Unleashing the Potential of Unidirectional Mechanical Materials: Breakthroughs and Promising Applications

The emergence of mechanically one-way materials presents an exciting opportunity for materials science and engineering. These substances exhibit unique nonreciprocal mechanical responses, enabling them to selectively channel mechanical energy and facilitate directed sound propagation, controlled mass transport, and concentration of mechanical energy amidst random motion. This article explores the fundamentals of mechanically one-way materials, their potential applications across various industries, and the economic and environmental considerations related to their production and use.

Direct Tunneling Effect in Metal-Semiconductor Contacts Simulated with Monte Carlo Method

Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the investigation into the tunneling current indicates that the tunneling effect is of great importance under reverse biases.The Schottky barrier diode current due to Schottky effect is in agreement with the theoretical one.The barrier lowering is found a profound effect on the current transport at the metal semiconductor interface.

Experiment and finite element method analysis mass erosion and transfer of Ag/La_2NiO_4-based electrical contacts during operation

A uniform transient temperature field model of electrical contacts operation was found by analyzing the process of closing arc constriction resistance Joule heat ~ breaking arc. Essential parameters of Ag/La2NiO4 electrical contact material for transient temperature field calculation were obtained through tests of electrical contact experimental instrument under 18 V DC in different cur- rents, other correlation experiments, and calculation anal- ysis. The finite element method was applied to solve the transient temperature field, and the features and distribution of the transient temperature field were obtained. The condition of material erosion and mass transfer can be forecasted by those calculation results. It is beneficial to research about the lifetime of Ag/La2NiO4 electrical material.

A Cell Model to Describe and Optimize Heat and Mass Transfer in Contact Heat Exchangers

A cell model to describe and optimize heat and mass transfer in contact heat exchangers for utilization of exhaust gases heat is proposed. The model is based on the theory of Markov chains and allows calculating heat and mass transfer at local moving force of the processes in each cell. The total process is presented as two parallel chains of cells (one for water flow and one for gas flow). The corresponding cells of the chains can exchange heat and mass, and water and gas can travel along their chains according to their transition ma-trices. The results of numerical experiments showed that the most part of heat transfer occurs due to moisture condensation from gas and the most intense heat transfer goes near the inlet of gas. Experimental validation of the model showed a good correlation between calculated and experimental data for an industrial contact heat exchanger if appropriate empirical equations were used to calculate heat and mass transfer coefficient. It was also shown that there exists the optimum height of heat exchanger that gave the maximum gain in heat energy utilization.

Transient Heat Transfer Study of Direct Contact Condensation of Steam in Spray Cooling Water

We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures ofcooling water on the efficiency ofsteam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature ofcooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering ofsteam.

The efficiency of direct integration methods in elastic contact-impact problems

A comparison of direct integration methods is madeand their efficiency is investigated for impact problems.New-mark,Wilson-θ,Central Difference and Houbolt Methodsare used as direct integration methods.Impact analysisincludes that of elastic and large deformation based uponupdated Lagrangian including buckling check.The resultsshow that the direct integration methods give differentresults in different contact-impact cases.

Parameters optimization for direct contact membrane distillation based on orthogonal experiment

Parameter optimization integrating operation parameters and structure parameters for the purpose of high permeate flux,high productivity and low exergy consumption of direct contact membrane distillation (DCMD) process was conducted based on Taguchi experimental design. L16(45) orthogonal experiments were carried out with feed inlet temperature,permeate stream inlet temperature,flow rate,module packing density and length-diameter ratio as optimization parameters and with permeate flux,water productivity per unit volume of module and water production per unit exergy loss separately as optimization objectives. By using range analysis method,the dominance degree of the various influencing factors for the three objectives was analyzed and the optimum condition was obtained for the three objectives separately. Furthermore,the multi-objectives optimization was performed based on a weight grade method. The combined optimum conditions are feed inlet temperature 75℃,packing density 30% ,length-diameter ratio 10,permeate stream inlet temperature 30 ℃ and flow rate 25 L/h,which is in order of their dominance degree,and the validity of the optimization scheme was confirmed.

Waste heat water pumping model with direct contact cooling

The performance of a patented water pumping model with steam-air power was presented, which operates automatically by direct contact cooling method. The main objective was to study feasibility of a pumping model for underground water. In this model, a heater installed within the heat tank represented sources of waste heat as energy input for finding appropriate conditions of the 10 L pump model. The system operation had five stages： heating, pumping, vapor flow, cooling, and water suction. The overall water heads of 3, 4.5, 6 and 7.5 m were tested. At the same time, it was found that the pump with 50% air volume is sufficient for pumping water to a desired level. In the experiment, the temperatures in the heating and pumping stages were 100-103 ℃and 80-90 ℃, respectively. The pressure in the pumping stage was 12-18 kPa, and the pressure in the suction stage was about-80 kPa, sufficient for the best performance. It could pump 170 L of water at a 2 m suction head, 120 L at a 3.5 m suction head, 100 L at a 5 m suction head, and 65 L at a 6.5 m suction head in 2 h. A mathematical model for larger pumps was also presented, which operates nearly the same as the present system. Economic analysis of the 10 L pump was also included.

