393 research outputs found
A new Tolman test of a cosmic distance duality relation at 21 cm
Under certain general conditions in an expanding universe, the luminosity
distance (d_L) and angular diameter distance (d_A) are connected by the
Etherington relation as d_L = d_A (1 + z)^2. The Tolman test suggests the use
of objects of known surface brightness, to test this relation. In this letter,
we propose the use of redshifted 21 cm signal from disk galaxies, where neutral
hydrogen (HI) masses are seen to be almost linearly correlated with surface
area, to conduct a new Tolman test. We construct simulated catalogs of
galaxies, with the observed size-luminosity relation and realistic redshift
evolution of HI mass functions, likely to be detected with the planned Square
Kilometer Array (SKA). We demonstrate that these observations may soon provide
the best implementation of the Tolman test to detect any violation of the
Etherington relation.Comment: 4 pages, 2 figures, 1 table, v2: published versio
Direct Access to Unnatural Cyclobutane ?-Amino Acids through Visible Light Catalyzed [2+2]-Cycloaddition
In this work, we report the first selective, photocatalyzed [2+2]-cycloaddition of dehydroamino acids with styrene-type olefins. This simple, mild, and scalable approach relies on the use of the triplet energy transfer catalyst [Ir(dFCF(3)ppy(2))dtbpy]PF6 under visible light irradiation and provides fast access to value-added substituted strained cyclobutane alpha-amino acid derivatives. © 2022 The Authors. Published by American Chemical Society
CCD photometric search for peculiar stars in open clusters. VII. Berkeley 11, Berkeley 94, Haffner 15, Lynga 1, NGC 6031, NGC 6405, NGC 6834 and Ruprecht 130
The detection of magnetic chemically peculiar (CP2) stars in open clusters of
the Milky Way can be used to study the influence of different galactic
environments on the (non-)presence of peculiarities, which has to be taken into
account in stellar evolution models. Furthermore it is still unknown if the CP2
phenomenon evolves, i.e. does the strength of the peculiarity feature at 5200A,
increase or decrease with age. We have observed eight young to intermediate age
open clusters in the Delta a photometric system. This intermediate band
photometric system samples the depth of the 5200A, flux depression by comparing
the flux at the center with the adjacent regions having bandwidths of 110A, to
230A. The Delta a photometric system is most suitable to detect CP2 stars with
high efficiency, but is also capable of detecting a small percentage of
non-magnetic CP objects. Also, the groups of (metal-weak) lambda Bootis, as
well as classical Be/shell stars, can be successfully investigated. This
photometric system allows one to determine the age, reddening and distance
modulus by fitting isochrones. Among the presented sample of eight galactic
clusters, we have detected twenty three CP2, eight Be/Ae and eight metal-weak
stars. Another six objects show a peculiar behaviour which is most probably due
to a non-membership,variability or duplicity. Fitting isochrones to Delta a
photometry yields estimates of the age, reddening and distance that are in
excellent agreement with published values
The Actinome of Dictyostelium discoideum in Comparison to Actins and Actin-Related Proteins from Other Organisms
Actin belongs to the most abundant proteins in eukaryotic cells which harbor usually many conventional actin isoforms as well as actin-related proteins (Arps). To get an overview over the sometimes confusing multitude of actins and Arps, we analyzed the Dictyostelium discoideum actinome in detail and compared it with the genomes from other model organisms. The D. discoideum actinome comprises 41 actins and actin-related proteins. The genome contains 17 actin genes which most likely arose from consecutive gene duplications, are all active, in some cases developmentally regulated and coding for identical proteins (Act8-group). According to published data, the actin fraction in a D. discoideum cell consists of more than 95% of these Act8-type proteins. The other 16 actin isoforms contain a conventional actin motif profile as well but differ in their protein sequences. Seven actin genes are potential pseudogenes. A homology search of the human genome using the most typical D. discoideum actin (Act8) as query sequence finds the major actin isoforms such as cytoplasmic beta-actin as best hit. This suggests that the Act8-group represents a nearly perfect actin throughout evolution. Interestingly, limited data from D. fasciculatum, a more ancient member among the social amoebae, show different relationships between conventional actins. The Act8-type isoform is most conserved throughout evolution. Modeling of the putative structures suggests that the majority of the actin-related proteins is functionally unrelated to canonical actin. The data suggest that the other actin variants are not necessary for the cytoskeleton itself but rather regulators of its dynamical features or subunits in larger protein complexes
A genome-wide study of HardyâWeinberg equilibrium with next generation sequence data
Statistical tests for HardyâWeinberg equilibrium have been an important tool for detecting genotyping errors in the past, and remain important in the quality control of next generation sequence data. In this paper, we analyze complete chromosomes of the 1000 genomes project by using exact test procedures for autosomal and X-chromosomal variants. We find that the rate of disequilibrium largely exceeds what might be expected by chance alone for all chromosomes. Observed disequilibrium is, in about 60% of the cases, due to heterozygote excess. We suggest that most excess disequilibrium can be explained by sequencing problems, and hypothesize mechanisms that can explain exceptional heterozygosities. We report higher rates of disequilibrium for the MHC region on chromosome 6, regions flanking centromeres and p-arms of acrocentric chromosomes. We also detected long-range haplotypes and areas with incidental high disequilibrium. We report disequilibrium to be related to read depth, with variants having extreme read depths being more likely to be out of equilibrium. Disequilibrium rates were found to be 11 times higher in segmental duplications and simple tandem repeat regions. The variants with significant disequilibrium are seen to be concentrated in these areas. For next generation sequence data, HardyâWeinberg disequilibrium seems to be a major indicator for copy number variation.Peer ReviewedPostprint (published version
