997 research outputs found
The Age-Redshift Relationship of Old Passive Galaxies
We use 32 age measurements of passively evolving galaxies as a function of
redshift to test and compare the standard model (CDM) with the Universe. We show that the latter fits the data with a reduced
for a Hubble constant km
. By comparison, the optimal flat CDM
model, with two free parameters (including and km ), fits the age-\emph{z} data with a reduced .
Based solely on their values, both models appear to account
for the data very well, though the optimized CDM parameters are only
marginally consistent with those of the concordance model ( and km ). Fitting the age-
data with the latter results in a reduced . However,
because of the different number of free parameters in these models, selection
tools, such as the Akaike, Kullback and Bayes Information Criteria, favour
over CDM with a likelihood of
versus . These results are suggestive, though not yet
compelling, given the current limited galaxy age- sample. We carry out Monte
Carlo simulations based on these current age measurements to estimate how large
the sample would have to be in order to rule out either model at a confidence level. We find that if the real cosmology is CDM, a
sample of galaxy ages would be sufficient to rule out
at this level of accuracy, while galaxy ages would be required to
rule out CDM if the real Universe were instead .Comment: 36 pages, 13 figures, 1 table; accepted for publication in The
Astronomical Journal. arXiv admin note: text overlap with arXiv:1405.238
Comparative transcriptome analysis and marker development of two closely related Primrose species (Primula poissonii and Primula wilsonii)
BACKGROUND: Primula species are important early spring garden plants with a centre of diversity and speciation in the East Himalaya-Hengduan Mountains in Western China. Studies on population genetics, speciation and phylogeny of Primula have been impeded by a lack of genomic resources. In the present study, we sequenced the transcriptomes of two closely related primrose species, Primula poissonii and Primula wilsonii, using short reads on the Illumina Genome Analyzer platform. RESULTS: We obtained 55,284 and 55,011 contigs with N50 values of 938 and 1,085 for P. poissonii and P. wilsonii, respectively, and 6,654 pairs of putative orthologs were identified between the two species. Estimations of non-synonymous/synonymous substitution rate ratios for these orthologs indicated that 877 of the pairs may be under positive selection (Ka/Ks > 0.5), and functional enrichment analysis revealed that significant proportions of the orthologs were in the categories DNA repair, stress resistance, which may provide some hints as to how the two closely related Primula species adapted differentially to extreme environments, such as habitats characterized by aridity, high altitude and high levels of ionizing radiation. It was possible for the first time to estimate the divergence time between the radiated species pair, P. poissonii and P. wilsonii; this was found to be approximately 0.90 ± 0.57 Mya, which falls between the Donau and Gunz glaciation in the Middle Pleistocene. Primers based on 54 pairs of orthologous SSR-containing sequences between the two Primula species were designed and verified. About half of these pairs successfully amplified for both species. Of the 959 single copy nuclear genes shared by four model plants (known as APVO genes), 111 single copy nuclear genes were verified as being present in both Primula species and exon-anchored and intron-spanned primers were designed for use. CONCLUSION: We characterized the transcriptomes for the two Primula species, and produced an unprecedented amount of genomic resources for these important garden plants. Evolutionary analysis of these two Primula species not only revealed a more precise divergence time, but also provided some novel insights into how differential adaptations occurred in extreme habitats. Furthermore, we developed two sets of genetic markers, single copy nuclear genes and nuclear microsatellites (EST-SSR). Both these sets of markers will facilitate studies on the genetic improvement, population genetics and phylogenetics of this rapidly adapting taxon
Stabilities of one-dimensional stationary states of Bose-Einstein condensates
We explore the dynamical stabilities of a quasi-one dimensional (1D)
Bose-Einstein condensate (BEC) consisting of fixed atoms with
time-independent external potential. For the stationary states with zero flow
density the general solution of the perturbed time evolution equation is
constructed, and the stability criterions concerning the initial conditions and
system parameters are established. Taking the lattice potential case as an
example, the stability and instability regions on the parameter space are
found. The results suggest a method for selecting experimental parameters and
adjusting initial conditions to suppress the instabilities.Comment: 12 page
Characterization of a newly isolated green microalga Scenedesmus sp. as a potential source of biodiesel
An oil-producing microalga SP-01 belonging to the genus Scenedesmus was shown to be able to grow on a media containing 5 to 30 g L-1 NaCl. Under mixotrophic condition, the maximum cell dry weight of 3.1 g L-1 and specific growth rate of 0.034 h-1 were obtained at 0.5 g L-1 NaNO3 and 6 g L-1 acetate. The effects of salinity on the biomass, lipid, and carotenoid productions of the alga SP-01 in mixotrophic mode were investigated. The biomass productivity increased with increasing NaNO3 concentrations, and addition of NaCl resulted in a higher biomass while NaNO3 was present. The maximum lipid content was obtained while no NaNO3 and NaCl was added, and the lipid content decreased with increasing NaNO3 concentrations or addition of NaCl. The maximum lipid productivities of 67.44 to 68.44 mg L-1day-1 were obtained while NaNO3 and NaCl were not added or while 20 g L-1 NaCl and 0.13 g L-1 NaNO3 were added. The algal lipid was mainly composed of C16 and C18 fatty acids accounting for more than 90% of total fatty acids. Furthermore, lutein and astaxanthin were the main carotenoids.Key words: Halotolerant, microalga, Scenedesmus sp., mixotrophic culture, lipid, carotenoid
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