804 research outputs found
Cholesterol concentration in bovine blood plasma relation with growth rate alkaline phosphatase activity and thyroxine degradation
International audienc
Transmission spectroscopy of the sodium 'D' doublet in WASP-17b with the VLT
The detection of increased sodium absorption during primary transit implies
the presence of an atmosphere around an extrasolar planet, and enables us to
infer the structure of this atmosphere. Sodium has only been detected in the
atmospheres of two planets to date - HD189733b and HD209458b. WASP-17b is the
least dense planet currently known. It has a radius approximately twice that of
Jupiter and orbits an F6-type star. The transit signal is expected to be about
five times larger than that observed in HD209458b. We obtained 24 spectra with
the GIRAFFE spectrograph on the VLT, eight during transit. The integrated flux
in the sodium doublet at wavelengths 5889.95 and 5895.92 {\AA} was measured at
bandwidths 0.75, 1.5, 3.0, 4.0, 5.0, and 6.0 {\AA}. We find a transit depth of
0.55 \pm 0.13 per cent at 1.5 {\AA}. This suggests that, like HD209458b,
WASP-17b has an atmosphere depleted in sodium compared to models for a
cloud-free atmosphere with solar sodium abundance. We observe a sharp cut-off
in sodium absorption between 3.0 and 4.0 {\AA} which may indicate a layer of
clouds high in the atmosphere.Comment: Amended for typographic conventions following publicatio
Silica-based highly nonlinear fibers with a high SBS threshold
Results on suppression of stimulated Brillouin scattering in highly nonlinear fibers with germanium-doped core as well as aluminum-doped core based on spooling the fiber with a linear strain gradient is presented
Development of new all-optical signal regeneration technique
All-optical signal regeneration have been the active research area since last decade due to evolution of nonlinear optical signal processing. Existing all-optical signal regeneration techniques are agitated in producing low Bit Error Rate (BER) of 10-10 at below than -10 dBm power received. In this paper, a new all-optical signal regeneration technique is developed by using phase sensitive amplification and designed optical phase locked signal mechanism. The developed all-optical signal regeneration technique is tested for different 10 Gb/s Differential Phase Shift Keying degraded signals. It is determined that the designed all-optical signal regeneration technique is able to provide signal regeneration with noise mitigation for degraded signals. It is analyzed that overall, for all degraded test signals, average BER of 10-13 is achieved at received power of -14 dBm. The designed technique will be helpful to enhance the performance of existing signal regeneration systems in the presence of severe noise by providing minimum BER at low received power
Who I Am: The Meaning of Early Adolescents’ Most Valued Activities and Relationships, and Implications for Self-Concept Research
Self-concept research in early adolescence typically measures young people’s self-perceptions of competence in specific, adult-defined domains. However, studies have rarely explored young people’s own views of valued self-concept factors and their meanings. For two major self domains, the active and the social self, this mixed-methods study identified factors valued most by 526 young people from socioeconomically diverse backgrounds in Ireland (10-12 years), and explored the meanings associated with these in a stratified subsample (n = 99). Findings indicate that self-concept scales for early adolescence omit active and social self factors and meanings valued by young people, raising questions about content validity of scales in these domains. Findings also suggest scales may under-represent girls’ active and social selves; focus too much on some school-based competencies; and, in omitting intrinsically salient self domains and meanings, may focus more on contingent (extrinsic) rather than true (intrinsic) self-esteem
Optical spectroscopic variability of Herbig Ae/Be stars
We analysed 337 multi-epoch optical spectra of 38 Herbig Ae/Be (HAeBe) stars
to gain insights into the variability behaviour of the circumstellar (CS)
atomic gas. Equivalent widths (EWs) and line fluxes of the Halpha, [OI]6300,
HeI5876 and NaID lines were obtained for each spectrum; the Halpha line width
at 10% of peak intensity (W10) and profile shapes were also measured and
classified. The mean line strengths and relative variabilities were quantified
for each star. Simultaneous optical photometry was used to estimate the line
fluxes.
