Surface structure determination by quasidynamical LEED intensity evaluation

The quasidynamical method for LEED intensity calculations is applied to Ir(100)1 × 1 over a broad energy range, 100–500 eV. The comparison with experiment and full dynamical calculations shows that peak positions and peak widths are well reproduced, but relative peak heights and therefore also shapes of peak groups can be considerably modified. This behaviour is discussed and explained in terms of the forward and backward diffraction properties of single layers. Finally, a structure determination is tried using the Pendry r-factor for the quantitative comparison of the experimental and quasidynamical data. The resulting value for the surface relaxation agrees with that determined from the full dynamical evaluation within the usual error of structure determination by LEED.     

Quasidynamical symmetry in an interacting boson model phase transition

The apparent persistence of symmetry in the face of strong symmetry-breaking interactions is examined in a many-boson model. The model exhibits a transition between two phases associated with U(5) and O(6) symmetries, respectively, as the value of a control parameter progresses from 0 to 1. The remarkable fact is that, in spite of strong mixing of the symmetries for intermediate values of the control parameter, the model continues to exhibit the characteristics of its closest symmetry limit for all but a relatively narrow transition region that becomes progressively narrower as the boson number increases. This phenomenon is explained in terms of quasidynamical symmetry.     

The structure of Si(OOl) 2 × 1 surface — Studied by low energy electron diffraction

Intensity-voltage spectra of low energy electron diffraction are calculated by the quasidynamical method and the results analyzed to determine the validity of new structural models proposed for the Si(001) surface.     

超子及K介子衰变的分枝比和平均寿命间的比例

本文应用了费曼和盖尔曼所提出的普适费米弱相互作用和同位旋守恒的强相互作用计算了各种超子、K介子衰变的分枝比和平均寿命的比例。在计算时应用了微扰论,并在大动量处将相互作用截断。在应用了查尔斯·瓦纳所给出的相互作用常数和对其余两个常数作了一定的选择之后,得到的分枝比和平均寿命之比大部分和实验结果符合,最坏相差一个因子二。如果选择本文所采用的相互作用常数,可以改进前一篇源文中K⁺介子分枝比计算结果和实验的符合程度。本文计算表明V-A普适弱相互作用确实适用于K分子和超子衰变现象,表明在解释这些现象时,必须考虑到“很强”和“较强”两类强相互作用所分别产生的影响。此外,本文还表明Λ和∑应具有相同的相对宇称,K分子和核子、超子之间的四种强相互作用中必须至少有一对是膺标量耦合。     

Studies on the surface modification of diatomite with polyethyleneimine and trapping effect of the modified diatomite for phenol

The adsorption isotherm of polyethyleneimine (PEI) on diatomite was studied using UV spectrophotometry, the surface of diatomite was modified with polyethyleneimine by using impregnation method, and the trapping behavior of the modified diatomite for phenol was investigated by using 4-aminoantipyrine (4-AAP) spectrophotometric method. The experiment results show that negatively charged diatomite particles have very strong absorption effect for cationic macromolecule PEI, the adsorption isotherm fits in Freundlich equation. The character that there is a maximum value after intitial sharp increase of adsorption capacity on the adsorption curve indicates that there is strong affinity between diatomite particles and polyethyleneimine macromolecules, and it attributes to the strong electrostatic interaction. After modification with PEI, the electric property of diatomite particle surface changes essentially, and the isoelectric point of diatomite particles moves from pH 2.0 to 10.5. In acidic solution, phenol exists as molecular state, and the modified diatomite particles adsorb phenol through hydrogen bond interaction. However, the hydrogen bond interaction between nitrogen atoms on PEI chains and phenol is weaker because of high degree of protonation of polyethyleneimine macromolecules, so the adsorption quantity is lower. In basic solution, phenol exists as negative benzene–oxygen ion, and the modified diatomite particles adsorb phenol through electrostatic interaction. However, the electrostatic interaction between PEI and negative benzene–oxygen ion is very weak because of low degree of protonation of polyethyleneimine macromolecules, so the adsorption quantity is much lower. The modified diatomite particles produce very strong trapping effect for phenol in neutral aqueous solution via the cooperating of strong electrostatic interaction and hydrogen bond interaction, and the saturated adsorption capacity can attain to 92 mg g⁻¹.     

