Size and Shape of Polymer Chain near a Flat Surface

The size and the shape of non-reversal random-walking polymerchains near an impenetrable, non- interacting flat surface areinvestigated by means of Monte Carlo simulation on the simple cubiclattice. It was found that both size and shape are dependent on thenormal-to-surface distance z_0 of the first segment of chain. We findthat the size and shape of chains, characterized by mean squareradius of gyration and mean asphericity parameter respectively, show similar dependence on distance z_0.

New approach for particle size and shape analysis of iron-based oxygen carriers at multiple oxidation states

One of the crucial issues in the chemical looping technology lies in its bed material:the oxygen carrier.Particle size analysis of an oxygen carrier is important since in a fluidized bed the material can only work well within a specific size range.While the favorable size ranges for oxygen carrier materials have already been reported,none of the published studies has analyzed the particle size and shape of oxygen carriers in detail.Furthermore,the effect of oxygen carriers'oxidation degree on such properties has not been considered either.This study aimed to report the particle size and shape analysis of five iron-based oxygen carriers,one natural ore,one synthetic material,and three residue products,at different oxidation degrees using dynamic image analysis(DIA).The oxygen carriers were prepared at different mass conversion degrees in a fluidized bed batch reactor.The size distribution,sphericity,and aspect ratio of the oxygen carrier particles were examined experimentally using a Camsizer instrument.Our results show that the DIA method was successfully able to analyze the particle size and shape of our oxygen carriers with satisfying accuracy for comparison.The oxidation state of the investigated materials seems to only affect the particle size and shape of oxygen carriers to a minor extent.However,exposures to redox cycles in a fluidized bed reactor may alter the particle size and shape of most oxygen carriers.

Size and shape control of LiFePO4 nanocrystals for better lithium ion battery cathode materials

Lithium iron phosphate （LiFePO4） is a potential high efficiency cathode material for lithium ion batteries, but the low electronic conductivity and single diffusion channel for lithium ions require good particle size and shape control during the synthesis of this material. In this paper, six LiFePO4 nanocrystals with different size and shape have been successfully synthesized in ethylene glycol. The addition sequence Fe-PO4-Li helps to form LiFePO4 nanocrystals with mostly {010} faces exposed, and increasing the amount of LiOH leads to a decrease in particle size. The electrochemical performance of the six distinct LiFePO4 particles show that the most promising LiFePO4 nanocrystals either have predominant {010} face exposure or high specific area, with little iron（II） oxidation.

Algorithm for repairing the damaged images of grain structures obtained from the cellular automata and measurement of grain size

Computational models are developed to create grain structures using mathematical algorithms based on the chaos theory such as cellular automaton, geometrical models, fractals, and stochastic methods. Because of the chaotic nature of grain structures, some of the most popular routines are based on the Monte Carlo method, statistical distributions, and random walk methods, which can be easily programmed and included in nested loops. Nevertheless, grain structures are not well defined as the results of computational errors and numerical incon- sistencies on mathematical methods. Due to the finite definition of numbers or the numerical restrictions during the simulation of solidifica- tion, damaged images appear on the screen. These images must be repaired to obtain a good measurement of grain geometrical properties. Some mathematical algorithms were developed to repair, measure, and characterize grain structures obtained from cellular automata in the present work. An appropriate measurement of grain size and the corrected identification of interfaces and length are very important topics in materials science because they are the representation and validation of mathematical models with real samples. As a result, the developed al- gorithms are tested and proved to be appropriate and efficient to eliminate the errors and characterize the grain structures.

Structural and Optical Properties and Emerging Applications of Metal Nanomaterials

Nanomaterials possess intriguing optical properties that depend sensitively on size, shape, and material content of the structures. Controlling such structural characteristics of the nanostructures allows the tailoring of their physical and chemical properties, e.g. optical, electronic, and catalytic, to achieve what is desired lot specific applications of interest. This review will cover the development of various shapes for silver and gold nanomaterials with emphasis on their relation to optical properties. Examples of various modern synthetic methods and characterization techniques are highlighted. The influence of the metal nanomaterial＇s shape and optical absorption on surface enhanced Raman scattering （SERS） and a final note on new emerging applications of metal nanostructures are also discussed.

