Influence of fractal surface dimension on the dissolution process of sparingly soluble CaCO<Subscript>3</Subscript> microparticles

The dissolution process of sparingly soluble CaCO₃ microparticles and how the fractal surface dimension of the particles changes during dissolution is analyzed. The particles and the dissolution process are studied using scanning electron microscopy, X-ray diffraction, nitrogen adsorption, laser diffraction and conductance measurements. Ball milling of the particles is shown to maintain the particle crystallinity, and to introduce an increased fractal surface dimension in the 1–10 μm size range. Dissolution is found to increase the surface dimension of initially smooth particles and to maintain the fractal surface roughness of milled particles. The dissolution process increases the relative number of small particles (50 nm–1 μm) whereas the larger ones decrease in size. The solubility of the milled fractal particles was ∼1.8 times higher than that for the initially smooth ones. The presented findings show that developing methods for increasing the fractal surface roughness of particles should be of interest for improving the solubility of poorly soluble drug candidates.     

Bending properties of two- and three-dimensional-shaped nanoparticles fabricated via substrate conformal imprint lithography

Nanoimprinting enables the implementation of nanoparticle shapes with complex 2D shapes involving different materials. In addition to these objects, this article presents 3D-shaped nanoparticles fabricated by substrate conformal imprint technique. The imprint polymer AMONIL is used either in pure form or in combination with fluorescent dyes for the preparation of particles. The substrate conformal imprint lithography process, including etching and particle release, is conducted for both materials in a similar fashion. In this work, cuboidal particles with a high aspect ratio (1:120) are compared to particles with a T-shaped cross section with respect to their abilities to enhance or reduce their stiffness. Additionally, particles with a high aspect ratio are compared to particles with a lower aspect ratio (1:20). The local stiffness is found to depend strongly on the particle thickness and the geometry of their cross section. Thicker and 3D T-shaped particles present higher local stiffness than thinner and 2D cuboidal-shaped particles. The local bending angle was determined to be 77° for 2D-shaped particles and 83° for 3D-shaped particles, of the same total height of 176 nm. Very thin particles (<50 nm) of high aspect ratio prefer to curl finally forming loops.     

Correlation effects of two interacting particles in a circular billiard

The maximal Lyapunov exponent is determined numerically for two classical unequal-mass interacting particles inside a circular billiard and subjected to a static magnetic field. A Yukawa potential is used for the interaction between the particles. Transitions from short to long interaction ranges and from equal to infinite mass ratio between particles are discussed. Correlations effects between particles strongly determine the dynamics inside the billiard. A qualitative change in the Lyapunov exponent dependence on the interaction range between particles is observed by the transition from weak to strong couplings. Poincaré surfaces of section are also used to describe the dynamics in the limit of infinite mass ratio.     

用于亚微米颗粒测量的后向散射光谱法

针对后向散射光谱粒径测量法对亚微米颗粒测量准确度较差的问题,提出了一种采用紫外光作为光源的测量方法.通过快速傅里叶变换计算了粒径为0.25~1 μm的聚苯乙烯亚微米颗粒的后向散射频谱,将频谱峰值对应的频率值与相应的颗粒粒径进行线性回归,各粒径值相对于回归直线的平均误差为±0.02 μm. 结果表明,本文提出的300~400 nm的紫外光适用于测量0.25~1 μm的亚微米颗粒,相比目前国外最新的采用可见光谱或红外光谱的方法准确度提高了一个数量级,同时该方法也适用于测量双峰分布亚微米颗粒系.     

Effective transport of passive particles induced by chiral-active particles in microchannel

Transport of passive particles induced by chiral-active particles in microchannel is investigated by using the overdamped Langevin dynamics simulation in a two-dimensional model system. Due to the chirality of active particles and special structure of microchannel, effective ratchet transport of passive particles is achieved. Effective transport of passive particles depends on the width of microchannel(d), the density(ρ), and the angular velocity(ω) of chiral-active particles.There exist optimal parameters for d and ω at which the transport efficiency for passive particles takes its maximal value.This investigation can help us understand the necessity of active motion for living systems to maintain a number of vital processes such as materials transport inside cells and the foraging dynamics of mobile organisms.     

分散相颗粒几何因素对电流变液体反应时间的影响

瞬变的反应时间是电流变液体的一个重要参数．本文通过实验和理论分析，建立了考虑分散相颗粒几何因素的电流变反应时间模型根据此模型，长椭球状颗粒的电流变液体反应时间比等效球状颗粒的短，扁椭球状和片状颗粒的电流变液体反应时间比等效球状颗粒的长，而棒状颗粒的电流变液体反应时间则视ε_p/ε_f比值大小或快于或慢于等效球状颗粒的反应时间．且反应时间与分散相尺寸的关系是（１）随体积增大，各种形状颗粒的电流变液体反应时间均变短；（２）同体积下，随长径比增大，长椭球状颗粒的电流变液体反应时间变短，而扁椭球状颗粒和片状颗粒的电流变液体反应时间变长，棒状颗粒的电流变液体反应时间则视。ε_p/ε_f比值大小或增快或减慢．因此，要获得反应快的电流变液体，颗粒形状除选择球状外，还可在使雷诺数较小范围内，选择一定尺寸的长椭球状或棒状颗粒。 关键词：     

