273 research outputs found
Free Form of the Foldy-Wouthuysen Transformation in External Electromagnetic Fields
We derive the exact Foldy-Wouthuysen transformation for Dirac fermions in a
time independent external electromagnetic field in the basis of the Ritus
eigenfunctions, namely the eigenfunctions of the operator , with . In this basis, the transformation
acquires a free form involving the dynamical quantum numbers induced by the
field.Comment: 8 pages. Accepted in J. Phys. A: Math. and Theo. (Fast Track
Communication
Stellar Populations in type Ia supernova host galaxies at intermediate-high redshift: Star formation and metallicity enrichment histories
We present a summary of our project that studies galaxies hosting type Ia
supernova (SN Ia) at different redshifts. We present Gran Telescopio de
Canarias (GTC) optical spectroscopy of six SN Ia host galaxies at redshift
. They are joined to a set of SN Ia host galaxies at
intermediate-high redshift, which include galaxies from surveys SDSS and
COSMOS. The final sample, after a selection of galaxy spectra in terms of
signal-to-noise and other characteristics, consists of 680 galaxies with
redshift in the range . We perform an inverse stellar population
synthesis with the code {\sc fado} to estimate the star formation and
enrichment histories of this set of galaxies, simultaneously obtaining their
mean stellar age and metallicity and stellar mass. After analysing the
correlations among these characteristics, we look for possible dependencies of
the Hubble diagram residuals and supernova features (luminosity, color and
strength parameter) on these stellar parameters. We find that the Hubble
residuals show a clear dependence on the stellar metallicity weighted by mass
with a slope of -0.061\,mag\,dex, when represented in logarithmic scale,
. This result supports our previous
findings obtained from gas oxygen abundances for local and SDSS-survey
galaxies. Comparing with other works from the literature that also use the
stellar metallicity, we find a similar value, but with more precision and a
better significance (2.08 vs 1.1), due to the higher number of objects
and wider range of redshift of our sample.Comment: 21 pages, 19 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Complementary Functions of Plant AP Endonucleases and AP Lyases during DNA Repair of Abasic Sites Arising from C:G Base Pairs
Abasic (apurinic/apyrimidinic, AP) sites are ubiquitous DNA lesions arising from spontaneous base loss and excision of damaged bases. They may be processed either by AP endonucleases or AP lyases, but the relative roles of these two classes of enzymes are not well understood. We hypothesized that endonucleases and lyases may be differentially influenced by the sequence surrounding the AP site and/or the identity of the orphan base. To test this idea, we analysed the activity of plant and human AP endonucleases and AP lyases on DNA substrates containing an abasic site opposite either G or C in different sequence contexts. AP sites opposite G are common intermediates during the repair of deaminated cytosines, whereas AP sites opposite C frequently arise from oxidized guanines. We found that the major Arabidopsis AP endonuclease (ARP) exhibited a higher efficiency on AP sites opposite G. In contrast, the main plant AP lyase (FPG) showed a greater preference for AP sites opposite C. The major human AP endonuclease (APE1) preferred G as the orphan base, but only in some sequence contexts. We propose that plant AP endonucleases and AP lyases play complementary DNA repair functions on abasic sites arising at C:G pairs, neutralizing the potential mutagenic consequences of C deamination and G oxidation, respectively
Gravitational waves during inflation from a 5D large-scale repulsive gravity model
We investigate, in the transverse traceless (TT) gauge, the generation of the
relic background of gravitational waves, generated during an early inflationary
stage, on the framework of a large-scale repulsive gravity model. We calculate
the spectrum of the tensor metric fluctuations of an effective 4D
Schwarzschild-de-Sitter metric, which is obtained after implementing a planar
coordinate transformation on a 5D Ricci-flat metric solution, in the context of
a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is
nearly scale invariant under certain conditions. One interesting aspect of this
model is that is possible to derive dynamical field equations for the tensor
metric fluctuations, valid not just at cosmological scales, but also at
astrophysical scales, from the same theoretical model. The astrophysical and
cosmological scales are determined by the gravity- antigravity radius, which is
a natural length scale of the model, that indicates when gravity becomes
repulsive in nature.Comment: Improved version, accepted in Physics Letters
PISCO: The Pmas/ppak Integral-field Supernova hosts COmpilation
We present the Pmas/ppak Integral-field Supernova hosts COmpilation (PISCO)
which comprises Integral Field Spectroscopy (IFS) of 232 supernova (SN) host
galaxies, that hosted 272 SNe, observed over several semesters with the 3.5m
telescope at the Calar Alto Observatory (CAHA). PISCO is the largest collection
of SN host galaxies observed with wide-field IFS, totaling 466,347 individual
spectra covering a typical spatial resolution of 380 pc. While focused
studies regarding specific SN Ia- related topics will be published elsewhere,
this paper aims to present the properties of the SN environments with stellar
population (SP) synthesis and the gas-phase ISM, providing additional results
separating stripped-envelope SNe into their subtypes. With 11,270 HII regions
detected in all galaxies, we present for the first time an HII region
statistical analysis, that puts HII regions that have hosted SNe in context
with all other SF clumps within their galaxies. SNe Ic are associated to more
metal-rich, higher EW(H{\alpha}) and higher SF rate environments within their
host galaxies than the mean of all HII regions detected within each host, on
contrary SNe IIb occur at the most different environments compared to other CC
SNe types. We find two clear components of young and old SP at SNe IIn
locations. We find that SNe II fast-decliners (IIL) tend to explode at
locations where {\Sigma}SFR is more intense. Finally, we outline how a future
dedicated IFS survey of galaxies in parallel to an untargeted SN search would
overcome the biases in current environmental studies.Comment: 21 pages, 10 Figures, 6 Tables. Accepted in Ap
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