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1.
A. M. Dikandé 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):397-402
Excitations of the polaron types are investigated in the spin-1/2 quantum chain with XY exchange and Dzyaloshinsky-Moriya
interaction, both coupled to acoustic vibrations of the substrate lattice. The study is carried out via Jordan-Wigner transformation
with the help of which the spin chain is mapped onto a chain of spinless fermions. From the resulting effective fermion-lattice
Hamiltonian, the discrete equations of motion are derived. These equations are solved in the continuum limit for self-trapped
states near the bottom of the fermion spectrum interacting with long-wavelength acoustic lattice modes. The associate polaron
solution, which has a pulse shape, is shown to propagate bound to the induced lattice kink distortion by translation along
the chain at a constant velocity v. The pair can also experience an additional acceleration ϑ0 when the free fermion charge is excited above its groundstate. The polaron binding energy is strongly reduced, depending
quadratically on the ratio D/J of the Dzyaloshinsky-Moriya interaction strength D to the isotropic XY exchange interaction
J. It is also found that polaron parameters depend only on the XY spin-lattice coupling but not on the Dzyaloshinsky-Moriya
contribution. 相似文献
2.
For solitary waves on a monoatomic chain with nearest neighbor interactions the continuum approximation has a limited validity range and exhibits certein mathematical problems. For pulse solitons these problems are overcome by the Quasicontinuum Approach (QCA), and the validity range is considerably extended. We generalize the QCA to oscillatory excitations and derive analytic expressions for bright and dark envelope solitons, limiting ourselves to a polynomial interaction potential with harmonic, cubic and quartic terms. Moreover we describe and apply a numerical iteration procedure in Fourier space in order to take into account discreteness effects in a systematic way. This procedure yields envelope solitons with a width in the order of the lattice constant. In the case of zero velocity these solutions can be compared with intrinsic localized modes derived by other authors. The stability and accuracy of all our solutions are tested by numerical simulations. 相似文献
3.
4.
Periodic, Quasiperiodic and Chaotic Discrete Breathers in a Parametrical Driven Two-Dimensional Discrete Klein-Gordon Lattice 下载免费PDF全文
We study a two-dimensional lattice of anharmonic oscillators with only quartic nearest-neighbor interactions, in which discrete breathers can be explicitly constructed by an exact separation of their time and space dependence. DBs can stably exist in the two-dimensional Klein-Gordon lattice with hard on-site potential. When a parametric driving term is introduced in the factor multiplying the harmonic part of the on-site potential of the system, we can obtain the stable quasiperiodic discrete breathers and chaotic discrete breathers by changing the amplitude of the driver. 相似文献
5.
All-Solid-State Nd:YAG Laser Operating at 1064nm and 1319nm under 885nm Thermally Boosted Pumping 下载免费PDF全文
We report a high-effciency Nd:YAG laser operating at 1064 nm and 1319nm, respectively, thermally boosted pumped by an all-solid-state Q-switched Ti:sapphire laser at 885 nm. The maximum outputs of 825.4 m W and 459.4mW, at 1064nm and 1319nm respectively, are obtained in a 8-ram-thick 1.1 at.% Nd:YAG crystal with 2.1 W of incident pump power at 885nm, leading to a high slope efficiency with respect to the absorbed pump power of 68.5% and 42.0%. Comparative results obtained by the traditional pumping at 808nm are presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power at 1064nm under the 885nm pumping are 12.2% higher and 7.3% lower than those of 808rim pumping. At 1319nm, the slope efficiency and the threshold with respect to the absorbed pump power under 885nm pumping are 9.9% higher and 3.5% lower than those of 808 nm pumping. The heat generation operating at 1064 nm and 1319 nm is reduced by 19.8% and 11.1%, respectively. 相似文献
6.
A. Claverie B. Colombeau B. de Mauduit C. Bonafos X. Hebras G. Ben Assayag F. Cristiano 《Applied Physics A: Materials Science & Processing》2003,76(7):1025-1033
Extended defects are often found after ion implantation and annealing of silicon and they are known to affect dopant diffusion.
