Evaluation of QCD sum rules for light vector mesons at finite density and temperature

QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of mass parameters for the lightest vector mesons ρ, ω and φ in a strongly interacting medium. For conditions relevant for the starting experiments at HADES we find that the in-medium mass shifts of the ρ- and ω-mesons are governed, within the Borel QCD sum rule approach, by the density and temperature dependence of the four-quark condensate. In particular, the variation of the strength of the density dependence of the four-quark condensate reflects directly the decreasing mass of the ρ-meson and can lead to a change of the sign of the ω-meson mass shift as a function of the density. In contrast, the in-medium mass of the φ-meson is directly related to the chiral strange quark condensate which seems correspondingly accessible. Received: 15 May 2002 / Accepted: 31 July 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: Kaempfer@fz.rossendorf.de Communicated by A. Sch?fer     

Schrödinger operators with symmetries

We consider the stationary Schrödinger operator H of a many-body system M with two-body rotation invariant interactions. The operator H is reduced with respect to the symmetries of permutation of identical particles, rotations and reflections, into a direct sum of operators H^τ̃, where τ̃ is an index of the irreducible representations of the symmetry group of the system.The spectra of the operators H^τ̃ were investigated in a series of papers of G.M. Zislin and A.G. Sigalov ([20], [21], [31]-[35]). In a recent paper [3] we have developed the spectral theory of these operators on the basis of the Weinberg equations.In the present work we complete and simplify this theory. In particular we treat in detail the case where the given system can be decomposed into two identical subsystems. For such systems there is a certain coupling between permutation and rotation-reflection symmetries, because a permutation, which interchanges the two subsystems, imposes a reflection on the relative position vector of the two centers of mass. This requires a modification of the theorem on essential spectrum as formulated in [3] in the case where such a division is not possible. The importance of this special case, as exemplified by diatomic molecules, fully justifies such a detailed treatment.This special case was treated by Zislin [34] under the assumption that the interactions are essentially multiplicative, relatively compact two-body interactions. Our method allows for general relatively compact two-body interactions, and can without difficulty be generalized to many-body interactions.Moreover, the method based on the Weinberg equation is suitable for a further analysis of the spectra of these operators.     

多价抗衡离子诱导聚甲基丙烯酸N,N-二甲基氨基乙酯(PDMAEMA)刷构象转变的UCST行为

本文应用分子场理论,研究pH、[Fe(CN)_6]~(3-)诱导聚甲基丙烯酸N,N-二甲基氨基乙酯(PDMAEMA)刷的上临界溶解温度(UCST)构象转变与结构特性.理论模型考虑p H和[Fe(CN)_6]~(3-)对PDMAEMA刷体系的静电调控作用.研究发现,在不同[Fe(CN)_6]~(3-)浓度、不同p H条件下,PDMAEMA刷呈现了UCST构象转变行为.由于p H调节PDMAEMA单体质子化,[Fe(CN)_6]~(3-)通过与PDMAEMA带正电荷的单体结合,形成了在PDMAEMA链内以[Fe(CN)_6]~(3-)为中介的带电单体间的静电吸引结合.随着温度升高,[Fe(CN)_6]~(3-)与PDMAEMA带正电荷的单体结合被破坏,[Fe(CN)_6]~(3-)在链内凝聚导致的静电屏蔽效应减弱,PDMAEMA链内带电单体间的静电排斥增强,PDMAEMA刷的构象呈现了从塌缩到溶胀的UCST转变行为,并且在较高[Fe(CN)_6]~(3-)浓度条件下,PDMAEMA刷构象转变的UCST增高.在较低p H值条件下,较多的PDMAEMA单体被质子化,[Fe(CN)_6]~(3-)与PDMAEMA带正电单体的结合增强,PDMAEMA刷构象转变的UCST增大.基于pH和[Fe(CN)_6]~(3-)对PDMAEMA刷体系中的静电调控效应,可以预言,在较小p H和较大[Fe(CN)_6]~(3-)浓度条件下,PDMAEMA链在垂直培基表面沿着链方向形成结节状结构.这是由于以[Fe(CN)_6]~(3-)为中介的链内带电单体间的静电吸引作用增强,导致临近单体间汇聚结节.我们的理论结果符合实验观测,由此表明,pH调节PDMAEMA单体的带电状态,以及[Fe(CN)_6]~(3-)在PDMAEMA链内凝聚导致的静电屏蔽效应,决定着PDMAEMA刷的UCST构象转变和结构特性.     

Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling

The magnetic properties of a charged spin-1 Bose gas with ferromagnetic interactions are investigated within mean-field theory. It is shown that a competition between paramagnetism, diamagnetism and ferromagnetism exists in this system. It is shown that diamagnetism, being concerned with spontaneous magnetization, cannot exceed ferromagnetism in a very weak magnetic field. The critical value of reduced ferromagnetic coupling of the paramagnetic phase to ferromagnetic phase transition [Formula: see text] increases with increasing temperature. The Landé-factor g is introduced to describe the strength of the paramagnetic effect which comes from the spin degree of freedom. The magnetization density [Formula: see text] increases monotonically with g for fixed reduced ferromagnetic coupling [Formula: see text] as [Formula: see text]. In a weak magnetic field, ferromagnetism makes an immense contribution to the magnetization density. On the other hand, at a high magnetic field, the diamagnetism tends to saturate. Evidence for condensation can be seen in the magnetization density at a weak magnetic field.     

Surface soft phonon and the sqrt[3] x sqrt[3] <--> 3x3 phase transition in Sn/Ge(111) and Sn/Si(111)

Density functional theory calculations show that the reversible Sn/Ge(111) sqrt[3]xsqrt[3]<-->3x3 phase transition can be described in terms of a surface soft phonon. The isovalent Sn/Si(111) case does not display this transition since the sqrt[3]xsqrt[3] phase is the stable structure at low temperature, although it presents a partial softening of the 3x3 surface phonon. The rather flat energy surfaces for the atomic motion associated with this phonon mode in both cases explain the experimental similarities found at room temperature between these systems. The driving force underlying the sqrt[3]xsqrt[3]<-->3x3 phase transition is shown to be associated with the electronic energy gain due to the Sn dangling bond rehybridization.     

Meandering Spiral Waves Induced by Time-Periodic Coupling Strength

Effects of time-periodic coupling strength (TPCS) on spiral waves dynamics are studied by numerical computations and mathematical analyses. We find that meandering or drifting spirals waves, which are not observed for the case of constant coupling strength, can be induced by TPCS. In particular, a transition between outward petal and inward petal meandering spirals is observed when the period of TPCS is varied. These two types of meandering spirals are separated by a drifting spiral, which can be induced by TPCS when the period of TPCS is very close to that of rigidly rotating spiral. Similar results can be obtained if the coupling strength is modulated by a rectangle wave. Furthermore, a kinetic model for spiral movement suggested by Di et al., [Phys. Rev. E 85 (2012) 046216] is applied for explaining the above findings. The theoretical results are in good qualitative agreement with numerical simulations.     

Impact of eigenvalues on the pseudopotential calculation of superconducting parameters of metals Ga, Cd and In

In the present paper some superconducting (SC) state parameters of metals Ga, Cd and In have been studied through Harrison’s First Principle [HFP] pseudopotential technique using McMillan’s formalism. The impact of choosing two different sets of core energy eigenvalues viz. Herman-Skillman and Clementi (or Experimental) has been studied. It has been observed that the choice of eigenvalues has appreciable impact on the form factor and consequently on the SC state transition parameter viz. electron-phonon coupling strength (λ) and superconducting transition temperature T _c . Hence the choice of suitable eigenvalues is essential for these computations. Reasonable agreement with experimental and theoretical data have been obtained.     

