967 research outputs found
Square-free class sizes in products of groups
We obtain some structural properties of a factorised group , given
that the conjugacy class sizes of certain elements in are not
divisible by , for some prime . The case when is a mutually
permutable product is especially considered
InAs/InP single quantum wire formation and emission at 1.5 microns
Isolated InAs/InP self-assembled quantum wires have been grown using in situ
accumulated stress measurements to adjust the optimal InAs thickness. Atomic
force microscopy imaging shows highly asymmetric nanostructures with average
length exceeding more than ten times their width. High resolution optical
investigation of as-grown samples reveals strong photoluminescence from
individual quantum wires at 1.5 microns. Additional sharp features are related
to monolayer fluctuations of the two dimensional InAs layer present during the
early stages of the quantum wire self-assembling process.Comment: 4 pages and 3 figures submitted to Applied Physics Letter
Cinemómetro piezoeléctrico de alta exactitud (VUAE)
Se ha desarrollado un sistema electrónico computerizado, portátil y de bajo consumo, denominado Medidor de Velocidad de
Vehículos por Ultrasonidos de Alta Exactitud, VUAE. La alta exactitud de la medida conseguida en el VUAE hace que pueda
servir de medida de referencia de la velocidad de un vehículo circulando en carretera. Por tanto el VUAE puede usarse como
medida de referencia que permita estimar el error de los cinemómetros comerciales. El VUAE está compuesto por n (n≥2)
parejas de emisores y receptores piezoeléctricos de ultrasonidos, denominados E-Rult. Los emisores de las n parejas E-Rult generan
n barreras de ultrasonidos, y los receptores piezoeléctricos captan la señal de los ecos cuando el vehículo atraviesa las
barreras. Estos ecos se procesan digitalmente para conseguir señales representativas. Posteriormente, utilizando la técnica de
la correlación cruzada de señales, se ha podido estimar con alta exactitud la diferencia de tiempos entre los ecos captados en
cada barrera. Con los tiempos entre ecos y con la distancia entre cada una de las n barreras de ultrasonidos se puede realizar
una estimación de la velocidad del vehículo con alta exactitud. El VUAE se ha contrastado con un sistema de velocidad de
referencia, basado en cables piezoeléctricos.Peer reviewe
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
We study the metal-insulator transition in individual self-assembled quantum
wires and report optical evidences of metallic liquid condensation at low
temperatures. Firstly, we observe that the temperature and power dependence of
the single nanowire photoluminescence follow the evolution expected for an
electron-hole liquid in one dimension. Secondly, we find novel spectral
features that suggest that in this situation the expanding liquid condensate
compresses the exciton gas in real space. Finally, we estimate the critical
density and critical temperature of the phase transition diagram at
cm and K, respectively.Comment: 4 pages, 5 figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
Magnetic topology of the north solar pole
We study the polar magnetism near an activity maximum when these regions
change their polarity, from which it is expected that its magnetism should be
less affected by the global field. To fully characterise the magnetic field
vector, we use deep full Stokes polarimetric observations of the 15648.5 {\AA}
and 15652.8 {\AA} FeI lines. We observe the north pole as well as a quiet
region at disc centre to compare their field distributions. In order to
calibrate the projection effects, we observe an additional quiet region at the
east limb. We find that the two limb datasets share similar magnetic field
vector distributions. This means that close to a maximum, the poles look like
typical limb, quiet-Sun regions. However, the magnetic field distributions at
the limbs are different from the distribution inferred at disc centre. At the
limbs, we infer a new population of magnetic fields with relatively strong
intensities (600-800 G), inclined by 30 deg with respect to the
line of sight, and with an azimuth aligned with the solar disc radial
direction. We propose that this new population at the limbs is due to the
observation of unresolved magnetic loops as seen close to the limb. These loops
have typical granular sizes as measured in the disc centre. At the limbs, where
the spatial resolution decreases, we observe them spatially unresolved, which
explains the new population of magnetic fields that is inferred. This is the
first (indirect) evidence of small-scale magnetic loops outside the disc centre
and would imply that these small-scale structures are ubiquitous on the entire
solar surface. This result has profound implications for the energetics not
only of the photosphere, but also of the outer layers since these loops have
been reported to reach the chromosphere and the low corona
Temperature Sensor Based on Colloidal Quantum Dots PMMA Nanocomposite Waveguides
In this paper, integrated temperature sensors based on active nanocomposite planar waveguides are presented. The nanocomposites consist of cadmium selenide (CdSe) and cadmium telluride (CdTe) quantum dots (QDs) embedded in a polymethylmethacrylate (PMMA) matrix. When the samples are heated in a temperature range from 25 to 50 , the waveguided photoluminescence of QDs suffers from a strong intensity decrease, which is approximately quadratic dependent on temperature. Moreover, the wavelength peak of the waveguided emission spectrum of CdTe-PMMA shows a blue shift of 0.25 , whereas it remains constant in the case of CdSe-PMMA. A temperature resolution of 0.1 is obtained. QD waveguides have great potential for the development of photonic sensors because of their integration, multiplexing, and roll-to-roll fabrication capabilities.Manuscript received February 21, 2012; revised May 8, 2012; accepted July 18, 2012. Date of publication July 24, 2012; date of current version August 9, 2012. This work was supported in part by the Spanish MICINN and Generalitat Valenciana under Grant TEC-2011-06756-C03-03 and Grant PROMETEO/2009/074, the Plan Nacional I + D under Project TEC2011-29120-C05-01 and Project TEC2011-29120-C05-05, and the Infraestructura FEDER UPVOV08-3E-008. The associate editor coordinating the review of this paper and approving it for publication was Prof. E. H. Yang.Bueno Martínez, A.; Suárez Álvarez, I.; Abargues, R.; Sales Maicas, S.; J. MARTÍNEZ-PASTOR (2012). Temperature Sensor Based on Colloidal Quantum Dots PMMA Nanocomposite Waveguides. IEEE Sensors Journal. 12(10):3069-3074. https://doi.org/10.1109/JSEN.2012.2210037S30693074121
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