Experimental analysis of floc size distributions in a 1-L jar under different hydrodynamics and physicochemical conditions

This study focuses on the relation among hydrodynamics, physicochemical conditions, and floc size. During ortho-kinetic flocculation, the floc size is controlled by a balance between hydrodynamic stress and aggregate strength. Special attention was paid to the influence of a hydrodynamic sequencing on both the aggregate strength and the flocculation processes. Experimental research was conducted in a 1-L jar for two different pH values. The hydrodynamic sequencing was made up of successive slow and rapid mixing periods, and different slow mixing intensities were studied. First, the large floc size was shown to decrease with increasing velocity gradient (G), with an expected trend (d proportional variant epsilon(-1/4)). Then, the aggregate strength was shown to depend on two main factors: the flocculation history and the physicochemical conditions, which control the cohesion forces between primary particles. Finally, flocculation processes are discussed in terms of aggregation and breakup phenomena, with relation to local hydrodynamics and physicochemical conditions.     

Anderson localization of expanding Bose-Einstein condensates in random potentials

We show that the expansion of an initially confined interacting 1D Bose-Einstein condensate can exhibit Anderson localization in a weak random potential with correlation length sigma(R). For speckle potentials the Fourier transform of the correlation function vanishes for momenta k>2/sigma(R) so that the Lyapunov exponent vanishes in the Born approximation for k>1/sigma(R). Then, for the initial healing length of the condensate xi(in)>sigma(R) the localization is exponential, and for xi(in)相似文献   

Quantum mechanics for space applications

This paper is an introduction to the following articles in the scope of quantum mechanics for space study initiated by ESA and lead by ONERA. The context of quantum mechanics for space is summarised, and the fields under development are briefly introduced. Technological applications of quantum mechanics in space are explored and some tests of quantum mechanics are outlined. We also give a brief presentation of the opto-electronic section of the European Space Agency, and the technology development activities it carries out, with particular emphasis on those activities related to the topics of interest of the quantum mechanics in space workshop. As an example, a summary of two ESA studies on gravity gradiometry and their relevance to the field of atomic interferometry is given. In view of the scientific requirements, derived for both Earth observation and planetology for future space missions, atom interferometry shows promise and may provide an advantage over currently available accelerometer and inertial sensor systems. PACS 04.25.Nx; 04.80.Cc; 07.60.Ly; 95.30.Sf     

Dual-wavelength laser source for onboard atom interferometry

We present a compact and stable dual-wavelength laser source for onboard atom interferometry with two different atomic species. It is based on frequency-doubled telecom lasers locked on a femtosecond optical frequency comb. We take advantage of the maturity of fiber telecom technology to reduce the number of free-space optical components, which are intrinsically less stable, and to make the setup immune to vibrations and thermal fluctuations. The source provides the frequency agility and phase stability required for atom interferometry and can easily be adapted to other cold atom experiments. We have shown its robustness by achieving the first dual-species K-Rb magneto-optical trap in microgravity during parabolic flights.     

Matter-wave cavity gravimeter

We propose a gravimeter based on a matter-wave resonant cavity loaded with a Bose–Einstein condensate and closed with a sequence of periodic Raman pulses. The gravimeter sensitivity increases quickly with the number of cycles experienced by the condensate inside the cavity. The matter wave is refocused thanks to a spherical wave-front of the Raman pulses. This provides a transverse confinement of the condensate which is discussed in terms of a stability analysis. We develop the analogy of this device with a resonator in momentum space for matter waves. PACS 06.30.Gv; 06.30.Ft; 03.75.-b; 03.75.Dg; 32.80.Lg; 32.80.-t; 32.80.Pj     

Coherent matter wave inertial sensors for precision measurements in space

We analyze the advantages of using ultra-cold coherent sources of atoms for matter-wave interferometry in space. We present a proof-of-principle experiment that is based on an analysis of results previously published, from which we extract the ratio h/m for ⁸⁷Rb. This measurement shows that a limitation in accuracy arises due to atomic interactions within the Bose–Einstein condensate. Finally, we discuss the promising role of coherent-matter-wave sensors, in particular inertial sensors, in future fundamental physics missions in space. PACS 03.75.-b; 32.80.Pj     

Density functional calculations for predicting structures and vibrational frequencies of aluminum chloride-fluoride complexes

Quantum chemical calculations are used to study AlCl_y−xF_x^3−y (y = 5 or 6, x = 0,…,y) species that can occur in aluminum electrorefining melts. These theoretical studies are included in a wider research program concerning the chemical instabilities in the bulk of molten salts during the refinement process. Stabilization energies, equilibrium geometries and vibrational frequencies of the complexes are calculated using the Delley functional methodology described in Ref. [1] (B. Delley, J. Chem. Phys., 92 (1990) 508). These computational simulations, discussed and compared with the experimental results demonstrate that density functional calculations can be reliably used in the study of complexes existing in molten salts. Quantum chemical calculations are accurate tools for theoretically predicting structures, physical and chemical properties and vibrational frequencies of known entities as well as unknown compounds.     

Geometrical and spectroscopical characterizations of some complex entities of aluminum(III) with fluoride ions by LDF-based calculations

The structure of cryolite is investigated with a theoretical approach based on LDF calculations. In fact, experimental techniques for structural studies are difficult to perform in cryolite melts because of hard experimental conditions (high temperature, corrosiveness, etc.). Use of the DMol software allows us to determine the stabilities and the vibrational frequencies of AlF, AlF, and AlF isolated complexes. The results obtained compared with published experimental works confirm that AlF should be considered in the dissociation scheme of cryolite as previously evidenced by other authors. © 1994 John Wiley & Sons, Inc.     

Weighted o-minimal hybrid systems

We consider weighted o-minimal hybrid systems, which extend classical o-minimal hybrid systems with cost functions. These cost functions are “observer variables” which increase while the system evolves but do not constrain the behaviour of the system. In this paper, we prove two main results: (i) optimal o-minimal hybrid games are decidable; (ii) the model-checking of WCTL, an extension of CTL which can constrain the cost variables, is decidable over that model. This has to be compared with the same problems in the framework of timed automata where both problems are undecidable in general, while they are decidable for the restricted class of one-clock timed automata.