Numerical simulation of temperature distribution and heat transfer during solidification of titanium alloy ingots in vacuum arc remelting process

In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.

Growth restriction effects during solidification of aluminium alloys

The effects of solute elements during solidification on the grain size are very important and can be quantified by the growth-restriction parameter Q,and Q possesses the better correlation with the grain size. Based on the constitutional undercooling generated by the growth of an adjacent grain during the initial solidification,the growth-restriction parameter Q is deduced and a comprehensive physical basis of Q is obtained by using an initial solute distributing equation. For the alloys with more potent nucleants,Q is a suitable predictor of the grain size. For less potent nucleants,the relative grain size(RGS) is a more accurate prediction of the grain size. This prediction coincides with the experimental behaviors for Al-Ti and Al-Cu alloys with lower solute content.

Wavelet Denoising of Flight Flutter Testing Data for Improvement of Parameter Identification

The accuracy of modal parameter estimation plays a crucial role in flutter boundary prediction. A new wavelet denoising method is introduced for flight flutter testing data, which can improve the estimation of frequency domain identification algorithms. In this method, the testing data is first preprocessed with a gradient inverse weighted filter to initially lower the noise. The redundant wavelet transform is then used to decompose the signal into several levels. A “clean” input is recovered from the noisy data by level dependent thresholding approach, and the noise of output is reduced by a modified spatially selective noise filtration technique. The advantage of the wavelet denoising is illustrated by means of simulated and real data.

Solidification of Mg-28%Zn-2%Y alloy involving icosahedral quasicrystal phase

Applying XRD, DTA, SEM and TEM techniques, an investigation on the solidification microstructure and solidification sequence of Mg-rich Mg-28%Zn-2%Y (mole fraction) alloy was carried out. It is found that, α-Mg dendrites, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified alloy, where the icosahedral quasicrystal, whose structure is indentified to be a face-centered type, originates from a peritectic reaction occurring at 416 ℃. The primary phase of this peritectic reaction has the composition of Mg20Zn66Y14, which is coincident with the H phase reported by TSAI as (Zn, Mg)5Y. Furthermore, the single I-phase grain morphology was observed and its growth evolution was also discussed.

Phase formation and electrical characteristic of NASICON ceramics

Hot pressed sintering were employed to prepare the sodium super ionic conductor(NASICON:Na3Zr2Si2PO12) ceramics using the powder with the corresponding composition from sol-gel method. The density,phase and microstructure of different samples sintered at different temperatures were analyzed and the dependences of density,phase formation,and the microstructure on the sintering temperature were investigated in detail. The AC electrical conductivity and the buck conductivity of the ceramics sintered at different temperatures were measured and discussed. Results show that the samples contain mainly monoclinic NASICON and no ZrO2 phase was found no matter the sintering temperature is high or not. The sintering temperature mainly dominated the density,the microstructure and the electrical characteristics of the ceramics. The densities of the samples increase obviously as the sintering temperature increases and reach 99.4% when the sintering temperature is 1 150 ℃. With the increase of sintering temperature,both the density and crystal size of the samples increase obviously,resulting in the visible increase of ionic conductivity of the samples as the sintering temperature. When sintering temperature reaches 1 150 ℃,the ionic conductivity of the sample has the highest value of 3.6×10-3 S/cm,which could be attribute to the highest density and least crystal boundary due to largest crystal size of the ceramics.

Effect of nonlinear liquidus and solidus on dendrite growth in bulk undercooled melts

On the base of nonlinear liquidus and solidus,an extended model for dendrite growth in bulk undercooled melts was developed under local non-equilibrium conditions both at the interface and in the bulk liquid.In terms of thermodynamic calculations of the phase diagram,the model predictions are relatively realistic physically,since few fitting parameters are used in the model predictions.Adopting three characteristic velocities,i.e.the critical velocity of absolute solute stability(VC*),the velocity of maximal tip radius(VRm),and the velocity of bulk liquid diffusion(VD),a quantitative agreement is obtained between the model predictions and the experimental results in undercooled Ni-0.7%B and Ni-1%Zr(molar fraction) alloys,and the overall solidification process can be categorized.

Microgravity Material Research in China:2016

Firstly,recent research works of high undercooling and rapid solidification of metallic alloys under ground simulation conditions in Northwestern Polytechnical University are reviewed.Secondly,under normal gravity and microgravity of binary to quinary Nickel-base single crystal alloys with different contents of W,Ta,Al and Ti elements are comparatively investigated by Institute of Metal Research using drop tube.Thirdly,solidification and crystal growth of SJ10-Recoverable Scientific Experiment Satellite by Institute of Semiconductors is introduced.

A Study on the Reform of China’s General Aviation

With the rapid development of China’s general aviation in recent years, the demand for general aviation aircraft is increasing, therefore, the standard for the security management of general aviation, technical standards and market access for general aviation companies, and flight crew is much higher than that of before. However, the current law and regulations of general aviation are based on the standard of public transport, taking the fact into account that the general aviation and public transport aviation are very different;the Chinese government has proposed a reform of general aviation management principles, contents and objectives, and aims to formulate legal system of general aviation by 2020.