Search for magnetic interaction in In doped AlN using perturbed angular correlation spectroscopy

The possible presence of a large magnetic field due to spin polarization of a Cd nucleus (decay product of ¹¹¹In) at an Al substitutional site in AlN is investigated with perturbed angular correlation (PAC) spectroscopy. The PAC spectra of ¹¹¹In/¹¹¹Cd in AlN show two probe environments: a weak quadrupole interaction (quadrupole interaction constant, $\nu _{\rm Q}^{\,\,\,\rm lattice} = 30$  MHz) due to ¹¹¹In probes at a defect free Al substitutional site and an unknown large interaction ( $\nu _{\rm Q}^{\,\,\,\rm complex} = 300$  MHz) tentatively attributed to a nearest neighbour pair between ¹¹¹In and a nitrogen vacancy (V_N) aligned along the c-axis. Surprisingly, in density functional theory (DFT) calculations, such a large electric field gradient (EFG) could not be reproduced. However, an inclusion of spin polarization in the calculations indicates a strong magnetic field at ~50 % of the ¹¹¹In/¹¹¹Cd site. An attempt to verify the presence of the strong magnetic field and to explain the origin of the strong interaction is made. Orientation measurements show, the large interaction is not characterised by a magnetic interaction and is predominantly due to the EFG. However, in the presence of an external magnetic field, the strong interaction probe environment becomes more uniform and the EFG increases by ~10 %. This definitely hints towards some sort of magnetic interaction at the strong interaction probe site.     

Cubic helimagnets in magnetic field and at pressure

Cubic helimagnets with B20 structure display several unusual properties such as anisotropy of the spin-wave spectrum al small momenta q, rotation of the helix vector k in magnetic field and quantum phase transition at pressure. We demonstrate that first two phenomena are a result of umklapp processes mixing excitations with momenta q, q+k and q−k. At very low magnetic field perpendicular to k the helical structure remains stable due to spin-wave gap Δ. Its square is sum of two parts. The first one is a result of the magnon interaction and the second negative part stems from magneto-elastic interaction. It is suggested that competition between these parts leads to the quantum phase transition observed in MnSi and FeGe. For MnSi from rough estimations at ambient pressure was shown that both parts are comparable with the experimentally observed gap. The magneto-elastic interaction is also responsible for 2k modulation of the lattice and contributes to the magnetic anisotropy. Experimental observation by X-ray and neutron scattering of this lattice modulation allows to determine the strength of the magneto-elastic interaction responsible for above phenomena and the lattice helicity.     

Photon-assisted shot noise due to the charging effect in a quantum dot device

We have investigated the spectral density of shot noise for an ultra-small quantum dot(QD) system in the Coulomb blockade regime when irradiated with microwave fields (MWFs) by employing a nonequilibrium Green’s function technique. The shot noise is sensitive to Coulomb interaction, and the photon-assisted Coulomb blockade behaviour strongly modifies the mesoscopic transport. We have calculated the first and second derivatives of shot noise in the strong and weak coupling regimes to compare the theoretical results with existing experimental results. In the strong coupling regime, the first and second derivatives of shot noise display Fano type peak-valley structures around the charging channel 2E _c due to Coulomb interaction. When the magnitudes of the MWFs are sufficiently large, the system displays channel blockade due to photon irradiation. The photon-assisted and Coulomb blockade steps in the noise — as well as the resonant behaviour in the differential noise — are smeared by increasing temperature. The Coulomb interaction suppresses the shot noise, but the ac fields can either suppress the shot noise(balanced case) or enhance the shot noise(unbalanced case). The suppression of shot noise caused by ac fields in the balanced case is greater than that caused by Coulomb interaction in our system. Super-Poissonian shot noise may be induced due to the compound effects of strong Coulomb interaction and photon absorption-emission processes.     

μ介子为质子所辐射俘获

本文利用重正化了的费米型V-A弱相互作用计算μ介子被质子吸收时所产生的辐射俘获现象。在计算中利用了余列多维奇等所指出的μ介子在俘获前停留在K层的单重态上的理论结果。计算的结果与李政道等忽略强相互作用的影响及忽略μ介子原子由三重态至单态的跃迁所得到的结果有很大的不同。我们得到当完全不考虑强相互作用的影响时μ介子被质子俘获时不能放出γ辐射的结论。其次我们考虑了两方面的强相互作用影响,一方面考虑了核子反常磁矩的影响,另一方面又考虑了强相互作用对V-A弱相互作用的重正化效应。计算结果指出:反常磁矩的贡献只为重正化效应的5％左右。由重正化效应所产生的辐射俘获几率只有李政道等所给出的几率的14％,放出的光子不再是100％右旋的,估计约有20％的左旋光子。     

Positronium formation by electron capture from hydrogen-like ions

Two different impulse approximations are provided for the problem of fast positron collisions with hydrogen-like ions. One of the impulse approximations is formulated by making a consistent expansion of the scattering wave function in powers of the weak interaction to the strong. The other impulse approximation is formulated by making a consistent expansion of theT-matrix in powers of the weak interaction to the strong. In this impulse approximation, the opposite limits of the target nuclear charge tending to zero and to infinity are examined. Differential and angle-integrated cross sections are computed for ground-state positronium formation from hydrogen within the impulse approximations. The full peaking approximation is employed in the evaluation of theT-matrix. By 300 eV, the impulse approximations for the angle-integrated cross section are in close agreement with the strong potential Born and the exact second Born calculations.     

