尖晶石型结构的微变化规律性

本文利用特征离子坐标变化的术语对尖晶石型结构的微变化规律性进行了讨论.总结出u值与A、B阳离子的变化规律.

金红石型结构的微变化几何学

根据金红石型结构中各离子的几何关系,从理想的等键长型结构开始,通过对各个方向的变形计算得出各个离子在不同变形情况下的几何关系。最后总结出在实际的晶体结构中c/a轴比与O^(2-)参数u的关系,并推导出在a、c已知的情况下,O^(2-)参数u的计算方法, u=0.353 6 c/[a·sin(2∠~1±δ)]或u=0.5-{(0.353 6 c)/[a·tan(2∠~1±δ)]}。

Electron Microscopic Studies on the Silver-stained Nucleolar Cycle of Physarum polycephalum

The dynamic changes of nucleolar ultrastructure in the cell cycle of Physarum polycephalum Schw. were studied by an en bloc silver-staining method. The results showed that the nucleolus was large in size and situated in the center of the nucleus in late G(2)-phase, and the fibrillar centers, dense fibrillar components and granular components could be observed in the nucleolus. During prophase, the nucleolus moved towards the periphery of the nucleus and in late prophase disintegrated near the nuclear envelope. in metaphase, the disintegrated nucleolar components were dispersed in masses and located at the periphery of the chromosomal region of the nucleus. No specifically silver-stained area and argentophilic protein sheath were observed on the chromosomes, but there were some big dispersed silver particles within the chromosomes. During telophase the nucleolar components moved towards the two poles along with the chromosomes and co-existed with the decondensing chromatin in daughter nuclei. The nucleolar components then gradually converged with one another and separated from the chromatin. A big nucleolus was formed in the nucleus about 120 min after the completion of mitosis.

Seasonal Changes in the Ultrastructure of the Vascular Cambium in Shoots of Populus tomentosa

Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the vascular cambium activity of Populus tonientosa Carr. planted in Beijing area were examined in shoot tissues collected during 15 months by means of transmission electron microscopy. Before xylem mother cells reactivated completely, the dividing fusiform cells in cambium and new phloem cells had appeared at the same time. The initiation of cambial activity may be related to the bud sprouting and the young leaf growth in shoots. More details about the ultrastructural changes of cambial cells at the onset of cambial activity have been gained. When the large vacuole in active cambial cells divided into smaller ones during the dormant phase, proteinaceous material that disappeared in active cambial cells refilled many of these small vactioles. In addition, lipid droplets and starch granules had the same cycles as proteinaceous material. The plasmalemma invaginations of fusiform cells were observed not only in active phase but also in dormancy. The endomembrane system consisting of nuclear membrane, endoplasmic reticulum (ER), dictyosomes and their secretory vesicles, changed in form and distribution at different phases during a cycle and performed important roles at the onset of active cambium and during the wall formation process of secondary xylem cells. The tangential walls remained relatively thin throughout the year but the radial walls thickened markedly when the cambium was dormant. During the transition from dormancy to activity, a partial autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. A notable feature of the cells at the onset of cambial activity was the thinning of the radial walls.

Microstructure and superhardness effect of VC/TiC superlattice films

Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.

Effect of salvianolate on intestinal epithelium tight junction protein zonula occludens protein 1 in cirrhotic rats

