosol variability that is absent in other simulations of spaceborne Doppler lidar instruments. To produce a realistic simulation of daytime performance, we include solar radiance values that are based on actual measurements and are allowed to vary as the viewing scene changes. Simulations are performed for two types of direct-detection Doppler lidar system: the double-edge and the multichannel techniques. Both systems were optimized to measure winds from Rayleigh backscatter at 355 nm. Simulations show that the measurement uncertainty during daytime is degraded by only approximately 10-20% compared with nighttime performance, provided that a proper solar filter is included in the instrument design.     

Adhesion force approximation at varying consolidation stresses for fine powder under humid conditions

Interparticle adhesion forces in fine powders are greatly influenced by varying relative humidity (RH) conditions. The present study estimated the interparticle adhesion forces developed in corn starch powder under humid conditions at varying applied consolidation stresses using tensile strength determination approach. Shear test was used to determine tensile strength of powder at 1–9 kPa consolidation pressures and extrapolated values of tensile strength at zero stress were used for force estimation in non-consolidated powders. A strong dependence of interparticle adhesion force on consolidation and RH conditions was observed, mainly due to alteration in the number of adhesive contacts and contact area. The results indicated that, at low consolidation and high RH, capillary force is the prevailing force contributing to the total interparticle adhesion in contrast to higher consolidation conditions where load induced contact force plays a dominant role. Furthermore, for nonconsolidated samples, the adhesion forces registered a steep jump above 60% RH which was primarily attributed to dominance of the liquid bridge forces. Also, forces determined from tensile strength approach and those predicted theoretically, as a summation of individual forces, yielded a similar trend. Overall, a simple and effective approach for interparticle force estimation of consolidated as well as loosely packed powders under varying humidity conditions is presented here.     

Conjugate problems of unsteady heat and mass conduction under varying external conditions

A closed system of algebraic and ordinary differential equations that enables one to simply and with a high degree of accuracy solve unsteady problems of heat conduction and diffusion extraction of a substance from solids of standard shapes - a plate, a cylinder, and a sphere - under varying external conditions is proposed. The method of solution is based on a unified universal dependence that describes with a high degree of accuracy the distribution of temperatures or concentrations of the substance in the above solids and on equations that determine variations in characteristics involved in this dependence with time and space as the solids move.     

Doses under automatic exposure control (AEC) for direct digital radiographic (DDR) X-ray systems

Current guidelines quote tolerances for automatic exposure control (AEC) device performance for X-ray systems as 'Baseline ± X %'. However, in the situation where a baseline figure has not yet been achieved, as in the case of commissioning assessments, this tolerance is not relevant. The purpose of this work is to provide mean doses for direct digital radiography (DDR) X-ray system, operating in AEC, against which comparisons can be made. Dose measurements have been recorded under AEC operation on 29 DDR detectors from three different manufacturers. Two different testing protocols were examined: (1) water equivalent phantoms in front of the DDR detector and (2) aluminium block at the tube head. The average patient exit dose, using the aluminium block was 4.6 μGy with the antiscatter grid in place and 4.0 μGy with the grid removed. Using the water phantoms, the average dose was measured at 17.1 μGy with the antiscatter grid in place and 5.4 μGy with grid removed. Based on these results, it is clear that different testing configurations significantly impact on the measured dose.     

Noise, clutter, and determinism in infrared spectral signatures under varying meteorological conditions

Infrared remote detection of chemical and biological agents in a complex environment depends on the ability to recognize threat signatures and differentiate them from the signatures of innocuous materials. In this paper, we addressed the methods of producing the constraint spectra needed to ensure reliable operation in a meteorologically changing environment. We collected arrays of background spectra of ground, woods, and low-angle sky on an irregular basis over a period of a year. Based on the hypothesis that the concentration fluctuations of species in the sensor's field of view can be exploited to form signatures, the standard deviations of the array (the result is characteristic of all fluctuations) and the difference array (the result is characteristic of sensor fluctuations) were computed. Subtracting these two spectra and filtering the result produced a spectrum, which is a measure of the IR fluctuations in the scene. The resulting set of scene spectra were processed into aberrant noise, and deterministic groups by numerical filtering and statistical methods.     

