THE EXISTENCE AND UNIQUENESS OF TIME-PERIODIC SOLUTIONS TO THE NON-ISOTHERMAL MODEL FOR COMPRESSIBLE NEMATIC LIQUID CRYSTALS IN A PERIODIC DOMAIN

In this paper,we are concerned with a three-dimensional non-isothermal model for the compressible nematic liquid crystal flows in a periodic domain.Under some smallness and structural assumptions imposed on the time-periodic force,we establish the existence of the time-periodic solutions to the system by using a regularized approximation scheme and the topological degree theory.We also prove a uniqueness result via energy estimates.

Performance enhancement mechanism of Mn-based catalysts prepared under N_2 for NO_x removal:Evidence of the poor crystallization and oxidation of MnO_x

Among multitudinous metal‐oxide catalysts for the selective catalytic reduction of NOx with NH3(NH3‐SCR),Mn‐based catalysts have become very popular and developed rapidly in recent years because of its superior low‐temperature denitrification activity,mainly originating from multi‐valence of Mn.Most studies suggest that the catalytic activity of multi‐component oxides is superior to that of single‐component catalysts owing to the synergistic effect among the metallic elements in such materials,of which more attentions have been given to Ce as an additive owing to its powerful oxygen storage capacity,redox ability and its ready availability.As the core of SCR technology,the research points in catalyst development at the present stage of all researchers in countries mainly centralize on the optimization of active components,carriers,calcination temperature,calcination time and temperature‐raising procedure,giving little thought to the effects of the calcination atmosphere.In the present work,Ce‐modified Mn‐based catalysts were prepared by a simple impregnation method.The effects of the calcination atmosphere(N2,air or O2)on the performance of the resulting materials during NH3‐SCR and its causes of the differences were subsequently investigated and characterized using various analytical methods.Data obtained from X‐ray diffraction,thermogravimetry and temperature‐programmed reduction with hydrogen show that calcination under N2reduces both the degree of oxidation and crystallization of the MnOx.Scanning electron microscopy also demonstrates that the use of N2inhibits the growth of grains and increases the dispersion of the catalysts.In addition,the results of temperature‐programmed desorption with ammonia indicate that catalysts calcined under N2exhibit a greater quantity of acid sites.Finally,X‐ray photoelectron spectrometry and activity results demonstrate that MnOx in the lower valence states is more favorable for NH3‐SCR reactions.In conclusion,catalysts calcined under N2show superior performance during NH3‐SCR for NOx removal,allowing NO conversions up to94%at473K.

Study of the near-field modulation property of microwaviness on a KH_2PO_4 crystal surface

The KH2PO4 crystal is a key component in optical systems of inertial confinement fusion （ICF）. The microwaviness on a KH2PO4 crystal surface is strongly related to its damage threshold which is a key parameter for application. To study the laser induced damage mechanism caused by microwaviness, in this paper the near-field modulation properties of microwaviness to the incident wave are discussed by the Fourier modal method. Research results indicate that the microwaviness on the machined surface will distort the incident wave and thus lead to non-uniform distribution of the light intensity inside the crystal; in a common range of microwaviness amplitude, the light intensity modulation degree increases about 0.03 whenever the microwaviness amplitude increases 10 nm; 1 order diffraction efficiencies are the key factors responsible for light intensity modulation inside the crystal; the light intensity modulation is just around the microwaviness in the form of an evanescent wave, not inside the crystal when the microwaviness period is below 0.712μm; light intensity modulation degree has two extreme points in microwaviness periods of 1.064μm and 1.6μm, remains unchanged between periods of 3μm and 150μm, and descends above the period of 150μm to 920μm.

A direct laser-synthesized magnetic metamaterial for low-frequency wideband passive microwave absorption

Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.

Three Stages of Zircon Growth in Magmatic Rocks from the Pingtan Complex,Eastern China

Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.

