864 research outputs found
Evidence of a radiation belt around a brown dwarf
Radio observations of ultracool dwarfs, objects comprising brown dwarfs and
the very lowest mass stars, have mainly focused on analyzing their light-curve
and spectral energy distributions providing valuable insights into their
magnetic fields. However, spatially-resolved studies of such magnetospheres
have been elusive so far. Radio interferometric observations of the brown dwarf
LSR J1835+3259 reveal an extended magnetosphere with a morphology compatible
with the presence of a radiation belt, similar to that of Jupiter and Earth,
consisting of energetic particles confined via magnetic mirroring. Our finding
suggests that radio emitting ultracool dwarfs may behave as scaled up versions
of Jupiter, validating the connection between dipole-ordered magnetic fields
and the presence of belt-like morphologies and aurorae beyond our Solar System.Comment: Submitted on 12 January 2023 to Science. In revie
82: Severe Hemorrhagic Cystitis (HC) After Allogeneic Hematopoeitic Stem Cell Transplantation (HSCT): Incidence and Risk Factors
With the purpose to investigate the radio emission of new ultracool objects,
we carried out a targeted search in the recently discovered system VHS
J125601.92125723.9 (hereafter VHS 12561257); this system is composed by
an equal-mass M7.5 binary and a L7 low-mass substellar object located at only
15.8\,pc. We observed in phase-reference mode the system VHS 12561257 with
the Karl G. Jansky Very Large Array at - and - band and with the European
VLBI Network at -band in several epochs during 2015 and 2016. We discovered
radio emission at -band spatially coincident with the equal-mass M7.5 binary
with a flux density of 60 Jy. We determined a spectral index between 8 and 12 GHz, suggesting that non-thermal,
optically-thin, synchrotron or gyrosynchrotron radiation is responsible for the
observed radio emission. Interestingly, no signal is seen at -band where we
set a 3- upper limit of 20 Jy. This might be explained by strong
variability of the binary or self-absorption at this frequency. By adopting the
latter scenario and gyrosynchrotron radiation, we constrain the turnover
frequency to be in the interval 5--8.5 GHz, from which we infer the presence of
kG-intense magnetic fields in the M7.5 binary. Our data impose a 3-
upper bound to the radio flux density of the L7 object of 9 Jy at 10\,GHz.Comment: 6 pages, 4 figures. Accepted for publication in A&
An Analysis of the Evolution Equations for a Generalized Bioconvective Flow
We prove results on existence and uniqueness of solutions of a system of
equations modeling the evolution of a generalized bioconvective flow. The
mathematical model considered in the present work describes the convective
motion generated by the upward swimming of a culture of microorganisms under
the influence of vertical gravitational forces, in an incompressible viscous
fluid whose viscosity may depend on the concentration of microorganisms
The milliarcsecond-scale radio structure of AB Dor A
Context: The fast rotator, pre-main sequence star AB Dor A is a strong and
persistent radio emitter. The extraordinary coronal flaring activity is thought
to be the origin of compact radio emission and other associated phenomena as
large slingshot prominences. Aim: We aim to investigate the radio emission
mechanism and the milliarcsecond radio structure around AB Dor A. Methods: We
performed phase-referenced VLBI observations at 22.3 GHz, 8.4 GHz, and 1.4 GHz
over more than one decade using the Australian VLBI array. Results: Our 8.4 GHz
images show a double core-halo morphology, similar at all epochs, with emission
extending at heights between 5 and 18 stellar radii. Furthermore, the sequence
of the 8.4 GHz maps shows a clear variation of the source structure within the
observing time. However, images at 1.4 GHz and 22.3 GHz are compatible with a
compact source. The phase-reference position at 8.4 GHz and 1.4 GHz are
coincident with those expected from the well-known milliarcsecond-precise
astrometry of this star, meanwhile the 22.3 GHz position is 4 off the
prediction in the north-west direction. The origin of this offset is still
unclear. Conclusions: We have considered several models to explain the
morphology and evolution of the inner radio structure detected in AB Dor A
which include emission from the stellar polar caps, a flaring,
magnetically-driven loop structure, and the presence of helmet streamers. A
possible close companion to AB Dor A has been also investigated. Our results
confirm the extraordinary coronal magnetic activity of this star, able to
produce compact radio structures at very large heights, so far only seen in
binary interacting systems.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
In vivo chromatin targets of the transcription factor Yin Yang 2 in trophoblast stem cells
Background: Yin Yang 2 (YY2) is a zinc finger protein closely related to the well-characterized Yin Yang 1 (YY1). YY1 is a DNA-binding transcription factor, with defined functions in multiple developmental processes, such as implantation, cell differentiation, X inactivation, imprinting and organogenesis. Yy2 has been treated as a largely immaterial duplication of Yy1, as they share high homology in the Zinc Finger-region and similar if not identical in vitro binding sites. In contrast to these similarities, gene expression alterations in HeLa cells with attenuated levels of either Yy1 or Yy2 were to some extent gene-specific. Moreover, the chromatin binding sites for YY2, except for its association with transposable retroviral elements (RE) and Endogenous Retroviral Elements (ERVs), remain to be identified. As a first step towards defining potential Yy2 functions matching or complementary to Yy1, we considered in vivo DNA binding sites of YY2 in trophoblast stem (TS) cells. Results: We report the presence of YY2 protein in mouse-derived embryonic stem (ES) and TS cell lines. Following up on our previous report on ERV binding by YY2 in TS cells, we investigated the tissue-specificity of REX1 and YY2 binding and confirm binding to RE/ERV targets in both ES cells and TS cells. Because of the higher levels of expression, we chose TS cells to understand the role of Yy2 in gene and chromatin regulation. We used in vivo YY2 association as a measure to identify potential target genes. Sequencing of chromatin obtained in chromatin-immunoprecipitation (ChIP) assays carried out with aYY2 serum allowed us to identify a limited number of chromatin targets for YY2. Some putative binding sites were validated in regular ChIP assays and gene expression of genes nearby was altered in the absence of Yy2. Conclusions: YY2 binding to ERVs is not confined to TS cells. In vivo binding sites share the presence of a consensus binding motif. Selected sites were uniquely bound by YY2 as opposed to YY1, suggesting that YY2 exerts unique contributions to gene regulation. YY2 binding was not generally associated with gene promoters. However, several YY2 binding sites are linked to long noncoding RNA (lncRNA) genes and we show that the expression levels of a few of those are Yy2-dependent
