Coupled heat and fluid flow model and experimental verification of aluminium plate die casting

Abstract

The present work aims to forecast mould filling, void shape, location and size as well as columnar to equiaxed transition (CET) in commercial pure aluminium casting. A model coupling the momentum equations of the fluid flow and heat transfer equations is presented, in which metallostatic pressure, air gap and oxide layer are considered. Different casting parameters were investigated such as casting configuration by varying the plate thickness from 5 to 20 mm, melt superheat from 40 to 120°C, mould preheat up to 200°C and different pouring heads ranging from 0·3 to 0·6 m. Regarding the microstructure and void formation, the approach based on the Niyama criterion, was considered. The experimental verification of the model was achieved by gravity die casting in the form of a rectangular cavity. Voids inside aluminium plate were investigated by X-ray imaging. Microstructure and CET was investigated microscopically. The supposed model proves its validity for mould filling and in detecting the void features and CET.     

Mild alkaline pre-treatments loosen fibre structure enhancing methane production from biomass crops and residues

Three ligno-cellulosic substrates representing varying levels of biodegradability (giant reed, GR; fibre sorghum, FS; barley straw, BS) were combined with mild alkaline pre-treatments (NaOH 0.05, 0.10 and 0.15 N at 25 °C for 24 h) plus untreated controls, to study pre-treatment effects on physical-chemical structure, anaerobic digestibility and methane output of the three substrates. In a batch anaerobic digestion (AD) assay (58 days; 35 °C; 4 g VS l⁻¹), the most recalcitrant substrate (GR) staged the highest increase in cumulative methane yield: +30% with NaOH 0.15 N over 190 ml CH₄ g⁻¹ VS in untreated GR. Conversely, the least recalcitrant substrate (FS) exhibited the lowest gain (+10% over 248 ml CH₄ g⁻¹ VS), while an intermediate behaviour was shown by BS (+15% over 232 ml CH₄ g⁻¹ VS). Pre-treatments speeded AD kinetics and reduced technical digestion time (i.e., the time needed to achieve 80% methane potential), which are the premises for increased production capacity of full scale AD plants. Fibre components (cellulose, hemicellulose and acid insoluble lignin determined after acid hydrolysis) and substrate structure (Fourier transform infra-red spectroscopy and scanning electron microscopy) outlined reductions of the three fibre components after pre-treatments, supporting claims of loosened binding of lignin with cellulose and hemicellulose. Hence, mild alkaline pre-treatments were shown to improve the biodegradability of ligno-cellulosic substrates to an extent proportional to their recalcitrance. In turn, this contributes to mitigate the food vs. fuel controversy raised by the use of whole plant cereals (namely, maize) as feedstocks for biogas production.     

A Comparison of the High-Temperature Oxidation of 17Cr-2Ni and 18Cr-8Ni Austenitic Stainless Steels at 973 K

The oxidation behavior in air at 973 K of theaustenitic stainless steels 18Cr8Ni and17Cr-2.5Ni-10.5Mn-2Cu-0.17N (low-nickel content), wasstudied in a thermobalance. The steels were heated fromroom temperature up to 973K at 10 K min^-1, oxidizedfor 80 hr and then cooled to room temperature at 80 Kmin^-1. The two steels had the same weightgains, 0.18 mg cm^-2, which is equivalent tooxidation layers about 1.15 m theoretical thickness. In both cases, thegeneral shapes of the WS^-1 (mgcm^-2) curves vs. t (hours) were parabolic,but X-ray diffraction of the oxidized surfaces, surfaceand crosssection optical microscopy and SEM observations and EDSmicroanalysis show important differences betweenthem.     

浅谈AIR技术

今年二月份Adobe公司推出了AIR1.0版本,AIR对大多数人来说,都非常的陌生。该文简要的概述了什么是AIR,AIR的优点,如何来构建AIR程序等问题。     

Towards a better understanding of the pectin structure-function relationship in broccoli during processing: Part I—macroscopic and molecular analyses

To investigate the structure-function relationship of pectin during (pre)processing, broccoli samples (Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca²⁺ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca²⁺ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. The macroscopic attributes of broccoli were linked to the chemical structure of broccoli pectin. By enhancing the cross-linking of pectic polymers, both LTB and HP reduced the texture loss that occurred during thermal processing of broccoli. During these pretreatments, homogalacturonan was de-esterified by pectin methylesterase, which led to changes in pectin solubility. When LTB or HP was combined with Ca²⁺ infusion, changes in the structure of pectin occurred, however not always reflected at the macroscopic level. The degree of esterification of pectin in Ca²⁺-soaked broccoli samples was lower compared to non-Ca²⁺-soaked samples and, in addition, a higher amount of ionically cross-linked pectin was retrieved.     

