光散射法测量颗粒尺寸、浓度的实验研究

为了能够准确快速地求解出微米量级颗粒系的尺寸和浓度,设计了一套基于Fraunhofer衍射,以线阵CCD为接收器件的实验颗粒测量装置.采用Shifrin积分变换方法,分析了给定样品颗粒的粒径分布、峰值、平均值和体积浓度.实验结果表明,与传统的Swithenbank方法采用环形光电管阵列为探测器接收衍射光强来反演颗粒分布方法相比,该方法不需要知道颗粒粒径上下限,各粒径区间间隔等预知信息,而且对粒径、浓度的实验测量值与理论值相差较小,样品峰值粒径为9.849 8 μm,与给定峰值的相对误差为3.432%,具有较高的测试准确度和较好的测试效果.     

Study on the multiple scattering effects of ultrasound contrast agents

In this paper, the multiple scattering of interacting encapsulated microbubbles in suspensions is calculated using two novel approaches--Kargl's effective medium approach and Ye and Ding's approach of 2nd-order correction. Two types of contrast agents with bubbles of different sizes and concentrations are chosen for our numerical simulations. One is Albunex, which is depicted by Church and has a size range of several microns, and the other is sodium laureate solution (before fractionation) described by Soetanto and Chan and has an average size of 35.5 microm. The numerical results from these two approaches are compared with that from the linear approximation. It is found that the multiple scattering effects on attenuation and dispersion of sound in suspensions are evident in the cases of high bubble volume fractions, basically greater than the order of 1 x 10(-4), and much more obvious for larger bubbles with average size of tens of microns.     

Light scattering by aggregates of magnetite nanoparticles in a magnetic field

The effect of variation of the scattered light intensity in a magnetic fluid with aggregates of magnetite particles several microns in size under the action of a magnetic field is studied. The effect relaxation times are determined when the magnetic field is turned on and off. This effect is found to be caused by the orientation of anisotropically magnetized aggregates. Experimental data are used to calculate the average anisotropy of the magnetic susceptibility of the aggregate and estimate its magnetic permeability.     

ZnS:Mn,Cu粉末DCEL器件表面态能级的研究

本文首次利用热激电流(TSC)法测量到两个出现于ZnS颗粒表面的陷阱能级(ΔEt1=0.64eV,ΔEt2=0.89eV),而且随着DCEL屏形成程度的提高(形成电压升高,形成时间延长),其表面陷阱的浓度将随之增大。我们认为,产生表面能级ΔEt1和ΔEt2的原因可能是由于形成过程中,Cu+离子从ZnS颗粒表面迁移走后颗粒表面又吸附了不同的氧离子(O-和O2-)所致。     

Toward efficient interactions of bubbles and coal particles induced by stable cavitation bubbles under 600 kHz ultrasonic standing waves

The interactions of bubbles and coal particles in 600 kHz ultrasonic standing waves (USW) field has been investigated. A high-speed camera was employed to record the phenomena occurred under the USW treatment. The formation and behaviors of cavitation bubbles were analyzed. Under the driving of these cavitation bubbles, whose size is from several microns to dozens of microns, coal particles were aggregated and then attracted by large bubbles due to the acoustic radiation forces. The results of USW-assisted flotation show a significant improvement in recoveries at 600 kHz, which indicates that the interactions of bubbles and particles in the USW field are more efficient than that in the conventional gravitational field. Furthermore, the sound pressure distribution of the USW was measured and predicted by a hydrophone. The analysis of gravity and buoyancy, primary and secondary Bjerknes forces shows that bubble-laden particles can be attracted by the rising bubbles under large acoustic forces. This study highlights the potential for USW technology to achieve efficient bubble-particle interactions in flotation.     

Spatial structures formed during high-temperature vacuum annealing of diamond-like film deposited on a silicon substrate

The process of an ultrahigh vacuum annealing of a diamond-like carbon film deposited on a silicon substrate has been studied in situ using a photoemission microscope mounted at the MAX-lab synchrotron’s radiation source. After the annealing the film was examined ex situ using an atomic force microscope. It is revealed that the graphitization of the film occurs and round formations of several microns in size with a core of ∼0.2 μm in size appear on its surface at the temperature exceeding 1000°C. Photoemission images of these formations have shown the presence of silicon on their surface. Apparently, the interaction between the carbon film and silicon substrate begins in the middle of the formation and spreads to the adjacent region at the following stage.     

