Circular dichroism in optical second harmonic generated in reflection from chiral G-shaped metamaterials

in Journal of Physics: Conference Series [=JPCS] (2012), 352

Influence of chirality on the optical second harmonic generated from planar array of G-shaped metamaterials is studied. Circular dichroism of these nanostructures manifests itself via different efficiency ... [more ▼]

Influence of chirality on the optical second harmonic generated from planar array of G-shaped metamaterials is studied. Circular dichroism of these nanostructures manifests itself via different efficiency of left and right circularly polarized second harmonic that is observed for the samples of different handedness. This difference allows to distinguish between the two enantiomers. [less ▲]

An experimental approach for synthesis of Fe-Al-O multiferroic fibrous material

in Journal of Physics: Conference Series [=JPCS] (2012), 398

Basic principles of the electro-hydrodynamics are applied for synthesis of solid state Fe-Al-O multi-ferroic fibrous material. For that purpose stable blend spinning solutions comprised of a high ... [more ▼]

Basic principles of the electro-hydrodynamics are applied for synthesis of solid state Fe-Al-O multi-ferroic fibrous material. For that purpose stable blend spinning solutions comprised of a high molecular assisting organic polymer and salts of iron and aluminum are developed. These solutions are tested under electrospinning conditions and synthesis of homogeneous as spun non-woven mats characterized by fibre mean diameters in the microand nano-size range is successfully demonstrated. Multi-step thermal procedure is applied for the consecutive solvent evaporation, polymer pyrolisis and final fibre calcination. Electronoptical imaging technique and XRD are applied for revealing the sample morphology and the phase composition correspondingly. The results obtained outline the wide possibilities for fabrication of multi-ferroics fibrous nano-materials on the basis of Fe-Al-O. [less ▲]

Using seismic targets as benchmarks for spectroscopic analyses of cool stars

in Journal of Physics: Conference Series [=JPCS] (2011), 328

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An ... [more ▼]

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An extensive comparison for about 40 well-studied pulsating stars with gravities derived by traditional means (ionization balance, pressure-sensitive spectral features or location with respect to evolutionary tracks) supports the validity of this technique and reveals an overall remarkable agreement with mean differences not exceeding 0.05 dex (although with a dispersion of up to ~0.2 dex). It is argued that interpolation in theoretical isochrones may be the most precise way of estimating the gravity by traditional means in nearby dwarfs. The use of seismic targets as benchmarks in the context of forthcoming large-scale surveys (such as the follow up of the Gaia mission) is briefly discussed. [less ▲]

CO2 valorization by means of dielectric barrier discharge

in Journal of Physics: Conference Series [=JPCS] (2011), 275(1, art_number=012016),

As atmospheric pollution is causing several environmental problems it is incumbent to reduce the impact of pollution on the environment. One particular problem is the production of CO2 by many transport ... [more ▼]

As atmospheric pollution is causing several environmental problems it is incumbent to reduce the impact of pollution on the environment. One particular problem is the production of CO2 by many transport and industrial applications. Instead of stocking CO2 and instead of being a product, it can be used as a source. The case considered is the CO2 reformation of methane producing hydrogen and CO. It is an endothermic reaction, for which the activation barrier needs to be surpassed. This can be done efficiently by the method of Dielectric Barrier Discharge. The process relies on the collision of electrons, which are accelerated under an electrical field that is created in the discharge area. This leads to the formation of reactive species, which facilitate the abovementioned reaction. This study is performed using a Matlab program with the Reaction Engineering module in COMSOL (with an incorporated kinetic mechanism) in order to model the discharge phase. Then COMSOL (continuity and Navier-Stokes equations) is used to model the flow in the post-discharge phase. The results showed that both a 2D and 3D model can be used to model the chemical-plasma process. These methods need strongly reduced kinetic mechanism, which in some cases can cause loss of precision. [less ▲]

Dynamical Regimes of a Granular Gas in Microgravity : a Molecular Dynamics Study

in Journal of Physics: Conference Series [=JPCS] (2011)

Modification of the trapped field in bulk HTS as a result of the drilling of a pattern of artificial holes

in Journal of Physics: Conference Series [=JPCS] (2010), 234

The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and ... [more ▼]

