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1.
M. Servidori F. Cembali S. Milita 《Applied Physics A: Materials Science & Processing》2001,73(1):83-90
The dimensional features of multi-crystal synchrotron X-ray topographs are explained by 3D DuMond diagrams for a flat double-crystal
monochromator and a curved sample. Symmetric Bragg-case reflections are assumed for all crystals. σ–σ and σ–π geometries are
considered, where the diffraction plane of the sample is parallel and perpendicular, respectively, to the vertical diffraction
plane of the monochromator (σ polarization). It is shown that the shape of the sample image is closely connected to the shape
of the volume shared by the diffraction domains of monochromator and sample in the 3D DuMond diagram. In particular, for the
σ–π set-up, the image shape depends on the curvature value and sign. An experiment is reported for this latter crystal geometry
to determine lattice mismatch, its lateral homogeneity and curvature value and sign in a sample made of epilayer and substrate.
Received: 31 July 2000 / Accepted: 25 January 2001 / Published online: 26 April 2001 相似文献
2.
Zhiyuan Tian Yazhou Zhang Yanli Zhang Aidong Peng Ying Ma Yu Chen Wensheng Yang Yalin Tang Jiannian Yao 《Journal of nanoparticle research》2006,8(1):65-77
Nanostructures with well-defined shape and highly monodisperse size were fabricated from model stilbazolium-like dyes with specific molecular structural and conformational characteristics. With the help of absorption and fluorescence optical spectroscopy, the correlated spectroscopy (COSY) and two- dimensional nuclear Overhauser effect spectroscopy (2D NOESY) techniques, along with X-ray diffraction (XRD) measurement, distinctively different aggregation processes of the model molecules are demonstrated. For model dye molecule with linear donor–π system–acceptor (D–π–A) structure, strong D–A pair, and planar conformation, specific intermolecular interaction was identified and special crystal structures as well as spectral properties were observed. For model dye molecules bearing nonlinear D–π–A–π–D structure, weak D–A pair but actual amphiphilic characteristics, a special aggregation process was confirmed and a focused size distribution of the produced nanostructures was obtained. 相似文献
3.
M.V. Polyakov V.V. Vereshagin 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):349-352
We derive and analyse inequalities relating masses of the lightest ππ resonances (ρ and σ) to coupling constants of the effective
chiral Lagrangian in the limit of a large number of colours.
Received: 15 July 2001 / Accepted: 23 October 2001 相似文献
4.
Properties of a scalar a meson are investigated in the two-flavor Nambu-Jona-Lasinio model with the Polyakov loop (PNJL).
Model analysis of the phase diagram of strong interacting matter is performed. The temperature dependence of the σ → ππ decay
width is studied at the zero chemical potential and near the critical end point. The calculated strong coupling constant g
σππ and the decay width are compared with available experimental data and other model results. Nonthermal enhancement of the
total decay width is noted for the σ meson near the critical end point when the condition m
σ ≥ 2m
π is broken. 相似文献
5.
A.Yu. Korchin 《The European Physical Journal A - Hadrons and Nuclei》2001,11(4):427-440
Magnetic moment and radius of the nucleon are calculated in a nonlocal extension of the chiral linear σ-model. Properties
of the nonlocal model under the vector and axial transformations are considered. The conserved electromagnetic and vector
currents, and partially conserved axial vector current are obtained. In the calculation of the nucleon electromagnetic vertex
the π- and σ-loop diagrams are included. Contribution from vector mesons is added in the vector meson dominance model with
a gauge-invariant photon-meson coupling. The nonlocality parameter associated with the πN interaction is fixed from the experimental magnetic moment of the neutron. Other parameters (nonlocality parameter for the
σN interaction and the mass of the σ-meson) are constrained by the magnetic moment of the proton. The calculated electric and
magnetic mean-square radii of the proton and neutron are in satisfactory agreement with experiment.
Received: 12 February 2001 / Accepted: 4 September 2001 相似文献
6.