多孔阵列聚合物模板的制备

金属纳米线阵列是X射线强辐射源研究中的重要材料之一,针对物理实验对纳米线阵列结构尺寸的特殊要求,采用集束热拉伸法制备了包埋高度取向的聚苯乙烯微纳米线有序阵列的聚乙烯复合丝,经切片、选择性溶解等后处理得到多孔聚乙烯模板材料。光学显微镜及扫描电镜（SEM）观测表明,模板中的小孔呈较规则的阵列结构分布,其孔径可在200 nm到几十m之间调节,孔间距可在1 m到几十m之间调节。通过比较实验的预设值和实测值表明,该方法可以实现对模板结构尺寸的设计和控制,进而将实现对纳米线阵列的尺寸控制。     

新型冲击式微位移机构在扫描隧道显微镜中的应用

冲击式微位移机构是利用压电陶瓷的冲击力使目标产生步进式微位移的一种微动机构,其特点是最小位移可达几纳米,具有实用的运动速度,运动范围不受限制,而且步距可从几纳米到几微米连续可调,使其可能在微米/纳米技术中得到广泛应用.本文提出一种由一对压电陶瓷驱动的新型冲击式微位移机构,介绍了该机构的工作原理,给出了它在扫描隧道显微镜中用于样品定位和成象的应用实例.     

Discrete-dipole approximation with surface interaction: Computational toolbox for MATLAB

We describe a MATLAB toolbox that utilizes the discrete-dipole approximation (DDA) method for modelling light interaction with arbitrarily-shape scatterers in free space as well with planar surface interaction (DDA-SI). The range of applicable models range from optical micromanipulation, plamonics, nano-antennae, near-field coupling and general light interaction with scatterers ranging from a few nanometers to several microns in size.     

Effect of technological characteristics of powder material on the fluorescence intensity of elemental analytical lines

The effect of technological and physical–mechanical characteristics of powder irradiators on the fluorescence intensity of elemental analytical lines was studied experimentally. Investigations were conducted with the use of ferroalloy powders of different grain size, in bulk and pelleted form, at various loads. A dependence of elemental analytical line intensity on the density of powders, both in bulk and pelleted at constant pressure, that was defined by the variation in particle size and surface interaction forces was found. Calculations revealed a correlation between the dependences obtained and the variation of the effective absorption characteristics of irradiators due to different concentrations of the solid irradiation phase, caused by the variations in density and autoadhesive properties of the particles. Variations in pelleting pressure led to similar dependences at other densities of the particle packing, the roughness of the irradiators not exceeding several microns and having a considerable effect on the formation of the irradiation layer. The parameters were found that have the greatest effect on the fluorescence intensity of powder materials. Copyright © 2003 John Wiley & Sons, Ltd.     

Bubble population phenomena in sonochemical reactor: II. Estimation of bubble size distribution and its number density by simple coalescence model calculation

A simple bubble population model, with emphasis on the bubble–bubble coalescence, is proposed. In this model, the bubble size distribution is simulated through the iteration of fundamental bubble population process: generation, dissolution, and coalescence. With this simple modelling, the bubble size distribution experimentally observed by the pulsed laser diffraction method and the void rate obtained by the capillary system at 443 kHz were successfully simulated. The experimental results on the bubble population growth by the repetitive pulsed sonication and the effect of pulse width on the bubble population were recreated by the numerical simulation in a semi-quantitative manner. The importance of coalescence of bubbles especially for the effect of addition of surfactant is demonstrated. By decreasing the coalescence frequency by one order of magnitude in the simulation, both the drastic decrease in the total bubble volume as well as the depression of bubble size distribution centring from a few tens of microns in water to a few microns in a dilute surfactant solution can be simultaneously derived.     

用表面微纳米技术研究细胞水平的生物力学

文章介绍了作者所在的实验小组近年来在用表面微纳米技术研究细胞生物学方面取得的进展.由于细胞的尺寸在数微米到数十微米之间,应用微纳米技术可以精细地调控细胞微观环境.作者所在的实验小组应用微流控系统以及表面化学修饰等方法,对细胞正常行为和病理行为进行了一系列研究.通过设计力学刺激装置,对细胞骨架的主要成分———肌动蛋白对细...     

Application of X-ray Computed Tomography to Cultural Heritage diagnostics

Physical methods of diagnosis are more and more frequently applied in the field of Cultural Heritage either for scientific investigations or for restoration and conservation purposes. X-ray Computed Tomography (CT) is one of the most powerful non-destructive testing techniques for the full-volume inspection of an object, as it is able to give morphological and physical information on the inner structure of the investigated sample. The great variety of size and composition that characterizes archaeological findings and art objects requires the development of tomographic systems specifically designed for Cultural Heritage analysis. In the last few years our research group has developed several acquisition systems for Digital Radiography and X-ray CT. We are able to perform high resolution micro-tomography of small objects (voxel size of few microns) as well as CT of large objects (up to 2 m of size). In this paper we will mainly focus the attention on the results of the investigation recently performed on two Japanese wooden statues with our CT system for large works of art. The CT analysis was carried out on site at the Conservation and Restoration Center “La Venaria Reale”, where the statues have been restored before their exposition at the Oriental Art Museum in Turin.     

