Non-scalar contribution of potential in crystals

Ewald-parameter dependence of Coulomb interaction in ionic crystals was studied using a point-charge model. In the presence of the long-range interaction, the ion configuration breaks spherical symmetry of local potential and charge at each ion site, and gives non-scalar contributions to them. This non-scalar potential has similar effects to Heisenberg interaction, while is intrinsically distinct from conventional multipole expansions of the scalar potential. Symmetry and magnitude of the scalar and non-scalar potentials are similar for most materials despite the different definitions, but one exception can be seen in parent materials of hole-doped high-_Tc$T_{\mathrm{c}}$ cuprates.     

Ultrasoft contribution to heavy-quark pair production near threshold

We compute the third-order correction to the heavy-quark current correlation function due to the emission and absorption of an ultrasoft gluon. Our result supplies a missing contribution to top-quark pair production near threshold and the determination of the bottom quark mass from QCD sum rules.     

Off-axial contribution of beam self-focusing in plasma with density ripple

Off-axial contribution of beam self-focusing in plasma with density ripple is investigated. Apply paraxial ray theory and Wentzel–Krammers–Brillouin approximation, the results shown that, in interaction of laser and plasma with density ripple, beam self-focusing presents some interesting diverse features when off-axial contribution is obvious. In the paper, we find, on the one hand, density ripple can minimize the defocusing and beam still retains a localized profile with an oscillatory self-focusing and defocusing, on the other hand, with the increase of off-axial contribution, laser beams presents four various self-focusing features, which laser beam intensity profile splits into three-splitted with central axial convex profile, three-splitted with equal amplitude profile, three-splitted with central axial concave profile and two-splitted intensity profile.     

Evaluation of the collisionless contribution to the measured infrared multiphoton decomposition

Some of the problems associated with modelling infrared multiphoton decomposition of gaseous molecules are presented. As an example, the cumulative log normal distribution function model is presented in an experimental context where the effects of laser beam geometry and molecular collisions have been taken into account. It is argued that any laser radial profile other than Gaussian, including tophat, can unnecessarily complicate the testing of a model and should be used with caution.     

Magneto-phonon contribution into the Young's modulus of gadolinium

Theoretical and experimental investigation has been made of the magnetic contribution to the Young's modulus of rare earth ferromagnet gadolinium. Experimental study includes measurements of the Young's modulus as a function of temperature, magnetic field and magnetization of gadolinium. Theoretical analysis is based on the account of phonon anharmonicity which gives rise to the dependence of Debye temperature on magnetization. Spontaneous magnetic contribution to the Young's modulus of Gd is found to be proportional to the squared magnetization of the metal. The magnetic contribution is also induced by magnetizing magnet due to the paraprocess. Received: 9 April 1996 / Revised: 26 January 1998 / Accepted: 26 February 1998     

Magnetic contribution to the Gibbs energy of elements versus temperature and pressure

A model for the pressure and temperature dependence of the magnetic contributions to the Gibbs energy of ferromagnetic and antiferromagnetic elements is presented. These contributions are described by three parameters: (1) a critical temperature which is represented by the Curie temperature for ferromagnetic elements or Néel temperature for antiferromagnetic elements, (2) the pressure dependence of that critical temperature, (3) the average magnetic moment per atom. Using thermal expansion data, all these parameters and consequently the pressure and temperature dependence of the magnetic contribution can be calculated. Nickel, a ferromagnetic element, is used as an example.     

On the contribution of nonlinear scattering to optical limiting in C60 solution

We present experimental results which bring out the contribution of nonlinear scattering to the energy limiting of 527 nm, 30 ns pulses in C₆₀ solution. To perform these measurements we used a specific experimental arrangement to separate the effects of nonlinear refraction and scattering. Our results show that scattering reduces the output significantly and contributes to limiting in C₆₀ solution.     

Magnetic measurements in thin film specimens: Rejecting the contribution of the substrate

We propose a new method for the rejection of the comparatively strong diamagnetic contribution usually observed in SQUID magnetization measurements, originating from the substrates that are widely used for the preparation of thin magnetic films either by sputtering or by laser ablation techniques. Our method relies on the use of a substrate of length exceeding significantly the scan length employed in the magnetization measurements. Simple symmetry considerations reveal that the substrate's signal can be removed efficiently. This is also verified by a simple quantitative model, which is based on the form of total response of the four SQUID pick-up coils for a long sample. Our experimental data show clear evidence that the direct rejection of the substrate's undesired diamagnetic signal is complete in all the different categories of films (CoPt uniform single layers, CoPt isolated nanoparticles and _La1-xCaxMnO3${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ multilayered specimens) studied in the present work. As a result, the real underlying mechanism that governs the physics of these magnetic films was uncovered.     

