196 research outputs found
Upper limits on neutrino masses from the 2dFGRS and WMAP: the role of priors
Solar, atmospheric, and reactor neutrino experiments have confirmed neutrino
oscillations, implying that neutrinos have non-zero mass, but without pinning
down their absolute masses. While it is established that the effect of
neutrinos on the evolution of cosmic structure is small, the upper limits
derived from large-scale structure data could help significantly to constrain
the absolute scale of the neutrino masses. In a recent paper the 2dF Galaxy
Redshift Survey (2dFGRS) team provided an upper limit m_nu,tot < 2.2 eV, i.e.
approximately 0.7 eV for each of the three neutrino flavours, or phrased in
terms of their contributioin to the matter density, Omega_nu/Omega_m < 0.16.
Here we discuss this analysis in greater detail, considering issues of assumed
'priors' like the matter density Omega_m and the bias of the galaxy
distribution with respect the dark matter distribution. As the suppression of
the power spectrum depends on the ratio Omega_nu/Omega_m, we find that the
out-of- fashion Mixed Dark Matter Model, with Omega_nu=0.2, Omega_m=1 and no
cosmological constant, fits the 2dFGRS power spectrum and the CMB data
reasonably well, but only for a Hubble constant H_0<50 km/s/Mpc. As a
consequence, excluding low values of the Hubble constant, e.g. with the HST Key
Project is important in order to get a strong constraint on the neutrino
masses. We also comment on the improved limit by the WMAP team, and point out
that the main neutrino signature comes from the 2dFGRS and the Lyman alpha
forest.Comment: 24 pages, 12 figures Minor changes to matched version published in
JCA
Einstein Probe - a small mission to monitor and explore the dynamic X-ray Universe
Einstein Probe is a small mission dedicated to time-domain high-energy
astrophysics. Its primary goals are to discover high-energy transients and to
monitor variable objects in the keV X-rays, at higher sensitivity by
one order of magnitude than those of the ones currently in orbit. Its
wide-field imaging capability, featuring a large instantaneous field-of-view
(, sr), is achieved by using established
technology of micro-pore (MPO) lobster-eye optics, thereby offering
unprecedentedly high sensitivity and large Grasp. To complement this powerful
monitoring ability, it also carries a narrow-field, sensitive follow-up X-ray
telescope based on the same MPO technology to perform follow-up observations of
newly-discovered transients. Public transient alerts will be downlinked
rapidly, so as to trigger multi-wavelength follow-up observations from the
world-wide community. Over three of its 97-minute orbits almost the entire
night sky will be sampled, with cadences ranging from 5 to 25 times per day.
The scientific objectives of the mission are: to discover otherwise quiescent
black holes over all astrophysical mass scales by detecting their rare X-ray
transient flares, particularly tidal disruption of stars by massive black holes
at galactic centers; to detect and precisely locate the electromagnetic sources
of gravitational-wave transients; to carry out systematic surveys of X-ray
transients and characterize the variability of X-ray sources. Einstein Probe
has been selected as a candidate mission of priority (no further selection
needed) in the Space Science Programme of the Chinese Academy of Sciences,
aiming for launch around 2020.Comment: accepted to publish in PoS, Proceedings of "Swift: 10 Years of
Discovery" (Proceedings of Science; ed. by P. Caraveo, P. D'Avanzo, N.
