15,309 research outputs found
The Discovery of Sgr A*
The compact radio source Sgr A* is associated with a 3.6 million black hole
at the center of the Milky Way. The radio source was discovered in February
1974 by Bruce Balick and Robert L.Brown. The National Radio Astronomy
Observatory's Green Bank 35 km radio link interferometer was used. We discuss
other observations in the years 1965-1985 as well as early VLBI observations.
The name Sgr A* was used for the first time in 1982 by Robert L.Brown and has
become the accepted name in the intervening years.Comment: 8 pages,2 figures. Conference proceedings: "The central 300 parsecs
of the Milky Way", editors A.Cotera, H.Falcke, T.R.Geballe, S.Markof
Light Propagation in Nonlinear Waveguide and Classical Two-Dimensional Oscillator
The quantum optical problem of the propagation of electromagnetic waves in a
nonlinear waveguide is related to the solutions of the classical nonstationary
harmonic oscillator using the method of linear integrals of motion [ Malkin
et.al., Phys Rev. 2D (1970) p.1371 ]. An explicit solution of the classical
oscillator with a varying frequency, corresponding to the light propagation in
an anisotropic waveguide is obtained using the expressions for the quantum
field fluctuations. Substitutions have been found which allow to establish
connections of the linear and quadratic invariants of Malkin et.al. to several
types of invariants of quadratic systems, considered in later papers. These
substitutions give the opportunity to relate the corresponding quantum problem
to that of the classical two-dimensional nonstationary oscillator, which is
physically more informative.Comment: 14 pages, including one Table, 29 bibliographic references; E-mail:
[email protected]
Effects of the Spin-Orbit and Tensor Interactions on the and Excitations in Light Nuclei
The effects of varying the spin-orbit and tensor components of a realistic
interaction on excitation rates and are studied on nuclei in the
and shells. Not only the total but also the spin and orbital
parts separately are studied. The single-particle energies are first calculated
with the same interaction that is used between the valence nucleons. Later this
stringent condition is relaxed somewhat and the level is raised relative
to . For nuclei up to , much better results i.e stronger
rates are obtained by increasing the strength of the spin-orbit interaction
relative to the free value. This is probably also true for , but
presents some difficulties. The effects of weakening the tensor
interaction are also studied. On a more subtle level, the optimum spin-orbit
interaction in the lower half of the shell, as far as excitations
are concerned, is substantially larger than the difference
in . A larger spin-orbit splitting
is also needed to destroy the triaxiality in . Also studied are how
much orbital and spin strength lies in an observable region and how much
is buried in the grass at higher energies. It is noted that for many nuclei the
sum is very close to , indicating
that the summed cross terms are very small.Comment: 39 pages, revtex 3.
Aspects of Relativistic Sum Rules
The status of our understanding of relativistic sum rules is reviewed. The
recent development of new theoretical methods for the evaluation of these sum
rules offers hope for further advances in this challenging field. These new
techniques are described, along with a discussion of the source of difficulties
inherent in such relativistic calculations. A connection is pointed out between
certain sum rules for atomic interactions with charged particles and those for
interactions with photons.Comment: 32 pages, accepted for publication in Advances in Quantum Chemistr
Design and fabrication of SiO2/TiO2 and MgO/TiO2 based high selective optical filters for diffuse reflectance and fluorescence signals extraction
This paper presents the design, optimization and fabrication of 16 MgO/TiO2 and SiO2/TiO2 based high selective narrow bandpass optical filters. Their performance to extract diffuse reflectance and fluorescence
signals from gastrointestinal tissue phantoms was successfully evaluated.
