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961.
S. Cohen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):31-38
Approximate analytical formulae describing the energy variation of line intensities, autoionization widths and lineshape asymmetries,
are derived for a Phase-Shifted Multichannel Quantum Defect Theory model composed of two closed interacting channels coupled
to two effective continua. This is accomplished by putting the two compatibility equation solutions, for the common phase
shifts of the two open channels, in such a form so the resonant behavior is attributed to one of them, the other accounting
for an energy dependent background. Then, the well-known procedures for the simpler case where only one continuum is considered
are applied, using only the resonant solution. The method is quite general and applicable to any MQDT model with two or more
open channels. The resulting analytical formulae are tested on experimental spectra of Sr, Ba and Cu and it is shown that
they are valid as long as: i) The resonances are non-overlapping, ii) The direct closed channel coupling is much stronger
than the indirect one through the continua and (when excitation matrix elements are involved) iii) The open channels excitation
strength is smaller or at least comparable to the closed channels one.
Received: 26 May 1998 / Accepted: 1st July 1998 相似文献
962.
Y.Q. Ma W. Figueiredo 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):103-106
By introducing boson operators, a quantum spherical XY model in the presence of a random field has been studied by the coherent state path integral approach. The phase diagram
is obtained, and the effects of the random-field fluctuations on the possibilities of the existence of a ferromagnetic phase are discussed. At the critical point, , the order parameter M describing the ordered ferromagnetic phase disappears as .Since the model is equivalent to a Bose system, we also show that the phase transition at zero temperature between the superfluid
and the disordered Mott insulator phases occurs at the chemical potential , where J0 is the strength of the exchange interaction. As the temperature T goes to zero, the asymptotic behavior of the entropy and the specific heat are and , respectively.
Received: 20 May 1997 / Accepted: 20 October 1997 相似文献
963.
We consider a chiral one-loop hedgehog soliton of the bosonized SU(2)f Nambu & Jona-Lasinio model which is embedded in a hot medium of constituent quarks. Energy and radius of the soliton are
determined in self-consistent mean-field approximation. Quasi-classical corrections to the soliton energy are derived by means
of the pushing and cranking approaches. The corresponding inertial parameters are evaluated. It is shown that the inertial
mass is equivalent to the total internal energy of the soliton. Corrected nucleon and δ isobar masses are calculated in dependence
on temperature and density of the medium. As a result of the self-consistently determined internal structure of the soliton
the scaling between constituent quark mass, soliton mass and radius is noticeably disturbed.
Received: 26 September 1997 相似文献
964.
B. Kotliński D. Androić G. Backenstoss D. Bosnar H. Breuer H. Döbbeling T. Dooling M. Furić P.A.M. Gram N.K. Gregory A. Hoffart C.H.Q. Ingram A. Klein K. Koch J. Köhler M. Kroedel G. Kyle A. Lehmann A.O. Mateos K. Michaelian T. Petković M. Planinić R.P. Redwine D. Rowntree U. Sennhauser N. Šimičević R. Trezeciak H. Ullrich H.J. Weyer M. Wildi K.E. Wilson 《The European Physical Journal A - Hadrons and Nuclei》1998,1(4):435-445
The pion absorption reaction (π+,3
p
) on Ar was studied at pion energies of 70, 118, 162 and 239 MeV, and on N and Xe at 239 MeV. The 3p cross section with a 50 MeV cut on the missing energy is presented. The existence of an initial state interaction (ISI) component
to the reaction was investigated. The portion of the 3p cross section assigned to the ISI process is less than one half and at lower energies significantly so.
Received: 11 December 1997 相似文献
965.
J. Dziesiaty M.U. Lehr P. Peka A. Klimakow S. Müller H.-J. Schulz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):269-277
ZnS:Ti crystals grown by different methods are investigated at low temperatures (2 K K) by electron paramagnetic resonance (EPR) and optical spectroscopies, mainly with regard to their photoluminescence properties,
including excitation and sensitisation spectra. The more familiar lattice-neutral Ti2+(d
2
) ion on a cubic site (AN) presents an isotropic EPR signal with g=1.928 observable up to 80 K. Signals of axial PN and AS sites are detected in the same temperature range. This Ti2+ ion exhibits the transition in emission, structured by no-phonon lines (NPL) of centres in various environments, with the AN site represented
at 3613 cm-1, and the 3
T
1
(F) and 3
T
1
(P) bands in excitation spectra. Substitutional Ti3+(d
1
) is identified by an anisotropic EPR spectrum at T = 3.5 K, indicating a quasistatic Jahn-Teller effect at the doubly degenerate 2
E(D) ground state, while in the first excited vibronic state a quasidynamic JT effect in the strain-split vibronic 2
E/2
A
2
manifold is found. A new luminescence band centred at 4500 cm-1 with NPL structures near 5000 cm-1 represents AN, PN and AS sites in the transition. Charge-transfer processes are described in a one-particle model, depicting the Ti3+/Ti2+ donor level at 12 900 cm-1 below the conduction-band edge.
