195 research outputs found
One-electron self-interaction error and its relationship to geometry and higher orbital occupation
Density Functional Theory (DFT) sees prominent use in computational chemistry
and physics, however, problems due to the self-interaction error (SIE) pose
additional challenges to obtaining qualitatively correct results. An unphysical
energy an electron exerts on itself, the SIE impacts most practical DFT
calculations. We conduct an in-depth analysis of the one-electron SIE in which
we replicate delocalization effects for simple geometries. We present a simple
visualization of such effects, which may help in future qualitative analysis of
the one-electron SIE. By increasing the number of nuclei in a linear
arrangement, the SIE increases dramatically. We also show how molecular shape
impacts the SIE. Two and three dimensional shapes show an even greater SIE
stemming mainly from the exchange functional with some error compensation from
the one-electron error, which we previously defined [Phys. Chem. Chem. Phys.
22, 15805 (2020)]. Most tested geometries are affected by the functional error,
while some suffer from the density error. For the latter we establish a
potential connection with electrons being unequally delocalized by the DFT
methods. We also show how the the SIE increases if electrons occupy
higher-lying atomic orbitals; seemingly one-electron SIE free methods in a
ground are no longer SIE free in excited states, which is an important insight
for some popular, non-empirical DFAs. We conclude that the erratic behavior of
the SIE in even the simplest geometries shows that robust density functional
approximations are needed. Our test systems can be used as a future benchmark
or contribute towards DFT development
Morphologically-Identified Merging Galaxies in the SWIRE Fields
We investigate the evolutional and environmental effects on star formation
efficiency for more than 400 merging galaxies. The ~400 merging systems, with
photometric redshifts smaller than 0.7, are obtained from a catalog of ~15000
morphologically identified merging galaxies derived from observations of the
Canada-France-Hawaii Telescope. We also obtained the IR data of the merging
galaxies from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE). The
redshift differences \Delta z between the member galaxies of these merging
pairs show a large distribution with 0 < \Delta z < 0.4. We divide our merging
pairs into two sub-samples with \Delta z 0.05 for further
analyses. We find a statistically significant anti-correlation between the
specific star formation rate (SSFR) and the separation of the merging galaxies
for both sub-samples. Our analyses also show that although most of the merging
systems do have enhanced star formation activity, only very rare ones display
extremely high SFRs. Additionally, the SSFR of the merging galaxies also
decreases when the magnitude difference between two member galaxies becomes
large. However, we find that for the merging pairs with large luminosity
contrast, the fainter components show higher SSFR than the brighter ones.
Finally, there is a higher fraction of gas-poor mergers in galaxy clusters, and
the SSFR of gas-rich mergers is reduced in cluster environments.Comment: 32 pages, 12 figures and 7 tables; accepted for publication in Ap
Enabling a High Throughput Real Time Data Pipeline for a Large Radio Telescope Array with GPUs
The Murchison Widefield Array (MWA) is a next-generation radio telescope
currently under construction in the remote Western Australia Outback. Raw data
will be generated continuously at 5GiB/s, grouped into 8s cadences. This high
throughput motivates the development of on-site, real time processing and
reduction in preference to archiving, transport and off-line processing. Each
batch of 8s data must be completely reduced before the next batch arrives.
Maintaining real time operation will require a sustained performance of around
2.5TFLOP/s (including convolutions, FFTs, interpolations and matrix
multiplications). We describe a scalable heterogeneous computing pipeline
implementation, exploiting both the high computing density and FLOP-per-Watt
ratio of modern GPUs. The architecture is highly parallel within and across
nodes, with all major processing elements performed by GPUs. Necessary
scatter-gather operations along the pipeline are loosely synchronized between
the nodes hosting the GPUs. The MWA will be a frontier scientific instrument
and a pathfinder for planned peta- and exascale facilities.Comment: Version accepted by Comp. Phys. Com
Far-Infrared Properties of Spitzer-selected Luminous Starbursts
We present SHARC-2 350 micron data on 20 luminous z ~ 2 starbursts with
S(1.2mm) > 2 mJy from the Spitzer-selected samples of Lonsdale et al. and
Fiolet et al. All the sources were detected, with S(350um) > 25 mJy for 18 of
them. With the data, we determine precise dust temperatures and luminosities
for these galaxies using both single-temperature fits and models with power-law
mass--temperature distributions. We derive appropriate formulae to use when
optical depths are non-negligible. Our models provide an excellent fit to the
6um--2mm measurements of local starbursts. We find characteristic
single-component temperatures T1 ~ 35.5+-2.2 K and integrated infrared (IR)
luminosities around 10^(12.9+-0.1) Lsun for the SWIRE-selected sources.