G. Tsilimis J. Kutzner H. Zacharias 《Applied Physics A: Materials Science & Processing》2003,76(5):743-749
An extreme ultraviolet (EUV) laser light source based on high-harmonic generation is presented. Coherent radiation in the
photon energy range hν=20–120 eV is produced in the conversion media argon, neon and helium. High-harmonic radiation in the
energy range 20–50 eV is applied to investigate photoemission spectra of Pt (111) and CO/Pt (111). In the photoemission spectra
of the clean surface, new secondary electron emission structures are found which influence the cross section analysis of the
CO states. When taking these Pt resonances into consideration, the 4σ and 5σ CO shape resonances are found at photon energies
of 37 eV and 28 eV, respectively. Additionally, a resonance at hν=31 eV is also observed for the CO 1π state, in contrast
to formerly published experimental data. Experimental and theoretical data suggest that this resonance is not connected to
the well-known shape resonances in the σ-channel. Based on theoretical approaches, it is identified as an autoionization resonance.
Received: 8 April 2002 / Accepted: 22 May 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +49-251/833-3604, E-mail: kutzner@uni-muenster.de 相似文献
7.
A. Kohen F. Giubileo Th. Proslier F. Bobba A. M. Cucolo W. Sacks Y. Noat A. Troianovski D. Roditchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):21-25
Using Scanning Tunneling Microscope at low temperature
we explore the superconducting phase diagram in the π-band of
the two-band superconductor MgB2. In this band the peculiar
shape of the local tunneling spectra and their dynamics in the
magnetic field reveal the complex character of the quasiparticle
density of states (DOS). The gap in the DOS is first rapidly
filled with states in raising the magnetic field up to 0.5 T and
then slowly approaches the normal state value: the gap is
observed up to 2 T. Such a change in the DOS dynamics suggests the
existence of two terms in the DOS of the π-band: a first one,
reflecting an intrinsic superconductivity in the band and a second
one, originating from an inter-band coupling to the σ-band.
Our findings allow a deeper understanding of the unique phase
diagram of MgB2. 相似文献
8.
D.V. Bugg 《The European Physical Journal C - Particles and Fields》2007,52(1):55-74
Claims have been made that f0(1370) does not exist. The five primary sets of data requiring its existence are refitted with suitable Breit–Wigner amplitudes.
Major dispersive effects due to the opening of the 4π threshold are included for the first time; the σ→4π amplitude plays
a strong role. Crystal Barrel data on p̄p→3π0 at rest require f0(1370) signals of at least 32 and 33 standard deviations (σ) in 1S0 and 3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass and width. Data on p̄p→ηηπ0 agree and require at least a 19σ contribution. This alone is sufficient to demonstrate the existence of f0(1370). BES II data for J/Ψ→φπ+π- contain a visible f0(1370) signal >8σ. In all cases, a resonant phase variation is required. Cern–Munich data for ππ elastic scattering are fitted
well with the inclusion of some mixing between σ, f0(1370) and f0(1500). Values of Γ2π for f2(1565), ρ3(1690), ρ3(1990) and f4(2040) are determined.
PACS 13.25.Gv; 14.40.Gx; 13.40.Hq 相似文献
9.
M. Carrascosa F. Agulló-López G. Montemezzani P. Günter 《Applied physics. B, Lasers and optics》2001,72(6):697-700
A simple model was developed to account for the generation of thin space–charge gratings induced by band-gap illumination
in photorefractive crystals. It includes the high-intensity regime where the contribution of free carriers to the space–charge
field cannot be neglected. The model was specifically applied to explain the occurrence of two mutually π-phase-shifted gratings
below the surface of KNbO3 as well as diffraction features that have been previously observed experimentally.
Received: 11 October 2000 / Revised version: 22 January 2001 / Published online: 20 April 2001 相似文献
10.
