96 research outputs found
Schur times Schubert via the Fomin-Kirillov algebra
We study multiplication of any Schubert polynomial by a
Schur polynomial (the Schubert polynomial of a Grassmannian
permutation) and the expansion of this product in the ring of Schubert
polynomials. We derive explicit nonnegative combinatorial expressions for the
expansion coefficients for certain special partitions , including
hooks and the 2x2 box. We also prove combinatorially the existence of such
nonnegative expansion when the Young diagram of is a hook plus a box
at the (2,2) corner. We achieve this by evaluating Schubert polynomials at the
Dunkl elements of the Fomin-Kirillov algebra and proving special cases of the
nonnegativity conjecture of Fomin and Kirillov.
This approach works in the more general setup of the (small) quantum
cohomology ring of the complex flag manifold and the corresponding (3-point)
Gromov-Witten invariants. We provide an algebro-combinatorial proof of the
nonnegativity of the Gromov-Witten invariants in these cases, and present
combinatorial expressions for these coefficients
Neutrino production in matter with time-dependent density or velocity
We show that neutrinos can be produced through standard electroweak
interactions in matter with time-dependent density.Comment: 4 pages, revte
Should aortic arch replacement be performed during initial surgery for aortic root aneurysm in patients with Marfan syndrome?†
OBJECTIVES The aim of this study was to investigate whether total arch replacement (TAR) during initial surgery for root aneurysm should be routinely performed in patients with Marfan syndrome (MFS). METHODS Retrospective analysis of 94 consecutive MFS patients fulfilling Ghent criteria who underwent 148 aortic surgeries and were followed at this institution during the past 16 years. RESULTS The mean follow-up interval was 8.8 ± 7 years. Initial presentation was acute aortic dissection (AAD) in 35% of patients (76% Type A and 24% Type B) and aneurismal disease in 65%. TAR was performed in 8% of patients during initial surgery for AAD (otherwise a hemi-arch replacement was performed) and 1.6% in elective root repair. Secondary TAR had to be performed in only 3% of patients without, but in 33% following AAD (33% Type A and 33% Type B; P = 0.0001). Thirty-day, 6-month, 1-year and overall mortalities were 3.2, 5.3, 6.4 and 11.7%, respectively. Operative and 30-day mortalities in secondary aortic arch replacement were zero. Secondary TAR after AAD did not increase the need for the replacement of the entire thoracoabdominal aorta during follow-up compared with patients without secondary TAR (37 vs 40%, P = 1.0). CONCLUSIONS MFS patients undergoing elective root repair have small risk of reinterventions on the aortic arch, and primary prophylactic replacement does not seem to be justified. In patients with AAD, the need for reinterventions is precipitated by the dissection itself and not by limiting the procedure to the hemi-arch replacement in the emergency setting. Limiting surgery to the aortic root, ascending aorta and proximal aortic arch is associated with low mortality in MFS patients presenting with AA
Relativistic kinetic equation for Compton scattering of polarized radiation in strong magnetic field
We derive the relativistic kinetic equation for Compton scattering of
polarized radiation in strong magnetic field using the Bogolyubov method. The
induced scattering and the Pauli exclusion principle are taken into account.
The electron polarization is also considered in the general form of the kinetic
equation. The special forms of the equation for the cases of the non-polarized
electrons, the rarefied electron gas and the two polarization mode description
of radiation are found. The derived equations are valid for any photon and
electron energies and the magnetic field strength below about 10^{16} G. These
equations provide the basis for formulation of the equation for polarized
radiation transport in atmospheres and magnetospheres of strongly magnetized
neutron stars.Comment: 23 pages, accepted for publication in Phys. Rev.
