Effect of solidification cooling rate on microstructure and tribology characteristics of Zn-4Si alloy

The main objective of this work was to modify the microstructure and enhance the tribological properties of a new Zn-4Si al-loy through a high solidification cooling rate(SCR).According to the results,by increasing the SCR from 2.0 to 59.5℃/s the average size of primary Si particles and that of the grains reduced from 76.1 and 3780μm to less than about 14.6 and 460μm,respectively.Augment-ing the SCR also enhanced the microstructural homogeneity,decreased the porosity content(by 50%),and increased the matrix hardness(by 36%).These microstructural changes enhanced the tribological behavior.For instance,under the applied pressure of 0.5 MPa,an in-crease in the SCR from 2.0 to 59.5℃/s decreased the wear rate and the average friction coefficient of the alloy by 57%and 23%,respect-ively.The wear mechanism was also changed from the severe delamination,adhesion,and abrasion in the slowly-cooled alloy to the mild tribolayer delamination/abrasion in the high-cooling-rate-solidified sample.

Data-Based Filters for Non-Gaussian Dynamic Systems With Unknown Output Noise Covariance

This paper proposes linear and nonlinear filters for a non-Gaussian dynamic system with an unknown nominal covariance of the output noise.The challenge of designing a suitable filter in the presence of an unknown covariance matrix is addressed by focusing on the output data set of the system.Considering that data generated from a Gaussian distribution exhibit ellipsoidal scattering,we first propose the weighted sum of norms(SON)clustering method that prioritizes nearby points,reduces distant point influence,and lowers computational cost.Then,by introducing the weighted maximum likelihood,we propose a semi-definite program(SDP)to detect outliers and reduce their impacts on each cluster.Detecting these weights paves the way to obtain an appropriate covariance of the output noise.Next,two filtering approaches are presented:a cluster-based robust linear filter using the maximum a posterior(MAP)estimation and a clusterbased robust nonlinear filter assuming that output noise distribution stems from some Gaussian noise resources according to the ellipsoidal clusters.At last,simulation results demonstrate the effectiveness of our proposed filtering approaches.

Nonlinear vibration of Timoshenko FG porous sandwich beams subjected to a harmonic axial load

In this study,the instability and bifurcation diagrams of a functionally graded(FG)porous sandwich beam on an elastic,viscous foundation which is influenced by an axial load,are investigated with an analytical attitude.To do so,the Timoshenko beam theory is utilized to take the shear deformations into account,and the nonlinear Von-Karman approach is adopted to acquire the equations of motion.Then,to turn the partial differential equations(PDEs)into ordinary differential equations(ODEs)in the case of equations of motion,the method of Galerkin is employed,followed by the multiple time scale method to solve the resulting equations.The impact of parameters affecting the response of the beam,including the porosity distribution,porosity coefficient,temperature increments,slenderness,thickness,and damping ratios,are explicitly discussed.It is found that the parameters mentioned above affect the bifurcation points and instability of the sandwich porous beams,some of which,including the effect of temperature and porosity distribution,are less noticeable.

Mapping Energy Expansion: Remote Sensing Insights into Oil and Gas Infrastructure and Land Use Changes in Midland, TX

Rapid expansion in global energy demand driven primarily by oil and gas consumption has spurred significant environmental concerns. This study delves into the intricate relationship between energy development and environmental impacts focusing on Midland County, Texas, a pivotal region within the Permian Basin. Leveraging satellite imagery and Geographic Information Systems (GIS) techniques, the research meticulously examines land use dynamics from 2001 to 2019. The findings illuminate a marked decline in vegetation health and density attributable to the burgeoning oil and gas infrastructure in the area. Moreover, the analysis underscores the emergence of barren lands and the displacement of agricultural areas, indicative of the profound alterations in land cover patterns over the study period. These insights underscore the urgent need for concerted efforts to mitigate the adverse environmental effects of energy expansion, emphasizing the importance of collaborative approaches to foster sustainable land use practices. Additionally, the study explores the socio-economic implications of land use changes, addressing how energy expansion affects local communities and economies. Previous studies have emphasized the need for comprehensive assessments of cumulative environmental impacts, advocating for the implementation of effective mitigation strategies.