The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and compared by means of numerical models and Hall probe mapping techniques. To this aim, we consider two bulk YBCO samples with a rectangular cross-section that are drilled each by six holes arranged either on a rectangular lattice (sample I) or on a centered rectangular lattice (sample II). For the numerical analysis, three different models are considered for calculating the trapped flux: (i), a two-dimensional (2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D finite-element model neglecting demagnetizing effects but incorporating magnetic relaxation in the form of an E – J power law, and, (iii), a 3D finite element analysis that takes into account both the finite height of the sample and flux creep effects. For the experimental analysis, the trapped magnetic flux density is measured above the sample surface by Hall probe mapping performed before and after the drilling process. The maximum trapped flux density in the drilled samples is found to be smaller than that in the plain samples. The smallest magnetization drop is found for sample II, with the centered rectangular lattice. This result is confirmed by the numerical models. In each sample, the relative drops that are calculated independently with the three different models are in good agreement. As observed experimentally, the magnetization drop calculated in the sample II is the smallest one and its relative value is comparable to the measured one. By contrast, the measured magnetization drop in sample (1) is much larger than that predicted by the simulations, most likely because of a change of the microstructure during the drilling process. [less ▲]

Asteroseismic probing of internal rotation in hot B subdwarf stars: Testing spin-orbit synchronism in two close binary systems

in Journal of Physics: Conference Series [=JPCS] (2009, June), 172

We present internal rotation profiles derived from asteroseismology for the hot pulsating B subdwarf stars PG 1336-018 and Feige 48. These two pulsators are primaries of close binary systems of known ... [more ▼]

We present internal rotation profiles derived from asteroseismology for the hot pulsating B subdwarf stars PG 1336-018 and Feige 48. These two pulsators are primaries of close binary systems of known orbital period and, therefore, provide laboratories to test, for the first time, spin-orbit synchronization as a function of depth. We show that PG 1336-018 and Feige 48 clearly rotate as solid bodies with periods equal to their orbital periods from the surface down to at least ~ 0.5 and ~ 0.3 their radius, respectively. Deep tidal locking has therefore developed within the relatively short lifetime of these stars (~ 10^8 yr). [less ▲]

The driving mechanism of roAp stars

in Journal of Physics: Conference Series [=JPCS] (2008), 118

We analyse in detail the driving mechanism of roAp stars and present the theoretical instability strip predicted by our models with solar metallicity. A particular attention is given to the interpretation ... [more ▼]

We analyse in detail the driving mechanism of roAp stars and present the theoretical instability strip predicted by our models with solar metallicity. A particular attention is given to the interpretation of the role played by the different eigenfunctions in the stabilization of the modes at the red edge of the instability strip. The gradient of temperature in the H[SUB]I[/SUB] opacity bump appears to play a major role in this context. We also consider the particular and complex role played by the shape of the eigenfunctions (location of the nodes, ...). [less ▲]

Modeling pulsations in hot stars with winds

in Journal of Physics: Conference Series [=JPCS] (2008), 118

The interaction pulsation/mass loss takes different aspects. Pulsations can trigger mass loss as in LBVs and Miras; on the other hand, mass loss can modify the driving conditions within the stars. But the ... [more ▼]

The interaction pulsation/mass loss takes different aspects. Pulsations can trigger mass loss as in LBVs and Miras; on the other hand, mass loss can modify the driving conditions within the stars. But the most spectacular aspect is the effect on stellar models which, in turn, opens a royal way to asteroseismology to test physical conditions inside massive stars, such as the extent of convective cores or the appearance of new driving mechanisms. We start with a discussion on MS stars and their strange mode instabilities. We then move on to the excitation of the LBV phenomenon. WR stars and the newly observed MOST period in WR123 are discussed in view of the power of asteroseismology. We then turn to B supergiants, in particular HD163899, and show how asteroseismology can really probe convection, semiconvection and mass loss. [less ▲]

Study of thermal effects in bulk RE-BCO superconductors submitted to a variable magnetic field

in Journal of Physics: Conference Series [=JPCS] (2006), 43

When bulk RE-BCO superconductors are used as permanent magnets in engineering applications, they are likely to experience transient variations of the applied magnetic field. The resulting vortex motion ... [more ▼]

When bulk RE-BCO superconductors are used as permanent magnets in engineering applications, they are likely to experience transient variations of the applied magnetic field. The resulting vortex motion may cause a significant temperature increase. As a consequence the initial trapped flux is reduced. In the present work, we first focus on the cause of a temperature increase. The temperature distribution within a superconducting finite cylinder subjected to an alternating magnetic field is theoretically predicted. Results are compared to experimental data obtained by two temperature sensors attached to a bulk YBCO pellet. Second, we consider curative methods for reducing the effect of heat flux on the temperature increase. Hall-probe mappings on YBCO samples maintained out of the thermal equilibrium are performed for two different morphologies : a plain single domain and a single domain with a regularly spaced hole array. The drilled single-domain displays a trapped induction which is weakly affected by the local heating while displaying a high trapped field. [less ▲]