共查询到20条相似文献,搜索用时 31 毫秒
1.
A. I. Belousova Yu. E. Lozovikb 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):251-264
A two dimensional (2D) classical system of dipole particles confined by a quadratic potential is studied. This system can
be used as a model for rare electrons in semiconductor structures near a metal electrode, indirect excitons in coupled quantum
dots etc. For clusters of N ≤ 80 particles ground state configurations and appropriate eigenfrequencies and eigenvectors for the normal modes are found.
Monte-Carlo and molecular dynamic methods are used to study the order-disorder transition (the “melting” of clusters). In
mesoscopic clusters (N < 37) there is a hierarchy of transitions: at lower temperatures an intershell orientational disordering of pairs of shells
takes place; at higher temperatures the intershell diffusion sets in and the shell structure disappears. In “macroscopic”
clusters (N > 37) an orientational “melting” of only the outer shell is possible. The most stable clusters (having both maximal lowest
nonzero eigenfrequencies and maximal temperatures of total melting) are those of completed crystal shells which are concentric
groups of nodes of 2D hexagonal lattice with a number of nodes placed in the center of them. The picture of disordering in
clusters is compared with that in an infinite 2D dipole system. The study of the radial diffusion constant, the structure
factor, the local minima distribution and other quantities shows that the melting temperature is a nonmonotonic function of
the number of particles in the system. The dynamical equilibrium between “solid-like” and “orientationally disordered” forms
of clusters is considered. 相似文献
2.
S. L?mmer R. Donner D. Helbing 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):341-347
The relevant dynamics of a queueing process can be anticipated by taking
future arrivals into account. If the transport from one queue to another is associated
with transportation delays, as it is typical for traffic or productions networks, future
arrivals to a queue are known over some time horizon and, thus, can be used for an
anticipative control of the corresponding flows.
A queue is controlled by switching its outflow between “on” and “off” similar to
green and red traffic lights, where switching to “on” requires a non-zero setup time.
Due to the presence of both continuous and discrete state variables, the queueing process
is described as a hybrid dynamical system. From this formulation, we derive one
observable of fundamental importance: the green time required to clear the queue. This
quantity allows to detect switching time points for serving platoons without delay, i.e.,
in a “green wave” manner. Moreover, we quantify the cost of delaying the start of a
service period or its termination in terms of additional waiting time. Our findings may
serve as a basis for strategic control decisions. 相似文献
3.
A. H. Rodríguez H. Y. Ramírez 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):235-238
With the help of metadynamics it is possible to calculate efficiently the free energy of systems displaying high energy barriers
as a function of few selected “collective variables”. In doing this, the contribution of all the other degrees of freedom
(“microscopic” variables) is averaged out and, thus, lost. In the following it is shown that it is possible to calculate the
thermal average of these microscopic degrees of freedom during the metadynamics, not loosing this piece of information. The
method is tested on a two-dimensional toy system and on a small molecule, that is dialanine. 相似文献
4.
A. Traulsen 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):363-371
Cooperation based on similarity has been discussed since Richard Dawkins introduced the term “green beard” effect. In these
models, individuals cooperate based on an aribtrary signal (or tag) such as the famous green beard. Here, two different models
for such tag based cooperation are analysed. As neutral drift is important in both models, a finite population framework is
applied. The first model, which we term “cooperative tags” considers a situation in which groups of cooperators are formed
by some joint signal. Defectors adopting the signal and exploiting the group can lead to a breakdown of cooperation.
In this case, conditions are derived under which the average abundance of the more cooperative strategy exceeds 50%.
The second model considers a situation in which individuals start defecting towards others that are not similar to them. This
situation is termed “defective tags”. It is shown that in this case, individuals using tags to cooperate exclusively with
their own kind dominate over unconditional cooperators. 相似文献
5.
