1,224 research outputs found
2XMMi J225036.9+573154 - a new eclipsing AM Her binary discovered using XMM-Newton
We report the discovery of an eclipsing polar, 2XMMi J225036.9+573154, using
XMM-Newton. It was discovered by searching the light curves in the 2XMMi
catalogue for objects showing X-ray variability. Its X-ray light curve shows a
total eclipse of the white dwarf by the secondary star every 174 mins. An
extended pre-eclipse absorption dip is observed in soft X-rays at phi=0.8-0.9,
with evidence for a further dip in the soft X-ray light curve at phi~0.4.
Further, X-rays are seen from all orbital phases (apart from the eclipse) which
makes it unusual amongst eclipsing polars. We have identified the optical
counterpart, which is faint (r=21), and shows a deep eclipse (>3.5 mag in white
light). Its X-ray spectrum does not show a distinct soft X-ray component which
is seen in many, but not all, polars. Its optical spectrum shows Halpha in
emission for a fraction of the orbital period.Comment: Accepted for publication in MNRA
Structural variation, dynamics, and catalytic application of palladium(II) complexes of di-N-heterocyclic carbene-amine ligands
A series of palladium(II) complexes incorporating di-NHC-amine ligands has been prepared and their structural, dynamic and catalytic behaviour investigated. The complexes [trans-(k(2)-(CN)-C-tBu(Bn)CN(Bn)C-tBu)PdCl2] (12) and [trans-(kappa(2)-(CN)-C-Mes(H)C-Mes)PdCl2] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between - 40 and 25 degrees C shows that the di-NHC-amine ligand is flexible expressing C-s symmetry and for 13 rotation of the mesityl groups is prevented. In the related C-1 complex [(kappa(3)-(CN)-C-tBu(H)C-tBu)PdCl][CI] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C. Reaction between 12 - 14 and two equivalents of AgBF4 in acetonitrile gives the analogous complexes [trans-(kappa(2)-(CN)-C-tBu(Bn)C-tBu)PdCl2] (12) and [trans-(kappa(CN)-C-2Mes(H)C-Mes)PdCl2] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between -40 ans 25 degrees C shows the di-NHC-amine ligand is flexible expressing C-s symmetry and for 13 rotation of the mesityl groups is prevented. In the related C-1 complex [kappa(3)-(CN)-C-tBu(H)C-tBu)PdCI][CI] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C.Reaction between 12-14 and two equivalents of AgBF4 in acetonitrile gives the analogous complexes [trans-(kappa(2)-(CN)-C-tBu(H)(CPd)-Pd-tBu(MeCN)(2)][BF4](2) (15), [trans-(kappa(CN)-C-2Mes(H)C-Mes)Pd(MeCN)(2)[BF4](2 (16)) and [(kappa(3)-(CN)-C-tBu(H)C-tBu)Pd(MeCN)][BF4](2) (17) indicating that ligand structure determines amine coordination. The single crystal X-ray structures of 12, 17 and two ligand imidazolium salt precursors C-tBu(H)N(Bn)C(H) (tBu)][CI](2) (2) and [C-tBu(H) N(H)C(H)(tBu)][BPh4](2) (4) have been determined. Complexes 12-14 and 15-17 have been shown to be active precatalysts for Heck and hydroamination reactions respectively
Possible detection of two giant extrasolar planets orbiting the eclipsing polar UZ Fornacis
We present new high-speed, multi-observatory, multi-instrument photometry of
the eclipsing polar UZ For in order to measure precise mid-eclipse times with
the aim of detecting any orbital period variations. When combined with
published eclipse times and archival data spanning ~27 years, we detect
departures from a linear and quadratic trend of ~60 s. The departures are
strongly suggestive of two cyclic variations of 16(3) and 5.25(25) years. The
two favoured mechanisms to drive the periodicities are either two giant
extrasolar planets as companions to the binary (with minimum masses of
6.3(1.5)M(Jupiter) and 7.7(1.2)M(Jupiter)) or a magnetic cycle mechanism (e.g.
Applegate's mechanism) of the secondary star. Applegate's mechanism would
require the entire radiant energy output of the secondary and would therefore
seem to be the least likely of the two, barring any further refinements in the
effect of magnetic fieilds (e.g. those of Lanza et al.). The two planet model
can provide realistic solutions but it does not quite capture all of the
eclipse times measurements. A highly eccentric orbit for the outer planet would
fit the data nicely, but we find that such a solution would be unstable. It is
also possible that the periodicities are driven by some combination of both
mechanisms. Further observations of this system are encouraged.Comment: 10 pages, 4 figures, 2 table
Not So Fast Kepler-1513: A Perturbing Planetary Interloper in the Exomoon Corridor
Transit Timing Variations (TTVs) can be induced by a range of physical
phenomena, including planet-planet interactions, planet-moon interactions, and
stellar activity. Recent work has shown that roughly half of moons would induce
fast TTVs with a short period in the range of two-to-four orbits of its host
planet around the star. An investigation of the Kepler TTV data in this period
range identified one primary target of interest, Kepler-1513 b. Kepler-1513 b
is a planet orbiting a late G-type dwarf at
AU. Using Kepler photometry, this initial analysis
showed that Kepler-1513 b's TTVs were consistent with a moon. Here, we report
photometric observations of two additional transits nearly a decade after the
last Kepler transit using both ground-based observations and space-based
photometry with TESS. These new transit observations introduce a previously
undetected long period TTV, in addition to the original short period TTV
signal. Using the complete transit dataset, we investigate whether a
non-transiting planet, a moon, or stellar activity could induce the observed
TTVs. We find that only a non-transiting perturbing planet can reproduce the
observed TTVs. We additionally perform transit origami on the Kepler
photometry, which independently applies pressure against a moon hypothesis.