Stimulated emission of relativistic particles by external sources in spacetime

Explicit solutions are derived for transition amplitudes associated with stimulated emission of relativistic particles by external sources inspacetime. More precisely, exact expressions are obtained for transition amplitudes for any process where there are initially, at a given time, an arbitrary number of particles localized in various regions of space, prior to the switching on of an intervening source, and then, finally, at a later time when the intervening source ceases to operate, a given number of particles are found to be localized in various regions of space. The analysis is given for massive particles ofarbitrary integer and half-integer spins. The solutions are obtained by carrying out a unitarity expansion inconfiguration space, where particles travel between emitters and detectors in the presence of an intervening source. Considered as an application is the process: particlearbitrary number of particles, where the latter particles emerge spatially with a cone.     

Fabrication of magnetic nickel–tungsten–phosphorus particles by electroless deposition

Nickel–tungsten–phosphorus (NiWP) particles with diameters ranging from 100 to 300 nm were fabricated by electroless deposition on silica particles and Au seeds. TEM, SEM equipped with EDX, and SQUID were employed to characterize these particles. It is found that 70 °C is sufficient to deposit NiWP particles, in contrast to 90 °C required for NiP or NiWP deposited on planar substrates. Magnetic properties of these particles are profoundly influenced by P-contents, whereas replacement of P with W changes the particles from paramagnetic to soft-ferromagnetic nature. Curie temperatures and saturation magnetization of these particles are around 300 K and from 0.1 to 20 emu/g, respectively.     

Effect of a dust component on the rates of elementary processes in low-temperature plasmas

Elementary processes in dusty, beam-driven plasma discharges are studied experimentally and theoretically for the first time. A theoretical model is constructed for a beam-driven plasma containing macroscopic particles. The effect of macroscopic particles on the electron energy distribution function is estimated assuming a Coulomb field for the particles. The resulting rate of electron-ion recombination on the macroscopic particles is compared with the electron loss constant calculated from the electron energy distribution function with an electron absorption constant in the orbital-motion approximation. This approximation, which is valid in the collisionless case, is found to work satisfactorily beyond its range of applicability. The distributions of the charged particles and electric fields created by macroscopic particles in a helium plasma are determined. The experimental data demonstrate the importance of secondary emission by high-energy electrons. Zh. éksp. Teor. Fiz. 115, 2020–2036 (June 1999)     

Asymmetry of Hawking Radiation of Dirac Particles in a Charged Vaidya–de Sitter Black Hole

The Hawking radiation of Dirac particles in a charged Vaidya–de Sitter black hole is investigated by using the method of generalized tortoise coordinate transformation. It is shown that the Hawking radiation of Dirac particles does not exist for P₁, Q₂ components, but for P₂, Q₁ components it does. Both the location and the temperature of the event horizon change with time. The thermal radiation spectrum of Dirac particles is the same as that of Klein-Gordon particles.     

Energy and charge distributions of fast hydrogen ions and atoms reflected from Cu in the case of grazing incidence

The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence angles are measured at energies of incident particles (H⁺ and H⁰) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in the material.     

Fabrication of diarylide yellow pigments/modified SiO2 core-shell hybrid composite particles for electrophoretic displays

Diarylide yellow pigments/modified SiO₂ core-shell hybrid composite particles were fabricated via a newly developed two-step procedure. The surface of diarylide yellow pigments was coated with SiO₂ by the hydrolysis of Na₂SiO₃. The obtained particles were then modified with in situ generated 3-aminopropylsilanetriol or succinic acid to form composite particles containing amino or carboxyl groups. The FT-IR spectra, TGA and TEM showed that the particles had a core-shell structure, the SEM suggested that the surface morphology of the composite particles was smooth, and the XPS and zeta potential measurement indicated that the composite particles had a high charge load. The obtained composite particles have been applied as electrophoretic particles in the electronic paper, which demonstrated that the newly developed procedure is an effective way to produce various organic/inorganic composite particles used for electrophoretic displays.     

