5,457 research outputs found
Better age estimations using UV-optical colours: breaking the age-metallicity degeneracy
We demonstrate that the combination of GALEX UV photometry in the FUV (~1530
angstroms) and NUV (~2310 angstroms) passbands with optical photometry in the
standard U,B,V,R,I filters can efficiently break the age-metallicity
degeneracy. We estimate well-constrained ages, metallicities and their
associated errors for 42 GCs in M31, and show that the full set of
FUV,NUV,U,B,V,R,I photometry produces age estimates that are ~90 percent more
constrained and metallicity estimates that are ~60 percent more constrained
than those produced by using optical filters alone. The quality of the age
constraints is comparable or marginally better than those achieved using a
large number of spectrscopic indices.Comment: Published in MNRAS (2007), 381, L74 (doi:
10.1111/j.1745-3933.2007.00370.x
Changes in ambient air pollutants in New York State from 2005 to 2019: Effects of policy implementations and economic and technological changes
Over the past 20 years, a number of regulatory efforts have been applied to improve air quality in the United States and specifically in New York State. These measures generally focused on mobile emissions through emissions controls and improved fuel quality, and controls on electricity generation to reduce emissions from older, uncontrolled electricity generation units (EGUs). In addition, economic drivers such as the major recession in 2007–2009 and the change in the relative costs of natural gas and coal also drove changes in the mixture of EGU technologies. To assess the effects of these changes and to define the baseline for future changes as the economy further decarbonizes through renewable electricity generation and electric vehicles, the concentrations of all pollutants measured at all regulatory monitoring sites in New York State were assessed for their trends. Trends were examined using seasonal-trend decomposition with local regression smoothing (STL), Mann-Kendall trend analysis with the Theil-Sen nonparametric slope estimation, and piecewise regression analysis to identify breakpoints in the slopes of the time series data. The concentrations of primary gaseous pollutants, CO, NO2, and SO2 have decreased substantially in step with the declining emissions. PM2.5 has substantially declined largely due to the reductions in particulate sulfate. However, in recent years, the rate of decline has diminished due to relatively constant or increasing particulate nitrate and secondary organic aerosol. O3 has also generally increased at the urban sites likely as a result of reduced NOx emissions, while it declined or remained constant at the rural sites. Thus, the promulgated regulations assisted by the economic drivers have improved air quality, but additional actions will be needed to further reduce urban O3 and PM2.5
Coherence of neutrino flavor mixing in quantum field theory
In the simplistic quantum mechanical picture of flavor mixing, conditions on
the maximum size and minimum coherence time of the source and detector regions
for the observation of interference---as well as the very viability of the
approach---can only be argued in an ad hoc way from principles external to the
formalism itself. To examine these conditions in a more fundamental way, the
quantum field theoretical -matrix approach is employed in this paper,
without the unrealistic assumption of microscopic stationarity. The fully
normalized, time-dependent neutrino flavor mixing event rates presented here
automatically reveal the coherence conditions in a natural, self-contained, and
physically unambiguous way, while quantitatively describing the transition to
their failure.Comment: 12 pages, submitted to Phys. Rev.
On the HI-Hole and AGB Stellar Population of the Sagittarius Dwarf Irregular Galaxy
Using two HST/ACS data-sets that are separated by ~2 years has allowed us to
derive the relative proper-motion for the Sagittarius dwarf irregular (SagDIG)
and reduce the heavy foreground Galactic contamination. The proper-motion
decontaminated SagDIG catalog provides a much clearer view of the young
red-supergiant and intermediate-age asymptotic giant branch populations. We
report the identification of 3 Milky Way carbon-rich dwarf stars, probably
belonging to the thin disk, and pointing to the high incidence of this class at
low Galactic latitudes. A sub-group of 4 oxygen-rich candidate stars depicts a
faint, red extension of the well-defined SagDIG carbon-rich sequence. The
origin of these oxygen-rich candidate stars remains unclear, reflecting the
uncertainty in the ratio of carbon/oxygen rich stars. SagDIG is also a gas-rich
galaxy characterized by a single large cavity in the gas disk (HI-hole), which
is offset by ~360 pc from the optical centre of the galaxy. We nonetheless
investigate the stellar feedback hypothesis by comparing the proper-motion
cleaned stellar populations within the HI-hole with appropriately selected
comparison regions, having higher HI densities external to the hole. The
comparison shows no significant differences. In particular, the centre of the
HI-hole (and the comparison regions) lack stellar populations younger than ~400
Myr, which are otherwise abundant in the inner body of the galaxy. We conclude
that there is no convincing evidence that the SagDIG HI-hole is the result of
stellar feedback, and that gravitational and thermal instabilities in the gas
are the most likely mechanism for its formation.Comment: Accepted for publication in A&A, 11 pages, 6 jpeg figure
Fluorescent species of 7-azaindole and 7-azatryptophan in water