M. Combescot O. Betbeder-Matibet F. Dubin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):181-189
We have recently constructed a many-body theory for composite excitons, in
which the possible carrier exchanges between N excitons can be treated
exactly through a set of dimensionless “Pauli scatterings” between two
excitons. Many-body effects with free excitons turn out to be rather
simple because these excitons are the exact one-pair
eigenstates of the semiconductor Hamiltonian, in the absence of localized
traps. They consequently form a complete orthogonal basis for one-pair
states. As essentially all quantum particles known as bosons are
composite bosons, it is highly desirable to
extend this free exciton many-body theory to other kinds of
“cobosons” — a contraction for composite bosons — the physically
relevant ones being possibly not the exact one-pair eigenstates of
the system Hamiltonian. The purpose of this paper is
to derive the “Pauli scatterings” and the “interaction scatterings” of
these cobosons in terms of their wave functions and the interactions
which exist between the fermions from which they are
constructed. It is also explained how to calculate many-body effects in
such a very general composite boson system. 相似文献
6.
Baker J.M. Machi I.Z. Connell S.H. Bharuth-Ram K. Butler J.E. Cox S.F.J. Fischer C.G. Jestadt T. Murphy P. Nilen R.W.N. Sellschop J.P.F. 《Hyperfine Interactions》1999,120(1-8):579-583
A new configuration for muonium, with hyperfine interaction parameters of less than axial symmetry, in nitrogen rich diamond
is identified in Longitudinal Field Muon Spin Relaxation (LF-μSR) measurements. The TF-μSR measurements on the same sample
show that almost the entire strength of the new configuration is accounted for by a “missing fraction”, typically seen in
nitrogen rich type Ia diamond. The “missing fraction” is therefore the result of a T2 relaxation. This is consistent with
muon trapping at or in some nitrogen related defect(s) followed by electron capture at random times.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
A. Abragam 《Hyperfine Interactions》1986,31(1-4):3-10
The purpose of this talk is to replace μSR into the general framework of what I shall term “Spin spectroscopy” and more specifically:
“Resonance spin spectroscopy”. 相似文献
8.
Funnels in energy landscapes 总被引:1,自引:0,他引:1
K. Klemm C. Flamm P. F. Stadler 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):387-391
Local minima and the saddle points separating them in the energy landscape
are known to dominate the dynamics of biopolymer folding. Here we
introduce a notion of a “folding funnel” that is concisely defined in
terms of energy minima and saddle points, while at the same time conforming
to a notion of a “folding funnel” as it is discussed in the protein folding
literature. 相似文献
9.
Ye.S. Golubeva L.A. Kondratyuk M. Büscher W. Cassing V. Hejny H. Ströher 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):237-245
The ω resonance production and its π0γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π0γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively.
The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for
the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different
kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between
the π0 and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated
π0's and γ's are produced.
Received: 2 April 2001 / Accepted: 5 June 2001 相似文献
10.
R. Thissen P. Lablanquie R.I. Hall M. Ukai K. Ito 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):335-342
Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron
and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence
states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve
as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer,
the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the
class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that
loses its innershell electron to its neutral partner.
Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998 相似文献
11.
M. Brut A. Estève G. Landa G. Renvez M. Djafari Rouhani 《The European physical journal. E, Soft matter》2009,28(1):17-25
We present a new competitive method for the atomic scale treatment of macromolecular flexibility called Static Mode method.
This method is based on the “induced-fit” concept, i.e. it maps the intrinsic deformations of a macromolecule subject to diverse external excitations. The algorithm makes it possible
to obtain a set of deformations, each one corresponding to a specific interaction on a specific molecular site, in terms of
force constants contained in the energy model. In this frame, the docking problem can be expressed in terms of interaction
sites between the two molecules, the molecular deformations being extracted from the pre-calculated Static Modes of each molecule.
Some preliminary basic examples aimed at illustrating potential applications where macro- or bio-molecular flexibility is
of key importance are given: flexibility inducing conformational changes in the case of furanose ring and flexibility for
the characterization, including allostery, of poly(N-isopropylacrylamide)(P-NIPAM) active sites. We also discuss how this
procedure allows “induced-fit” flexible molecular docking, beyond state-of-the-art semi-rigid methods. 相似文献
12.