Air-Flow-Based Single-Cell Dispensing System

We discuss a design and fabrication approach to increase the success rate of single-cell dispensing. Two pairs of capacitance sensors are placed in a biochip to detect the flow velocity of cells and air pressure is applied to eject cells by synchronizing the timing. A comprehensive design theory, which takes into account the back-pressure caused by the air pressure, the response time of the system, the sensor properties and the delay of the dispensing from the air pressure, is developed in order to minimize the disturbance of the system and maximize the throughput of the ejection system. Then, the system theoretically has a capability to eject 3 cells/s and the maximum flow velocity is 10 mm/s. The novelty of the system is that the biochip is disposable, which is unlike the conventional mechanical inkjet system; because the biochip is low cost and disposable this prevents contamination and means the drive system is reusable. Finally, we succeeded in automatic dispensing of a single polystyrene bead (100 μm) from a biochip to a culture well atmosphere using the developed cell ejection system with a success rate of 50%. Furthermore, we also succeeded in single swine oocyte dispensing by using the developed system.     

三鸣"爱儿多"儿童多不饱和脂肪酸AD滴剂的保健功能研究

三鸣“爱儿多”滴剂富含儿童成长所必需的VA 、VD ,以及二十二碳六烯酸、γ -亚麻酸、亚油酸等必需多不饱和脂肪酸。经保健食品功能评价实验证明具有促进生长发育、增强免疫、改善学习记忆能力的功效 ,已被卫生部批准为儿童专用保健品。文中介绍该产品保健功能评价实验的结果。     

A human-machine interface evaluation method: A difficulty evaluation method in information searching (DEMIS)

A human-machine interface (HMI) evaluation method, which is named “difficulty evaluation method in information searching (DEMIS)”, is proposed and demonstrated with an experimental study. The DEMIS is based on a human performance model and two measures of attentional-resource effectiveness in monitoring and detection tasks in nuclear power plants (NPPs). Operator competence and HMI design are modeled to be most significant factors to human performance. One of the two effectiveness measures is fixation-to-importance ratio (FIR) which represents attentional resource (eye fixations) spent on an information source compared to importance of the information source. The other measure is selective attention effectiveness (SAE) which incorporates FIRs for all information sources. The underlying principle of the measures is that the information source should be selectively attended to according to its informational importance. In this study, poor performance in information searching tasks is modeled to be coupled with difficulties caused by poor mental models of operators or/and poor HMI design. Human performance in information searching tasks is evaluated by analyzing the FIR and the SAE. Operator mental models are evaluated by a questionnaire-based method. Then difficulties caused by a poor HMI design are evaluated by a focused interview based on the FIR evaluation and then root causes leading to poor performance are identified in a systematic way.     

基于声学脉冲响应的室内建图算法研究

由于室内环境下噪声及混响干扰造成声学脉冲响应(Acoustic Impulse Response,AIR)的波达时间(Time of Arrival,TOA)模糊,导致现有室内空间几何建图技术存在计算复杂等缺点,提出一种基于AIR可信度判断与霍夫变换结合的定位和建图一步完成的方法。该方法基于到达时间差(Time Difference of Arrival,TDOA)迭代估计声源位置并计算准确的TOA,随后基于声收发设备与一阶反射TOA关于反射面的椭圆约束关系,结合可信度判断与霍夫变换,筛选可信低阶TOA以实现室内反射面的二维位置估计。蒙特卡洛仿真结果表明,在混响时间T60为0.1347 s、AIR误差标准差为22.7×10^-3 ms、大小为10 m×8 m×4 m复杂室内环境下,墙面定位平均距离误差为10.1 cm,平均角度误差为2.7958°。在大小为5.26 m×3.5 m×3.35 m的真实房间中,该方法可以实现声源与墙体位置的同时定位,完成规则盒型房间的二维地图重构,且墙面定位平均距离误差为2.6 cm,平均角度误差为2.17°。