We present a homogeneous spectroscopic database of HAeBe stars. The lines are
variable in practically all stars and timescales, although 30 % of the objects
show a constant EW in [OI]6300, which is also the only line that shows no
variability on timescales of hours. The HeI5876 and NaID EW relative
variabilities are typically the largest, followed by those in [OI]6300 and
Halpha. The EW changes can be larger than one order of magnitude for the
HeI5876 line, and up to a factor 4 for Halpha. The [OI]6300 and Halpha EW
relative variabilities are correlated for most stars in the sample. The Halpha
mean EW and W10 are uncorrelated, as are their relative variabilities. The
Halpha profile changes in 70 % of the objects. The massive stars in the sample
usually show more stable Halpha profiles with blueshifted self-absorptions and
less variable 10% widths.
Our data suggest multiple causes for the different line variations, but the
[OI]6300 and Halpha variability must share a similar origin in many objects.
The physical mechanism responsible for the Halpha line broadening does not
depend on the amount of emission; unlike in lower-mass stars, physical
properties based on the Halpha luminosity and W10 would significantly differ.
Our results provide additional support to previous works that reported
different physical mechanisms in Herbig Ae and Herbig Be stars.Comment: 10 pages, 5 figures, 2 appendixe
Probing For New Physics and Detecting non linear vacuum QED effects using gravitational wave interferometer antennas
Low energy non linear QED effects in vacuum have been predicted since 1936
and have been subject of research for many decades. Two main schemes have been
proposed for such a 'first' detection: measurements of ellipticity acquired by
a linearly polarized beam of light passing through a magnetic field and direct
light-light scattering. The study of the propagation of light through an
external field can also be used to probe for new physics such as the existence
of axion-like particles and millicharged particles. Their existence in nature
would cause the index of refraction of vacuum to be different from unity in the
presence of an external field and dependent of the polarization direction of
the light propagating. The major achievement of reaching the project
sensitivities in gravitational wave interferometers such as LIGO an VIRGO has
opened the possibility of using such instruments for the detection of QED
corrections in electrodynamics and for probing new physics at very low
energies. In this paper we discuss the difference between direct birefringence
measurements and index of refraction measurements. We propose an almost
parasitic implementation of an external magnetic field along the arms of the
VIRGO interferometer and discuss the advantage of this choice in comparison to
a previously proposed configuration based on shorter prototype interferometers
which we believe is inadequate. Considering the design sensitivity in the
strain, for the near future VIRGO+ interferometer, of in the range 40 Hz Hz leads to a variable
dipole magnet configuration at a frequency above 20 Hz such that Tm/ for a `first' vacuum non linear QED detection
A photometric and spectroscopic study of the new dwarf spheroidal galaxy in Hercules
Our aim is to provide as clean and as complete a sample as possible of red
giant branch stars that are members of the Hercules dSph galaxy. With this
sample we explore the velocity dispersion and the metallicity of the system.
Stromgren photometry and multi-fibre spectroscopy are combined to provide
information about the evolutionary state of the stars (via the Stromgren c_1
index) and their radial velocities. Based on this information we have selected
a clean sample of red giant branch stars, and show that foreground
contamination by Milky Way dwarf stars can greatly distort the results. Our
final sample consists of 28 red giant branch stars in the Hercules dSph galaxy.
Based on these stars we find a mean photometric metallicity of -2.35 dex which
is consistent with previous studies. We find evidence for an abundance spread.
Using those stars for which we have determined radial velocities we find a
systemic velocity of 45.2 km/s with a dispersion of 3.72 km/s, this is lower
than values found in the literature. Furthermore we identify the horizontal
branch and estimate the mean magnitude of the horizontal branch of the Hercules
dSph galaxy to be V_0=21.17, which corresponds to a distance of 147 kpc. We
have shown that a proper cleaning of the sample results in a smaller value for
the velocity dispersion of the system. This has implications for galaxy
properties derived from such velocity dispersions.Comment: 24 pages, 28 figure
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