Atomic and electronic structure of a carbon nitride compound prepared by magnetron sputtering

The atomic structure, chemical composition and chemical bonding state of a carbon nitride compound, synthesized by rf magnetron sputtering, have been studied by high-resolution electron microscopy, nanobeam diffraction and electron energy loss spectroscopy. It is revealed that the grain sizes of a crystalline compound in an amorphous matrix lie in the range 5-10 nm, and that the compound has a hexagonal structure with a = 0.324 nm and c = 0.404 nm. The C and N K edges are observed in the high-energy region of the electron-energy-loss spectrum. Only features corresponding to C sigma* bonds are found in the C K edge spectrum, which provides evidence for sp³ hybridization of C orbitals in the compound. Quantifying the electron-energy-loss spectra suggests that the compound is C₇N₁₀.     

Fractal growth of graphite nodules in iron

It has been found from a large number of statistical tests that graphite nodules in malleable iron grow with time according to a power law. The growth of the nodules and their fractal dimension have been investigated experimentally as a function of annealing time. Based on the assumption of carbon-diffusion-controlled growth in the initial stage, the growth equation is R _G = K ₁ t ^1/(D-1), where R _G is the radius of the graphite nodules, t the time, D the fractal dimension and K ₁ a constant. Assuming cementite-dissolution-controlled growth in the later stages of growth, the relation is R _G = K ₃ t ^3/D , where K ₃ is a constant. The fractal dimension, or the aggregate state of the graphite nodules, strongly influences the growth process.     

Spontaneous atom mixing and unmixing in metallic nanoparticles

The behaviour of atom mixing and unmixing in metallic nanoparticles has been studied in situ by transmission electron microscopy, using particles in the Au₂Pb-Sn system. It is confirmed that not only spontaneous mixing but also spontaneous unmixing take place in Au₂Pb particles. At room temperature, spontaneous mixing of tin atoms into Au₂Pb particles takes place, and this mixing induces unmixing of lead from Au₂Pb, resulting in the formation of AuSn particles accompanied by lead precipitates.     

Influence of Zn incorporation on the microstructural and magnetic properties of La0.67Sr0.33Mn1−xZnxO3 nanoparticles synthesised by the sol–gel method

Perovskite manganite nanoparticles with the chemical formula La_0.67Sr_0.33Mn_1?xZn_xO₃ (x = 0, 0.1 and 0.2) were prepared by the sol–gel process and the influence of Zn substitution on their microstructural and magnetic properties studied in detail. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed for crystal structure determination and microstructural analysis. The results of XRD analysis confirmed the polycrystalline nature and rhombohedral crystal structure with space group R(-3c) for all compositions. SEM micrographs of the samples revealed an agglomeration/well-connected appearance of the particles. The composition and uniform distribution of all the elements were established by energy-dispersive spectroscopy. TEM images clearly confirmed an almost spherical shape of the nanoparticles with an average particle size of about 11, 14 and 13 nm for the 0, 10 and 20% Zn-doped samples, respectively. The magnetic behaviour of the nanoparticles was studied at room temperature with a vibrating sample magnetometer (VSM) up to a field of 1.8 Tesla. These measurements established a superparamagnetic nature with a variation in the saturation magnetization (M_s) with Zn content.     

A new allotropic structure of silver nanocrystals nucleated and grown over planar polymer molecules

Polymer molecules of polyvinyl alcohol (PVA) serve as a good Ag⁺?→?Ag⁰ reducer as well as a template to produce Ag⁰ nanocrystals of anisotropic shapes. Thin Ag–PVA films (50–100?µm thick) were prepared by carrying out the reaction in aqueous PVA (under heating conditions) and then spin casting the sample in this shape. A topotactic Ag⁺?→?Ag⁰ reaction and in-situ Ag⁰ growth occur in support over the PVA molecules (as per the local structure and Ag⁰–PVA interactions) of elongated surfaces. The Ag⁰ state is confirmed with 3d _5/2 and 3d _3/2 XPS signals of 368.37 and 374.13?eV binding energies, respectively. As analyzed with X-ray diffraction, it is a new allotrope with an orthorhombic structure, lattice parameters a?=?0.8535, b?=?0.8410?nm and c?=?0.4119?nm, and density ρ?=?9.69?g?cm^?3. On heating in air, the well-known cubic structure develops, a?=?0.4082?nm (ρ?=?10.53?g?cm^?3) after 150°C, whereas a?=?0.4071?nm (ρ?= 10.61?g?cm^?3) after 300°C for 2?h. According to proposed models, it is a vacancy-stabilized allotrope, which evolves from multiply twinned particles.     