Specifically, we find that Kepler-1513 b's TTVs are consistent with an exterior
non-transiting Saturn mass planet, Kepler-1513 c, on a wide orbit,
5 outside a 5:1 period ratio with Kepler-1513 b. This example
introduces a previously unidentified cause for planetary interlopers in the
exomoon corridor, namely an insufficient baseline of observations.Comment: 20 pages, 13 figures. Accepted to MNRAS. Code available at
https://github.com/dyahalomi/Kepler151
Mind the Outgroup and Bare Branches in Total-Evidence Dating: a Case Study of Pimpliform Darwin Wasps (Hymenoptera, Ichneumonidae)
Taxon sampling is a central aspect of phylogenetic study design, but it
has received limited attention in the context of total-evidence dating, a
widely used dating approach that directly integrates molecular and
morphological information from extant and fossil taxa. We here assess
the impact of commonly employed outgroup sampling schemes and missing
morphological data in extant taxa on age estimates in a total-evidence
dating analysis under the uniform tree prior. Our study group is
Pimpliformes, a highly diverse, rapidly radiating group of parasitoid
wasps of the family Ichneumonidae. We analyze a data set comprising 201
extant and 79 fossil taxa, including the oldest fossils of the family
from the Early Cretaceous and the first unequivocal representatives of
extant subfamilies from the mid Paleogene. Based on newly compiled
molecular data from ten nuclear genes and a morphological matrix that
includes 222 characters, we show that age estimates become both older
and less precise with the inclusion of more distant and more poorly
sampled outgroups. These outgroups not only lack morphological and
temporal information, but also sit on long terminal branches and
considerably increase the evolutionary rate heterogeneity. In addition,
we discover an artefact that might be detrimental for total-evidence
dating: “bare-branch attraction”, namely high attachment probabilities
of certain fossils to terminal branches for which morphological data are
missing. Using computer simulations, we confirm the generality of this
phenomenon and show that a large phylogenetic distance to any of the
extant taxa, rather than just older age, increases the risk of a fossil
being misplaced due to bare-branch attraction. After restricting
outgroup sampling and adding morphological data for the previously
attracting, bare branches, we recover a Jurassic origin for Pimpliformes
and Ichneumonidae. This first age estimate for the group not only
suggests an older origin than previously thought, but also that
diversification of the crown group happened well before the
Cretaceous-Paleogene boundary. Our case study demonstrates that in order
to obtain robust age estimates, total-evidence dating studies need to
be based on a thorough and balanced sampling of both extant and fossil
taxa, with the aim of minimizing evolutionary rate heterogeneity and
missing morphological information.</p
Nonequilibrium pion dynamics near the critical point in a constituent quark model
We study static and dynamical critical phenomena of chiral symmetry breaking
in a two-flavor Nambu--Jona-Lasinio constituent quark model. We obtain the
low-energy effective action for scalar and pseudoscalar degrees of freedom to
lowest order in quark loops and to quadratic order in the meson fluctuations
around the mean field. The \emph{static} limit of critical phenomena is shown
to be described by a Ginzburg-Landau effective action including \emph{spatial}
gradients. Hence \emph{static} critical phenomena is described by the
universality class of the O(4) Heisenberg ferromagnet. \emph{Dynamical}
critical phenomena is studied by obtaining the equations of motion for pion
fluctuations. We find that for the are stable long-wavelength pion
excitations with dispersion relation described by isolated
pion poles. The residue of the pion pole vanishes near as and long-wavelength fluctuations are damped out by Landau
damping on a time scale , reflecting
\emph{critical slowing down} of pion fluctuations near the critical point. At
the critical point, the pion propagator features mass shell logarithmic
divergences which we conjecture to be the harbinger of a (large) dynamical
anomalous dimension. We find that while the \emph{classical spinodal} line
coincides with that of the Ginzburg-Landau theory, the growth rate of
long-wavelength spinodal fluctuations has a richer wavelength dependence as a
consequence of Landau damping. We argue that Landau damping prevents a
\emph{local} low energy effective action in terms of a derivative expansion in
real time.Comment: 22 pages 5 figures. to appear in Nucl. Phys.
Recommended from our members
Allograft rejection is associated with development of functional IgE specific for donor MHC antigens.
