Aging behavior of a copper-bearing high-strength low-carbon steel

The effects of aging temperature and time on the hardness and impact toughness of a copper-bearing high-strength low-carbon steel were investigated. The hardness of the aged samples reached maxima after 1 h and 5 h of aging at 500 and 450℃, respectively; this increase in hardness was followed by a decrease in hardness until a temperature of 700℃, at which secondary hardening was observed. The impact toughness of the aged steel was found to be higher for 5 h of aging. Transmission electron microscopy confirmed the presence of carbide and copper precipitates; also, the secondary hardening could be the result of the transformation of austenite (formed in the aging treatment) to martensite. Differential scanning calorimetry of the steel was performed to better understand the precipitation behavior. The results revealed that the precipitation of the steel exhibited two significant stages of copper precipitate nucleation and coarsening of the precipitates, with corresponding activation energies of 49 and 238 kJ·mol-1, respectively.     

Combined Moho Parameters Determination Using CRUST1.0 and Vening Meinesz-Moritz Model

According to Vening Meinesz-Moritz (VMM) global inverse isostatic problem, either the Moho density contrast (crust-mantle density contrast) or the Moho geometry can be estimated by solv-ing a non-linea...     

Muḥyī al-Dīn al-Maghribī’s lunar measurements at the Maragha observatory

This paper is a technical study of the systematic observations and computations made by Mu?yī al-Dīn al-Maghribī (d. 1283) at the Maragha observatory (north-western Iran, c. 1259–1320) in order to newly determine the parameters of the Ptolemaic lunar model, as explained in his Talkhī? al-majis?ī, “Compendium of the Almagest.” He used three lunar eclipses on March 7, 1262, April 7, 1270, and January 24, 1274, in order to measure the lunar epicycle radius and mean motions; an observation on April 20, 1264, to determine the lunar eccentricity; an observation on August 29, 1264, to test the model; and another on March 15, 1262, for measuring the lunar parallax. In the second period of activity at the Maragha observatory, Shams al-Dīn Mu?ammad al-Wābkanawī (c. 1254–1320) adopted all of al-Maghribī’s parameter values in his Zīj, but decreased his value for the mean longitude of the moon at epoch by 0;13,11 $^{\circ }$ . By comparing the times of the new moons and lunar eclipses in the period of 1270–1320 as computed from the astronomical tables of the Maragha tradition with the true modern ones, it is argued that this correction was very probably the result of actual observations.     

基于云和高斯过程的网联车辆协同式道路参数估计

近年来智能网联汽车发展迅速,云端预先存储的道路参数信息对于提升网联汽车的悬架控制以及检测路面不规则度至关重要。目前关于道路参数估计的工作大多在单个车辆上完成,此类算法对于车辆模型不确定性以及测量误差较敏感。针对该问题,提出了一种新的协同式估计架构,该架构能够充分利用多个同质的网联汽车的测量信息以提高估计精度。首先,在云端利用前方行驶的全部车辆的数据对高斯过程模型进行训练以通过众包方式获取道路参数的估计结果。然后,该结果以未测量的方式发送到后方相邻车辆,后方单个车辆结合自车车载传感器（如加速度计、横摆角速度以及侧倾角速度）和由云端获取的基于众包高斯过程估计结果,使用卡尔曼滤波对该估计结果进一步优化。进而估计结果被发送到云端以更新高斯过程模型。大量的仿真实验结果表明,以该种方式使用云端估计的道路参数作为额外的未测量信息能够提高道路参数的估计精度,验证了该算法的有效性。     

Interference-Aware Multipath Routing Protocol for QoS Improvement in Event-Driven Wireless Sensor Networks

The existing multipath routing protocols for wireless sensor networks demonstrate the efficacy of traffic distribution over multiple paths to fulfill the Quality of Service (QoS) requirements of different applications.However,the performance of these protocols is highly affected by the characteristics of the wireless channel and may be even inferior to the performance of single-path approaches.Specifically,when multiple adjacent paths are being used concurrently,the broadcast nature of wireless channels res...     

