Phase stability of α-, γ-, and ε-Ce: DFT+DMFT study

We present the total energy calculation of α-, γ-, and ε-Ce phases in the frame of GGA, GGA+U, and DFT+DMFT methods. It has been shown that taken into account of Coulomb correlations in the frame of dynamical mean-field theory allows reproducing the phase diagram of Ce in correct way. Equilibrium volume calculated within the DFT+DMFT method for face-centered cubic (fcc) structure agrees with experimental Ce-γ cell volume. With temperature decrease energy minimum shifts toward α cell volume. Moreover, the DFT+DMFT total energy for body-centered tetragonal (bct) structure becomes smaller than for fcc one with increase in pressure in agreement with experimental phase diagram. Importance of accounting of Coulomb correlation in the frame of DMFT is discussed.     

Multiple relaxation in α- and γ-loss bands of polyethylene

Dielectric and NMR behavior of linear polyethylene was observed in the α-and γ-loss bands in order to investigate the nature of the multiple loss patterns of these loss bands. The results obtained are compared with those of mechanical measurements. In the dielectric behavior of oxidized linear polyethylene, three relaxations are found in the γ-loss band, while only one relaxation is found in the α-loss band. The β-relaxation is found as a plateau region between the α-and γ-loss bands. The loss pattern of the α-loss band is different from that for the mechanical case which is composed of three relaxations. The effects of difference in morphology, addition of diluent, and heat treatment on the multiple loss patterns are examined. The results suggest that there are two noncrystalline regions in the exterior part of lamellae, including lamellar surfaces, and the two modes of molecular motion in each of these regions are responsible for each pair of relaxations; of the three relaxations found in the γ-loss band the γ₂-relaxation is related to the dielectric α-relaxation, while the γ₁-relaxation is related to the β-relaxation. The relation between the two relaxations in each pair is similar to that between the primary relaxation due to micro-Brownian motion and the local mode relaxation of amorphous polymers which are caused by the two modes of motion of the same molecules. The γ₃-relaxation seems to be caused by some different mechanism.     

Modeling texture evolution during rolling of a Cu–Nb multilayered system

A polycrystal plasticity model is proposed to predict the unique rolling texture of Cu/Nb nanostructured multilayers. At this length scale, the model accounts for the interface between Cu and Nb layers by computing the aggregate response of composite grains using a viscoplastic self–consistent scheme. Each composite grain is divided into Cu and Nb crystals with the interface parallel to the rolling plane, and compatibility and equilibrium are enforced across the interface. A latent hardening effect is introduced to account for the interaction between glide and interface dislocations. The latter are accumulated during slip transmission. This unconventional hardening confines the movement of glide dislocations by promoting symmetry of slip activities. Consequently, it slows development of the rolling texture for Cu/Nb nanolayers, and partially preserves the initial interface orientation defined by the Kurdjumov–Sachs relationship.     

Phonon density of states in γ-, β-, and α-AgCuS

The ternary superionic conductor AgCuS was studied by means of inelastic neutron scattering at temperatures of 150 to 398 K. The experimental time-of-flight spectra were recalculated into the generalized phonon density of states G(ɛ) in an incoherent approximation. It is shown that G(ɛ) of AgCuS has a nontrivial temperature dependence over the low-energy range. The relation between the temperature dependence of G(ɛ) and the existence of a low-energy mode in AgCuS is discussed. The text was submitted by the authors in English.     

Molecular dynamics study of roughness and stress evolution using a Lennard–Jones potential

A three-dimensional molecular dynamics (MD) simulation is proposed to study the film growth, roughness and stress evolution during atom deposition on the (100) plane of a fcc regular crystal. We use the cubic system with an x–y periodic boundary condition. At the bottom we have an atomic surface and at the top a reflecting wall. The model uses the Lennard-Jones potential to describe the interatomic forces. The simulation results show that the film grows with the Volmer–Weber mode and exhibits specific curve shape of the stress evolution. The mean biaxial stress obtained during the simulation attains a local tension maximum at a coverage of two monolayers. The stress in the normal direction is smaller than the biaxial stress. The main contribution to the stress in the film arises from the first monolayer. The curves describing roughness possess maximum values at the same substrate coverage. The dependence of the roughness on the temperature is examined.     