Quadrupole relaxation enhancement--application to molecular crystals

A general theory of field dependent spin-lattice relaxation for nuclei of the spin quantum number 1/2 (1H, 19F, 13C) caused by dipole-dipole interactions with neighboring quadrupolar nuclei (nuclei possessing a quadrupolar moment) is presented. The theory is valid for arbitrary motional conditions and should be treated as a quadrupolar counterpart of the paramagnetic relaxation enhancement theory. When the energy level splitting of the dipolar spin (I=1/2) matches one of the transition frequencies of the quadrupolar nuclei one can observe a local enhancement of the dipolar spin relaxation (referred to as "quadrupolar peaks"). To see such effects the dynamics modulating the spin interactions has to be relatively slow. This brings the system beyond the validity range of perturbation approaches and requires the stochastic Liouville equation to be applied. The presented theory describes the quadrupolar relaxation enhancement (QRE) for an arbitrary spin quantum number of the quadrupolar nuclei and includes the asymmetry of the quadrupolar coupling. It has been applied to interpret the shape of magnetization curves (amplitude of 1H magnetization versus magnetic field) for the molecular crystal [C3N2H5]6[Bi4Br18] ([C3N2H5]-imidazolium). The magnetization curves show several dips (local minima) attributed to 1H-14N quadrupolar relaxation enhancement effects. In addition, as a limiting case a perturbation approach to QRE has been presented and its validity conditions have been discussed.     

Meandering Spiral Waves Induced by Time-Periodic Coupling Strength

Effects of time-periodic coupling strength （TPCS） on spiral waves dynamics are studied by numerical computations and mathematical analyses. We find that meandering or drifting spirals waves, which are not observed for the case of constant coupling strength, can be induced by TPCS. In particular, a transition between outward petal and inward petal meandering spirals is observed when the period of TPCS is varied. These two types of meandering spirals are separated by a drifting spiral, which can be induced by TPCS when the period of TPCS is very close to that of rigidly rotating spiral. Similar results can be obtained if the coupling strength is modulated by a rectangle wave. Furthermore, a kinetic model for spiral movement suggested by Diet al., [Phys. Rev. E 85 （2012） 046216] is applied for explaining the above findings. The theoretical results are in good qualitative agreement with numerical simulations.     

Synthesis,Characterization Luminiscence Studies and Microbial Activity of Ethylenediamine Ruthenium (II) Complexes with Dipyridophenazine Ligands

Three symmetric ligands 7-methyl dipyrido-[3,2-a;2′,3′-c]phenazine (dppz-CH₃), 7-nitro dipyrido-[3,2-a;2′,3′-c]phenazine (dppz-NO₂) and benzo[i]dipyrido-[3,2-a;2′,3′-c]phenazine (dppn) and their ruthenium(II) complexes [Ru(en)₂(L)][ClO₄]₂ (en= ethylenediamine), L= dppz-CH₃, dppz-NO₂ and dppn have been synthesized and characterized by IR, ¹H, ¹³C NMR and Mass spectra. The interactions of these complexes with calf thymus DNA have been investigated by spectrophotometric, spectrofluorimetric, circular dichroism, viscosity and thermal denaturation studies. As the planar extension of the intercalative ligand increases, the interaction of the complex with DNA increases, indicating that the size and shape of the intercalalative ligand has a marked effect on the strength of interaction. The plot of log K versus log [Na⁺] yield a slope of -1.26, -1.53, -1.60 for the complexes 1, 2 and 3 respectively. These three complexes have been found to promote the cleavage of plasmid pBR 322 DNA upon irradiation.     

Evolution of the ferroelectric phase in ?001?-oriented (100 ? x )PbMg1/3Nb2/3O3- x PbTiO3 single crystals

The effect of a dc electric field on the nucleation and evolution of the phase with long-range order in a cubic nonpolar matrix in 〈001〉-oriented (100 − x)PbMg_1/3Nb_2/3O₃-xPbTiO₃ single-crystal relaxors as the content of PbTiO₃ is gradually increased (6 ≤ x ≤ 20, where x is the PbTiO₃ content given in molecular percent) is investigated. The optical properties of these solid solutions are studied in different modes of application of an electric field. It is shown that an applied electric field with a strength above a threshold value induces a first-order ferroelectric phase transition with a temperature hysteresis occurring between measurements performed under cooling and heating of the crystal in the electric field. As the PbTiO₃ content or electric field strength increases, the hysteresis becomes less pronounced and the first-order phase transition is suppressed. At x ∼ 20, the induced transition resembles a second-order rather than first-order transformation. It is assumed that, for compositions with x > 10 in electric fields higher than 4 kV/cm, the formation of the rhombohedral phase is accompanied by the appearance of another (possibly, monoclinic) phase associated with the rotation of the polarization vector from the [111] direction of the rhombohedral phase to the [001] direction of the tetragonal phase. Original Russian Text ? L.S. Kamzina, E.V. Snetkova, I.P. Raevskiĭ, A.S. Emel’yanov, Jiayue Xu, Weidong Xiang, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 725–730.     

