2,312 research outputs found
ELT requirements for future observations of the Intergalactic Medium
We summarise the science cases for an ELT that were presented in the parallel
session on the intergalactic medium, and the open discussion that followed the
formal presentations. Observations of the IGM with an ELT provides tremendous
potential for dramatic improvements in current programmes in a very wide
variety of subjects. These range from fundamental physics (expansion of the
Universe, nature of the dark matter, variation of physical constants),
cosmology (geometry of the Universe, large-scale structure), reionisation
(ionisation state of the IGM at high redshift>6, to more traditional astronomy,
such as the interactions between galaxies and the IGM (metal enrichment,
galactic winds and other forms of feedback), and the study of the interstellar
medium in high redshift galaxies through molecules. The requirements on ELTs
and their instruments for fulfilling this potential are discussed.Comment: proceedings IAU 232 "Extremely Large Telescopes", eds Whitelock,
Leibundgut and Dennefeld, comments welcom
Changes on the viral capsid surface during the evolution of porcine circovirus type 2 (PCV2) from 2009 till 2018 may lead to a better receptor binding
Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases (PCVAD). Three major PCV2 genotypes (PCV2a, PCV2b, and PCV2d) have been identified globally. Despite their worldwide distribution, the prevalence and genetic evolution of PCV2 in Belgium has not previously been determined. In this study, 319 samples from animals suffering from diseases likely to be associated with PCV2 were collected from 2009 to 2018 and analysed by virus titration. The overall prevalence of PCV2 in PCVAD-suspected cases was 15.7 per cent (50/319). The phylogenetic analysis demonstrated that at least three genotypes (PCV2a, PCV2b, and PCV2d) circulated in Belgium from 2009 till 2018, and that PCV2 evolved from PCV2a to PCV2b and from PCV2d-1 to PCV2d-2. Sequence comparison among the forty-three PCV2 isolates showed that they had 89.7-100 per cent nucleotide-sequence and 88.5-100 per cent amino-acid-sequence identities. Three amino acid sites were under positive selection. Three-dimensional analysis of genotype-specific amino acids revealed that most of the mutations were on the outside of the cap protein with a few conserved mutations present on the inner side. Mutations toward more basic amino acids were found on the upper and tail parts of two connecting capsid proteins which form one big contact region, most probably involved in receptor binding. The lower part was relatively conserved. This polarity change together with the formation of an extruding part drive the virus to a more efficient GAG receptor binding. Taken together, these results showed a genotype shift from PCV2a to PCV2b and later on from PCV2d-1 to PCV2d-2, and a PCV2 evolution toward a better receptor binding capacity
Was the Universe Reionized by Massive Population-III Stars?
The WMAP satellite has measured a large optical depth to electron scattering
after cosmological recombination of 0.17+-0.04, implying significant
reionization of the primordial gas only ~200 million years after the big bang.
However, the most recent overlap of intergalactic HII regions must have occured
at z<9 based on the Lyman-alpha forest constraint on the thermal history of the
intergalactic medium. Here we argue that a first generation of metal-free stars
with a heavy (rather than Salpeter) mass function is therefore required to
account for much of the inferred optical depth. This conclusion holds if
feedback regulates star formation in early dwarf galaxies as observed in
present-day dwarfs.Comment: 4 pages, 1 figure, replaced to match version accepted by ApJ Letter
Cosmological HII Bubble Growth During Reionization
We present general properties of ionized hydrogen (HII) bubbles and their
growth based on a state-of-the-art large-scale (100 Mpc/h) cosmological
radiative transfer simulation. The simulation resolves all halos with atomic
cooling at the relevant redshifts and simultaneously performs radiative
transfer and dynamical evolution of structure formation. Our major conclusions
include: (1) for significant HII bubbles, the number distribution is peaked at
a volume of at all redshifts. But, at ,
one large, connected network of bubbles dominates the entire HII volume. (2)
HII bubbles are highly non-spherical. (3) The HII regions are highly biased
with respect to the underlying matter distribution with the bias decreasing
with time. (4) The non-gaussianity of the HII region is small when the universe
becomes 50% ionized. The non-gaussianity reaches its maximal near the end of
the reionization epoch . But at all redshifts of interest there is a
significant non-gaussianity in the HII field. (5) Population III galaxies may
play a significant role in the reionization process. Small bubbles are
initially largely produced by Pop III stars. At even the largest HII
bubbles have a balanced ionizing photon contribution from Pop II and Pop III
stars, while at Pop II stars start to dominate the overall ionizing
photon production for large bubbles, although Pop III stars continue to make a
non-negligible contribution. (6) The relationship between halo number density
and bubble size is complicated but a strong correlation is found between halo
number density and bubble size for large bubbles.Comment: 10 pages, 14 figures; accepted version; higher resolution figures and
supplementary material can be found at
http://www.astro.princeton.edu/~msshin/reionization/web.ht
The Impact of the Implementation of an Enterprise Resource Planning System on a Typical Governmental Office
Enterprise Resource Planning (ERP) systems are part of Information Systems which organisations depend on when conducting business. An ERPsystem offers useful functionality in the smooth running of an organisation. This study investigated the impact on ERP implementation at SASSA North West Regional Office, a typical governmental office. It highlighted problems of the current ERP system by delineating the weakness and pitfalls. ERP systems are focused on standardisation and synchronisation of information as a result improved organisational efficiency, unfortunately problems with ERP system can create challenges and dissatisfaction among the end users, and that they fail to deliver the anticipated benefits. The findings of this study revealed that there was deficiency in ERP system; employees were worried about data loss when they use the system, found system errors, experienced difficulty in exporting data, and were not satisfied with quality of output from ERP system. 
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