143 research outputs found
TEOBResumS: Analytic systematics in next-generation of effective-one-body gravitational waveform models for future observations
The success of analytic waveform modeling within the effective-one-body (EOB)
approach relies on the precise understanding of the physical importance of each
technical element included in the model. The urgency of constructing
progressively more sophisticated and complete waveform models (e.g. including
spin precession and eccentricity) partly defocused the research from a careful
comprehension of each building block (e.g. Hamiltonian, radiation reaction,
ringdown attachment). Here we go back to the spirit of the first EOB works. We
focus first on nonspinning, quasi-circular, black hole binaries and analyze
systematically the mutual synergy between numerical relativity (NR) informed
functions and the high post-Newtonian corrections (up to 5PN) to the EOB
potentials. Our main finding is that it is essential to correctly control the
noncircular part of the dynamics during the late plunge up to merger. When this
happens, either using NR-informed non-quasi-circular corrections to the
waveform (and flux) or high-PN corrections in the radial EOB potentials
, it is easy to obtain EOB/NR unfaithfulness with the
noise of either Advanced LIGO or 3G detectors. We then improve the {\tt
TEOBResumS-GIOTTO} waveform model for quasi-circular, spin-aligned binaries
black hole binaries. We obtain maximal EOB/NR unfaithfulness (with Advanced LIGO noise and in the
total mass range ) for the dominant mode all over the
534 spin-aligned configurations available through the Simulating eXtreme
Spacetime catalog. The model performance, also including higher modes, is then
explored using NR surrogate waveform models to validate {\tt TEOBResumS-GIOTTO}
up to mass ratio .Comment: 23 pages, 27 figures, submitted to Phys. Rev.
Local and system mechanisms for action execution and observation in parietal and premotor cortices
The action observation network (AON) includes a system of brain areas largely shared with action execution in both human and nonhuman primates. Yet temporal and tuning specificities of distinct areas and of physiologically identified neuronal classes in the encoding of self and others’ action remain unknown. We recorded the activity of 355 single units from three crucial nodes of the AON, the anterior intraparietal area (AIP), and premotor areas F5 and F6, while monkeys performed a Go/No-Go grasping task and observed an experimenter performing it. At the system level, during task execution, F6 displays a prevalence of suppressed neurons and signals whether an action has to be performed, whereas AIP and F5 share a prevalence of facilitated neurons and remarkable target selectivity; during task observation, F5 stands out for its unique prevalence of facilitated neurons and its stronger and earlier modulation than AIP and F6. By applying unsupervised clustering of spike waveforms, we found distinct cell classes unevenly distributed across areas, with different firing properties and carrying specific visuomotor signals. Broadly spiking neurons exhibited a balanced amount of facilitated and suppressed activity during action execution and observation, whereas narrower spiking neurons showed more mutually facilitated responses during the execution of one’s own and others’ action, particularly in areas AIP and F5. Our findings elucidate the time course of activity and firing properties of neurons in the AON during one’s own and others’ action, from the system level of anatomically distinct areas to the local level of physiologically distinct cell classes
Comparing second-order gravitational self-force and effective one body waveforms from inspiralling, quasi-circular and nonspinning black hole binaries II: the large-mass-ratio case
We compare recently computed waveforms from second-order gravitational
self-force (GSF) theory to those generated by a new, GSF-informed, effective
one body (EOB) waveform model for (spin-aligned, eccentric) inspiralling black
hole binaries with large mass ratios. We focus on quasi-circular, nonspinning,
configurations and perform detailed GSF/EOB waveform phasing comparisons,
either in the time domain or via the gauge-invariant dimensionless function
, where is the gravitational
wave frequency. The inclusion of high-PN test-mass terms within the EOB
radiation reaction (notably, up to 22PN) is crucial to achieve an EOB/GSF
phasing agreement below 1~rad up to the end of the inspiral for mass ratios up
to 500. For larger mass ratios, up to , the contribution of
horizon absorption becomes more and more important and needs to be accurately
modeled. Our results indicate that our GSF-informed EOB waveform model is a
promising tool to describe waveforms generated by either intermediate or
extreme mass ratio inspirals for future gravitational wave detectorsComment: 13 pages, 8 figures. Submitted to Phys. Rev.
Comparing second-order gravitational self-force, numerical relativity and effective one body waveforms from inspiralling, quasi-circular and nonspinning black hole binaries
We present the first systematic comparison between gravitational waveforms
emitted by inspiralling, quasi-circular and nonspinning black hole binaries
computed with three different approaches: second-order gravitational self-force
(2GSF) theory, as implemented in the 1PAT1 model; numerical relativity (NR), as
implemented by the SXS collaboration; and the effective one body (EOB)
formalism, as implemented in the TEOBResumS waveform model. To compare the
models we use both a standard, time-domain waveform alignment and a
gauge-invariant analysis based on the dimensionless function
, where is the
gravitational wave frequency. We analyse the domain of validity of the 1PAT1
model, deriving error estimates and showing that the effects of the final
transition to plunge, which the model neglects, extend over a significantly
larger frequency interval than one might expect. Restricting to the inspiral
regime, we find that, while for mass ratios TEOBResumS is
largely indistinguishable from NR, 1PAT1 has a significant dephasing rad; conversely, for , 1PAT1 is estimated to have phase errors
rad on a large frequency interval, while TEOBResumS develops phase
differences rad with it. Most crucially, on that same large frequency
interval we find good agreement between TEOBResumS and 1PAT1 in the
intermediate regime , with rad dephasing between
them. A simple modification to the TEOBResumS flux further improves this
agreement for , reducing the dephasing to rad even at
. Our results pave the way for the construction of GSF-informed EOB
models for both intermediate and extreme mass ratio inspirals for the next
generation of gravitational wave detectors.Comment: 31 pages, 19 figures, submitted to Phys. Rev.
Human Mitochondrial Ferritin Expressed in HeLa Cells Incorporates Iron and Affects Cellular Iron Metabolism
Mitochondrial ferritin (MtF) is a newly identified ferritin encoded by an intronless gene on chromosome 5q23.1. The mature recombinant MtF has a ferroxidase center and binds iron in vitro similarly to H-ferritin. To explore the structural and functional aspects of MtF, we expressed the following forms in HeLa cells: the MtF precursor (approximately 28 kDa), a mutant MtF precursor with a mutated ferroxidase center, a truncated MtF lacking the approximately 6-kDa mitochondrial leader sequence, and a chimeric H-ferritin with this leader sequence. The experiments show that all constructs with the leader sequence were processed into approximately 22-kDa subunits that assembled into multimeric shells electrophoretically distinct from the cytosolic ferritins. Mature MtF was found in the matrix of mitochondria, where it is a homopolymer. The wild type MtF and the mitochondrially targeted H-ferritin both incorporated the (55)Fe label in vivo. The mutant MtF with an inactivated ferroxidase center did not take up iron, nor did the truncated MtF expressed transiently in cytoplasm. Increased levels of MtF both in transient and in stable transfectants resulted in a greater retention of iron as MtF in mitochondria, a decrease in the levels of cytosolic ferritins, and up-regulation of transferrin receptor. Neither effect occurred with the mutant MtF with the inactivated ferroxidase center. Our results indicate that exogenous iron is as available to mitochondrial ferritin as it is to cytosolic ferritins and that the level of MtF expression may have profound consequences for cellular iron homeostasis
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