Approximant phases,phason planes and domain-boundary networks in Al−Ni−Rh alloys

Structurally complicated ξ′- and ξ-phases have been found, for the first time, in as-cast Al₇₃Ni₅Rh₂₂ and Al₇₅Ni₁₅Rh₁₀ alloys. The lattice parameters of these two phases were determined by means of electron diffraction and high-resolution transmission electron microscopy (HREM). These two phases have similar orthorhombic structures but with different lattice parameters of a?=?23.2?Å, b?=?16.4?Å, c?=?12.0?Å for the ξ′-phase and a?=?20.3?Å, b?=?16.4?Å, c?=?14.8?Å for the ξ-phase. A new two-dimensional domain-boundary network has also been observed in these two phases. Domain boundaries with normals closely parallel to the [001] direction are actually phason planes represented by a translation vector of r?=(1/2)a?+(1/2τ)c in the ξ′-phase and r=±(1/2τ²) a?+(τ/2)c in the ξ-phase, whereas the newly-found wide and zigzag boundaries perpendicular to the above set were attributed from the step-like boundary structures of domains related by a translation vector of r?=(1/τ)((1/2)a?+(1/2τ)c). The structural difference between the two types of planar faults is discussed.     

Morphological and magnetic response of copper-substituted nickel ferrite nanoparticles

Ferrite nanoparticles are interesting materials owing to their unique physical and chemical properties. The metal-doped ferrites have well-defined structures and magnetic response, such as high permeability for a specific frequency range. In this study, copper-substituted nickel ferrite (Ni_1?xCu_xFe₂O₄) nanoparticles with a compositional range of 0?≤?x?≤?0.3 were synthesised through a co-precipitation technique. Metal chlorides were used as precursors and NaOH as a precipitating agent for the growth of ferrite nanoparticles. To minimise the internal stresses and maximise the magnetic response, ferrite nanoparticles were annealed in a furnace at 700°C for 6 h. The structural and magnetic response of Ni_1?xCu_xFe₂O₄ ferrite with different values of x were investigated using Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FT-IR), Vibrating Sample Magnetometer (VSM) and X-ray Diffraction (XRD) techniques. XRD analysis confirmed the formation of cubic spinel structure of single phase for all the compositions. The lattice constant decreased with increase in the value of x. FT-IR study showed two main metal oxygen bonds in the range 500–700 cm^?1 confirming the formation of a single-phase cubic inverse structure of Cu-substituted Ni ferrite. VSM results revealed the formation of ferrimagnetic nanoparticles. The optical and magnetic response of the ferrite nanoparticles changed with Cu content.     

Changes in microstructure near the R-phase transformation in Ti50Ni48Fe2 studied by in-situ electron microscopy

Microstructural changes associated with the martensitic transformation from cubic (parent phase) to trigonal (R phase) which occurs with decreasing temperature in Ti₅₀Ni₄₈Fe₂ have been intensively studied by in-situ electron microscopy. Although the parent phase shows a characteristic microstructure with small domains, which are due to lattice modulation as a precursor to the transformation, their temperature dependence is contrasted with that of domains which appear below the transformation temperature in the R phase. The observations convince us that there is an essential difference between the natures of the domains observed in each state, and also reveal the formation of peculiar antiphase-like boundaries within a needle-like variant of the R phase. We also estimate the approximate size of the R phase just after nucleation and compare this with a theoretical consideration on the size of nuclei in martensites.     

