共查询到20条相似文献,搜索用时 31 毫秒
1.
K. Fan J. Wang W. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):381-391
We propose a modified Gō model in which the pairwise interaction energies vary as local environment changes. The stability
difference between the surface and the core is also well considered in this model. Thermodynamic and kinetic studies suggest
that this model has improved folding cooperativity and foldability in contrast with the Gō model. The free energy landscape
of this model has broad barriers and narrow denatured states, which is consistent with that of the two-state folding proteins
and is lacked for the Gō model. The role of non-native interactions in protein folding is also studied. We find that appropriate
consideration of the contribution of the non-native interactions may increase the folding rate around the transition temperature.
Our results show that conformation-dependent interaction between the residues is a realistic representation of potential functions
in protein folding.
Received 10 April 2002 / Received in final form 20 August 2002
Published online 19 December 2002
RID="a"
ID="a"e-mail: wangwei@nju.edu.cn 相似文献
2.
The internal energy of small ammonia clusters in a supersonic beam and after scattering off LiF(100)
C. Menzel H. Zacharias 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):109-114
The photoionization efficiency (PIE) of neutral ammonia clusters is studied as a function of photon energy. From these curves
the internal energies of clusters in the incident supersonic beam and of clusters surviving after scattering off a LiF(100)
surface are derived. A supersonic expansion of ammonia seeded in He produces small clusters of various size but with uniform
kinetic energy of about 285 meV per monomer molecule. The mass distribution of clusters in the jet and of the scattered particles
is measured in a reflecting time-of-flight mass spectrometer by single photon photoionization using vacuum ultraviolet (VUV)
laser radiation tunable between
and
. In the incident beam the internal energies of clusters up to n = 15 do not vary significantly and amount to an average of about . After scattering off LiF(100) the internal energy of clusters up to n = 4 increases with fragment size and amounts to about half a monomer binding energy.
Received 18 October 1999 and Received in final form 10 December 1999 相似文献
3.
Zu Wei Yan Xi Xia Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):531-538
A variational theory is proposed to study the surface states of electrons in a semi-infinite ternary mixed crystal, by taking
the effect of electron-surface optical (SO) phonon interaction into account. The energy and the wave function of the electronic
surface-states are calculated. The numerical results of the energies of the surface states of the polarons and the self-trapping
energies are obtained as functions of the composition x and surface potential V0 for several ternary mixed crystal materials. The results show that the electron-phonon interaction lowers the surface-state
levels with the energies from several to scores of meV. It is also found that the self-trapping energy of the surface polaron
has a minimum at some middle value of the composition x. It is indicated that the electron-phonon coupling effect can not be neglected.
Received 4 January 1999 and Received in final form 7 January 2000 相似文献
4.
V. Baru J. Haidenbauer C. Hanhart A. Kudryavtsev P. Moskal J. Speth 《The European Physical Journal A - Hadrons and Nuclei》1999,6(4):445-450
The near threshold behaviour of the reaction cross section for pp→ppη′, recently measured in experiments at COSY and SATURNE, is analyzed. The interaction in the pp as well as in the η′
p final states is taken into account. The suppression of the total cross section for this process at excess energies Q < 3 MeV observed in these experiments is interpreted as an evidence for a strong repulsive η′
p interaction.
Received: 26 May 1999 / Revised version: 8 July 1999 相似文献
5.
A.S. Shalabi M.M. Assem S. Abd El-Aal M.A. Kamel M.M. Abd El-Rahman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):181-189
Ab initio calculations were performed for several suggested mechanisms of energy transfer between helium metastable particles and neon.
Optimized geometries and excited-state energies were calculated for neon excited-state complexes and the convergence properties
of the non-additive contributions to the interaction energies were examined. The most probable excitation-transfer mechanism
was found to be based on an energy difference of 0.0674 eV between the triplet excited state of and the singlet excited state of . No theoretical evidence was found for the production of neon singlet excited-state complexes other than 20.0858 to 20.4875
eV by the considered two-, three- and four-body models of energy transfer processes. The energy curves of the reactions involving
the excited-state complexes and are provided and compared with the previously reported experimental results on the reaction . The relation between the probability of energy transfer and laser activity is discussed. The non-additive contribution to
the total interaction energy of the nominated intermediate complex was found to be negligible, pointing to the possibility of constructing model potentials and simulation
of larger systems.
Received: 15 December 1998 / Received in final form: 20 March 1999 相似文献
6.