Constraints on Cold Magnetized Shocks in Gamma-Ray Bursts
We consider a model in which the ultra-relativistic jet in a gamma-ray burst
(GRB) is cold and magnetically accelerated. We assume that the energy flux in
the outflowing material is partially thermalized via internal shocks or a
reverse shock, and we estimate the maximum amount of radiation that could be
produced in such magnetized shocks. We compare this estimate with the available
observational data on prompt gamma-ray emission in GRBs. We find that, even
with highly optimistic assumptions, the magnetized jet model is radiatively too
inefficient to be consistent with observations. One way out is to assume that
much of the magnetic energy in the post-shock, or even pre-shock, jet material
is converted to particle thermal energy by some unspecified process, and then
radiated. This can increase the radiative efficiency sufficiently to fit
observations. Alternatively, jet acceleration may be driven by thermal pressure
rather than magnetic fields. In this case, which corresponds to the traditional
fireball model, sufficient prompt GRB emission could be produced either from
shocks at a large radius or from the jet photosphere closer to the center.Comment: MNRAS, in press. 9 pages, 4 figures, uses mn2e.cl
Spinning-Up the Envelope Before Entering a Common Envelope Phase
We calculate the orbital evolution of binary systems where the primary star
is an evolved red giant branch (RGB) star, while the secondary star is a
low-mass main sequence (MS) star or a brown dwarf. The evolution starts with a
tidal interaction causes the secondary to spiral-in. Than either a common
envelope (CE) is formed in a very short time, or alternatively the system
reaches synchronization and the spiraling-in process substantially slows down.
Some of the latter systems later enter a CE phase. We find that for a large
range of system parameters, binary systems reach stable synchronized orbits
before the onset of a CE phase. Such stable synchronized orbits allow the RGB
star to lose mass prior to the onset of the CE phase. Even after the secondary
enters the giant envelope, the rotational velocity is high enough to cause an
enhanced mass-loss rate. Our results imply that it is crucial to include the
pre-CE evolution when studying the outcome of the CE phase. We find that many
more systems survive the CE phase than would be the case if these preceding
spin-up and mass-loss phases had not been taken into account. Although we have
made the calculations for RGB stars, the results have implications for other
evolved stars that interact with close companions.Comment: New Astronomy, in pres
Efficiency of Magnetic to Kinetic Energy Conversion in a Monopole Magnetosphere
Unconfined relativistic outflows from rotating, magnetized compact objects
are often well-modeled by assuming the field geometry is approximately a
split-monopole at large radii. Earlier work has indicated that such an
unconfined flow has an inefficient conversion of magnetic energy to kinetic
energy. This has led to the conclusion that ideal magnetohydrodynamical (MHD)
processes fail to explain observations of, e.g., the Crab pulsar wind at large
radii where energy conversion appears efficient. In addition, as a model for
astrophysical jets, the monopole field geometry has been abandoned in favor of
externally confined jets since the latter appeared to be generically more
efficient jet accelerators. We perform time-dependent axisymmetric relativistic
MHD simulations in order to find steady state solutions for a wind from a
compact object endowed with a monopole field geometry. Our simulations follow
the outflow for 10 orders of magnitude in distance from the compact object,
which is large enough to study both the initial "acceleration zone" of the
magnetized wind as well as the asymptotic "coasting zone." We obtain the
surprising result that acceleration is actually {\it efficient} in the polar
region, which develops a jet despite not being confined by an external medium.
Our models contain jets that have sufficient energy to account for moderately
energetic long and short gamma-ray burst (GRB) events (~10^{51}--10^{52} erg),
collimate into narrow opening angles (opening half-angle \theta_j \approx 0.03
rad), become matter-dominated at large radii (electromagnetic energy flux per
unit matter energy flux \sigma<1), and move at ultrarelativistic Lorentz
factors (\gamma_j ~ 200 for our fiducial model). (abridged)Comment: Accepted to ApJ, 22 pages, 10 figures, uses emulateapj.cls. Changes
in v2: new section in the Appendi
Adipokines and inflammation: is it a question of weight?
Obesity has reached epidemic proportions in the Western society and is increasing in the developing world. It is considered as one of the major contributors to the global burden of disability and chronic diseases, including autoimmune, inflammatory and degenerative diseases. Research conducted on obesity and its complications over the last two decades has transformed the outdated concept of white adipose tissue (WAT) merely serving as an energy depot. WAT is now recognized as an active and inflammatory organ capable of producing a wide variety of factors known as adipokines. These molecules participate through endocrine, paracrine, autocrine, or juxtacrine cross-talk mechanisms in a great variety of physiological or pathophysiological processes, regulating food intake, insulin sensitivity, immunity, and inflammation.
