连铸板坯中心线偏析的预测

从生产经验和文献可知,结晶过程中产生的凝固收缩会导致中心线偏析,很多情况下,在热轧产品的中心也会发现结晶过程中产生的微细缩孔。从这方面讲,板坯凝固过程中形成缩孔簇的尺寸大小,以及形成这种缩孔的条件是首要的,在全面分析统计数据的基础上,对此进行了讨论,得出一个重要结论:当固液比率达到一定的值后,在此部位的铸坯中心只有糊状物,实际上没有更多的液体可以补充。建立了数学模型,用于计算板坯中心部位的流动速度和方向以及预测的疏松。计算表明,在给定的成分和冷却条件下,中心线偏析主要受支承辊的设置、形变和偏心度的影响,同时支承辊之间铸坯的鼓肚也是重要影响因素之一。     

The effect of graphene nanoplatelet thickness on the fracture toughness of Si3N4 composites

Si₃N₄ composites with 3 and 5?wt% of graphene nanoplatelet (GNP) additions were prepared by spark plasma sintering. We used both commercially available GNPs and thinner few-layer graphene nanoplatelets (FL-GNPs) prepared by further exfoliation through ball milling with melamine addition. We found that by employing thinner FL-GNPs as filler material a 100% increase in the fracture toughness of Si₃N₄/3?wt% FL-GNP composites (10.5?±?0.2?MPa?m^1/2) can be achieved as compared to the monolithic Si₃N₄ samples (5.1?±?0.3?MPa?m^1/2), and 60% increase compared to conventional Si₃N₄/3?wt% GNP composites (6.6?±?0.4?MPa?m^1/2). For 5?wt% filler content the increase of the fracture toughness was near 50% for both GNP and FL-GNP fillers. The hardness of the composites decreased with increasing GNP content. However, composites reinforced with 5?wt% of FL-GNPs displayed 30% higher Vickers hardness (12.8?±?0.2?GPa) than their counterparts comprising conventional GNP fillers (9.8?±?0.2?GPa). We attribute the enhanced mechanical properties obtained with thinner FL-GNPs to their higher aspect ratio leading to a more homogeneous dispersion, higher interface area, as well as smaller pores in the ceramic matrix.     

Laser surface modification of metallic biomaterials

Load-bearing metal implants often fail prematurely due to inadequate biocompatibility, mechanical/tribological properties, and poor osseointegration. It is well known that biomaterials’ surface plays a vital role in the response to these metal implants in the biological environment. The biological effectiveness of artificial implants is determined mainly by their surface characteristics such as surface morphology, microstructure, composition, mechanical properties, wettabilility, and surface free energy. Hence, there is significant interest toward surface modification and effective design of load-bearing metal implants so as to improve their surface properties and thereby elicit a specific, desired, and timely response from the surrounding cells and tissues. In this article, we provide an insight into laser surface modification of Ti/Ti6Al4V alloy with or without functional gradation in composition and their microstructural, in vitro wear and biological properties for various loadbearing orthopedic applications.     

Ellipsometric study of SixC films: Analysis of Tauc-Lorentz and Gaussian oscillator models

In this study, the suitability of Tauc-Lorentz and Gaussian oscillator models to describe amorphous silicon-carbon alloys of various compositions was tested. The dependence of the model parameters on the composition showed that the amplitude and broadening of both oscillators behave similarly and significant differences can only be observed in the oscillators’ position in case of high broadening parameter values. It was shown that this difference originates from the different mathematical forms of the oscillators and from the high broadening values. Sensitivity analysis of the parameters showed that the models became less sensitive to their parameters with large broadening values. Furthermore the model parameters were correlated to the various types of chemical bonding present within the samples.     

Characterization of pulsed laser deposited hydrogenated amorphous silicon films by spectroscopic ellipsometry

The wide absorption band of hydrogenated amorphous silicon (a-Si:H) is being realized as a key component of solar cells on glass. In this study, a-Si:H films were prepared by reactive pulsed laser deposition onto silicon and glass substrates. Ellipsometry showed that the optical properties of the films are effectively independent on the choice of substrate. According to the optical properties, the character of the films changes from amorphous silicon to dielectric as the hydrogen background pressure increases from 0 to 25 Pa. This observation was attributed to oxygen incorporation indicated by Rutherford Backscattering Spectrometry. Furthermore, a refractive index gradient in depth was revealed, which was attributed to the oxygen concentration gradient.     

