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See detailPhase referencing in optical interferometry
Filho, Mercedes E; Garcia, Paulo; Duvert, Gilles et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

One of the aims of next generation optical interferometric instrumentation is to be able to make use of information contained in the visibility phase to construct high dynamic range images. Radio and ... [more ▼]

One of the aims of next generation optical interferometric instrumentation is to be able to make use of information contained in the visibility phase to construct high dynamic range images. Radio and optical interferometry are at the two extremes of phase corruption by the atmosphere. While in radio it is possible to obtain calibrated phases for the science objects, in the optical this is currently not possible. Instead, optical interferometry has relied on closure phase techniques to produce images. Such techniques allow only to achieve modest dynamic ranges. However, with high contrast objects, for faint targets or when structure detail is needed, phase referencing techniques as used in radio interferometry, should theoretically achieve higher dynamic ranges for the same number of telescopes. Our approach is not to provide evidence either for or against the hypothesis that phase referenced imaging gives better dynamic range than closure phase imaging. Instead we wish to explore the potential of this technique for future optical interferometry and also because image reconstruction in the optical using phase referencing techniques has only been performed with limited success. We have generated simulated, noisy, complex visibility data, analogous to the signal produced in radio interferometers, using the VLTI as a template. We proceeded with image reconstruction using the radio image reconstruction algorithms contained in aips imagr (clean algorithm). Our results show that image reconstruction is successful in most of our science cases, yielding images with a 4 milliarcsecond resolution in K band. We have also investigated the number of target candidates for optical phase referencing. Using the 2MASS point source catalog, we show that there are several hundred objects with phase reference sources less than 30 arcseconds away, allowing to apply this technique. [less ▲]

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See detailPhase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 566

Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star ... [more ▼]

Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. <BR /> Aims: Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. <BR /> Methods: X-ray spectra have been collected at three key orbital phases to probe the winds of both stars. Optical photometry has been gathered to set constraints on the orbital inclination of the system. <BR /> Results: The X-ray spectra reveal prominent variations of the intervening column density toward the X-ray emission zone, which are in line with the expectations for a wind-wind collision. We use a toy model to set constraints on the stellar wind parameters by attempting to reproduce the observed variations of the relative fluxes and wind optical depths at 1 keV. <BR /> Conclusions: The lack of strong optical eclipses sets an upper limit of ~ 68° on the orbital inclination. The analysis of the variations of the X-ray spectra suggests an inclination in the range 54-61° and indicates that the secondary wind momentum ratio exceeds that of the primary by at least a factor 5. Our models further suggest that the bulk of the X-ray emission arises from the innermost region of the wind interaction zone, which is from a region whose outer radius, as measured from the secondary star, lies between 0.5 and 1.5 times the orbital separation. Based on observations collected with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA), and on data collected at the San Pedro Mártir observatory (Mexico). [less ▲]

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See detailPhase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star (Corrigendum)
Rauw, Grégor ULg; Mahy, Laurent; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 569

Based on observations collected with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA), and on data collected at the San Pedro ... [more ▼]

Based on observations collected with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA), and on data collected at the San Pedro Mártir observatory (Mexico). Corrigendum [less ▲]

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See detailPhase resonance testing of nonlinear vibrating structures
Peeters, Maxime ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg

in 28th International Modal Analysis Conference, Jacksonville, 2010 (2011)

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See detailPhase retarders in liquid crystals polymers
Piron, Pierre ULg

Scientific conference (2012, March 12)

Liquid crystals polymers posses birefringent properties and they are locally orientable, they allow the realization of space variant optical retarders which creates non uniformly polarized beam. To ... [more ▼]

Liquid crystals polymers posses birefringent properties and they are locally orientable, they allow the realization of space variant optical retarders which creates non uniformly polarized beam. To realize a retarder, liquid crystals are exposed to a UV linearly polarized beam, the optical axis of the retarder will be parallel to the incident polarization. We shall present an innovative way to produce space-variant retarders without mechanical interaction polarization holography . Superposing several beams differently polarized, results in a non-uniformly polarized recording beam used to realize space variant retarders. We shall also present our research retarders for two applications based on this method polarization analysis and coronagraphy. [less ▲]

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See detailPhase segregation and avalanches in multispecies sandpiles
Vandewalle, Nicolas ULg

in Physica A: Statistical Mechanics and its Applications (1999), 272(3-4), 450-458

A stochastic lattice model for the simulation of sandpiles is presented. The model allows for the numerical investigation of the phase segregation phenomenon occurring when different granular species are ... [more ▼]