AIM:To study the effect of salvianolate on tight junctions(TJs) and zonula occludens protein 1(ZO-1) in small intestinal mucosa of cirrhotic rats.METHODS:Cirrhosis was induced using carbon tetrachloride.Rats were randomly divided into the untreated group,low-dose salvianolate(12 mg/kg) treatment group,medium-dose salvianolate(24 mg/kg) treatment group,and high-dose salvianolate(48 mg/kg) treatment group,and were treated for 2 wk.Another 10 healthy rats served as the normal control group.Histological changes in liver tissue samples were observed under a light microscope.We evaluated morphologic indices of ileal mucosa including intestinal villi width and thickness of mucosa and intestinal wall using a pathological image analysis system.Ultrastructural changes in small intestinal mucosa were investigated in the five groups using transmission electron microscopy.The changes in ZO-1 expression,a tight junction protein,were analyzed by immunocytochemistry.The staining index was calculated as the product of the staining intensity score and the proportion of positive cells.RESULTS:In the untreated group,hepatocytes showed a disordered arrangement,fatty degeneration was extensive,swelling was obvious,and disorganized lobules were divided by collagen fibers in hepatic tissue,which were partly improved in the salvianolate treated groups.In the untreated group,abundant lymphocytes infiltrated the fibrous tissue with proliferation of bile ducts,and collagen fibers gradually decreased and damaged hepatic lobules were partly repaired following salvianolate treatment.Compared with the untreated group,no differences in intestinal villi width between the five groups were observed.The villi height as well as mucosa and intestinal wall thickness gradually thickened with salvianolate treatment and were significantly shorter in the untreated group compared with those in the salvianolate treatment groups and normal group(P < 0.01).The number of microvilli decreased and showed irregular lengths and arrangements in the untreated group.The intercellular space between epithelial cells was wider.The TJs were discontinuous,which indicated disruption in TJ morphology in the untreated group.In the treated groups,the microvilli in the intestinal epithelium were regular and the TJs were gradually integrated and distinct.The expression of ZO-1 decreased in the small intestine of the untreated cirrhotic rats.The high expression rate of ZO-1 in ileal mucosa in the untreated group was significantly lower than that in the medium-dose salvianolate group(21.43% vs 64.29%,χ 2 = 5.25,P < 0.05),high-dose salvianolate group(21.43% vs 76.92%,χ 2 = 8.315,P < 0.01) and normal group(21.43% vs 90%,χ 2 = 10.98,P < 0.01).CONCLUSION:Salvianolate improves liver histopathological changes,repairs intestinal mucosa and TJ structure,and enhances ZO-1 expression in the small intestinal mucosa in cirrhotic rats.

Microstructural evolution during partial remelting of AM60B magnesium alloy refined by MgCO_3

AM60B magnesium alloy was refined by MgCO3 and its microstmcturat evolution was investigated during partial remelting. The results indicate that MgCO3 is an effective grain refiner for AM60B alloy and can decrease the grain size from 329 pm of the unrefined alloy to 69 μm. A semisolid microstructure with small and spheroidal primary particles can be obtained after being partially remelted. The microstructure evolution can be divided into four steps： the initial rapid coarsening, structure separation, spheroidization and final coarsening. Correspondingly, these four steps result from the phase transformations of β→α, α＋β→L and α→L, α→L and two reverse reactions of α→L and L→α, respectively. One spheroidal primary particle in the semisolid microstmcture usually originates one dendrite in the as-cast microstructure. The variation of primary particle size with holding time does not obey the LSW law, Dt^3-Do^3=Kt, after the semisolid system is in its solid-liquid equilibrium state. Longer heating duration makes the primary particles more globular, but it makes their size larger at the same time.

Characterization of the Microstructure Changes of Polypropylene Induced by Pan-milling

The microstructure changes of polypropylene induced by a complex combination of shearing, friction, compression and stretching actions during pan-milling were revealed by spectroscopic techniques. X-ray diffraction analysis showed that the structure of polypropylene transferred from crystal into amorphous after undergoing enough milling operation. No transformation between crystal forms was observed. The study of the high-frequency region of the Raman spectrum between 2800 and 3100cm-1 of polypropylene indicated that molecular motion and chain deformation of PP led to amorphization and deterioration of packing regularity during pan-milling. By co-panmilling PP with bis-(2,2,6,6-tetramethyl-4-piperidinyl) sebacate under ambient condition, ESR signals of free radicals formed by mechanochemical scission of main chain were observed, and an increase of ESR intensity with milling was detected.

Mechanism of microwave assisted suspension magnetization roasting of oolitic hematite ore

Oolitic hematite is an iron ore resource with rich reserves,complex composition,low grade,fine disseminated particle sizes,and a unique oolitic structure.In this study,a microwave-assisted suspension magnetization roasting technology was proposed to recover and utilize the ore.The results showed that under the conditions of microwave pretreatment temperature of 1050℃ for 2 min,a magnetic concentrate with an iron grade of 58.72%at a recovery of 89.32%was obtained by microwave suspension magnetization roasting and magnetic separation.Moreover,compared with the no microwave pretreatment case,the iron grade and recovery increased by 3.17%and 1.58%,respectively.Microwave pretreatment increased the saturation magnetization of the roasted products from 24.974 to 39.236(A∙m^(2))/kg and the saturation susceptibility from 0.179×10^(−3) m^(3)/kg to 0.283×10^(−3) m^(3)/kg.Microcracks were formed between the iron and gangue minerals,and they gradually extended to the core of oolite with the increase in the pretreatment time.The reducing gas diffused from outside to inside along the microcracks,which promoted the selective transformation of the weak magnetic hematite into the strong magnetic magnetite.

