10,223 research outputs found
Can hidden correlations mimic a variable fine structure constant?
Murphy et al. (2003a, MNRAS, 345, 609) claim to find evidence of cosmological
variations of the fine structure constant in the spectra of
intervening QSO absorption line systems. We find that this result is affected
by systematic effects. The values estimated in individual line systems
depend on the set of atomic transitions used and therefore the quoted
dependence on the cosmic age may reflect the fact that different sets of
transitions are used at different redshifts. A correlation between line shifts
and relative optical depths of the atomic transitions is also present. This
correlation is very tight for a high-redshift subsample and accounts for the
anomalous dispersion of the values found by Murphy et al. (2003a) in
this subsample. The above correlations are consistent with a scenario in which
gravitational redshift, caused by the gravity of the dark halo, contributes to
the shift in frequency of individual components. Gravitational redshift causes
differential spectral shifts of the same order as magnitude of those measured.
In the presence of line misidentification, these shifts can be interpreted in
terms of a variable . In order to verify the gravitational redshift
hypothesis, a direct access to Murphy et al. (2003a) data, or to a large amount
of new high resolution data, is necessary.Comment: 10 pages, 5 figures, 3 tables, to appear on Astronomy and
Astrophysic
The Radio Continuum, Far-Infrared Emission, And Dense Molecular Gas In Galaxies
A tight linear correlation is established between the HCN line luminosity and
the radio continuum (RC) luminosity for a sample of 65 galaxies (from Gao &
Solomon's HCN survey), including normal spiral galaxies and luminous and
ultraluminous infrared galaxies (LIRGs/ULIRGs). After analyzing the various
correlations among the global far-infrared (FIR), RC, CO, and HCN luminosities
and their various ratios, we conclude that the FIR-RC and FIR-HCN correlations
appear to be linear and are the tightest among all correlations. The
combination of these two correlations could result in the tight RC-HCN
correlation we observed. Meanwhile, the non-linear RC-CO correlation shows
slightly larger scatter as compared with the RC-HCN correlation, and there is
no correlation between ratios of either RC/HCN-CO/HCN or RC/FIR-CO/FIR. In
comparison, a meaningful correlation is still observed between ratios of
RC/CO-HCN/CO. Nevertheless, the correlation between RC/FIR and HCN/FIR also
disappears, reflecting again the two tightest FIR-RC and FIR-HCN correlations
as well as suggesting that FIR seems to be the bridge that connects HCN with
RC. Interestingly, despite obvious HCN-RC and RC-CO correlations,
multi-parameter fits hint that while both RC and HCN contribute significantly
(with no contribution from CO) to FIR, yet RC is primarily determined from FIR
with a very small contribution from CO and essentially no contribution from
HCN. These analyses confirm independently the former conclusions that it is
practical to use RC luminosity instead of FIR luminosity, at least globally, as
an indicator of star formation rate in galaxies including LIRGs/ULIRGs, and HCN
is a much better tracer of star-forming molecular gas and correlates with FIR
much better than that of CO.Comment: 11 ApJ pages, 7 figures; ApJ in pres
NGC 2992 in an X-ray high state observed by XMM: Response of the Relativistic Fe K Line to the Continuum
We present the analysis of an XMM observation of the Seyfert galaxy NGC 2992.