V. E. Chernov N. L. Manakov A. F. Starace 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(3):347-359
The relation between the quantum defects, , and scattering phases, , in the single-channel Quantum Defect Theory (QDT) is discussed with an emphasis on their analyticity properties for both
integer and noninteger values of the orbital angular momentum parameter . To derive an accurate relation between and for asymptotically-Coulomb potentials, the QDT is formally developed for the Whittaker equation in its general form “perturbed”
by an additional short-range potential. The derived relations demonstrate that is a complex function for above-threshold energies, which is analogous to the fact that is complex for below-threshold energies. The QDT Green's function, , of the “perturbed” Whittaker equation is parameterized by the functions and for the continuous and discrete spectrum domains respectively, and a number of representations for are presented for the general case of noninteger . Our derivations and analyses provide a more general justification of known results for nonrelativistic and relativistic
cases involving Coulomb potentials and for a Coulomb plus point dipole potential.
Received 25 June 1999 相似文献
13.
The present paper develops a Statistical Mechanics approach to the inherent states of glassy systems and granular materials
by following the original ideas proposed by Edwards for granular media. We consider three lattice models (a diluted spin glass,
a system of hard spheres under gravity and a hard-spheres binary mixture under gravity) introduced to describe glassy and
granular systems. They are evolved using a “tap dynamics” analogous to that of experiments on granular media. We show that
the asymptotic states reached in such a dynamics are not dependent on the particular sample history and are characterized
by a few thermodynamical parameters. We assume that under stationarity these systems are distributed in their inherent states
satisfying the principle of maximum entropy. This leads to a generalized Gibbs distribution characterized by new “thermodynamical”
parameters, called “configurational temperatures” (related to Edwards compactivity for granular materials). Finally, we show
by Monte Carlo calculations that the average of macroscopic quantities over the tap dynamics and over such distribution indeed
coincide. In particular, in the diluted spin glass and in the system of hard spheres under gravity, the asymptotic states
reached by the system are found to be described by a single “configurational temperature”. Whereas in the hard-spheres binary
mixture under gravity the asymptotic states reached by the system are found to be described by two thermodynamic parameters,
coinciding with the two configurational temperatures which characterize the distribution among the inherent states when the
principle of maximum entropy is satisfied under the constraint that the energies of the two species are independently fixed.
Received 19 March 2002 and Received in final form 14 June 2002 相似文献
14.
15.
Progress in direct-drive inertial confinement fusion research at the
laboratory for laser energetics
R. L. McCrory D. D. Meyerhofer S. J. Loucks S. Skupsky R. Betti T. R. Boehly T. J.B. Collins R. S. Craxton J. A. Delettrez D. H. Edgell R. Epstein K. A. Fletcher C. Freeman J. A. Frenje V. Yu. Glebov V. N. Goncharov D. R. Harding I. V. Igumenshchev R. L. Keck J. D. Kilkenny J. P. Knauer C. K. Li J. Marciante J. A. Marozas F. J. Marshall A. V. Maximov P. W. McKenty S. F.B. Morse J. Myatt S. Padalino R. D. Petrasso P. B. Radha S. P. Regan T. C. Sangster F. H. Séguin W. Seka V. A. Smalyuk J. M. Soures C. Stoeckl B. Yaakobi J. D. Zuegel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):233-238
Direct-drive inertial confinement fusion (ICF) is
expected to demonstrate high gain on the National Ignition Facility (NIF) in
the next decade and is a leading candidate for inertial fusion energy
production. The demonstration of high areal densities in hydrodynamically
scaled cryogenic DT or D2 implosions with neutron yields that are a
significant fraction of the “clean” 1-D predictions will validate the
ignition-equivalent direct-drive target performance on the OMEGA laser at
the Laboratory for Laser Energetics (LLE). This paper highlights the
recent experimental and theoretical progress leading toward achieving this
validation in the next few years.
