Size effect study in magnetoelectric BiFeO3 system

In this paper, we report for the first time finite size effects on Néel temperature (T _N) of magnetoelectric BiFeO₃ system. Novel wet chemical route has been developed to produce fine particles of BiFeO₃ with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with decrease in particle size. The decrease in T _N is co-related to unit cell volume contraction occurring with reduction in particle size.     

Identification of the Dilute Regime in Particle Sedimentation

We investigate the dynamics of rigid, spherical particles of radius R sinking in a viscous fluid. Both the inertia of the particles and the fluid are neglected. We are interested in a large number N of particles with average distance dR. We investigate in which regime (in terms of N and R/d) the particles do not significantly interact and approximately sink like single particles. We rigorously establish the lower bound for the critical number N_crit of particles. This lower bound agrees with the heuristically expected N_crit in terms of its scaling in R/d. The main difficulty lies in showing that the particles cannot get significantly closer over a relevant time scale. We use the method of reflection for the Stokes operator to bound the strength of the particle interaction.     

Infinite Volume Limit for the Stationary Distribution of Abelian Sandpile Models

We study the stationary distribution of the standard Abelian sandpile model in the box Λ_n = [-n, n] ^d ∩ ℤ ^d for d≥ 2. We show that as n→ ∞, the finite volume stationary distributions weakly converge to a translation invariant measure on allowed sandpile configurations in ℤ ^d . This allows us to define infinite volume versions of the avalanche-size distribution and related quantities. The proof is based on a mapping of the sandpile model to the uniform spanning tree due to Majumdar and Dhar, and the existence of the wired uniform spanning forest measure on ℤ ^d . In the case d > 4, we also make use of Wilson’s method. An erratum to this article is available at .     

Structure and magnetic properties of wedged Co/Ti multilayers

Co/Ti multilayers with wedge-shaped Co or Ti sublayers were prepared using UHV (5×10⁻¹⁰ mbar) DC/RF magnetron sputtering. The planar growth of the Co and Ti layers was confirmed in situ by X-ray photoelectron spectroscopy. Cobalt sublayers grow on sufficiently thick titanium sublayers in the soft magnetic nanocrystalline phase up to a critical thickness d_crit3.0 nm. For a thickness greater than d_crit, the Co sublayers undergo a structural transition to the polycrystalline phase with much higher coercivity. Furthermore, for the Co/Ti multilayers with nanocrystalline Co sublayers with d_Co=2.7 nm we have observed a significant drop of the coercivity — typically from H_c3.5 kA/m to H_c0.2 kA/m — for Ti thickness d_Ti0.35 nm. The above effect could be explained by the existence of a minimum Ti sublayer thickness (d_min0.35 nm), which is required for the nanocrystalline growth of Co, and/or the formation of quasi-continuous non-magnetic layers for d_Tid_min giving rise to a decrease of the exchange energy between Co sublayers. Magnetic domains and walls studies revealed the structural transitions of the Co sublayers.     

Procedure for Predicting a Minimum Volume or Mass of Sample to Provide a Given Size Parameter Precision

Previous work to predict the minimum count or mass of particles to achieve a given repeatability of a size parameter has focussed on relatively narrow size distributions. Work by Masuda and Gotoh [1], based upon the log‐normal distribution by number, produce a prediction of the number of particles to be counted to achieve a defined accuracy of median volume mean MVD and mass median diameter MMD. The published paper limited the geometric standard deviations (s_g) to a maximum of 1.6. This equates to a size distribution covering just less than 1 decade of size. Modern laser diffraction units have optical arrangements enabling a range of particle sizes between 0.05 microns to 2000 microns to be determined. With the laser diffraction unit in mind the predictions of Masuda and Gotoh were extended to higher values of (s_g) where limitations were seen. An alternative prediction was then explored whose results compare very favourably with practical measurements of a characterised certified reference material CRM.     

