10,121 research outputs found
Metallic and Insulating Adsorbates on Graphene
We directly compare the effect of metallic titanium (Ti) and insulating
titanium dioxide (TiO2) on the transport properties of single layer graphene.
The deposition of Ti results in substantial n-type doping and a reduction of
graphene mobility by charged impurity scattering. Subsequent exposure to oxygen
largely reduces the doping and scattering by converting Ti into TiO2. In
addition, we observe evidence for short-range scattering by TiO2 impurities.
These results illustrate the contrasting scattering mechanisms for identical
spatial distributions of metallic and insulating adsorbates
Quantum Evolution of Inhomogeneities in Curved Space
We obtain the renormalized equations of motion for matter and semi-classical
gravity in an inhomogeneous space-time. We use the functional Schrodinger
picture and a simple Gaussian approximation to analyze the time evolution of
the model, and we establish the renormalizability of this
non-perturbative approximation. We also show that the energy-momentum tensor in
this approximation is finite once we consider the usual mass and coupling
constant renormalizations, without the need of further geometrical
counter-terms.Comment: 22 page
Jets and Jet Multiplicities in High Energy Photon-Nucleon Inetraction:
We discuss the theory of jet events in high-energy photon-proton interactions
using a model which gives a good description of the data available on total
inelastic cross sections up to =210 GeV. We show how to
calculate the jet cross sections and jet multiplicities and give predictions
for these quantities for energies appropriate for experiments at the HERA
collider and for very high energy cosmic ray observations.Comment: 12 pages + 4 figs, MAD/TH/92-8, submitted to Phys. Rev. D(Rapid
Communications), figs. available on request from [email protected]
Oscillatory Spin Polarization and Magneto-Optic Kerr Effect in Fe3O4 Thin Films on GaAs(001)
The spin dependent properties of epitaxial Fe3O4 thin films on GaAs(001) are
studied by the ferromagnetic proximity polarization (FPP) effect and
magneto-optic Kerr effect (MOKE). Both FPP and MOKE show oscillations with
respect to Fe3O4 film thickness, and the oscillations are large enough to
induce repeated sign reversals. We attribute the oscillatory behavior to
spin-polarized quantum well states forming in the Fe3O4 film. Quantum
confinement of the t2g states near the Fermi level provides an explanation for
the similar thickness dependences of the FPP and MOKE oscillations.Comment: to appear in Phys. Rev. Let
Pinning of quantized vortices in helium drop by dopant atoms and molecules
Using a density functional method, we investigate the properties of liquid
4He droplets doped with atoms (Ne and Xe) and molecules (SF_6 and HCN). We
consider the case of droplets having a quantized vortex pinned to the dopant. A
liquid drop formula is proposed that accurately describes the total energy of
the complex and allows one to extrapolate the density functional results to
large N. For a given impurity, we find that the formation of a
dopant+vortex+4He_N complex is energetically favored below a critical size
N_cr. Our result support the possibility to observe quantized vortices in
helium droplets by means of spectroscopic techniques.Comment: Typeset using Revtex, 3 pages and 5 figures (4 Postscript, 1 jpeg
Space-Time Picture of Fragmentation in PYTHIA/JETSET for HERMES and RHIC
We examine the space-time evolution of (pre-)hadron production within the
Lund string fragmentation model. The complete four-dimensional information of
the string breaking vertices and the meeting points of the prehadron
constituents are extracted for each single event in Monte Carlo simulations
using the Jetset-part of Pythia. We discuss the implication on the deep
inelastic lepton scattering experiments at HERMES as well as on observables in
ultra-relativistic heavy ion collisions at RHIC, using Pythia also for modeling
the hard part of the interaction.Comment: 15 pages, 7 figures, final version as accepted by Phys Lett
Moteurs et conséquences de la resuspension dans un lac sahélien peu profond : le lac de Guiers au Sénégal
La dynamique des particules dans les systèmes aquatiques est régit par l’interaction entre la resuspension et la sédimentation. Cette étude est consacrée à la détermination des processus responsables de la resuspension des particules dans le lac de Guiers situé au nord du Sénégal. Des échantillons ont été collectés au cours d’un cycle annuel au niveau de trois stations prises dans la partie centrale du lac. Dans ce site, la resuspension des particules est liée à l’action des vents mais aussi à la crue du fleuve Sénégal. La resuspension sous l’effet des vents se produit pendant l’harmattan, alors qu’en période d’alizés maritimes, c’est la crue du fleuve Sénégal qui est responsable de la remise en suspension des particules. Le taux de particule en suspension est plus important en période d’harmattan qui est marquée par des vitesses du vent plus élevées (moyenne de 3,6 m.s-1 fluctuant entre 1 et 7 m.s-1), mais surtout par un fetch fort (24 km). Cette évolution saisonnière de la resuspension affecte la turbidité de l’eau, les taux de matière en suspension, la biomasse phytoplanctonique, le coefficient d’atténuation lumineuse, le flux des particules et la structure de la colonne d’eau. La resuspension sous l’effet des vagues créées par le vent associé au fetch élevé constitue dans ce système peu profond le principal processus contrôlant la dynamique des particules.Mots clés : Vagues, crue du fleuve, resuspension, particule, turbidité, lac de Guiers
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