LBO晶体Ⅱ类相位匹配走离角及互作用长度的计算

从非线性光学理论出发,数值计算了LBO晶体Ⅱ类相位匹配1064 nm光波倍频的走离角及互作用长度。在全匹配角范围内,1064 nm慢、快两光间夹角的范围是0-1.0°,θ≈0°。Ф≈90°时,夹角为0°;θ≈45°,Ф≈55°时,最大夹角约为1.0°。慢、快两基频光光斑线度相同时,波矢沿θ≈0°,Ф≈88°方向入射时,其互作用长度最大。

Controlling the Collision Between Two Solitons in a Two-Component Condensate by Interspecies Interactions

We present a family of the solutions of two-component Bose-Einstein condensates with time-dependentscattering length by means of multiple-scale method.Our numerical calculations show that the collision properties (theposition,the time,and the frequency of the collision) between two solitons can be controlled by the time-dependentinterspecies scattering length.Meanwhile,we also find that the amplitude of the solitons is close related to the timedependentinterspecies scattering length.

New method of designing anti-slide piles——the strength reduction FEM

At present,the thrust of an anti-slide pile can be worked out with some calculation methods. However,the resistance in front of the pile,the distributions of resistance and thrust,and appropriate pile length cannot be easily obtained. In this paper,the authors applied the strength-reduction finite element method (FEM) to several design cases of anti-slide piles. Using this method,it is possible to take the pile-soil interactions into consideration,obtain reasonable resistance in front of pile and the distributions of thrust and resistance,and reasonable lengths of anti-slide piles. In particular,the thrust and resistance imposed on embedded anti-slide piles can be calculated and composite anti-slide pile structures such as anchored piles and braced piles can be optimized. It is proved through the calculation examples that this method is more reliable and economical in the design of anti-slide pile.

Exact Analytical Solutions in Bose-Einstein Condensates with Time-Dependent Atomic Scattering Length

In the paper, the generalized Riccati equation rational expansion method is presented. Making use of the method and symbolic computation, we present three families of exact analytical solutions of Bose-Einstein condensates with the time-dependent interatomic interaction in an expulsive parabolic potential. Then the dynamics of two anlytical solutions are demonstrated by computer simulations under some selectable parameters including the Feshbach-managed nonlinear coefficient and the hyperbolic secant function coefficient.

拉曼-纳斯衍射声光Q开关的实验研究

实验研究了拉曼-纳斯(R-N)衍射的声光相互作用长度与声波光波参数之间的关系,确定了最佳声光相互作用长度。在此基础上,分别设计以水和TeO2晶体为声光介质的R-N衍射Q开关器件。测量了器件的衍射效率、衍射角和插入损耗等参数。应用TeO2晶体开关器件调制长脉冲Nd:YAG/KTP激光器,当重复频率为10 kHz时得到了脉宽约为200 ns的绿激光输出。

A two-scale contact model for collisions between blocks in CDEM

Contact detection between interacting blocks is of great importance to discontinuity-based numerical methods, such as DDA, DEM, and NMM. A rigorous contact theory is a prerequisite to describing the interactions of multiple blocks. Currently, the penalty method, in which mathematical springs with high stiffness values are employed, is always used to calculate the contact forces. High stiffness values may cause numerical oscillations and limit the time step. Furthermore, their values are difficult to identify. The intention of this study is to present a two-scale contact model for the calculation of forces between colliding blocks. In this new model, a calculation step taken from the moment of contact will be divided into two time stages: the free motion time stage and the contact time stage. Actually, these two time stages correspond to two real physical processes. Based on this, we present a new numerical model that is intended to be more precise and useful in calculating the contact forces without mathematical springs. The propagation of the elastic wave during collision is of a characteristic length, which determines the volume of material involved in the contact force calculation. In conventional contact models, this range is always regarded as the length of one element, which may lead to an inaccurate calculation of contact forces. In fact, the real scale of this range is smaller than the length of a single element, and subdivided elements, which are refined according to the characteristic length and are presented in the new contact model.

Investigation on the interaction length and access resistance of a nanopore with an atomic force microscopy

Nanopore devices have attracted a lot of attention for their potential application in DNA sequencing. Here, we study how an occluding object placed near a nanopore affects its access resistance by integrating an atomic force microscopy with a nanopore sensor. It is found that there exists a critical hemisphere around the nanopore, inside which the tip of an atomic force microscopy will affect the ionic current. The radius of this hemisphere, which is a bit smaller than the theoretical capture radius of ions, increases linearly with the applied bias voltage and quadratically with the nanopore diameter, but is independent of the operation modes and scanning speeds of the atomic force microscopy. A theoretical model is also proposed to describe how the tip position and geometrical parameters affect the access resistance.

Scaling Theory of Strongly Charged Cylindrical Polyelectrolyte Brushes

Scaling theory of charged cylindrical polyelectrolyte brushes is developed. The dependence of brush thickness on the grafting density, charge fraction, and chain length is analyzed. A full phase diagram is established. Characteristics and boundaries between different regimes of cylindrical polyelectrolyte brushes are summarized. Special attentions are paid to electrostatic interaction induced stiffening and counterion condensation effects. If the Bjerrum length of the solution is larger than the Kuhn length of the polyelectrolyte chains, counterion condensation occurs in the strongly charged polyeleetrolyte brushes. On the contrary, the electrostatic interaction stretches the strongly charged grafted polyelectrolyte chains to their contour length.

Fulde-Ferrell-Like Molecular States in Spin-Orbit Coupled Ultracold Fermi Gases

We study the molecular state in three-component Fermi gases with a single impurity of ~6Li immersing in a no-interacting Fermi sea of ^(40)K in the presence of an equal weight combination of Rashba-type and Dresselhaustype spin-orbit coupling. In the region where the Fermi sea has two disjointed Fermi surfaces, we find that there are two Fulde–Ferrell-like molecular states with dominating contributions from the lower helicity branch. Decreasing the scattering length or the spin-orbit coupled Fermi energy, we find the Fulde–Ferrell-like molecular state with small center-of-mass momentum is always energy favored and the other one will suddenly disappear.