Interfacial behavior of a thermoelectric film bonded to a graded substrate

To improve the thermoelectric converting performance in applications such as power generation,reutilization of heat energy,refrigeration,and ultrasensitive sensors in scramjet engines,a thermoelectric film/substrate system is widely designed and applied,whose interfacial behavior dominates the strength and service life of thermoelectric devices.Herein,a theoretical model of a thermoelectric film bonded to a graded substrate is proposed.The interfacial shear stress,the normal stress in the thermoelectric film,and the stress intensity factors affected by various material and geometric parameters are comprehensively studied.It is found that adjusting the inhomogeneity parameter of the graded substrate,thermal conductivity,and current density of the thermoelectric film can reduce the risk of interfacial failure of the thermoelectric film/graded substrate system.Selecting a stiffer and thicker thermoelectric film is advantageous to the reliability of the thermoelectric film/graded substrate system.The results should be of great guiding significance for the present and upcoming applications of thermoelectric materials in various fields.

Peridynamic Study on Fracture Mode and Crack Propagation Path of a Plate with Multiple Cracks Subjected to Uniaxial Tension

How to simulate fracture mode and crack propagation path in a plate with multiple cracks is an attractive but difficult issue in fracture mechanics.Peridynamics is a recently developed nonlocal continuum formulation that can spontaneously predict the crack nucleation,branch and propagation in materials and structures through a meshfree discrete technique.In this paper,the peridynamic motion equation with boundary traction is improved by simplifying the boundary transfer functions.We calculate the critical cracking load and the fracture angles of the plate with multiple cracks under uniaxial tension.The results are consistent with those predicted by classical fracture mechanics.The fracture mode and crack propagation path are also determined.The calculation shows that the brittle fracture process of the plate with multiple cracks can be conveniently and correctly simulated by the peridynamic motion equation with boundary conditions.

Revisiting the peridynamic motion equation due to characterization of boundary conditions

The peridynamic motion equation was investigated once again.The origin of incompatibility between boundary conditions and peridynamics was analyzed.In order to eliminate this incompatibility,we proposed a new peridynamic motion equation in which the effects of boundary traction and boundary displacement constraint were introduced.The new peridynamic motion equation is invariant under the transformations of rigid translation and rotation.Meanwhile,it also satisfies the requirements of total linear and angular momentum equilibrium.By this motion equation,three kinds of boundary value problems containing the displacement boundary condition,the traction boundary condition and mixed boundary condition are characterized in peridynamics.As examples,we calculated static tension and longitudinal vibration of a finite rod.The acquired solutions exhibit obvious nonlocal features,and the vibration has the dispersion similar to one dimensional atom chain vibration.

Geometric effects of cross sections on equilibrium of helical and twisted ribbon

In the framework of elastic rod model, the Euler-Lagrange equations characterizing the equilibrium configuration of the polymer chain are derived from a free energy functional associated with the curvature, torsion, twisting angle, and its derivative with respect to the arc-length. The configurations of the helical ribbons with different crosssectional shapes are given. The effects of the elastic properties, the cross-sectional shapes,and the intrinsic twisting on the helical ribbons are discussed. The results show that the pitch angle of the helical ribbon decreases with the increase in the ratio of the twisting rigidity to the bending rigidity and approaches the intrinsic twisting. If the bending rigidity is much greater than the twisting rigidity, the bending and twisting of the helical ribbon always appear simultaneously.

A Possible Reason About Origin of Singularity and Anomalous Dispersion in Peridynamics

In the benchmark problems of peridynamics,there are some eccentric results,for example,singularity of uniaxial tension and anomalous dispersion of wave.The reasons to give rise to these results are investigated.We calculated local tension and wave of an infinite rod after adding a divergence of local stress in the peridynamic motion equation.The acquired results verify that the singularity in the peridynamic solution of local tension problem and anomalous dispersion of peridynamic wave are all eliminated.Therefore,the anomalous features of some peridynamic solutions likely stem from the lack of local stress characterizing contact interactions.

The singularity in the state-based peridynamic solution of uniaxial tension

We solve the local uniaxial tension of an infinite rod in the framework of non-ordinary state-based peridynamics.The singular solutions of stress and displacement are acquired.When the influencing range of the window function approaches zero,these two solutions will return to the solutions of the classical elasticity.The analysis shows that the singularities of the solutions stem from such a feature of the window function that must be represented by a rapidly decreasing function in physics.Contrary to the classical elasticity,the stress solution of peridynamics is smoother than the displacement solution.In addition,a criterion used to select the window function is proposed in this paper.