Massive star formation around I05345+3157 -- I. The dense gas
We present observations of the intermediate to massive star-forming region
I05345+3157 using the molecular line tracer CS(2-1) with CARMA to reveal the
properties of the dense gas cores. Seven gas cores are identified in the
integrated intensity map of CS(2-1). Among these, core 1 and core 3 have
counterparts in the 2.7 millimeter continuum data. We suggest that core 1 and
core 3 are star-forming cores that may already or will very soon harbor young
massive protostars. The total masses of core 1 estimated from the LTE method
and dust emission by assuming a gas-to-dust ratio are 5 +- 1 solar masses and
18 +- 6 solar masses, and that of core 3 are 15 +- 7 solar masses and 11 +- 3
solar masses. The spectrum of core 3 shows blue-skewed self-absorption, which
suggests gas infall -- a collapsing core. The observed broad linewidths of the
seven gas cores indicate non-thermal motions. These non-thermal motions can be
interactions with nearby outflows or due to the initial turbulence; the former
is observed, while the role of initial turbulence is less certain. Finally, the
virial masses of the gas cores are larger than the LTE masses, which for a
bound core implies a requirement on the external pressure of ~ 10^8 K/cm^3. The
cores have the potential to further form massive stars.Comment: Accepted for publication in MNRA
A 20 GHz bright sample for {\delta} > +72{\deg}: I. Catalogue
During 2010-2011, the Medicina 32-m dish hosted the 7-feed 18-26.5 GHz
receiver built for the Sardinia Radio Telescope, with the goal to perform its
commissioning. This opportunity was exploited to carry out a pilot survey at 20
GHz over the area for {\delta} > + 72.3{\deg}. This paper describes all the
phases of the observations, as they were performed using new hardware and
software facilities. The map-making and source extraction procedures are
illustrated. A customised data reduction tool was used during the follow-up
phase, which produced a list of 73 confirmed sources down to a flux density of
115 mJy. The resulting catalogue, here presented, is complete above 200 mJy.
Source counts are in agreement with those provided by the AT20G survey. This
pilot activity paves the way to a larger project, the K-band Northern Wide
Survey (KNoWS), whose final aim is to survey the whole Northern Hemisphere down
to a flux limit of 50 mJy (5{\sigma}).Comment: 10 pages, 10 figures. Accepted by MNRA
Is a Classical Language Adequate in Assessing the Detectability of the Redshifted 21cm Signal from the Early Universe?
The classical radiometer equation is commonly used to calculate the
detectability of the 21cm emission by diffuse cosmic hydrogen at high
redshifts. However, the classical description is only valid in the regime where
the occupation number of the photons in phase space is much larger than unity
and they collectively behave as a classical electromagnetic field. At redshifts
z<20, the spin temperature of the intergalactic gas is dictated by the
radiation from galaxies and the brightness temperature of the emitting gas is
in the range of mK, independently from the existence of the cosmic microwave
background. In regions where the observed brightness temperature of the 21cm
signal is smaller than the observed photon energy, of 68/(1+z) mK, the
occupation number of the signal photons is smaller than unity. Neverethless,
the radiometer equation can still be used in this regime because the weak
signal is accompanied by a flood of foreground photons with a high occupation
number (involving the synchrotron Galactic emission and the cosmic microwave
background). As the signal photons are not individually distinguishable, the
combined signal+foreground population of photons has a high occupation number,
thus justifying the use of the radiometer equation.Comment: 4 pages, Accepted for publication in JCA
Prediction of the Cosmic Evolution of the CO-Luminosity Functions
We predict the emission line luminosity functions (LFs) of the first 10
rotational transitions of CO in galaxies at redshift z=0 to z=10. This
prediction relies on a recently presented simulation of the molecular cold gas
content in ~3e7 evolving galaxies based on the Millennium Simulation. We
combine this simulation with a model for the conversion between molecular mass
and CO-line intensities, which incorporates the following mechanisms: (i)
molecular gas is heated by the CMB, starbursts (SBs), and active galactic
nuclei (AGNs); (ii) molecular clouds in dense or inclined galaxies can overlap;
(iii) compact gas can attain a smooth distribution in the densest part of
disks; (iv) CO-luminosities scale with metallicity changes between galaxies;
(v) CO-luminosities are always detected against the CMB. We analyze the
relative importance of these effects and predict the cosmic evolution of the
CO-LFs. The most notable conclusion is that the detection of regular galaxies
(i.e. no AGN, no massive SB) at high z>7 in CO-emission will be dramatically
hindered by the weak contrast against the CMB, in contradiction to earlier
claims that CMB-heating will ease the detection of high-redshift CO. The full
simulation of extragalactic CO-lines and the predicted CO-LFs at any redshift
can be accessed online, prior registration required} and they should be useful
for the modeling of CO-line surveys with future telescopes, such as ALMA, the
LMT, or the SKA.Comment: 8 figures, 1 tabl
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