Deformation and tearing of circular plates with varying support conditions under uniform impulsive loads

Transient dynamic finite element analysis of circular plates with varying support configurations under uniform single square wave form impulsive load has been carried out in FEA package ANSYS. Experimental results of Teeling-Smith and Nurick [The deformation and tearing of thin circular plates subjected to impulsive loads. Int J Impact Eng 1991;11(1):77–91] and Nurick et al. [Tearing of blast loaded plates with clamped boundary conditions. Int J Impact Eng 1996;18(7–8):803–27] for the onset of thinning and tearing at the boundary of clamped circular plates subjected to uniformly loaded air blasts have been used to compare and validate the numerical simulation and procedure. The Mode II failure with respect to clamped circular plates has been simulated using a rupture strain criteria. Mode III failure or plastic shear sliding, has been considered using a shear strain failure criteria as proposed by Wen and Jones for plates. A stiffness reduction scheme has been proposed to decide on the initiation and progression of tearing in conjunction with suitable failure model under Modes II and III. The evolution of deflections, plastic zones, rupture zones and failure modes under the blast loading conditions are found to match well with the experimental results. The validated numerical model has further been used to study the effect of plate thickness on the deformation and tearing response of the circular plates subjected to impulsive loads. The deformation, tearing and shock absorption response of clamped circular plates under uniform impulsive loads with ring support of varying edge configurations at the boundary have also been numerically studied. Further, the response of circular plate–tube combination with varying boundary support configurations has been studied. The plate has been considered at the mid-span of the tube of length equal to the plate diameter with the ends of the tube modelled as clamped. The numerical model has been used to study the effect of tube thickness variations on the deformation and tearing response of the circular plate under shock loads. The response of tube–plate combinations under uniform impulsive loads with ring support at the plate–tube junction have also been numerically studied.     

基于独立特征选择与相关向量机的变载荷轴承故障诊断

在线状态监控与故障诊断具有很大的经济与安全意义,提出了一种基于独立特征选择(IFS)与相关向量机(RVM)的智能故障诊断模型用于变载荷条件下识别多类轴承故障及其故障程度。首先混合空载(0hp)与满载(3hp)两种载荷状态下的实验数据作为训练样本;其次提取时域统计特征与全小波包域节点能量特征作为候选特征;接着采用一种改进的Fisher特征选择方法为每两类故障状态独立选择具有最大分类能力的最优特征子集;然后用“一对一”的方法训练多个RVM二类子分类器;最后采用“最大概率赢”的策略组合所有子分类器构成IFS_RVM多类故障诊断模型。用未知载荷(1hp,2hp)下的实验数据验证了模型的有效性,得到99.58%的极高诊断精度,实验结果表明,该模型精度高、鲁棒性强,满足变载荷条件下在线故障诊断的需要     

Synthesizing higher nitride of molybdenum (Mo) and iron (Fe) in ammonia (NH3) gas stream under irradiation of concentrated solar beam in a solar furnace

Flowing gaseous ammonia NH₃ with suppressed extent of dissociation (un‐cracked NH₃) is acknowledged to function as a powerful nitriding medium to realize formation of metal nitride MN_x with considerably high N/M ratio x that cannot be achieved through reaction of M with N₂ gas. For example, mono‐nitride δ‐MoN of Mo and ε‐FeN_x phase of Fe with x = 0.33 ? 0.50 (i. e. hypo‐stoichiometric sub‐nitride ε‐Fe₂N) were reported to be difficult to prepare in N₂ gas environment even at elevated pressure but might be synthesized in flowing NH₃ gas at normal pressure when reaction temperature and NH₃ gas flow rate were set adequately. In the present work, nitriding experiments for Mo and Fe were carried out in flowing NH₃ gas under irradiation with concentrated solar beam. The acquired experimental evidences demonstrated that temperature range for formation of δ‐MoN was somewhat extended in flowing NH₃ gas under heating with concentrated solar beam compared with that under heating in conventional laboratory or industrial electric furnace. On the other hand, no such merit of extending temperature range for formation of ε‐Fe₂N in flowing NH₃ gas was detected in the present work under heating with concentrated solar beam.     

