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Selected AbstractsUltralow Dielectric Constant Tetravinyltetramethylcyclotetrasiloxane Films Deposited by Initiated Chemical Vapor Deposition (iCVD)ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Nathan J. Trujillo Abstract Simultaneous improvement of mechanical properties and lowering of the dielectric constant occur when films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated chemical vapor deposition (iCVD) are thermally cured in air. Clear signatures from silsesquioxane cage structures in the annealed films appear in the Fourier transform IR (1140,cm,1) and Raman (1117,cm,1) spectra. The iCVD method consumes an order of magnitude lower power density than the traditional plasma-enhanced CVD, thus preserving the precursor's delicate ring structure and organic substituents in the as-deposited films. The high degree of structural retention in the as-deposited film allows for the beneficial formation of intrinsically porous silsesquioxane cages upon annealing in air. Complete oxidation of the silicon creates ,Q' groups, which impart greater hardness and modulus to the films by increasing the average connectivity number of the film matrix beyond the percolation of rigidity. The removal of labile hydrocarbon moieties allows for the oxidation of the as-deposited film while simultaneously inducing porosity. This combination of events avoids the typical trade-off between improved mechanical properties and higher dielectric constants. Films annealed at 410,°C have a dielectric constant of 2.15, and a hardness and modulus of 0.78 and 5.4,GPa, respectively. The solvent-less and low-energy nature of iCVD make it attractive from an environmental safety and health perspective. [source] Platinum group elements provide no indication of a meteoritic component in ICDP cores from the Bosumtwi crater, GhanaMETEORITICS & PLANETARY SCIENCE, Issue 4-5 2007S. GODERIS The majority of the samples come from the impactite material recovered by cores LB-07A and LB-08A, which were drilled by the International Continental Scientific Drilling program (ICDP). One sample originates from the fallback material found at the contact between the impactite and the overlying lake sediment in core LB-05B. No clear signature of a meteoritic contamination was identified in the 13 impactite samples. The target rock apparently dominates the PGE contribution in the impactites. These results agree with the PGE concentrations reported for the suevites collected at the crater rim and in other parts of the Bosumtwi ICDP cores. However, based on Cr and Os isotopic signatures, a meteoritic component could be present in the sample of fallback material, supporting the reports of the existence of meteoritic material in the Ivory Coast tektites. Further analyses of the fallback material from the Bosumtwi drill cores should confirm (or not) this first result. [source] Likely multiple origins of a diploid hybrid sunflower speciesMOLECULAR ECOLOGY, Issue 9 2002A. E. Schwarzbach Abstract The recurrent origin of diploid hybrid species is theoretically improbable because of the enormous diversity of hybrid genotypes generated by recombination. Recent greenhouse experiments, however, indicate that the genomic composition of hybrid lineages is shaped in part by deterministic forces, and that recurrent diploid hybrid speciation may be more feasible than previously believed. Here we use patterns of variation from chloroplast DNA (cpDNA), nuclear microsatellite loci, cross-viability and chromosome structure to assess whether a well-characterized diploid hybrid sunflower species, Helianthus anomalus, was derived on multiple occasions from its parental species, H. annuus and H. petiolaris. Chloroplast DNA and crossability data were most consistent with a scenario in which H. anomalus arose three times: three different H. anomalus fertility groups were discovered, each with a unique cpDNA haplotype. In contrast, there was no clear signature of multiple, independent origins from the microsatellite loci. Given the age of H. anomalus (> 100 000 years bp), it may be that microsatellite evidence for recurrent speciation has been eroded by mutation and gene flow through pollen. [source] Possibilities and Limits of Application of Electrical Resistance Tomography in Hydrodynamics of Bubble ColumnsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2005Dominique Toye Abstract Knowing the hydrodynamic regime in which is working a bubble column is of great importance because the regime affects strongly the mass transfer between the phases. To this end, we examine the potentialities of an Electrical Resistance Tomography (ERT) device. We analyse cross correlation of electrode pair measurements, of neighbouring pixels and power spectra of averaged pixels within a single plane as well as cross correlations of averaged pixels between two planes, without finding a clear signature of the churn turbulent flow. Variable gas flow rate inputs are used to determine the time resolution of the ERT. L'objet du présent travail est de déterminer dans quelle mesure la Tomographie Électrique Résistive (ERT) peut être utilisée pour détecter le régime hydrodynamique dans lequel fonctionne une colonne à bulles. La connaissance de ce régime est extrêmement importante, en raison notamment de son influence sur les valeurs des paramètres de transfert. Dans ce but, nous avons analysé les spectres de puissance de la valeur moyenne des pixels dans un plan de mesure donné, ainsi que la corrélation temporelle existant entre les mesures de différence de potentiel, entre les pixels voisins d'un plan de mesure donné et entre les valeurs moyennes des pixels appartenant à deux plans de mesure différents. Nous n'avons trouvé aucune signature claire du régime hétérogène. La résolution temporelle de l'ERT a par ailleurs été évaluée en utilisant une alimentation de gaz variable. [source] Geomagnetism by the North Pole, anno 1769: The Magnetic Observations of Maximilian Hell during his Venus Transit ExpeditionCENTAURUS, Issue 2 2007Per Pippin Aspaas Hell's site of observation was Vardø in the remote northeastern corner of Norway. He had ambitions to present his journey and scientific results,which reached far beyond astronomy,in a grand work entitled Expeditio litteraria ad Polum arcticum. This work was never printed, although several fragments were published otherwise. Among the pieces not published were his geomagnetic observations. Hell's original manuscripts contain a considerable amount of declination readings as well as notes on instruments, practical procedures, and theoretical reflections involved in his work. In Vardø he set up a magnetic observatory, along with the astronomical one, and recorded, on an irregular schedule, the magnetic declination several times a day from April to June 1769. The records exhibit a clear signature of the diurnal variation as well as magnetic storms. Hell