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1.
da Costa EC Figueiredo W 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(2):1134-1138
We studied in this work a three-monomer reaction model on one- and two-dimensional lattices. We have taken different reactivity rates among pairs of monomers and the reaction between two selected monomers was forbidden. We have employed the mean field and the pair approximation to decouple the equations of motion for the densities of single and pairs of monomers. We found the stationary states and the phase diagram of the model. We have shown that, in two dimensions and within the pair approximation, there is a first-order transition line between active and poisoned steady states. 相似文献
2.
M. Combescot M.-A. Dupertuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):459-464
We show that the carrier “antibinding” observed recently in
semiconductor quantum dots, i.e., the fact that the ground state
energy of two electron-hole pairs goes above twice the ground-state
energy of one pair, can entirely be assigned to a charge separation
effect, whatever its origin. In the absence of external electric field, this charge
separation comes from different “spreading-out” of the electron and
hole wavefunctions linked to the finite height of the barriers. When
the dot size shrinks, the two-pair energy always stays below when the
barriers are infinite. On the opposite, because barriers are less
efficient for small dots, the energy of two-pairs in a dot with
finite barriers, ends by behaving like the one in bulk, i.e., by
going above twice the one-pair energy when the pairs get too close.
For a full understanding of this “antibinding” effect, we have also
reconsidered the case of one pair plus one carrier. We find that,
while the carriers just have to spread out of the dot differently for
the “antibinding” of two-pairs to appear, this “antibinding” for
one pair plus one carrier only appears if this carrier is the one
which spreads out the less. In addition a remarkable sum rule exists
between the “binding energies” of two pairs and of one pair plus one carrier. 相似文献
3.
S.-W. Son H. Jeong J. D. Noh 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):431-437
We propose a method to determine the community
structure of a complex network. In this method the ground state
problem of a ferromagnetic random field Ising model is considered
on the network with the magnetic field Bs = +∞, Bt =
-∞, and Bi≠s,t=0 for a node pair s and t. The
ground state problem is equivalent to the so-called maximum flow
problem, which can be solved exactly numerically with the help of
a combinatorial optimization algorithm. The community structure is
then identified from the ground state Ising spin domains for all
pairs of s and t. Our method provides a criterion for the
existence of the community structure, and is applicable equally
well to unweighted and weighted networks. We demonstrate the
performance of the method by applying it to the Barabási-Albert
network, Zachary karate club network, the scientific collaboration
network, and the stock price correlation network.
(Ising, Potts, etc.) 相似文献
4.
C. Poulain N. Mazellier L. Chevillard Y. Gagne C. Baudet 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):219-224
We present the results of an experimental study of the spatial Fourier modes of the vorticity in a turbulent jet flow.
By means of an acoustic scattering setup we have recorded the evolution in time of Fourier modes of the vorticity field, characterized
by well defined wavevectors k.
By computing the auto-correlation of the amplitude of the Fourier modes we evidence that, whatever the length scale (or equivalently
k), the dynamic evolution of
the vorticity field involves two well separated time scales.
We have also performed the simultaneous acquisitions of pairs of Fourier modes with two wavevectors k and k'.
Whatever the spectral gap k- k', any pair of Fourier modes exhibits a significant cross-correlation over long time delays, indicating a strong statistical
dependence between
scales. 相似文献
5.
We consider a model in which an electric field induces quantum nucleation of kink-antikink pairs in a pinned charge or spin density wave. Pair nucleation events, prevented by Coulomb blockade below a pair creation threshold, become correlated in time above threshold. The model provides a natural explanation for the observed (i) small density wave polarization below threshold in NbSe (3), (ii) narrow band noise, (iii) coherent oscillations, and (iv) mode-locking at high drift frequencies. 相似文献
6.
G. Campi E. Cappelluti Th. Proffen X. Qiu E. S. Bozin S. J.L. Billinge S. Agrestini N. L. Saini A. Bianconi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(1):15-21
We have studied temperature evolution of the local as well as the
average crystal structure of MgB2 using real-space atomic pair
distribution function (PDF) measured by high resolution neutron powder
diffraction in a wide temperature range of T=10–600 K. We find small
positive correlation factors for the B–B and B–Mg pairs, determined by
mean-square displacements (MSD) and the mean-square relative
displacements (MSRD). We analyze the PDF using both Einstein and
force constant models finding a good agreement between the
experimental data and the two models. This indicates that B and Mg
atomic correlations are not sensitive to the details of phonon
dispersion. 相似文献
7.
We have studied entanglement evolution and transfer in a double
Tavis--Cumming model where two pairs of entangled two-level atoms
AB and CD interact with two single-mode cavity fields a and
b. We show that the Bell-like initial state of atoms AB can
exhibit entanglement sudden death which should be independent of the
initial entanglement of atoms CD. Also, we show that the initial
entanglement of one atomic pair can be transferred into another
pair, as well as the possible subsystems, that become entangled
during evolution. 相似文献
8.
