Generation of nonground-state condensates and adiabatic paradox

The problem of resonant generation of nonground-state condensates is addressed aiming at resolving the seeming paradox that arises when one resorts to the adiabatic representation. In this picture, the eigenvalues and eigenfunctions of a time-dependent Gross-Pitaevskii Hamiltonian are also functions of time. Since the level energies vary in time, no definite transition frequency can be introduced. Hence no external modulation with a fixed frequency can be made resonant. Thus, the resonant generation of adiabatic coherent modes is impossible. However, this paradox occurs only in the frame of the adiabatic picture. It is shown that no paradox exists in the properly formulated diabatic representation. The resonant generation of diabatic coherent modes is a well defined phenomenon. As an example, the equations are derived, describing the generation of diabatic coherent modes by the combined resonant modulation of the trapping potential and atomic scattering length.

Optimal beam forming for laser beam propagation through random media

Focusing optical beams on a target through random propagation media is very important in many applications such as free space optical communica- tions and laser weapons. Random media effects such as beam spread and scintillation can degrade the optical system's performance severely. Compensation schemes are needed in these applications to overcome these random media effcts. In this research, we investigated the optimal beams for two different optimization criteria: one is to maximize the concentrated received intensity and the other is to minimize the scintillation index at the target plane. In the study of the optimal beam to maximize the weighted integrated intensity, we derive a similarity relationship between pupil-plane phase screen and extended Huygens-Fresnel model, and demonstrate the limited utility of maximizing the average integrated intensity. In the study ofthe optimal beam to minimize the scintillation index, we derive the first- and second-order moments for the integrated intensity of multiple coherent modes. Hermite-Gaussian and Laguerre-Gaussian modes are used as the coherent modes to synthesize an optimal partially coherent beam. The optimal beams demonstrate evident reduction of scintillation index, and prove to be insensitive to the aperture averaging effect.

Coherent analysis of quantum optical sideband modes

We demonstrate a device that allows for the coherent analysis of a pair of optical frequency sidebands in an arbitrary basis. We show that our device is quantum noise limited, and hence applications for this scheme may be found in discrete and continuous variable optical quantum information experiments. (c) 2005 Optical Society of America.

Entangled coherent-state qubits in an ion trap

We show how entangled qubits can be encoded as entangled coherent states of two-dimensional center-of-mass vibrational motion for two ions in an ion trap. The entangled qubit state is equivalent to the canonical Bell state, and we introduce a proposal for entanglement transfer from the two vibrational modes to the electronic states of the two ions in order for the Bell state to be detected by resonance fluorescence shelving methods.

Les modes de conceptualisation métaphorique en neuroanatomie : étude de la description anatomique du cervelet et de la moelle spinale

La présente étude s’inscrit dans une lignée de travaux de recherche en traductologie réalisés dans un cadre de sémantique cognitive et visant à dégager les modes de conceptualisation métaphorique dans les domaines de spécialité, et plus précisément dans les sciences biomédicales. Notre étude se concentre sur les modes de conceptualisation métaphorique utilisés en neuroanatomie en français, en anglais et en allemand, dans une perspective d’application à la traduction. Nous nous penchons plus spécifiquement sur la description anatomique de deux structures du système nerveux central : la moelle spinale et le cervelet. Notre objectif est de repérer et de caractériser les indices de conceptualisation métaphorique (ICM). Notre méthode s'appuie sur un corpus trilingue de textes de référence traitant de ces structures et fait appel à une annotation sémantique en langage XML, ce qui autorise une interrogation des corpus annotés au moyen du langage XQuery. Nous mettons en évidence que les ICM jouent un rôle prédominant dans la phraséologie et les dénominations propres à la description anatomique du système nerveux, comme c'est le cas en biologie cellulaire et en anatomie des muscles, des nerfs périphériques et des vaisseaux sanguins. Sous l’angle lexical, il faut distinguer les ICM prédicatifs, les ICM non prédicatifs ainsi que les ICM quasi prédicatifs. La plupart des modes de conceptualisation métaphorique préalablement repérés en biologie cellulaire et en anatomie sont également présents dans le domaine plus spécifique de la neuroanatomie. Certains ICM et modes de conceptualisation sont toutefois spécifiques à des éléments des régions étudiées. Par ailleurs, les modes de conceptualisation métaphorique en français, en anglais et en allemand sont semblables, mais sont exprimés par des réseaux lexicaux d'ICM dont la richesse varie. De plus, la composition nominale étant une des caractéristiques de l'allemand, la forme linguistique des ICM présente des caractéristiques spécifiques. Nos résultats mettent en évidence la richesse métaphorique de la neuroanatomie. Cohérents avec les résultats des études antérieures, ils enrichissent cependant la typologie des ICM et soulignent la complexité, sur les plans lexical et cognitif, de la métaphore conceptuelle.

