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We present several time dependent analytical solutions for the incompressible Euler system with free surface. These analytical solutions give quantitative descriptions of some physical phenomena and can be used as reference solutions when validating numerical simulation codes. They concern fluid flows governed by Euler equations with or withouthydrostatic hypothesis including wet/dry interface, variable density, wide variety of boundary conditions and possibly non-uniform bottom topographies. Some of these analytical solutions concern shallow water type models or free surface Navier-Stokes model i.e. with a viscous fluid.

We show that a strained wire of a Weyl semimetal supports a new type of gapless excitation, the chiral sound wave (CSW). It is a longitudinal charge density wave analog to the chiral magnetic wave predicted in the quark-gluon plasma but driven by an elastic axial pseudo-magnetic field. It involves the axial-axial-axial contribution to the chiral anomaly which couples the chiral charge density to the elastic axial gauge field. The chiral sound is unidirectional: it propagates along the elastic magnetic field and not in the opposite direction. The CSW may propagate for long distances as it does not couple directly to quickly dissipating electromagnetic plasmons, while its damping is controlled by the slow chirality flip rate. We propose an experimental setup to directly detect the chiral sound, which is excited by mechanical vibrations of the crystal lattice in the GHz frequency range. Our findings contribute to a new trend, the chiral acoustics, in strained Weyl semimetals., Comment: 5 pages, 3 figures; v2: minor changes, published version

In the paper the features of energy transformation processes in activated with erbium ions laser materials were discussed based on optical transitions in 4f shell of Er3+ ion. Methods of excitation of the luminescence inchalcogenide glasses doped with Er3+ ions were described and found how its intensity depends on concentrationof the ions. Up-conversion and cross-relaxation play an important role in the transformation of excitations in erbium doped materials. In cross-relaxation the energy of one center can be nonradiatively transferred to another centeror divided between the two centers, while in the up-conversion, however, energy of several centers summed up inone center, bringing it acts as an additional channel of luminescence quenching, or as a way of pumping of thehigher energy levels.To improve the efficiency of optical excitation of many laser materials doped with erbium ions thesensitization with ytterbium ions that have intense absorption band in the range of ~(0.9-1)μm with "effective"width of about 1000 cm-1 as well a channel of the efficient nonradiative excitation energy transfer to Er3+ ions iswidely used. Scheme of energy transfer from Yb3+ ion to Er3+ ion was discussed and necessary conditions foreffective settlement of the upper laser level 4I13/2 of Er3+ ions in the ytterbium-erbium laser medium wereclarified.Keywords: lasermaterials, rareearthelements, up-conversion, cross-relaxation., В статті проведений аналіз різних літературних джерел, в яких описані основні процеси трансформації енергії в активованих йонами Er3+ лазерних матеріалах. Встановлено, що в основі цих процесів лежать ап-конверсійні та крос-релаксаційні переходи, які дають можливість реалізувати генерацію в ербієвих лазерах. Ефективним сенсибілізатором для йонів ербію є йони ітербію, які за рахунок безвипромінювального перенесення збудження ефективно передеють енергію йонам Er3+.

International audience; In this work, we propose to study and design a coil used to magnetize, by means of a Pulsed Field Magnetization (PFM) process, an inductor of a radial flux superconducting machine with one pair of poles. Each pole contains four similar HTS bulks of 30 mm diameter arranged in a square pattern. The cryostat already exists for this application and the temperature of the HTS bulks can vary from 4.2 K to their critical temperature, in transient state. For a given primary source of energy, here a capacitor bank of 10 kJ (5 mF, 2 kV) is available, the PFM process depends strongly on the value of the coil inductance used to generate pulsed field, because it defines the waveform of the current: peak value and time constant. Thus, 3D modeling of the coil is required in order to be sure that its inductance and the magnetic field produced will provide a full magnetization of HTS bulks. From the practical point of view, we would like to achieve an average magnetization of each pole around 3 T. In this paper, numerical modeling of coils with different number of turns coupled with circuit's equations is achieved. The maximum magnetic field obtained on the HTS bulks and estimated magnetization at the top center of each HTS bulk, are presented and discussed.

The electronic structure of recently synthesized square superlattices with atomic coherence composed of PbSe, CdSe, or CdTe nanocrystals (NCs) attached along {100} facets is investigated using tight-binding calculations. In experimental realizations of these systems [W. H. Evers et al., Nano Lett. 13, 2317 (2013)], NC facets are atomically bonded, resulting in single-crystalline sheets, which, due to their nanogeometry, have an effective dimensionality below two. We predict electronic structures composed of successive bands formed by strong coupling between the wave functions of nearest-neighbor NCs. This coupling is mainly determined by the number of atoms at the NC bonding plane. The band structures deviate markedly from that of the corresponding two-dimensional (2D) quantum well; the 2D case can be recovered, however, if the effects of the nanogeometry are gradually reduced. The width of the bands can reach hundreds of meV, ascribing highly promising transport properties to square superlattices. The band edges are located at k=0 except for PbSe superlattices, where their position in k space surprisingly depends on the parity of the number of {100} atomic planes in the NCs. Our calculations demonstrate that semiconductors with dimensionality below two have a strong potential for (opto-)electronic, photovoltaic, and spintronic applications.

International audience; The concept of nonlinear modes is applied in order to analyze the behavior of a model of woodwind reed instruments. Using a modal expansion of the impedance of the instrument, and by projecting the equation for the acoustic pressure on the normal modes of the air column, a system of second order ordinary differential equations is obtained. The equations are coupled through the nonlinear relation describing the volume flow of air through the reed channel in response to the pressure difference across the reed. The system is treated using an amplitude-phase formulation for nonlinear modes, where the frequency and damping functions, as well as the invariant manifolds in the phase space, are unknowns to be determined. The formulation gives, without explicit integration of the underlying ordinary differential equation, access to the transient, the limit cycle, its period and stability. The process is illustrated for a model reduced to three normal modes of the air column.