T. Barhoumi J. L. Monge H. Bouchriha 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):453-458
We have adapted the model of two consecutive pairs to the study of the
triplet-doublet (T-D) interaction in molecular crystals. We have applied
this model to the modulation of the photoconductivity in crystalline
anthracene by a static magnetic field (MFE) and a microwave field (PDMR). We
were able to reproduce, for the first time, quite perfectly two types of
experiments with the same set of kinetic constants. 相似文献
9.
Fertig HA 《Physical review letters》2002,89(3):035703
The unbinding of vortex-antivortex pairs for the classical two-dimensional XY model in a magnetic field is studied. A single such pair is connected by a string of overturned spins, leading to linear confinement. We show that this system supports two phase transitions, one in which closed strings proliferate, and a second in which vortices unbind. The transitions are shown to be dual to one another, and are remarkably continuous. Possible consequences for a variety of systems are discussed. 相似文献
10.
Nanoscale guiding for cold atoms based on surface plasmons along the tips of metallic wedges 下载免费PDF全文
We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87 Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices. 相似文献
11.
半经典闭合轨道理论已经成功地计算了在外加磁场和平行电磁场中的里德堡原子的回归谱.但对于垂直电磁场中的里德堡原子,理论和计算都变得更为复杂.本文把闭合轨道理论推广到三维情况,采用 B.Hüpper的模型势计算了ε=-0.03,主量子数n≈ 40,m=0下He原子在垂直电磁场中的光吸收谱和回归谱,并和H原子在垂直电磁场中的回归谱作比较,突出了实散射的贡献.计算中应用了离子实散射的分区自洽迭代方法,并考虑到轨道的多次重复和离子实的多次散射效应.这是对闭合轨道理论的验证和进一步推广. 相似文献
12.
M. Cini G. Stefanucci A. Balzarotti 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):293-304
The Cu-O plane and the clusters that possess the same C4v symmetry around a Cu ion have 2-hole eigenstates of the kinetic energy with vanishing on-site repulsion (W=0 pairs). Cluster calculations by exact diagonalisation show that these are the quasiparticles that lead to a paired ground
state, and have superconducting flux-quantisation properties. Here, we extend the theory to the full plane, and show that
the W=0 quasiparticles are again the natural explanation of superconducting flux-quantisation. Moreover, by a new approach which
is exact in principle, we calculate the effective interaction between two holes added to the ground state of the repulsive three-band Hubbard model. To explain how a noninteracting electron
gas becomes a superconductor when switching the local Coulomb interaction, we obtain a closed-form analytic expression including
the effects of all virtual transitions to 4-body intermediate states (exchange of an electron-hole pair). Our scheme is ready
to include other interactions which are not considered in the Hubbard model but may be important. In the plane, the W=0 pairs have 1
B
2
and 1
A
2
symmetry. The effective interaction in these channels is attractive and leads to a Cooper-like instability of the Fermi liquid,
while it is repulsive for triplet pairs. From , we derive an integral equation for the pair eigenfunction; the binding energy of the pairs is in the range of tens of meV. However, our symmetry-based method is far more general than the model.
Received 18 December 1998 相似文献
13.
We have achieved dual synchronization of chaos in two pairs of one-way coupled Nd:YVO4 microchip lasers, using only one transmission channel, by experiment and numerical calculation. We observed the individual synchronization of chaos in each pair of two lasers by adjusting the optical frequencies for injection locking between the corresponding pairs. The achievement of dual synchronization is dependent on the injection-locking condition, which is different from the locking condition for a single pair of lasers because of the presence of an additional injection signal from the master laser of the other pair. 相似文献
14.
Eigen-Tamm模型认为水溶液中的离子对从单水分子桥链离子对到紧密离子对是离子对溶剂化平衡的动力学控制性步骤,两态之间自由能垒最高,相互转化速率最慢. 设计了两类带有单位电荷的离子对模型(2.0:x和x:2.0,固定离子对中的阳离子或阴离子的半径为2 ?,另一个为不同半径的阴阳离子),通过计算离子对不同距离的平均力势来获取自由能曲线,发现2.0:x系列离子对由于溶剂水的作用,从单水分子桥链离子对到紧密离子对转化的自由能垒有明显减低,并不是离子成对动力学平衡中的最慢步骤,与Eigen-Tamm 模型描述存在偏差. 相似文献
15.
We report a practical non-postselection entanglement concentration scheme in which a maximally entangled Bell-state photon pair is produced from two pairs of partially (or non-maximally) entangled photons. Since this scheme is built only upon linear optical elements and does not require photon-number resolving detectors, it has immediate applications in experimental implementations of various quantum information protocols which require two-photon Bell-states. 相似文献
16.