Flame front tracking in turbulent lean premixed flames using?stereo PIV and time-sequenced planar LIF of OH

This paper describes the simultaneous application of time-sequenced laser-induced fluorescence imaging of OH radicals and stereoscopic particle image velocimetry for measurements of the flame front dynamics in lean and premixed LP turbulent flames. The studied flames could be acoustically driven, to simulate phenomena important in LP combustion technologies. In combination with novel image post processing techniques we show how the data obtained can be used to track the flame front contour in a plane defined by the illuminating laser sheets. We consider effects of chemistry and convective fluid motion on the dynamics of the observed displacements and analyse the influence of turbulence and acoustic forcing on the observed contour velocity, a quantity we term as s _d ^2D. We show that this quantity is a valuable and sensitive indicator of flame turbulence interactions, as (a) it is measurable with existing experimental methodologies, and (b) because computational data, e.g. from large eddy simulations, can be post processed in an identical fashion. s _d ^2D is related (to a two-dimensional projection) of the three-dimensional flame displacement speed s _d , but artifacts due to out of plane convective motion of the flame surface and the uncertainty in the angle of the flame surface normal have to be carefully considered. Monte Carlo simulations were performed to estimate such effects for several distributions of flame front angle distributions, and it is shown conclusively that s _d ^2D is a sensitive indicator of a quantity related to s _d in the flames we study. s _d ^2D was shown to increase linearly both with turbulent intensity and with the amplitude of acousting forcing for the range of conditions studied.     

Dependence of Néel temperature on the particle size of MnFe2O4

Mn-ferrite nanoparticles having diameter in the range 17-45 nm were synthesized by modified co-precipitation method using metal nitrate solutions. Different concentrations of NaOH were found to affect the growth of particle size. Néel temperature (T_N) was found to increase with increasing particle size. The obtained Néel temperature was higher than that of the bulk. The shift in the Néel temperature is described by the finite size-scaling theory [T_N(d)−T_N(bulk)]/T_N(bulk)=(d/d₀)^−1/v, where d is particle size, v=0.6±0.1 and d₀=1.7±0.1 nm.     

Sizing Polydisperse Dispersions by Focused Beam Reflectance and Small Angle Static Light Scattering

In this work, two different methods for particle characterization, namely focused beam reflectance and small angle static light scattering, are quantitatively compared. The results are presented in the form of moment ratios of the particle size distribution, i.e., the number weighted diameter, D_1/0, and the volume weighted diameter, D_4/3, for a broad range of particle size distributions ranging from 20 to 400 μm. Various aqueous dispersions including narrow, broad, and bimodal particle size distributions of spherical shaped ceramic beads were used in the comparison. It was found that the moment ratios obtained by focused beam reflectance measurements and small angle static light scattering correlate well, in the case of spherical particles. Furthermore, it was found that the D_1/0 values obtained by focused beam reflectance measurements are more sensitive to the presence of a small fraction of fine particles in a bimodal distribution than those obtained by small angle static light scattering.     

Use of an electrical aerosol detector (EAD) for nanoparticle size distribution measurement

Recently, Nanoparticle Surface Area Monitor (NSAM, TSI model 3550) and EAD (EAD, TSI Model 3070A) have been commercially available to measure the integral parameters (i.e., total particle surface area and total particle length) of nanoparticles. By comparison, the configuration of the EAD or NSAM is similar to that of electrical mobility analyzer of the early generation for particle size distribution measurement. It is therefore possible to use the EAD or NSAM as a particle sizer. To realize the objective of using the EAD as a sizer, we characterized the average electrical charges of monodisperse particles passing through the EAD particle charger and ion trap set at voltages ranging from 20 to 2500 V. The average charge data collected at different ion-trap voltages were then summarized by the empirical correlation using the parameter of Z _p *V, where Z _p is the particle electrical mobility and V is the ion-trap voltage. A data-reduction scheme was further proposed to retrieve the size distribution of sampled particles from the EAD readout at different ion-trap voltages. In the scheme, the functional format of each mode in a number size distribution of particles was assumed as log-normal, but the number of modes in an entire size distribution is not limited. A criterion was used to best fit the simulated EAD readouts with experimental ones by varying the count median diameter (CMD), geometric standard deviation (σ _g), and total particle number (N _t ) of each mode in a particle size distribution. Experiments were performed to verify the proposed scheme.     