A Numerical Investigation Based on Exponential Collocation Method for Nonlinear SITR Model of COVID-19

In this work,the exponential approximation is used for the numerical simulation of a nonlinear SITR model as a system of differential equations that shows the dynamics of the new coronavirus(COVID-19).The SITR mathematical model is divided into four classes using fractal parameters for COVID-19 dynamics,namely,susceptible(S),infected(I),treatment(T),and recovered(R).The main idea of the presented method is based on the matrix representations of the exponential functions and their derivatives using collocation points.To indicate the usefulness of this method,we employ it in some cases.For error analysis of the method,the residual of the solutions is reviewed.The reported examples show that the method is reasonably efficient and accurate.

Future meteorological drought conditions in southwestern Iran based on the NEX-GDDP climate dataset

Investigation of the climate change effects on drought is required to develop management strategies for minimizing adverse social and economic impacts.Therefore,studying the future meteorological drought conditions at a local scale is vital.In this study,we assessed the efficiency of seven downscaled Global Climate Models(GCMs)provided by the NASA Earth Exchange Global Daily Downscaled Projections(NEX-GDDP),and investigated the impacts of climate change on future meteorological drought using Standard Precipitation Index(SPI)in the Karoun River Basin(KRB)of southwestern Iran under two Representative Concentration Pathway(RCP)emission scenarios,i.e.,RCP4.5 and RCP8.5.The results demonstrated that SPI estimated based on the Meteorological Research Institute Coupled Global Climate Model version 3(MRI-CGCM3)is consistent with the one estimated by synoptic stations during the historical period(1990-2005).The root mean square error(RMSE)value is less than 0.75 in 77%of the synoptic stations.GCMs have high uncertainty in most synoptic stations except those located in the plain.Using the average of a few GCMs to improve performance and reduce uncertainty is suggested by the results.The results revealed that with the areas affected by wetness decreasing in the KRB,drought frequency in the North KRB is likely to increase at the end of the 21st century under RCP4.5 and RCP8.5 scenarios.At the seasonal scale,the decreasing trend for SPI in spring,summer,and winter shows a drought tendency in this region.The climate-induced drought hazard can have vast consequences,especially in agriculture and rural livelihoods.Accordingly,an increasing trend in drought during the growing seasons under RCP scenarios is vital for water managers and farmers to adopt strategies to reduce the damages.The results of this study are of great value for formulating sustainable water resources management plans affected by climate change.

MEAN APPROXIMATION BY DILATATIONS IN BERGMAN SPACES ON THE UPPER HALF-PLANE

We study sufficient conditions on radial and non-radial weight functions on the upper half-plane that guarantee norm approximation of functions in weighted Bergman,weighted Dirichlet,and weighted Besov spaces on the upper half-plane by dilatations and eventually by analytic polynomials.

Radon CLF:A Novel Approach for Skew Detection Using Radon Transform

In the digital world,a wide range of handwritten and printed documents should be converted to digital format using a variety of tools,including mobile phones and scanners.Unfortunately,this is not an optimal procedure,and the entire document image might be degraded.Imperfect conversion effects due to noise,motion blur,and skew distortion can lead to significant impact on the accuracy and effectiveness of document image segmentation and analysis in Optical Character Recognition(OCR)systems.In Document Image Analysis Systems(DIAS),skew estimation of images is a crucial step.In this paper,a novel,fast,and reliable skew detection algorithm based on the Radon Transform and Curve Length Fitness Function(CLF),so-called Radon CLF,was proposed.The Radon CLF model aims to take advantage of the properties of Radon spaces.The Radon CLF explores the dominating angle more effectively for a 1D signal than it does for a 2D input image due to an innovative fitness function formulation for a projected signal of the Radon space.Several significant performance indicators,including Mean Square Error(MSE),Mean Absolute Error(MAE),Peak Signal-to-Noise Ratio(PSNR),Structural Similarity Measure(SSIM),Accuracy,and run-time,were taken into consideration when assessing the performance of our model.In addition,a new dataset named DSI5000 was constructed to assess the accuracy of the CLF model.Both two-dimensional image signal and the Radon space have been used in our simulations to compare the noise effect.Obtained results show that the proposed method is more effective than other approaches already in use,with an accuracy of roughly 99.87%and a run-time of 0.048(s).The introduced model is far more accurate and timeefficient than current approaches in detecting image skew.