The Jónsson-Kiefer Property

The least element 0 of a finite meet semi-distributive lattice is a meet of meet-prime elements. We investigate conditions under which the least element of an algebraic, meet semi-distributive lattice is a (complete) meet of meet-prime elements. For example, this is true if the lattice has only countably many compact elements, or if |L| < 2^ℵ0, or if L is in the variety generated by a finite meet semi-distributive lattice. We give an example of an algebraic, meet semi-distributive lattice that has no meet-prime element or join-prime element. This lattice L has |L| = |LC| = 2^ℵ0 where L_c is the set of compact elements of L. Dedicated to the memory of Willem Johannes Blok AMS subject classification: 06B05 While working on this paper, the first author was supported by the INTAS grant no. 03-51-4110, the second author was partially supported by the Hungarian National Foundation for Scientific Research (OTKA) grant no. T37877, and the third author was supported by the US National Science Foundation grant no. DMS0245622.     

Real temperature of nanoparticles in electron microscope beams

Abstract

This Letter presents a solution of the problem of the real temperature of nanoparticles under conditions of electron microscope beam irradiation. It is shown that the average temperature of the nanoparticles (NPs) may increase to several hundred degrees depending on contact conditions with the substrate, the intensity of the beam and the size of the NPs. The temperature increases with NP size a according to the dependence: T α a² for sufficiently small particles.     

On the Closure Properties of the Class of Full G-models of a Deductive System

In this paper we consider the structure of the class FGModS of full generalized models of a deductive system S from a universal-algebraic point of view, and the structure of the set of all the full generalized models of S on a fixed algebra A from the lattice-theoretical point of view; this set is represented by the lattice FACS_s A of all algebraic closed-set systems C on A such that (A, C) ε FGModS. We relate some properties of these structures with tipically logical properties of the sentential logic S. The main algebraic properties we consider are the closure of FGModS under substructures and under reduced products, and the property that for any A the lattice FACS_s A is a complete sublattice of the lattice of all algebraic closed-set systems over A. The logical properties are the existence of a fully adequate Gentzen system for S, the Local Deduction Theorem and the Deduction Theorem for S. Some of the results are established for arbitrary deductive systems, while some are found to hold only for deductive systems in more restricted classes like the protoalgebraic or the weakly algebraizable ones. The paper ends with a section on examples and counterexamples. Dedicated to the memory of Willem Johannes Blok     

Strain-induced submicrocrystalline grains developed in austenitic stainless steel under severe warm deformation

Strain-induced grain evolution in a 304 type austenitic stainless steel has been studied in multiple compression with the loading direction being changed in each pass. The tests were carried out to total strains above 6 at 873 K (0.5 T _m) at a strain rate of about 10^-3 s^-1. Multiple deformation promotes the rapid formation of many mutually crossing subboundaries because various slip systems operate from pass to pass. The gradual rise in misorientations across dislocation subboundaries with increasing strain finally leads to the evolution of very fine grains with large-angle boundaries. It is concluded that a new grained structure can result from a kind of continuous reaction during deformation, namely continuous dynamic recrystallization. Such deformation-induced grains are characterized by relatively low densities of dislocations, and considerable lattice curvatures developed in their interiors. The latter observations suggest that high elastic distortions are developed in the grain interiors and so such strain-induced grain structures are in a non-equilibrium state.     

The flow stress contribution of the dislocation 'forest' in bcc lattices

The athermal flow stress contribution by junction reactions of a glide dislocation with a 'forest' of density rho is usually written as tau = alpha mu b rho ^1/2. The strength coefficient alpha has been computed for the bcc lattice by virtual displacement of triple nodes following the method of Puschl et al. (1982, Physica status solidi (a), 74, 211). In the isotropic approximation, the values for glide dislocations with 0, 30, 60 and 90^o character are as alpha = 0.18, 0.21, 0.19 and 0.22 respectively. A comparison with values calculated previously by Frydman is made, and good agreement is found when differences in the cut-off radii of the linear elastic solution are accounted for.     

Children Exposed to Intra-Familial Violence

Abstract

This investigation examined factors associated with attrition and retention within a sample of children with a history of intra-familial violence referred for outpatient services. The sample included 118 children, aged 4-17 years; of these 64% completed treatment, 20% did not engage in treatment and 16% terminated prematurely. Caregivers reporting high child-related parental distress (F(2, 32) = 3.9, p = 0.03) and high psychological distress (F(2, 70) = 3.3, p = 0.04) were less likely to engage in treatment. Making a child abuse report during assessment or treatment was not found to be associated with treatment engagement or attrition, χ² ₍₂₎= 0.4, p = 0.82. The implications of these findings for clinical practice and treatment outcome research are discussed.     