Peculiarities of the SERS Spectra of 4,4′-Bipyridine Molecule in a Single Molecule Detection Regime

The paper describes briefly main statements of the theory of the SERS spectra with regards to the single molecule regime, when the enhancement achieves the values ~10¹⁴?10¹⁵. Analysis of the spectra of 4,4′-bypyridine, obtained on the dimer lattice of sharp nanoparticles points out that the observed enhancement is caused exclusively by a strong quadrupole light-molecule interaction, which manifests in the presence of lines, caused by vibrations with the unit irreducible representations of the D₂ and D_2h symmetry groups, which apparently describe the symmetry properties of the molecule. The study of the spectra, obtained by tip enhanced spectroscopy demonstrates that the strong quadrupole light-molecule interaction still has a governing role, however the strong dipole interaction still manifests in the existence of very weak forbidden lines. This result apparently is associated with another experimental geometry.     

Two-leg spin ladder model for Ag2VOP2O7 from mapping analysis based on first principles density functional calculations

The magnetic properties of Ag₂V OP₂O₇ were examined by evaluating its spin exchange interactions in terms of spin dimer analysis based on tight binding calculations and mapping analysis based on first principles density functional theory calculations. Both calculations show that a strong spin exchange interaction occurs through the super-superexchange path J₁ with the V…V distance of 5.293 Å. This strong antiferromagnetic interaction forms isolated spin dimer units, which are coupled antiferromagnetically by the spin exchange path J₃ to form a two-leg spin ladder that has no spin frustration. The inter–dimer interaction J₂ is found to be ferromagnetic, and does not lead to spin frustration.     

On the effect of inhomogeneous magnetoelectric (flexomagnetoelectric) interaction on the spectrum and properties of magnons in multiferroics

The features of the magnon spectrum in easy-plane multiferroics (such as BiFeO₃), which allow inhomogeneous magnetoelectric (flexomagnetoelectric) interaction P[(L?)L ? LdivL], where L and P are the antiferromagnetic moment and electric polarization, respectively, have been theoretically analyzed. It has been shown that, in contrast to the magnon spectrum of a usual easy-plane antiferromagnet, a multiferroic with this magnetic structure is characterized by, first, the interaction between magnons of both branches propagating along the weak ferromagnetic moment and the appearance of a minimum (or zero) of the frequency of one of the branches, which reflects the instability of the system with respect to the transition to an inhomogeneous state with increasing flexomagnetoelectric interaction and, second, the nonequivalence (nonreciprocity) of the propagation of spin waves along and against the antiferromagnetism vector, which coincides with the toroidal moment in this system.     

Competition between the Coulomb and phonon fields: superconductivity in a quiescent Fermi gas

Co-existence of and competition between the screened Coulomb and phonon fields are fundamental facts in superconductors. In the conventional superconductors the strong screening greatly suppresses the Coulomb interaction and the phonon field that mediates a given attractive interaction between electrons may thus play a leading role. A quiescent Fermi sea hence applies, as proposed by Cooper and adopted in BCS.In this model a graphical derivative technique, based on Ward's identity, is developed to consider the contributions to the interparticle interaction. This technique allows one to evaluate the effective two-particle interaction (T-matrix). It is shown that the conventional Cooper instability in a quiescent Fermi gas is only caused by agivenattractive interaction. Of more importance is that the methodology presented in this work can be extended to the investigation of the intermediate and strong coupling cases where the well-known Migdal theorem is not applicable and the vertex corrections must be evaluated.     

Contributions of weak and strong interactions to the anomalous magnetic moment of the electron

Based on Weinberg - Salam weak interaction theory, we have determined the addition to the anomalous magnetic moment of the electron arising from interaction between the electron and quantum fluctuations of the vector field (the carrier of the weak interaction). We also estimate the contribution of the strong interaction to the anomalous magnetic moment of the electron due to polarization of the quark — gluon vacuum. The overall contribution of the weak and strong interactions to the anomalous magnetic moment proves to be equal to 1·10^–12, and the contribution of the weak interaction is 2.2 times greater than the contribution of the strong interaction.Kamskii Polytechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 13–19, November, 1993.     