A stochastic lattice model for the simulation of sandpiles is presented. The model allows for the numerical investigation of the phase segregation phenomenon occurring when different granular species are initially mixed together before deposition. The model includes the collective motion of grains along the pile surface and produces the so-called landslides. The parameters of the model are discussed. The distribution of avalanche sizes is found to broaden when the number of grain types increases. This result raises new questions about previously reported experimental observations of avalanche size distributions. [less ▲]

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See detailPhase segregation in binary sandpiles on fractal bases
Vandewalle, Nicolas ULg; D'hulst, R.; Ausloos, Marcel ULg

in Physical Review. E : Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (1999), 59(1), 631-635

We have built experimentally and have numerically studied sandpiles on a base having a prefractal perimeter. This type of perimeter induces the formation of quite complex pile shapes characterized by both ... [more ▼]

We have built experimentally and have numerically studied sandpiles on a base having a prefractal perimeter. This type of perimeter induces the formation of quite complex pile shapes characterized by both ridges and valleys. The effects of a fractal base on the phase segregation of a binary granular system have been investigated. Both demixing and self-stratification phenomena have been investigated. It is found that the demixing of binary granular piles is enhanced by the prefractal perimeter character. The concentration profiles are given. This is briefly discussed in terms of length scale selection. [less ▲]

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See detailPhase separation during silica gel formation followed by time-resolved SAXS
Gommes, Cédric ULg; Goderis, Bart; Pirard, Jean-Paul ULg et al

Poster (2004, August)

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See detailPhase separation during silica gel formation followed by time-resolved SAXS
Gommes, Cédric; Blacher, Silvia ULg; Goderis, Bart et al

in Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2005), 238(1-4), 141-145

Time-resolved small angle X-ray scattering data are collected during the formation of silica gels from the base catalyzed polymerization of tetraethoxysilane in ethanol with 3-(2-aminoethylamino ... [more ▼]

Time-resolved small angle X-ray scattering data are collected during the formation of silica gels from the base catalyzed polymerization of tetraethoxysilane in ethanol with 3-(2-aminoethylamino)propyltrimethoxysilane and 3-aminopropyltriethoxysilane as additives. It is shown that a polymerization-induced spinodal demixing occurs during the gel formation. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailPhase shift effective range expansion from supersymmetric quantum mechanics
Samsonov, B. F.; Stancu, Floarea ULg

in Physical Review C (2003), 67(5), 054005

Supersymmetric or Darboux transformations are used to construct local phase equivalent deep and shallow potentials for lnot equal0 partial waves. We associate the value of the orbital angular momentum ... [more ▼]

Supersymmetric or Darboux transformations are used to construct local phase equivalent deep and shallow potentials for lnot equal0 partial waves. We associate the value of the orbital angular momentum with the asymptotic form of the potential at infinity, which allows us to introduce adequate long-distance transformations. The approach is shown to be effective in getting the correct phase shift effective range expansion. Applications are considered for the P-1(1) and D-1(2) partial waves of the neutron-proton scattering. [less ▲]

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See detailPhase slips in mesoscopic superconducting triangles
Schildermans, N.; Salenbien, R.; Silhanek, Alejandro ULg et al

in Physica C: Superconductivity (2008), 468(7-10), 757-760

Voltage-current (V(I)) characteristics are investigated in the superconducting state of an equilateral triangle of 2.2 mu m(2) area. Several steps in the V(I) curves indicate the presence of phase slip ... [more ▼]

Voltage-current (V(I)) characteristics are investigated in the superconducting state of an equilateral triangle of 2.2 mu m(2) area. Several steps in the V(I) curves indicate the presence of phase slip centers in the triangle. The field dependence of these steps follows the Little-Parks oscillations of the phase boundary, associated with the change of vorticity. The influence of the contacts manifests itself as an excess voltage and a negative differential resistance. In addition we show that the position of the current contacts modify the superconducting phase boundary measurements. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailPhase stability of Triphylite, LiFePO4, and the Phases of the Mason-Quensel-Sequence
Schmid-Beurmann, Peter ULg; Moavenian, M.; Hatert, Frédéric ULg

in Berichte der Deutschen Mineralogischen Gesellschaft : Beihefte zum European Journal of Mineralogy (2004), 16

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See detailPhase Transformations and Crack Initiation in a High-Chromium Cast Steel Under Hot Compression Tests
Tchuindjang, Jérôme Tchoufack ULg; Neira Torres, Ingrid; Fores, Paulo et al

in Journal of Materials Engineering and Performance (2015), 24(5), 2025-2041

The mechanical behavior of the fully austenitic matrix of high-chromium cast steel (HCCS) alloy is determined by external compression stress applied at 300 and 700 C. The microstructure is roughly ... [more ▼]