Photoisomerization Efficiency of a Solar Thermal Fuel in the Strong Coupling Regime
Strong exciton-photon coupling is achieved when the interaction between molecules and an electromagnetic field is increased to a level where they cannot be treated as separate systems. This leads to the formation of polaritonic states and an effective rearrangement of the potential energy surfaces, which opens the possibility to modify photochemical reactions. This work investigates how the strong coupling regime is affecting the photoisomerization efficiency and thermal backconversion of a norbornadieneâquadricyclane molecular photoswitch. The quantum yield of photoisomerization shows both an excitation wavelength and exciton/photon constitution dependence. The polariton-induced decay and energy transfer processes are discussed to be the reason for this finding. Furthermore, the thermal back conversion of the system is unperturbed and the lower polariton effectively shifts the absorption onset to lower energies. The reason for the unperturbed thermal backconversion is that it occurs on the ground state, which is unaffected. This work demonstrates how strong coupling can change material properties towards higher efficiencies in applications. Importantly, the experiments illustrate that strong coupling can be used to optimize the absorption onset of the molecular photoswitch norbonadiene without affecting the back reaction from the uncoupled quadricyclane
Evidence of a substellar companion to AB Dor C
Studies of fundamental parameters of very low-mass objects are indispensable
to provide tests of stellar evolution models that are used to derive
theoretical masses of brown dwarfs and planets. However, only objects with
dynamically determined masses and precise photometry can effectively evaluate
the predictions of stellar models. AB Dor C (0.090 solar masses) has become a
prime benchmark for calibration of theoretical evolutionary models of low-mass
young stars. One of the ambiguities remaining in AB Dor C is the possible
binary nature of this star. We observed AB Dor C with the VLTI/AMBER instrument
in low-resolution mode at the J, H and K bands. The interferometric observables
at the K-band are compatible with a binary brown dwarf system with tentative
components AB Dor Ca/Cb with a K-band flux ratio of 51% and a separation
of 381 mas. This implies theoretical masses of 0.0720.013 M and 0.0130.001 M for each component, near the
hydrogen-burning limit for AB Dor Ca, and near the deuterium-burning limit,
straddling the boundary between brown dwarfs and giant planets, for AB Dor Cb.
The possible binarity of AB Dor C alleviates the disagreement between observed
magnitudes and theoretical mass-luminosity relationships.Comment: 8 pages, 5 figures, accepted for publication in ApJ Letter
Peripheral neuropathy caused by fenugreek (Trigonella foenum-graecum) straw intoxication in cattle and experimental reproduction in sheep and goats
Trigonella foenum-graecum (fenugreek) is a legume widely used as a food supplement in humans and less frequently in ruminants. Toxicity has been described sporadically in ruminants grazing mature fenugreek plants or stubble; however, the pathological features are unclear. This report describes a natural outbreak of intoxication in cattle fed fenugreek straw and the experimental reproduction using 8 sheep and 8 goats. Affected cattle presented clinical signs approximately 1 month after consuming the straw and 100 of 400 cattle (25%) were affected, of which 60 of 100 (60%) died or were euthanized. Clinical signs were characterized by proprioceptive positioning defects with abnormal postures and weakness of hindlimbs. Forelimbs were also affected in severely affected animals, and cattle became recumbent. Locomotion was characterized by trembling, and some cattle showed high-stepping movements of their forelimbs and knuckled over in their fetlocks. Experimental intoxication induced clinical signs only in sheep and were similar to cattle, although with signs starting in the forelegs. Gross and microscopic lesions were similar in spontaneous and experimental intoxications. Macroscopic changes corresponded with muscular hemorrhages and edema, mainly surrounding the peripheral nerves. Microscopic examination only demonstrated lesions in the distal peripheral nerves, which included edema, hemorrhages, and Wallerian degeneration. Neurofilament immunohistochemistry revealed altered axon labeling and S100 showed a decrease in myelin intensity and loss of its typical compact arrangement around axons. Biochemical and hematological abnormalities included elevated levels of muscle and liver enzymes and thrombocytopenia. These findings indicate that fenugreek straw induces peripheral neuropathy in cattle and sheep, but not in goats
Radiation-Induced Leiomyosarcoma after Breast Cancer Treatment and TRAM Flap Reconstruction
The development of a radiation-induced sarcoma (RIS) in the post mastectomy thoracic treatment volume is an infrequent, but recognized, event. Its frequency is rising in relation with increasing survival of breast cancer patients treated with adjuvant radiation therapy, and is associated with poor prognosis despite treatment.
We present a case of leiomyosarcoma in a patient who underwent mastectomy followed by radiotherapy for invasive ductal carcinoma. A delayed TRAM flap reconstruction was performed 10 years after and a rapid growing mass under the reconstructed flap appeared, on routine follow-up, twenty years later. This report analyzes the diagnostic and therapeutic approach of patients with RIS
- âŠ