Optical switching in a Ξ system: A comparative study on DROP and EIT

Liquid Lennard-Jones clusters with magic number of atoms N = 55, 147, 309, 561 and 923 were cooled down in Monte Carlo simulations until freezing. Structural properties of the clusters, including the radial dependence of atomic concentration/density and the local regular structure in arrangement of atoms, just before freezing were analysed. Existence of spherical layers in atomic density around the centre of mass of liquid LJ clusters was confirmed. Formation of layers is explained by central net forces acting on every cluster atom and leading to positioning an atom close to the cluster centre of mass. The strong layering in small clusters of N = 55 and 147 affects atomic diffusion in radial and tangential directions inside the cluster, leading to easier movement of atoms on the layer surface. Analysis of radial profiles of four types of structural units detected in liquid clusters reveals that icosahedral units are the most numerous and are located mainly near cluster surface of all clusters and also in the centre of small clusters.     

Fluence rate linear response limit of a scintillators to γ-rays

Scintillation detectors based on LSO, CeF and PbWO are the main candidates for measuring γ-rays in a mixed γ/n pulsed radiation field with high intensity. An experiment using the Lissajous figure method to study the high fluence rate response behavior of three kinds of commonly used scintillators is introduced in this paper. The result shows that the fluence rate linear response limit of LSO and CeF is 1.9×10¹⁹ and 2.1×10¹⁸MeV/(cm²·s), respectively, and the PbWO scintillator still maintains linear response when the fluence rate of γ-ray is up to 2.0 × 10²⁰ MeV/(cm²·s).     

INDO-MO study of γ-CH formyl-proton couplings in aliphatic α-formyloxy radicals

In aqueous solution at approximately 25°C, simple aliphatic formate radicals of general formula ·C(X₁)(X₂)OCHO, where an (X-) group is an H- or a substituent such as CH₃-, generally display γ-CH formyl-proton couplings. The size of these couplings depends on the identity of the (X-) groups. An earlier, detailed INDO-MO-SCF investigation of the radical ·CH₂OCHO carried out by considering all conceivable bond rotations suggested a simple interpretation of this dependence, namely, that it followed from the likelihood that substituents at C_α would influence the conformational preferences and these would determine the formyl-proton coupling according to the W-plan rule. As a continuation of this earlier work, the present paper reports the results of a comprehensive INDO-MO-SCF study of the α-formyloxy radicals ·CH(CH₃)OCHO, ·CH(CH₂CH₃)OCHO, ·CH(CH(CH₃)₂)OCHO, and ·C(CH₃)₂OCHO. We found the only bond rotations which appreciably affected the γ-CH formyl-proton coupling in these species to be those about C_αO_β and O_βC_γ. The other results of the present calculations confirm the tentative conclusions of the earlier study about the origin of the dependence of the formyl-proton couplings on the nature of the substituents at C_α. Furthermore, by examining the INDO data in comparison with the experimentally observed formyl-proton couplings, we have been able to assign preferred radical conformations for all members of the ·C(X₁)(X₂)OCHO series, in general agreement with the known conformational preferences of the parent formate molecules, HC(X₁)(X₂)OCHO.     

Effect of γ-irradiation and semiconducting oxide (tio2) on the thermal decomposition of mgc2o4: A comparative study

The simultaneous rising temperature (DTA-TG) technique and the gas evolution method are adopted for studying the thermal decomposition of unirradiated and irradiated MgC₂O₄ and MgC₂O₄ + TiO₂ mixtures. The data are applied to theories of different solid state reaction models and the best fit is obtained for the Avrami-Erofeev mechanism (n=2) suggesting that both the nucleation and growth processes occur at the reactant product interface in a two dimensional chain branching manner. Low irradiation doses decrease the rate of reaction remarkably whereas the reverse phenomenon takes place at higher doses. The n-type semiconducting oxide, TiO₂ (5-40 mol%) enhances the rate of decomposition which increases with increasing concentration of the catalyst. The influence of n -irradiation is explained in the light of defects, dislocations and electron-hole (e^?, h⁺) pairs generated in the lattice, whereas the influence of TiO₂ is understood on the basis of electron transfer process involved in the reaction.     

Shearing of γ′ precipitates in Ni-base superalloys: a phase field study incorporating the effective γ-surface

An extended phase field model of dislocations in Ni-base superalloys is presented. It incorporates the recently developed effective γ-surfaces for both matrix and precipitate phases, obtained from atomistic simulations. These novel γ-surfaces feature extrinsic stacking faults as additional local minima. Thus, they offer an increased number of available dislocation dissociation pathways within the phase field system. The new model has been used to simulate a variety of mechanisms for γ′ precipitate shearing proposed in literature. A critical assessment is made based on the modelling observations.     

