2,459 research outputs found
Accurate numerical simulations of inspiralling binary neutron stars and their comparison with effective-one-body analytical models
Binary neutron-star systems represent one of the most promising sources of
gravitational waves. In order to be able to extract important information,
notably about the equation of state of matter at nuclear density, it is
necessary to have in hands an accurate analytical model of the expected
waveforms. Following our recent work, we here analyze more in detail two
general-relativistic simulations spanning about 20 gravitational-wave cycles of
the inspiral of equal-mass binary neutron stars with different compactnesses,
and compare them with a tidal extension of the effective-one-body (EOB)
analytical model. The latter tidally extended EOB model is analytically
complete up to the 1.5 post-Newtonian level, and contains an analytically
undetermined parameter representing a higher-order amplification of tidal
effects. We find that, by calibrating this single parameter, the EOB model can
reproduce, within the numerical error, the two numerical waveforms essentially
up to the merger. By contrast, analytical models (either EOB, or Taylor-T4)
that do not incorporate such a higher-order amplification of tidal effects,
build a dephasing with respect to the numerical waveforms of several radians.Comment: 25 pages, 17 figs. Matched published versio
WhiskyMHD: a new numerical code for general relativistic magnetohydrodynamics
The accurate modelling of astrophysical scenarios involving compact objects
and magnetic fields, such as the collapse of rotating magnetized stars to black
holes or the phenomenology of gamma-ray bursts, requires the solution of the
Einstein equations together with those of general-relativistic
magnetohydrodynamics. We present a new numerical code developed to solve the
full set of general-relativistic magnetohydrodynamics equations in a dynamical
and arbitrary spacetime with high-resolution shock-capturing techniques on
domains with adaptive mesh refinements. After a discussion of the equations
solved and of the techniques employed, we present a series of testbeds carried
out to validate the code and assess its accuracy. Such tests range from the
solution of relativistic Riemann problems in flat spacetime, over to the
stationary accretion onto a Schwarzschild black hole and up to the evolution of
oscillating magnetized stars in equilibrium and constructed as consistent
solutions of the coupled Einstein-Maxwell equations.Comment: minor changes to match the published versio
Influence of autonomic control on the specific intermittent performance of judo athletes
Judo is a high-intensity intermittent combat sport which causes cardiac adaptations both morphologically and related to the autonomic nervous system (ANS). Therefore, this study aims to verify the correlation between heart rate variability (HRV) at rest with performance in the Special Judo Fitness Test (SJFT) and whether groups with different RR values at rest show different performance in the SJFT and during post-test recovery. Sixteen judo athletes with 7.2 +/- 3.9 years of training experience participated in the study. Before and after the SJFT execution HRV and lactate measurements were conducted. For HRV analysis, we used the mean interval RR, the standard deviation of the RR interval (SDNN), the root mean square of successive differences in RR intervals (RMSSD), the low frequency (LF) and high frequency (HF) in normalized and absolute units. The sample was split into two groups (low RR and high RR) to verify if this variable could differentiate between specific performance. For the SDNN, a significant and moderate correlation (r = 0.53) was found with the total number of throws and throws in the series A (r = 0.56) and B (r = 0.54) and for the RMSSD a correlation with throws during series B (r = 0.59) in the SJFT. However, the groups did not differ in performance and recovery. Therefore, HRV is related to intermittent judo performance; however, it cannot differentiate between judokas at different levels of performance
Accurate evolutions of inspiralling neutron-star binaries: prompt and delayed collapse to black hole
Binary neutron-star (BNS) systems represent primary sources for the
gravitational-wave (GW) detectors. We present a systematic investigation in
full GR of the dynamics and GW emission from BNS which inspiral and merge,
producing a black hole (BH) surrounded by a torus. Our results represent the
state of the art from several points of view: (i) We use HRSC methods for the
hydrodynamics equations and high-order finite-differencing techniques for the
Einstein equations; (ii) We employ AMR techniques with "moving boxes"; (iii) We
use as initial data BNSs in irrotational quasi-circular orbits; (iv) We exploit
the isolated-horizon formalism to measure the properties of the BHs produced in
the merger; (v) Finally, we use two approaches, based either on gauge-invariant
perturbations or on Weyl scalars, to calculate the GWs. These techniques allow
us to perform accurate evolutions on timescales never reported before (ie ~30
ms) and to provide the first complete description of the inspiral and merger of
a BNS leading to the prompt or delayed formation of a BH and to its ringdown.
