The European Physical Journal Special Topics

We recently proposed in a Letter [Phys. Rev. Lett. 108, 255303] a novel scheme to detect topological edge states in an optical lattice, based on a generalization of Bragg spectroscopy. The scope of the present article is to provide a more detailed and pedagogical description of the system – the Hofstadter optical lattice – and probing method. We first show the existence of topological edge states, in an ultra-cold gas trapped in a 2D optical lattice and subjected to a synthetic magnetic field. The remarkable robustness of the edge states is verified for a variety of external confining potentials. Then, we describe a specific laser probe, made from two lasers in Laguerre-Gaussian modes, which captures unambiguous signatures of these edge states. In particular, the resulting Bragg spectra provide the dispersion relation of the edge states, establishing their chiral nature. In order to make the Bragg signal experimentally detectable, we introduce a “shelving method”, which simultaneously transfers angular momentum and changes the internal atomic state. This scheme allows to directly visualize the selected edge states on a dark background, offering an instructive view on topological insulating phases, not accessible in solid-state experiments.

The thermal shock problem in a strip made of functionally graded composite with an interpenetrating network micro-structure of Al2O3 and Al is analysed numerically. The material considered here could be used in brake disks or cylinder liners. In both applications it is subjected to thermal shock. The description of the position-dependent properties of the considered functionally graded material are based on experimental data. Continuous functions were constructed for the Young’s modulus, thermal expansion coefficient, thermal conductivity and thermal diffusivity and implemented as user-defined material properties in user-defined subroutines of the commercial finite element software ABAQUS™. The thermal stress and the residual stress of the manufacturing process distributions inside the strip are considered. The solution of the transient heat conduction problem for thermal shock is used for crack propagation simulation using the XFEM method. The crack length developed during the thermal shock is the criterion for crack resistance of the different graduation profiles as a step towards optimization of the composition gradient with respect to thermal shock sensitivity.

We give an introduction to the application of small angle X-ray and neutron scattering techniques to the study of the structure of polyelectrolyte solutions. The goal is not to be exhaustive and to describe the latest progress in the field of polyelectrolytes but rather to present the potential of the technique. We aim to give an overview on the main features of the scattering curves, and discuss the structural information that can be drawn. We will first give the basics of small angle scattering and highlight the role played by neutron scattering and isotopic labeling. Thus, we will discuss the significance of the monomer and counterion partial scattering functions according to the scattering length densities of both components, and will emphasize the unique possibility to separate out the intra- and intermolecular correlations. Then, some examples will show how the dispersion state and the average conformation of macroions can be addressed. We will however focus on salt-free aqueous solutions of linear flexible hydrophilic polyelectrolytes in the semidilute regime.

We investigate a system of coupled oscillators on the circle, which arises from a simple model for behavior of large numbers of autonomous vehicles where the acceleration of each vehicle depends on the relative positions and velocities between itself and a set of local neighbors. After describing necessary and sufficient conditions for asymptotic stability, we derive expressions for the phase velocity of propagation of disturbances in velocity through this system. We show that the high frequencies exhibit damping, which implies existence of well-defined signal velocities c + > 0 and c − < 0 such that low frequency disturbances travel through the flock as f +(x − c + t) in the direction of increasing agent numbers and f −(x − c − t) in the other.

The Sivers and Collins asymmetries are the most prominent Single Spin Asymmetries (SSA) in Semi-Inclusive Deeply Inelastic Scattering (SIDIS) with transverse target polarization. In this talk we present our understanding of these phenomena.

Modelling the variability of wind speed and direction is very useful for estimating the wind potential of a typical site. In this article, we present the results of a study on the wind regimes and the wind potential in Constantine. This work is based on hourly and daily meteorological observations of Constantine Airport Station for the period 2000–2015. The average annual wind speed at 10 m varied between 3.4 to 3.9 m/s and the potential of the wind ressource, estimated by Weibull’s law, varied from 53.5 to 71 W/m2. The seasonal variation of wind speed and wind intensity studied in this work is useful to know the wind behaviour and we can exploit it in the optimal selection of wind turbine generator suitable for this region.

In recent years, one of the most promising new actuator technologies is based on the use of Shape Memory Alloys (SMA). The main challenge for the application of devices that use these materials is the hysteresis in the phase transition they suffer during actuation. Finite element analysis (FEA) is an important aid in the simulation of mechanical properties and thermal fields in actuators. Dynamic simulations give in many cases enough information without the necessity of building a prototype. We have used ABAQUS to simulate a Nitinol wire used in a micropositioning actuator. The model parameters, not given by the supplier but required by the FEA program, have been obtained by thermal and mechanical characterization of the material used. The output force is computed and compared with the measurements.

In this paper we discuss the relationship between permutation entropy and Kolmogorov-Sinai entropy in the one-dimensional case. For this, we consider partitions of the state space of a dynamical system using ordinal patterns of order (d + n− 1) on the one hand, and using n-letter words of ordinal patterns of order d on the other hand. The answer to the question of how different these partitions are provides an approach to comparing the entropies.

Các trạng thái định dạng không gian tĩnh cuáa hai hình thức đối lưu quay và đối lưu từ hiện diện. Trong hệ đối lưu hai chiều với điều kiện biên không bị giới hạn, sự hình thành các trạng thái này là kết quả của sự tương tác giữa đối lưu và một chế độ quy mô lớn: vận tốc zonal trong đối lưu quay và tiềm năng từ trường trong đối lưu từ. Chúng tôi phát triển một lý thuyết bậc cao hơn, phương trình Ginzburg-Landau bậc năm không địa phương để mô tả các ảnh hưởng của sự điều biến không gian gần một điểm có kích thước hai. Hai kịch bản phân nhánh khác nhau được xác định. Kết quả của chúng tôi làm sáng tỏ các nghiên cứu số về các hệ thống đối lưu hai chiều với điều kiện biên không bị giới hạn. Bài báo này được dành tặng cho Giáo sư Helmut Brand nhân dịp sinh nhật lần thứ 60 của ông.

We propose a mean-field free energy approach to simulate multi- component fluids. The model has been validated in terms of the Laplace equation of capillarity and dispersion relation of interfacial waves. Simulations of a ternary system shows that the total free energy decreases and reaches a minimum after phase separation has occurred. Different drop shapes can be obtained by adjusting the interaction strengths between individual components. These results demonstrate that both macroscopic free energy and microscopic fluid-fluid interactions have been well described in our multicomponent model.