V. Meden W. Metzner U. Schollwöck O. Schneider T. Stauber K. Schönhammer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(4):631-646
We present a study of the one-particle spectral properties for a variety of models of Luttinger liquids with open boundaries.
We first consider the Tomonaga-Luttinger model using bosonization. For weak interactions the boundary exponent of the power-law
suppression of the spectral weight close to the chemical potential is dominated by a term linear in the interaction. This
motivates us to study the spectral properties also within the Hartree-Fock approximation. It already gives power-law behavior
and qualitative agreement with the exact spectral function. For the lattice model of spinless fermions and the Hubbard model
we present numerically exact results obtained using the density-matrix renormalization-group algorithm. We show that many
aspects of the behavior of the spectral function close to the boundary can again be understood within the Hartree-Fock approximation.
For the repulsive Hubbard model with interaction U the spectral weight is enhanced in a large energy range around the chemical potential. At smaller energies a power-law suppression,
as predicted by bosonization, sets in. We present an analytical discussion of the crossover and show that for small U it occurs at energies exponentially (in -1/U) close to the chemical potential, i.e. that bosonization only holds on exponentially small energy scales. We show that such a crossover can also be found in other
models.
Received 8 February 2000 and Received in final form 25 April 2000 相似文献
7.
K. E. Stiebing K. A. Müller J. Baumann K. Bethge J. Bernhardt H. Bokemeyer H. Folger O. Fröhlich O. Hohn G. Kavermann G. Lambrinidis A. Müller J. Peter S. Runkel L. Schmidt H. Schmidt-Böcking P. Senger P. Thee J. Ullrich 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):87-96
The feasibility of the spectroscopy of dynamically ionized electrons (positrons) from heavy-ion collisions at intermediate
energies, e.g. Pb+Pb at 60 AMeV has been studied. We propose a magnetic toroid spectrometer for lepton spectroscopy in an energy range between 5 and 50
MeV. Special emphasis was laid on large solid angles, on broad-band characteristics and on a good suppression of secondary
events. The device is a versatile compact-size instrument for lepton detection in in-beam experiments at a moderate energy
resolution of %.
Received: 28 December 1999 / Accepted: 29 March 2000 相似文献
8.
J.M. Weber I.I. Fabrikant E. Leber M.-W. Ruf H. Hotop 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):247-256
Using laser photoelectron attachment to methyl iodide clusters in a differentially-pumped seeded supersonic helium beam and
mass spectrometric ion detection, we have measured the rate coefficients for formation of (q = 0-2) ions over the electron energy range 0-100 meV with an effective energy width of about 2.5 meV. Whereas a prominent
vibrational Feshbach resonance just below the onset for the C-I stretch vibration ( ) is observed for dissociative attachment to monomers (yielding I- ions), only weak and broad structure, shifted to lower energies, is detected for formation of ions and essentially no structure is left in the attachment spectrum for . These observations are interpreted by model R-matrix calculations which successfully describe the DA cross-section for the monomer and qualitatively recover the trend
observed for cluster ion formation. For the clusters, the effects of increased electron-target long-range interaction and
of solvation as well as coupling to soft vibrational modes lead to strong broadening and shifting of the vibrational Feshbach
resonance and, ultimately, to its disappearance.
Received 29 November 1999 and Received in final form 14 January 2000 相似文献
9.
I.G. Medvedev 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):189-200
Using the perturbation expansion in the rebonding interaction near the surface molecule limit, the new diagram technique for
the calculation of the chemisorption energy in the Anderson model is proposed. The new expression for the chemisorption energy
in the ring diagram approximation is presented. The approximate expression for the contribution of the non- ring diagrams
is suggested. The chemisorption energies are calculated and compared with the available exact results and others in the literature.
A simple explanation of observable trends in hydrogen chemisorption energies along the transition metal series is given based
on the rebonding surface molecule picture.
Received 8 July 1999 and Received in final form 24 January 2000 相似文献
10.
S.H. Patil 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(3):341-347
We have developed a simple model potential with a hard core and the correct large-r Coulombic behaviour, to describe the interaction of an electron with a closed shell. One has an exact, analytic ground state
wave function for this potential. This potential is used to develop two-electron perturbed and unperturbed wave functions,
with the correct asymptotic behaviour and cusp conditions. These wave functions allow us to obtain accurate values for the
two-electron energies, polarisabilities, hyperpolarisabilities, and dispersion coefficients of alkaline earth sequences. Many
of these results are the only ones available in the literature.
Received 29 July 1999 and Received in final form 16 November 1999 相似文献
11.