Stabilization of saline silty sand using lime and micro silica

Many construction and post-construction problems have been reported in the literature when saline soils have been used without understanding of their abnormal behavior,especially their inferior bearing capacity in the natural condition.The strength of these soils further decreases on soaking.Saline soil deposits cover extensive areas in central Iran and are associated with geotechnical problems such as excessive differential settlement,susceptibility to strength loss and collapse upon wetting.Because of these characteristics,some of the roads constructed on saline soils in Taleghan area have exhibited deterioration in the form of raveling,cracking and landslides.The main objective of this work is to improve the load-bearing capacity of pavements constructed on Taleghan saline soils using lime and micro silica.Soil samples from Hashtgerd-Taleghan road were collected and tested for improving their properties using lime and micro silica at different dosages ranging from 0 to 6%.The load-bearing capacity of stabilized soil mixtures was evaluated using California Bearing Ratio(CBR) and unconfined compressive strength tests.The test results indicate that the lime improves the performance of soil significantly.The addition of 2% lime with 3% micro silica has satisfied the strength-deformation requirements.Therefore,improved soil can be used as a good subbase in flexible pavements.

Effects of nanobubble and hydrodynamic parameters on coarse quartz flotation

Quartz, the second most abundant mineral in the earth's crust, is a gangue mineral in practically every flotation process. Coarse quartz flotation has been a long standing problem in various mineral processing plants to reduce milling cost and increase valuable mineral recovery. Based on this, the effects of nanobubbles(NBs) and hydrodynamic parameters on coarse quartz particle flotation were systematically investigated. Mechanical flotation experiments were carried out using the 7 cm and 9 cm diameter impellers in order to produce different hydrodynamic conditions. 900–1300 rpm impeller speeds were used for the 7 cm diameter impeller and 554–786 rpm for the 9 cm diameter impeller. The results show that the presence of NBs increased the flotation recovery of à425 + 106 lm quartz by up to 21%. For the7 cm diameter impeller, the maximum flotation recoveries of 86.4% and 98% were obtained in the absence and presence of NBs at Reynolds number(Re) of 81,000 and 66,000, respectively. For the 9 cm diameter impeller, the maximum recoveries of 86.3% and 97.5% were obtained in the absence and presence of NBs at Re of 90,000 and 75,000, respectively. NBs increased the flotation rate constant up to 36%.

3D finite elements analysis of vertically loaded composite piled raft

In recent years,a new type of foundation named composite piled raft foundation (also called long short composite piled raft) has been developed.Where designing shallow foundations would mean unacceptable settlement,or other environmental risks exist which could impair the structure in the future,composite piled raft foundations could be used.Finite element method was applied to study the behavior of this type of foundation subjected to vertical loading.In order to determine an optimal pile arrangement pattern which yields the minimum settlement,various pile arrangements under different vertical stress levels were investigated.Results show that with increasing the vertical stress on the raft,the effectiveness of the arrangements of short and long piles become more visible.In addition,a new factor named "composite piled raft efficiency" (CPRE) has been defined which determines the efficiency of long short piles arrangement in a composite piled raft foundation.This factor will increase when short piles take more axial stresses and long piles take less axial stresses.In addition,it is found that the changes in settlements for different long short piles arrangement are in a well agreement with changes in values of CPRE ratio.Thus,CPRE ratio can be used as a factor to determine the efficiency of piles arrangements in composite piled raft foundation from the view point of reducing raft settlements.

Bearing capacity and settlement of strip footing on geosynthetic reinforced clayey slopes

The effect of geosynthetic reinforcing on bearing capacity of a strip footing resting on georeinforced clayey slopes was investigated.The results of a series of numerical study using finite element analyses on strip footing upon both reinforced and unreinforced clayey slopes were presented.The objectives of this work are to:1) determine the influence of reinforcement on the bearing-capacity of the strip footings adjacent slopes,2) suggest an optimum number of reinforcement and 3) survey the effect of friction angle in clayey soils reinforced by geogrids.The investigations were carried out by varying the edge distance of the footing from slope.Also different numbers of geosynthetic layers were applied to obtaining the maximum bearing capacity and minimum settlement.To achieve the third objective,two different friction angles were used.The results show that the load?settlement behavior and ultimate bearing capacity of footing can be considerably improved by the inclusion of reinforcing layer.But using more than one layer reinforcement,the ultimate bearing capacity does not change considerably.It is also shown that for both reinforced and unreinforced slopes,the bearing capacity increases with an increase in edge distance.In addition,as the soil friction angle is increased,the efficiency of reinforcing reduces.

Tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe and Si

This study was undertaken to investigate the tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe(up to 1.5 wt%)and Si(up to 2.5 wt%).According to the results,the optimum tensile properties and hot tearing resistance were achieved at Fe/Si mass ratio of 1,where theα-Fe phase was the dominant Fe compound.Increasing the Fe/Si mass ratio above unity increased the amounts of detrimentalβ-Cu Fe platelets in the microstructure,deteriorating the tensile properties and hot tearing resistance.Decreasing the mass ratio below unity increased the size and fraction of Si needles and micropores in the microstructure,also impairing the tensile properties and hot tearing resistance.The investigation of hot-torn surfaces revealed that theβ-Cu Fe platelets disrupted the tear healing phenomenon by blocking interdendritic feeding channels,while theα-Fe intermetallics improved the hot tearing resistivity due to their compact morphology and high melting point.

Al-7Si-0.35Mg-xCu合金的品质系数和热裂敏感性（英文）

研究铜添加量(0.5%、1%、1.5%、2%、3%,质量分数)对A356合金的品质系数(Q_i)和热裂敏感性(HTS)的影响。结果显示,当铜添加量达到1.5%时,Q_i增加了约10%,这可能是由于富铜的Al_2Cu相和AlMgCuSi化合物的固溶强化和弥散硬化。然而,继续提高Cu添加量到3%,Q_i反而降低了近12%,这很可能是因为显微组织中脆性富Cu金属间化合物和微孔体积的增加导致抗拉强度和伸长率降低。用约束杆铸造法测试A356合金的热裂敏感性,结果显示随着铜含量的增加,其HTS也增加。热分析结果表明,铜拓宽了合金的凝固范围,进而降低了其流动性,增加了糊状合金暴露在热裂易感区的时间。高铜合金热裂表面的SEM也表明,其表面粗糙,且存在枝晶间/晶粒间微裂纹,这也证明了在凝固后期,合金萌生了热裂,没有足够的裂纹修复时间。

等径角挤压7075铝合金的显微组织和织构演变（英文）

等径角挤压是一种有效的控制金属和合金显微组织和织构的技术。采用X射线衍射仪和取向成像显微镜评价通过90°模具反复等径角挤压7075铝合金的显微组织和织构。定性和定量分析结果表明,不同的路径会产生不同的织构类型。利用Labotex软件计算的织构表明,经第1道次等径角挤压后合金织构增强,而经第4道次挤压后合金织构减弱。显微组织研究表明,经过Bc和A路径等径角挤压4道次后,出现了平均尺寸分别为700 nm和1μm的细小晶粒,且大多数晶粒演化为大角度晶界排列。研究了铜管包覆对7075铝合金显微组织和织构的影响。

Fe杂质对Al-15Mg_2Si复合材料摩擦性能的影响（英文）

研究了Fe杂质(0.2%~2%,质量分数)对Al-15Mg_2Si复合材料的显微组织、干滑动磨损和摩擦性能的影响。摩擦实验采用销盘式试验机,压力分别为0.25、0.5和1 MPa,固定滑动速度为0.13 m/s。结果显示,Fe使初始Mg_2Si颗粒从不规则枝晶状转变为多面体形状的较小颗粒,细化伪共晶结构,并导致基体中形成硬质相β-Al_5Fe Si片晶。尽管这些显微组织的变化提高了复合材料的硬度,但其抗干滑动磨损的能力却受到了损害。磨损表面、磨屑和下表层的SEM结果证实了β相对摩擦学性能的不利影响。β相颗粒较易断裂,从而降低基体抗滑动应力的能力,造成摩擦层的不稳定,使其易剥离,形成大的剥落碎片。摩擦实验结果还表明,Fe降低材料的平均摩擦因数,但增加摩擦因素的波动。

多道次搅拌摩擦加工改善传统铸造Al−8.5Fe−1.3V−1.7Si合金的摩擦学性能

研究多道次搅拌摩擦加工(FSP)对传统铸造Al−8.5Fe−1.3V−1.7Si(FVS0812)合金摩擦学性能的影响。分别在0.25、0.50、和0.75 MPa的载荷下,于室温下进行销−盘式干滑动磨损实验。结果表明,FSP大幅细化合金显微组织中粗大的θ-Al_(13)Fe_(4)片状晶和α-Al_(12)(Fe,V)_(3)Si金属间化合物,改善其分布,并消除金属间化合物相关的缺陷,从而提高合金的力学性能,特别是其延展性,进而提高在其磨损表面形成的摩擦保护层的稳定性。磨损实验结果表明,经FSP的复合材料其摩擦学性能得到改善,尤其是在较高的外加载荷下。例如,当载荷为0.75 MPa时,与铸态样品相比,经四道次FSP的样品其磨损率和平均摩擦因数分别降低97%和52%。磨损表面和磨屑的扫描电镜分析表明,铸态样品的磨损机制为摩擦层严重的剥层/磨粒磨损和微裂纹,FSP态样品的磨损机制为轻度的剥层/磨粒磨损和轻微的塑性磨损。

