植物叶片中叶绿素含量测定方法的优化

本文通过阐述研究西南某气田的大气对该气田常见绿色植物叶片叶绿素总含量（ct）的影响。通过实验研究对比发现,污染严重的是某厂区周边区域几个大气采样点,栽种的植物叶片叶绿素总含量ct较低;无污染的对照区域,其叶绿素总含量ct较高。通过数据分析,不同污染地点植物的叶绿素含量随着污染程度加剧而减少。     

Growth responses of three ornamental plants to Cd and Cd-Pb stress and their metal accumulation characteristics

Up to now, there was no document on ornamental plants that had been applied to phytoremediation, which can remedy contaminated environment and beautify it at the same time. Thus, the growth responses and possible phytoremediation ability of three ornamental plants selected from the previous preliminary experiments were further examined under single Cd or combined Cd-Pb stress. The results showed that these tested plants had higher tolerance to Cd and Pb contamination and could effectively accumulate the metals, especially for Calendula officinalis and Althaea rosea. For C. officinalis, it grew normally in soils containing 100 mg kg(-1) Cd without suffering phytotoxicity, and the Cd concentration in the roots was up to 1084 mg kg(-1) while the Cd concentration in the shoots was 284 mg kg(-1). For A. rosea, the Cd accumulation in the shoots was higher than that in the roots when the Cd concentration in soils was <100 mg kg(-1), and reached 100 mg kg(-1) as the criteria of a Cd hyperaccumulator when the Cd concentration in soils was 100 mg kg(-1). Their accumulation and tolerance to Cd and Pb were further demonstrated through the hydroponic-culture method. And A. rosea had a great potential as a possible Cd hyperaccumulator under favorable or induced conditions. Furthermore, the interactive effects of Cd and Pb in the three ornamentals were complicated, not only additive, antagonistic or synergistic, but also related to many factors including concentration combinations of heavy metals, plant species and various parts of plants. Thus, it can be forecasted that this work will provide a new way for phytoremediation of contaminated soils.     

Experimental study of creep of hardened Portland cement paste at variable water content

Tests of creep under axial load and torque have been made using tubular specimens of extremely small wall thickness (0.7 mm) in order to achieve sufficiently rapid moisture exchange with the environment. The changes of relative humidity and temperature in a program-controlled environmental chamber have been gradual, so as to minimize the differences in pore humidity throughout the specimen wall and the accompanying residual stresses and microcracking. A number of different humidity and temperature histories, including the drying before and during the creep test, and the humidity changes during the creep test and during the recovery, have been tested. The measurements have revealed a decline of the slope of creep curve in log-time after a sufficiently long drying period; acceleration of creep as well as recovery by both drying and wetting; a smaller and more delayed acceleration at lower humidities; a delay of this acceleration with respect to the weight loss; a similarity of these effects in axial and torsional creep; a higher recovery as well as creep at higher humidities when moisture equilibrium has been approached before loading; a higher creep acceleration by temperature increases or decreases when the humidity is below saturation, but a smaller acceleration at nearly dry state; and other effects.     

Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (C_SC) region (C_SC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower C_SC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at C_SC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at C_SC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at C_SC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at C_SC = 85 wt.% in rheological measurements.     

Hardening behavior of three metallic alloys under combined stresses at elevated temperature

Summary. Initial and subsequent yield loci for type 316 stainless steel, Haynes 188, and Inconel 718 are determined experimentally in the axial-shear stress plane at 650 C. Each of these materials has a face centered cubic (fcc) crystal structure, but entirely different chemical compositions and strengthening mechanisms. Material hardening behavior is described along three cyclic strain paths having a maximum equivalent strain of 0.015 m/m: fully reversed axial (Path I), fully reversed shear (Path II), and a nonproportional hourglass shaped path (Path III). Yielding is defined by a Mises-type equivalent offset strain definition having a target value of 30 m/m. These types of yield surface determination tests are difficult, but fairly common in lower temperature ranges where precision strain gages can be used. Due to the high temperature in this study, axial and shear strains were measured by an extensometer. These results, which describe material hardening by the evolution of size, shape, and position of the current yield surface can be used in support of constitutive models for high temperature metallic materials. Hardening behavior of all three alloys is well described by a mixed hardening rule comprised of isotropic, kinematic, and distortional components. Relative to published work at lower temperatures, the isotropic hardening component is larger and the distortional hardening component is smaller than anticipated.     

Analysis of spectroscopic measurements of leaf water content at terahertz frequencies using linear transforms

We provide a unified framework for a range of linear transforms that can be used for the analysis of terahertz spectroscopic data, with particular emphasis on their application to the measurement of leaf water content. The use of linear transforms for filtering, regression, and classification is discussed. For illustration, a classification problem involving leaves at three stages of drought and a prediction problem involving simulated spectra are presented. Issues resulting from scaling the data set are discussed. Using Lagrange multipliers, we arrive at the transform that yields the maximum separation between the spectra and show that this optimal transform is equivalent to computing the Euclidean distance between the samples. The optimal linear transform is compared with the average for all the spectra as well as with the Karhunen-Loève transform to discriminate a wet leaf from a dry leaf. We show that taking several principal components into account is equivalent to defining new axes in which data are to be analyzed. The procedure shows that the coefficients of the Karhunen-Loève transform are well suited to the process of classification of spectra. This is in line with expectations, as these coefficients are built from the statistical properties of the data set analyzed.     

Some comparisons in the behaviour of materials at elevated temperatures under uniaxial and under multiaxial stress

Most data on the mechanical behaviour of materials at elevated temperature concerns the influence of a uniaxial stress. For many purposes such information may suffice but there is increasing awareness of its inadequacy when used in the design or service life estimation of engineering components operating under more complex stress systems. Such stress systems do not only arise from the external stresses that are applied but may also result from thermal effects, particularly at interfaces and joints, or from the special geometrical features of a component. Some experimental techniques to provide information on creep behaviour under multiaxial stresses are described together with a discussion and evaluation of the results obtained. It is noted that data from uniaxial stress tests can be used to predict such behaviour when the material is isotropic and is not subject to volume changes, microstructural instability or creep damage. Frequently, materials do not fulfill these conditions and information is presented on the influence of some of these complicating features both on creep rate and on fracture.     

Fracture behaviour of plain and fiber-reinforced concrete with different water content under mixed mode loading

In the present paper, plain concrete and fiber-reinforced concrete are considered from the point of view of the mechanical characteristics, with particular emphasis on the fracture resistance, for different values of the water/cement ratio and different amount and type (metallic or polymeric) of reinforcing fibers. The main mechanical characteristics (such as compressive strength and tensile strength) of the examined materials have experimentally been determined, and several pre-cracked specimens have been tested under three-point bending up to the final failure in order to study the fracture behaviour by also evaluating the fracture energy. Furthermore, the crack paths for static tests under displacement control have been obtained, and the load–displacement deflection curves have been determined for different crack configurations. Assuming the fracture surface characterised by a fractal dimension, some quantitative evaluations of the fracture energy are carried out. Then, the fracture behaviour and the post-peak behaviour of plain and fiber-reinforced specimens are discussed, and the effects of reinforcing fibers are quantified. Some conclusions are finally drawn.