Molecular gas masses are estimated at 4 x 10^(10) Msun, assuming
kappa(850um)=0.15 m^2/kg and a submillimeter-selected galaxy (SMG)-like
gas-to-dust mass ratio. The best-fit models imply >~2 kpc emission scales. We
also note a tight correlation between rest-frame 1.4 GHz radio and IR
luminosities confirming star formation as the predominant power source. The
far-IR properties of our sample are indistinguishable from the purely
submillimeter-selected populations from current surveys. We therefore conclude
that our original selection criteria, based on mid-IR colors and 24 um flux
densities, provides an effective means for the study of SMGs at z ~ 1.5--2.5.Comment: 13 pages, 4 figures, edited to match published version in ApJ 717,
29-39 (2010
The infrared compactness-temperature relation for quiescent and starburst galaxies
IRAS observations show the existence of a correlation between the infrared
luminosity Lir and dust temperature Td in star-forming galaxies, in which
larger Lir leads to higher dust temperature. The Lir-Td relation is commonly
seen as reflecting the increase in dust temperature in galaxies with higher
star formation rate. Even though the correlation shows a significant amount of
dispersion, a unique relation has been commonly used to construct spectral
energy distributions of galaxies in distant universe studies, such as source
number counting or photometric redshift determination. In this work, we
introduce a new parameter, namely the size of the star-forming region Rir and
lay out the empirical and modelled relation between the global parameters Lir,
Td and Rir of IR-bright non-AGN galaxies. IRAS 60-to-100um color is used as a
proxy for the dust temperature and the 1.4GHz radio contiuum emission for the
infrared spatial distribution. The analysis has been carried out on two
samples. The first one is made of the galaxies from the 60um flux-limited IRAS
Revised Bright Galaxy Samples which have a reliable RC size estimate from the
VLA follow-ups of the IRAS Bright Galaxy Samples. The second is made of the
sources from the 170um ISOPHOT Serendipity Sky Survey which are resolved by the
NVSS or FIRST surveys. We show that the dispersion in the Lir-Td diagram can be
reduced to a relation between the infrared surface brightness and the dust
temperature, a relation that spans 5 orders of magnitude in surface brightness.
We explored the physical processes giving rise to the Sir-Td relation, and show
that it can be derived from the Schmidt law, which relates the star formation
rate to the gas surface density.Comment: 13 pages, 7 figures, accepted for publication in A&
Mid-infrared spectroscopy of infrared-luminous galaxies at z~0.5-3
We present results on low-resolution mid-infrared (MIR) spectra of 70
infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS)
onboard Spitzer. We selected sources from the European Large Area Infrared
Survey (ELAIS) with S15 > 0.8 mJy and photometric or spectroscopic z > 1. About
half of the sample are QSOs in the optical, while the remaining sources are
galaxies, comprising both obscured AGN and starbursts. We classify the spectra
using well-known infrared diagnostics, as well as a new one that we propose,
into three types of source: those dominated by an unobscured AGN (QSOs),
obscured AGN, and starburst-dominated sources. Starbursts concentrate at z ~
0.6-1.0 favored by the shift of the 7.7-micron PAH band into the selection 15
micron band, while AGN spread over the 0.5 < z < 3.1 range. Star formation
rates (SFR) are estimated for individual sources from the luminosity of the PAH
features. An estimate of the average PAH luminosity in QSOs and obscured AGN is
obtained from the composite spectrum of all sources with reliable redshifts.