Removal of ions from produced water using Powder River Basin coal

In addition to being used as an energy source,coal also has significant potential for other,more sustainable uses including water treatment.In this study,we present a simple approach to treat water that was produced during oil production and contained a total dissolved solids(TDS)content of over 150 g/L using Powder River Basin(PRB)coal.PRB coal used as packing material in a flow-through column effectively removed 60%–80%of the cations and anions simultaneously.Additionally,71%–92%of the total organic carbon in the produced water was removed as was all of the total suspended solids.The removal mechanisms of both cations and anions were investigated.Cations were removed by ion exchange with protons from oxygen-containing functional groups such as carboxylic and phenolic hydroxyl groups.Anions,mainly Cl−1,appeared to be removed through either the formation of resonance structures as a result of delocalization of electrons within coal molecules or through ion–πinteractions.We propose that coal is a“pseudo-amphoteric”exchange material that can remove cations and anions simultaneously by exchanging ions with both ionized and non-ionized acids that are ubiquitous in coal structure or resonance effect.

巨菌草不同生长时期对砒砂岩地区土壤理化性质及细菌群落结构的影响

【目的】揭示巨菌草种植前及其不同生长时期对砒砂岩地区土壤基本理化性质及细菌群落结构的影响,为更好应用巨菌草改良砒砂岩地区土壤提供理论依据。【方法】运用IlluminaMiSeq高通量测序技术,在门、属水平上比较砒砂岩地区巨菌草不同生长时期对土壤细菌结构及多样性的影响。【结果】巨菌草种植后,三块样地的含水量在巨菌草分蘖期最低,在成熟期达到最高,土壤有机含量有所增加,土壤pH值变化不明显。细菌菌群结构:各样地的土壤细菌在巨菌草种植前及其生长的四个时期,门水平上的优势菌群均为放线菌门(Actinobacteria)、变形菌门(Proteobacteria);在属水平上,含量最高的是未分类(unidentified)的细菌。Alpha多样性及群落组成丰度分析表明,三块样地种植巨菌草后,其细菌多样性和物种丰度均比种植前高,农田地土壤细菌多样性和物种丰度在巨菌草拔节期达到峰值,在分蘖期土壤细菌数量最大,比种植前土壤细菌数量高出8倍多,达2.09×107 CFU/g干土,山顶地土壤细菌多样性和物种丰度在巨菌草分蘖期达到峰值,河滩地土壤细菌多样性在巨菌草苗期达到峰值,其丰富度在拔节期达到最大。【结论】砒砂岩地区土壤细菌群落结构在巨菌草不同生长时期相似,巨菌草能明显促进砒砂岩地区土壤细菌菌群多样性和丰富度,能有效提高土壤有机质含量,但砒砂岩地区各样地土壤细菌多样性、数量和有机质含量达到峰值的时期不同。

典型生境巨菌草根内生固氮菌的群落多样性

【目的】探究不同生境巨菌草内生固氮菌群落组成多样性及其分异规律。【方法】采用高通量测序固氮酶nif H标靶基因方法,研究了我国6个典型地区的巨菌草内生固氮菌群,包括福建闽侯县、新疆墨玉县、内蒙古阿拉善左旗、青海贵德县、甘肃安定区、海南那大镇,结合地理气候因子统计,分析了固氮菌多样性的环境驱动机制。【结果】共获得64122条nif H基因的有效序列,640个OTUs,归属于6个门、10个纲、17个目、24个科、33个属和39个种。不同地区巨菌草中优势内生固氮菌群的种类和丰度存在较大的差异。在门水平上,福州闽侯县、甘肃安定区、新疆墨玉县、内蒙古阿拉善左旗和青海贵德县5个地区的优势菌门均为变形菌门,海南那大镇的优势菌门为变形菌门和蓝藻菌门;属水平上,不同地区巨菌草最优势内生固氮菌类群分别为:福州闽侯县(变形菌门中未定属,80.56%);新疆墨玉县(变形菌门中未定属,33.14%);内蒙古阿拉善左旗(变形菌门中未定属,76.23%);甘肃安定区(α-变形菌纲中的未定属,53.78%);海南那大镇(变形菌门中未定属,38.37%);青海贵德县(变形菌门中未定属,46.12%)。Alpha多样性和Beta多样性分析表明,不同地区巨菌草内生固氮菌群落的多样性存在较大的差异,海南那大镇样本中巨菌草各类内生固氮菌群的多样性及丰富度最高,福建闽侯县样本中巨菌草各类内生固氮菌群的多样性及丰富度最低。典范对应分析(CCA)结果表明,年均降雨量和年均气温是影响巨菌草内生固氮菌群变化的主要因素,其次是土壤有机质、土壤全氮和土壤p H。【结论】不同地区巨菌草内生固氮菌群落的组成及丰度存在着较大的差异,海南那大镇巨菌草内生固氮菌群的种类及相对丰度较高,本研究可为巨菌草内生固氮菌群的资源开发及其固氮微生物肥料的菌种选育和生产应用提供理论支持。

