Characterization of lead and lead leaching properties of lead glazed ceramics from the Solis Valley, Mexico, using inductively coupled plasma-mass spectrometry (ICP-MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT)

Ingestion of relatively small amounts of lead is now recognized to cause significant neurological and cognitive effects in humans. Large quantities may be fatal, yet lead poisoning, especially of children, is still a major public health concern in many parts of the world. In rural Mexican communities lead oxide (PbO) is added to ceramic glaze as a fluxing agent, lowering starting firing temperatures to 500 °C. The purpose of this study is to characterize the lead chemical forms in ceramic glazes from the Solis Valley, Mexico, to investigate lead leaching properties of these ceramics, and to demonstrate the applicability of lead isotope signatures as a means of tracing lead source origins. Ceramics were collected from the rural village of Santa Maria de Canchesda, State of Mexico, Mexico. Dried liquid glazes, post-fired glaze material, and pure PbO were analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Results from DRIFT analysis indicate that PbO (1429 cm⁻¹ band) is the active form of lead found in liquid glazes and ceramics. Some shifting of 1429 cm⁻¹ PbO peak to lower wavenumbers occurs in post-fired ceramics, and this may be due to the formation of lead bisilicate during firing. Ceramics samples were leached in 0.02 M citric acid solution for 1 min, and leached lead concentrations were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Lead concentrations in these leachates varied from 0.4-80.4 μg ml⁻¹, while the control pottery from the US leached only 0.1 μg ml⁻¹ lead. Elemental distributions on glaze surfaces were identified by laser ablation (LA)-ICP-MS. Nitric acid extracts of soils, teeth, and ceramic glazes were analyzed for lead isotope ratios (²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb) using ICP-MS. Similarities of tooth and ceramic lead isotope ratios indicate that ceramics may be a substantial source of body lead burden in the Solis Valley. This study demonstrates the applicability of lead isotope ratios for lead source identification, and it identifies potential health risks from ceramic use induced lead toxicity within the Solis Valley.     

Measurements of diffuse backscattering Mueller matrices of turbid media

We report on the development of a method that records spatially dependent intensity patterns of polarized light that arise from illuminating a turbid media with a polarized laser beam and being diffusely backscattered. Our technique employs polarized light from a He-Ne laser () which is focused onto the surface of the scattering medium. A surface area of approximately 2×2 cm centered on the light input point is imaged through polarization analysis optics onto a CCD camera. The Mueller matrix is reconstructed by 49 intensity measurements with various orientations of polarizer and analyzer. The measured Mueller matrix of polystyrene spheres was compared with the theory result of incoherent scattering of light by spheres. The experimental and theory results are in excellent agreement. It appears that the azimuthal patterns of the Mueller matrix are determined by the symmetry of the turbid media.     

轴对称件超塑约束胀形中的摩擦效应

尽管超塑胀形作为一种金属成形方法正日渐受到世界各国的普遍关注，但对超塑约束胀形理论的研究报道却还很少，尤其对胀形过程的有限元模拟研究就更为罕见。针对这种情况，采用大变形刚粘塑性有限元法模拟了轴对称零件向圆筒形凹模内超塑约束胀形的变形过程，着重研究了工具工件之界面摩擦对胀形件厚度分布不均匀性和胀形板料向凹模角部充填性的影响．结果表明，随着摩擦的降低，胀形件的侧向较厚部分能有所减薄，可以改善整个胀形件的厚度均匀性，但当摩擦因子Ａｍ≤０．２（相当于摩擦系数μ≤０．１２）时，胀形件极顶部分的减薄过大；摩擦较小时，胀形板料向凹模角部的充填性较好；在考虑到极点附近厚度适度减薄和胀形板料对凹模角部充填性好的前提下，工艺上应当适当减小摩擦，其最佳状态是μ值约为０．３．为了检验所用刚粘塑性有限元法模拟的可靠性，将计算结果与试验结果作了对比，发现两者相当吻合。     

Tuning the properties of a black TiO2-Ag visible light photocatalyst produced by a rapid one-pot chemical reduction

A highly efficient black TiO₂-Ag photocatalytic nanocomposite, active under both UV and visible light illumination, was synthesized by decorating the surface of 25 nm TiO₂ particles with Ag nanoparticles. The material was obtained via a rapid, one-pot, simple (surfactant and complexing agent free) chemical reduction method using silver nitrate and formaldehyde as a metal salt and reducing agent, respectively. The nanocomposite shows an increase of over 800% in the rate of photocatalytic methylene blue dye degradation, compared to commercial unmodified TiO_2, under UV-VIS illumination. Unlike pure TiO₂, the nanocomposite exhibits visible light activation, with a corresponding drop in optical reflectance from 100% to less than 10%. The photocatalytic properties were shown to be strongly enhanced by post-reduction annealing heat treatments in air, which were observed to decrease, rather than coarsen, silver particle size, and increase particle distribution. This, accompanied by a variation in the silver surface oxidation states, appear to dramatically affect the photocatalytic efficiency under both UV and visible light. This highly active photocatalyst could have wide ranging applications in water and air pollution remediation and solar fuel production.     