Stress intensity factors for curvilinear cracks loaded under anti-plane strain (mode III) conditions

A general solution to the elastic and thermoelastic problems with a rigid circular-arc inclusion is presented. The proposed analysis is based upon the complex variable theory dealing with sectionally holomorphic functions which is reduced to the solution of the Hilbert problem. It is indicated that both the stress and thermal stress fields near the inclusion tip possess a square-root singularity similar to that for the corresponding crack problem. In analogy to the stress intensity factors defined for crack problem, stress singularity coefficients are introduced in this paper to characterize the near tip fields. Complete stress fields and the corresponding stress singularity coefficients as the circular-arc inclusion are under uniform remote load, concentrated force and uniform heat flux are given. Failure initiation of an infinite plate embedded with a rigid arc inclusion under different loading conditions is also discussed.     

Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions

The adoption of biodegradable polymeric materials is increasing in food and consumer goods packaging applications, due to concerns about the disposal of petroleum‐based polymers and the increasing cost of petroleum‐based polymer resins. Currently, poly(lactide) (PLA) polymers are the biggest commercially available bio‐based polymeric packaging materials. As the main motivation for adopting biopolymers is environmental, there is a need to address the degradability and environmental performance of biodegradable packages. The aim of this study was to investigate and compare the degradation of two commercially available biodegradable packages made of PLA under real compost conditions and under ambient exposure, using visual inspection, gel permeation chromatography, differential scanning calorimetry and thermal gravimetric analysis. A novel technique to study and track the degradability of these packages under real compost conditions was used. Both packages were subjected to composting and ambient exposure conditions for 30 days, and the degradation of the physical properties was measured at 1, 2, 4, 6, 9, 15 and 30 days. PLA bottles made of 96% l ‐lactide exhibited lower degradation than PLA delicatessen (‘deli’) containers made of 94% l ‐lactide, mainly due to their highly ordered structure and, therefore, their higher crystallinity. The degradation rate changed as the initial crystallinity and the l ‐lactide content of the packages varied. Temperature, relative humidity and pH of the compost pile played an important role in the rate of degradation of the packages. First‐order degradation kinetics and linear degradation trends were observed for both packages subjected to composting conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

Aggregation of self-assembled Ni(OH)2 nanosheets under hydrothermal conditions

We investigate aggregation process of the Ni(OH)₂ under hydrothermal condition. The samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the self-assembled Ni(OH)₂ nanosheets with the hexagonal structure is about 30 nm in thickness. We investigate the effect of reaction temperature on the morphology of the product. The nanosheets can aggregate together when the temperature and reaction time are suitable. And a possible mechanism is also proposed to explain the growth and aggregation process of Ni(OH)₂ nanosheets.     

Efficient photodegradation of methylene blue (MB) under solar radiation by ZrC nanoparticles

Due to increase in water pollution, there is a need to dwindle this problem for a clean and green future. Photocatalysts like ZnO, CaO and TiO₂ have proved to be triumphant in removal of environmental contaminants. In this present work, ZrC nanopowder has been synthesized using a single-step reduction technique by heating zirconium oxide (ZrO₂) and hexane (C₆H₁₄) in metallic Mg powder and is used as a photocatalyst for the degradation of methylene blue (MB) dye under solar radiation. Optimization of synthesis parameters (temperature, holding time and carbon content) has been done to obtain single phase ZrC. Various characterization techniques like X-ray diffraction (XRD), transmission electron microscope (TEM), differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA) and X-ray photoelectron spectroscopy (XPS) were studied for various structural, thermal and surface characteristics of as-synthesized samples. The effect of synthesis parameters on crystal distortion of ZrC particles was studied with the help of Double Voigt analysis. Further, the comparative catalytic activity as photodegradation of MB dye with the help of optimized sample was studied under UV and solar radiations. As an effect of illumination source with the same concentration of catalyst and dye, 80% degradation was observed under solar radiations which is quite higher than that observed under UV in 5?h.     