Workplace air measurements and likelihood of exposure to manufactured nano-objects,agglomerates, and aggregates

Workplace exposure to nanoparticles from gas metal arc welding (GMAW) process in an automobile manufacturing factory was investigated using a combination of multiple metrics and a comparison with background particles. The number concentration (NC), lung-deposited surface area concentration (SAC), estimated SAC and mass concentration (MC) of nanoparticles produced from the GMAW process were significantly higher than those of background particles before welding (P < 0.01). A bimodal size distribution by mass for welding particles with two peak values (i.e., 10,000–18,000 and 560–320 nm) and a unimodal size distribution by number with 190.7-nm mode size or 154.9-nm geometric size were observed. Nanoparticles by number comprised 60.7 % of particles, whereas nanoparticles by mass only accounted for 18.2 % of the total particles. The morphology of welding particles was dominated by the formation of chain-like agglomerates of primary particles. The metal composition of these welding particles consisted primarily of Fe, Mn, and Zn. The size distribution, morphology, and elemental compositions of welding particles were significantly different from background particles. Working activities, sampling distances from the source, air velocity, engineering control measures, and background particles in working places had significant influences on concentrations of airborne nanoparticle. In addition, SAC showed a high correlation with NC and a relatively low correlation with MC. These findings indicate that the GMAW process is able to generate significant levels of nanoparticles. It is recommended that a combination of multiple metrics is measured as part of a well-designed sampling strategy for airborne nanoparticles. Key exposure factors, such as particle agglomeration/aggregation, background particles, working activities, temporal and spatial distributions of the particles, air velocity, engineering control measures, should be investigated when measuring workplace exposure to nanoparticles.     

Generalized Locking Profile for Angular Particles - Locked Particle Theory

Locked particles are defined as those comminuted or particles which contain both gangue and target material. By considering the shape of the comminuted particles and assuming their random distribution in the ore body prior to comminution, it is possible to derive locking profiles which give the frequency of occurrence of particles which have a given fraction of their volume occupied by target material. For most particle shapes (spheres, angular particles, angular plates and rods) the locking profile is a deep U-shaped curve. This suggests that few particles by number contain about 50% target material while a far greater number contain either very little or very much target material. Such a conclusion is important in planning separation processes for locked particles in the mineral industry.     

Mössbauer and magnetization studies of iron oxide nanocrystals

Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.     

Spin analysis of supersymmetric particles

The spin of supersymmetric particles can be determined at e⁺e^- colliders unambiguously. This is demonstrated for a characteristic set of non-colored supersymmetric particles – smuons, selectrons, and charginos/neutralinos. The analysis is based on the threshold behavior of the excitation curves for pair production in e⁺e^- collisions, the angular distribution in the production process and decay angular distributions. In the first step we present the observables in the helicity formalism for the supersymmetric particles. Subsequently we confront the results with corresponding analyses of Kaluza–Klein particles in theories of universal extra space dimensions which behave distinctly different from supersymmetric theories. It is shown in the third step that a set of observables can be designed which signal the spin of supersymmetric particles unambiguously without any model assumptions. Finally in the fourth step it is demonstrated that the determination of the spin of supersymmetric particles can be performed experimentally in practice at an e⁺e^- collider.     

Mössbauer spectroscopy of magnetic small particles with emphasis on barium ferrite

Ferromagnetic and ferrimagnetic particles have been of scientific and technological interest for several decades. The study of nanometer clusters or particles is currently a developing subject. Such materials may be in a non-equilibrium or quasi-equilibrium phase; different properties as compared to the bulk and indeed even new physical phenomena may be expected. Some ways to synthesize clusters and fine particles are described. Mössbauer spectroscopy is shown to be particularly useful for the study of nanometer particles; an outline of how it actually works is given. As an illustration, barium ferrite small particles, a material of topical interest, is considered in detail. In particular, methods of preparation, the crystal and magnetic structure, the magnetic characteristics, recently obtained Mössbauer results, and potential and realized applications are reviewed.     

Quaternary fission

Quaternary fission is a nuclear reaction where the two customary fragments from fission are accompanied by two light charged particles. The process has been investigated at the ILL, Grenoble, for thermal neutron induced fission of ²³³U and ²³⁵U. The light particles were identified to be α particles and H isotopes (mostly tritons). Two different types of processes could be disentangled: in one of these processes all four charged particles are born in coincidence while the second process is in fact merely a special case of ternary fission where the ternary particle decays into two charged particles before reaching the detectors.     

Combustion of micron-sized particles of titanium and zirconium

Particles of titanium and zirconium in the size range of 2–25 μm are ignited while passing through a CO₂ laser beam and their combustion is monitored optically. Prior to ignition, particles pass through a low-power auxiliary laser beam so that the diameter of each ignited particle is measured in situ based on the amplitude of the scattered light pulse. The particles of both Ti and Zr are observed to exhibit micro explosions, similar to those observed for larger size particles of these metals. Particle emission traces are recorded, and a data processing routine is established for discounting emission signals produced by unignited particles and particles partially combusted within the CO₂ laser beam. Burn times and combustion temperatures are measured and compared to earlier measurements for coarser particles of the same metals. For both metals, average combustion temperatures implied by the emission spectra are very close to their respective adiabatic flame temperatures. For both metals, for the particle size range considered, particle combustion temperatures do not depend on the particle size. The particle burn times were found to be only weak functions of the particle size; burn times for Zr are shorter and temperatures are higher compared to the similarly sized Ti particles.