The influence of fractionation of REE-enriched minerals on the zircon partition coefficients

Zircon is widely used to simulate melt generation,migration and evolution within the crust and mantle.The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients(D).However,a large range of D_(REE) values for zircon from natural samples and experimental studies has been reported,with values spanning up to 3 orders of magnitude.Unfortunately,a gap of knowledge on this variability is evident.In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon D_(REE) would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon.Nevertheless,compared to zircon D_(REE) values measured from experimental studies,this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon.Combined with recently published studies,this work supports that analysis of natural zircon/host groundmass pairs provides more robust D_(REE) values applicable to natural systems than those measured from experimental studies,which can be used to constrain the provenance of detrital zircons.

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin

In this study,element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag,Zhujiang River Mouth Basin.The experimental results are discussed with respect to weathering conditions,parent rock lithologies,and provenances.The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering.Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements,"V"-shaped negative Eu anomalies,and negligible Ce anomalies.The rare earth element distribution curves are obviously right-inclined,with shapes and contents similar to those of post-Archean Australian shale and upper continental crust,indicating that the samples originated from acid rocks in the upper crust.The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area.For the samples from the upper Enping deltas,the overall age spectrum shows four major age peaks ca.59–68 Ma,98–136 Ma,153–168 Ma and 239–260 Ma.For the Zhuhai Formation samples,the overall age spectrum shows three major age peaks ca.149 Ma,252 Ma and 380 Ma.The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation,the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances:Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift,and the former supply became stronger through time.Thus,the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.

Zircon U-Pb-Hf isotopes and mineral chemistry of Early Cretaceous granodiorite in the Lunggar iron deposit in central Lhasa, Tibet Y, China

The Lunggar iron deposit belongs to the Bangong-Nujiang metallogenic belt and is located in central Lhasa on the Tibetan Plateau.In the Lunggar deposit,iron mineralization formed in the skarnization contact zone between the Early Cretaceous granodiorite and the late Permian Xiala Formation limestone.In this study,we achieved detailed zircon U-Pb-Hf isotopes and mineral chemistry for the Early Cretaceous granodiorite.Zircon U-Pb dating results indicate that the Early Cretaceous granodiorite emplaced at ca.119 Ma.Based on the trace elements in zircons and the mineral chemical composition of amphibole and biotite,the Early Cretaceous granodiorite was believed to form under condition of high temperature(>700°C),low pressure(100400 MPa),and relatively high oxygen fugacity(lgfO2)(13.6 to 13.9)and H2O content(4%8%).Zircon trace elements,Hf isotope and biotite chemistry collectively reveal that significant juvenile mantle-derived magmas contributed to the source of the granodiorite.The relatively high logfO2 and shallow magma chamber are beneficial for skarn iron mineralization,implying remarkable potential for further prospecting in the Lunggar iron deposit.

Electrical Conduction in Deuterated Ammonium Dihydrogen Phosphate Crystals with Different Degrees of Deuteration

Conductivity measurements of deuterated ammonium dihydrogen phosphate （DADP） crystals with different deuterated degrees are described. The conductivities increase with the deuterium content, and the value of the a-direction is larger than that of the e-direction. Compared with DKDP crystals, DADP crystals have larger conductivities, which is partly due to the existence of A defects. The ac conductivity over the temperature range 25-170℃has shown a knee in the curve ofln（σT） versus T-1. The conductivity activation energy calculated by the slope of the high temperature region decreases with the deuterium content. The previously reported phase transition is not seen.

Optimization of Parameters for Melt Crystallization of p-Cresol

Laboratory-scale experiments were carried out to evaluate the influences of operational parameters on the melt crystallization efficiency for p-cresol purification.The optimal crystallization conditions were determined:dynamic pulsed aeration at 90 L·h-1 and the cooling rate of 0.6-0.8 ℃·min-1,followed by sweating at 0.2-0.3 ℃·min-1 for 40 min.Results also demonstrate that the melt crystallization efficiency is sensitive to feed concentration,which highlights this technology for separation and purification of high purity products.