Simulation of interphase boundary of Ni_(75)Al_xV_(25-x )alloys using microscopic phase-field method

The evolution of ordered interphase boundary (IPB) of Ni75AlxV25-x alloys was simulated using the microscopic phase-field method. Based on the atomic occupation probability figure on 2D and order parameters, it was found that the IPB formed by different directions ofθ phase has great effect on the precipitation of γ ′ phase. The γ ′ phase precipitated at the IPB that is formed by [1 00]θ direction where the ( 001)θ plane is opposite, and then grows up and the shape is strap at final. The IPB structure between γ ′phase andθ phase is the same. There is no γ ′ phase precipitate at the IPB where the ( 002)θ and ( 001)θ planes are opposite, the ordered IPB is dissolved into disordered area. There is γ ′ phase precipitation at the IPB formed by the [ 001]θ and [1 00]θ directions, and the IPB structure is different between γ ′ phase and the different directions ofθ phase. The IPB where ( 001)γ′ and (1 00)θ plane opposite does not migrate during the γ ′ phase growth, and γ ′ phase grows along [1 00]θdirection.

Preparation and properties of scintillating glass doped with organic activators

A series of scintillating glasses were developed by doping organic activators into low melting temperature glasses according to different ratios. The fluorescence spectra and the transmission spectra of some scintillating glasses were explored and the actual concentration organic in scintillating glass was estimated. The results show that it is feasible to prepare the scintillating glass by doing organic scintillating activators into the low-melting glasses. There are two main reasons for the weak optical properties of the scintillation glasses: one is that the actual concentration of organic activators doped in the glasses is very low, and the other is the existence of lots of defects formed in the scintillating glasses due to the evaporation of organic activator, lowering the transmission of glasses. The fluorescence emission peaks of the glasses move to a longer wavelength compared with those in organic matrixes. To increase the light output of the glass, the optical transmittance of the glasses must be improved and the concentration of activators in the glasses must be increased.

Phase selection in highly undercooled Fe-B eutectic alloy melts

The high undercooling technique by molten glass slag purification and cyclical superheating in Ar atmosphere was applied to bulk Fe-B alloy melts. A hypercooling was achieved which suppressed the formation of stable phase and consequently promoted the nucleation of metastable phase. Fe-17%B and Fe-20%B alloys were investigated, respectively. TEM and X-ray powder diffraction analyses verify the formation of metastable phase in the highly undercooled Fe-B alloy melts. Besides, the critical nucleation work of Fe2B and Fe3B phases was calculated to predict phase selection in the undercooled melts. The results show that the metastable phase formation is a function of the undercooling achieved prior to nucleation. And the amount of undercooling is an important factor in determining microstructural development by controlling phase selection in the undercooled melts.

Effect of the fluctuant acoustic channel on the gain of a linear array in the ocean waveguide

The inhomogenous ocean waveguide,which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate,is one of the causes that make the array gain deviate from its ideal value.The relationship between the array gain and the fluctuant acoustic channel is studied theoretically.The analytical expression of the array gain is derived via an acoustic channel transfer function on the assumption that the ambient noise field is isotropic.The expression is expanded via the Euler formula to give an insight into the effect of the fluctuant acoustic channel on the array gain.The result demonstrates that the amplitude fluctuation of the acoustic channel transfer functions has a slight effect on the array gain;however,the uniformity of the phase difference between the weighting coefficient and the channel transfer function on all the hydrophones in the array is a major factor that leads the array gain to further deviate from its ideal value.The numerical verification is conducted in the downslope waveguide,in which the gain of a horizontal uniform linear array(HLA)with a wide-aperture operating in the continental slope area is considered.Numerical result is consistent with the theoretical analysis.

Modeling and Performance Analysis of Spiral Fishbone Network Using NS-2

In this research, we have projected and carried out a novel fishbone network that shows better performance in the term of minimizing the packet delay with respect to sink speed. Previous study implies that sector angle affects greatly on designing fishbone network. Finite Set of nodes arranges to sense the physical condition of any system is called wireless sensor. Our designed fishbone network can be potentially applied for a wireless sensing system to formulate a whole network. The network is a novel design which has been finalized by comparing sector angle. Analysis takes place by varying packet delay according to sink speed. Future analysis takes place for Quality of Service (QoS) and Quality of Experience (QoE). Latency of Packet and its size is the measurement criteria of any network or service is called Quality of Service (QoS). On the other hand the user experience of using the designed network is called Quality of Experience (QoE). Our designed network has been analyzed in TCP Tracer to find out the latency or packet delay for different users. The user data has been shorted and equated among them for latency with different no of packets. Our proposed spiral fishbone network shows better QoS and QoE. In future more nodes can be added to design extended fishbone network for wireless.