BACKGROUND: Donor-specific antibodies of the IgG isotype are measured routinely for diagnostic purposes in renal transplant recipients and are associated with antibody-mediated rejection and long-term graft loss. OBJECTIVE: This study aimed to investigate whether MHC-specific antibodies of the IgE isotype are induced during allograft rejection. METHODS: Anti-MHC/HLA IgE levels were measured in sera of mice grafted with skin or heart transplants from various donor strains and in sera of kidney transplant patients with high levels of HLA IgG. Mediator release was triggered in vitro by stimulating basophils that were coated with murine or human IgE-positive serum, respectively, with specific recombinant MHC/HLA antigens. Kidney tissue samples obtained from organ donors were analyzed by using flow cytometry for cells expressing the high-affinity receptor for IgE (FcεRI). RESULTS: Donor MHC class I- and MHC class II-specific IgE was found on acute rejection of skin and heart grafts in several murine strain combinations, as well as during chronic antibody-mediated heart graft rejection. Anti-HLA IgE, including donor HLA class I and II specificities, was identified in a group of sensitized transplant recipients. Murine and human anti-MHC/HLA IgE triggered mediator release in coated basophils on stimulation with specific MHC/HLA antigens. HLA-specific IgE was not linked to atopy, and allergen-specific IgE present in allergic patients did not cross-react with HLA antigens. FcεRI+ cells were found in the human renal cortex and medulla and provide targets for HLA-specific IgE. CONCLUSION: These results demonstrate that MHC/HLA-specific IgE develops during an alloresponse and is functional in mediating effector mechanisms
Identification of 24 new microsatellite loci in the sweat bee Lasioglossum malachurum (Hymenoptera: Halictidae)
OBJECTIVE: The objective here is to identify highly polymorphic microsatellite loci for the Palaearctic sweat bee Lasioglossum malachurum. Sweat bees (Hymenoptera: Halictidae) are widespread pollinators that exhibit an unusually large range of social behaviours from non-social, where each female nests alone, to eusocial, where a single queen reproduces while the other members of the colony help to rear her offspring. They thus represent excellent models for understanding social evolution. RESULTS: 24 new microsatellite loci were successfully optimized. When amplified across 23-40 unrelated females, the number of alleles per locus ranged from 3 to 17 and the observed heterozygosities 0.45 to 0.95. Only one locus showed evidence of significant deviation from Hardy-Weinberg equilibrium. No evidence of linkage disequilibrium was found. These 24 loci will enable researchers to gain greater understanding of colony relationships within this species, an important model for the study of eusociality. Furthermore, 22 of the same loci were also successfully amplified in L. calceatum, suggesting that these loci may be useful for investigating the ecology and evolution of sweat bees in general
Cabozantinib Versus Mitoxantrone-prednisone in Symptomatic Metastatic Castration-resistant Prostate Cancer: A Randomized Phase 3 Trial with a Primary Pain Endpoint
Background: Bone metastases in patients with metastatic castration-resistant prostate cancer (mCRPC) are associated with debilitating pain and functional compromise. Objective: To compare pain palliation as the primary endpoint for cabozantinib versus mitoxantrone-prednisone in men with mCRPC and symptomatic bone metastases using patient-reported outcome measures. Design, setting, and participants: A randomized, double-blind phase 3 trial (COMET-2; NCT01522443) in men with mCRPC and narcotic-dependent pain from bone metastases who had progressed after treatment with docetaxel and either abiraterone or enzalutamide. Intervention: Cabozantinib 60 mg once daily orally versus mitoxantrone 12 mg/m2 every 3 wk plus prednisone 5 mg twice daily orally. Outcome measurements and statistical analysis: The primary endpoint was pain response at week 6 confirmed at week 12 (≥30% decrease from baseline in patient-reported average daily worst pain score via the Brief Pain Inventory without increased narcotic use). The planned sample size was 246 to achieve ≥90% power. Results and limitations: Enrollment was terminated early because cabozantinib did not demonstrate any survival benefit in the companion COMET-1 trial. At study closure, 119 participants were randomized (cabozantinib: N =61; mitoxantrone-prednisone: N = 58). Complete pain and narcotic use data were available at baseline, week 6, and week 12 for 73/106 (69%) patients. There was no significant difference in the pain response with cabozantinib versus mitoxantrone-prednisone: the proportions of responders were 15%versus 17%,a −2%difference(95%confidenceinterval:−16%to11%, p = 0.8). Barriers to accrual included pretreatment requirements for a washout period of prior anticancer therapy and a narcotic optimization period to maximize analgesic dosing. Conclusions: Cabozantinib treatment did not demonstrate better pain palliation than mitoxantrone-prednisone in heavily pretreated patients with mCRPC and symptomatic bone metastases. Future pain-palliation trials should incorporate briefer timelines from enrollment to treatment initiation. Patient summary: Cabozantinib was not better than mitoxantrone-prednisone for pain relief in patients with castration-resistant prostate cancer and debilitating pain from bone metastases
- …