High-angle annular dark field scanning transmission electron microscopy of the antiphase boundary in a rapidly solidified B2 type TiPd compound

High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast is applied to characterize the antiphase boundary (APB) of the B2 structure in a rapidly solidified TiPd melt-spun compound. The atomic shift associated with the R ?=?(1/2) a ₀ ?111? type displacement vector is directly observed at the boundary. A microstructure modification of the melt-spun compound with the cooling rate during solidification is also described.     

ω-phase formation in a rapidly solidified Cr-40 at.% Al alloy

The diffuse ω structure has been identified by electron diffraction for the first time in a C11_b matrix of the melt-spun Cr-40 at.% Al alloy ribbon. The C11_b matrix consists of nanometre-scale ordered domains produced by a long-period chemical ordering in the precursor A2-B2 structure. Each C11 _b unit cell in the Cr-40 at.% Al alloy is based on three cubic B2 cells along the c axis and contains two antiphase boundaries. The structure of the diffuse ω is consistent with that observed by De Fontaine. The relative stability of the crystalline ω structure has been predicted with respect to bcc-type precursor phases as a function of the displacement parameter z from calculation of the cohesive energy of the ω phase using the full-potential linear muffin-tin orbital method. The results show that the three-dimensional crystalline ω structure is stable with respect to bcc-type precursor phases in the Cr-Al system and reveals the physical background as to why the ω structure in Cr-40 at% Al is diffuse in nature.     

Rapid dendritic growth within an undercooled Ni–Cu–Fe–Sn–Ge quinary alloy

A liquid quinary alloy with composition Ni–5%Cu–5%Fe–5%Sn–5%Ge has been prepared from a containerless state by undercooling. Dendritic growth of α-Ni phase took place with a velocity of 28 m s^?1 at the maximum degree of undercooling, which was as high as 405 K (0.24T _L). All of the four solute elements Cu, Fe, Sn and Ge exhibited a significant solute trapping effect during the rapid dendrite growth. Segregation-less solidification is consequently realized when the degree of undercooling is sufficiently large. The lattice constant of α-Ni solid solution phase is found to increase with the amount of multicomponent solute trapping.     

High-resolution electron microscopy of a microporous carbon

The structure of a microporous carbon prepared by the carbonization of sucrose was examined using high-resolution electron microscopy. It was found to be disordered and isotropic and primarily made up of tightly curved individual carbon layers, enclosing pores typically about 1nm in size. Completely closed carbon particles were also present. These observations suggest that the carbon may have a fullerene-related structure, in which pentagons and heptagons are distributed randomly throughout a hexagonal network, producing continuous curvature.     

Intermediate logics with the same disjunctionless fragment as intuitionistic logic

Given an intermediate prepositional logic L, denote by L ^–d its disjuctionless fragment. We introduce an infinite sequence {J _n}_n1 of propositional formulas, and prove:(1)For any L: L ^–d =I ^–d (I=intuitionistic logic) if and only if J _n L for every n 1.Since it turns out that L{J _{n} n}1 = Ø for any L having the disjunction property, we obtain as a corollary that L ^–d = I ^–d for every L with d.p. (cf. open problem 7.19 of [5]). Algebraic semantic is used in the proof of the if part of (1). In the last section of the paper we provide a characterization in Kripke's semantic for the logics J _n =I+ +J _n (n 1).     

What is the upper part of the lattice of bimodal logics?

We define an embedding from the lattice of extensions ofT into the lattice of extensions of the bimodal logic with two monomodal operators ₁ and ₂, whose ₂-fragment isS5 and ₁-fragment is the logic of a two-element chain. This embedding reflects the fmp, decidability, completenes and compactness. It follows that the lattice of extension of a bimodal logic can be rather complicated even if the monomodal fragments of the logic belong to the upper part of the lattice of monomodal logics.Presented byWolfgang Rautenberg