84 research outputs found
Evidence for the absence of regularization corrections to the partial-wave renormalization procedure in one-loop self energy calculations in external fields
The equivalence of the covariant renormalization and the partial-wave
renormaliz ation (PWR) approach is proven explicitly for the one-loop
self-energy correction (SE) of a bound electron state in the presence of
external perturbation potentials. No spurious correctio n terms to the
noncovariant PWR scheme are generated for Coulomb-type screening potentia ls
and for external magnetic fields. It is shown that in numerical calculations of
the SE with Coulombic perturbation potential spurious terms result from an
improper treatment of the unphysical high-energy contribution. A method for
performing the PWR utilizing the relativistic B-spline approach for the
construction of the Dirac spectrum in external magnetic fields is proposed.
This method is applied for calculating QED corrections to the bound-electron
-factor in H-like ions. Within the level of accuracy of about 0.1% no
spurious terms are generated in numerical calculations of the SE in magnetic
fields.Comment: 22 pages, LaTeX, 1 figur
The Distance to NGC 1316 (Fornax A) From Observations of Four Type Ia Supernovae
The giant elliptical galaxy NGC 1316 (Fornax A) is a well-studied member of
the Fornax Cluster and a prolific producer of Type Ia supernovae, having hosted
four observed events since 1980. Here we present detailed optical and
near-infrared light curves of the spectroscopically normal SN 2006dd. These
data are used, along with previously published photometry of the normal SN
1980N and SN 1981D, and the fast-declining, low-luminosity SN 2006mr, to
compute independent estimates of the host reddening for each supernova, and the
distance to NGC 1316. From the three normal supernovae, we find a distance of
17.8 +/- 0.3 (random) +/- 0.3 (systematic) Mpc for Ho = 72. Distance moduli
derived from the "EBV" and Tripp methods give values that are mutually
consistent to 4 -- 8%. Moreover, the weighted means of the distance moduli for
these three SNe for three methods agree to within 3%. This consistency is
encouraging and supports the premise that Type Ia supernovae are reliable
distance indicators at the 5% precision level or better. On the other hand, the
two methods used to estimate the distance of the fast-declining SN 2006mr both
yield a distance to NGC 1316 which is 25-30% larger. This disparity casts doubt
on the suitability of fast-declining events for estimating extragalactic
distances. Modest-to-negligible host galaxy reddening values are derived for
all four supernovae. Nevertheless, two of them (SN 2006dd and SN 2006mr) show
strong NaID interstellar lines in the host galaxy system. The strength of this
absorption is completely inconsistent with the small reddening values derived
from the supernova light curves if the gas in NGC 1316 is typical of that found
in the interstellar medium of the Milky Way. In addition, the equivalent width
of the NaID lines in SN 2006dd appear to have weakened significantly some
100-150 days after explosion.Comment: 50 pages, 13 figures, 10 tables; constructive comments welcome.