Zafer Gedik 《Solid State Communications》2006,138(2):82-85
We study an analytically solvable model for decoherence of a two spin system embedded in a large spin environment. As a measure of entanglement, we evaluate the concurrence for the Bell states (Einstein-Podolsky-Rosen pairs). We find that while for two separate spin baths all four Bell states lose their coherence with the same time dependence, for a common spin bath, two of the states decay faster than the others. We explain this difference by the relative orientation of the individual spins in the pair. We also examine how the Bell inequality is violated in the coherent regime. Both for one bath and two bath cases, we find that while two of the Bell states always obey the inequality, the other two violate the inequality at early times. 相似文献
17.
Fluctuation spectra of fluid compound membrane systems are calculated. The systems addressed contain two (or more) almost
parallel membranes that are connected by harmonic tethers or by a continuous, harmonic confining potential. Additionally,
such a compound system can be attached to a supporting substrate. We compare quasi-analytical results for tethers with analytical
results for corresponding continuous models and investigate under what circumstances the discrete nature of the tethers actually
influences the fluctuations. A tethered, supported membrane pair with similar bending rigidities and stiff tethers can possess
a nonmonotonic fluctuation spectrum with a maximum. A nonmonotonic spectrum with a maximum and a minimum can occur for an
either free or supported membrane pair of rather different bending rigidities and for stiff tethers. Typical membrane displacements
are calculated for supported membrane pairs with discrete or continuous interacting potentials. Thereby an estimate of how
close the constituent two membranes and the substrate typically approach each other is given. For a supported membrane pair
with discrete or continuous interactions, the typical displacements of each membrane are altered with respect to a single
supported membrane, where those of the membrane near the substrate are diminished and those of the membrane further away are
enhanced. 相似文献
18.
Quantum photon-number fluctuation and correlation of bound soliton pairs in mode-locked fiber lasers are studied on the basis of the complex Ginzburg-Landau equation model. We find that, depending on their phase difference, the total photon-number noise of the bound soliton pair can be larger or smaller than that of a single soliton, and the two solitons in the soliton pair have a corresponding positive or negative photon-number correlation. It is predicted for the first time to our knowledge that out-of-phase soliton pairs can exhibit less noise as a result of negative correlation. 相似文献
19.
E. Nir Ch. Plützer K. Kleinermanns M. de Vries 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):317-329
The vibronic spectra of laser desorbed and jet cooled guanine (G) adenine (A), and cytosine (C) consist of bands from four,
two and two major tautomers respectively, as revealed by UV-UV and IR-UV double resonance spectroscopy. The vibronic spectrum
of adenine around 277 nm consists of weak nπ* and strong ππ* transitions, based on IR-UV and deuteration experiments. Precise ionization potentials of G and A were determined with 2-color,
2-photon ionization. We also measured vibronic and IR spectra of several base pairs. GC exhibits a HNH ... OH/NH ... N/C=O ... HNH bonding similar to the Watson-Crick GC base pair but with C as enol tautomer. One GG isomer exhibits non-symmetric hydrogen
bonding with HNH ... N/NH ... N/C=O ... HNH interactions. A second observed GG isomer has a symmetrical hydrogen bond arrangement with C=O ... NH/NH ... O=C bonding. Two CC isomers were observed with symmetrical C=O ... NH/NH ... O=C bonding and nonsymmetrical C=O ... HNH/NH ... N interaction, respectively. Guanosine (Gs), 2-DeoxyGs und 3-DeoxyGs each exhibit only one isomer in the investigated wavelength
range around 290 nm with a strong intramolecular sugar(5-OH) ... enolguanine(3-N) hydrogen bond.
Received 16 June 2002 / Received in final form 15 July 2002 Published online 13 September 2002 相似文献
20.
W. Aulbur J. Mählmann M. Tondera J. Pollmann 《Zeitschrift für Physik B Condensed Matter》1994,93(2):219-238
We present a variational approach for treating the Hubbard Hamiltonian in one, two and three dimensions. It is based on 2M-fermion wavefunctions which are allowed to form correlated spin-singlet pairs. Expressions for the ground state energy and correlation functions are derived in terms of general pair coefficient functions. The presented approach offers a convenient starting point for improved variational treatments that allow to include different specific types of pair correlations. We present first applications to the attractive and to the extended Hubbard model using a very simple ansatz for the pair coefficient functions. The ground state energy, chemical potential, order parameter, momentum distribution as well as spin-spin and density-density correlation functions follow from a system of coupled nonlinear equations that has to be solved selfconsistently. All quantities are given for arbitrary band-filling in one, two and three dimensions. Our results are compared with those of other approximations and for the one-dimensional case with the exact results of Krivnov and Ovchinnikov. 相似文献