Circuit designs of ultra-fast all-optical modified signed-digit adders using semiconductor optical amplifier and Mach-Zehnder interferometer

The need for increasingly high-speed digital optical systems and optical processors demands ultra-fast all-optical logic and arithmetic units. In this paper, we combine the attractive and powerful parallelism property of the modified signed-digit (MSD) number representation with the ultra-fast all-optical switching property of the semiconductor optical amplifier and Mach-Zehnder interferometer (SOA-MZI) to design and implement all-optical MSD adder/subtracter circuits. Non-minimized and minimized techniques are presented to design and realize efficient circuits to perform arithmetic operations. Several all-optical circuits’ designs are proposed with the objective to minimize the number of the SOA-MZI switches, the time delay units in the adders, and other optical elements. To use the switching property of the SOA-MZI structure, two bits per digit binary encoding for each of the trinary MSD digits are used. The proposed optical circuits will be very helpful in developing hardware modules for optical digital computing processors.     

ReALE: A reconnection-based arbitrary-Lagrangian–Eulerian method

We present a new reconnection-based arbitrary-Lagrangian–Eulerian (ALE) method. The main elements in a standard ALE simulation are an explicit Lagrangian phase in which the solution and grid are updated, a rezoning phase in which a new grid is defined, and a remapping phase in which the Lagrangian solution is transferred (conservatively interpolated) onto the new grid. In standard ALE methods the new mesh from the rezone phase is obtained by moving grid nodes without changing connectivity of the mesh. Such rezone strategy has its limitation due to the fixed topology of the mesh. In our new method we allow connectivity of the mesh to change in rezone phase, which leads to general polygonal mesh and allows to follow Lagrangian features of the mesh much better than for standard ALE methods. Rezone strategy with reconnection is based on using Voronoi tessellation. We demonstrate performance of our new method on series of numerical examples and show it superiority in comparison with standard ALE methods without reconnection.     

A two-dimensional unstructured cell-centered multi-material ALE scheme using VOF interface reconstruction

We present a new cell-centered multi-material arbitrary Lagrangian–Eulerian (ALE) scheme to solve the compressible gas dynamics equations on two-dimensional unstructured grid. Our ALE method is of the explicit time-marching Lagrange plus remap type. Namely, it involves the following three phases: a Lagrangian phase wherein the flow is advanced using a cell-centered scheme; a rezone phase in which the nodes of the computational grid are moved to more optimal positions; a cell-centered remap phase which consists of interpolating conservatively the Lagrangian solution onto the rezoned grid. The multi-material modeling utilizes either concentration equations for miscible fluids or the Volume Of Fluid (VOF) capability with interface reconstruction for immiscible fluids. The main original feature of this ALE scheme lies in the introduction of a new mesh relaxation procedure which keeps the rezoned grid as close as possible to the Lagrangian one. In this formalism, the rezoned grid is defined as a convex combination between the Lagrangian grid and the grid resulting from condition number smoothing. This convex combination is constructed through the use of a scalar parameter which is a scalar function of the invariants of the Cauchy–Green tensor over the Lagrangian phase. Regarding the cell-centered remap phase, we employ two classical methods based on a partition of the rezoned cell in terms of its overlap with the Lagrangian cells. The first one is a simplified swept face-based method whereas the second one is a cell-intersection-based method. Our multi-material ALE methodology is assessed through several demanding two-dimensional tests. The corresponding numerical results provide a clear evidence of the robustness and the accuracy of this new scheme.     

A hybrid variational front tracking-level set mesh generator for problems exhibiting large deformations and topological changes

We present a method for generating 2-D unstructured triangular meshes that undergo large deformations and topological changes in an automatic way. We employ a method for detecting when topological changes are imminent via distance functions and shape skeletons. When a change occurs, we use a level set method to guide the change of topology of the domain mesh. This is followed by an optimization procedure, using a variational formulation of active contours, that seeks to improve boundary mesh conformity to the zero level contour of the level set function. Our method is advantageous for Arbitrary-Lagrangian–Eulerian (ALE) type methods and directly allows for using a variational formulation of the physics being modeled and simulated, including the ability to account for important geometric information in the model (such as for surface tension driven flow). Furthermore, the meshing procedure is not required at every time-step and the level set update is only needed during a topological change. Hence, our method does not significantly affect computational cost.     