Polymer-assisted crystallization of low-dimensional lead sulfide particles

PbS micro- and nanoparticles were synthesized by a simple precipitation reaction of lead nitrate with thioacetamide in hydrosoluble polymer water solutions. The effects of four water soluble polymers: polyacrylamide (PAM), polyvinyl alcohol (PVA), polyethylene glycol (PEG) and poly-N-vinyl pyrrolidone (PVP) on the PbS crystallites morphology and structural properties were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that for the PbS particles obtained in the PVA, PEG and PVP, the (2 0 0) diffraction peak of the nanocrystals becomes dominant. The highest texture in the [2 0 0] direction was observed for the crystallites obtained in the presence of PVP. Polydisperse PbS particles with cubic morphology and size ranging from 100 nm to several microns are obtained in the case of PAM and PEG. Monodisperse cubic PbS crystallites with an average size of 200 nm are formed in the presence of PVA and PVP.     

Particle Size Determination by Impact Measurement in Pneumatically Conveyed Solids

A technique is described for measuring particle size in pneumatically conveyed powders. Particle size is inferred from measurement of the peak compression of a specially designed ultrasonic transducer subject to impact of the particles. The technique is well adapted to measure the coarser fractions of the particle size distribution, which have the largest compressions. Monitoring coarse fractions of powder distributions is essential for control of dry grinding processes such as those used in the cement and coal industries. In the laboratory the impact size monitor (ISM) has demonstrated the ability to discriminate between powders with a difference in peak particle size of 2% at an approximate peak size of 150 microns. The ISM operated successfully in the laboratory at a loading of 0.5 kg/m³ of powder and measured particles down to 50 microns in size. As well as size information the ISM can provide powder distribution across a pneumatic transport pipe.     

Frequency relationships for ultrasonic activation of free microbubbles, encapsulated microbubbles, and gas-filled micropores.

The ultrasonic activation of free microbubbles, encapsulated microbubbles, and gas-filled micropores was explored using available linear theory. Encapsulated microbubbles, used in contrast agents for diagnostic ultrasound, have relatively high resonance frequencies and damping. At 2 MHz the resonance radii are 1.75 microns for free microbubbles, 4.0 microns for encapsulated microbubbles, and 1.84 microns for gas-filled micropores. Higher-pressure amplitudes are needed to elicit equivalent subharmonic, fundamental, or second-harmonic responses from the encapsulated microbubbles, and this behavior increases for higher frequencies. If an encapsulated microbubble becomes destabilized during exposure,the resulting liberated microbubble would be about twice the linear resonance size, which would be likely to produce subharmonic signals. Scattered signals used for medical imaging purposes may be indicative of bioeffects potential: The second harmonic signal is proportional to local shear stress for a microbubble on a boundary, and a strong subharmonic signal may imply destabilization and nucleation of free-microbubble cavitation activity. The potential for bioeffects from contrast agent gas bodies decreases rapidly with increasing frequency. This information should be valuable for understanding of the etiology of bioeffects related to contrast agents and for developing exposure indices and risk management strategies for their use in diagnostic ultrasound.     

Die Anlagerung radioaktiver Atome an Aerosole (Schwebstoffe) im Größenbereich 0,7–5 μ (Radius)

The attachment of the decay products of thorium emanation to aerosol particles has been studied. The dependence of the attached activity on the particle size was determined for spherical particles with radii ranging from 0,7 to 5 microns. The particles used were solid spheres of paraffin wax. It is found that the attached activity is proportional to theradius of the particles which is in good agreement with theory in this size range.     

Raman analysis of epitaxial graphene grown on 4Hben SiC (0001) substrate under low pressure condition

In this paper, we report a feasible route of growing epitaxial graphene on 4H-SiC (0001) substrate in a low pressure of 4 mbar (1 bar=10⁵ Pa) with an argon flux of 2 standard liters per minute at 1200, 1300, 1400, and 1500 ℃ in a commercial chemical vapour deposition SiC reactor. Using Raman spectroscopy and scanning electron microscopy, we confirm that epitaxial graphene evidently forms on SiC surface above 1300 ℃ with a size of several microns. By fitting the 2D band of Raman data with two-Lorentzian function, and comparing with the published reports, we conclude that epitaxial graphene grown at 1300 ℃ is four-layer graphene.     

Electrochemical lithium storage properties of desert sands

SiO₂ is one of the most promising lithium storage materials for lithium-ion batteries anodes due to its low cost, good environmental compatibility, low working voltage, and high-specific capacity. In this work, the desert sands, which are rich in SiO₂, are investigated as the anode material for lithium-ion batteries. The electrochemical activation, lithium storage capacity, and cycle properties are highly dependent on the particle size distribution of sands. As the average particle sizes of sands gradually decrease, the reversible lithium storage capacity increases from 137 mAh g^?1 (several microns) to 492 mAh g^?1 (several submicrons). The 72 h-milled sands (average particle size: ~1 μm) deliver a stable lithium storage capacity of ~400 mAh g^?1 over 400 cycles with the capacity retention as high as 95%. The reason for the electrochemical activation, lithium storage capacity, and cycle properties of sands associated with their particle size distribution is also discussed.