Interactive contribution of grain size and grain orientation to coercivity of melt spun ribbons

During melt spinning process, the improvement of certain grain orientation and the refinement of grain size with surface velocity have interactive and contradictory effects on the magnetic properties. The contributions of these effects have seldom been taken into account and they were discussed in this paper via Fe-2, 4, 6.5 wt% Si alloys. Heat treatment at 1173 K for 1 h was performed to show the annealing impact. The X-ray diffraction patterns show that the high surface velocity and heat treatment increase the intensity ratio of line (2 0 0) to (1 1 0) of A2 phase. The (2 0 0) line corresponds to (2 0 0) plane in 〈0 0 1〉 direction, easy magnetization direction of α-Fe phase in Fe-Si alloy. The improvement of this grain orientation with the surface velocity decreases the coercivity, which should increase due to the grain refinement. It is revealed that the 〈0 0 1〉 texture promoted by the anisotropic heat release during melt spinning process is one factor to improve the magnetic properties and should be considered when preparing soft magnetic materials.     

Electromagnetic polarizabilities of the nucleon and properties of the σ-meson pole contribution

The t-channel contribution to the difference of electromagnetic polarizabilities of the nucleon, (α - β)^t, can be quantitatively understood in terms of a σ-meson pole in the complex t-plane of the invariant scattering amplitude A ₁(s, t) with properties of the σ-meson as given by the quark-level Nambu-Jona-Lasinio model (NJL). Equivalently, this quantity may be understood in terms of a cut in the complex t-plane where the properties of the σ-meson are taken from the ππ → σ → ππ, γγ → σ → ππ and Nˉ → σ → ππ reactions. This equivalence may be understood as a sum rule where the properties of the σ-meson as predicted by the NJL model are related to the f ₀(600) particle observed in the three reactions. In the following, we describe details of the derivation of (α - β)^t making use of predictions of the quark-level NJL model for the σ-meson mass. An erratum to this article is available at .     

Systematic theoretical investigations for contribution of lattice constraint to novel atomic arrangements in alloy semiconductor thin films

The atomic arrangements in zinc blende structured GaN_xAs_1−x thin films coherently grown on V-grooved substrates are theoretically investigated using empirical interatomic potentials and Monte Carlo simulation. The resultant atomic arrangements in GaN_xAs_1−x strongly depend on concentration x and substrate lattice parameter a_sub. Surface segregation of As or N is mainly found in GaN_xAs_1−x with large lattice mismatch to the substrate. On the other hand, the novel atomic arrangements such as layered segregation or ordered structure are found in GaN_xAs_1−x at the specific region such as (x, a_sub) = (0.5, 5.3), (0.3, 5.3), and (0.3, 5.1). This specific region corresponds to that with negative excess energy and with sufficient N and As atoms remaining in thin film layers even after their surface segregation. The formation of the novel atomic arrangements is discussed in terms of bond lengths in the surface layers. These results suggest that various novel atomic arrangements in alloy semiconductor thin films appear depending on x and a_sub which control degree of lattice constraint.     

钡准分子光谱及其对钡原子跃迁线之贡献

用染料激光对热管炉中Ba蒸气进行研究时,在4200～4340A波长范围内,发现一宽带结构及一系列Ba原子的非基态能级产生的跃迁线,用Ba_2准分子的解离对可能产生跃迁的动力学过程做了分析,此宽带结构被归结为Ba_2准分子峰.     

The contribution of grain boundary and defects to the resistivity in the ferromagnetic state of polycrystalline manganites

In the present study we report the precise resistivity measurements for the polycrystalline bulk sample as well as highly oriented thin-films of La_0.8Ca_0.2MnO₃. The poly crystalline sample was prepared by standard solid-state reaction route and the oriented thin film was prepared by pulsed laser deposition (PLD). The phase purity of these samples was confirmed by X-ray diffraction and the back-scattered electron imaging using scanning electron microscopy (SEM). The oxygen stoichiometry analysis was done by iodimetry titration. The resistivities of these samples were carried out with four-probe resistivity measurement setup. The observed temperature dependence of resistivity data for both the samples was fitted using the polaron model. We have found that polaronic model fits well with the experimental data of both polycrystalline and single crystal samples. A new phenomenological model is proposed and used to estimate contribution to the resistivity due to grain boundary in the ferromagnetic state of polycrystalline manganites and it has been shown that the scattering of electrons from the grain boundary (grain surface) is a function of temperature and controlled by the effective grain resistance at that temperature.     