Accepted for publication in A
Epitaxial growth of perovskite oxide films facilitated by oxygen vacancies
The authors would like to thank P. Yudin for valuable discussions, N. Nepomniashchaia for VASE studies, and S. Cichon for XPS analysis. The authors acknowledge support from the Czech Science Foundation (Grant No. 19-09671S), the European Structural and Investment Funds and the Ministry of Education, Youth and Sports of the Czech Republic through Programme ‘‘Research,
Development and Education’’ (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16-019/0000760), and ERA NET project Sun2Chem (E. K. and L. R.). Calculations have been done on the LASC Cluster in the ISSP UL.Single-crystal epitaxial films of technologically important and scientifically intriguing multifunctional ABO3 perovskite-type metal oxides are essential for advanced applications and understanding of these materials. In such films, a film-substrate misfit strain enables unprecedented crystal phases and unique properties that are not available in their bulk counterparts. However, the prerequisite growth of strained epitaxial films is fundamentally restricted by misfit relaxation. Here we demonstrate that introduction of a small oxygen deficiency concurrently stabilizes epitaxy and increases lattice strain in thin films of archetypal perovskite oxide SrTiO3. By combining experimental and theoretical methods, we found that lattice distortions around oxygen vacancies lead to anisotropic local stresses, which interact with the misfit strain in epitaxial films. Consequently, specific crystallographic alignments of the stresses are energetically favorable and can facilitate epitaxial growth of strained films. Because anisotropic oxygen-vacancy stresses are inherent to perovskite-type and many other oxides, we anticipate that the disclosed phenomenon of epitaxial stabilization by oxygen vacancies is relevant for a very broad range of functional oxides.This work is licensed under CC BY, CC BY-NC licenses.Czech Science Foundation (Grant No. 19-09671S); European Structural and Investment Funds and the Ministry of Education, Youth and Sports of the Czech Republic through Programme ‘‘Research, Development and Education’’ (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16-019/0000760), and ERA NET project Sun2Chem; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²
MULTI-WAVELENGTH OBSERVATIONS OF THE ENDURING TYPE IIn SUPERNOVAE 2005ip AND 2006jd
We present an observational study of the Type IIn supernovae (SNe IIn) 2005ip
and 2006jd. Broad-band UV, optical and near-IR photometry, and
visual-wavelength spectroscopy of SN 2005ip complement and extend upon
published observations to 6.5 years past discovery. Our observations of SN
2006jd extend from UV to mid-infrared wavelengths, and like SN 2005ip, are
compared to reported X-ray measurements to understand the nature of the
progenitor. Both objects display a number of similarities with the 1988Z-like
subclass of SN IIn including: (i) remarkably similar early- and late-phase
optical spectra, (ii) a variety of high ionization coronal lines, (iii)
long-duration optical and near-IR emission and, (iv) evidence of cold and warm
dust components. However, diversity is apparent including an unprecedented
late-time r-band excess in SN 2006jd.The observed differences are attributed to
differences between the mass-loss history of the progenitor stars. We conclude
that the progenitor of SN 2006jd likely experienced a significant mass-loss
event during its pre-SN evolution akin to the great 19th century eruption of
\eta Carinae. Contrarily, as advocated by Smith et al. (2009), we find the
circumstellar environment of SN 2005ip to be more consistent with a clumpy wind
progenitor.Comment: Submitted May 2012 and to appear in ApJ. Manuscript consists of 61
pages, including 19 figures and 11 tables. Comments welcome; referee approves
for publicatio
Predicting bee community responses to land-use changes: Effects of geographic and taxonomic biases
Land-use change and intensification threaten bee populations worldwide, imperilling pollination services. Global models are needed to better characterise, project, and mitigate bees' responses to these human impacts. The available data are, however, geographically and taxonomically unrepresentative; most data are from North America and Western Europe, overrepresenting bumblebees and raising concerns that model results may not be generalizable to other regions and taxa. To assess whether the geographic and taxonomic biases of data could undermine effectiveness of models for conservation policy, we have collated from the published literature a global dataset of bee diversity at sites facing land-use change and intensification, and assess whether bee responses to these pressures vary across 11 regions (Western, Northern, Eastern and Southern Europe; North, Central and South America; Australia and New Zealand; South East Asia; Middle and Southern Africa) and between bumblebees and other bees. Our analyses highlight strong regionally-based responses of total abundance, species richness and Simpson's diversity to land use, caused by variation in the sensitivity of species and potentially in the nature of threats. These results suggest that global extrapolation of models based on geographically and taxonomically restricted data may underestimate the true uncertainty, increasing the risk of ecological surprises