A survey on multi-sensor fusion based obstacle detection for intelligent ground vehicles in off-road environments

With the development of sensor fusion technologies, there has been a lot of research on intelligent ground vehicles, where obstacle detection is one of the key aspects of vehicle driving. Obstacle detection is a complicated task, which involves the diversity of obstacles, sensor characteristics, and environmental conditions. While the on-road driver assistance system or autonomous driving system has been well researched, the methods developed for the structured road of city scenes may fail in an off-road environment because of its uncertainty and diversity.A single type of sensor finds it hard to satisfy the needs of obstacle detection because of the sensing limitations in range, signal features, and working conditions of detection, and this motivates researchers and engineers to develop multi-sensor fusion and system integration methodology. This survey aims at summarizing the main considerations for the onboard multi-sensor configuration of intelligent ground vehicles in the off-road environments and providing users with a guideline for selecting sensors based on their performance requirements and application environments.State-of-the-art multi-sensor fusion methods and system prototypes are reviewed and associated to the corresponding heterogeneous sensor configurations. Finally, emerging technologies and challenges are discussed for future study.

宗教与政治:对欧洲和美国的比较分析

通过对美国和欧洲共10个国家(英国、法国、德国、意大利、西班牙、丹麦、荷兰、奥地利、波兰)的16,000名成年人进行的跨国调查(2002及2003年),本文考察了当地的宗教信仰状况,着重于他们对神权、生命的实质及生命的开始等三方面的理解认识,并进一步研究了他们的一些宗教行为(如祈祷及参与宗教活动的频率)和对宗教领袖的信任程度。本文的重点在于分析个人宗教价值观对其就新兴生化科技所持政治态度的影响。为此收集了广泛的研究数据,考察受访者对主要生化科技,如胚胎干细胞应用、转基因食品和克隆等的观点和态度。最后,使用多元回归研究模式的结构方程模型(SEM)分别描述了人们的宗教价值观、对生命的理解、年龄、性别和教育水平等几个变量对于堕胎、胚胎干细胞应用研究和安乐死等三项公共政策争论的影响。

Reducing partition skew on MapReduce: an incremental allocation approach

MapReduce,a parallel computational model,has been widely used in processing big data in a distributed cluster.Consisting of alternate map and reduce phases,MapReduce has to shuffle the intermediate data generated by mappers to reducers.The key challenge of ensuring balanced workload on MapReduce is to reduce partition skew among reducers without detailed distribution information on mapped data.In this paper,we propose an incremental data allocation approach to reduce partition skew among reducers on MapReduce.The proposed approach divides mapped data into many micro-partitions and gradually gathers the statistics on their sizes in the process of mapping.The micropartitions are then incrementally allocated to reducers in multiple rounds.We propose to execute incremental allocation in two steps,micro-partition scheduling and micro-partition allocation.We propose a Markov decision process (MDP)model to optimize the problem of multiple-round micropartition scheduling for allocation commitment.We present an optimal solution with the time complexity of O(K· N2),in which K represents the number of allocation rounds and N represents the number of micro-partitions.Alternatively,we also present a greedy but more efficient algorithm with the time complexity of O(K.N ln N).Then,we propose a minmax programming model to handle the allocation mapping between micro-partitions and reducers,and present an effective heuristic solution due to its NP-completeness.Finally,we have implemented the proposed approach on Hadoop,an open-source MapReduce platform,and empirically evaluated its performance.Our extensive experiments show that compared with the state-of-the-art approaches,the proposed approach achieves considerably better data load balance among reducers as well as overall better parallel performance.

A polarization-insensitive fishnet/spacer/mirror plasmonic absorber for hot electron photodetection application

A polarization-insensitive plasmonic absorber is designed consisting of Au fishnet structures on a TiO2 spacer/Ag mirror. The fishnet structures excite localized surface plasmon and generate hot electrons from the absorbed photons, while the TiO2 layer induces Fabry–Perot resonance, and the Ag mirror acts as a back reflector.Through optimizing the TiO2 layer thickness, numerical simulation shows that 97% of the incident light is absorbed in the Au layer. The maximum responsivity and external quantum efficiency of the device can approach 5 mA/W and ~1%, respectively, at the wavelength of 700 nm.

Molecular engineering on all ortho-linked carbazole/oxadiazole hybrids toward highly-efficient thermally activated delayed fluorescence materials in OLEDs

The highest efficiency thermally activated delayed fluorescence(TADF)emitters in OLEDs are mostly based on twisted donor/acceptor(D/A)type organic molecules.Herein,we report the rational molecular design on twisted all ortho-linked carbazole/oxadiazole(Cz/OXD)hybrids with tunable D-A interactions by adjusting the numbers of donor/acceptor units and electron-donating abilities.Singlet-triplet energy bandgaps(ΔEST)are facilely tuned from^0.4,0.15 to^0 eV in D-A,D-A-D to A-D-A type compounds.This variation correlates well with triplet-excited-state frontier orbital spatial separation efficiency.NonTADF feature with solid state photoluminescence quantum yield(PLQY)<10%is observed in D-A type 2CzOXD and D-A-D type 4CzOXD.Owing to the extremely lowΔEST for efficient reverse intersystem crossing,strong TADF with PLQY of 71%-92%is achieved in A-D-A type 4CzDOXD and 4tCzDOXD.High external quantum efficiency from 19.4%to 22.6%is achieved in A-D-A typed 4CzDOXD and 4tCzDOXD.