Low temperature disordered phase of alpha-Pb/Ge(111)

A new structural phase transition has been observed at low temperature for the one-third of a monolayer (alpha phase) of Pb on Ge(111) using a variable-temperature scanning tunneling microscope. The well-known (sqrt[3] x sqrt[3])R30 degrees to (3 x 3) transition is accompanied by a new structural phase transition from (3 x 3) to a disordered phase at approximately 76 K. The formation of this "glasslike" phase is a consequence of competing interactions on different length scales.     

Frequency and intensity readouts of micro-wave electric field using Rydberg atoms with Doppler effects

A scheme of electric-field measurement of micro-waves is proposed in Rydberg atoms with Doppler effects. A cascade-type electromagnetically-induced-transparency (EIT) system is disturbed by a perturbative field coupling a metastable transition. The original dark state splits and two EIT window appear with a central absorption peak. When a micro-wave (MW) field couples the Rydberg transition, the central absorption peak is divided into two. The frequency splitting of two central peaks is proportional to the MW field intensity, which can be used to probe MW electric field strength. This frequency-readout method based on a double-dark state system increases the probe sensitivity nearly by a factor of 7, compared with that of the single-dark state case. At room temperature, Doppler effects can enhance the absorption spectrum, moreover, its peak value varies linearly with the MW field strength. This can also serve to measure MW electric field strength. Numerical results show that the latter intensity-readout method after Doppler averaging improves the probe sensitivity by a factor of 10 with respect to the case without Doppler effects.     

Excitonic polaron and phonon assisted photoluminescence of ZnO nanowires

The coupling strength of the radiative transition of hexagonal ZnO nanowires to the longitudinal optic (LO) phonon polarization field is deduced from temperature dependent photoluminescence spectra. An excitonic polaron formation is discussed to explain why the interaction of free excitons with LO phonons in ZnO nanowires is much stronger than that of bound excitons with LO phonons. The strong exciton-phonon coupling in ZnO nanowires affects not only the Haung-Ray S factor but also the FXA-1LO phonon energy spacing, which can be explained by the excitonic polaron formation.     

Phase stability theory of Bloch eigenstates in active photonic lattices with coupled microlaser arrays

An generic model for the lattice dynamics of coupled microlaser arrays is employed for the lattice stability analysis. Nonlinear cross-cavity gain-coupling effects, characterizing active lattices, are included via the gain dependence on carrier depletion and cross-cavity hole burning. Passive near neighbor interactions (inter-cavity absorption and mirror reflection interference) are also included. The introduction of lattice-orthogonal modes simplifies the derivation of the coupled rate equations. The interaction phase among sites exhibits spontaneous long range “crystallization" into periodic Bloch states whereby the cavity radiation envelopes behave as laser “macro-atoms". The sign of the coupling coefficients as a function of geometry determines in- vs. out-of-phase locking and has practical implications for array design. Emphasis is placed on the stability analysis of Bloch states by including earlier omitted [1] effects of phase perturbations. The importance of the linewidth factor ι is uncovered: unconditional stability results for ι ≤1, otherwise a stability threshold exists for the coupling strength among sites. Choice of low ι gain material permits phase stability with high coupling strength, beneficial in overcoming manufacturing variations among array cavity parameters.     