Metallographic etching and microstructure characterization of NiCrMoV rotor steels for nuclear power

The grain size of prior austenite has a distinct influence on the microstructure and final mechanical properties of steels. Thus, it is significant to clearly reveal the grain boundaries and therefore to precisely characterize the grain size of prior austenite. For NiCrMoV rotor steels quenched and tempered at high temperature, it is really difficult to display the grain boundaries of prior austenite clearly, which limits a further study on the correlation between the properties and the corresponding microstructure. In this paper, an effective etchant was put forward and further optimized. Experimental results indicated that this agent was effective to show the details of grain boundaries, which help analyze fatigue crack details along the propagation path. The optimized corrosion agent is successful to observe the microstructure characteristics and expected to help analyze the effect of microstructure for a further study on the mechanical properties of NiCrMoV rotor steels used in the field of nuclear power.

A cellular automata model for simulating grain structures with straight and hyperbolic interfaces

A description of a mathematical algorithm for simulating grain structures with straight and hyperbolic interfaces is shown. The presence of straight and hyperbolic interfaces in many grain structures of metallic materials is due to different solidification conditions, in- eluding different solidification speeds, growth directions, and delaying on the nucleation times of each nucleated node. Grain growth is a complex problem to be simulated; therefore, computational methods based on the chaos theory have been developed for this purpose. Straight and hyperbolic interfaces are between columnar and equiaxed grain structures or in transition zones. The algorithm developed in this work involves random distributions of temperature to assign preferential probabilities to each node of the simulated sample for nucleation according to previously defined boundary conditions. Moreover, more than one single nucleation process can be established in order to gen- erate hyperbolic interfaces between the grains. The appearance of new nucleated nodes is declared in sequences with a particular number of nucleated nodes and a number of steps for execution. This input information influences directly on the final grain structure （grain size and dislribution）. Preferential growth directions are also established to obtain equiaxed and columnar grains. The simulation is done using rou- tines for nucleation and growth nested inside the main function. Here, random numbers are generated to place the coordinates of each new nucleated node at each nucleation sequence according to a solidification probability. Nucleation and growth routines are executed as a func- tion of nodal availability in order to know if a node will be part of a grain. Finally, this information is saved in a two-dimensional computa- tional array and displayed on the computer screen placing color pixels on the corresponding position forming an image as is done in cellular automaton.

Reduction Process of Blue Tungsten Oxide and its Microcomputer Process Control

Grain size control of tungsten powder is essential for high quality tungsten products. Based on studies on the hydrogen reduction process of tungsten oxide, a microcomputer system is described for reduction process control. The system, now running in Zhuzhou Tungsten and Molybdenum Materials Plant, controls the temperature of the reduction furnace and hydrogen pressure. It also controls a mechanical pusher which pushs the boats charged with blue tungsten oxide into the furnace tubes. Some of the technical problems in the process are analysed.

Natural diatomite particles： Size-, dose- and shape- dependent cytotoxicity and reinforcing effect on injectable bone cement

Natural diatomite （DT） is the ancient deposit of diatom skeleton with many regular pores of 50-200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an increasing interest of using natural diatomite for biomedical applications, the toxicity information about natural diatomite is still missing. Here, cytotoxicity of natural diatomite on osteoblasts and fibroblasts were compared to hydroxyapatite and the relationships between cytotoxicity and diatomite sizes, dose, geometry or impurity were systematically investigated. Cell adhesion and interaction with diatomite particles were also fluorescently observed, The results clearly suggested a size-, dose- and shape-dependent cytotoxicity of natural diatomite. Disk-shaped diatomite particles with average size of 30μm in diameter revealed the least toxicity, while the diatomite particles with irregular shapes and sizes less than 10 μm were remarkably toxic. Diatomite particles with proper sizes were then selected to investigate the reinforcing effect on injectable calcium phosphate bone cement. Results showed that diatomite significantly improved the compressive strength of bone cement but did not alter the injectability of the cement, This work provided important biocompatibility information of natural diatomite and demonstrated the feasibility of using selected diatomite as bone implant material.