Characteristic Features and U-Pb Isotopic Ages of Zircons in a Middle Proterozoic Granite Pluton from Baoban Area, Hainan Province, China

The crystal form,chemical composition and U-Pb isotopic composition of various zircon fractions is a Middle Proterozoic granite pluton from the Baoban area suggest that the zircons are typically magmatogenic in nature,and different from those of sedimentary and epigenetic orgins.The various zircon fractions yielded and age of about 1440.87Ma,which may represent the ge of zircon crystallization.The so-called aoban-group migmatite is,as a matter of fact,a Middle Proterozoic granite pluton.

组成对钠铝硅玻璃中钇锆酸盐纳米晶析晶性能的影响

基于含Y2O_(3)和ZrO_(2)的钠铝硅玻璃体系,研究了玻璃组分中Al_(2)O_(3)/Na2O摩尔比值(MAN)与SiO_(2)/Al_(2)O_(3)摩尔比值(MSA)对玻璃析晶性能的影响。研究结果表明,当MAN<1时,玻璃经热处理后表面析出钠霞石晶体;当MAN≥1时,玻璃热处理后析出钇锆酸盐纳米晶体,且此时微晶玻璃仍然具有不小于90%的高可见光透过率。对于固定MAN的玻璃,调整其MSA也能实现钇锆酸盐纳米晶的析出,且析出晶体尺寸随MSA增加而减小。随着热处理温度升高微晶玻璃样品中纳米晶体尺寸增大,维氏硬度也增大。

Genesis of the mega-crystal zircons in the dunite veins of North Qaidam Mountains,northwestern China

A megacrystal zircon occurs in serpentinized dunite veins from North Qaidam, northwestern China. It is red-brown and 3―4 mm long and 2 mm wide in size. BSE imaging shows the presence of micro-grains (30―50 μm) of zircon between olivine and serpentine, part of them gathering into clusters (100―300 μm). Thus we infer that these zircon crystals were precipitated from hydrothermal fluid. Inclusions of baddeleyite (white) in the shape of isolated island locally occur in the large zircon (grey), implying that the former formed earlier than the latter. The mirco-baddeleyite (50―100 μm) aggregate consists of baddeleyite (3―5 μm) and olivine (<5 μm), indicating the zircon formation through interaction between baddeleyite and silica-bearing fluid. Therefore, we consider a genetic link between the formation of the large zircon and the serpentinization of dunite. SHIRIMP U-Pb dating of the large zircon gave two groups of concordant ages at 414 ± 13 Ma and 371 ± 9 Ma, respectively. This might reflect two episodes of zircon growth in response to two episodes of fluid action.

海南岛抱板岩群的形成时代及其大地构造意义

抱板岩群(原称抱板群)是目前海南岛发现的最古老的前寒武纪结晶基底,经历了多期构造热事件的改造,是研究海南(海南岛)地块大地构造属性及块体划分的重要载体。在总结前人已有研究成果的基础上,本文对海南岛东方市抱板地区抱板岩群混合岩及后期侵入的花岗岩、基性岩开展了SHRIMP和LA-ICP-MS锆石U-Pb年代学研究,厘定了抱板杂岩的形成时代、经历的构造热事件,并探讨其所代表的大地构造意义。根据岩石组合特征,本文将抱板岩群进一步划分为戈枕村岩组和峨文岭岩组,二者均被晚期花岗质和基性岩浆侵入,它们一起构成了抱板杂岩。锆石年代学结果表明:戈枕村岩组形成时代应介于1480~1440 Ma之间,峨文岭岩组形成时代介于1460~1430 Ma之间,片麻状花岗岩侵入时代为1450~1430 Ma,基性岩侵入时代为1425~1410 Ma。抱板岩群在中元古代早中期经历了花岗岩侵入、混合岩化作用、基性岩侵入等多期构造热事件的改造,中元古代晚期-新元古代早期经历了与罗迪尼亚超大陆汇聚有关的构造热事件。区域上块体对比分析表明,海南地块与越南昆嵩地块具有相似的前寒武纪结晶基底组成及多期构造热事件记录,显示二者具有亲缘关系。