Polaronic behavior in single- and many-electron Holstein model: A new perturbation approach

A new perturbation approach is developed for single- and many-electron Holstein model in one-, two-, and three-dimension. The results show that this approach has a good agreement with the Migdal theory in the adiabatic regime when the coupling is moderate (λ < 1), but with the Lang-Firsov theory in the antiadiabatic regime ( ω/W≫ 1). In the intermediate region, our approach can describe the transition from a large-polaron Fermi-liquid to the small-polaron, and this transition may be discontinuous in adiabatic regime, which means a phase transition appears in many-electron system. In single-electron case, we eliminate the abrupt transition using the degenerate perturbation theory, and the calculated ground state energy and effective mass are successfully compared with those of previous authors. Besides, the method has the advantage of requiring little computational effort. Received 27 December 2001 / Received in final form 8 April 2002 Published online 31 July 2002     

Rotational line strengths in4Σ-4Π transition of diatomic molecules

A theoretical derivation of closed form expressions for the intensities of all the rotational branches arising out of⁴Σ-⁴Π electronic transition in a diatomic molecule is described. In the present theory the tradition of treating the coupling in the⁴Σ state as belonging to Hund’s case (b) is discarded; instead a full-fledged intermediate coupling treatment which rigorously takes into account the spin-spin and second order spin-orbit effects is presented. Since accurate intermediate coupling treatment of⁴Π, in analytically closed form, is not possible, the⁴Π is first restricted to the extreme coupling scheme Hund’s case (a)(or case (b)); the effect of spin uncoupling (or spin-orbit and spin-spin interactions) is then incorporated through a first order perturbation calculation.     

Moment coupling in the interaction of atoms and their ions with a 3<Emphasis Type="Italic">d</Emphasis>-electron shell

The moment coupling of an interacting ion and an atom with a 3d-electron shell is analyzed for the ground state of identical atoms and ions where resonant charge exchange proceeds with transition of a 4s-electron. The interaction of the ion charge with the atom quadrupole moment is important for this system along with the exchange interactions and spin-orbit interactions inside an isolated atom and an ion. The quadrupole moment for 3d-atoms in the ground states is evaluated. The hierarchy of interactions in a molecular ion is analyzed depending on ion-atom distances and is compared with the standard Hund scheme. The resonant charge exchange proceeds effectively at separations corresponding to an intermediate case between cases “a” and “c” of the Hund coupling scheme.     

Flow equations for the spin-boson problem

Using continuous unitary transformations recently introduced by Wegner [1], we obtain flow equations for the parameters of the spin-boson Hamiltonian. Interactions not contained in the original Hamiltonian are generated by this unitary transformation. Within an approximation that neglects additional interactions quadratic in the bath operators, we can close the flow equations. Applying this formalism to the case of Ohmic dissipation at zero temperature, we calculate the renormalized tunneling frequency. We find a transition from an untrapped to trapped state at the critical coupling constant α _c =1. We also obtain the static susceptibility via the equilibrium spin correlation function. Our results are both consistent with results known from the Kondo problem and those obtained from mode-coupling theories. Using this formalism at finite temperature, we find a transition from coherent to incoherent tunneling atT ₂ ^* ≈2T ₁ ^* , whereT ₁ ^* is the crossover temperature of the dynamics known from the NIBA.     

Fluorescence Properties and Dipole Moments of Novel Fused Thienobenzofurans. Solvent and Structural Effects

The electronic absorption, fluorescence excitation and emission spectra, and fluorescence quantum yields of novel fused thienobenzofurans, including thieno[3,2-b][1]benzofuran (1), [1]benzothieno[3,2-b]furan (2), and [1]benzothieno[3,2-b][1]benzofuran (3), were recorded in fourteen solvents of different polarities at room temperature. Compound 2 was not fluorescent. Experimental ground-state dipole moments of compounds 1–3 were measured in benzene at 298 K and compared with the corresponding theoretical dipole moment values. The solvent effects on the electronic absorption and fluorescence spectra of these thienobenzofurans were quantitatively investigated by means of solvatochromic correlations based on the Kawski-Chamma-Viallet and McRae equations. A weak negative solvatochromic behavior was found for these compounds, showing that their dipole moments are slightly lower in the excited singlet-state than in the ground-state. Kamlet-Abboud-Taft multiparameter relationships were also established for electronic absorption and fluorescence wavenumbers, and fluorescence quantum yields in most solvents, demonstrating the occurrence of specific solute-solvent interactions.