44,331 research outputs found
Type I seesaw mechanism for quasi degenerate neutrinos
We discuss symmetries and scenarios leading to quasi-degenerate neutrinos in
type-I seesaw models. The existence of degeneracy in the present approach is
not linked to any specific structure for the Dirac neutrino Yukawa coupling
matrix and holds in general. Basic input is the application of the
minimal flavour violation principle to the leptonic sector. Generalizing this
principle, we assume that the structure of the right handed neutrino mass
matrix is determined by and the charged lepton Yukawa coupling matrix
in an effective theory invariant under specific groups
contained in the full symmetry group of the kinetic energy terms.
invariance also leads to specific structure for the departure from degeneracy.
The neutrino mass matrix (with degenerate mass ) resulting after seesaw
mechanism has a simple form in one
particular scenario based on supersymmetry. This form is shown to lead to
correct description of neutrino masses and mixing angles. The thermal
leptogenesis after inclusion of flavour effects can account for the observed
baryon asymmetry of the universe within the present scenario. Rates for lepton
flavour violating processes can occur at observable levels in the
supersymmetric version of the scenario.Comment: 14 pages; two figure
Flux Tube Model Signals for Baryon Correlations in Heavy Ion Collisions
The flux tube model offers a pictorial description of what happens during the
deconfinement phase transition in QCD. The 3-point vertices of a flux tube
network lead to formation of baryons upon hadronisation. Therefore,
correlations in the baryon number distribution at the last scattering surface
are related to the preceding pattern of the flux tube vertices, and provide a
signature of the nearby deconfinement phase transition. I discuss the nature of
the expected signal, which should be observable in heavy ion collisions at RHIC
and LHC.Comment: LaTeX, 9 pages, 5 figures, (v2) Several arguments expanded for
clarity, (v3) Minor typesetting changes, published versio
Morphology of the recently re-classified Tasman masked booby (Sula dactylatra tasmani) breeding on the Kermadec Islands
Once thought to be extinct, the Tasman Booby Sula tasmani has recently been re-classified as a subspecies of the Masked Booby S. dactylatra on the basis of genetic data. This re-classification raises the issue of whether this novel clade has a distinct morphology. Morphological differences in size, as well as coloration of integuments, bill and iris have been found in other subspecies of the Masked Booby but have not yet been reported for live Kermadec Islands breeding individuals. Museum specimens from this breeding location have been separated from other Pacific breeding subspecies by their longer wings. We sampled a total of 21 individuals from North Meyer Islet, Kermadec Group, New
Zealand, and applied molecular sexing to obtain sex-specific morphometric measurements. We matched dimorphism in vocalization with genetic sexing results and photographic documentation of human-assessed bill, foot and eye coloration. While culmen measurements were consistent with reports from museum specimens, wing chords from living specimens of Tasman Masked Boobies were 3% and 4% larger in males and females, respectively. Females had larger culmens and wings than males, consistent with the low extent of sexual dimorphism reported from museum skins. Adult Tasman Masked Boobies had yellow to buff-yellow feet, while fledglings, as in most sulids, had grey
to greyish-yellow feet. Our findings confirm the distinctively long wing and particular iris coloration previously reported for the taxon and provide the first description of integument coloration of live specimens. This study highlights the importance of including in situ assessment in taxon descriptions
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Mars simulated exposure and the characteristic Raman biosignatures of amino acids and halophilic microbes
Though Raman bands of α-amino acids (AA) are well documented, often only the strongest intensity bands are quoted as identifiers (e.g. Jenkins et al., 2005; De Gelder et al., 2007; Zhu et al., 2011). Unknown regolith mixtures on Mars-sampling missions could obscure these bands. Here the case is made for determining, via a statistical method, sets of characteristic bands to be used as identifiers, independent of band intensity or number of bands (Rolfe et al., 2016). AA have upwards of 25 potentially identifying bands and this method defines sets of 10–19 bands per AA. Examination of AA-doped Mars-like basalt resulted in a maximum of eight bands being identified, as some characteristic bands were obscured by mineral bands, including the strongest intensity band in some cases. This proved the need for characteristic bands to be defined, enabling successful identification of AA. The ESA ExoMars Rover mission will crush and then pass the sample to the Raman Laser Spectrometer. We crushed a Mars-like basalt to a similar grain size expected to be created by the rover. Our samples were doped with 1 % (by weight) AA samples, resulting in no detection of AA, because of loss of original spatial context and spaces between the grains. We recommend that Raman spectroscopy on future missions should be conducted before the sample is crushed. Halite-entombed halophilic microbes, known to survive being entombed, were exposed to Mars-like surface (including temperature, pressure, atmospheric composition and UV) and freeze-thaw cycle (plus pressure and atmospheric composition) conditions. This test on the survival of the microbes showed that survival rates quickly deteriorated in surface conditions, but freeze-thaw cycle samples had well preserved Raman biosignatures, indicating that similar signatures could be detectable on Mars if similar life persists in evaporitic material or brines today
Interstitial cell network volume is reduced in the terminal bowel of ageing mice
Ageing is associated with impaired neuromuscular function of the terminal gastrointestinal (GI) tract, which can result in chronic constipation, faecal impaction and incontinence. Interstitial cells of cajal (ICC) play an important role in regulation of intestinal smooth muscle contraction. However, changes in ICC volume with age in the terminal GI tract (the anal canal including the anal sphincter region and rectum)have not been studied. Here, the distribution, morphology and network volume of ICC in the terminal GI tract of 3‐to 4‐month‐old and 26‐to 28‐month‐old C57BL/6mice were investigated. ICC were identified by immunofluorescence labelling of wholemount preparations with an antibody against c‐Kit. ICC network volume was measured by software‐based 3D volume rendering of confocal Z stacks. A significant reduction in ICC network volume per unit volume of muscle was measured in aged animals. No age‐associated change in ICC morphology was detected. The thickness of the circular muscle layer of the anal sphincter region and rectum increased with age, while that in the distal colon decreased. These results suggest that ageing is associated with a reduction in the network volume of ICC in the terminal GI tract, which may influence the normal function of these regions
Dust-forming molecules in VY Canis Majoris (and Betelgeuse)
The formation of inorganic dust in circumstellar environments of evolved
stars is poorly understood. Spectra of molecules thought to be most important
for the nucleation, i.e. AlO, TiO, and TiO2, have been recently detected in the
red supergiant VY CMa. These molecules are effectively formed in VY CMa and the
observations suggest that non-equilibrium chemistry must be involved in their
formation and nucleation into dust. In addition to exploring the recent
observations of VY CMa, we briefly discuss the possibility of detecting these
molecules in the dust-poor circumstellar environment of Betelgeuse.Comment: contribution to Betelgeuse Workshop 2012: "The physics of Red
Supergiants: recent advances and open questions", 26-29 Nov 2012 Paris
(France
Pure rotational spectra of TiO and TiO_2 in VY Canis Majoris
We report the first detection of pure rotational transitions of TiO and TiO_2
at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational
temperature, T_rot, of about 250 K was derived for TiO_2. Although T_rot was
not well constrained for TiO, it is likely somewhat higher than that of TiO_2.
The detection of the Ti oxides confirms that they are formed in the
circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of
inorganic-dust formation, but alternative explanations for our observation of
TiO and TiO_2 in the cooler regions of the envelope cannot be ruled out at this
time. The observations suggest that a significant fraction of the oxides is not
converted to dust, but instead remains in the gas phase throughout the outflow.Comment: to appear in Astronomy and Astrophysic
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