Module-Based Reinforcement Learning: Experiments with a Real Robot

The behavior of reinforcement learning (RL) algorithms is best understood in completely observable, discrete-time controlled Markov chains with finite state and action spaces. In contrast, robot-learning domains are inherently continuous both in time and space, and moreover are partially observable. Here we suggest a systematic approach to solve such problems in which the available qualitative and quantitative knowledge is used to reduce the complexity of learning task. The steps of the design process are to:i) decompose the task into subtasks using the qualitative knowledge at hand; ii) design local controllers to solve the subtasks using the available quantitative knowledge and iii) learn a coordination of these controllers by means of reinforcement learning. It is argued that the approach enables fast, semi-automatic, but still high quality robot-control as no fine-tuning of the local controllers is needed. The approach was verified on a non-trivial real-life robot task. Several RL algorithms were compared by ANOVA and it was found that the model-based approach worked significantly better than the model-free approach. The learnt switching strategy performed comparably to a handcrafted version. Moreover, the learnt strategy seemed to exploit certain properties of the environment which were not foreseen in advance, thus supporting the view that adaptive algorithms are advantageous to non-adaptive ones in complex environments.     

Magnetic field sensitive functional elastomers with tuneable elastic modulus

The main purpose of the present work was to establish the effect of external magnetic field on the elastic modulus. We have prepared poly(dimethyl siloxane) networks loaded with randomly distributed carbonyl iron particles. It was found, that the elastic modulus of magnetoelasts could be increased by uniform magnetic field. In order to enhance the magnetic reinforcement effect, we have prepared anisotropic samples under uniform magnetic field. This procedure results in formation of chain-like structures from the carbonyl iron particles aligned parallel to the field direction. The effect of particle concentration, the intensity of uniform magnetic field as well as the spatial distribution of particles on the magnetic field induced excess modulus were studied. It was established that the uniaxial field structured composites exhibit larger excess modulus compared to the random particle dispersions. The most significant effect was found if the applied field is parallel to the particle alignment and to the mechanical stress. A phenomenological approach was proposed to describe the dependence of elastic modulus on the magnetic induction. The magnetic field sensitive soft materials with tuneable elastic properties may find usage in elastomer bearings and vibration absorber.     

Development of an innovative immunoassay for CP4EPSPS and Cry1AB genetically modified protein detection and quantification

An innovative immunoassay, called enzyme-linked immunoabsorbant assay (ELISA) Reverse, based on a new conformation of the solid phase, was developed. The solid support was expressly designed to be immersed directly in liquid samples to detect the presence of protein targets. Its application is proposed in those cases where a large number of samples have to be screened simultaneously or when the simultaneous detection of different proteins is required. As a first application, a quantitative immunoassay for Cry1AB protein in genetically modified maize was optimized. The method was tested using genetically modified organism concentrations from 0.1 to 2.0%. The limit of detection and limit of quantitation of the method were determined as 0.0056 and 0.0168 (expressed as the percentage of genetically modified organisms content), respectively. A qualitative multiplex assay to assess the presence of two genetically modified proteins simultaneously was also established for the case of the Cry1AB and the CP4EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) present in genetically modified maize and soy, respectively.     

Presence of cancerostatic platinum compounds in hospital wastewater and possible elimination by adsorption to activated sludge

Platinum originating from the excreted cancerostatic platinum compounds (CPC) cisplatin, carboplatin and oxaliplatin was monitored over a period of 28 days in the wastewater of the oncologic ward of the Vienna University Hospital. Concentration levels ranging from 4.7 to 145 microg L(-1) were measured by inductively coupled plasma mass spectrometry (ICP-MS). An average ratio of weekly drug emission/drug consumption of 0.27+/-0.12 was assessed. Model studies were carried out for fundamental understanding of CPC interaction with the solid phases present at different stages of the water cycle. Wastewater and activated sludge were spiked with CPC at concentration levels as found in the sewer of the oncologic ward. The platinum concentration remaining in the tested solution was measured after 24 h of incubation. Depending on pH, the three substances exhibited considerably different adsorption rates in wastewater. At pH 7, cisplatin was adsorbed by 88%, whereas only 26% of carboplatin and 54% of oxaliplatin were removed from the aqueous phase. Adsorption by activated sludge was higher, less affected by pH variation and comparable for all investigated CPC (96% for cisplatin, 70% for carboplatin and 74% for oxaliplatin at pH 6.8). In a next step, the dependence of CPC adsorption was tested for wastewater and activated sludge of different sampling sites. Strong variations were found only for wastewater, whereas activated sludge showed more consistent elimination rates (average values: cisplatin 92%, carboplatin 72%, and oxaliplatin 78%). These findings indicate that the major part of the excreted CPC is adsorbed by the solid phase in the water cycle and is thus expected to be removed from the wastewater by sewage treatment plants.