A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 2:Validation and mechanical replicability

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and
|V_(Hp100)|
<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.

Low-resistance ohmic contacts on InAlN/GaN heterostructures with MOCVD-regrown n+-InGaN and mask-free regrowth process

This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting in an extremely low contact resistance of 0.102Ω·mm between n^(+)-InGaN and InAlN/GaN channels.Mask-free regrowth process was also used to significantly improve the sheet resistance of InAlN/GaN with MOCVD regrown ohmic contacts.Then,the diffusion mechanism between n^(+)-InGaN and InAlN during regrowth process was investigated with electrical and structural characterizations,which could benefit the further process optimization.

直接稀释-电感耦合等离子体质谱法测定母乳中17种元素的含量

提出了直接稀释-电感耦合等离子体质谱法(ICP-MS)同时测定母乳中钒、铬、锰、钴、镍、铜、锌、砷、硒、锶、钡、钼、镉、锡、锑、汞、铅等17种元素含量的方法。取母乳0.5 mL,用含2%(体积分数)硝酸和0.01%(体积分数)四甲基氢氧化铵的0.01%(体积分数)曲拉通X-100溶液定容至10 mL,涡旋混匀,以转速4000 r·min^(-1)离心5 min,将上清液用0.45μm水相滤膜过滤,在动能歧视(KED)模式下采用ICP-MS测定滤液中上述17种元素的含量,在线加入含6μg·L^(-1)钪、锗、铑、铋的混合内标使用液。结果表明:各元素的质量浓度在一定范围内与所对应的信号强度与内标元素信号强度比呈线性关系,检出限(3s)为0.019~0.768μg·L^(-1);方法用于分析美国国家标准参考材料,除锌元素外,其他元素的测定值均在认定值的不确定度范围内,并且日内和日间的变异系数均小于13%;按照标准加入法进行回收试验,回收率为81.3%~119%。

蒸汽射流直接接触凝结的界面及声压特性

蒸汽射流在液体中的直接接触凝结引发的剧烈界面振荡及声压振荡,可能导致工业管道系统振动甚至失效,采用高速摄像机与高频水听器,捕捉了射流的界面演化行为及其诱导的声压。研究了3种典型凝结流型下射流界面的径向、轴向振荡与声压振荡特性,并阐明声压振荡产生机理。研究发现:声压波动的概率密度函数在间歇流型下呈左偏单峰分布,在界面振荡流型下呈双峰分布,而在稳定流型下呈对称单峰分布;随蒸汽质量流速升高,无量纲径向、轴向界面振荡强度及声压振荡强度整体呈下降趋势,表现出极强的相关性。建立了基于声压参数的射流喷射长度预测模型,预测值与实验值的误差在±1%内。概率密度及相关性分析结果表明,蒸汽射流凝结的声压振荡是由其界面振荡引起的。

小车运行状态下岸桥结构动力响应分析

本文对在役岸桥整机金属结构的动力学响应机理进行分析。基于Euler-Bernoulli梁理论建立起重机单梁结构数值模型,分析不同工况对梁结构动力响应的影响,并分析动力学方程中“离心加速度项”对岸桥的动力学响应的影响。利用一岸桥结构数据建立包含结构重要分析部位如铰点、轨道梁等结构的几何特征的整机精细化数值模型。以简化质量点模拟小车,将质量与板壳单元接触,实现小车与大梁的相互作用,并应用于岸桥结构动力学分析中,考虑轨道梁非中心受力,计算得到大梁铰点的加速度响应,与实测信号结果基本一致。经计算分析发现,岸桥大梁铰点处测点的加速度实测信号频谱和计算信号频谱均表明小车运行对岸桥结构的主要影响为经过轨道接头时产生的高频冲击。同时,岸桥模型大梁上10个测点及小车的位移结果表明,当小车带额定载荷以额定速度匀速运行时,岸桥前大梁前端产生垂向拟静态位移,位移频谱表明小车主要受到垂向强迫振动。

水下振动台竖向动水附加质量特征与机理试验研究

工程结构与水体耦合抗震研究需求越来越大,推动了水下振动台的建设与发展,水下振动台竖向动水附加质量及特征直接影响其设计和自身性能。本文通过试验方法,共设计135个工况,台面负载20 t惯性质量块,分别考虑不同激励量级、不同频率、不同水深,研究水下振动台竖向动水附加质量特征,并试探从机理层面进行解释。试验结果表明:激励量级与动水附加质量之间相关性较为复杂,不同频率之间存在分组现象,水深比(水深/台面直径)可作为水下振动台设计重要参数,不同水下振动台动水附加质量最小值频率拐点不同。试验研究为水下振动台设计以及模型试验可靠性等提供参考。

地震作用下车辆-公路桥梁耦合作用的能量机理

由于地震作用下车辆和公路桥梁相互耦合作用的复杂性,目前对其相互作用机理的研究较少,导致各国现行公路桥梁抗震设计规范关于桥梁在地震作用时是否需要考虑活载作用仍然存在分歧.现有研究表明,车辆既可能对桥梁的地震响应产生有利影响,也可能产生不利的影响.本文在已有的研究基础上,对车桥耦合接触行为进行简化模拟,采用能量法对车辆-公路桥梁耦合作用机理进行分析.结果表明:车桥耦合作用对输入到桥梁水平方向能量的影响可以忽略不计,但会导致输入到桥梁竖向总能量的减小,因而使桥梁的竖向地震响应减小,而输入到车辆竖向的能量则主要来自桥面振动;此外,车辆质量越小,桥梁振动产生的对车辆水平方向的能量输入越大.