Axisymmetric bifurcation analysis in soils by the tangential-subloading surface model

This article discusses localized bifurcation modes corresponding to shear band formation and diffuse bifurcation modes corresponding to bulge formation for cylindrical soil specimen subjected to an axisymmetric load under undrained conditions. We employ the tangential-subloading surface model, which exhibits the characteristic regimes of the governing equations: elliptic, hyperbolic and parabolic. Also, conditions for shear band formation, shear band inclination, diffuse bulging formation, and the long and short wavelength limits of diffuse bulging modes are discussed in relation to material properties and their state of stress, i.e. the stress ratio and the normal-yield ratio. Tangential-plastic strain rate term is required for the analyses of shear band and diffuse bulging. The shear band and the diffuse bulging are generated in not only normal-yield but also subyield states and they are severely affected by the normal-yield ratio describing the degree of approach to the normal-yield state.     

Diffuse mode bifurcation of soil causing convection-like shear investigated by group-theoretic image analysis

Diffuse mode bifurcation of soil under plane-strain compression test is shown, by means of an image analysis based on group-theoretic bifurcation theory, to trigger convection-like shear and to precede shear band formation. First digital photos of Toyoura sand specimens are processed by PIV (particle image velocimetry) to gather digitized images of deformation. Next bifurcation from a uniform state is detected by expanding these images into the double Fourier series and finding a predominant harmonic diffuse bifurcation mode based on that theory. This harmonic bifurcation mode, which is the mixture of a few harmonic functions, expresses complex convection-like shear. Last bifurcation from a non-uniform state is detected by decomposing each image into a few images with different symmetries to extract non-harmonic diffuse bifurcation modes. Diffuse modes of bifurcation, which hitherto were hidden behind predominant uniform compressive deformation, have thus been made transparent by virtue of the group-theoretic image analysis proposed. A possible course of deformation suggested herein is the evolution of diffuse mode bifurcation with a convection-like bifurcation mode breaking uniformity and symmetry, followed by the formation of shear bands through localization.     

多位置可见/近红外光谱检测与种鸡蛋受精信息的关系研究

种鸡蛋孵化过程耗时、耗能,但种蛋由于未受精导致胚胎发育率不足100%,种鸡蛋孵化早期快速判别,可有效提高种蛋孵化效率和降低经济损失。近红外光谱分析技术可实现快速、无损检测,用于判别研究孵化早期种鸡蛋受精信息,但现有光谱检测方法未能满足孵化早期受精判别位置要求,亟需构建采集数据时的检测位置与内部信息之间的关系。该研究利用可见/近红外光谱检测系统采集种蛋壳漫反射光谱强度,试验选用壳色相近、表面无裂纹的181个新鲜种鸡蛋,从中随机选择61个样本完成交叉验证。为消除暗电流的影响,进行光谱校正,得出种蛋壳漫反射率,发现受精蛋与未受精蛋的光谱曲线趋势相同,受精蛋和无精蛋赤道处的光谱曲线均高于两端。剔除光谱曲线两端噪声大、信噪比低的波段,选择440.27～874.6 nm作为有效光谱波段,并采用Savitzkg-Golay（S-G）平滑法、二阶导数法Second Derivative、标准正态变量校正SNV、变量标准化Normalization和多元散射校正MSC预处理法分别构建PCA-SVM判别模型。通过对入孵后24,48,72,96和120 h不同位置所采光谱数据,与受精信息综合分析,结果发现二阶导数法Second Derivative和多元散射校正MSC两种预处理方式在同一时间、不同位置的训练集和验证集的判别准确率均相同,说明这两种预处理方法对数据来源位置不敏感;变量标准化Normalization预处理和S-G平滑法预处理验证集的判别准确率则随着时间的推移在一定范围内波动,在种鸡蛋胚胎发育120h时的判别准确率可达91.71%;SNV预处理赤道处验证集判别准确率随着时间的推移呈现上升趋势,对数据来源时间及位置敏感,种鸡蛋胚胎发育越长判别效果越佳,120 h赤道侧的判别准确率为91.16%。且平滑处理、标准正态变量校正和变量标准化三种预处理方式均存在赤道侧判别准确率高于种蛋端部的现象,这主要是由于赤道侧较种鸡蛋两端表面平缓,采集到的信息更多,该研究为早期判别受精蛋与无精蛋的数据采集位置提供新思路和新方法。     

Fiber Optic Spectrophotometer for Noninvasive Transmission and Diffuse Reflection Studies

We describe the construction of a simple but versatile single-beam spectrophotometer that uses no sample holder at all; one arm of a bifurcated fiber optic bundle illuminates the specimen, while the other receives the remitted light. Though designed with an eye to recording the diffuse reflection spectra of scattering-and-absorbing substances, it can also be used for conventional studies (ie transmission spectroscopy) by merely placing a plane mirror behind the cuvette. The performance of the instrument is evaluated and representative spectra of several powders, solutions, and biomaterials are presented.     

An improved broad-spectrum room acoustics model including diffuse reflections

More and more literature has paid attention to the diffuse reflections in enclosed space during the past few years. In this paper, the current computer models including diffuse reflections have been reviewed briefly at first. Then, to realize the broad-spectrum simulation for enclosed sound fields including diffuse reflections, an improved ray-tracing algorithm, which combines the splitting coefficient diffusion model and a dynamic sound ray receiving method, has been given. The algorithm can deal with broad frequency bands simultaneously by using the frequency independent splitting coefficient. To test the algorithm and also to investigate the significance of the diffuse reflections in enclosed sound fields, experiments have been made in three spaces including a virtual room and two real rooms. The results and discussions have validated the applicability of the improved algorithm and they have also shown that diffuse reflections can improve room acoustic prediction, although it not always promote a sound field to be more diffused.