The etching and structural response of Makrofol-N and Makrofol-KG polycarbonate to γ-irradiation

In order to estimate the damage densities produced by γ-rays to Makrofol-N and Makrofol-KG, some structural, optical and etching studies have been performed. It is found that both polymers are insensitive to low γ-doses (up to 10³ krad) but are influenced at higher doses. The changes in etching parameters have been noticed along with the changes in the FTIR and UV–VIS spectra. The results have been discussed on the basis of some basic mechanisms of radiation interactions with organic materials.     

Condensation and evolution of a space–time network

In this work, we try to propose in a novel way, using the Bose and Fermi quantum network approach, a framework studying condensation and evolution of a space–time network described by the Loop quantum gravity. Considering quantum network connectivity features in Loop quantum gravity, we introduce a link operator, and through extending the dynamical equation for the evolution of the quantum network posed by Ginestra Bianconi to an operator equation, we get the solution of the link operator. This solution is relevant to the Hamiltonian of the network, and then is related to the energy distribution of network nodes. Showing that tremendous energy distribution induces a huge curved space–time network may indicate space time condensation in high-energy nodes. For example, in the case of black holes, quantum energy distribution is related to the area, thus the eigenvalues of the link operator of the nodes can be related to the quantum number of the area, and the eigenvectors are just the spin network states. This reveals that the degree distribution of nodes for the space–time network is quantized, which can form space–time network condensation. The black hole is a sort of result of space–time network condensation, however there may be more extensive space–time network condensations, such as the universe singularity (big bang).     

Optical spectroscopy and diode-pumped laser characteristics of codoped Tm-Ho : YLF and Tm-Ho : BaYF : a comparative analysis

Single crystals of monoclinic BaY₂F₈ and tetragonal LiYF₄ codoped with the same Tm³⁺ and Ho³⁺ concentrations were successfully grown by the Czochralski method. Here we present a comparative analysis of the two hosts including spectroscopic characterization and cw diode-pumped laser experiments in the 2-μm wavelength region at room temperature. The main differences between the two hosts are a lower slope efficiency associated with a much wider tuning range (2005–2094 nm) of BaY₂F₈ with respect to LiYF₄. Received: 29 July 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/2214-333, E-mail: toncelli@df.unipi.it     

X-ray diffraction study of effect of deposition conditions on α--β phase transition and stress evolution in sputter-deposited W coatings

Pure W and W-Cu-W trilayer coatings were deposited on an Fe substrate by d.c. magnetron sputtering. The α-β phase evolution, intragranular stress evolution in sputter-deposited W layer were investigated by x-ray diffraction. They are directly related to the film microstructure, density and adhesion. Therefore, control of the film stress and phase component transition is essential for its applications. The phase component transition from β-W to α-W and intragranular stress evolution from tensile to compressive strongly depend on the deposition parameters and can be induced by lowering Ar pressure and rising target power. The compressively stressed films with α-W phase have a dense microstructure and high adhesion to Fe substrate.     

A comparative study of F_0 patterns between Chinese and other languages

I.IntroductionEady[1]examinedhowthefundamentalfrequencyF,patternsintone1anguage-Chinesearcdifferentfromthatinstresslang1agnEnglish.HearguedthatthcF,patternsinatonelanguagearesystematica1lydifferentfromthoseinastress1anguageandhisfindingcontradictstheclaimofBo1ingerthat-humanspcakerseverywhercdoessentiallythesamethingwithfundamentalpiteh'.EadyusedcepstalmethodtOdoF,extractionsohecannotgetaninsightintothemicrostructureofthelaryngea1vibrahonsprecisely,althoughanaveragerateofchangeinF,forevery…     

Mechanism of texture and microstructure evolution during warm rolling of Ti–6Al–4V alloy

Ti–6Al–4V (Ti64) plates were subjected to rolling at 600°C and 800°C, respectively, for reductions up to 90% reduction in thickness. The mechanism of texture and microstructure evolution during rolling was studied in the present study. Extension twins of coherent nature were observed in the samples rolled up to 50% of reduction. The deformation was relatively inhomogeneous in the samples rolled at 600°C compared to that at 800°C. Visco-plastic self-consistent (VPSC) simulation showed that relative activity of pyramidal <c+a> slip was higher during rolling at 800°C compared to that at 600°C. The average activity of slip systems per grain was less than five for the samples rolled at 600°C and this might be responsible for the strain heterogeneity in the large grains. Further, twinning activity was found to be limited to a true strain of 0.5, as supported by the microstructural observation. VPSC simulation also showed the presence of contraction twins in the samples which was further supported by X-ray texture measurement. Dominant basal texture was observed in the samples irrespective of the temperature of rolling.