Although initially restricted to metabolic activities (regulation of glucose and lipid metabolism), adipokines currently represent a new family of proteins that can be considered key players in the complex network of soluble mediators involved in the pathophysiology of immune/inflammatory diseases. However, the complexity of the adipokine network in the pathogenesis and progression of inflammatory diseases has posed, since the beginning, the important question of whether it may be possible to target the mechanism(s) by which adipokines contribute to disease selectively without suppressing their physiological functions.
Here we explore in depth the most recent findings concerning the involvement of adipokines in inflammation and immune responses, in particular in rheumatic, inflammatory and degenerative diseases. We also highlight several possible strategies for therapeutic development and propose that adipokines and their signalling pathways may represent innovative therapeutic strategies for inflammatory disorders.ACKNOWLEDGMENTS: OG and FL are Staff Personnel of Xunta de Galicia (Servizo Galego de Saude, SERGAS) through a research-staff stabilization contract (ISCIII/SERGAS). VF is a “Sara Borrell” Researcher funded by ISCIII and FEDER. RG is a “Miguel Servet” Researcher funded by Instituto de Salud Carlos III (ISCIII) and FEDER. OG, MAGG and RG are members of RETICS Programme, RD16/0012/0014 (RIER: Red de Investigación en Inflamación y Enfermedades Reumáticas) via Instituto de Salud Carlos III (ISCIII) and FEDER. FL is a member of CIBERCV (Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares). The work of OG (PIE13/00024 and PI14/00016, PI17/00409), FL (PI15/00681 and CB16/11/00226) and RG (PI16/01870 and CP15/00007) was funded by Instituto de Salud Carlos III and FEDER. OG is a beneficiary of a project funded by Research Executive Agency of the European Union in the framework of MSCA-RISE Action of the H2020 Programme (Project number 734899). AM has received funding from the European Commission Framework 7 programme (EU FP7; HEALTH.2012.2.4.5-2, project number 305815; Novel Diagnostics and Biomarkers for Early Identification of Chronic Inflammatory Joint Diseases) plus generous support from the Innovative Medicines Initiative Joint Undertaking under grant agreement No. 115770, resources of which are composed of financial contribution from the European Union’s Seventh Framework programme (FP7/2007-2013) and EFPIA companies’ in kind contribution. The funders had no role in study design, data collection, and analysis, decision to publish, or preparation of the manuscript
Assessment of Mitochondrial Respiration During Hypothermic Storage of Liver Biopsies Following Normothermic Machine Perfusion
Organ quality can be assessed prior to transplantation, during normothermic machine perfusion (NMP) of the liver. Evaluation of mitochondrial function by high-resolution respirometry (HRR) may serve as a viability assessment concept in this setting. Freshly collected tissue is considered as optimal sample for HRR, but due to technical and personnel requirements, more flexible and schedulable measurements are needed. However, the impact of cold storage following NMP before processing biopsy samples for mitochondrial analysis remains unknown. We aimed at establishing an appropriate storage protocol of liver biopsies for HRR. Wedge biopsies of 5 human livers during NMP were obtained and assessed by HRR. Analysis was performed after 0, 4, 8, and 12 h of hypothermic storage (HTS) in HTK organ preservation solution at 4°C. With HTS up to 4 h, mitochondrial performance did not decrease in HTS samples compared with 0 h (OXPHOS, 44.62 [34.75–60.15] pmol·s−1·mg wet mass−1 vs. 43.73 [40.69–57.71], median [IQR], p > 0.999). However, at HTS beyond 4 h, mitochondrial respiration decreased. We conclude that HTS can be safely applied for extending the biopsy measurement window for up to 4 h to determine organ quality, but also that human liver respiration degrades beyond 4 h HTS following NMP
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