Check of the scaling procedure of track structures of ionizing radiation in nanometric volumes

In nanodosimetry, the track structure of ionizing radiation is characterized by the probability distribution of the number of ionizations produced by an ionizing particle in a target volume. By Monte-Carlo simulations of the track structure, this so called ionization cluster size distribution can be determined for nanometric cylindrical water targets used as substitute for the radiation sensitive biological target, namely a DNA-segment of about 20 base pairs length. Measurements of ionization cluster size distributions are carried out in an ion-counting nanodosimeter filled with an appropriate working gas at low pressure. A scaling procedure was proposed by Grosswendt (2006) to derive an operating pressure depending on the working gas for which the measured ionization cluster size distribution becomes equivalent to the ionization cluster size distribution within a nanometric target of liquid water. This scaling procedure was previously tested by means of Monte-Carlo simulations and is now tested experimentally.Ionization cluster size distributions produced by mono-energetic proton and alpha particle beams in the energy range between 0.1 MeV and 20 MeV were measured at the accelerator facilities of the PTB. The working gases used in this experiment were C₃H₈ and N₂. According to the NIST databases for stopping power and mean ionization energy (NIST, 2009), equivalent cluster size distributions for protons and alpha particles should be obtained for pressures of 0.25 mbar C₃H₈ and 1.2 mbar N₂. Measurements reveal the best agreement with pressures of 0.425 mbar C₃H₈ and 1.2 mbar N₂ for protons and 0.46 mbar C₃H₈ and 1.2 mbar N₂ for alpha particles.     

Availability of the thermodynamics and weak cosmic censorship conjecture for a charged AdS black hole in the large dimension limit

The thermodynamics and the weak cosmic censorship conjecture (WCCC) in a high dimensional RN ? AdS_d+?1 black hole with energy-momentum relation are investigated by absorbing a charged particle in the phase space. In the RN ? AdS_d+?1 space-time, the cosmological constant Λ is treated as a thermodynamic pressure and its conjugate quantity as a thermodynamic volume. We use the energy-momentum relation of the absorbed particle to discuss the thermodynamics of the RN ? AdS_d+?1 black hole and to prove the WCCC in the phase space. Based on this assumption, we find that the first law and the second law of thermodynamics are satisfied in normal phase space. On the other hand, in the extend phase space, the first law is satisfied and the second law is violated. Then we study the WCCC in the phase space, we find that the WCCC is satisfied for an extreme black and a near-extreme black hole in the normal phase space. In the extend phase space, the WCCC is satisfied for an extreme black hole and unidentified for a near-extreme black hole.

     

Kinetics and mechanism of the growth of gold nanoparticles by reduction of tetrachloroauric acid by hydrazine in Triton N-42 reverse micelles

The kinetics of the growth of gold nanoparticles during the reduction of tetrachloroauric acid by hydrazine in dispersed aqueous solution encapsulated by reverse micelles of Triton N-42 surfactant (with decane as dispersion medium) was studied by means of spectrophotometry. According to DLS data, at a set value of solubilization capacity V _s/V _o = 0.005 initial micelles have an aqueous core hydrodynamic diameter d _c = 3.6±0.2 nm. The final particles obtained after full reduction of Au^III have a metallic core of defect-free single-crystalline gold with a narrow size distribution and average core diameter d _Au = 7.7 ± 1.4 nm as shown by TEM. The rate of the particle growth is limited by the rate of gold reduction. The process kinetics corresponds to the model consisting of two stages of reduction Au^III → Au^I → Au⁰. The stages involve the formation and redox decay of the intermediate complexes Au(N₂H₄)Cl₃ and Au(N₂H₄)Cl, and each stage proceeds via two routes: (1) homogeneous in the dispersed aqueous phase, and (2) heterogeneous on the particle surfaces. Reactions taking route (2) are autocatalytic because they proceed with participation of the surface atoms of particles as the final products of Au^III reduction. The dependencies of observed rate constants on reagent concentrations, temperature, and solubilization capacity of the micellar solution are studied.     

Permeability of mixed soft and hard granular material: Hydrogels as drainage modifiers

We measure the flow of water through mixed packings of glass spheres and soft swellable hydrogel grains, at constant sample volume. Permeability values are obtained at constant sample volume and at porosities smaller than random close packing, for different glass bead diameters D and for variable gel grain diameter d, as controlled by the salinity of the water. The gel content is also varied. We find that the permeability decays exponentially in n(D/d ) ^b , where n = N _gel/N _glass is the gel to glass bead number ratio and b is approximately 3. Therefore, flow properties are determined by the volume fraction of gel beads. A simple model based on the porosity of overlapping spheres is used to account for these observations.     