大柳塔长焰煤中灰分和无机矿物对生物产气的影响

【目的】以不同密度等级大柳塔长焰煤作为产气底物,前期驯化培养厌氧菌群进行生物模拟产气实验,研究不同密度等级煤中的灰分和无机矿物对生物产气的影响。【方法】利用小浮沉将大柳塔长焰煤分成不同密度等级的煤样,采用工业分析、XRD、XRF分析小浮沉处理得到煤样的理化性质,利用这些煤样进行生物产气模拟实验,以甲烷产量作为评价指标,分析不同密度等级煤样中灰分对产气的影响。最后,通过添加几种标准矿物方式比较了煤中无机矿物对生物产气的可能影响。【结果】不同密度等级煤样中灰分对产气量存在一般显著影响(P=0.035),且灰分与甲烷含量呈负相关关系,其灰分中的无机矿物如高岭土、菱铁矿、氧化亚铁镁等的积累对产气有抑制作用。不同矿物配比产气实验证实低含量的粘土矿物促进甲烷的生成,高含量的粘土矿物抑制产气。【结论】不同密度等级煤中的灰分对生物产气存在一般显著的影响,高灰分煤的产气量低,而低灰分煤的产气量高。

基于转录组测序的姬松茸镉胁迫下内参基因筛选

【目的】筛选不同实验条件下,尤其是镉胁迫下的姬松茸内参基因,为研究姬松茸镉富集相关基因功能研究奠定基础。【方法】根据不同浓度Cd(0、2、5 mg/L)胁迫下菌丝中转录组表达量数据,筛选出18个候选基因,设计了30对引物;根据引物扩增的特异性、扩增效率初步筛选出来自不同基因的5对引物;运用qRT-PCR检测了5个基因在不同浓度Cd胁迫下的菌丝样品、原基、菌柄和菌盖中的Ct值,利用geNorm、NormFinder和BestKeeper对这些基因的表达稳定性进行评价。【结果】SGT2和STK是菌丝阶段Cd胁迫下最稳定的2个候选内参基因,GAPDH是不同组织中最稳定的内参基因,SGT2、STK和GAPDH是所有实验条件下最稳定的3个内参基因。【结论】在姬松茸镉胁迫条件下,本研究筛选出的SGT2和STK比常用的内参基因表现出更强的稳定性。

Coal and coal byproducts:A large and developable unconventional resource for critical materials—Rare earth elements

Rare earth elements(REEs) are critical materials and provide significant values to national security,energy production, environmental protection and economic growth. The supply of REEs in U.S. solely relies on import as domestic production of REEs was ceased because of the environmental concerns during mining and lack of competitiveness. Nonetheless, unconventional REEs-containing resources,including produced water. acid mine drainage, and coal and coal byproducts(C&CBs) contain significant amounts of REEs. However, the concentrations of REEs in these resources are several orders of magnitude lower than that of REEs ores. Thus, extraction of REEs from these materials is challenging. Here we report REEs extraction with environmentally friendly method that successfully concentrated REEs from312 ppm in fly ash to 99.4% in the final product. Especially, the five critically important REEs(Dy, Eu, Nd.Tb. and Y) account for up to ～63% of the total weight of all REEs in the final 99.4%-purity product. Coal fly ash is one of the major solid coal utilization byproducts, representing great potential resources for REEs extraction. Extraction of REEs from these unconventional resources could be the way to secure domestic supply of these critical materials.

Rare earth elements of fly ash from Wyoming’s Powder River Basin coal

The advancement and increasing interests in green energy production and environmental protection technologies have spurred the demand for rare earth elements.On the other hand,the U.S.has to rely 100% on import of these materials as the industry was crashed because of the environmental issues associated with mining and processing,and more importantly lack competitiveness.As rare earth elements have many applications in defense and national security sectors,some of the elements were listed as strategic materials or critical materials because of the uncertainties in supply and prices.Therefore,it has become imperative in searching for alternative resources for supplying rare earth elements including unconventional resources.With the strong incentive,coal fly ash is identified as one of the candidates among them.In this study,we present rare earth element data for the 42 ash samples(all derived from Powder River Basin coal) that we collected from seven states(UT,WY,10,WI,ND,CO,and MI) representing 158 million tons of fly ash.The results indicate scattered distributions of rare earth elements with concentration ranging from 156 to 590 ppm although all the ash samples originated from the same coal basin(Powder River Basin).The rare earth element resource in these ashes is estimated between 74000 and 106000 t.The ash samples were also characterized by elemental analysis,XRD,SEM-EDS and BET surface area.The characterizations of the ashes were discussed as they might have implications in the subsequent rare earth element extraction processes.In summary,fly ash may represent a potential resource for rare earth element production.