多道次多向锻造对富硅共析ZA合金摩擦性能的影响

研究多道次多向锻造(MDF)对ZA22−xSi(x=0,4,8,质量分数,%)合金摩擦性能的影响。结果表明,MDF破坏合金的铸造组织,形成由细小分布的α相和η相,以及原始Si颗粒组成的显微组织。研究还发现,尽管基体出现加工软化,多向锻造ZA22−xSi合金仍具有较高的耐磨性。经5道次多向锻造的ZA22−4Si合金具有最高的耐磨性能,当外加载荷为10和30 N时,其磨损率分别比铸态ZA22合金的低80%和75%。MDF也显著降低样品的平均摩擦因数和摩擦因数波动。摩擦性能提高的主要因素有:基体具有较高的抗微裂纹能力,硬质Si增强相的形成,显微组织中细小的α相和η相再分布,以及富Al和Zn氧化物摩擦层。

3D Modeling and Determination of Factors Responsible for Zinc-Lead Mineralization in the Mehdiabad Deposit,Central Iran,based on Statistical Analysis of Geochemical Data

Although the Mehdiabad zinc-lead deposit is one of the most well-known deposits in the central Iran structural zone,the genesis of the deposit remains controversial.The host rock of the ore is a dolomitic limestone of the Lower Cretaceous Taft Formation.In the two main orebodies of the deposit,which includes the Black Hill and East Ridge ore zones,the oxide and sulfide ores are observed at the surface and at depth,respectively.The elements Zn,Fe,Mn and Mg are more abundant in the East Ridge ore zone(in both sulfide and oxide ores),with Ba,Pb,Ag and Cu being more abundant in the Black Hill oxide ore.Based on the distribution of elements and their correlation with each other in these ore zones,the elements are divided into three general groups,that of terrigenous elements,chemically-deposited elements and oreforming(hydrothermally deposited)elements,a division that is supported by the results of factor analyses.The spatial distribution of elements is jointly affected by contact with host rocks,the boundary of oxide-sulfide ores and fault zones.The main factors governing the distribution of elements are the mechanical transfer of detrital sediments,chemical sedimentation,transfer by hydrothermal fluids,oxidation and surface dissolution,all of which affected the spatial distribution of elements.The ore-forming elements are mostly affected by hydrothermal fluids and oxidation.This study not only provides additional information about the genesis of the Mehdiabad deposit,but also could assist in the exploitation of ore and further exploration purposes.The results of this study can aid in the exploration and exploitation of the Mehdiabad deposit and similar deposits in the region.

Introduction of table sugar as a soft second template in ZSM-5 nanocatalyst and its effect on product distribution and catalyst lifetime in methanol to gasoline conversion

Methanol to gasoline reaction was investigated on two prepared ZSM-5 catalysts. The first one was a conventional catalyst denoted as ZSM-5（C） and the other was a hierarchical catalyst-ZSM-5（S） which was prepared by incorporation of table sugar in catalyst gel during the synthesis procedure. The catalysts were characterized by FTIR, XRD, FE-SEM, N2 adsorption-desorption, NH3-TPD and TGA analytical technics. The proposed material showed pore modification as well as acidity moderating properties in ZSM-5 catalyst. The methanol to gasoline reaction was conducted in a fixed bed reactor with a WHSV of 1.5 h-1.Methanol conversions, gasoline yield and selectivity in production for the synthesized catalysts were determined by gas chromatography method. The sugar modified catalyst converted more methanol than the conventional one and an enhancement in catalyst’s life time was observed. The selectivity to aromatics and durene were reduced compared to the conventional catalyst, so the gasoline quality was also further improved. The coking rate of catalysts was calculated employing TGA method. A reduction in coking rate and an increase in coke capacity of the modified catalyst were observed.