2,057 research outputs found
Carrier relaxation in GaAs v-groove quantum wires and the effects of localization
Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove
quantum wires (QWRs) with a large subband separation (46 meV). Signatures of
inhibited carrier relaxation mechanisms are seen in temperature-dependent
photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we
observe strong emission from the first excited state of the QWR below ~50 K.
This is attributed to reduced inter-subband relaxation via phonon scattering
between localized states. Theoretical calculations and experimental results
indicate that the pinch-off regions, which provide additional two-dimensional
confinement for the QWR structure, have a blocking effect on relaxation
mechanisms for certain structures within the v-groove. Time-resolved PL
measurements show that efficient carrier relaxation from excited QWR states
into the ground state, occurs only at temperatures > 30 K. Values for the low
temperature radiative lifetimes of the ground- and first excited-state excitons
have been obtained (340 ps and 160 ps respectively), and their corresponding
localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct
corrupt figure
Stellar parameters for stars of the CoRoT exoplanet field
Aims:To support the computation and evolutionary interpretation of periods
associated with the rotational modulation, oscillations, and variability of
stars located in the CoRoT fields, we are conducting a spectroscopic survey for
stars located in the fields already observed by the satellite. These
observations allow us to compute physical and chemical parameters for our
stellar sample. Method: Using spectroscopic observations obtained with UVES/VLT
and Hydra/Blanco, and based on standard analysis techniques, we computed
physical and chemical parameters (, , ,
, , , and ) for a large
sample of CoRoT targets. Results: We provide physical and chemical parameters
for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in
our sample are located in different evolutionary stages, ranging from the main
sequence to the red giant branch, and range in spectral type from F to K. The
physical and chemical properties for the stellar sample are in agreement with
typical values reported for FGK stars. However, we report three stars
presenting abnormal lithium behavior in the CoRoT fields. These parameters
allow us to properly characterize the intrinsic properties of the stars in
these fields. Our results reveal important differences in the distributions of
metallicity, , and evolutionary status for stars belonging to
different CoRoT fields, in agreement with results obtained independently from
ground-based photometric surveys. Conclusions: Our spectroscopic catalog, by
providing much-needed spectroscopic information for a large sample of CoRoT
targets, will be of key importance for the successful accomplishment of several
different programs related to the CoRoT mission, thus it will help further
boost the scientific return associated with this space mission.Comment: 43 pages, 17 figures, accepted for publication in A&
Use of technology radiation as a method of reducing the microorganism and conservation postharvest of caja during storage
The caja fruit (Spondias spp.) are among the species considered exotic presents excellent view of economic exploitation to the Northeast of Brazil. However, contamination by microorganisms is a major factor in postharvest losses of fruits and other cultivated in Brazilian territory. Use of ionizing radiation aiming to reduce the use of pesticide products in pest control and microorganisms phytopathological and maintaining the quality of agricultural products has been studied by several researchers of postharvest fruit. This technology meets the requirements of food safety imposed by the various organs of public health. In order to evaluate the action of ionizing radiation on agents phytopathological and the effects on the quality of postharvest of caja fruits when stored under temperature of shelf, the experiment was conducted with application of doses 1.0 and 2.0 kGy, dose zero as fruit control, and storage under temperature of 23°C for twelve days. Control fruit had higher contamination by microorganisms phytopathological throughout the storage period. Analysis of total soluble solids, total titratable acidity, hydrogen potential, soluble solids/titratable acidity ratio, ascorbic acid and color of the flesh have suffered minor variations between the different doses studied.Keywords: Conservation; caja fruit; gamma radiation; postharvest storage; microorganism spoilage
Nature of the constant factor in the relation between radial breathing mode frequency and tube diameter for single-wall carbon nanotubes
Resonance Raman scattering is used to determine the radial breathing mode (RBM) frequency (ωRBM) dependence on tube diameter (dt) for single-wall carbon nanotubes (SWNTs). We establish experimentally the ωRBM=227.0/dt as the fundamental relation for pristine SWNTs. All the other RBM values found in the literature can be explained by an upshift in frequency due mostly to van der Waals interaction between SWNTs and environment
Corotation: its influence on the chemical abundance pattern of the Galaxy
A simple theory for the chemical enrichment of the Galaxy which takes into
account the effects of spiral arms on heavy elements output was developed. In
the framework of the model with the corotation close to the position of the Sun
in the Galaxy the observed abundance features are explained.Comment: LaTeX, 6 pages, 5 jpg figures, uses aastex.sty, submitted to ApJ Let
Neuroferritinopathy: missense mutation in FTL causing early-onset bilateral pallidal involvement
The authors identified a missense mutation in the FTL gene
(474G>A; A96T) in a 19-year-old man with parkinsonism, ataxia, corticospinal
signs, mild nonprogressive cognitive deficit, and episodic psychosis. This mutation
was also present in his asymptomatic mother and younger brother, who
had abnormally low levels of ferritin in the serum. The patient and his mother
displayed bilateral involvement of the pallidum.Fundação para a Ciência e a Tecnologia/Fundo Europeu de Desenvolvimento Regional (FCT)/(FEDER) - CBO/33485/99
Experimental implementation of a NMR entanglement witness
Entanglement witnesses (EW) allow the detection of entanglement in a quantum
system, from the measurement of some few observables. They do not require the
complete determination of the quantum state, which is regarded as a main
advantage. On this paper it is experimentally analyzed an entanglement witness
recently proposed in the context of Nuclear Magnetic Resonance (NMR)
experiments to test it in some Bell-diagonal states. We also propose some
optimal entanglement witness for Bell-diagonal states. The efficiency of the
two types of EW's are compared to a measure of entanglement with tomographic
cost, the generalized robustness of entanglement. It is used a GRAPE algorithm
to produce an entangled state which is out of the detection region of the EW
for Bell-diagonal states. Upon relaxation, the results show that there is a
region in which both EW fails, whereas the generalized robustness still shows
entanglement, but with the entanglement witness proposed here with a better
performance
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