The contribution of Gd and Mn neighbours to the Gd hyperfine field in GdMn6Ge6

With the help of ^155,157Gd NMR in we derive the contribution of Gd and Mn neighbours to the hyperfine field at the rare earth site in the spiral spin phase of the intermetallic compound GdMn₆Ge₆. The substitution of Gd for Y atoms allows the determination of the separate contribution of remote Gd neighbours. The different temperature dependence of the hyperfine contributions of the Gd and Mn neighbours gives the possibility to estimate the transferred hyperfine field of Mn at the rare earth site both in magnitude and sign. Received 31 May 2000 and Received in final form 26 September 2000     

A generic model for the ionic contribution to the equation of state

Abstract

We describe an extended standard model that yields the thermodynamics of the ionic contribution for general materials, from the low temperature solid region, through melting, to the ideal gas limit. We use the Debye model for the solid. Melting is determined by the Lindemann formula with standard rules of thumb used to determine density and energy discontinuities. The model interpolates through the liquid regime to the ideal gas assuming that the specific heat drops monotonically from about 3R at melting, to 9R/4 at five times melting, and continuing to 3R/2 at high temperatures. The area under the specific heat curve is constrained in the model to reproduce the correct high temperature entropy. Thus, for a compound the extra contribution from the entropy of mixing forces into the model, in a crude way, the extra specific heat due to dissociation.     

关于照相物镜色贡献指数容限的讨论

关于照相物镜色贡献指数的国际标准于1983年公布。但是,关于色贡献指数(ISO/CCI)的容限仍保留在附录中,并以建议的形式给出。本文从色度学基本公式出发,对相应于容限范围内六个边缘点的照相物镜,计算了它们摄影效果的色度坐标。同时计算了它们和ISO标准照相物镜的摄影效果在均匀颜色空间的色差值。据此讨论了该容限的合理性,并提出把容限范围划分成两个区域的建议。     

Magnetic contribution to heat capacity and entropy of nickel ferrite (NiFe2O4)

The heat capacity of nickel ferrite was measured as a function of temperature from 50 to 1200 °C using a differential scanning calorimeter. A thermal anomaly was observed at 584.9 °C, the expected Curie temperature, T_C. The observed behavior was interpreted by recognizing the sum of three contributions: (1) lattice (vibrational), (2) a spin wave (magnetic) component and (3) a λ-transition (antiferromagnetic-paramagnetic transition) at the Curie temperature. The first was modeled using vibrational frequencies derived from an experimentally-based IR absorption spectrum, while the second was modeled using a spin wave analysis that provided a T^3/2 dependency in the low-temperature limit, but incorporated an exchange interaction between cation spins in the octahedral and tetrahedral sites at elevated temperatures, as first suggested by Grimes [15]. The λ-transition was fitted to an Inden-type model which consisted of two truncated power law series in dimensionless temperature (T/T_C). Exponential equality (m=n=7) was observed below and above T_C, indicating symmetry about the Curie temperature. Application of the methodology to existing heat capacity data for other transition metal ferrites (AFe₂O₄, A=Fe, Co) revealed nearly the same exponential equality, i.e., m=n=5.     

On the contribution of nearly critical spin and charge collective modes to the Raman spectra of high-Tc cuprates

We discuss how Raman spectra are affected by nearly critical spin and charge collective modes, which are coupled to charge carriers near a stripe quantum critical point. We show that specific fingerprints of nearly critical collective modes can indeed be observed in Raman spectra and that the selectivity of Raman spectroscopy in momentum space may also be exploited to distinguish the spin and charge contribution. We apply our results to discuss the spectra of high-T_c superconducting cuprates finding that the collective modes should have masses with substantial temperature dependence in agreement with their nearly critical character. Moreover, spin modes should be more diffusive than charge modes indicating that in stripes the charge is nearly ordered, while spin modes are strongly overdamped and fluctuate with high frequency.