The NIF will initially be configured for X-ray drive and with no beams
placed at the target equator to provide a symmetric irradiation of a
direct-drive capsule. LLE is developing the “polar-direct-drive” (PDD)
approach that repoints beams toward the target equator. Initial 2-D
simulations have shown ignition. A unique “Saturn-like” plastic ring
around the equator refracts the laser light incident near the equator toward
the target, improving the drive uniformity.
LLE is currently constructing the multibeam, 2.6-kJ/beam, petawatt laser
system OMEGA EP. Integrated fast-ignition experiments, combining the OMEGA
EP and OMEGA Laser Systems, will begin in FY08. 相似文献
16.
Paul W. Percival 《Hyperfine Interactions》1991,65(1-4):901-911
As “rapporteur” for the papers submitted to this conference in the general area of muonium chemistry, I briefly review the
major developments since μSR86, and attempt to show how the papers presented at μSR90 relate to each other and work published
in the intervening years. Some topics are discussed in more detail than others, reflecting my own interests and views on what
is of current importance. Nevertheless, I try to cover all current research in muonium chemistry. The major areas are: early
events following muon thermalization, including subsequent loss of muon polarization (the “missing fraction”); molecular structure
and dynamics, primarily of muonium-substituted free radicals: and reaction kinetics. 相似文献
17.
M. Buiatti 《Il Nuovo Cimento D》1998,20(1):79-89
Summary The molecular revolution and the development of biology-derived industry have led in the last fifty years to an unprecedented
“leap forward” of life sciences in terms of experimental data. Less success has been achieved in the organisation of such
data and in the consequent development of adequate explanatory and predictive theories and models. After a brief historical
excursus inborn difficulties of mathematisation of biological objects and processes derived from the complex dynamics of life
are discussed along with the logical tools (simplification, choice of observation points etc.) used to overcome them. “Autistic”,
monodisciplinary attitudes towards biological modeling of mathematicians, physicists, biologists aimed in each case at the
use of the tools of other disciplines to solve “selfish” problems are also taken into account and a warning against derived
dangers (reification of monodisciplinary metaphors, lack of falsification etc.) is given. Finally “top-down” (deductive) and
“bottom up” (inductive) heuristic interactive approaches to mathematisation are critically discussed with the help of a serie
of examples. 相似文献
18.
A. Faccinetto K. Thomson M. Ziskind C. Focsa 《Applied Physics A: Materials Science & Processing》2008,92(4):969-974
The response of polycyclic aromatic hydrocarbons (PAHs) to different desorption and ionization fluences has been investigated
in a laser desorption/multiphoton ionization/time-of-flight mass spectrometry scheme. The results evidence an intricate relationship
between the desorption and ionization steps, tentatively attributed to the amount of internal energy acquired by the desorbed
molecules. Different behaviors have been found for the various PAHs considered, leading to a parametric “signature” for each
species. Moreover, some insights on the fragmentation mechanism of the desorbed PAHs have been obtained, with possible interpretation
in the frame of a “ladder-switching” model. 相似文献
19.
E. Abad J. Ortega Y. J. Dappe F. Flores 《Applied Physics A: Materials Science & Processing》2009,95(1):119-124
A local orbital DFT-approach combined with a “scissor”-operator is used to obtain the Charge Neutrality Level and the screening
parameter in the benzene/Au(111) and C60/Au(111) interfaces. The “pillow” dipole and interface Fermi level are also calculated. The total dipole induced across the
interface is compared with the experimental evidences: while the agreement for C60/Au(111) is excellent, for benzene/Au(111), some discrepancies appear that are discussed in the light of other models. 相似文献
20.
Z. Bak R. Jaroszewicz 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):231-235
A localized spin system of fractal symmetry with indirect exchange between them is considered. We define a specific class
of fractals as the “net fractals” which display multidimensional logarithmic periodicity. Basing on this property we model
the effective indirect exchange interaction by the conventional RKKY exchange with the logarithmic coordinates playing role
of the real space ones. Finally, we discuss the case of non-ideal “net fractals” in which fractional dynamics of the electrons
is expected. In this case we show that RKKY exchange integrals are given by the formulas derived under assumption that a system
has a fractional spectral dimension. 相似文献