Received: 3 October 1997 / Revised: 17 December 1998 / Accepted: 18 May
1998 相似文献
966.
Z.-C. Wang Z.-Y. Chen Y. Xu 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):185-190
A theoretical study is made of the steady-state populations of a three-level atom in a ladder configuration, driven by a superposition
of a monochromatic laser wave with a broad-band squeezed vacuum. The master equation for the system and the atomic Bloch equations
are derived. The steady-state populations are calculated numerically and shown graphically as functions of two-photon detuning
for various cases of the squeezed vacuum. It is shown that, the atomic populations depend strongly on the relative phase of
the driving field and the squeezed vacuum. When the phase matching condition is fulfilled, there will be a strong two-photon
resonant absorption from the squeezed vacuum, a characteristic different from absorption of photons from a classical field.
Received: 28 May 1997 / Revised and Accepted: 10 December 1997 相似文献
967.
I start with a brief introduction to Higgs mechanism and supersymmetry. Then I discuss the theoretical expectations, current
limits and search strategies for Higgs boson(s) at LHC — first in the SM and then in the MSSM. Finally I discuss the signatures
and search strategies for the superparticles. 相似文献
968.
T. S. Petkevich Yu. G. Egiazarov N. A. Kovalenko T. L. Sen’ko 《Journal of Applied Spectroscopy》1998,65(1):117-123
Activity of alumocopper-palladium catalysts (0.5 at.% Pd, 0.1–3.0 at.% Cu) which differ in preparation method in CO, C2H4 and CH4 oxidation is studied. It is shown that preliminary modification of a carrier by copper leads to an enhancement of catalyst
activity as compared with an alumopalladium one. With the methods of EDRS, TPR-TRS, and TPR of adsorbed CO and O2, the Pd/Cu/Al2O3, Cu/Pd/Al2O3 and (Pd−Cu)/Al2O3, systems are studied. It is established that premodification of the carrier leads to a weakening of its interaction with
the second metal while the combined deposition from one impregnating solution in subsequent thermal treatment is accompanied
by a strong metal aggregation.
Institute of Physicoorganic Chemistry, National Academy of Sciences of Belarus, 13, Surganov St., Minsk, 220072. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 114–120, January–February, 1998. 相似文献
969.
M.A. Bouchene V. Blanchet C. Nicole N. Melikechi B. Girard H. Ruppe S. Rutz E. Schreiber L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(2):131-141
The interaction of a sequence of two identical ultrashort laser pulses with an atomic system results in quantum interferences
as in Ramsey fringes experiments. These interferences allow achievement of temporal coherent control of the excitation probability.
We present the results of a temporal coherent control experiment on two different atomic systems: one-photon absorption in
K (4s-4p) and two-photon absorption in Cs (6s-7d). In K, the quantum interferences between the two excitation paths associated with the laser pulses are revealed through
rapid oscillations of the excitation probability as a function of the time delay between the two pulses. These oscillations
take place at the transition frequency (period T = 2.56 fs). The interferences are modulated by beats (at about 580 fs) resulting from the doublet structure of the excited
state (4p (2
P
1/2
, 2
P
3/2
)). Three complementary interpretations of this experiment are presented: in terms of beats of quantum interferences, of variation
in the spectrum intensity, and of wave packet interferences. Whenever the two laser pulses are temporally overlapped, optical
interferences are superimposed on to the quantum interferences. The distinction between these two types of interference is
clearly revealed in the two-photon excitation scheme performed on Cs (6s-7d (2
D
3/2
, 2
D
5/2
)) because quantum interferences occur at twice the frequency of the optical interferences.
Received: 30 December 1997 / Revised: 28 February 1998 / Accepted: 4 March 1998 相似文献
970.
E. Cormier P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):15-20
We report on observable new features related to ionization of atoms by laser pulses of only few cycles and some intensity.
We show that for particular photo-electron energies, the angular distribution becomes asymmetric and that this asymmetry is
related to the initial phase of the field.
Received: 4 November 1997/Revised: 21 January 1998/Accepted: 23 February 1998 相似文献