Gehrels and G. Tagliaferri). Minor changes in text, references update
Characterization of small planets with Kepler and HARPS-N
A. S. Bonomo, L. Malavolta, and X. Dumusque acknowledge fundings from the European Union Seventh Framework Programme (FP7/2007-2013) under agreement No. 313014 “Measuring ETAEARTH: characterization of terrestrial planetary systems with Kepler, HARPS-N, and Gaia” [PI: Dr. Alessandro Sozzetti].The high-accuracy and high-precision HARPS-N spectrograph has been installed at the italian Telescopio Nazionale Galileo in La Palma approximately two years and a half ago. Eighty nights per year of Guaranteed Time of Observation are mostly dedicated to the radial-velocity (RV) follow up of Kepler small-size planetary candidates to establish their nature and to determine accurately their masses. We report on recent results of this ongoing RV campaign, including the recent characterization of the planetary system Kepler-101.Publisher PD
Understanding the core density profile in TCV H-mode plasmas
Results from a database analysis of H-mode electron density profiles on the
Tokamak \`a Configuration Variable (TCV) in stationary conditions show that the
logarithmic electron density gradient increases with collisionality. By
contrast, usual observations of H-modes showed that the electron density
profiles tend to flatten with increasing collisionality. In this work it is
reinforced that the role of collisionality alone, depending on the parameter
regime, can be rather weak and in these, dominantly electron heated TCV cases,
the electron density gradient is tailored by the underlying turbulence regime,
which is mostly determined by the ratio of the electron to ion temperature and
that of their gradients. Additionally, mostly in ohmic plasmas, the Ware-pinch
can significantly contribute to the density peaking. Qualitative agreement
between the predicted density peaking by quasi-linear gyrokinetic simulations
and the experimental results is found. Quantitative comparison would
necessitate ion temperature measurements, which are lacking in the considered
experimental dataset. However, the simulation results show that it is the
combination of several effects that influences the density peaking in TCV
H-mode plasmas.Comment: 23 pages, 12 figure
Construction of an interactive online phytoplasma classification tool, iPhyClassifier, and its application in analysis of the peach X-disease phytoplasma group (16SrIII)
Phytoplasmas, the causal agents of numerous plant diseases, are insect-vector-transmitted, cell-wall-less bacteria descended from ancestral low-G+C-content Gram-positive bacteria in the Bacillus–Clostridium group. Despite their monophyletic origin, widely divergent phytoplasma lineages have evolved in adaptation to specific ecological niches. Classification and taxonomic assignment of phytoplasmas have been based primarily on molecular analysis of 16S rRNA gene sequences because of the inaccessibility of measurable phenotypic characters suitable for conventional microbial characterization. In the present study, an interactive online tool, iPhyClassifier, was developed to expand the efficacy and capacity of the current 16S rRNA gene sequence-based phytoplasma classification system. iPhyClassifier performs sequence similarity analysis, simulates laboratory restriction enzyme digestions and subsequent gel electrophoresis and generates virtual restriction fragment length polymorphism (RFLP) profiles. Based on calculated RFLP pattern similarity coefficients and overall sequence similarity scores, iPhyClassifier makes instant suggestions on tentative phytoplasma 16Sr group/subgroup classification status and ‘Candidatus Phytoplasma’ species assignment. Using iPhyClassifier, we revised and updated the classification of strains affiliated with the peach X-disease phytoplasma group. The online tool can be accessed at http://www.ba.ars.usda.gov/data/mppl/iPhyClassifier.html
Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system
We analytically compute the long-term orbital variations of a test particle
orbiting a central body acted upon by an incident monochromatic plane
gravitational wave. We assume that the characteristic size of the perturbed
two-body system is much smaller than the wavelength of the wave. Moreover, we
also suppose that the wave's frequency is much smaller than the particle's
orbital one. We make neither a priori assumptions about the direction of the
wavevector nor on the orbital geometry of the planet. We find that, while the
semi-major axis is left unaffected, the eccentricity, the inclination, the
longitude of the ascending node, the longitude of pericenter and the mean
anomaly undergo non-vanishing long-term changes. They are not secular trends
because of the slow modulation introduced by the tidal matrix coefficients and
by the orbital elements themselves. They could be useful to indepenedently
constrain the ultra-low frequency waves which may have been indirectly detected
in the BICEP2 experiment. Our calculation holds, in general, for any
gravitationally bound two-body system whose characteristic frequency is much
larger than the frequency of the external wave. It is also valid for a generic
perturbation of tidal type with constant coefficients over timescales of the
order of the orbital period of the perturbed particle.Comment: LaTex2e, 24 pages, no figures, no tables. Changes suggested by the
referees include
Contextual socioeconomic determinants of cardiovascular risk factors in rural south-west China: a multilevel analysis
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