9,572 research outputs found
Topological Dirac states in asymmetric Pb1-xSnxTe quantum wells
The electronic structure of lead-salt (IV-VI semiconductor) topological
quantum wells (T-QWs) is investigated with analytical solutions of the
effective 4x4 Dimmock k & BULL; p model, which gives an accurate
description of the bands around the fundamental energy gap. Specific
results for three-layer Pb1-xSnxTe nanostructures with varying Sn
composition are presented and the main differences between topological
and normal (N) QWs highlighted. A series of new features are found in
the spectrum of T-QWs, in particular in asymmetric QWs where large
(Rashba spin-orbit) splittings are obtained for the topological Dirac
states inside the gap
Extreme Quiescent Variability of the Transient Neutron Star Low-mass X-ray Binary EXO 1745-248 in Terzan 5
EXO 1745-248 is a transient neutron-star low-mass X-ray binary that resides
in the globular cluster Terzan 5. We studied the transient during its quiescent
state using 18 Chandra observations of the cluster acquired between 2003 and
2016. We found an extremely variable source, with a luminosity variation in the
0.5-10 keV energy range of orders of magnitude (between
erg s and erg s) on timescales
from years down to only a few days. Using an absorbed power-law model to fit
its quiescent spectra, we obtained a typical photon index of ,
indicating that the source is even harder than during outburst and much harder
than typical quiescent neutron stars if their quiescent X-ray spectra are also
described by a single power-law model. This indicates that EXO 1745-248 is very
hard throughout the entire observed X-ray luminosity range. At the highest
luminosity, the spectrum fits better when an additional (soft) component is
added to the model. All these quiescent properties are likely related to strong
variability in the low-level accretion rate in the system. However, its extreme
variable behavior is strikingly different from the one observed for other
neutron star transients that are thought to still accrete in quiescence. We
compare our results to these systems. We also discuss similarities and
differences between our target and the transitional millisecond pulsar IGR
J18245-2452, which also has hard spectra and strong variability during
quiescence.Comment: Accepted for publication in MNRA
New Cataclysmic Variables and other Exotic Binaries in the Globular Cluster 47 Tucanae
We present 22 new (+3 confirmed) cataclysmic variables (CVs) in the non
core-collapsed globular cluster 47 Tucanae (47 Tuc). The total number of CVs in
the cluster is now 43, the largest sample in any globular cluster so far. For
the identifications we used near-ultraviolet (NUV) and optical images from the
Hubble Space Telescope, in combination with X-ray results from the Chandra
X-ray Observatory. This allowed us to build the deepest NUV CV luminosity
function of the cluster to date. We found that the CVs in 47 Tuc are more
concentrated towards the cluster center than the main sequence turnoff stars.
We compared our results to the CV populations of the core-collapsed globular
clusters NGC 6397 and NGC 6752. We found that 47 Tuc has fewer bright CVs per
unit mass than those two other clusters. That suggests that dynamical
interactions in core-collapsed clusters play a major role creating new CVs. In
47 Tuc, the CV population is probably dominated by primordial and old
dynamically formed systems. We estimated that the CVs in 47 Tuc have total
masses of approx. 1.4 M_sun. We also found that the X-ray luminosity function
of the CVs in the three clusters is bimodal. Additionally, we discuss a
possible double degenerate system and an intriguing/unclassified object.
Finally, we present four systems that could be millisecond pulsar companions
given their X-ray and NUV/optical colors. For one of them we present very
strong evidence for being an ablated companion. The other three could be CO- or
He-WDs.Comment: Published on MNRAS. 31 Pages, 23 Figures, 5 Tables. Minor changes
with respect to previous arXiv versio
Flavor changing neutral currents from lepton and B decays in the two Higgs doublet model
Constraints on the whole spectrum of lepton flavor violating vertices are
shown in the context of the standard two Higgs doublet model. The vertex
involving the mixing is much more constrained than the others, and
the decays proportional to such vertex are usually very supressed. On the other
hand, bounds on the quark sector are obtained from leptonic decays of the
mesons and from . We emphasize that
although the mixing restricts severely the
mixing vertex, the upper bound for this vertex could still give a sizeable
contribution to the decay respect to the standard
model contribution, from which we see that such vertex could still play a role
in the phenomenology.Comment: 9 pages, 2 figures, LaTeX2e. Minor typos corrected. References added
and corrected. Introduction change
Arabidopsis natural variation in insect egg-induced cell death reveals a role for LECTIN RECEPTOR KINASE-I.1.