低成本二代镍基单晶高温合金的研究进展

镍基单晶高温合金因其优异的高温力学性能,目前已广泛应用于制备航空发动机中的单晶涡轮叶片。Re元素的添加在显著提高单晶高温合金蠕变性能的同时,也显著增加了合金的成本。因此,研发新型低Re含量(低成本)和蠕变性能优异的单晶高温合金具有重要的意义。本文对比了几种低成本二代单晶高温合金与典型二代单晶高温合金CMSX-4的中温与高温蠕变性能,并从γ相和γ'相的固溶强化程度、γ/γ'错配度和有效扩散系数三个参量,探讨了二代单晶高温合金中温与高温蠕变性能的主控因素,发现高温蠕变性能的主控因素是γ相的固溶强化程度与γ/γ'错配度,而中温蠕变性能的主控因素是γ'相的固溶强化程度。以此为基础,提出了低成本二代单晶高温合金的成分设计策略。

Temperature of Prograde Metamorphism, Decompressional Partial Melting and Subsequent Melt Fractional Crystallization in the Weihai Migmatitic Gneisses,Sulu UHP Terrane:Constraints from Ti-in-Zircon Thermometer

In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic gneisses from the Weihai region in the Sulu ultra-high pres- sure （UHP） metamorphic terrane, eastern China. The Weihai migmatitic gneisses are composed of in- tercalated compositional layers of melanosome and plagioclase （Pl）-rich lencosome and K-feldspar （Kfs）-rich pegmatite veins. Four stages of zircon growth were recognized in the Weihai migmatitic gneisses. They successively recorded informations of protolith, prograde metamorphism, decompres- sional partial melting during early stage exhumation and subsequent fractional crystallization of pri- mary melt during later stage cooling exhumation. The inherited cores in zircon from the melanosome and the Pl-rich leucosome suggest that the pro- tolith of the migmatitic gneiss is Mid- Neoproterozoic （-780 Ma） magmatic rock. Metamorphic zircons with concordant ages ranging from 243 to 256 Ma occur as over- growth mantles on the protolith magmatic zir- con cores. The estimated growth temperatures （625-717 ＂C） of the metamorphic zircons have a negative correlation with their ages, indicating a progressive metamorphism in HP eciogite-facies condition during subduction. Zircon recrystal- lized rims （228-2 Ma） in the PI-rich ieucosome layers provide the lower limit of the decompress-sional partial melting time during exhumation. The ages from 228^-2 to 219~2 Ma recorded in the Pl-rich leucosome and the Kfs-rich pegmatite vein, respectively, suggest the duration of the fractional crystallization of primary melt during exhumation. The calculated growth temperatures of the zircon rims from the Pl-rich leucosome range from 858 to 739 , and the temperatures of new growth zircon grains （219±2 Ma） in Kfs-rich vein are between 769 and 529 . The estimated temperatures have a positive correlation with ages from the Pl-rich leucosome to the Kfs-rich pegmatite vein, strongly indi- cating that a process of fractional crystallization of the partial melt during exhumation.

Effect of Dy on Structure and Magnetic Properties of CoPt Alloys

The effects of Dy on the microstructure and magnetic properties of DyxCo50-xPt50 alloys were investigated. The XRD results indicate that all the alloys homogenized at 1000 ℃ contain only a single A 1 （fcc） phase, while the alloys annealed at 675℃ consist of a hard-magnetic face-eentered-tetragonal （fct） phase and a magnetically soft face-centered-cube （fcc） phase. Maximum values for the coercivity and remanence ratio mr were achieved in DY0.4Co49.6Pt50 alloys annealed at 675 ℃ for 80 min. For the series of Dy Co50-xPt50 alloys annealed at 675 ℃ for 60 min, H decreases monotonically with increasing Dy concentration, but mr is first enhanced and then weakened,

Study on incident laser modulation using surface micro-defects on KH_2PO_4 crystal

KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.

