545 research outputs found
The WFCAM Multi-wavelength Variable Star Catalog
Stellar variability in the near-infrared (NIR) remains largely unexplored.
The exploitation of public science archives with data-mining methods offers a
perspective for the time-domain exploration of the NIR sky. We perform a
comprehensive search for stellar variability using the optical-NIR multi-band
photometric data in the public Calibration Database of the WFCAM Science
Archive (WSA), with the aim of contributing to the general census of variable
stars, and to extend the current scarce inventory of accurate NIR light curves
for a number of variable star classes. We introduce new variability indices
designed for multi-band data with correlated sampling, and apply them for
pre-selecting variable star candidates, i.e., light curves that are dominated
by correlated variations, from noise-dominated ones. Pre-selection criteria are
established by robust numerical tests for evaluating the response of
variability indices to colored noise characteristic to the data. We find 275
periodic variable stars and an additional 44 objects with suspected variability
with uncertain periods or apparently aperiodic variation. Only 44 of these
objects had been previously known, including 11 RR~Lyrae stars in the outskirts
of the globular cluster M3 (NGC~5272). We provide a preliminary classification
of the new variable stars that have well-measured light curves, but the
variability types of a large number of objects remain ambiguous. We classify
most of the new variables as contact binary stars, but we also find several
pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are
likely Cepheids. We also identify 32 highly reddened variable objects close to
previously known dark nebulae, suggesting that these are embedded young stellar
objects. We publish our results and all light-curve data as the WFCAM Variable
Star Catalog.Comment: 21 pages, 11 figure
Integrin-mediated RON growth factor receptor phosphorylation requires tyrosine kinase activity of both the receptor and c-Src.
Rodrigo Terra Cambará: um herói muito problemático e suas mediações
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Programa de Pós-Graduação em Letra
Atomic force microscopy techniques for nanomechanical characterization : a polymer case study
Atomic force microscopy (AFM) is a versatile tool to perform mechanical
characterization of surface samples at the nanoscale. In this work, we review
two of such methods, namely contact resonance AFM (CR-AFM) and torsional
harmonics AFM (TH-AFM). First, such techniques are illustrated and their
applicability on materials with elastic moduli in different ranges are discussed,
together with their main advantages and limitations. Then, a case
study is presented in which we report the mechanical characterization using
both CR-AFM and TH-AFM of polyaniline and polyaniniline doped with
nanodiamond particles tablets prepared by a pressing process. We determined
the indentation modulus values of their surfaces, which were found in fairly
good agreement, thus demonstrating the accuracy of the techniques. Finally,
the determined surface elastic moduli have been compared with the bulk ones
measured through standard indentation testing.
INTRODUCTION
In the field of nanotechnology, the development of
innovative and nondestructive characterization
techniques plays a crucial role. Indeed, the characterization
of nanostructured hybrid materials (e.g.,
thin films and nanocomposites) and devices requires
the capability of acquiring maps of the local mechanical
properties at the nanoscale. Nanoindentation
is the most common method for determining the
mechanical properties of thin films. However, its
applicability is strictly limited by the thickness of
the sample. Furthermore, its poor spatial resolution
does not allow the reconstruction of an accurate
distribution of the sample surface mechanical
properties. For this reason, alternative methods,
based on atomic force microscopy (AFM), have been
developed. By exploiting the high resolution of the
AFM, maps of the surface mechanical properties
(i.e., indentation modulus) can be achieved. Among
these techniques, AFM nanoindentation1 is the
simplest method used to evaluate the local mechanical
properties o
Band edge oscillator strength of colloidal CdSe CdS dot in rods comparison of absorption and time resolved fluorescence spectroscopy
We studied the oscillator strength f(gap) of the band gap transition in heteronanocrystals (hNCs) with a spherical CdSe core embedded in an elongated CdS shell. A comparison with fgap of core-only CdSe NCs confirmed a reduction of the electron-hole overlap in hNCs with a band gap larger than 2.05 eV or smaller than 1.98 eV. However, the decrease in fgap is limited to about 50% when compared to CdSe NCs, suggesting that residual confinement still localizes the electron near the core. We correlated fgap with the radiative lifetime obtained from multiexponential photoluminescence (PL) decay traces. The different components were attributed to radiative decay, or deep and shallow carrier trapping, respectively, using the PL quantum efficiency (QE) as a guideline. Our data highlight the challenges associated when extracting the radiative decay, and demonstrate the added value of absorption spectroscopy to obtain the band-edge oscillator strength and the associated radiative recombination rate in colloidal hNCs
Analysis of a new homozygous deletion in the tumor suppressor region at 3p12.3 reveals two novel intronic non-coding RNA genes
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