氧化物晶体的成核机理与晶粒粒度

从微观动力学角度研究了晶粒的成核机理,认为晶粒的成核机理主要包括生长基元的形成,生长基元之间的氧桥合作用和Ｏ桥转变为ＯＨ桥。并从核核速度角度分析了影响晶粒粒度的主要原因,揭示了影响晶粒粒度的内部原因为生长基元的生成能、晶体的晶格能,由此总结出不同结构类型的氧化物粉体的晶粒粒度的相对大小,即具有ＣａＦ２或ＴｉＯ２结构的氧化物粉体的晶粒粒度比具有α－Ａｌ２Ｏ３结构的氧化的晶粒粒度小,具有α－Ａｌ２Ｏ３     

Neutron detection on the Foton-M2 satellite by a track etch detector stack

In the frame of a European Space Agency (ESA) project called 'Biology and Physics in Space', a returning satellite, Foton-M2, was orbiting a container, the BIOPAN-5, loaded with biological experiments and facilities for radiation dosimetry (RADO) in the open space. One of the RADO experiments was dedicated to the detection of the primary cosmic rays and secondary neutrons by a track etch detector stack. The system was calibrated at high-energy particle accelerators and neutron generators. The developed detectors were investigated by an image analyser, and from the track parameters the linear energy transfer spectra and the absorbed dose were determined (26 microGy/d). Also, the neutron flux was estimated below 5 MeV and found to be 2.4 cm(-2) s(-1) directly from the space. The construction of the stack allowed to investigate the neutrons also from the direction of the carrying satellite, where the flux was found somewhat higher.     

Agent-based computational modeling of wounded epithelial cell monolayers

Computational modeling of biological systems, or in silico biology, is an emerging tool for understanding structure and order in biological tissues. Computational models of the behavior of epithelial cells in monolayer cell culture have been developed and used to predict the healing characteristics of scratch wounds made to urothelial cell cultures maintained in low- and physiological [Ca/sup 2+/] environments. Both computational models and in vitro experiments demonstrated that in low exogenous [Ca/sup 2+/], the closure of 500-/spl mu/m scratch wounds was achieved primarily by cell migration into the denuded area. The wound healing rate in low (0.09 mM) [Ca/sup 2+/] was approximately twice as rapid as in physiological (2 mM) [Ca/sup 2+/]. Computational modeling predicted that in cell cultures that are actively proliferating, no increase in the fraction of cells in the S-phase would be expected, and this conclusion was supported experimentally in vitro by bromodeoxyuridine incorporation assay. We have demonstrated that a simple rule-based model of cell behavior, incorporating rules relating to contact inhibition of proliferation and migration, is sufficient to qualitatively predict the calcium-dependent pattern of wound closure observed in vitro. Differences between the in vitro and in silico models suggest a role for wound-induced signaling events in urothelial cell cultures.     

Numerical and experimental investigation of solid particle motion in a fluid cell under microgravity

This research aims at understanding the mechanisms and parameters that affect particle motion induced by g-jitter. Simultaneous experimental (parabolic flights) and numerical work was conducted to study the motion of a spherical particle in a microgravity environment subjected to vibrations in either horizontal or vertical direction. The data from both vertically and horizontally vibrated experiments clearly show that the investigated particle properties, size and density, affect the amplitude of the particle motion. In all experiments the amplitude of the particle motion increased with the density and diameter of the particle in the cell frame of reference. It was also observed that the particles moved at the frequency equal to that of applied vibration. These results are consistent with the preliminary numerical simulation predictions. Numerical simulations also showed that increasing the viscosity of the surrounding fluid would reduce the amplitude of the particle motion.     

Efficiency of Cathodoluminescence Emission by Nitrogen‐Vacancy Color Centers in Nanodiamonds

Correlated electron microscopy and cathodoluminescence (CL) imaging using functionalized nanoparticles is a promising nanoscale probe of biological structure and function. Nanodiamonds (NDs) that contain CL‐emitting color centers are particularly well suited for such applications. The intensity of CL emission from NDs is determined by a combination of factors, including particle size, density of color centers, efficiency of energy deposition by electrons passing through the particle, and conversion efficiency from deposited energy to CL emission. This paper reports experiments and numerical simulations that investigate the relative importance of each of these factors in determining CL emission intensity from NDs containing nitrogen‐vacancy (NV) color centers. In particular, it is found that CL can be detected from NV‐doped NDs with dimensions as small as ≈40 nm, although CL emission decreases significantly for smaller NDs.     