A study of the fluorescence lifetimes and quantum yields of 7-azaindole and its methylated derivatives NImethyl- Famindole (1 M7AI) and 7-methyl-7H-pyrrolo[ 2,341 pyridine (7M7AI) in water is performed in order to explain the observation that the fluorescence spectrum of 7-azaindole apparently consists of one band (A, = 386 nm) whereas in alcohols the spectrum is bimodal (e.g., for methanol, A,, = 374, 505 nm). Careful measurements of the fluorescence decay as a function of emission wavelength indicate a small amplitude of an -70-ps decaying component at the bluer wavelengths and a rising component of the same duration at the redder wavelengths. The small amplitude component, which comprises no more than 20% of the fluorescence decay, is attributed to excited-state tautomerization that is mediated by the solvent. Particular attention is paid to the pH dependence of the fluorescence lifetimes and yields. We propose that upon tautomerization the basic l-nitrogen (NIo)f 7-azaindole is rapidly protonated givingrise to a species whose emission maximum is at -440 nm. The fluorescence emission maximum and lifetime of 7-azaindole is dominated by the 80% of the solute molecules that are blocked by unfavorable solvation from executing excited-state tautomerization. It is proposed that 210 ns is required for the surrounding water molecules to attain a configuration about 7-azaindole that is propitious for tautomerization
Probing Solvation by Alcohols and Water with 7-Azaindole
The nonradiative pathways of 7-azaindole are extremely sensitive to solvent. In alcohols, 7-azaindole executes an excited-state double-proton transfer. In water, this tautomerization is frustrated. Proton inventory experiments suggest a concerted double-proton transfer in the alcohols and point to another nonradiative process in water. We propose the following idealized picture. Whereas at room temperature 7-azaindole can form a cyclic hydrogen-bonded intermediate with a single alcohol molecule facilitating tautomerization, in water more than one solvent molecule coordinates to the solute and thus prohibits the concerted process. More detailed measurements, however, indicate that water and alcohols do not solvate 7-azaindole in fundamentally different ways, but rather that they represent two extremes of the same phenomenon
Oxygen abundances in the Galactic Bulge: evidence for fast chemical enrichment
AIMS: We spectroscopically characterize the Galactic Bulge to infer its star
formation timescale, compared to the other Galactic components, through the
chemical signature on its individual stars.
METHODS: We derived iron and oxygen abundances for 50 K giants in four fields
towards the Galactic bulge. High resolution (R=45,000) spectra for the target
stars were collected with FLAMES-UVES at the VLT.
RESULTS: Oxygen, as measured from the forbidden line at 6300 \AA, shows a
well-defined trend with [Fe/H], with [O/Fe] higher in bulge stars than in thick
disk ones, which were known to be more oxygen enhanced than thin disk stars.
CONCLUSIONS: These results support a scenario in which the bulge formed
before and more rapidly than the disk, and therefore the MW bulge can be
regarded as a prototypical old spheroid, with a formation history similar to
that of early-type (elliptical) galaxies.Comment: A&A Letters, in pres
Neutrino oscillations: Entanglement, energy-momentum conservation and QFT
We consider several subtle aspects of the theory of neutrino oscillations
which have been under discussion recently. We show that the -matrix
formalism of quantum field theory can adequately describe neutrino oscillations
if correct physics conditions are imposed. This includes space-time
localization of the neutrino production and detection processes. Space-time
diagrams are introduced, which characterize this localization and illustrate
the coherence issues of neutrino oscillations. We discuss two approaches to
calculations of the transition amplitudes, which allow different physics
interpretations: (i) using configuration-space wave packets for the involved
particles, which leads to approximate conservation laws for their mean energies
and momenta; (ii) calculating first a plane-wave amplitude of the process,
which exhibits exact energy-momentum conservation, and then convoluting it with
the momentum-space wave packets of the involved particles. We show that these
two approaches are equivalent. Kinematic entanglement (which is invoked to
ensure exact energy-momentum conservation in neutrino oscillations) and
subsequent disentanglement of the neutrinos and recoiling states are in fact
irrelevant when the wave packets are considered. We demonstrate that the
contribution of the recoil particle to the oscillation phase is negligible
provided that the coherence conditions for neutrino production and detection
are satisfied. Unlike in the previous situation, the phases of both neutrinos
from decay are important, leading to a realization of the
Einstein-Podolsky-Rosen paradox.Comment: 30 pages, 3 eps figures; presentation improved, clarifications added.
To the memory of G.T. Zatsepi
Remarks upon the mass oscillation formulas
The standard formula for mass oscillations is often based upon the
approximation and the hypotheses that neutrinos have been
produced with a definite momentum or, alternatively, with definite energy
. This represents an inconsistent scenario and gives an unjustified
reduction by a factor of two in the mass oscillation formulas. Such an
ambiguity has been a matter of speculations and mistakes in discussing flavour
oscillations. We present a series of results and show how the problem of the
factor two in the oscillation length is not a consequence of gedanken
experiments, i.e. oscillations in time. The common velocity scenario yields the
maximum simplicity.Comment: 9 pages, AMS-Te
- …