893 research outputs found
Mid-Infrared diagnostics of metal-rich HII regions from VLT and Spitzer Spectroscopy of Young Massive Stars in W31
We present near-IR VLT/ISAAC and mid-IR Spitzer/IRS spectroscopy of the young
massive cluster in the W31 star-forming region. H-band spectroscopy provides
refined classifications for four cluster members O stars with respect to Blum
et al. In addition, photospheric features are detected in the massive Young
Stellar Object (mYSO) #26. Spectroscopy permits estimates of stellar
temperatures and masses, from which a cluster age of ~0.6 Myr and distance of
3.3 kpc are obtained, in excellent agreement with Blum et al. IRS spectroscopy
reveals mid-infrared fine structure line fluxes of [Ne II-III] and [S III-IV]
for four O stars and five mYSOs. In common with previous studies, stellar
temperatures of individual stars are severely underestimated from the observed
ratios of fine-structure lines, despite the use of contemporary stellar
atmosphere and photoionization models. We construct empirical temperature
calibrations based upon the W31 cluster stars of known spectral type,
supplemented by two inner Milky Way ultracompact (UC) HII regions whose
ionizing star properties are established. Calibrations involving [NeIII]
15.5um/[NeII] 12.8um, [SIV] 10.5um/[NeII] 12.8um or [ArIII] 9.0um/[NeII] 12.8um
have application in deducing the spectral types of early- to mid- O stars for
other inner Milky Way compact and UCHII regions. Finally, evolutionary phases
and timescales for the massive stellar content in W31 are discussed, due to the
presence of numerous young massive stars at different formation phases in a
`coeval' cluster.Comment: 16 pages, 13 figures, accepted for MNRA
Predictors of walking capacity in peripheral arterial disease patients
OBJECTIVE: To estimate walking capacity in intermittent claudication patients through a prediction model based on clinical characteristics and the walking impairment questionnaire.
METHODS: The sample included 133 intermittent claudication patients of both genders aged between 30 and 80 years. Data regarding clinical characteristics, the walking impairment questionnaire and treadmill walking test performance were obtained. Multiple regression modeling was conducted to predict claudication onset distance and total walking distance using clinical characteristics (age, height, mass, body mass index, ankle brachial index lower, gender, history of smoking and co-morbid conditions) and walking impairment questionnaire responses. Comparisons of claudication onset distance and total walking distance measured during treadmill tests and estimated by a regression equation were performed using paired t-tests.
RESULTS: Co-morbid conditions (diabetes and coronary artery disease) and questions related to difficulty in walking short distances (walking indoors - such as around your house and walking 5 blocks) and at low speed (walking 1 block at average speed - usual pace) resulted in the development of new prediction models high significant for claudication onset distance and total walking distance (p0.05) were observed.
CONCLUSION: The current study demonstrated that walking capacity can be adequately estimated based on co-morbid conditions and responses to the walking impairment questionnaire
Effect of band anisotropy on electronic structure of PbS, PbSe, and PbTe quantum dots
We have calculated the electronic structure of spherical PbS, PbSe, and PbTe quantum dots using a four-band envelope-function formalism that accounts for band anisotropy. By comparing our results with an analytical calculation that assumes a spherical approximation of the (k) over right arrow.(p) over right arrow Hamiltonian, we show that the effects of band anisotropy are more pronounced for the excited states and increase with the confinement. We also show how the same technique can be applied to ellipsoidal quantum dots.62117357736
QUANTUM SIZE EFFECTS ON CDTEXS1-X SEMICONDUCTOR-DOPED GLASS
We present experimental evidences of quantum confinement in borosilicate glasses with a new microcrystallite CdTexS1-x semiconductor. The microcrystallite sizes are controlled by the heat-treatment time and temperature. Transmission electron microscopy measurements show the microcrystallites average diameters near 55 angstrom for the sample treated for the longest time. We observe a red shift from 570 to 640 nm in the absorption and photoluminescence spectra as the size increases. These shifts agree with the expected quantum-confined energies, varying from 0.80 to 0.60 eV. The absorption spectra also show a second feature which can be assigned to the second quantum-confined transition.59212715271
Seismic analysis of a viaduct in Mexico considering soil-structure interaction
De modo a prevenir e minimizar os riscos s?smicos das estruturas, existe a necessidade crescente de compreender os sismos e a forma como estes afetam as constru??es. Essa necessidade aumenta