Measurement of propagation constant in waveguides with wideband coherent terahertz spectroscopy

A quasi-optical technique for characterizing micromachined waveguides is demonstrated with wideband time-resolved terahertz spectroscopy. A transfer-function representation is adopted for the description of the relation between the signals in the input and output port of the waveguides. The time-domain responses were discretized, and the waveguide transfer function was obtained through a parametric approach in the z domain after describing the system with an autoregressive with exogenous input model. The a priori assumption of the number of modes propagating in the structure was inferred from comparisons of the theoretical with the measured characteristic impedance as well as with parsimony arguments. Measurements for a precision WR-8 waveguide-adjustable short as well as for G-band reduced-height micromachined waveguides are presented. (C) 2003 Optical Society of America.

Cosmological perturbations in coherent oscillating scalar field models

The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V(ϕ) = λ|ϕ|^n /n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c_eff^ 2  = ω = (n − 2)/(n + 2) with ω the effective equation of state. We also obtain the first order correction in k^ 2/ω_eff^ 2 , when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω_eff. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet’s theorem.

Representational modes of thinking employed by children aged thirteen and fourteen, and their relationship to performance in standardised tests of ability, measures of creativity and personality

This thesis proposes that despite many experimental studies of thinking, and the development of models of thinking, such as Bruner's (1966) enactive, iconic and symbolic developmental modes, the imagery and inner verbal strategies used by children need further investigation to establish a coherent, theoretical basis from which to create experimental curricula for direct improvement of those strategies. Five hundred and twenty-three first, second and third year comprehensive school children were tested on 'recall' imagery, using a modified Betts Imagery Test; and a test of dual-coding processes (Paivio, 1971, p.179), by the P/W Visual/Verbal Questionnaire, measuring 'applied imagery' and inner verbalising. Three lines of investigation were pursued: 1. An investigation a. of hypothetical representational strategy differences between boys and girls; and b. the extent to which strategies change with increasing age. 2. The second and third year children's use of representational processes, were taken separately and compared with performance measures of perception, field independence, creativity, self-sufficiency and self-concept. 3. The second and third year children were categorised into four dual-coding strategy groups: a. High Visual/High Verbal b. Low Visual/High Verbal c. High Visual/Low Verbal d. Low Visual/Low Verbal These groups were compared on the same performance measures. The main result indicates that: 1. A hierarchy of dual-coding strategy use can be identified that is significantly related (.01, Binomial Test) to success or failure in the performance measures: the High Visual/High Verbal group registering the highest scores, the Low Visual/High Verbal and High Visual/Low Verbal groups registering intermediate scores, and the Low Visual/Low Verbal group registering the lowest scores on the performance measures. Subsidiary results indicate that: 2. Boys' use of visual strategies declines, and of verbal strategies increases, with age; girls' recall imagery strategy increases with age. Educational implications from the main result are discussed, the establishment of experimental curricula proposed, and further research suggested.

Statistical properties of partially coherent CW fiber lasers

A detailed quantitative numerical analysis of partially coherent quasi-CW fiber laser is performed on the example of high-Q cavity Raman fiber laser. The key role of precise spectral performances of fiber Bragg gratings forming the laser cavity is clarified. It is shown that cross phase modulation between the pump and Stokes waves does not affect the generation. Amplitudes of different longitudinal modes strongly fluctuate obeying the Gaussian distribution. As intensity statistics is noticeably non-exponential, longitudinal modes should be correlated. © 2011 SPIE.