Interfacial energy issues in ceramic particulate reinforced metal matrix composites

One major scientific issue that needs to be resolved and understood in order to design ceramic particle reinforced metal matrix composites is the interfacial energy state between the matrix and the reinforcement. Solid-solid interfacial energy between the particle and the matrix effects the final interface characteristics and also significantly influences the particle redistribution due to its effect on particle pushing engulfment by the melt interface. The paper analyses the physics behind the particle pushing and engulfment by the solidifying interface considering models utilizing interfacial force as energy difference between the particle in the solid and particle in the liquid melt. Various methods of evaluating solid-solid interfacial energy have been discussed. Velocity of melt interface movement at which the particles are engulfed by the matrix referred to as critical velocity of the system under given conditions has been shown to be directly related to the interfacial energy. Critical appraisal of experiments to determine the critical velocity have been presented for aluminium matrix dispersed with zirconia particles. Advantages of carrying out experiments under μg environment have been pointed out.     

Effect of particle size and boundary conditions on the shear stress in an annular shear cell

The effect of particle size and boundary geometry in granular shear flows is investigated. The measured shear stress of glass spheres in an annular shear cell experiment is reported. In order to explore the particle size effect, the experiments are run using four different particle diameters, d = 2, 3, 4, and 5 mm. It is found that the shear stress follows the Bagnold scaling with respect to the apparent shear rate, but deviates from it with respect to particle size. For high solids concentration the results deviate qualitatively from the kinetic theory for bounded granular shear flows, where the non-dimensional shear stress measured with large particles exceeds that measured for small particles by as much as one order of magnitude. The effect of the boundary geometry is explored by using three different boundary types; type 1 employs aluminum radial half-cylinders, type 2 employs aluminum hemispheres arranged in a polar hexagonal closed packed configuration, and type 3 employs sandpaper. It is shown that the geometry of the boundary has an insignificant effect on dilute flows of small particles. For denser flows and/or larger particles the difference is evident. The sandpaper boundary, which is different from the aluminum ones both in geometry and in its material properties, yields the lowest stress. These results imply that in granular materials-structure interaction, the structure’s properties are just as important as the properties of the granular material. Their interaction may also depend on the relative size between the structure and the grain size.     

Thermal stresses and related phenomena in composite ceramics

The paper deals with elastic thermal stresses in an isotropic multi-particle-matrix system consisted of periodically distributed spherical particles in an infinite matrix, imaginarily divided into cubic cells containing a central spherical particle. Originating during a cooling process as a consequence of the difference in thermal expansion coefficients between the matrix and the particle, and investigated within the cubic cell, the thermal stresses, as functions of the particle volume fraction v, being transformed for v = 0 to those of an isotropic one-particle-matrix system, are maximal at the critical particle volume fraction, representing a considerable value related to maximal resistance of the thermal-stress strengthened multi-particle-matrix system against mechanical loading. The thermal stresses are derived for such temperature range within which the multi-particle-matrix system exhibits elastic deformations, considering the yield stress and the particle-matrix boundary adhesion strength. With regard to a curve integral of the thermal-stress induced elastic energy density, critical particle radii related to crack initiation in ideal-brittle particle and matrix, functions describing crack shapes in a plane perpendicular to the direction of crack formation in the particle and in the matrix, and consequently dimensions of a crack in the particle and in the matrix are derived along with the condition concerning the direction of the crack formation. Additionally, derived by two equivalent mathematical techniques, the elastic energy gradient within the cubic cell, representing a surface integral of the thermal-stress induced elastic energy density, is presented to derive the thermal-stress induced strengthening in the spherical particle and in the cubic cell matrix. The former parameters for v = 0 are derived using the model of a spherical cell with the radius . Derived formulae are applied to the SiC–Si₃N₄ multi-particle-matrix system, and calculated values of investigated parameters are in a good agreement with those from published experimental results.     