Surface grain refinement mechanism of SMA490BW steel cross joints by ultrasonic impact treatment

Ultrasonic impact treatment (UIT) is a postweld technique for improving the fatigue strength of welded joints. This technique makes use of ultrasonic vibration to impact and plastically deform a weld toe and can achieve surface grain refinement of the weld toe, which is considered as the main reason for the improvement of fatigue strength. In this paper, the microstructure of the surface of a treated weld toe was observed by metallographic microscopy and transmission electron microscopy (TEM). The results show that UIT could produce severe plastic deformation on the surface layer of the weld toe and the maximum depth of plastic deformation extended to approximately 260 μm beneath the treated surface. Repeated processing could exacerbate the plastic deformation on the surface layer, resulting in finer grains. We can conclude that the surface grain refinement mechanism of SMA490BW welded joints is related to the high density of dislocation tangles and dislocation walls. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

Geographic Variation in the Skull Morphometry of Four Populations of Batrachuperus karlschmidti(Urodela:Hynobiidae)

Geographic variation of morphology is an important topic of evolutionary biology,and research on geographic variation can provide insights on the formation,evolution,and adaptation of species and subspecies.The vertebrate skull is a developmentally and functionally complex morphological structure with multiple functions,that is susceptible to vary according to selection pressure.In this study,geographic variations in skull morphology of Batrachuperus karlschmidti from four different geographic populations(Shade,Gexi,Shangluokema,and Xinduqiao)were examined via geometric morphometrics.No significant differences were found among these populations with regard to skull size;however,significant variation was found in skull shape.The most notable shape changes are the relative sizes and positions of the frontal,maxilla,pterygoid,and vomer.Skull shape changes were not related to allometry.However,due to limitation of sample populations and size,the results of this study need to be further verified by more sample populations and individuals in the future.The results of this study contribute to our knowledge about these aspects of morphological variability in this species as well as in hynobiid salamanders.

Effects of oxygen partial pressure on optical absorption edge and UV emission energy of ZnO films

The optical absorption edge and ultraviolet (UV) emission energy of ZnO films deposited by direct current (DC) reactive magnetron sputtering at room temperature have been investigated. With the oxygen ratio increasing, the structure of films changes from zinc and zinc oxide coexisting phase to single-phase ZnO and finally to the highly (002) orientation. Both the grain size and the stress of ZnO film vary with the oxygen partial pressure. Upon increasing the oxygen partial pressure in the growing ambient, the visible emission in the room-temperature photoluminescence spectra was suppressed without sacrificing the band- edge emission intensity in the ultraviolet region. The peaks of photoluminescence spectra were located at 3.06—3.15 eV. Prom optical transmittance spectra of ZnO films, the optical band gap edge was observed to shift towards shorter wavelength with the increase of oxygen partial pressure.

Application of multi-phase particle swarm optimization technique to retrieve the particle size distribution

The multi-phase particle swarm optimization （MPPSO） technique is applied to retrieve the particle size distribution （PSD） under dependent model. Based on the Mie theory and the Lambert-Beer theory, three PSDs, i.e., the Rosin-Rammer （R-R） distribution, the normal distribution, and the logarithmic normal distribution, are estimated by MPPSO algorithm. The results confirm the potential of the proposed approach and show its effectiveness. It may provide a new technique to improve the accuracy and reliability of the PSD inverse calculation.

Preparation of nanophase M-type ferrite and its laser-attenuated characteristics

By citrate sol-gel auto-combustion method,the nanophase M-type planar hexagonal ferrite is prepared.The transmission electron microscopy(TEM),X-ray diffraction(XRD) and thermal analysis are used to study the grain size,phase composition,microstructure and crystallization process.The results show that the nanophase M-type Sr-ferrite prepared by this method is single,and its grain size is smaller than 100 nm.Moreover,most of the grains present hexagonal sheet shape.Tests are carried out for its attenuation to 1.06 mm laser.It is found that the extinction capability of the nanophase M-type Sr-ferrite smoke is good,and its mass extinction coefficient is 1.628 m2/g.