Different coordination modes for disulfoxides towards diorganotin(IV) dichlorides. X-ray crystal structures of 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) and adducts [{Ph2SnCl2(meso-bpse)}n] and [{n-Bu2SnCl2(pdtd)}2]

The reactions of meso-1,2-bis(phenylsulfinyl)ethane (meso-bpse) with Ph2SnCl2, 2-phenyl-1,3-dithiane trans-1-trans-3-dioxide (pdtd) with n-Bu2SnCl2 and 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) with Ph2SnCl2, in 1:1 molar ratio, yielded [{Ph2SnCl2(meso-bpse)}n], [{n-Bu2SnCl2(pdtd)}2] and [{Ph2SnCl2(rac,cis-cbpse)}x] (x = 2 or n), respectively. All adducts were studied by IR, Mössbauer and 119Sn NMR spectroscopic methods, elemental analysis and single crystal X-ray diffractometry. The X-ray crystal structure of [{Ph2SnCl2(meso-bpse)}n] revealed the occurrence of infinite chains in which the tin(IV) atoms appear in a distorted octahedral geometry with Cl atoms in cis and Ph groups in trans positions. The X-ray crystal structure of [{n-Bu2SnCl2(pdtd)}2] revealed discrete centrosymmetric dimeric species in which the tin(IV) atoms possess a distorted octahedral geometry with bridging disulfoxides in cis and n-butyl moieties in trans positions. The spectroscopic data indicated that the adduct containing the rac,cis-cbpse ligand can be dimeric or polymeric. The X-ray structural analysis of the free rac-,cis-cbpse sulfoxide revealed that the crystals belong to the C2/c space group.

Quasinormal modes of black holes in anti-de Sitter space: A numerical study of the eikonal limit

Using series solutions and time-domain evolutions, we probe the eikonal limit of the gravitational and scalar-field quasinormal modes of large black holes and black branes in anti-de Sitter backgrounds. These results are particularly relevant for the AdS/CFT correspondence, since the eikonal regime is characterized by the existence of long-lived modes which (presumably) dominate the decay time scale of the perturbations. We confirm all the main qualitative features of these slowly damped modes as predicted by Festuccia and Liu [G. Festuccia and H. Liu, arXiv:0811.1033.] for the scalar-field (tensor-type gravitational) fluctuations. However, quantitatively we find dimensional-dependent correction factors. We also investigate the dependence of the quasinormal mode frequencies on the horizon radius of the black hole (brane) and the angular momentum (wave number) of vector- and scalar-type gravitational perturbations.

Brittle and ductile removal modes observed during diamond turning of carbon nanotube composites

Ultraprecision diamond turning was used to evaluate the surface integrity of a carbon nanotube (CNT) composite as a function of the cutting conditions and the percentage of CNT in the epoxy matrix. The effects of cutting conditions on the chip morphology and surface roughness were analysed. The results showed that an increase in the percentage of CNT may influence the mechanism of material removal and consequently improve the quality of the machined surface. When smaller quantities of CNT (0.02 and 0.07 wt %) are present in the matrix, microcracks form within the cutting grooves (perpendicular to the cutting direction). This indicates that the amount of CNT on the epoxy matrix may have a direct influence on the mechanical properties of these materials. Chips removed from the CNT composite samples were analysed by scanning electron microscopy in order to correlate the material removal mechanism and the surface generation process. The area average surface roughness Sa was influenced by the material removal mechanism (Sa ranging from 0.28 to 1.1 mu m).

Kinetic ion effect on geodesic acoustic Alfven modes in tokamaks

Using a quasitoroidal set of coordinates with coaxial circular magnetic surfaces, the Vlasov equation is solved for collisionless plasmas, and the dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account q-profile and charge separation parallel electric field, it is found that the Alfven wave continuum is deformed by ion geodesic effects producing continuum minimum at the rational magnetic surfaces. Low frequency geodesic ion induced Alfven waves are found below the continuum minimum where collisionless damping has a gap for Maxwell distribution. In kinetic approach, the ion thermal motion defines the geodesic effect but the mode frequency is strongly corrected due to parallel motion of electrons.

Localized modes of binary mixtures of Bose-Einstein condensates in nonlinear optical lattices

The properties of the localized states of a two-component Bose-Einstein condensate confined in a nonlinear periodic potential (nonlinear optical lattice) are investigated. We discuss the existence of different types of solitons and study their stability by means of analytical and numerical approaches. The symmetry properties of the localized states with respect to nonlinear optical lattices are also investigated. We show that nonlinear optical lattices allow the existence of bright soliton modes with equal symmetry in both components and bright localized modes of mixed symmetry type, as well as dark-bright bound states and bright modes on periodic backgrounds. In spite of the quasi-one-dimensional nature of the problem, the fundamental symmetric localized modes undergo a delocalizing transition when the strength of the nonlinear optical lattice is varied. This transition is associated with the existence of an unstable solution, which exhibits a shrinking (decaying) behavior for slightly overcritical (undercritical) variations in the number of atoms.