The obtained results prove their feasibility to correctly extract those spectroscopic signals, through a Spearman’s rank correlation test (Spearman’s correlation coefficient higher than 0.981) performed between
the original spectra and the ones obtained using those 16 fabricated optical filters. These results are an important step for the implementation of a miniaturized, low-cost and minimal invasive microsystem that could help in the detection of gastrointestinal dysplasia.This work is funded by FEDER funds through the “Eixo I do Programa Operacional Fatores
de Competitividade” (POFC) QREN, project reference COMPETE: FCOMP-01-0124-
FEDER-020241 and by FCT—Fundação para a Ciência e a Tecnologia, project reference
PTDC/EBB-EBI/120334/2010. The authors thank to the PEst-C/FIS/UI0607/2013 for the use
of spectroscopic equipment. The authors also thank to V. Pinto from CMEMS-UMinho for
the support during the profilometry measurements. S.P. thanks the FCT for the
SFRH/BD/87605/2012 PhD grant
Plumes in stellar convection zones
All numerical simulations of compressible convection reveal the presence of
strong downwards directed flows. Thanks to helioseismology, such plumes have
now been detected also at the top of the solar convection zone, on super-
granular scales. Their properties may be crudely described by adopting Taylor's
turbulent entrainment hypothesis, whose validity is well established under
various conditions. Using this model, one finds that the strong density
stratification does not prevent the plumes from traversing the whole convection
zone, and that they carry upwards a net energy flux (Rieutord & Zahn 1995).
They penetrate to some extent in the adjacent stable region, where they
establish a nearly adiabatic stratification. These plumes have a strong impact
on the dynamics of stellar convection zones, and they play probably a key role
in the dynamo mechanism.Comment: Proceedings of the 14th Florida Workshop in Nonlinear Astronomy and
Physics, "Astrophysical Turbulence and Convection", Eds. J.R. Buchler and H.
Kandrup, to appear in the Annals of the New York Academy of Sciences (15
pages, 3 figures
Higher order antibunching in intermediate states
Since the introduction of binomial state as an intermediate state, different
intermediate states have been proposed. Different nonclassical effects have
also been reported in these intermediate states. But till now higher order
antibunching or higher order subpoissonian photon statistics is predicted only
in one type of intermediate state, namely shadowed negative binomial state.
Recently we have shown the existence of higher order antibunching in some
simple nonlinear optical processes to establish that higher order antibunching
is not a rare phenomenon (J. Phys. B 39 (2006) 1137). To establish our earlier
claim further, here we have shown that the higher order antibunching can be
seen in different intermediate states, such as binomial state, reciprocal
binomial state, hypergeometric state, generalized binomial state, negative
binomial state and photon added coherent state. We have studied the possibility
of observing the higher order subpoissonian photon statistics in different
limits of intermediate states. The effect of different control parameters have
also been studied in this connection and it has been shown that the depth of
nonclassicality can be tuned by controlling various physical parameters.Comment: 12 Pages LaTeX 2e, 11 figure
Effect of zinc intake on serum/plasma zinc status in infants: A meta-analysis
A systematic review and meta-analysis of available RCTs was conducted to evaluate the effect of zinc (Zn) intake on serum/plasma Zn status in infants. Out of 5500 studies identified through electronic searches and reference lists, 9 RCTs were selected after applying the exclusion/inclusion criteria. The influence of zinc intake on serum/plasma Zn concentration was considered in the overall meta-analysis. Other variables were also taken into account as possible effect modifiers: doses of zinc intake, intervention duration, nutritional status and risk of bias. From each selected study, final measures of serum/plasma Zn were assessed.
RESULTS: The pooled β of status was 0.09 (95%CI 0.06 to 0.12). However, a substantial heterogeneity was present in the analyses (I2=95%; p=0.00001). When we performed a meta-regression, the effect of Zn intake on serum/plasma Zn status changed depending on the duration of the intervention, the dose of supplementation and the nutritional situation (p ANCOVA= 0.005; 20 weeks). A positive effect was seen also when doses ranged from 8.1 to 12 mg/day. In all cases, the pooled β showed high evidence of heterogeneity.
CONCLUSION: Zinc supplementation increases serum/plasma Zn status in infants, although high evidence of heterogeneity was found. Further standardized research is urgently needed to reach evidence-based conclusions to clarify the role of zinc supplementation upon infant serum/plasma Zn status, particularly in Europe
- …