14,507 research outputs found
Realistic Sensitivity Curves For Pulsar Timing Arrays
We construct realistic sensitivity curves for pulsar timing array searches for gravitational waves, incorporating both red and white noise contributions to individual pulsar noise spectra, and the effect of fitting to a pulsar timing model. We demonstrate the method on both simulated pulsars and a realistic array consisting of a subset of NANOGrav pulsars used in recent analyses. A comparison between the results presented here and measured upper limit curves from actual analyses shows agreement to tens of percent. The resulting sensitivity curves can be used to assess the detectability of predicted gravitational-wave signals in the nanohertz frequency band in a coherent, flexible, and computationally efficient manner
Realistic Sensitivity Curves For Pulsar Timing Arrays
We construct realistic sensitivity curves for pulsar timing array searches for gravitational waves, incorporating both red and white noise contributions to individual pulsar noise spectra, and the effect of fitting to a pulsar timing model. We demonstrate the method on both simulated pulsars and a realistic array consisting of a subset of NANOGrav pulsars used in recent analyses. A comparison between the results presented here and measured upper limit curves from actual analyses shows agreement to tens of percent. The resulting sensitivity curves can be used to assess the detectability of predicted gravitational-wave signals in the nanohertz frequency band in a coherent, flexible, and computationally efficient manner
A general hidden variable model for the two-qubits system
We generalize Bell's hidden variable model describing the singlet state of a
two-qubits system by extending it to arbitrary states and observables. As in
the original work, we assume a uniform, state-independent probability
distribution for the hidden variables which are identified with the unit
vectors of a 3-dimensional real space. By slightly modifying our model, we
provide also a minimal hidden variable description of the two-qubits system,
relying on a single hidden variable. We discuss the main features and the
implications of the model.Comment: 4 pages, submitted for publicatio
Quantum and Superquantum Nonlocal Correlations
We present a simple hidden variable model for the singlet state of a pair of
qubits, characterized by two kinds, hierarchically ordered, of hidden
variables. We prove that, averaging over both types of variables, one
reproduces all the quantum mechanical correlations of the singlet state. On the
other hand, averaging only over the hidden variables of the lower level, one
obtains a general formal theoretical scheme exhibiting correlations stronger
than the quantum ones, but with faster-than-light communication forbidden. This
result is interesting by itself since it shows that a violation of the quantum
bound for nonlocal correlations can be implemented in a precise physical manner
and not only mathematically, and it suggests that resorting to two levels of
nonlocal hidden variables might led to a deeper understanding of the physical
principles at the basis of quantum nonlocality.Comment: 5 pages, 1 figure. Submitted for publicatio
Two years of monitoring Supergiant Fast X-ray Transients with Swift
We present two years of intense Swift monitoring of three SFXTs, IGR
J16479-4514, XTE J1739-302, and IGR J17544-2619 (since October 2007).
Out-of-outburst intensity-based X-ray (0.3-10keV) spectroscopy yields absorbed
power laws with by hard photon indices (G~1-2). Their outburst broad-band
(0.3-150 keV) spectra can be fit well with models typically used to describe
the X-ray emission from accreting NSs in HMXBs. We assess how long each source
spends in each state using a systematic monitoring with a sensitive instrument.
These sources spend 3-5% of the total in bright outbursts. The most probable
flux is 1-2E-11 erg cm^{-2} s^{-1} (2-10 keV, unabsorbed), corresponding to
luminosities in the order of a few 10^{33} to 10^{34} erg s^{-1} (two orders of
magnitude lower than the bright outbursts). The duty-cycle of inactivity is 19,
39, 55%, for IGR J16479-4514, XTE J1739-302, and IGR J17544-2619, respectively.
We present a complete list of BAT on-board detections further confirming the
continued activity of these sources. This demonstrates that true quiescence is
a rare state, and that these transients accrete matter throughout their life at
different rates. X-ray variability is observed at all timescales and
intensities we can probe. Superimposed on the day-to-day variability is
intra-day flaring which involves variations up to one order of magnitude that
can occur down to timescales as short as ~1ks, and whichcan be explained by the
accretion of single clumps composing the donor wind with masses
M_cl~0.3-2x10^{19} g. (Abridged)Comment: Accepted for publication in MNRAS. 17 pages, 11 figures, 8 table
Half-life of cost-of-illness estimates: the case of Spina Bifida
ManuscriptNeural tube defects, which include spina bifida, are one of the most frequent and important categories of birth defects. Accordingly, there has been considerable interest in studying the impact of spina bifida as a public health problem. This impact can be measured in various ways, including disease-specific mortality, morbidity, functional limitation or disability, and quality of life impairment. Each of these measures captures one component of the total burden of disease. Such measures of impact are important because they allow public health agencies, researchers, and health care providers to understand the effects of preventive or diagnostic interventions, changes in disease incidence or prevalence, and new technologies
Corrections to the apparent value of the cosmological constant due to local inhomogeneities
Supernovae observations strongly support the presence of a cosmological
constant, but its value, which we will call apparent, is normally determined
assuming that the Universe can be accurately described by a homogeneous model.
Even in the presence of a cosmological constant we cannot exclude nevertheless
the presence of a small local inhomogeneity which could affect the apparent
value of the cosmological constant. Neglecting the presence of the
inhomogeneity can in fact introduce a systematic misinterpretation of
cosmological data, leading to the distinction between an apparent and true
value of the cosmological constant. We establish the theoretical framework to
calculate the corrections to the apparent value of the cosmological constant by
modeling the local inhomogeneity with a solution. Our assumption
to be at the center of a spherically symmetric inhomogeneous matter
distribution correspond to effectively calculate the monopole contribution of
the large scale inhomogeneities surrounding us, which we expect to be the
dominant one, because of other observations supporting a high level of isotropy
of the Universe around us.
By performing a local Taylor expansion we analyze the number of independent
degrees of freedom which determine the local shape of the inhomogeneity, and
consider the issue of central smoothness, showing how the same correction can
correspond to different inhomogeneity profiles. Contrary to previous attempts
to fit data using large void models our approach is quite general. The
correction to the apparent value of the cosmological constant is in fact
present for local inhomogeneities of any size, and should always be taken
appropriately into account both theoretically and observationally.Comment: 16 pages,new sections added analyzing central smoothness and accuracy
of the Taylor expansion approach, Accepted for publication by JCAP. An essay
based on this paper received honorable mention in the 2011 Essay Context of
the Gravity Research Foundatio
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