Evaluation of Simulated Microgravity Environments Induced by Diamagnetic Levitation of Plant Cell Suspension Cultures

Ground-Based Facilities (GBF) are essetial tools to understand the physical and biological effects of the absence of gravity and they are necessary to prepare and complement space experiments. It has been shown previously that a real microgravity environment induces the dissociation of cell proliferation from cell growth in seedling root meristems, which are limited populations of proliferating cells. Plant cell cultures are large and homogeneous populations of proliferating cells, so that they are a convenient model to study the effects of altered gravity on cellular mechanisms regulating cell proliferation and associated cell growth. Cell suspension cultures of the Arabidopsis thaliana cell line MM2d were exposed to four altered gravity and magnetic field environments in a magnetic levitation facility for 3 hours, including two simulated microgravity and Mars-like gravity levels obtained with different magnetic field intensities. Samples were processed either by quick freezing, to be used in flow cytometry for cell cycle studies, or by chemical fixation for microscopy techniques to measure parameters of the nucleolus. Although the trend of the results was the same as those obtained in real microgravity on meristems (increased cell proliferation and decreased cell growth), we provide a technical discussion in the context of validation of proper conditions to achieve true cell levitation inside a levitating droplet. We conclude that the use of magnetic levitation as a simulated microgravity GBF for cell suspension cultures is not recommended.     

MS/MS methodology to improve subcellular mapping of cholesterol using TOF-SIMS

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) can be utilized to map the distribution of various molecules on a surface with submicrometer resolution. Much of its biological application has been in the study of membrane lipids, such as phospholipids and cholesterol. Cholesterol is a particularly interesting molecule due to its involvement in numerous biological processes. For many studies, the effectiveness of chemical mapping is limited by low signal intensity from various biomolecules. Because of the high energy nature of the SIMS ionization process, many molecules are identified by detection of characteristic fragments. Commonly, fragments of a molecule are identified using standard samples, and those fragments are used to map the location of the molecule. In this work, MS/MS data obtained from a prototype C60(+)/quadrupole time-of-flight mass spectrometer was used in conjunction with indium LMIG imaging to map previously unrecognized cholesterol fragments in single cells. A model system of J774 macrophages doped with cholesterol was used to show that these fragments are derived from cholesterol in cell imaging experiments. Examination of relative quantification experiments reveals that m/z 147 is the most specific diagnostic fragment and offers a 3-fold signal enhancement. These findings greatly increase the prospects for cholesterol mapping experiments in biological samples, particularly with single cell experiments. In addition, these findings demonstrate the wealth of information that is hidden in the traditional TOF-SIMS spectrum.     

Experimental investigation of the impact breakage characteristics between grinding media and iron ore particle in ball mills

The particle breakage of the ball mill is an extremely complicated breakage process. It is difficult to quantify and describe the particle breakage behavior. In this study, a drop-ball experimental setup was developed to demonstrate the impact process of grinding media on ore particles. The quantitative analysis of the effects of particle size, impact energy, and the number of impacts on particle breakage behavior was performed separately. The results show that the breakage probability model and product size distribution model used can be excellent to predict the particle breakage behavior for the single-particle impact experiments. The breakage probability of particles is highly sensitive to impact energy and particle size, exponentially increasing with the increase of impact energy. In addition, the application of the t_n-t₁₀ relationship provides a convenient means to characterize and predict the particle size distribution. In multi-layer particle impact experiments, the captured thickness of ore particles is approximately 2 layers during the crushing process. The broken mass of iron ore particles is proportional to the number of concessive impacts at different impact energies. This paper provides theoretical and methodological support for the evaluation and optimization of particle breakage in ball mills.     