vigorously refuted contemporary suggestions of a connection between magnetic storms and Northern Lights. On the return voyage, a number of observations of magnetic declination along Norway were carried out, with a technique combining a gnomon with observations of the Sun's altitude with a quadrant. [source] Evolution of the winonaite parent body: Clues from silicate mineral trace element distributionsMETEORITICS & PLANETARY SCIENCE, Issue 4 2008Christine FLOSS Textural evidence in these meteorites, including the presence of a plagioclase/clinopyroxene-rich lithology and coarse-grained olivine lithologies, suggests that they may have experienced some silicate partial melting. However, trace element distributions in these lithologies do not show any clear signatures for such an event. Pyroxene trace element compositions do exhibit systematic trends, with abundances generally lowest in Pontlyfni and highest in Winona. The fact that the same trends are present for both incompatible and compatible trace elements suggests, however, that the systematics are more likely the result of equilibration of minerals with initially heterogeneous and distinct compositions, rather than partial melting of a compositionally homogeneous precursor. The winonaites have experienced brecciation and mixing of lithologies, followed by varying degrees of thermal metamorphism on their parent body. These factors probably account for the variable bulk rare earth element (REE) patterns noted for these meteorites and may have led to re-equilibration of trace elements in different lithologies. [source] Gas and stellar dynamics in NGC 1068: probing the galactic gravitational potentialMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006Eric Emsellem ABSTRACT We present SAURON integral field spectrography of the central 1.5 kpc of the nearby Seyfert 2 galaxy NGC 1068, encompassing the well-known near-infrared (NIR) inner bar observed in the K band. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their two-dimensional distribution and kinematics. The [O iii] and H, emission lines exhibit a very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inward streaming motions are observed in both the H, and [O iii] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and Gauss,Hermite h3 fields. We re-examined the long-slit data of Shapiro, Gerssen & van der Marel using a pPXF: a strong decoupling of the Gauss,Hermite term h3 is revealed, and the central decrease of Gauss,Hermite term h4 hinted in the SAURON data is confirmed. These data also suggest that NGC 1068 is a good candidate for a so-called , drop. We confirm the possible presence of two separate pattern speeds applying the Tremaine,Weinberg method to the Fabry,Perot H, map. We also examine the stellar kinematics of bars formed in N -body + smoothed particle hydrodynamics (SPH) simulations built from axisymmetric initial conditions approximating the luminosity distribution of NGC 1068. The resulting velocity, dispersion and higher order Gauss,Hermite moments successfully reproduce a number of properties observed in the two-dimensional kinematics of NGC 1068 and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are likely mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models nevertheless suggest that the inner bar could drive a significant amount of gas down to a scale of , 300 pc. This would be consistent with the interpretation of the , drop in NGC 1068 being the result of central gas accretion followed by an episode of star formation. [source] Populating dark matter haloes with galaxies: comparing the 2dFGRS with mock galaxy redshift surveysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004Xiaohu Yang ABSTRACT In two recent papers, we developed a powerful technique to link the distribution of galaxies to that of dark matter haloes by considering halo occupation numbers as a function of galaxy luminosity and type. In this paper we use these distribution functions to populate dark matter haloes in high-resolution N -body simulations of the standard ,CDM cosmology with ,m= 0.3, ,,= 0.7 and ,8= 0.9. Stacking simulation boxes of 100 h,1 Mpc and 300 h,1 Mpc with 5123 particles each we construct mock galaxy redshift surveys out to a redshift of z= 0.2 with a numerical resolution that guarantees completeness down to 0.01L*. We use these mock surveys to investigate various clustering statistics. The predicted two-dimensional correlation function ,(rp, ,) reveals clear signatures of redshift space distortions. The projected correlation functions for galaxies with different luminosities and types, derived from ,(rp, ,), match the observations well on scales larger than ,3 h,1 Mpc. On smaller scales, however, the model overpredicts the clustering power by about a factor two. Modelling the ,finger-of-God' effect on small scales reveals that the standard ,CDM model predicts pairwise velocity dispersions (PVD) that are ,400 km s,1 too high at projected pair separations of ,1 h,1 Mpc. A strong velocity bias in massive haloes, with bvel,,gal/,dm, 0.6 (where ,gal and ,dm are the velocity dispersions of galaxies and dark matter particles, respectively) can reduce the predicted PVD to the observed level, but does not help to resolve the overprediction of clustering power on small scales. Consistent results can be obtained within the standard ,CDM model only when the average mass-to-light ratio of clusters is of the order of 1000 (M/L), in the B -band. Alternatively, as we show by a simple approximation, a ,CDM model with ,8, 0.75 may also reproduce the observational results. We discuss our results in light of the recent WMAP results and the constraints on ,8 obtained independently from other observations. [source] Impact of traveling phonon wave packets on the optical response of quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2009J. Huneke Abstract The influence of phonon wave packets created by the optical excitation of a quantum dot (QD) structure on four-wave-mixing (FWM) signals is analyzed theoretically. Two different structures are compared: a single QD in a half-space geometry located close to the surface, where the emitted phonon wave packet after reflection at the surface reenters the QD and a pair of QDs in an infinite medium, where the phonon wave packet created in one QD travels across the other QD. Although the strain fields are very similar pronounced differences in the FWM polarizations are found. In the single QD system we observe clear signatures of the reflected wave packet in the FWM signal at positive delay times, which can also be observed in the time-integrated FWM signal from an inhomogeneously broadened ensemble of such QDs. In the two QD case no signatures of the traveling wave packet are seen in the signal at positive delays and, consequently, in the ensemble signal. However, they are clearly seen in the FWM signal at negative delay times. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||