605 research outputs found
Higher signal harmonics, LISA's angular resolution, and dark energy
It is generally believed that the angular resolution of the Laser
Interferometer Space Antenna (LISA) for binary supermassive black holes (SMBH)
will not be good enough to identify the host galaxy or galaxy cluster. This
conclusion, based on using only the dominant harmonic of the binary SMBH
signal, changes substantially when higher signal harmonics are included in
assessing the parameter estimation problem. We show that in a subset of the
source parameter space the angular resolution increases by more than a factor
of 10, thereby making it possible for LISA to identify the host galaxy/galaxy
cluster. Thus, LISA's observation of certain binary SMBH coalescence events
could constrain the dark energy equation of state to within a few percent,
comparable to the level expected from other dark energy missions.Comment: 15 pages, no figures. Final version to appear in Phys. Rev.
LISA as a dark energy probe
Recently it was shown that the inclusion of higher signal harmonics in the
inspiral signals of binary supermassive black holes (SMBH) leads to dramatic
improvements in parameter estimation with the Laser Interferometer Space
Antenna (LISA). In particular, the angular resolution becomes good enough to
identify the host galaxy or galaxy cluster, in which case the redshift can be
determined by electromagnetic means. The gravitational wave signal also
provides the luminosity distance with high accuracy, and the relationship
between this and the redshift depends sensitively on the cosmological
parameters, such as the equation-of-state parameter of dark energy. With a single binary SMBH event at having
appropriate masses and orientation, one would be able to constrain to
within a few percent. We show that, if the measured sky location is folded into
the error analysis, the uncertainty on goes down by an additional factor of
2-3, leaving weak lensing as the only limiting factor in using LISA as a dark
energy probe.Comment: 11pages, 1 Table, minor changes in text, accepted for publication in
Classical and Quantum Gravity (special issue for proceedings of 7th LISA
symposium
The molecular diversity of Luminal A breast tumors
Breast cancer is a collection of diseases with distinct molecular traits, prognosis, and therapeutic options. Luminal A breast cancer is the most heterogeneous, both molecularly and clinically. Using genomic data from over 1,000 Luminal Atumors from multiple studies, we analyzed the copy number and mutational landscape of this tumor subtype. This integrated analysis revealed four major subtypes defined by distinct copy-number and mutation profiles. We identified an atypical Luminal A subtype characterized by high genomic instability, TP53 mutations, and increased Aurora kinase signaling; these genomic alterations lead to a worse clinical prognosis. Aberrations of chromosomes 1, 8, and 16, together with PIK3CA, GATA3, AKT1, and MAP3K1 mutations drive the other subtypes. Finally, an unbiased pathway analysis revealed multiple rare, but mutually exclusive, alterations linked to loss of activity of co-repressor complexes N-Cor and SMRT. These rare alterations were the most prevalent in Luminal A tumors and may predict resistance to endocrine therapy. Our work provides for a further molecular stratification of Luminal A breast tumors, with potential direct clinical implications.Electronic supplementary materialThe online version of this article (doi:10.1007/s10549-013-2699-3) contains supplementary material, which is available to authorized users
Massive Black Hole Binary Inspirals: Results from the LISA Parameter Estimation Taskforce
The LISA Parameter Estimation (LISAPE) Taskforce was formed in September 2007
to provide the LISA Project with vetted codes, source distribution models, and
results related to parameter estimation. The Taskforce's goal is to be able to
quickly calculate the impact of any mission design changes on LISA's science
capabilities, based on reasonable estimates of the distribution of
astrophysical sources in the universe. This paper describes our Taskforce's
work on massive black-hole binaries (MBHBs). Given present uncertainties in the
formation history of MBHBs, we adopt four different population models, based on
(i) whether the initial black-hole seeds are small or large, and (ii) whether
accretion is efficient or inefficient at spinning up the holes. We compare four
largely independent codes for calculating LISA's parameter-estimation
capabilities. All codes are based on the Fisher-matrix approximation, but in
the past they used somewhat different signal models, source parametrizations
and noise curves. We show that once these differences are removed, the four
codes give results in extremely close agreement with each other. Using a code
that includes both spin precession and higher harmonics in the
gravitational-wave signal, we carry out Monte Carlo simulations and determine
the number of events that can be detected and accurately localized in our four
population models.Comment: 14 pages, 2 figures, 5 tables, minor changes to match version to be
published in the proceedings of the 7th LISA Symposium. For more information
see the Taskforce's wiki at http://www.tapir.caltech.edu/dokuwiki/lisape:hom
The impact of time to death in donors after circulatory death on recipient outcome in simultaneous pancreas-kidney transplantation
Time to arrest in donors after circulatory death is unpredictable and can vary. This leads to variable periods of warm ischaemic damage prior to pancreas transplantation. There is little evidence supporting procurement team stand-down times based on donor time to death (TTD). We examined what impact TTD had on pancreas graft outcomes following DCD SPK transplantation. Data were extracted from the UK transplant registry from 2014 to 2022. Predictors of graft loss were evaluated by a Cox proportional hazards model. Adjusted restricted cubic spline (RCS) models were generated to further delineate the relationship between TTD and outcome. Three-hundred-and-seventy-five DCD simultaneous kidney-pancreas transplant recipients were included. Increasing TTD was not associated with graft survival (aHR 0.98, 95% CI 0.68-1.41, P=0.901). Increasing asystolic time worsened graft survival (aHR 2.51, 95% CI 1.16-5.43, P=0.020). RCS modelling revealed a non-linear relationship was demonstrated between asystolic time and graft survival, and no relationship between TTD and graft survival. We found no evidence that TTD impacts on pancreas graft survival after DCD SPK transplantation, however increasing asystolic time was a significant predictor of graft loss. Procurement teams should attempt to minimise asystolic time to optimize pancreas graft survival rather than focus on the duration of TTD
- …