Corrosion behavior of three Ag–50Cu alloys prepared by different processes in NaCl solutions

Corrosion behavior of two nanocrystalline bulk Ag–50Cu alloys and one coarse-grained counterpart prepared by liquid-phase reduction(LPR), mechanical alloying(MA) and powder metallurgy(PM) methods,respectively, were investigated in Na Cl solutions. They were finished by means of PARM273 A and M5210 electrochemical apparatus through potentiodynamic polarization method and electrochemical impedance spectroscopy(EIS) technique. The results show that corrosion rates of three Ag–50Cu alloys increase with the increment of Na Cl solution concentrations. Corrosion rates of LPRAg–50Cu alloy are a little higher than those of PMAg–50Cu alloy,but evidently lower than those of MAAg–50Cu alloy. The difference in corrosion rates is attributed to the large reduction in the grain size and homogeneous microstructure of nanocrystalline alloys. Passive current densities decrease and afterward increase for PMAg–50Cu alloy,decrease for MAAg–50Cu alloy, and increase for LPRAg–50Cu alloy with the increment of Na Cl solution concentrations. After the grain sizes are refined, passive current densities become lower.

TRANSPORTATION CHARACTERISTIC OF BED LOAD FOR NON-UNIFORM SEDIMENT WITH EQUIVALENT GRAIN

The incipient velocity of sediment is one of the most important basic theoretical problems of hydraulic engineering. The initial motion of sediment is a random process. Based on the combination methods of classical mechanics with statistics theory the formula to calculate the incipient motion of sediment was established. According to the standard of incipient motion, motion status, relative degree of expose for sediment and equivalent grain were defined. The coefficient in the formula included the flow fluctuation and relative degree of exposition. The value of the coefficient was calculated by using some parameters value. The results show that the value of dimensionless shear stress coefficient is not a constant, but locating in a range from 0.022 to 0.063 for weak and middle motion status, and varying with the relative degree of sediment expose. The value of dimensionless Shields numbers that put forward in the text can explain the reason that why the coefficients in difference formulas have wide scatter. The theoretical formula has been verified with amount of data collected from both natural rivers and flumes. The results can reflect the motion characteristic of the sediment.

Femtosecond laser microstructuring of nickel foil

We observe the morphological change and grain structure of Ni foil when it is ablated with femtosecond laser pulses. Scanning electron microscopy and field emission transmission electron microscopy are used to study the nature of the morphology and grain structure of nickel foil and determine the essential features. The results indicate that there are many random uanostructures in the center of the ablated region composed of nanocrystalline grains as well as some core-shell structures phase explosion and extremely high cooling rate are the for the formation of surface nanostructures. The observed morphologies seem to suggest that most probable physical mechanisms responsible

Quantifying the characteristics of particulate matters captured by urban plants using an automatic approach

It is widely accepted that urban plant leaves can capture airborne particles. Previous studies on the particle capture capacity of plant leaves have mostly focused on particle mass and/or size distribution. Fewer studies, however, have examined the particle density, and the size and shape characteristics of particles, which may have important implications for evaluating the particle capture efficiency of plants, and identifying the particle sources. In addition, the role of different vegetation types is as yet unclear. Here, we chose three species of different vegetation types, and firstly applied an object-based classification approach to automatically identify the particles from scanning electron microscope（SEM）micrographs. We then quantified the particle capture efficiency, and the major sources of particles were identified. We found（1） Rosa xanthina Lindl（shrub species） had greater retention efficiency than Broussonetia papyrifera（broadleaf species） and Pinus bungeana Zucc.（coniferous species）, in terms of particle number and particle area cover.（2） 97.9% of the identified particles had diameter ≤10 μm, and 67.1% of them had diameter ≤2.5 μm. 89.8% of the particles had smooth boundaries, with 23.4% of them being nearly spherical.（3） 32.4%–74.1% of the particles were generated from bare soil and construction activities, and 15.5%–23.0% were mainly from vehicle exhaust and cooking fumes.