Modeling of cyclic stress–strain behavior and damage mechanisms under thermomechanical fatigue conditions

A multi-component model was applied to predict the cyclic stress–strain response of different alloys under thermomechanical fatigue conditions based upon isothermal hysteresis loops. A ductile AISI 304 L-type stainless steel and two high strength alloys, the near-α titanium alloy IMI 834 and the nickel-base superalloy IN 100, were chosen as test materials. These represent alloys with rather different dislocation slip modes, stress–strain characteristics and damage mechanisms. Model predictions are compared with experiments and the differences in cyclic stress–strain response and damage mechanisms under isothermal and thermomechanical fatigue conditions, respectively, are discussed based upon microstructural observations.     

太阳电池填充因子随日照强度变化的理论分析与计算

根据太阳电池直流模型和最大功率点数学条件,推出短路电流、开路电压、最大功率点电流和电压 以及填充因子随日照强度变化的数学关系式;并选取２个电池分别计算出在不同日照强度下上述电池参数随日 照强度的变化率。验证了短路电流和最大功率点电流是近似跟日照强度成正比,开路电压和最大功率点电压是 近似跟日照强度的自然对数成正比。并提出了填充因子随日照强度的变化关系不具有简单的函数形式,而对不 同的太阳电池其变化关系也迥异。最后用Multisim的模拟结果检验了理论分析计算的正确性。     

Modeling of particle size distribution and energy consumption of wet milled maize at varying soaking period and method in the production of Ogi

Energy consumptions and particles size distribution of soaked maize grains at varying time were studied and modeled. Rosin–Rammler–Bennet (RRB) model well fitted first milling size distribution with a high coefficient of determination (R²) and low root mean square error (RSME). The milling energy of maize grains decreased significantly (p?<?0.05) with increase in soaking time. The milling energy decrease from 32 to 8.72?kWh/kg and 32.00 to 9.00?kWh/kg for maize variety E9W at 24th hour soaking conditions of 28 and 65°C, respectively. Similar observations for A4W, B2Y and C3Y at 24?h of soaking were recorded. The Work index, Kick’s and Rittinger’s constants decreased with increase in soaking time. There was significant difference (p?<?0.05) in values obtained for Bond work index, Rittinger’s and Kick’s constants; these decreased with increase in soaking time. Predicted energy consumption followed similar trend. The interaction effect between energy consumption, Moisture content, and Milling time showed a high R² (0.8767–0.99349); while the regressed model for determining energy consumption from relationship between the mass, moisture content, milling time and the ratio of the geometric diameter mean and final size of the product were also established in this work with R² ranging from 0.9355 to 0.967.     

Modeling quantum transport under AC conditions: application to intrinsic high-frequency limits for nanoscale double-gate Si MOSFETs

An approach for studying the performance of phase-coherent devices under high-frequency conditions is presented. Quantum predictions on cutoff frequencies are obtained by directly solving the time-dependent Schrodinger equation under oscillating potential profiles at frequencies comparable with the inverse of the electron transit time. As an example, the small-signal admittance parameters for a simple double-gate Si transistor are computed, showing that its intrinsic amplifying properties are degraded at terahertz frequencies. Classical results, obtained by solving the classical Boltzmann equation through the standard Monte Carlo technique, are comparable to quantum predictions. The approach opens a new path for the understanding of the electron phenomenology in phase-coherent devices under ac conditions.