Focal Conic Domains (FCDs) in smectic phases often assemble according to a particular rule, experimentally discovered by G.
Friedel, the law of corresponding cones (l.c.c.). This paper reports various results relating to this type of association. First we show that a l.c.c. contact between
2 focal conic domains has a vanishing energy, yielding metastable local equilibrium. Then we use some projective properties of conic sections to extend the celebrated Apollonian tiling, which describes a tilt grain boundary (TiGB) of vanishing disorientation
made of toric focal conic domains, to any TiGB. Finally we present a realistic model of the energy of the TiGB, which we compare to the energy of a TiGB split into dislocations, and to the energy of a curvature wall. This model
explains why FCD tilings show macroscopic zones not filled with FCDs.
Received 21 June 1999 and Received in final form 10 September 1999 相似文献
12.
A. Hazareesing J.-P. Bouchaud 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):713-724
We reconsider the problem of the static thermal roughening of an elastic manifold at the critical dimension d=2 in a periodic potential, using a perturbative Functional Renormalization Group approach. Our aim is to describe the effective
potential seen by the manifold below the roughening temperature on large length scales. We obtain analytically a flow equation
for the potential and surface tension of the manifold, valid for low temperatures. On a length scale L, the renormalized potential is made up of a succession of quasi parabolic wells, matching onto one another in a singular
region of width for large L. For strong periodic potential, the perturbation theory breaks down, and we argue, based on a variational calculation, that
the transition becomes first order. We also obtain numerically the step energy as a function of temperature, and relate our
results to the existing experimental data on 4He. Finally, we examine the case of a non local elasticity which is realized physically for the contact line.
Received 16 April 1999 and Received in final form 11 October 1999 相似文献
13.
I.A. Nyrkova A.N. Semenov A. Aggeli M. Bell N. Boden T.C.B. McLeish 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):499-513
The classical isodesmic one-dimensional model for equilibrium polymerization is generalized in order to describe self-assembly
in systems forming fibrils. The model was applied to peptide solutions forming -sheet tapes which can further aggregate into stacks of various thickness: double tapes and fibrils (several double tapes
stacked together). We found that in some cases the model yields several step-like transitions as the concentration increases:
first from monomers to single or double tapes, and then to fibrils. The abruptness of the first transition is controlled by
the free energy penalty for transformation of a peptide from random coil to a straight -strand conformation (the latter is characteristic for tapes). If both single and double tapes are allowed, the length of
the aggregates after the first transition can be very large with high scission energies. For very low energies of attraction
between double tapes, the transition from double tapes to fibrils happens separately (above the first transition), and it
is even more abrupt and produces extremely long fibrils. The theoretical findings are used to extract the characteristic molecular
parameters for the self-assembly of the de
novo peptide DN1 forming polymeric -sheets in water.
Received 28 June 1999 相似文献
14.
We report on a numerical analysis of the temporal and spatial beam properties of nanosecond optical parametric oscillators
(OPOs). The analysis is performed for a 355-nm-pumped critically phase-matched OPO of beta-barium borate. The calculations
provide detailed information on the dependence of the OPO beam quality (measured by the quality factor M
2) on pump energy. An important result is the strong increase of the M
2 value for pump energies exceeding 1–2 times the energy at threshold. Furthermore, a temporal analysis of single OPO pulses
indicates that the M
2 value strongly increases during the first few nanoseconds of the OPO oscillation. This increase is understood by considering
the temporal dynamics of the spatial profiles of the OPO signal beam and the depleted pump radiation.
Received: 1 April 1999 / Revised version: 26 July 1999 / Published online: 20 October 1999 相似文献
15.
B. Nath S. Chattopadhyaya C. Sinha 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):31-36
Triple differential cross-sections (TDCS) of a hydrogenic (He+) ion has been studied by positron impact using coplaner geometry for both symmetric and asymmetric kinematics in the intermediate
and medium high incident energy region. TDCS has also been studied of He+ ion by electron impact for symmetric kinematics taking account of the electron exchange effect. The final state wavefunction
is chosen as the correlated 3-body Coulomb wavefunction satisfying the exact asymptotic boundary condition. The long range
Coulomb interaction in the initial channel between the ionic target and the projectile has also been taken into account properly.
For positron impact, the collision is found to be almost recoilless at lower incident energies, in contrast to the strong
recoil peak noted in the case of electron impact ionisation. For electron impact, the exchange effect is found to be significantly
high for equal energy sharing in the final channel.
Received 10 July 1999 and Received in final form 7 December 1999 相似文献
16.