Johnson's SB distribution function as applied in the mathematical representation of particle size distributions. Part 1: Theoretical background and numerical simulation

An investigation was carried out of the transformation between the number, length, surface and volume size distributions expressed by Johnson's S_B distribution function – the bounded log-normal distribution function. As is well known, if any of the number, length, surface and volume distributions is log-normal, all the others will also be log-normal. Theoretical analysis suggests that the S_B function may have a similar property. This was confirmed by a computer-aided numerical simulation, in which emphasis was given to the transformation between successive order size distributions, i.e. ?_i(x) → ?_{i + 1}(x) or ?_i(x) → ?_{i ? 1}(x). The numerical results can be applied to the particle size distribution transformation because this transformation can generally be made step by step, for example, ?_i → ?_i?1 (x) → ?_{i ? 2}(x) → … → ?_j(x) for ?_i(x) → ?_j(x) ( i > j).     

用X射线激光M-Z干涉仪诊断点聚焦CH等离子体电子密度

在神光Ⅱ装置上，用软X射线激光Mach-Zehnder干涉仪诊断了点聚焦CH等离子体电子密度N_e分布，介绍了实验结果. 通过Abel变换进行了密度反演， 给出了N_e的2D分布，测得的最高N_e为3.2×10²¹cm^-3. 通过同1.5维JB19程序以及二维XRL2D程序的模拟结果的比较，发现高密度区，限流因子取0.05的理论结果同实验相符，但是低密度区实验得到的N_e分布下降得更快，而且理论模拟的N_e二维分布同实验结果在细节上有比较大的差别. 粗略的误差分析显示，干涉仪面型误差是实验误差的主要来源. 关键词： 类镍银X射线激光 Mach-Zehnder干涉仪 密度反演 Abel变换     

空间网络上的随机游走

本文以一维均匀环为基础, 通过添加有限数量的长程连接构造出了一维有限能量约束下的空间网络, 环上任意节点i与j之间存在一条长程连接的概率满足p_ijα d_ij^-α (α≥ 0),其中d_ij为节点i与j之间的网格距离, 并且所有长程连接长度总和受到总能量∧=cN(c≥ 0)的约束, N为网络节点总数.通过研究该空间网络上的随机游走过程,存在最优幂指数α₀ 使得陷阱问题的平均首达时间最短.进一步研究发现,平均首达时间与网络规模N之间存在着幂律关系, 随着网络规模N和总能量∧的增加,最优幂指数α₀单调增加,并趋近最优值1.5.     

Polarizing Microscopic and 31P NMR Studies of Decylammonium Chloride/Potassium Chloride/Water System. Containing Phosphoric Acid Monodecyl Ester and H3PO4

The decylammonium chloride (DACl), KCl and D₂O system forms two phases(N_c+N_d) in the nematic range. The N_d phase was ca. 15% by volume and exhibited extinct appearance. From conoscopic measurements it was inferred that the optical axis of the N_d phase was tilted. The lamellar phase of the DACl-KCl-D₂O system as well as the lamellar phase obtained by adding phosphoric acid decylester/phosphoric acid (PDE/H₃PO₄) showed the following phase sequence: L_α + N_d 35°C H_α + N_d 40°C N_c + N_d 45°C N_c 50°C isotropic The line shapes of ³¹P NMR of PDE/H₃PO₄ were found to be sensitive to micelle size and dynamics occuring in the lyotropic system, but they do not differentiate between different micelle shapes.     

Four particle harmonic-oscillator transformation brackets and their simplifications for special values of the mass-ratio parameters

We present a new independent scheme of SO(3) group transformations suitable for the N particle system, composed of N − 1 and 1 particle subsystems, where N − 1 particles have their own intrinsic clusterization. The simple expressions for corresponding four-particle harmonic-oscillator transformation brackets are presented, as well as their simplifications for the special values of mass ratio parameters d = 0, d → ∞ and d ₁ = 0, d ₁ → ∞.     

Multiplicity distributions and charged-neutral fluctuations

Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158A GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as N _part ^1.07±0.05 and photos as N _part ^1.12±0.03 have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed. For the WA98 Collaboration     

Realistic searches on stretched exponential networks

We consider navigation or search schemes on networks which have a degree distribution of the form P(k) ∝ exp(−k ^γ). In addition, the linking probability is taken to be dependent on social distances and is governed by a parameter λ. The searches are realistic in the sense that not all search chains can be completed. An estimate of μ = ρ/s _d, where ρ is the success rate and s _d the dynamic path length, shows that for a network of N nodes, μ ∝ N ^−δ in general. Dynamic small world effect, i.e., δ ≃ 0 is shown to exist in a restricted region of the λ−γ plane.