Viscosity profile prediction of a heavy crude oil during lifting in two deep artesian wells

It has been known that the productivity of artesian wells is strongly dependent on the rheological properties of crude oils. This work targets two deep artesian wells(>5000 m) that are producing heavy crude oil. The impacts of well conditions including temperature, pressure and shear rate, on the crude oil rheology were comprehensively investigated and correlated using several empirical rheological models. The experimental data indicate that this heavy oil is very sensitive to temperature as result of microstructure change caused by hydrogen bonding. The rheological behavior of the heavy oil is also significantly impacted by the imposed pressure, i.e., the viscosity flow activation energy(Eμ) gently increases with the increasing pressure. The viscosity–shear rate data are well fitted to the power law model at low temperature. However, due to the transition of fluid feature at high temperature(Newtonian fluid), the measured viscosity was found to slightly deviate from the fitting data. Combining the evaluated correlations, the viscosity profile of the heavy crude oil in these two deep artesian wells as a function of well depth was predicted using the oilfield producing data.

Microstructure evolution of 7050 aluminum alloy during hot deformation

Hot compression of 7050 aluminum alloy was performed on Gleeble 1500D thermo-mechanical simulator at 350 ℃ and 450 ℃ with a constant strain rate of 0.1 s-1 to different nominal strains of 0.1, 0.3 and 0.7. Microstructures of 7050 alloy under various compression conditions were observed by TEM to investigate the microstructure evolution process of the alloy deformed at various temperatures. The microstructure evolves from dislocation tangles to cell structure and subgrain structure when being deformed at 350 ℃, of which dynamic recovery is the softening mechanism. However, continuous dynamic recrystallization (DRX) occurs during hot deformation at 450 ℃, in which the main nucleation mechanisms of DRX are subgrain growth and subgrain coalescence rather than particle-simulated nucleation (PSN).

Altered cytoskeletal structures in transformed cells exhibiting obviously metastatic capabilities

Oytoskeletal changes in transformed cells (LM-51) exhibiting obviously metastatie eapabilities were investigated by utilization of double-fluorescent labelling through combinations of:(1) tubulin indirect immunofluoresoenoe plus Khodamine-phalloidin staining of F-artins;(2) indirect immunofluorescent staining with α-aotinin polyolonal- and vinoulin monoclonal antibodies. The LM-51 cells which showed metastatic index of >50% were derived from lung metastasis in nude mice after subcutaneous inoculation of human highly metastatic tumor DNA transfected NIH3T3 cell transformants. The parent NIH3T3 cells exhibited well-organized miorotubu-les, prominent stress fibers and adhesion plaques while their transformants showed remarkable oytoskeletal alterations: (1) reduced microtubules but increased MTOC fluorescence; (2) disrupted stress fibers and fewer adhesion plaques with their protein components redistributed in the cytoplasm; (3) F-aotin-and α-actinin/vinculin aggregates appeared in the cytoplasm. These aggregates were dot-like, varied in size (0.1-0.4u,m) and number, located near the ventral surface of the cells. TPA-induced aotin/vinoulin bodies were studied too. Indications that aotin and α-actinin/vinoulin redistribution might be important alterations involved in the expression of metastatio capabilities of LM-51 transformed cells were discussed.