The Binding of rhBMP‐2 to the Receptors of viable MC3T3‐E1 Cells and the Question of Cooperativity

The binding of rhBMP‐2 to its receptors, the signal transduction cascade and the final responses of bone cells, osteoprogenitor cells and derived cell lines is of high fundamental and clinical interest. In this report concentration‐response curves of the osteoblast cell line MC3T3‐E1 under influence of rhBMP‐2 was investigated. The biological response of the cells (corresponding to a down‐stream effect of the receptor state‐function) was monitored in pilot experiments by the MC3T3‐cell alkaline phosphatase‐induction test (MC3T3‐cell ALP‐induction test). It is shown that the MC3T3‐cell ALP‐induction test is a good tool for measuring biologically active recombinant human BMP‐2 (rhBMP‐2) in crude extracts of E. coli as well as in highly purified form. In addition this test is very sensitive to chemically induced structural changes of rhBMP‐2 such as those resulting from a radiolabeling of rhBMP‐2 by the Bolton‐Hunter procedure. The latter procedure reduces the biological activity of rhBMP‐2 by a factor of 3–4. The measured concentration‐response curves could all be non‐linearly fitted to a rectangular hyperbola. The half‐maximal saturation, K_0.5, is found between 30–100 nM rhBMP‐2 (= 0.8–2.5 μg/ml). The effect of rhBMP‐2 shows a plateau i.e. maximal response at ca. 300–1000 nM rhBMP‐2 (= 8–25 μg/ml). The data thus indicate a non‐cooperative binding‐response behavior. This was unexpected since BMP‐2 binds simultaneously to two cooperating receptors of type 1 and type 2. However in the very low concentration range of employed rhBMP‐2 a variable response of the cells was measured so that a full exclusion of cooperativity cannot be concluded at the present time. This will be clarified by future experiments.     

Using the annular shear cell as a rheometer for rapidly sheared granular materials: a DEM study

Discrete element simulations are performed to examine the kinematics of granular shear flows in an annular shear cell at high shearing rates. The interstitial fluid is absent and gravity is included. To investigate the feasibility of using annular shear cells as rheometers for rapidly sheared dense granular materials, this study focuses on the coupled effect of boundary conditions and the relative particle to shear cell size. Four different particle diameters and three different boundary types are used in the same annular shear cell. These cases correspond to physical experiments reported earlier by the authors. For many cases both shearing and non-shearing regions coexist. The transition from partially to fully shearing flow is shown to depend on the particle diameter, solids concentration, and the boundary conditions. The particles form layers at high solids concentration and with larger particles, as evidenced by the reduction of the flow diffusivity. The slip velocity at the bottom boundary is absent; at the top it varies. This variation is sensitive to the type of boundaries but insensitive to bulk solids concentration. This study shows the interconnectivity of the boundary, the particle to shear cell size, and the flow condition in an annular shear cell. Prior to using these cells as rheometers, a thorough understanding of this interconnectivity needs to be developed.     

颗粒运动学行为对阻尼器耗能特性影响的研究

为了进一步探究颗粒阻尼器的耗能机理,基于离散单元法,建立了圆柱形颗粒阻尼器仿真模型,研究了阻尼器内颗粒在不同激励条件下运动形态的变化规律。通过对颗粒在六种运动形态下的耗能分析,发现颗粒不同的运动形态会以不同的冲击形式影响阻尼器的耗能频率和耗能幅值,进而影响阻尼器整体耗能。基于以上结论,提出一种能显著改善颗粒运动形态的波纹管型颗粒阻尼器,与传统圆柱形颗粒阻尼器相比其耗能效果显著增加,验证了相关结论并为颗粒阻尼器在实际工程中的应用中的优化设计提供了理论参考。     

Dancing with the Cells: Acoustic Microflows Generated by Oscillating Cells

The interaction of a sound or ultrasound wave with an elastic object, such as a microbubble, can give rise to a steady‐state microstreaming flow in its surrounding liquid. Many microfluidic strategies for cell and particle manipulation, and analyte mixing, are based on this type of flow. In addition, there are reports that acoustic streaming can be generated in biological systems, for instance, in a mammalian inner ear. Here, new observations are reported that individual cells are able to induce microstreaming flow, when they are excited by controlled acoustic waves in vitro. Single adherent cells are exposed to an acoustic field inside a microfluidic device. The cell‐induced microstreaming is then investigated by monitoring flow tracers around the cell, while the structure and extracellular environment of the cell are altered using different chemicals. The observations suggest that the maximum streaming flow induced by an MDA‐MB‐231 breast cancer cell can reach velocities on the order of mm s^?1, and this maximum velocity is primarily governed by the overall cell stiffness. Therefore, such cell‐induced microstreaming measurements, including flow pattern and velocity magnitude, may be used as label‐free proxies of cellular mechanical properties, such as stiffness.     