Heat bath coupling effects on interaction between Fröhlich vibration systems

The energy supplied to the Fröhlich vibration system in a living cell may condense in certain normal modes provided the coupling of the vibration system with a heat bath is nonlinear. The strong coupling of a coherent vibration system with a heat bath causes reduced energy condensation; high frequency modes are not excited and the energy condensed in the lowest frequency mode is smaller than the energy condensed in a system with weak coupling. The vibrations are polar and generate an electromagnetic field. The electromagnetic field mediates a long range interaction between the Fröhlich vibration systems; the interaction depends on the intensity of the generated electromagnetic field, and, therefore, on the energy condensed in the vibration system. The systems with strong coupling with a heat bath have weak interaction forces, which may be attractive as well as repulsive. The effect of coupling with a heat bath on interaction between the Fröhlich systems is a new contribution of this paper. The coherent vibration systems are assumed to be excited in protein molecules in cellular membranes. Protein phosphorylation may cause the strong Coulomb coupling of vibration systems with a heat bath and may have a fundamental effect on energy condensation.The work was supported, in part, by grant COST 244.     

Electrostatic interaction between two macroparticles in the Poisson-Boltzmann model

Considering the electrostatic energy of the system of two macroparticles in a plasma in the Poisson-Boltzmann model, Resendes et al. [Phys. Lett. A 239, 181 (1998)], Ivanov [Phys. Lett. A 290, 304 (2001)], Gerasimov and Sinkevich {Teplofiz. Vys. Temp. 37, 853 (1999) [High Temp. 37, 823 (1999)]}, and D’achkov {Teplofiz. Vys. Temp. 43, 331 (2005) [High Temp. 43, 322 (2005)]} conclude that attraction between identically charged macroparticles is possible. In the Poisson-Boltzmann model, the distribution of electrons and ions has the Boltzmann form in a self-consistent field that is determined by the Poisson equation. In this work, on the basis of the analysis of the force between two macroparticles in a plasma by using the Maxwell stress tensor, it has been shown that two macroparticles with the same charge always repulse each other in both isothermal and nonisothermal plasmas. The interaction between macroparticles at distances, where Boltzmann exponentials can be linearized, is completely described by the Debye-Hückel theory. The free energy of the system of two particles has been found. It coincides with the Yukawa potential and has no minimum; therefore, such a system is thermodynamically unstable. Since the interaction energy obtained by integrating the interaction force coincides with the free energy of the electric field, the interaction between two macroparticles in the equilibrium plasma is potential.     

Preferred states of open electronic systems

System-environment interaction may introduce dynamic destruction of quantum coherence, resulting in a special representation named as pointer states. In this work, pointer states of an open electronic system are studied. The decoherence effect is taken into account through two different ways which are Büttiker's virtual probe model and strong electron-phonon interaction in the polaron picture. The pointer states of the system with different coupling strength are investigated. The pointer states are identified by tracking the eigenstates of the density matrix in real-time propagation. It is found that the pointer states can emerge for arbitrary coupling strength. And the pointer states deform to the eigenstates of the system in the strong coupling limit, which indicates the vanish of quantumness in the strong coupling limit.     

Is strong gravity an aspect of strong interaction?

A more general treatment is given of the field equations of the model for strong gravity proposed by the author in 1976. It seems possible to treat strong gravity and strong interaction by the same formalism, suggesting that strong gravity is just an aspect of strong interaction. The essential idea in these models is that a hadron is a de Sitter microsphere of radius of about 1 fm and the requisite gauge field is a fourth-rank tensor in the de Sitter space of the hadron. A three-dimensional formulation of the model is presented and further possibilities outlined.     

Nucleation of microcracks during dislocation interactions in a Ti<Subscript>3</Subscript>Al single crystal

Reactions between superdislocations involved in deformation in the basal, prismatic, and type-I and II pyramidal planes in single-crystal Ti₃Al are considered. The types of dislocation interactions are established that result in the formation dislocation barriers (microcrack nuclei). The force and energy conditions for microcracks to arise are found. The interaction between a and 2c + a superdislocations results in microcracks with the plane of opening lying in basal and pyramidal planes; the interaction of 2c + a superdislocations in different pyramidal planes results in the formation of microcracks in prismatic and pyramidal planes; and the interaction of a superdislocations in basal and/or pyramidal planes does not cause the formation of dislocation barriers. The types of microcracks are classified in terms of the orientation of deformation axes of single crystals, and the regions of the stereographic triangle are determined characterized by a preferential type of crack opening.