We consider either a polytropic or an ideal fluid EOS and show that already
with this idealized EOSs a very interesting phenomenology emerges. In
particular, we show that while high-mass binaries lead to the prompt formation
of a rapidly rotating BH surrounded by a dense torus, lower-mass binaries give
rise to a differentially rotating NS, which undergoes large oscillations and
emits large amounts of GWs. Eventually, also the NS collapses to a rotating BH
surrounded by a torus. Finally, we also show that the use of a non-isentropic
EOS leads to significantly different evolutions, giving rise to a delayed
collapse also with high-mass binaries, as well as to a more intense emission of
GWs and to a geometrically thicker torus.Comment: 35 pages, 29 figures, corrected few typos to match the published
version. High-resolution figures and animations can be found at
http://numrel.aei.mpg.de/Visualisations/Archive/BinaryNeutronStars/Relativistic_Meudon/index.htm
Accurate evolutions of inspiralling neutron-star binaries: assessment of the truncation error
We have recently presented an investigation in full general relativity of the
dynamics and gravitational-wave emission from binary neutron stars which
inspiral and merge, producing a black hole surrounded by a torus (see
arXiv:0804.0594). We here discuss in more detail the convergence properties of
the results presented in arXiv:0804.0594 and, in particular, the deterioration
of the convergence rate at the merger and during the survival of the merged
object, when strong shocks are formed and turbulence develops. We also show
that physically reasonable and numerically convergent results obtained at
low-resolution suffer however from large truncation errors and hence are of
little physical use. We summarize our findings in an "error budget", which
includes the different sources of possible inaccuracies we have investigated
and provides a first quantitative assessment of the precision in the modelling
of compact fluid binaries.Comment: 13 pages, 5 figures. Minor changes to match published version. Added
figure 5 right pane
An improved formulation of the relativistic hydrodynamics equations in 2D Cartesian coordinates
A number of astrophysical scenarios possess and preserve an overall
cylindrical symmetry also when undergoing a catastrophic and nonlinear
evolution. Exploiting such a symmetry, these processes can be studied through
numerical-relativity simulations at smaller computational costs and at
considerably larger spatial resolutions. We here present a new
flux-conservative formulation of the relativistic hydrodynamics equations in
cylindrical coordinates. By rearranging those terms in the equations which are
the sources of the largest numerical errors, the new formulation yields a
global truncation error which is one or more orders of magnitude smaller than
those of alternative and commonly used formulations. We illustrate this through
a series of numerical tests involving the evolution of oscillating spherical
and rotating stars, as well as shock-tube tests.Comment: 19 pages, 9 figure
Linking compact dwarf starburst galaxies in the resolve survey to downsized blue nuggets
Abstract We identify and characterize compact dwarf starburst (CDS) galaxies in the RESOLVE survey, a volume-limited census of galaxies in the local universe, to probe whether this population contains any residual “blue nuggets,” a class of intensely star-forming compact galaxies first identified at high redshift z. Our 50 low-z CDS galaxies are defined by dwarf masses (stellar mass M* < 109.5 M⊙), compact bulged-disk or spheroid-dominated morphologies (using a quantitative criterion, \mu _\Delta > 8.6), and specific star formation rates above the defining threshold for high-z blue nuggets (log SSFR [Gyr−1] > −0.5). Across redshifts, blue nuggets exhibit three defining properties: compactness relative to contemporaneous galaxies, abundant cold gas, and formation via compaction in mergers or colliding streams. Those with halo mass below Mhalo ∼ 1011.5 M⊙ may in theory evade permanent quenching and cyclically refuel until the present day. Selected only for compactness and starburst activity, our CDS galaxies generally have Mhalo ≲ 1011.5 M⊙ and gas-to-stellar mass ratio ≳1. Moreover, analysis of archival DECaLS photometry and new 3D spectroscopic observations for CDS galaxies reveals a high rate of photometric and kinematic disturbances suggestive of dwarf mergers. The SSFRs, surface mass densities, and number counts of CDS galaxies are compatible with theoretical and observational expectations for redshift evolution in blue nuggets. We argue that CDS galaxies represent a maximally-starbursting subset of traditional compact dwarf classes such as blue compact dwarfs and blue E/S0s. We conclude that CDS galaxies represent a low-z tail of the blue nugget phenomenon formed via a moderated compaction channel that leaves open the possibility of disk regrowth and evolution into normal disk galaxies