Siderite pyrolysis in suspension roasting:An in-situ study on kinetics,phase transformation,and product properties

Siderite,as an abundant iron ore,has not been effectively utilized,with a low utilization rate.In this study,the in-situ kinetics and mechanism of siderite during suspension magnetization roasting(SMR)were investigated to improve the selective conversion of siderite to magnetite and CO,enriching the theoretical system of green SMR using siderite as a reductant.According to the gas products analyses,the peak value of the reaction rate increased with increasing temperature,and its curves presented the feature of an early peak and long tail.The mechanism function of the siderite pyrolysis was the contraction sphere model(R_(3)):f(α)=3(1−α)2/3;E_(α)was 46.4653 kJ/mol;A was 0.5938 s^(−1);the kinetics equation was k=0.5938exp[−46.4653/(RT)].The in-situ HT-XRD results indicated that siderite was converted into magnetite and wüstite that exhibited a good crystallinity in SMR under a N_(2) atmosphere.At 620℃,the saturation magnetization(M_(s)),remanence magnetization(Mr),and coercivity(Hc)of the product peaked at 53.63×10^(-3)A·m^(2)/g,10.23×10^(-3)A·m^(2)/g,and 12.40×10^(3)A/m,respectively.Meanwhile,the initial particles with a smooth surface were transformed into particles with a porous and loose structure in the roasting process,which would contribute to reducing the grinding cost.

Influence of minor Sc additions on grain refinement and microstructure characteristics of a high Zn-containing Al-Zn-Mg-Cu-Zr alloy

In the present work, scandium elements with a series of contents(0.06 wt.%, 0.10 wt.%, 0.14 wt.%,0.17 wt.%, 0.20 wt.% and 0.25 wt.%) were added in a high Zn-containing Al-Zn-Mg-Cu-Zr alloy and the corresponding as-cast microstructure characteristics including grains and phases were thoroughly investigated. The results indicated that fine grain boundaries existed in these alloys and fine MgZn2phases discontinuously distributed on them. Besides,AlZnMgCu eutectic phases and Sc, Zr-containing phases with flocculent morphology were observed. As scandium contents vary from 0.06 wt.% to 0.17 wt.%, the average grain size continuously decreased and its equiaxial characteristics were strengthened. Meanwhile, the content of AlZnMgCu eutectic phase showed a decrease trend. When scandium contents were 0.20 wt.% and 0.25 wt.%, no further enhancement on grain refinement was observed, so as to the reduction of AlZnMgCu eutectic phase content. Besides, Sc, Zr-containing phases with blocky morphology were observed and the alloy with a scandium content of 0.25 wt.% possessed a larger amount of blocky Sc, Zr-containing phase than the alloy with a scandium content of 0.20 wt.%. Grain refinement and reduction of AlZnMgCu eutectic phase content associated with scandium addition were discussed.

Suspension roasting process of vanadium-bearing stone coal:Characterization,kinetics and thermodynamics

The thermodynamics,kinetics,phase transformation,and microstructure evolution of vanadium-bearing stone coal during suspension roasting were systematically investigated.Thermodynamic calculations showed that the carbon in the stone coal burned and produced CO_(2) in sufficient oxygen during roasting.The mass loss of stone coal mainly occurred within the temperature range from 600 to 840℃,and the thermal decomposition reaction rate increased to the peak at approximately 700℃.Verified by the Flynn−Wall−Ozawa(FWO)and Kissinger−Akahira−Sunose(KAS)methods,the thermal decomposition reaction of stone coal was described by the Ginstling−Brounshtein equation.The apparent activation energy and pre-exponential factors were 136.09 kJ/mol and 12.40 s^(−1),respectively.The illite in stone coal lost hydroxyl groups and produced dehydrated illite at 650℃,and the structure of sericite was gradually destroyed.The surface of stone coal became rough and irregular as the temperature increased.Severe sintering occurred at the roasting temperature of 850℃.

Characteristics of hot tensile deformation and microstructure evolution of twin-roll cast AZ31B magnesium alloys

High temperature tensile properties and microstructure evolutions of twin-roll-cast AZ31B magnesium alloy were investigated over a strain rate range from 10-3 to 1 s-1.It is suggested that the dominant deformation mechanism in the lower strain rate regimes is dislocation creep controlled by grain boundary diffusion at lower temperature and by lattice diffusion at higher temperatures,respectively.Furthermore,dislocation glide and twinning are dominant deformation mechanisms at higher strain-rate.The processing map,the effective diffusion coefficient and activation energy map of the alloy were established.The relations of microstructure evolutions to the transition temperature of dominant diffusion process,the activation energy platform and the occurrence of the full dynamic recrystallization with the maximum peak efficiency were analyzed.It is revealed that the optimum conditions for thermo-mechanical processing of the alloy are at a temperature range from 553 to 593 K,and a strain rate range from 7×10-3 to 2×10-3 s-1.