The source was found in its highest level of X-ray activity yet detected, a
factor higher in 2--10 keV flux than the historical minimum. NGC
2992 is known to exhibit X-ray flaring activity on timescales of days to weeks,
and the XMM data provide at least factor of better spectral resolution
in the Fe K band than any previously measured flaring X-ray state. We find that
there is a broad feature in the \sim 5-7 keV band which could be interpreted as
a relativistic Fe K emission line. Its flux appears to have increased
in tandem with the 2--10 keV continuum when compared to a previous Suzaku
observation when the continuum was a factor of lower than that during
the XMM observation. The XMM data are consistent with the general picture that
increased X-ray activity and corresponding changes in the Fe K line
emission occur in the innermost regions of the putative accretion disk. This
behavior contrasts with the behavior of other AGN in which the Fe K
line does not respond to variability in the X-ray.Comment: 30 pages, 6 figures, Accepted to Ap
Comparing treatment policies with assistance from the structural nested mean model
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142500/1/biom12391-sup-0001-SuppData.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142500/2/biom12391_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142500/3/biom12391.pd
Phase transition in the fine structure constant
Within the context of mass-varying neutrinos, we construct a cosmological
model that has a phase transition in the electromagnetic fine structure
constant \alpha at a redshift of 0.5. The model accommodates hints of a time
variable \alpha in quasar spectra and the nonobservance of such an effect at
very low redshifts. It is consistent with limits from the recombination and
primordial nucleosynthesis eras and is free of instabilities.Comment: 6 pages, 1 figure. Version to appear in PL
Expression and evolutionary divergence of the non-conventional olfactory receptor in four species of fig wasp associated with one species of fig
<p>Abstract</p> <p>Background</p> <p>The interactions of fig wasps and their host figs provide a model for investigating co-evolution. Fig wasps have specialized morphological characters and lifestyles thought to be adaptations to living in the fig's syconium. Although these aspects of natural history are well documented, the genetic mechanism(s) underlying these changes remain(s) unknown. Fig wasp olfaction is the key to host-specificity. The <it>Or83b</it> gene class, an unusual member of olfactory receptor family, plays a critical role in enabling the function of conventional olfactory receptors. Four <it>Or83b</it> orthologous genes from one pollinator (PFW) (<it>Ceratosolen solmsi</it>) and three non-pollinator fig wasps (NPFWs) (<it>Apocrypta bakeri, Philotrypesis pilosa </it>and <it>Philotrypesis </it>sp.) associated with one species of fig (<it>Ficus hispida</it>) can be used to better understand the molecular mechanism underlying the fig wasp's adaptation to its host. We made a comparison of spatial tissue-specific expression patterns and substitution rates of one orthologous gene in these fig wasps and sought evidence for selection pressures.</p> <p>Results</p> <p>A newly identified <it>Or83b </it>orthologous gene was named <it>Or2</it>. Expressions of <it>Or2 </it>were restricted to the heads of all wingless male fig wasps, which usually live in the dark cavity of a fig throughout their life cycle. However, expressions were widely detected in the antennae, legs and abdomens of all female fig wasps that fly from one fig to another for oviposition, and secondarily pollination. Weak expression was also observed in the thorax of PFWs. Compared with NPFWs, the <it>Or2 </it>gene in <it>C. solmsi </it>had an elevated rate of substitutions and lower codon usage. Analyses using Tajima's <it>D</it>, Fu and Li's <it>D* </it>and <it>F* </it>tests indicated a non-neutral pattern of nucleotide variation in all fig wasps. Unlike in NPFWs, this non-neutral pattern was also observed for synonymous sites of <it>Or2 </it>within PFWs.</p> <p>Conclusion</p> <p>The sex- and species-specific expression patterns of <it>Or2 </it>genes detected beyond the known primary olfactory tissues indicates the location of cryptic olfactory inputs. The specialized ecological niche of these wasps explains the unique habits and adaptive evolution of <it>Or2 </it>genes. The <it>Or2 </it>gene in <it>C. solmsi </it>is evolving very rapidly. Negative deviation from the neutral model of evolution reflects possible selection pressures acting on <it>Or2 </it>sequences of fig wasp, particularly on PFWs who are more host-specific to figs.</p
Characterization of Fumonisin B1-GlucoseReaction Kinetics and Products
The reaction of fumonisin B1 with the reducing sugar D-glucose can block the primary amine group of fumonisin B1 and may detoxify this mycotoxin. A method to separate hundred milligram quantities of fumonisin B1-glucose reaction products from the excess D-glucose with a reversed-phase C18 cartridge was developed. Mass spectrometry revealed that there were four primary products in this chain reaction when fumonisin B1 was heated with D-glucose at 65 C for 48 h: N-methyl-fumonisin B1, N-carboxymethyl-fumonisin B1, N-(3-hydroxyacetonyl)-fumonisin B1, and N-(2-hydroxy, 2-car- boxyethyl)-fumonisin B1. The N-(1-deoxy-D-fructos-1-yl) fumonisin B1 (fumonisin B1-glucose Schiff’s base) was detected by mass spectrometry when fumonisin B1 was heated with D-glucose at 60 C. The nonenzymatic browning reaction of fumonisin B1 with excess D-glucose followed apparent first- order kinetics. The activation energy, Ea, was 105.7 kJ/mol. Fumonisin B1 in contaminated corn could precipitate the nonenzymatic browning reaction with 0.1 M D-glucose at 60 and 8
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