Kinetics of magnetite oxidation under non-isothermal conditions

Oxidation of magnetite concentrates, which occurs during the pellet induration process, must be deeply understood to enable the appropriate design of induration machines. In the present paper, the kinetics of the magnetite oxidation reaction was studied. Primary samples were obtained from the Gol-e-Gohar iron ore deposit. Magnetic separation and flotation decreased the sulfur content in the samples to be approximately 0.1wt%. Thermogravimetric analysis was used to measure mass changes during the oxidation of magnetite and, consequently, the conversion values. The aim of this study was to use isoconversional methods to calculate the kinetic parameters. The Coats-Redfern method was also used to obtain the activation energy. Thermogravimetric analyses were run at three different heating rates. The Coats-Redfern results were too ambiguous for a meaningful interpretation. In the case of the isoconversional method, however, the mean activation energy and pre-exponential factor of the oxidation reaction were obtained as 67.55 kJ and 15.32×108 min-1, respectively. Such a large activation energy implies that temperature strongly affects the reaction rate. The oxidation reaction exhibits a true multi-step nature that is predominantly controlled by chemical reaction and diffusion mechanisms.     

Synthesis of WC powder through microwave heating of WO3-C mixture

A simple, easy, and low-cost process for the fabrication of tungsten carbide (WC) powder through microwave heating of WO₃-C mixtures was developed. Thermodynamic calculations and experimental investigations were carried out for WO₃-C and W-C systems, and a formation mechanism was proposed. In the results, for the synthesis of WC, the use of over stoichiometric amount of C together with a specially assembled experimental setup (which effectively retains heat in the system) is necessary. The WC powder is successfully obtained by heating WO₃:5C mixture for 900s in a domestic microwave oven.     

Mechanical properties of TiO2-hydroxyapatite nanostructured coatings on Ti-6Al-4V substrates by APS method

TiO₂-hydroxyapatite (HA) nanostructured coatings were produced by atmospheric plasma spray method. The effects of starting powder composition and grain size on their mechanical properties were investigated. The microstructure and morphology were characterized by X-ray diffraction and scanning electron microscopy (SEM). It is found that the coating with 10% HA has the best mechanical properties. Based on Rietveld refinement method, the mean grain size of the as-received powder (212 nm) extensively decreases to 66.4 nm after 20 h of high-energy ball milling. In spite of grain growth, the deposited coatings maintain their nanostructures with the mean grain size of 112 nm. SEM images show that there is a lower porosity in the coating with a higher HA content. Optical microscopy images show that uniform thickness is obtained for all the coatings.     

Contact and hybrid zone hotspots and evolution of birds in the Middle East

The Middle East is an important contact zone for a considerable number of bird taxa from the western and eastern Palearctic and from the great Saharo-Sindian desert belt.Using WORLDMAP software,we analyzed the geographical distribution of secondary contact zones for parapatric species pairs of birds in the Middle East.We identified 56 species(29 species pairs)that make contact in the Middle East.The species pairs belong to three orders,i.e.Falconiformes,Piciformes,and Passeriformes.Almost half(46%)of these species pairs hybridize in their contact zones.Although contact zones occur over a large part of northern Middle East,spatially they were not evenly distributed.Contact zone richness was highest in the mountain ranges south of the Caspian Sea and the Caucasus.The hottest hotspots,where up to nine bird species pairs occur sympatrically,are situated in north-eastern Iran and Azerbaijan.We discuss the relevance of these hotspots for improving our understanding of the biogeography and evolution of the avifauna in the Middle East.     

质环的Jordan理想上的Jordan自同构

证明了下列结果： 设R是一个2-非挠质环； J 是一个Jordan理想， 且是R的子环. 如果φ: R→R是一个自同构， 且对所有的u∈J, 满足: φ(u²)=φ(u)², 则对所有的u,v∈J, 有 φ(uv)=φ(u)φ(v)或φ(uv)=φ(v)φ(u).