The article reviews the structure and energetics of the most often found extended defects and describes the mechanisms by
which all these defects grow in size and transform during annealing. Defects grow by interchanging the Si atoms they are composed
of and thus maintain large supersaturations of free Si interstitials in the region. A model has been developped to describe
such an evolution in presence of a free surface. It is shown that after low energy implantation, the surface of the wafer
may recombine large amounts of these free Si interstitials, driving defects into dissolution before transformation into more
stable forms.
Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003
RID="*"
ID="*"Corresponding author. Fax: +33-56/2257-999, E-mail: claverie@cemes.fr 相似文献
7.
L. Gao X. P. Yu 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):403-409
We derive expressions for the effective nonlinear susceptibility
tensors for both the second harmonic generation (SHG) and induced
third harmonic generation (THG) of nonlinear composite materials,
in which nondilute coated particles with radial dielectric
anisotropy are randomly embedded in the linear host. Two types of
coated particles are considered. The first is that the core
possesses a second order nonlinear susceptibility and the shell is
linear and radially anisotropic, while the second is that the
core is linear with radial anisotropy and the shell has a second
order nonlinear susceptibility. We observe greatly enhanced SHG
and THG susceptibilities at several surface plasmon resonant
frequencies. For the second model, due to the coating material
being metallic, there exists two fundamental resonant frequencies
ωc1 and ωc2, whose difference
ωc2-ωc1 is strongly dependent on the interfacial
parameter and the radial dielectric anisotropy. Furthermore, in
both systems, the adjustment of the dielectric anisotropy results
in larger enhancement of both SHG and induced THG susceptibilities
at surface plasmon resonant frequencies than the corresponding
isotropic systems. Therefore, both the core-shell structure and
the dielectric anisotropy play important roles in determining the
nonlinear enhancement and the surface resonant frequencies. 相似文献
8.
In order to solve the issues in Si nanoelectronics such as fluctuation in the device functions and poor reliability of devices due to relative increase in mass transport in nm size structures and to yield novel functions by rather taking advantage of the nm size, we need to understand the phenomena peculiar to nm size structures. Based on the fact that a practical method to fabricate nm structures in terms of throughput, process time, and cost is to combine modification of solid surfaces with energetic particles (especially with single ions) and subsequent chemical processing in solutions, we describe single ion irradiation effects as a tool to modify solid surfaces in nm scale, a method for nm scale in-situ observation of solid surfaces, and some examples of the acquired knowledge. 相似文献
9.
Existence and Stability of Compact-Like Discrete Breather in Discrete One-Dimensional Monatomic Chains 下载免费PDF全文
Compact-like discrete breathers in discrete one-dimensional monatomic chains are investigated by discussing a generalized discrete one-dimensional monatomic model. It is proven that compact-like discrete breathers exist not only in soft Ф^4 potential but also in hard Ф^4 potential and K4 chains. The measurements of compact-like discrete breathers' core in soft and hard Ф^4 potential are determined by coupling parameter K4, while the measurements of compact-like discrete breathers' core in K4 chains are not related to coupling parameter K4. The stabilities of compact-like discrete breathers correlate closely to coupling parameter K4 and the boundary condition of lattice. 相似文献
10.
K. Ya. Kondratyev 《Il Nuovo Cimento C》1990,13(5):835-846
Summary Principal purposes of the International Space Year (ISY) have been discussed. In view of the increasing significance of ecological
problems it is becoming clear that there have to be two key directions of the ISY programmes: 1) various problems relevant
to the International Geosphere-Biosphere Programme (global climate change, global biosphere dynamics, regional ecological
problems: desertification, forest decline, acid rains etc.); 2) comparative planetology. One of the most urgent problems is
connected with the accomplishment, of the ?Mission to Planet Earth? which has to be based on the creation of an optimal global
system of satellite and conventional ecological observations (especially for various typical ecosystems). Studies of the other
planets have to be coordinated with requirements of further investigations in the field of the Earth's ecology. 相似文献