Error-analysis and comparison to analytical models of numerical waveforms produced by the NRAR Collaboration
The Numerical-Relativity-Analytical-Relativity (NRAR) collaboration is a
joint effort between members of the numerical relativity, analytical relativity
and gravitational-wave data analysis communities. The goal of the NRAR
collaboration is to produce numerical-relativity simulations of compact
binaries and use them to develop accurate analytical templates for the
LIGO/Virgo Collaboration to use in detecting gravitational-wave signals and
extracting astrophysical information from them. We describe the results of the
first stage of the NRAR project, which focused on producing an initial set of
numerical waveforms from binary black holes with moderate mass ratios and
spins, as well as one non-spinning binary configuration which has a mass ratio
of 10. All of the numerical waveforms are analysed in a uniform and consistent
manner, with numerical errors evaluated using an analysis code created by
members of the NRAR collaboration. We compare previously-calibrated,
non-precessing analytical waveforms, notably the effective-one-body (EOB) and
phenomenological template families, to the newly-produced numerical waveforms.
We find that when the binary's total mass is ~100-200 solar masses, current EOB
and phenomenological models of spinning, non-precessing binary waveforms have
overlaps above 99% (for advanced LIGO) with all of the non-precessing-binary
numerical waveforms with mass ratios <= 4, when maximizing over binary
parameters. This implies that the loss of event rate due to modelling error is
below 3%. Moreover, the non-spinning EOB waveforms previously calibrated to
five non-spinning waveforms with mass ratio smaller than 6 have overlaps above
99.7% with the numerical waveform with a mass ratio of 10, without even
maximizing on the binary parameters.Comment: 51 pages, 10 figures; published versio
Novel prokaryotic expression of thioredoxin-fused insulinoma associated protein tyrosine phosphatase 2 (IA-2), its characterization and immunodiagnostic application
Background
The insulinoma associated protein tyrosine phosphatase 2 (IA-2) is one of the immunodominant autoantigens involved in the autoimmune attack to the beta-cell in Type 1 Diabetes Mellitus. In this work we have developed a complete and original process for the production and recovery of the properly folded intracellular domain of IA-2 fused to thioredoxin (TrxIA-2ic) in Escherichia coli GI698 and GI724 strains. We have also carried out the biochemical and immunochemical characterization of TrxIA-2icand design variants of non-radiometric immunoassays for the efficient detection of IA-2 autoantibodies (IA-2A).
Results
The main findings can be summarized in the following statements: i) TrxIA-2ic expression after 3 h of induction on GI724 strain yielded ≈ 10 mg of highly pure TrxIA-2ic/L of culture medium by a single step purification by affinity chromatography, ii) the molecular weight of TrxIA-2ic (55,358 Da) could be estimated by SDS-PAGE, size exclusion chromatography and mass spectrometry, iii) TrxIA-2ic was properly identified by western blot and mass spectrometric analysis of proteolytic digestions (63.25 % total coverage), iv) excellent immunochemical behavior of properly folded full TrxIA-2ic was legitimized by inhibition or displacement of [35S]IA-2 binding from IA-2A present in Argentinian Type 1 Diabetic patients, v) great stability over time was found under proper storage conditions and vi) low cost and environmentally harmless ELISA methods for IA-2A assessment were developed, with colorimetric or chemiluminescent detection.
Conclusions
E. coli GI724 strain emerged as a handy source of recombinant IA-2ic, achieving high levels of expression as a thioredoxin fusion protein, adequately validated and applicable to the development of innovative and cost-effective immunoassays for IA-2A detection in most laboratories.Fil: Guerra, Luciano Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Faccinetti, Natalia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Trabucchi, Aldana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Rovitto, Bruno David. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Sabljic, Adriana Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Poskus, Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Iacono, Ruben Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; ArgentinaFil: Valdez, Silvina Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentin
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