2,941 research outputs found
Recommended from our members
Estimating Residual Faults from Code Coverage
Many reliability prediction techniques require an estimate for the number of residual faults. In this paper, a new theory is developed for using test coverage to estimate the number of residual faults. This theory is applied to a specific example with known faults and the results agree well with the theory. The theory is used to justify the use of linear extrapolation to estimate residual faults. It is also shown that it is important to establish the amount of unreachable code in order to make a realistic residual fault estimate
Wireless recording of the calls of Rousettus aegyptiacus and their reproduction using electrostatic transducers
Bats are capable of imaging their surroundings in great detail using echolocation. To apply similar methods to human engineering systems requires the capability to measure and recreate the signals used, and to understand the processing applied to returning echoes. In this work, the emitted and reflected echolocation signals of Rousettus aegyptiacus are recorded while the bat is in flight, using a wireless sensor mounted on the bat. The sensor is designed to replicate the acoustic gain control which bats are known to use, applying a gain to returning echoes that is dependent on the incurred time delay. Employing this technique allows emitted and reflected echolocation calls, which have a wide dynamic range, to be recorded. The recorded echoes demonstrate the complexity of environment reconstruction using echolocation. The sensor is also used to make accurate recordings of the emitted calls, and these calls are recreated in the laboratory using custom-built wideband electrostatic transducers, allied with a spectral equalization technique. This technique is further demonstrated by recreating multi-harmonic bioinspired FM chirps. The ability to record and accurately synthesize echolocation calls enables the exploitation of biological signals in human engineering systems for sonar, materials characterization and imaging
Modeling the Redshift Evolution of the Normal Galaxy X-ray Luminosity Function
Emission from X-ray binaries (XRBs) is a major component of the total X-ray
luminosity of normal galaxies, so X-ray studies of high redshift galaxies allow
us to probe the formation and evolution of X-ray binaries on very long
timescales. In this paper, we present results from large-scale population
synthesis models of binary populations in galaxies from z = 0 to 20. We use as
input into our modeling the Millennium II Cosmological Simulation and the
updated semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently
account for the star formation history (SFH) and metallicity evolution of each
galaxy. We run a grid of 192 models, varying all the parameters known from
previous studies to affect the evolution of XRBs. We use our models and
observationally derived prescriptions for hot gas emission to create
theoretical galaxy X-ray luminosity functions (XLFs) for several redshift bins.
Models with low CE efficiencies, a 50% twins mass ratio distribution, a steeper
IMF exponent, and high stellar wind mass loss rates best match observational
results from Tzanavaris & Georgantopoulos (2008), though they significantly
underproduce bright early-type and very bright (Lx > 10d41) late-type galaxies.
These discrepancies are likely caused by uncertainties in hot gas emission and
SFHs, AGN contamination, and a lack of dynamically formed Low-mass XRBs. In our
highest likelihood models, we find that hot gas emission dominates the emission
for most bright galaxies. We also find that the evolution of the normal galaxy
X-ray luminosity density out to z = 4 is driven largely by XRBs in galaxies
with X-ray luminosities between 10d40 and 10d41 erg/s.Comment: Accepted into ApJ, 17 pages, 3 tables, 7 figures. Text updated to
address referee's comment
Early Advanced LIGO binary neutron-star sky localization and parameter estimation
2015 will see the first observations of Advanced LIGO and the start of the
gravitational-wave (GW) advanced-detector era. One of the most promising
sources for ground-based GW detectors are binary neutron-star (BNS)
coalescences. In order to use any detections for astrophysics, we must
understand the capabilities of our parameter-estimation analysis. By simulating
the GWs from an astrophysically motivated population of BNSs, we examine the
accuracy of parameter inferences in the early advanced-detector era. We find
that sky location, which is important for electromagnetic follow-up, can be
determined rapidly (~5 s), but that sky areas may be hundreds of square
degrees. The degeneracy between component mass and spin means there is
significant uncertainty for measurements of the individual masses and spins;
however, the chirp mass is well measured (typically better than 0.1%).Comment: 4 pages, 2 figures. Published in the proceedings of Amaldi 1
Altered Cortical Microarchitecture and Bone Metabolism in Patients with Monoclonal Gammopathy of Undetermined Significance
Patients with monoclonal gammopathy of undetermined significance (MGUS) are at increased fracture risk, and we have previously shown that MGUS patients have altered trabecular bone microarchitecture compared with controls. However, there are no data on whether the porosity of cortical bone, which may play a greater role in bone strength and the occurrence of fractures, is increased in MGUS. Thus, we studied cortical porosity and bone strength (apparent modulus) using high-resolution peripheral quantitative computed tomography imaging of the distal radius in 50 MGUS patients and 100 age-, gender-, and body mass index–matched controls. Compared with controls, MGUS patients had both significantly higher cortical porosity (+16.8%; P < .05) and lower apparent modulus (–8.9%; P < .05). Despite their larger radial bone size, MGUS patients have significantly increased cortical bone porosity and reduced bone strength relative to controls. This increased cortical porosity may explain the increased fracture risk seen in MGUS patients
Binary evolution with LOFT
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of very faint X-ray binaries,
orbital period distribution of black hole X-ray binaries and neutron star spin
up. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timing. (v2 few typos corrected
Constraining Unmodeled Physics with Compact Binary Mergers from GWTC-1
We present a flexible model to describe the effects of generic deviations of observed gravitational wave signals from modeled waveforms in the LIGO and Virgo gravitational wave detectors. With the detection of 11 gravitational wave events from the GWTC-1 catalog, we are able to constrain possible deviations from our modeled waveforms. In this paper we present our coherent spline model that describes the deviations, then choose to validate our model on an example phenomenological and astrophysically motivated departure in waveforms based on extreme spontaneous scalarization. We find that the model is capable of recovering the simulated deviations. By performing model comparisons we observe that the spline model effectively describes the simulated departures better than a normal compact binary coalescence (CBC) model. We analyze the entire GWTC-1 catalog of events with our model and compare it to a normal CBC model, finding that there are no significant departures from the modeled template gravitational waveforms used
Time evolution of a non-singular primordial black hole
There is growing notion that black holes may not contain curvature
singularities (and that indeed nature in general may abhor such spacetime
defects). This notion could have implications on our understanding of the
evolution of primordial black holes (PBHs) and possibly on their contribution
to cosmic energy. This paper discusses the evolution of a non-singular black
hole (NSBH) based on a recent model [1]. We begin with a study of the
thermodynamic process of the black hole in this model, and demonstrate the
existence of a maximum horizon temperature T_{max}, corresponding to a unique
mass value. At this mass value the specific heat capacity C changes signs to
positive and the body begins to lose its black hole characteristics. With no
loss of generality, the model is used to discuss the time evolution of a
primordial black hole (PBH), through the early radiation era of the universe to
present, under the assumption that PBHs are non-singular. In particular, we
track the evolution of two benchmark PBHs, namely the one radiating up to the
end of the cosmic radiation domination era, and the one stopping to radiate
currently, and in each case determine some useful features including the
initial mass m_{f} and the corresponding time of formation t_{f}. It is found
that along the evolutionary history of the universe the distribution of PBH
remnant masses (PBH-RM) PBH-RMs follows a power law. We believe such a result
can be a useful step in a study to establish current abundance of PBH-MRs.Comment: To appear in Int. J. Mod. Phys.
- …