82 research outputs found
Structural and optical properties of Zn0.9 Mn0.1 O/ZnO core-shell nanowires designed by pulsed laser deposition
Partilhar documento na coleção da comunidade Laboratório Associado I3NCore-shell ZnO/ZnMnO nanowires on a-Al2O3 and GaN (buffer layer)/Si (111) substrates were fabricated by pulsed laser deposition using a Au catalyst. Two ZnO targets with a Mn content of 10% were sintered at 1150 and 550 °C in order to achieve the domination in them of paramagnetic MnO2 and ferromagnetic Mn2O3 phases, respectively. Cluster mechanism of laser ablation as a source of possible incorporation of secondary phases to the wire shell is discussed. Raman spectroscopy under excitation by an Ar+ laser revealed a broad peak related to the Mn-induced disorder and a redshift in the A1-LO phonon. Resonant Raman measurements revealed an increase in the multiphonon scattering caused by disorder in ZnO upon doping by Mn. Besides the UV emission, a vibronic green emission band assisted by a ∼ 71 meV LO phonon is also observed in the photoluminescence spectra. Core-shell structures with smooth shells show a high exciton to green band intensity ratio ( ∼ 10) even at room temperature.
© 2009 American Institute of PhysicsSANDiE Network of Excellence of the EUFCT-PTDC/FIS/72843/200
Ácido ascórbico, betalaínas, e fenóis totais em ecótipos de Opuntia spp.
O género Opuntia spp. pertence à família Cactaceae, sendo a espécie Opuntia ficus-indica (OFI) a que tem maior importância económica. Em frutos de vinte populações provenientes de quatro espécies do género Opuntia spp. (OFI, O. robusta, O. dillenii and O. elata), com origem em Portugal, foram estudadas as características cromáticas, a acidez, o pH, o teor em sólidos solúveis totais (SST) e ainda os teores em ácido ascórbico (AA), betalaínas e fenóis totais (FT). As cultivares Italianas de OFI ‘Bianca’, ‘Gialla’ e ‘Rossa’ foram incluídas como termo de comparação. Os valores mais elevados de acidez foram registados nos frutos de O. dillenii e O. elata e os menores em OFI. Os frutos de O. dillenii apresentaram os teores mais elevados de betalaínas e FT, ao passo que as concentrações mais elevadas de AA foram registadas nos frutos de O. elata. Os ecótipos de OFI mostraram variação na concentração de compostos bioativos. Em OFI, a cv. de polpa vermelha ‘Rossa’ é a que apresenta maior concentração de betalaínas, seguida pelos ecótipos de polpa laranja e, finalmente, os ecótipos de polpa branca. Os valores mais elevados de FT foram encontrados nos ecótipos de polpa branca. O género Opuntia spp. é uma fonte de compostos bioativos, pelo que o consumo dos seus frutos representa uma boa forma de ingestão de compostos de elevado valor nutricional.info:eu-repo/semantics/publishedVersio
Ácido ascórbico, betalaínas, e fenóis totais em ecótipos de Opuntia spp.
O género Opuntia spp. pertence à família Cactaceae, sendo a espécie Opuntia ficus-indica (OFI) a que tem maior importância económica. Em frutos de vinte populações provenientes de quatro espécies do género Opuntia spp. (OFI, O. robusta, O. dillenii and O. elata), com origem em Portugal, foram estudadas as características cromáticas, a acidez, o pH, o teor em sólidos solúveis totais (SST) e ainda os teores em ácido ascórbico (AA), betalaínas e fenóis totais (FT). As cultivares Italianas de OFI ‘Bianca’, ‘Gialla’ e ‘Rossa’ foram incluídas como termo de comparação. Os valores mais elevados de acidez foram registados nos frutos de O. dillenii e O. elata e os menores em OFI. Os frutos de O. dillenii apresentaram os teores mais elevados de betalaínas e FT, ao passo que as concentrações mais elevadas de AA foram registadas nos frutos de O. elata. Os ecótipos de OFI mostraram variação na concentração de compostos bioativos. Em OFI, a cv. de polpa vermelha ‘Rossa’ é a que apresenta maior concentração de betalaínas, seguida pelos ecótipos de polpa laranja e, finalmente, os ecótipos de polpa branca. Os valores mais elevados de FT foram encontrados nos ecótipos de polpa branca. O género Opuntia spp. é uma fonte de compostos bioativos, pelo que o consumo dos seus frutos representa uma boa forma de ingestão de compostos de elevado valor nutricional
Characterization of the Positivity of the Density Matrix in Terms of the Coherence Vector Representation
A parameterization of the density operator, a coherence vector
representation, which uses a basis of orthogonal, traceless, Hermitian matrices
is discussed. Using this parameterization we find the region of permissible
vectors which represent a density operator. The inequalities which specify the
region are shown to involve the Casimir invariants of the group. In particular
cases, this allows the determination of degeneracies in the spectrum of the
operator. The identification of the Casimir invariants also provides a method
of constructing quantities which are invariant under {\it local} unitary
operations. Several examples are given which illustrate the constraints
provided by the positivity requirements and the utility of the coherence vector
parameterization.Comment: significantly rewritten and submitted for publicatio