The mechanical behavior of the fully austenitic matrix of high-chromium cast steel (HCCS) alloy is determined by external compression stress applied at 300 and 700 C. The microstructure is roughly characterized toward both optical and scanning electron microscopy analyses. Dilatometry is used during heating from room temperature up to austenitization to study the solid-state phase transformations, precipitation, and dissolution reactions. Two various strengthening phenomena (precipitation hardening and stress-induced bainite transformation) and one softening mechanism (dynamic recovery) are highlighted from compression tests. The influence of the temperature and the carbide type on the mechanical behavior of the HCCS material is also enhanced. Cracks observed on grain boundary primary carbides allow establishing a rough damage model. The crack initiation within the HCCS alloy is strongly dependent on the temperature, the externally applied stress, and the matrix strength and composition. [less ▲]

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See detailPhase transition and thermodynamics of a hot and dense system in a scaled NJL model
Cugnon, Joseph ULg; Jaminon, Martine ULg; Van den Bossche, Bruno

in Nuclear Physics A (1996), 598

he chiral phase transition of a hot and dense system of quarks is studied within a modified SU(3) NJL Lagrangian that implements the QCD scale anomaly. The u- and s-quark condensates can or can not feel ... [more ▼]

he chiral phase transition of a hot and dense system of quarks is studied within a modified SU(3) NJL Lagrangian that implements the QCD scale anomaly. The u- and s-quark condensates can or can not feel the same chiral restoration depending on the considered region of the three-dimensional space (Tc, muuc, musc). The temperature behaviour of the pressure and the energy and entropy densities of the u- and s-quark system is investigated. At high temperature, the non-vanishing bare s-quark mass only modifies slightly the usual behaviour associated with an ideal quark gas. [less ▲]

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See detailPhase transition in granular gases
Terwagne, Denis ULg; Frère, Benjamin; Masabo, Jean-Pierre et al

Conference (2005, April)

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See detailPhase transitions in LaFeAsO: Structural, magnetic, elastic, and transport properties, heat capacity and Mossbauer spectra
McGuire, Michael A; Christianson, Andrew D; Sefat, Athena S et al

in Physical Review. B (2008), 78(9),

We present results from a detailed experimental investigation of LaFeAsO, the parent material in the series of "FeAs" based oxypnictide superconductors. Upon cooling, this material undergoes a tetragonal ... [more ▼]

We present results from a detailed experimental investigation of LaFeAsO, the parent material in the series of "FeAs" based oxypnictide superconductors. Upon cooling, this material undergoes a tetragonal-orthorhombic crystallographic phase transition at similar to 160 K followed closely by an antiferromagnetic ordering near 145 K. Analysis of these phase transitions using temperature dependent powder x-ray and neutron-diffraction measurements is presented. A magnetic moment of similar to 0.35 mu(B) per iron is derived from Mossbauer spectra in the low-temperature phase. Evidence of the structural transition is observed at temperatures well above the transition temperature (up to near 200 K) in the diffraction data as well as the polycrystalline elastic moduli probed by resonant ultrasound spectroscopy measurements. The effects of the two phase transitions on the transport properties (resistivity, thermal conductivity, Seebeck coefficient, and Hall coefficient), heat capacity, and magnetization of LaFeAsO are also reported, including a dramatic increase in the magnitude of the Hall coefficient below 160 K. The results suggest that the structural distortion leads to a localization of carriers on Fe, producing small local magnetic moments which subsequently order antiferromagnetically upon further cooling. Evidence of strong electron-phonon interactions in the high-temperature tetragonal phase is also observed. [less ▲]

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See detailPhase transitions in vibrated granular systems in microgravity
Opsomer, Eric ULg; Vandewalle, Nicolas ULg; Ludewig, François ULg

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2011)

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See detailPhase-Change Materials: Vibrational Softening upon Crystallization and Its Impact on Thermal Properties
Matsunaga, Toshiyuki; Yamada, Noboru; Kojima, Rie et al

in Advanced Functional Materials (2011), 21(12), 2232-2239

Crystallization of an amorphous solid is usually accompanied by a significant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the ... [more ▼]

Crystallization of an amorphous solid is usually accompanied by a significant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the importance of crystalline order for the transport of charge and heat. Phase-change materials, however, reveal a remarkably low thermal conductivity in the crystalline state. The small change in this conductivity upon crystallization points to unique lattice properties. The present investigation reveals that the thermal properties of the amorphous and crystalline state of phase-change materials show remarkable differences such as higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase. These findings are related to the change of bonding upon crystallization, which leads to an increase of the sound velocity and a softening of the optical phonon modes at the same time. [less ▲]

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