隧道穿越岩堆体围岩剪切特性及分级

为解决隧道穿越岩堆体围岩分级不准确的问题,通过相似材料直剪试验分析岩堆体的直剪特性,将含水率和填充土含量两个因素带入熵权可拓物元法,并结合地质指标进行分级研究。结果表明岩堆体的抗剪强度随着含水率、填充土含量的增大,先增大后减小,最终趋于平稳,过高或过低的含水率和填充土都会“弱化”岩堆体的抗剪强度。根据岩堆体的特点,选取岩石单轴饱和抗压强度、节理裂隙密度、岩体完整性系数、含水率和填充土含量作为分级指标,结合熵权可拓物元法,将所选指标和熵权可拓物元法结合并在工程实例进行验证,分级结果比原方法准确性更好,证明研究提出的围岩分级方法是合理可行的。研究结果能够为岩堆体隧道的围岩分级提供指导,为施工设计和支护方式提供依据。

非稳态点接触EHL问题高效直接算法研究

发展了一种研究非稳态点接触弹流润滑(Elastohydrodynamic Lubrication,简称EHL)的快速直接算法。在弹流求解过程中,通过分析计算域网格离散的特点,对离散后的Reynolds方程采取按列分块、逐列求解的求解策略,使每个时间步长上求解的方程维数显著减小,从而极大地提高了计算效率。运用新算法获得了点接触EHL纯挤压工况下油膜和压力演变过程中的典型特征,证明了新算法的正确性;数值实验和比较证明,新算法具有复合直接迭代法无可比拟的高效率,与逐行迭代法相比,新算法也具有显著的、更高的计算效率,并且随着网格数量的增加,新算法的高效性愈加凸显。

基于三维裂隙网络的岩体剪切特性尺寸效应分析

为研究复杂裂隙岩体剪切特性的尺寸效应,以西藏怒江松塔水电站PDC3平硐为例,在现场采集裂隙信息的基础上,基于颗粒流PFC3D软件通过统计学方法及蒙特卡洛原理生成三维裂隙网络,构建等效岩体,进行大尺度直剪模拟试验得到裂隙岩体的抗剪强度、内摩擦系数及内聚力,分别研究其尺寸效应并确定不同参数下的REV尺寸,继而对相关参数和试样尺寸分别进行非线性回归拟合,探究其函数关系。结果表明:抗剪强度、内聚力及内摩擦系数随着试样尺寸的变化而趋于稳定,且不同参数得到的REV大小不同;综合分析不同参数的REV尺寸,得出研究区裂隙岩体的剪切特性REV尺寸为11 m×11 m×11 m;通过函数关系拟合,抗剪强度、内聚力和内摩擦系数与试样尺寸之间均存在指数函数关系。该成果为研究复杂裂隙岩体的力学REV以及合理确定力学参数提供了依据。

质谱技术在食品及食品接触材料的典型有机污染物中的应用研究进展

食品及食品接触材料有机污染物种类繁多,给环境和消费者健康带来诸多影响。质谱技术具有灵敏度高、分析速度快等特点,在分析检测领域发挥着重要作用。本文主要介绍了液相色谱-质谱联用技术在近年来比较关注的全氟多氟化合物(PFASs)、双酚类化合物(BPs)、季铵盐类化合物(QACs)3类典型有机污染物中的应用研究进展,并对未来发展趋势进行了展望。

中空纤维膜臭氧接触式反应器传质机理分析

将疏水性聚四氟乙烯(PTFE)中空纤维膜组装成膜接触器,开发了膜接触式臭氧(O_(3))传质技术。对比了气泡传质和膜接触传质的差异,通过O_(3)传质模型和阻力模型对该技术的主要影响因素和传质机理进行了研究。结果表明,O_(3)可以有效地通过疏水性PTFE膜进行传质,当搅拌速度达到1500r/min时,膜传质的表观传质系数(0.3049min-1)与气泡传质(0.3109min-1)相当。同时,膜表面的疏水结构将尾气的湿度降低到0.8g/m^(3)以下,远低于气泡传质(>11.5g/m^(3)),符合进入臭氧发生器的标准,具备回收氧气的可行性。O_(3)的传质通量受液体流速、p H、污染物浓度、气体流量以及进气O_(3)浓度的影响。在pH=11、苯酚浓度为0或pH=7、苯酚浓度为20mg/L时,传质通量达到了0.16g/(m^(2)·h)。O_(3)传质过程的传质阻力主要由膜阻力和液相阻力组成,而通过液相条件控制可以有效减小液相阻力,因此进一步降低传质阻力需要膜技术的发展。