烟煤变质程度对焦耳热闪蒸多孔碳孔隙和晶体结构的影响

以不同变质程度的烟煤为原料,K_(2)CO_(3)为活化剂,采用焦耳热闪蒸法在不同电压下制备了多孔碳。通过场发射扫描电子显微镜(FESEM)、低温氮气吸附、拉曼光谱等表征手段考察了烟煤变质程度以及闪蒸电压对多孔碳的孔隙特征及晶体结构的影响。结果表明:焦耳热闪蒸方法产生的瞬间高温在有限空间内产生的压力效应和热膨胀效应是孔隙形成和扩展的驱动力;低变质程度的朔州煤在碱碳比3∶1,闪蒸电压80 V时,制备的多孔碳的比表面积为601.95 m^(2)/g、总孔容为0.44 cm^(2)/g,孔隙结构最发达;高变质程度的长治煤在碱碳比3∶1,闪蒸电压160 V时,制备的多孔碳的石墨化程度最高。

北疆卡鲁安Li-Be-Nb-Ta伟晶岩岩浆-热液过渡过程与晶体-熔体-流体相互作用:锆石矿物学记录

新疆卡鲁安伟晶岩型Li-Be-Nb-Ta矿床是阿尔泰造山带内重要的锂矿床之一。本文研究发现,卡鲁安富锂伟晶岩的各内部结构带,即钠长石-石英-白云母带(Ⅰ)、锂辉石-钠长石-石英带(Ⅱ)和锂云母-锂辉石-钠长石-石英带(Ⅲ)中的锆石结构和成分变化复杂,均发育三类、不同世代的锆石:Zr-P、Zr-A和Zr-O。Zr-P为原生岩浆锆石,它们具有均匀或振荡CL结构,相似的低HfO_(2)和Li、Be、Al、P、Ca、Fe、Nb、Cs、Ta含量。Zr-P_(Ⅰ)和Zr-P_(Ⅱ)的稀土元素配分模式呈左倾型,而Zr-P_(Ⅲ)的稀土配分模式呈平坦型,这与磷灰石和锰铝榴石分离结晶或熔-流体相互作用有关。Zr-A的CL结构不均匀,发育孔洞、微小富U/Th矿物包裹体,并含较高的Be、Al、P、Ca、Fe、Nb、Cs和Ta含量。Zr-A_(Ⅰ)和Zr-A_(Ⅱ)锆石显示相似的富集轻稀土、平坦式重稀土的M型稀土元素配分模式,而Zr-A_(Ⅲ)显示与Zr-P_(Ⅲ)相同的平坦型稀土配分模式。显微结构和成分差异表明,Zr-A是由原生岩浆锆石溶解-再沉淀而来,其中Zr-A_(Ⅰ)、Zr-A_(Ⅱ)锆石形成于岩浆热液过渡阶段的晶体-熔体-流体相互作用,而Zr-A_(Ⅲ)为流体交代的产物。Zr-O形成最晚,它们的CL结构均匀且强度最高,含最低UO_(2),而HfO_(2)、Li、Be、Al、P、Ca、Fe、Nb、Cs和Ta含量与原生岩浆锆石Zr-P相似,为热液成因。因此,卡鲁安富锂伟晶岩经历了岩浆、岩浆-热液过渡和热液多阶段演化,流体出溶后的晶体-熔体-流体相互作用活化早期锂辉石中的Li为伟晶岩晚期锂云母矿化(锂再富集)提供了重要物质条件。