Microstructure and damage evolution of SiCf/PyC/SiC and SiCf/BN/SiC mini-composites: A synchrotron X-ray computed microtomography study

SiC_f/PyC/SiC and SiC_f/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiC_f/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiC_f/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiC_f/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B₂O₃ molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B₂O₃, the SiC_f/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO₂ grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiC_f/PyC/SiC and SiC_f/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale.     

Metabolism and biochemical effects of 3,3',4,4'-tetrachlorobiphenyl in pregnant and fetal rats

The metabolism and distribution of a single oral dose of 25 mumol 14C-labelled 3,3',4,4'-tetrachlorobiphenyl (14C-TCB) were investigated in pregnant female Wistar rats and their fetuses. TCB was administered on day 13 of gestation and the elimination was followed for 7 days. Non-pregnant rats were treated similarly for comparison. Fecal elimination of 14C-TCB derived radioactivity was significantly lower in pregnant rats than in non-pregnant rats. The major metabolite found in adult liver and plasma, placental tissue, whole fetuses and fetal plasma was 3,3',4',5-tetrachloro-4-biphenylol (4-OH-TCB). Tissue levels (liver, abdominal fat, skin, skeletal muscle, kidney and plasma) of 14C-TCB-derived radioactivity declined by 65-85% over a 7-day period following administration in the adult animals. However, 14C-TCB-derived radioactivity accumulated more than 100-fold in the fetuses over the same time period, and GC/MS analysis revealed that the fetal accumulation in radioactivity was due primarily to 4-OH-TCB, and not the parent compound. On day 20 of gestation, concentrations of 4-OH-TCB were 14 times greater in fetal plasma than maternal plasma. Treatment with 14C-TCB significantly reduced plasma thyroxine levels by at least 28% up to 7 days after administration in non-pregnant animals and up to 4 days after administration in pregnant rats (31% decrease). By 7 days after administration plasma thyroxine levels had returned to control levels in the TCB-treated pregnant rats. However, fetal plasma thyroxine levels were significantly decreased by 35% in fetuses from 14C-TCB-treated dams 7 days after TCB administration. Hepatic microsomal ethoxyresorufin-O-deethylase (EROD) activity was significantly induced in TCB-treated dams relative to controls at 4 and 7 days after administration, while no EROD activity was detected in hepatic microsomes from control or TCB treated fetal rats at day 20 of gestation. These data suggest that hydroxylated metabolites of polychlorinated biphenyls may play a role in the development toxicity of these compounds.     

SURF1, encoding a factor involved in the biogenesis of cytochrome c oxidase, is mutated in Leigh syndrome

A drug with cationic characteristics such as procaine can be conveyed in a Carbomer hydrogel in two different ways: (i) in the form of salt in solution in the aqueous phase, and (ii) in the base form salified with the same polymer. Introduction of the drug into the hydrogel with different concentrations of polymer produced, in both cases, a reduction in viscosity in relation to drug concentration. The gels with procaine salified with the polymer showed greater viscosity. The drug release rate, in general, diminished with the increase in polymer concentration. Nevertheless, when this concentration was maintained, there was no variation in release rate when the viscosity produced as a consequence of drug concentration was changed. Gels with procaine salified with the carboxyvinylic polymer had a faster release rate than those with procaine in the hydrochloride form dissolved in the aqueous phase. These results have also been confirmed by a simulated absorption test.     

Effects of Silicon on Growth,Yield and Fruit Quality of Cantaloupe under Drought Stress

Silicon - Silicon (Si) plays an important role in mitigating adverse effects of various biotic and abiotic stresses including drought. Polyhouse experiment was conducted to evaluate the effects of...     

Location-Dependent Lane-Changing Behavior for Arterial Road Traffic

Lane-changing behavior plays an important role in characterizing urban arterial road traffic dynamics. This paper investigates efficiency-driven and objective-driven motives for drivers to change lanes on arterial roads. The former motive is determined by the circumstances of the surrounding traffic flow, whereas the latter depends on position. A location-dependent lane changing model is then established by weighing the two motives for lane changing. Both continuous and discrete versions of the arterial traffic model are obtained using the LWR (Lighthill–Whitham–Richards) model with the two types of lane changing. Simulations show that the proposed model can reproduce macroscopic traffic phenomena such as spillover and a decrease in the concomitant departure flow, which is the reason for capacity loss. It is concluded that 1) there exists a critical condition under which there is no capacity loss and that 2) a different flow composition could result in a different capacity loss, which varies according to the flow direction. Hence, traffic management and control should take this loss into account.     

Square-root unscented Kalman filtering-based localization and tracking in the Internet of Things

The Internet of Things (IoT), which is usually established over architectures of wireless sensor networks, provides an actual platform for various applications of personal and ubiquitous computing. Recently, moving target localization and tracking in an IoT environment have been paid more and more attention. This paper proposes a square-root unscented Kalman filtering (SR-UKF)-based algorithm to discover real-time location of a moving target in an IoT environment where there exist quantities of sensors. The data generated from wireless sensor nodes of the IoT make contributions to localization and tracking of the moving target. First, a least-square (LS) criterion-based mathematical model is proposed for localization initialization in an IoT scenario. Next, we employ an SR-UKF idea for the further localization and tracking. By using the data coming from sensor nodes near the target, real-time location of the moving target can be estimated by implementation of SR-UKF in an iterative fashion so as to achieve target status tracking. Simulation results show that the proposed algorithm achieves good performance in estimation of both position and velocity of the target with either uniform linear motion or variable-speed curve motion. Compared with some existing conventional extended Kalman filtering (EKF) or UKF-based methods, the proposed algorithm shows lower location/velocity estimation error under the same computational complexity, which demonstrates its potential significance in ubiquitous computing applications for an IoT environment.     

细粒石墨材料的热压制备

以细粒石墨粉为原料、改质和高温煤沥青为黏结剂,采用热压成型工艺制备炭块,并对其进行炭化和石墨化处理后得到石墨块体。结果表明,随着热处理温度的上升,热压制备炭块的体积密度和电阻率发生了明显的变化,与改质沥青相比,以高残炭率沥青为黏结剂所制细粒石墨材料具有较高的体积密度和较低的电阻率;X射线衍射XRD和扫描电镜SEM分析表明,细粒石墨在块体材料中具有明显的取向性。     

论高等教育大众化与农村人口转移

促进我国农村人口转移是当前解决“三农”问题、促进经济腾飞和社会进步的重大的战略之一。然而，农村人口素质低是制约着转移的“瓶颈”。高等教育要充分发挥提高农村人口素质，促进农村人口转移的积极作用，应逐渐完善大众化高等教育体系。具体而言，可采取以下改革举措：高等教育资源向农村地区倾斜；大力发展高等职业教育；调整、优化学科结构；发展农村高等教育等。