Variation law of microscopic pore of loess-like soil after several freeze-thaw cycles in seasonal frozen soil region

In seasonal frozen soil region,the engineering geological properties of loess-like soil will be deteriorated after freeze-thaw cycles.Through the freeze-thaw cycle experiment of remolded loess-like soil,under different freezing temperatures,the authors carried out freeze-thaw cycle tests for 3 times and 20 times,respectively.With mercury intrusion porosimetry and granulometric analysis,from the micro-structure,the authors studied the law that freeze-thaw cycle times and frozen temperature effect on the variation of microscopic pore of loesslike soil.This result can provide theoretical basis for comprehensive treatment of problems in the construction of the project in seasonal frozen loess-like soil region.

Effects of alkaline earth oxides on precipitation behavior of metallic iron under CO atmosphere

In gaseous reduction of iron ore fines, alkaline earth oxides have profound effects on the precipitation behavior of fresh metal- lic iron on the particle surface. In this work, in situ observation was performed to reveal the influence of alkaline earth oxides on the precipitation morphology and micro-structure variation of fresh metallic iron from microscopic level by simulation of the gas-solid reaction condition on the surface of ore particles. Experimental results indicate that doping MgO in the particle surface can inhibit the reduction of iron oxide and however doping CaO, SrO and BaO promote; all alkaline earth oxides tested in this study can change the precipitation morphology of fresh metallic iron; minimum doping mole fraction of one oxide to inhibit iron whiskers growth （ NAO ） is related to its cation radius （ r：＋ ） and its extranuclear electronic layers（nAD ）, which can be expressed as NAO = 1.3 × 10^-5r^2AD,√nA^2.

Numerical simulation of microstructure evolution during directional solidification process in directional solidified (DS) turbine blades

Directional solidified(DS) turbine blades are widely used in advanced gas turbine engine. The size and orientation of columnar grains have great influence on the high temperature property and performance of the turbine blade. Numerical simulation of the directional solidification process is an effective way to investigate the grain's growth and morphology,and hence to optimize the process. In this paper,a mathematical model was presented to study the directional solidified microstructures at different withdrawal rates. Ray-tracing method was applied to calculate the temperature variation of the blade. By using a Modified Cellular Automation(MCA) method and a simple linear interpolation method,the mushy zone and the microstructure evolution were studied in detail. Experimental validations were carried out at different withdrawal rates. The calculated cooling curves and microstructure agreed well with those experimental. It is indicated that the withdrawal rate affects the temperature distribution and growth rate of the grain directly,which determines the final size and morphology of the columnar grain. A moderate withdrawal rate can lead to high quality DS turbine blades for industrial application.

The Micromechanics of Biological and Biomimetic Staggered Composites

Natural materials such as bone, tooth and nacre achieve attractive properties through the ＂staggered structure＂, which consists of stiff, parallel inclusions of large aspect ratio bonded together by a more ductile and tougher matrix. This seemingly simple structure displays sophisticated micromechanics which lead to unique combinations of stiffness, strength and toughness. In this article we modeled the staggered structure using finite elements and small Representative Volume Elements （RVEs） in order to explore microstructure-property relationships. Larger aspect ratio of inclusions results in greater stiffiless and strength, and also significant amounts of energy dissipation provided the inclusions do not fracture in a brittle fashion. Interestingly the ends of the inclusions （the junctions） behave as crack-like features, generating theoretically infinite stresses in the adjacent inclusions. A fracture mechanics criterion was therefore used to predict the failure of the inclusions, which led to new insights into how the interfaces act as a ＂＇soft wrap＂ for the inclusions, completely shielding them from excessive stresses. The effect of statistics on the mechanics of the staggered structure was also assessed using larger scale RVEs. Variations in the microstructure did not change the modulus of the material, but slightly decreased the strength and significantly decreased the failure strain. This is explained by strain localization, which can in turn be delayed by incorporating waviness to the inclusions. In addition, we show that the columnar and random arrangements, displaying different deformation mechanisms, lead to similar overall prop- erties. The guidelines presented in this study can be used to optimize the design of staggered synthetic composites to achieve mechanical performances comparable to natural materials.