1,017 research outputs found
Dynamics of Long-Living Excitons in Tunable Potential Landscapes
A novel method to experimentally study the dynamics of long-living excitons
in coupled quantum well semiconductor heterostructures is presented.
Lithographically defined top gate electrodes imprint in-plane artificial
potential landscapes for excitons via the quantum confined Stark effect.
Excitons are shuttled laterally in a time-dependent potential landscape defined
by an interdigitated gate structure. Long-range drift exceeding a distance of
150 um at an exciton drift velocity > 1000 m/s is observed in a gradient
potential formed by a resistive gate stripe.Comment: 4 pages, 4 figures. To appear in Phys. E (MSS-12-Proceedings
Aplicación de las técnicas de suavizado en la variación negativa contingente (CNV)
El presente trabajo recoge de forma breve laproblemática de la estimación de la serial en series temporales de datos obtenidos en registros ERP. Se centra en aquellos componentes de frecuencia mis baja, como es el caso de la CNV: Sepropone la utilización alternativa de las técnicas de suavizado del Análisis Exploratorio de Datos (EDA), para mejorar la estimación obtenida, en comparación con la técnica del promediado simple de diferentes ensayos
Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process
Manufacturing superconducting circuits out of ultrathin films is a
challenging task when it comes to patterning complex compounds, which are
likely to be deteriorated by the patterning process. With the purpose of
developing high-T superconducting photon detectors, we designed a novel
route to pattern ultrathin YBCO films down to the nanometric scale. We believe
that our method, based on a specific use of a focused-ion beam, consists in
locally implanting Ga^{3+} ions and/or defects instead of etching the film.
This protocol could be of interest to engineer high-T superconducting
devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to
treat other sensitive compounds.Comment: 13 pages, 7 figure
The Dependence of Star Formation Rates on Stellar Mass and Environment at z~0.8
We examine the star formation rates (SFRs) of galaxies in a redshift slice
encompassing the z=0.834 cluster RX J0152.7-1357. We used a low-dispersion
prism in the Inamori Magellan Areal Camera and Spectrograph (IMACS) to identify
galaxies with z<23.3 AB mag in diverse environments around the cluster out to
projected distances of ~8 Mpc from the cluster center. We utilize a
mass-limited sample (M>2x10^{10} M_sun) of 330 galaxies that were imaged by
Spitzer MIPS at 24 micron to derive SFRs and study the dependence of specific
SFR (SSFR) on stellar mass and environment. We find that the SFR and SSFR show
a strong decrease with increasing local density, similar to the relation at
z~0. Our result contrasts with other work at z~1 that find the SFR-density
trend to reverse for luminosity-limited samples. These other results appear to
be driven by star-formation in lower mass systems (M~10^{10} M_sun). Our
results imply that the processes that shut down star-formation are present in
groups and other dense regions in the field. Our data also suggest that the
lower SFRs of galaxies in higher density environments may reflect a change in
the ratio of star-forming to non-star-forming galaxies, rather than a change in
SFRs. As a consequence, the SFRs of star-forming galaxies, in environments
ranging from small groups to clusters, appear to be similar and largely
unaffected by the local processes that truncate star-formation at z~0.8.Comment: 5 pages, 3 figures, accepted for publication in ApJ
Electric-Field Tuning of Spin-Dependent Exciton-Exciton Interactions in Coupled Quantum Wells
We have shown experimentally that an electric field decreases the energy
separation between the two components of a dense spin-polarized exciton gas in
a coupled double quantum well, from a maximum splitting of meV to
zero, at a field of 35 kV/cm. This decrease, due to the field-induced
deformation of the exciton wavefunction, is explained by an existing
calculation of the change in the spin-dependent exciton-exciton interaction
with the electron-hole separation. However, a new theory that considers the
modification of screening with that separation is needed to account for the
observed dependence on excitation power of the individual energies of the two
exciton components.Comment: 5 pages, 4 eps figures, RevTeX, Physical Review Letters (in press
Electron--Electron Scattering in Quantum Wires and it's Possible Suppression due to Spin Effects
A microscopic picture of electron-electron pair scattering in single mode
quantum wires is introduced which includes electron spin. A new source of
`excess' noise for hot carriers is presented. We show that zero magnetic field
`spin' splitting in quantum wires can lead to a dramatic `spin'-subband
dependence of electron--electron scattering, including the possibility of
strong suppression. As a consequence extremely long electron coherence lengths
and new spin-related phenomena are predicted. Since electron bands in III-V
semiconductor quantum wires are in general spin-split in zero applied magnetic
field, these new transport effects are of general importance.Comment: 11 pages, LaTeX and APS-RevteX 2, Rep.No. GF66,Figures from author,
Physical Review Letters, scheduled for 7 June 199
Topology of six degrees of freedom magnetic bearing
A novel magnetic topology has been designed for a six degrees of freedom, magnetically levitated and driven mirror, to be used in a three dimensional (3D) measurement system based on laser interferometry. The translations of the mirror are to be kept small, whereas the rotations are to be controlled over a large range with a high bandwidth and high accuracy. Finite element modelling (FEM) is used to analyze the proposed topology. For computational load reduction, a 2D FEM model has been derived from the actual 3D topology, which incorporates most of the magnetic subsystems. Simulations show that cross-influence between the actuators is small, that the forces and torques are proportional to the applied currents and that the angle of the rotor is of little influence. This allows the multiple in multiple out system to be regarded as multiple linear single in single out systems. ©2000 American Institute of Physics
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