In Arabidopsis (Arabidopsis thaliana), a hypersensitive-like response (HR-like response) is triggered underneath the eggs of the large white butterfly Pieris brassicae (P. brassicae), and this response is dependent on salicylic acid (SA) accumulation and signaling. Previous reports indicate that the clade I L-type LECTIN RECEPTOR KINASE-I.8 (LecRK-I.8) is involved in early steps of egg recognition. A genome-wide association study was used to better characterize the genetic structure of the HR-like response and discover loci that contribute to this response. We report here the identification of LecRK-I.1, a close homolog of LecRK-I.8, and show that two main haplotypes that explain part of the variation in HR-like response segregate among natural Arabidopsis accessions. Besides, signatures of balancing selection at this locus suggest that it may be ecologically important. Disruption of LecRK-I.1 results in decreased HR-like response and SA signaling, indicating that this protein is important for the observed responses. Furthermore, we provide evidence that LecRK-I.1 functions in the same signaling pathway as LecRK-I.8. Altogether, our results show that the response to eggs of P. brassicae is controlled by multiple LecRKs
Demographic fitness of Belminus ferroae (Hemiptera: Triatominae) on three different hosts under laboratory conditions
Triatominae are widely recognised for their role as vectors of Trypanosoma cruzi. One of the main biological characteristics of this subfamily is their obligate haematophagous condition. However, previous studies on Belminus herreri and Belminus ferroae suggested that cockroaches are their principal hosts in domiciles. Due to this peculiar behaviour, the aim of this study was to analyse several demographic and reproductive parameters of B. ferroae fed on three different hosts (mice, cockroaches and Rhodnius prolixus) and relate B. ferroae fitness to these alternative hosts. The cohorts were reared under constant conditions. The egg hatching rate was similar for cohorts fed on cockroaches (69.4%) and R. prolixus (63.8%), but was much lower for the cohort fed on mice (16%). The development time from the nymph to adult stage and the average age of first reproduction (α) presented lower values in the cohort fed on cockroaches, which is consistent with the higher population growth rate associated with this host. Demographic parameters [intrinsic rate of natural increase, finite rate of population growth, net reproductive rate and damping ratio] showed statistically significant differences between the cohorts. Analysis of the life history of B. ferroae revealed a higher fitness related to the cockroach. The implications of these results for the origin of the subfamily are discussed.Centro de Estudios Parasitológicos y de Vectore
Demographic fitness of Belminus ferroae (Hemiptera: Triatominae) on three different hosts under laboratory conditions
Triatominae are widely recognised for their role as vectors of Trypanosoma cruzi. One of the main biological characteristics of this subfamily is their obligate haematophagous condition. However, previous studies on Belminus herreri and Belminus ferroae suggested that cockroaches are their principal hosts in domiciles. Due to this peculiar behaviour, the aim of this study was to analyse several demographic and reproductive parameters of B. ferroae fed on three different hosts (mice, cockroaches and Rhodnius prolixus) and relate B. ferroae fitness to these alternative hosts. The cohorts were reared under constant conditions. The egg hatching rate was similar for cohorts fed on cockroaches (69.4%) and R. prolixus (63.8%), but was much lower for the cohort fed on mice (16%). The development time from the nymph to adult stage and the average age of first reproduction (α) presented lower values in the cohort fed on cockroaches, which is consistent with the higher population growth rate associated with this host. Demographic parameters [intrinsic rate of natural increase, finite rate of population growth, net reproductive rate and damping ratio] showed statistically significant differences between the cohorts. Analysis of the life history of B. ferroae revealed a higher fitness related to the cockroach. The implications of these results for the origin of the subfamily are discussed.Centro de Estudios Parasitológicos y de Vectore
The Effect of Pre-Harvest Application of Pectic Oligosaccharides and Abscisic Acid on Technological Ripening and Anthocyanin Profile of ‘Syrah’ Must and Grapes Grown in a Warm Climate
The progressive increase of environmental temperature as a consequence of climate change is a challengefor the wine industry. Elevated temperatures during grape ripening affect the development of grape skincolor by inhibiting the synthesis of pigments and promoting their degradation, which causes an imbalancein the chromatic quality of must and red wine. The application of pectic oligosaccharides (POs) and abscisicacid (ABA) triggers the phenylpropanoid pathway and increases the color index in grapes. Since the atharvestpigments and phenolic compounds are determinant for wine quality, this work addressed the preharvestapplication of POs and ABA as an in-field strategy for improving the quality of Syrah must andgrapes grown in a warm climate. The color development, physicochemical parameters, phenolic content,and pigments in berries and must were evaluated. Results showed POs and ABA improved berry colordevelopment and anthocyanin content during ripening. Musts from POs-treated berries exhibited thehighest phenols concentration and the most intense color, related to higher chroma values and anthocyanincontent, particularly delphinidin, petunidin, and malvidin 3-glucosides, while ABA improved must tonalityby reducing the hue angle. In summary, POs and ABA application at veráison, differentially modulatedthe technological ripening of Syrah grapes and can be an alternative to conventional agrochemicals topreserve the quality of musts elaborated from grapes grown in warm climates, by increasing the content ofphenolic compounds and enhancing berry skin color development through the differential accumulationof anthocyanins
- …