We consider the branching and annihilating random walk and with reaction rates σ and λ, respectively, and hopping rate D, and study the phase diagram in the λ/D,σ/D) plane. According to standard mean-field theory, this system is in an active state for all σ/D≥0, and perturbative renormalization suggests that this mean-field result is valid for d>2; however, nonperturbative renormalization predicts that for all d there is a phase transition line to an absorbing state in the λ/D,σ/D) plane. We show here that a simple single-site approximationreproduces with minimal effort the nonperturbative phase diagram both qualitatively and quantitatively for all dimensions d>2. We expect the approach to be useful for other reaction-diffusion processes involving absorbing state transitions. 相似文献
11.
Chengyou Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):45-48
The photorefractive effect (PR) of a novels σ-π alternating polymer having 2,2'-bipyridyl in the polymer backbone and their
ruthenium complexes has been investigated. The ruthenium complex was used as the charge generator, the σ-π alternating polymer
backbone as the charge transporting channel and second-order nonlinear (NLO) optical chromophore. The photorefractive properties
were demonstrated by two-beam coupling (2BC), degenerated four-wave mixing (DFWM) and field-induced orientation birefringence
at wavelength of 532 nm. This polymer shows a enhanced photorefractive effect due to the efficient photoinduced metal-to-ligand
charge transfer (MLCT) inside the ruthenium complex. A net optical gain of about 22 cm-1 and the diffraction efficiency about 10% were obtained at the external electric field of 30 V/μm.
Received 21 December 1999 and Received in final form 7 July 2001 相似文献
12.
Sergey V. Donskov Anatoly K. Likhoded Alexey V. Luchinsky Vladimir D. Samoylenko 《Central European Journal of Physics》2010,8(3):393-399
The decay η′ → ηπ
0
π
0 is studied in the framework of isobar model. It is shown, that good agreement with the experiment is achieved if α
0- and σ-meson contributions are taken into account. The contribution of α
0-meson is dominant, but σ-meson is necessary to reproduce the form of the Dalitz plot. Instead of the usual Breit-Wigner form of σ-meson propagator we use parametrization of the ππ-amplitude, which satisfies analyticity, crossing, unitarity and chirality constraints. This amplitude has a pole in the complex
plane, which corresponds to σ-meson and describe experimental data on ππ-scattering in K
e4 decay. 相似文献
13.
The decays η → 3π
0 and η → π
0
π
+
π
− are considered within the isobar model. It is shown that, in order to explain the branching ratio and the shape of the Dalitz
plot for the decay η′ → 3π
0, it is sufficient to take into account the contributions of the σ and a
0 mesons. The inclusion of the σ meson is necessary for reproducing the shape of the distribution over the Dalitz plot. The branching ratio for the decay
η′ → π
0
π
+
π
− is obtained. The predictions for the distributions over the Dalitz plot for this decay are presented. These predictions depend
strongly on model parameters. 相似文献
14.
D. Blaschke Yu. L. Kalinovsky A. E. Radzhabov M. K. Volkov 《Physics of Particles and Nuclei Letters》2006,3(5):327-330
The properties and temperature behavior of the π and σ bound states are studied in the framework of the nonlocal model with
a separable interaction kernel, based on the quark Dyson-Schwinger and meson Bethe-Salpeter equations. M
π(T), f
π(T), M
σ(T), and Γσ → ππ(T) are considered above and below the deconfinement and chiral restoration transitions.
Talk at the Round-Table Discussion “Searching for a Mixed Phase of Strongly Interacting Matter at the JINR Nuclotron,” Dubna,
July 7–9, 2005.
The text was submitted by the authors in English. 相似文献
15.
W. von Oertzen 《The European Physical Journal A - Hadrons and Nuclei》2001,11(4):403-411
Using the concept of covalent molecular orbitals for neutrons and the known properties of the local α + 16O potential the formation of asymmetric molecular structures in neon isotopes is discussed. Experimental evidence for parity doublets in 21Ne is reviewed and a corresponding band structure for the states in 21Ne at moderate excitation energy of E
x = 0-8 MeV is proposed. The structure of some bands can be interpreted as consisting of an instrinsic asymmetric ( 4He + 16O) structure bound by a covalent neutron in σ and π orbitals. An extension of the observed structures to symmetric molecular structures in isotopes of Mg and heavier nuclei is suggested. In particular shape isomers in isotopes of magnesium, namely (He)2O molecules, can be predicted and an extended Ikeda diagram is proposed.