quando se estudam projetos em zonas de grande sismicidade, como ? o caso do M?xico. Assim, o presente estudo, elaborado em parceria com o GEG ? Gabinete de Estruturas e Geotecnia, pretende analisar as v?rias abordagens de c?lculo inerentes ao dimensionamento e avalia??o de estruturas sismo-resistentes, sendo o principal objetivo compar?-las e avaliar a adequabilidade de cada uma delas ao caso de estudo. S?o essas abordagens a an?lise din?mica linear ou espetral, a an?lise est?tica n?o-linear, tamb?m designada an?lise pushover, e a an?lise din?mica n?o linear ou time-history. Simultaneamente ser? levado a cabo um estudo detalhado ao n?vel dos par?metros que afetam o amortecimento proveniente da intera??o solo-estrutura.6612-034D-AE05 | PEDRO DA SILVA DELGADOinfo:eu-repo/semantics/publishedVersio
Size effects on the phonon spectra of quantum dots in CdTe-doped glasses
We studied the confinement effects on the phonon Spectra of CdTe quantum dots by means of resonant Raman scattering measurements. The spectra show clearly longitudinal optical phonons, surface phonons and some of their overtone combinations. We show that the scattering due to surface phonons increases as the quantum dot size decreases. The results are obtained by tuning the laser excitation energy to resonance for quantum dots of different sizes inside the broad size distribution in CdTe-doped glasses. (C) 1996 American Institute of Physics.69335735
Structure of PbTe(SiO2)/SiO2 multilayers deposited on Si(111)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO2, named as PbTe(SiO2), between homogeneous layers of amorphous SiO2 deposited on a single-crystal Si( 111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO2)/SiO2 multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers. (C) 2010 International Union of Crystallography Printed in Singapore - all rights reserved433385393Brazilian Synchrotron Light Laboratory (LNLS)PRONEXConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
Preparation and characterisation of high refractive index PhO-TiO2-TeO2 glass systems
We describe the predaration and characterisation of high refractive index PbO-TiO2-TeO2 glass systems. Highly homogeneous glasses were obtained by agitating the oxide mixture during the melting process in an alumina crucible. The characterisation was performed by X-ray diffraction, density, dilatometry, Raman scattering, light absorption and linear refractive index measurements. The results show a change in the glass structure as the PbO content increases: the TeO4 trigonal bipyramids characteristic of TeO4 glasses transform into TeO, trigonal pyramids. However, the measured refractive indices are almost independent of the glass composition. We show that third-order non-linear optical susceptibilities calculated from the measured refractive indices using Lines' theoretical model are also independent of the glass composition.6111811181
Raman, hyper-Raman, hyper-Rayleigh, two-photon luminescence and morphology-dependent resonance modes in a single optical tweezers system
We present a setup of optical tweezers combined with linear and nonlinear microspectroscopies that enhances the capabilities of capture and analysis of both techniques. We can use either a continuous-wave (cw) Ti:sapphire laser for Raman measurements or a pulsed femtosecond Ti:sapphire laser that permitted the observation of nonlinear results such as hyper-Raman, hyper-Rayleigh, and two-photon luminescence. Only the high peak intensity of the femtosecond laser allows the observation of all these nonlinear spectroscopies. The sensitivity of our system also permitted the observation of morphology-dependent resonance (MDR) modes of a single stained trapped microsphere of 6 mu m. The possibility of performing spectroscopy in a living microorganism optically trapped in any desired neighborhood would mean that one can dynamically observe the chemical reactions and/or mechanical properties changing in real time.721
Evaluation of standard API casing connections and parametric API buttress improvement by finite element analysis.
Threaded and coupled connections generally present a non-uniform stress distribution, which is
related to the higher stiffness of the box when compared to the pin. The non-uniform stress distribution
can contribute to fatigue cracks and other failure modes in high pressure oil wells. An API 5CT P110
steel obtained from a seamless pipe was mechanically characterized. FEA models were carried out
to investigate and compare two API casing connections under make-up torque and tensile efforts. A
parametric study was performed using numerical models to determine the influence of some geometric
features on the behavior of the API Buttress threaded connection. The API Buttress connection supported
higher tensile loads than the API Short Round, however both standard connections showed high stress
concentration in the last engaged thread and a non-uniform stress distribution. The manufacturing
of grooves at the first and the last engaged threads proved to be an efficient way to reduce the stress
concentration of Buttress casing connection and could be an alternative to the development of new
products
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