MRI features of perifibrinous deposits in the placenta due to COVID-19
COVID-19 has been linked to pregnancy complications and loss (1). Infection during pregnancy is usually mild (2). The risk is highest in the third trimester with increased hospital admission rates and maternal and fetal compromise (3). Post-COVID placentitis is uncommon but the effect on the placenta and the fetus is extensive (4). We present a case correlating clinical, imaging, and pathological findings. Case Report: A 29-year-old para 2 gravida 1, with a normal fetal anomaly scan at 22 weeks gestational age (GA) contracted COVID at 24 weeks gestation. Fully recovered but reported reduced fetal movements at 27 weeks and 1 day. Imaging: US scan showed bright echoes within the brain, small lungs, and oligohydramnios. MRI showed abnormal brain signals, small lungs, and oligohydramnios but also a very abnormal placenta. Reduced and heterogeneous T2 signal and a marked reduction in the DWI signal intensity. The placental size was markedly reduced (volume 785.6 cm3 expected for GA is 5604.8–5952.4 cm3. The surface area of attachment was 3220 mm2, expected 22180.4–29293.2 mm2). Pathology: The placenta was small (fifth centile) with massive perivillous fibrin deposition and multifocal chronic deciduitis. Histology revealed placental chorionic villi showing diffuse sclerotic changes surrounded by perivillous fibrin deposition in the intervillous space. The basal plate revealed multifocal chronic deciduitis. When imaging the fetus, it is important to examine the placenta and correlate any abnormalities. The placenta is a forgotten organ and should be routinely included and assessed to allow the detection of important abnormalities
Microwave dielectric permittivity and photoluminescence of Eu 2O3 doped laser heated pedestal growth Ta 2O5 fibers
Partilhar documento na coleção da comunidade Laboratório Associado I3NWe report the microwave dielectric properties and photoluminescence of undoped and europium
oxide doped Ta2O5 fibers, grown by laser heated pedestal growth technique. The effects of Eu2O3
doping 1–3 mol % on the structural, optical, and dielectric properties were investigated. At a
frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for Eu2O3
doped Ta2O5 samples it increases, reaching up to 36 for the highest doping concentration.
Nevertheless, the dielectric losses maintain a very low value. For this wide band gap oxide, Eu3+
optical activation was achieved and the emission is observed up to room temperature. Thus, the
transparency and high permittivity make this material promising for electronic devices and
microwave applications. © 2008 American Institute of Physics.FCT-PTDC/FIS/66262/06FCT-PTDC/CTM/66195/200
Quantum cloning machines for equatorial qubits
Quantum cloning machines for equatorial qubits are studied. For the case of 1
to 2 phase-covariant quantum cloning machine, we present the networks
consisting of quantum gates to realize the quantum cloning transformations. The
copied equatorial qubits are shown to be separable by using Peres-Horodecki
criterion. The optimal 1 to M phase-covariant quantum cloning transformations
are given.Comment: Revtex, 9 page
An alternative approach to the construction of Schur-Weyl transform
We propose an alternative approach for the construction of the unitary matrix
which performs generalized unitary rotations of the system consisting of
independent identical subsystems (for example spin system). This matrix, when
applied to the system, results in a change of degrees of freedom, uncovering
the information hidden in non-local degrees of freedom. This information can be
used, inter alia, to study the structure of entangled states, their
classification and may be useful for construction of quantum algorithms.Comment: 6 page
Structural and optical properties on thulium-doped LHPG-grown Ta2O5 fibres
Structural, spectroscopic and dielectric properties of thulium-doped laser-heated pedestal Ta2O5 as-grown fibres were studied. Undoped samples grow preferentially with a single crystalline monoclinic structure. The fibre with the lowest thulium content (0.1 at%) also shows predominantly a monoclinic phase and no intra-4f12 Tm3+ recombination was observed. For sample with the highest thulium amount (1.0 at%), the appearance of a dominant triclinic phase as well as intraionic optical activation was observed. The dependence of photoluminescence on excitation energy allows identification of different site locations of Tm3+ ions in the lattice. The absence of recombination between the first and the ground-state multiplets as well as the temperature dependence of the observed transitions was justified by an efficient energy transfer between the Tm3+ ions. Microwave dielectric properties were investigated using the small perturbation theory. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for thulium-doped Ta2O5 samples it decreases to 18 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value.FCT - PTDC/CTM/66195/2006FCT - PTDC/FIS/66262/2006FCT - PTDC/FIS/72843/200
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