1,022 research outputs found
Anisotropic Decay Dynamics of Photoexcited Aligned Carbon Nanotube Bundles
We have performed polarization-dependent ultrafast pump-probe spectroscopy of
a film of aligned single-walled carbon nanotube bundles. By taking into account
imperfect nanotube alignment as well as anisotropic absorption cross sections,
we quantitatively determined distinctly different photo-bleaching dynamics for
polarizations parallel and perpendicular to the tube axis. For perpendicular
polarization, we observe a slow (1.0-1.5 ps) relaxation process, previously
unobserved in randomly-oriented nanotube bundles. We attribute this slower
dynamics to the excitation and relaxation of surface plasmons in the radial
direction of the nanotube bundles.Comment: 4 pages, 3 figure
Correcting for Distortions due to Ionization in the STAR TPC
Physics goals of the STAR Experiment at RHIC in recent (and future) years
drive the need to operate the STAR TPC at ever higher luminosities, leading to
increased ionization levels in the TPC gas. The resulting ionic space charge
introduces field distortions in the detector which impact tracking performance.
Further complications arise from ionic charge leakage into the main TPC volume
from the high gain anode region. STAR has implemented corrections for these
distortions based on measures of luminosity, which we present here.
Additionally, we highlight a novel approach to applying the corrections on an
event-by-event basis applicable in conditions of rapidly varying ionization
sources.Comment: 6 pages, 7 figures, proceedings of the Workshop on Tracking in High
Multiplicity Environments (TIME 05) in Zurich, Switzerland, submitted to
Nucl. Instr. and Meth.
Alignement experience in STAR
The STAR experiment at RHIC uses four layers of silicon strip and silicon drift detectors for secondary vertex reconstruction. An attempt for a direct charm meson measurement put stringent requirements on alignment and calibration. We report on recent alignment and drift velocity calibration work performed on the inner silicon tracking system
Nuevos métodos de fabricación digital de paneles de GRC de forma libre
Free-form GRC panels are widely used in lightweight facade elements. Such panels can be manufactured through a variety of methods. Nevertheless, its advantages such as moldability, durability and lightness, are penalized by the high price of the corresponding molds, especially if there is not a sufficient repetition of units. New digital technologies enable innovative possibilities in the field of construction and manufacture of molds with complex geometries. In this paper, a series of manufacturing methods for free-form GRC panels are presented. Advantages and drawbacks of these methods are discussed, especially the role played by the mold and its economic impact. Finally, conclusions of this analysis about its technical feasibility and possibilities are drawn.Los paneles de forma libre de GRC son de gran aplicación en elementos de fachadas ligeras. Dichos paneles pueden fabricarse a través de una gran variedad de procesos. Sin embargo, a pesar de sus ventajas como la moldeabilidad, durabilidad y ligereza, se ven penalizados por el elevado precio de los correspondientes moldes, sobre todo si no hay una repetición suficiente de las piezas y la forma del panel difiere de lo convencional. Las nuevas tecnologÃas digitales permiten diversas posibilidades en el campo de la construcción y la producción de moldes con geometrÃas complejas. En el presente artÃculo se presenta una serie de métodos recientes en la fabricación de paneles de GRC de forma libre. Se discutirán ventajas e inconvenientes de dichos métodos, sobre todo la importancia del molde y su repercusión económica. Finalmente se extraerán conclusiones sobre la viabilidad técnica y las posibilidades que se abren con este análisis
14th International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2011): Preface
No abstract available
Excitation transfer and luminescence in porphyrin-carbon nanotube complexes
Functionalization of carbon nanotubes with hydrosoluble porphyrins (TPPS) is
achieved by "-stacking". The porphyrin/nanotube interaction is studied by
means of optical absorption, photoluminescence and photoluminescence excitation
spectroscopies. The main absorption line of the porphyrins adsorbed on
nanotubes exhibits a 120 meV red shift, which we ascribe to a flattening of the
molecule in order to optimize interactions. The porphyrin-nanotube
complex shows a strong quenching of the TPPS emission while the
photoluminescence intensity of the nanotubes is enhanced when the excitation
laser is in resonance with the porphyrin absorption band. This reveals an
efficient excitation transfer from the TPPS to the carbon nanotube
Examine the species and beam-energy dependence of particle spectra using Tsallis Statistics
Tsallis Statistics was used to investigate the non-Boltzmann distribution of
particle spectra and their dependence on particle species and beam energy in
the relativistic heavy-ion collisions at SPS and RHIC. Produced particles are
assumed to acquire radial flow and be of non-extensive statistics at
freeze-out. J/psi and the particles containing strangeness were examined
separately to study their radial flow and freeze-out. We found that the strange
hadrons approach equilibrium quickly from peripheral to central A+A collisions
and they tend to decouple earlier from the system than the light hadrons but
with the same final radial flow. These results provide an alternative picture
of freeze-outs: a thermalized system is produced at partonic phase; the
hadronic scattering at later stage is not enough to maintain the system in
equilibrium and does not increase the radial flow of the copiously produced
light hadrons. The J/psi in Pb+Pb collisions at SPS is consistent with early
decoupling and obtains little radial flow. The J/psi spectra at RHIC are also
inconsistent with the bulk flow profile.Comment: 12 pages, 4 figures, added several references and some clarifications
et
Third-order nonlinear optical response and photoluminescence characterization of tellurite glasses with different alkali metal oxides as network modifiers
Studies of the third-order nonlinear optical properties in TeO(2)-MO-R(2)O glasses with three different alkali metal oxides R(2)O (R - Li, Na, K) as network modifiers and two network intermediates MO (M - Zn, Mg) are reported. The influence of such modifiers and intermediates on the nonlinear optical properties of these glasses was investigated using the standard Z-scan and the thermally managed Z-scan techniques under femtosecond pulse excitation at 800 nm. For different modifiers and intermediates, the nonlinear refraction indices n(2) of these glasses varied in the range 1.31-2.81 (x10(-15) cm(2)/W). It was found that n(2) increases as the ionic radius of both network modifiers and intermediates decreases. Furthermore, the measurements show that the contribution from thermo-optical effects to the nonlinear refraction index is negligible for all of the studied glass compositions. In addition, the effect of modifiers and intermediates in the formation of localized states in the vicinity of the optical bandgap was also studied through photoluminescence experiments. These experiments revealed the presence of two emission bands (red and blue) originating from these localized states that can be populated after optical excitation and subsequent relaxation
- …