CHARACTERIZING THE V -BAND LIGHT-CURVES OF HYDROGEN-RICH TYPE II SUPERNOVAE
We present an analysis of the diversity of V-band light-curves of
hydrogen-rich type II supernovae. Analyzing a sample of 116 supernovae, several
magnitude measurements are defined, together with decline rates at different
epochs, and time durations of different phases. It is found that magnitudes
measured at maximum light correlate more strongly with decline rates than those
measured at other epochs: brighter supernovae at maximum generally have faster
declining light-curves at all epochs. We find a relation between the decline
rate during the 'plateau' phase and peak magnitudes, which has a dispersion of
0.56 magnitudes, offering the prospect of using type II supernovae as purely
photometric distance indicators. Our analysis suggests that the type II
population spans a continuum from low-luminosity events which have flat
light-curves during the 'plateau' stage, through to the brightest events which
decline much faster. A large range in optically thick phase durations is
observed, implying a range in progenitor envelope masses at the epoch of
explosion. During the radioactive tails, we find many supernovae with faster
declining light-curves than expected from full trapping of radioactive
emission, implying low mass ejecta. It is suggested that the main driver of
light-curve diversity is the extent of hydrogen envelopes retained before
explosion. Finally, a new classification scheme is introduced where
hydrogen-rich events are typed as simply 'SNII' with an s2 value giving the
decline rate during the 'plateau' phase, indicating its morphological type.Comment: Accepted for publication in ApJ. Revised edition corrects errors in
affiliation number
The Carnegie Supernova Project: Second Photometry Data Release of Low-Redshift Type Ia Supernovae
The Carnegie Supernova Project (CSP) was a five-year observational survey
conducted at Las Campanas Observatory that obtained, among other things,
high-quality light curves of ~100 low-redshift Type Ia supernovae (SNe Ia).
Presented here is the second data release of nearby SN Ia photometry consisting
of 50 objects, with a subset of 45 having near-infrared follow-up observations.
Thirty-three objects have optical pre-maximum coverage with a subset of 15
beginning at least 5 days before maximum light. In the near-infrared, 27
objects have coverage beginning before the epoch of B-band maximum, with a
subset of 13 beginning at least 5 days before maximum. In addition, we present
results of a photometric calibration program to measure the CSP optical
(uBgVri)bandpasses with an accuracy of ~1%. Finally, we report the discovery of
a second SN Ia, SN 2006ot, similar in its characteristics to the peculiar SN
2006bt.Comment: 115 pages, 7 figures, 7 tables. To be published in the Astronomical
Journal. Comments welcom
Beyond the Global Brain Differences:Intraindividual Variability Differences in 1q21.1 Distal and 15q11.2 BP1-BP2 Deletion Carriers
BACKGROUND: Carriers of the 1q21.1 distal and 15q11.2 BP1-BP2 copy number variants exhibit regional and globalbrain differences compared with noncarriers. However, interpreting regional differences is challenging if a globaldifference drives the regional brain differences. Intraindividual variability measures can be used to test for regionaldifferences beyond global differences in brain structure.METHODS: Magnetic resonance imaging data were used to obtain regional brain values for 1q21.1 distal deletion (n =30) and duplication (n = 27) and 15q11.2 BP1-BP2 deletion (n = 170) and duplication (n = 243) carriers and matchednoncarriers (n = 2350). Regional intra-deviation scores, i.e., the standardized difference between an individual’sregional difference and global difference, were used to test for regional differences that diverge from the globaldifference.RESULTS: For the 1q21.1 distal deletion carriers, cortical surface area for regions in the medial visual cortex, posterior cingulate, and temporal pole differed less and regions in the prefrontal and superior temporal cortex differedmore than the global difference in cortical surface area. For the 15q11.2 BP1-BP2 deletion carriers, cortical thicknessin regions in the medial visual cortex, auditory cortex, and temporal pole differed less and the prefrontal andsomatosensory cortex differed more than the global difference in cortical thickness.CONCLUSIONS: We find evidence for regional effects beyond differences in global brain measures in 1q21.1 distaland 15q11.2 BP1-BP2 copy number variants. The results provide new insight into brain profiling of the 1q21.1 distaland 15q11.2 BP1-BP2 copy number variants, with the potential to increase understanding of the mechanismsinvolved in altered neurodevelopment
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