A Survey of One-Dimensional Random Polymers

In the last decade there has been an enormous progress in the mathematical understanding of one-dimensional polymer measures, which are path measures that suppress self-intersections. We are currently in the situation that many interesting questions have either been answered, or that essential new ideas are needed. In this survey paper, we discuss the most relevant results, open questions, and heuristics.     

Physics at the closed shells

Radioactive beams obtained via fragmentation of the projectile on a primary target have shown to be a powerful tool to produce exotic nuclei and some typical results obtained at GANIL in this area will be shown. To go further, and in particular, to get beams of exotic nuclei, new facilities have been developed recently. The physics expected from the use of these radioactive ion beam facilities is extremely ambitious as stated in the scientific motivations justifying their construction. At GANIL the SPIRAL facility is ready and will hopefully deliver the first radioactive beams in 2001. New experimental devices have been developed to fully exploit the potentiality expected from SPIRAL. EXOGAM is a new, efficient and powerful gamma ray spectrometer currently under installation at GANIL. The design and the performances expected from this array will be discussed.     

神奇有趣的五夸克态

对今年国际上有关五夸克态的实验与理论研究现状作一个总体的评述 ,指出了有待解决的主要问题和相关的一些背景知识 ,并简单介绍了作者所在研究小组的有关研究工作 .     

The refined theory of deep rectangular beams for symmetrical deformation

Based on elasticity theory, various one-dimensional equations for symmetrical deformation have been deduced systematically and directly from the two-dimensional theory of deep rectangular beams by using the Papkovich-Neuber solution and the Lur’e method without ad hoc assumptions, and they construct the refined theory of beams for symmetrical deformation. It is shown that the displacements and stresses of the beam can be represented by the transverse normal strain and displacement of the mid-plane. In the case of homogeneous boundary conditions, the exact solutions for the beam are derived, and the exact equations consist of two governing differential equations: the second-order equation and the transcendental equation. In the case of non-homogeneous boundary conditions, the approximate governing differential equations and solutions for the beam under normal loadings only and shear loadings only are derived directly from the refined beam theory, respectively, and the correctness of the stress assumptions in classic extension or compression problems is revised. Meanwhile, as an example, explicit expressions of analytical solutions are obtained for beams subjected to an exponentially distributed load along the length of beams. Supported by the National Natural Science Foundation of China (Grant Nos. 10702077, 10672001, and 10602001), the Beijing Natural Science Foundation (Grant No. 1083012), and the Alexander von Humboldt Foundation in Germany     

Excited baryons and heavy pentaquarks in large- N<Subscript>c</Subscript> QCD

We briefly discuss the large-N_c picture for excited baryons, present a new method for the calculation of matrix elements and illustrate it by computing the strong decays of heavy exotic states.     

Thermodynamic studies on the interactions of diglycine with magnesium chloride in aqueous medium at different temperatures

Apparent molar heat capacities (C_P2,?), apparent molar volumes (V_2,?), and viscosities (η) of diglycine in water and in aqueous magnesium chloride (MgCl₂) solutions of molality m_S ≈ (0.05 to 0.70) mol · kg⁻¹ over the temperature range T = (288.15 to 328.15) K have been determined using high sensitivity micro-differential scanning calorimeter, vibrating-tube digital density meter, and automatic viscosity measuring unit (AVS 350), respectively. The data have been used to calculate the partial molar heat capacities and partial molar volumes at infinite dilution. The viscosity B-coefficients have also been obtained from viscosity data using Jones-Dole equation. The and values of diglycine in aqueous MgCl₂ solutions are higher than those in water and thus exhibit positive transfer functions ( and ), which are indicative of strong interactions between diglycine and MgCl₂. Corresponding viscosity B-coefficients of transfer are also generally positive. The transfer functions decrease with increase in temperature and increase with the concentration of MgCl₂. The free energies, enthalpies and entropies of activation for viscous flow of diglycine in aqueous MgCl₂ solutions have been obtained by using the Feakins transition-state theory. Partial molar expansibilities and at infinite dilution along with their temperature dependence, the interaction coefficients from the volume, heat capacity, and viscosity B-coefficients have been used to divulge the various kinds of plausible interactions between solute (diglycine) and cosolute (MgCl₂) in solutions.