An Euler–Lagrange particle approach for modeling fragments accelerated by explosive detonation

In this paper, a method is proposed for modeling explosive‐driven fragments as spherical particles with a point‐particle approach. Lagrangian particles are coupled with a multimaterial Eulerian solver that uses a three‐dimensional finite volume framework on unstructured grids. The Euler–Lagrange method provides a straightforward and inexpensive alternative to directly resolving particle surfaces or coupling with structural dynamics solvers. The importance of the drag and inviscid unsteady particle forces is shown through investigations of particles accelerated in shock tube experiments and in condensed phase explosive detonation. Numerical experiments are conducted to study the acceleration of isolated explosive‐driven particles at various locations relative to the explosive surface. The point‐particle method predicts fragment terminal velocities that are in good agreement with simulations where particles are fully resolved, while using a computational cell size that is eight times larger. It is determined that inviscid unsteady forces are dominating for particles sitting on, or embedded in, the explosive charge. The effect of explosive confinement, provided by multiple particles, is investigated through a numerical study with a cylindrical C4 charge. Decreasing particle spacing, until particles are touching, causes a 30–50% increase in particle terminal velocity and similar increase in gas impulse. Copyright © 2015 John Wiley & Sons, Ltd.     

An investigation into the parameters affecting the breakdown voltage and inter-particle bonding in the electrical discharge compaction of metal powders

The aim of present investigation is to gain deeper understanding of breakdown behavior and inter-particle bonding by conducting experimental tests. This may lead to improve the state of compaction by relative arrangement of initial parameters to maintain uniform distribution of current density and producing compacts with sufficient mechanical strength. Experimental work was carried out using two different set-ups. The first arrangement was employed to provide steady-state alternating voltage. The effect of column geometry and particle size on breakdown voltage was investigated under this condition. The second set-up, capacitor discharge circuit, was used to provide impulse voltage. Under this condition, the influence of column geometry, particle size, application of axial pressure, evacuation of air, energy input, electrode material and configuration on breakdown voltage was studied. Also, scanning electron microscopy was employed to study the effect of different parameters on inter-particle bonding. The results of experiments conducted on the influence of each of the voltage and capacitance on the compaction properties are also discussed.     

Langevin acoustic radiation force of a high-order bessel beam on a rigid sphere

The acoustic radiation force of Langevin type resulting from the interaction of a high-order Bessel beam with a rigid immovable sphere in an ideal fluid is theoretically investigated. The analysis is based on applying the generalized Rayleigh series used in the near-field acoustic scattering problem to calculate the force. With appropriate selection of specific Bessel beam parameters, results for the rigid sphere unexpectedly reveal a negative radiation force caused by the Lagrangean energy density. Specifically, the negative force on the rigid sphere arises when the kinematic energy density is larger than the potential energy density. This condition provides an impetus for further designing acoustic tweezers operating with high-order Bessel beams of progressive waves for potential applications in particle entrapment and manipulation.     

Chromosome aberration induction is dependent on the spatial distribution of energy deposition through a cell nucleus

The importance of the spatial distribution of energy deposition through the nucleus in determining the resultant chromosome rearrangements was investigated using fluorescent in situ hybridisation technique following either uniform or partial irradiation of HF19 human fibroblast cells with low-LET 1.5 keV ultrasoft X-rays. Irradiations were performed with and without a copper irradiation mask with a Poisson distribution of micron-sized holes immediately below the irradiation dish and the results are compared with previous results obtained following exposure to a Poisson distribution of alpha particles. For the same radiation quality, the spatial distribution of energy deposition within the nucleus was found to be important in determining the ultimate biological response, with an increased ratio of complex-to-simple aberrations observed for partial compared to uniform irradiation. Comparisons between low-LET ultrasoft X-rays and high-LET alpha particles indicate that the sub-micron clustering of damage along the alpha particle track is more important than just the total number of double-strand breaks produced.