The estimated mean SFR in the QSOs is 50-100 Mo yr^-1, but the implied FIR
luminosity is 3-10 times lower than that obtained from stacking analysis of the
FIR photometry, suggesting destruction of the PAH carriers by energetic photons
from the AGN. The SFR estimated in obscured AGN is 2-3 times higher than in
QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity
effects or selection bias alone, but could instead indicate a connection
between obscuration and star formation. However, the observed correlation
between silicate absorption and the slope of the near- to mid-infrared spectrum
is compatible with the obscuration of the AGN emission in these sources being
produced in a dust torus.Comment: 32 pages, 24 figures, 15 tables, accepted for publication in MNRA
FIRBACK IV: Towards the nature of the 170microns source population
We present a detailed study of the brighter ( detections) sources
in the 170m FIRBACK northern N1 ISO survey, with the help of complementary
data in the optical, radio, and mid-IR domain. For 82% of them, an optical
galaxy counterpart is identified, either as the unique source of the IR
emission, or as part of a multiple identification. With less than 15% of AGNs,
these sources are essentially local, moderate starbursters with a dominating
cold dust component. and represent a population of cold galaxies rather
neglected up to now. Their colours do not match those of the far-IR Cosmic IR
Background (CIB), to which they contribute less than 5%. The bulk of the
sources contributing to the CIB is thus to be searched for in more distant
galaxies, possibly counterparts of the fainter FIRBACK sources still under
study. These bright, local, galaxies however play an important role in the
evolution of IR galaxies: they dominate the number counts at high 170 m
fluxes, and represent half of the contribution at 250 mJy. Although not
particularly massive (typically M*), they form more stars than a typical spiral
galaxy and many are bulge dominated, that could represent the remnant of a
former merger. The fainter part of this population may represent the missing
link with the higher-z sources found in sub-mm observations.Comment: 40 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
Similarities between stratum corneum basic protein and histidine-rich protein II from newborn rat epidermis
The stratum corneum basic protein and histidine-rich protein II were each isolated from newborn rat epidermis and compared by biochemical and immunologic methods. The proteins were indistinguishable by immunodiffusion using antiserum elicited to either protein. The migration of the proteins on SDS-polyacrylamide gel electrophoresis was identical giving a molecular weight of 49 000. These proteins, which have similar but unusual amino acid compositions, give very similar tryptic peptide maps. Both proteins aggregate with keratin filaments to form macrofibrils. These results suggest that histidine-rich protein II and stratum corneum basic protein are the same protein. We suggest that this protein be called histidine-rich basic protein.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24422/1/0000693.pd
Galaxy Colours in the AKARI Deep SEP Survey
We investigate the segregation of the extragalactic population via colour
criteria to produce an efficient and inexpensive methodology to select specific
source populations as a function of far-infrared flux. Combining galaxy
evolution scenarios and a detailed spectral library of galaxies, we produce
simulated catalogues incorporating segregation of the extragalactic population
into component types (Normal, star-forming, AGN) via color cuts. As a practical
application we apply our criteria to the deepest survey to be undertaken in the
far-infrared with the AKARI (formerly ASTRO-F) satellite. Using the
far-infrared wavebands of the Far-Infrared Surveyor (FIS, one of the
focal-plane instruments on AKARI) we successfully segregate the normal,
starburst and ULIRG populations. We also show that with additional MIR imaging
from AKARI's Infrared Camera (IRC), significant contamination and/or degeneracy
can be further decreased and show a particular example of the separation of
cool normal galaxies and cold ULIRG sources. We conclude that our criteria
provide an efficient means of selecting source populations (including rare
luminous objects) and produce colour-segregated source counts without the
requirement of time intensive ground-based follow up to differentiate between
the general galaxy population.Comment: Accepted for publication in Advances in Space Research. COSPAR,
Beijing, 2006, E1.6 Advances in FIR and Submillimeter Astrophysics. (13
pages, 2 colour figures
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