Received: 11 July 2001 / Accepted: 22 August 2001 相似文献
16.
We compute the expansion of the surface tension of the 3D random cluster model for q≥ 1 in the limit where p goes to 1. We also compute the asymptotic shape of a plane partition of n as n goes to ∞. This same shape determines the Wulff crystal to order o(ɛ) in the 3D Ising model (and more generally in the 3D random cluster model for q≥ 1) at temperature ɛ.
Received: 15 February 2001/ Accepted: 11 May 2001 相似文献
17.
N. Rehfeld U. Gerhardt E. Dietz 《Applied Physics A: Materials Science & Processing》1973,1(4):229-232
We use a 0.5 m Seya-Namioka monochromator and two gold plated cylindrical mirrors to set up an optical system which produces
a collimated beam of plane polarized, monochromatic radiation in the vacuum ultraviolet region. The two mirrors compensate
for the astigmatism of the Seya-Namioka monochromator, thereby increasing the spectral resolution drastically. The degree
of linear polarization is about 0.97–1.00 in the spectral region of 6–11.5 eV. 相似文献
18.
E. San-Fabián A. Guijarro J. A. Vergés G. Chiappe E. Louis 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(2):253-262
Total energies of charged states and configurations of different spin multiplicity of two polar non-alternant polycyclic aromatic
hdrocarbons (PAH), namely, pentaheptafulvalene and azulene, calculated by means of a Multi-Configurational (MCSCF) method
which includes correlation only amongst π orbitals, have been fitted by exact solutions of the Pariser-Parr-Pople (PPP) and the Hubbard Hamiltonians for π electrons. As both molecules are planar, such an approach is in principle feasible. As found in our previous analysis of
PAH, PPP fittings are significantly better than those attained with the Hubbard Hamiltonian. In addition, parameters for the
Hubbard Hamiltonian are around twice those derived for the PPP model, indicating that parameters are not model independent.
Fitted PPP parameters are close to those derived from a similar study of the PAH 2, 5, 8-trihydrogenated phenalene and those
originally proposed by Pariser et al. providing further support to a wide applicability of the fitted parameters. Fittings
obtained for a MCSCF method that MM298001also includes σσ and σπ correlations (MCSCF/MP2) are slightly less accurate giving an on-site repulsion 10–15% smaller. The accuracy of the fittings
further diminishes when parameters are derived from energies obtained by means of a DFT method (B3LYP) with an additional
decrease in U of 5–25%. In the latter two cases, parameters have to be considered as effective, accounting for effects of σ orbitals not explicitly included in the model Hamiltonians. Electron affinities, ionization energies and dipole moments,
calculated by means of the model Hamiltonians, are compared to those derived from DFT and ab initio methods and, whenever
available, to experimental data. 相似文献
19.
D. Cabrera D. Fernández-Fraile A. Gómez Nicola 《The European Physical Journal C - Particles and Fields》2009,61(4):879-892
We present a study of the π
π scattering amplitude in the σ and ρ channels at finite temperature and nuclear density within a chiral unitary framework. Meson resonances are dynamically generated
in our approach, which allows us to analyze the behavior of their associated scattering poles when the system is driven towards
chiral-symmetry restoration. Medium effects are incorporated in three ways: (a) by thermal corrections of the unitarized scattering
amplitudes, (b) by finite nuclear-density effects associated to a renormalization of the pion decay constant, and complementarily
(c) by extending our calculation of the scalar–isoscalar channel to account for finite nuclear-density and temperature effects
in a microscopic many-body implementation of pion dynamics. Our results are discussed in connection with several phenomenological
aspects relevant for nuclear-matter and heavy-ion collision experiments, such as ρ mass scaling versus broadening from dilepton spectra and chiral restoration signals in the σ channel. We also elaborate on the molecular nature of π
π resonances. 相似文献
20.
M. Schumacher 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):413-422
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 . 相似文献