D.S. Dean 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):493-498
In this paper we calculate the mean number of metastable states for spin glasses on so called random thin graphs with couplings
taken from a symmetric binary distribution . Thin graphs are graphs where the local connectivity of each site is fixed to some value c. As in totally connected mean field models we find that the number of metastable states increases exponentially with the
system size. Furthermore we find that the average number of metastable states decreases as c in agreement with previous studies showing that finite connectivity corrections of order 1/c increase the number of metastable states with respect to the totally connected mean field limit. We also prove that the average
number of metastable states in the limit is finite and converges to the average number of metastable states in the Sherrington-Kirkpatrick model. An annealed calculation
for the number of metastable states of energy E is also carried out giving a lower bound on the ground state energy of these spin glasses. For small c one may obtain analytic expressions for .
Received 14 October 1999 and Received in final form 14 December 1999 相似文献
17.
L.M. Pant R.K. Choudhury A. Saxena D.C. Biswas 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):47-58
Fission fragment mass and energy distributions and their correlations have been measured for the 16O and 19F + 209Bi reactions over a wide range of excitation energies ( E
* = 30-50 MeV). It is observed that in the case of 16O + 209Bi reaction, the average total fragment kinetic energy, <TKE> is nearly independent of the bombarding energy. However, in the case of 19F + 209Bi reaction, the average total kinetic energy of the fission fragments shows a peaking behaviour near the barrier. The variation
in <TKE> at near barrier energies in the 19F + 209Bi system seems to be correlated with corresponding strong variation in the variance of the fragment mass distribution. The
present results may imply certain dynamical effects leading to compact scission configurations in the fission of 19F + 209Bi system at near barrier bombarding energies.
Received: 9 April 2001 / Accepted: 26 May 2001 相似文献
18.
E.Ya. Paryev 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):127-137
The inclusive K+ meson production in photon–induced reactions in the near threshold and subthreshold energy regimes is analyzed with respect
to the one–step (γN→K
+
Y, Y=Λ,Σ) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account
the struck target nucleon removal energy and internal momentum distribution (nucleon spectral function), extracted from recent
quasielastic electron scattering experiments and from many–body calculations with realistic models of the NN interaction.
Simple parametrizations for the total and differential cross sections of the K+ production in photon–nucleon collisions are presented. Comparison of the model calculations of the K+ differential cross sections for the reaction γ+C12 in the threshold region with the existing experimental data is given, that displays the contributions to the K+ production at considered incident energies coming from the use of the single–particle part as well as high momentum and high
removal energy part of the nucleon spectral function. Detailed predictions for the K+ total and differential cross sections from γH2, γC12 and γPb208 reactions at subthreshold and near threshold energies are provided. The influence of the uncertainties in the elementary
K+ production cross sections on the K+ yield is explored.
Received: 12 April 1999 / Revised version: 11 September 1999 相似文献
19.
H. Razafimandimby M. Taguchi J. C. Parlebas 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):21-26
We investigate the competition between magnetic order and local Kondo effect in a Kondo lattice model (i.e. the Coqblin-Schrieffer Hamiltonian extended to a lattice) in a mean-field approximation, taking account of the spin-orbit
degeneracy of each localized f level. This leads to the definition of a dependent Kondo temperature. We study the Kondo phase and compare its energy with the energies of magnetic phases, when the
number of the conduction band electron per site is near one. We present a phase diagram which shows the occurrence of three
phases: Kondo, antiferromagnetic and paramagnetic phases. Our model in the mean-field approximation also shows a somewhat
flat Kondo temperature, for large values of , as a function of the exchange coupling J between conduction and localized f electrons. Finally we show some scaling effects between and J and we define a corresponding Kondo temperature.
Received 21 September 1998 and Received in final form 8 February 1999 相似文献
20.
K. Orlovsky V. Grushevsky A. Ekers 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):133-146
We present results of theoretical studies of the non-resonant excitation transfer in Rb(7S) + Rb(5S) and Rb(5D) + Rb(5S) collisions
at thermal collision energies. Rb2 adiabatic molecular terms correlating with the 5S+7S, 5S+5D and 5P+5P states of separated atoms were calculated for internuclear
distances R > 20 a.u. using asymptotic approximation. Mechanisms of collisional population and quenching of the 5D state were treated
on the basis of the computed molecular terms, and the respective cross-sections were calculated. Theoretical cross-sections
are in good agreement with the experimental values at thermal collision energies ( K).
Received 13 November 1998 and Received in final form 22 November 1999 相似文献