497 research outputs found
Long-Term Observations Of The Pulsars In 47 Tucanae – Ii. Proper Motions, Accelerations And Jerks
This paper is the second in a series where we report the results of the long-term timing of the millisecond pulsars (MSPs) in 47 Tucanae with the Parkes 64-m radio telescope. We obtain improved timing parameters that provide additional information for studies of the cluster dynamics: (a) the pulsar proper motions yield an estimate of the proper motion of the cluster as a whole (μα = 5.00 ± 0.14 mas yr − 1, μδ = − 2.84 ± 0.12 mas yr − 1) and the motion of the pulsars relative to each other. (b) We measure the second spin-period derivatives caused by the change of the pulsar line-of-sight accelerations; 47 Tuc H, U and possibly J are being affected by nearby objects. (c) For 10 binary systems, we now measure changes in the orbital period caused by their acceleration in the gravitational field of the cluster. From all these measurements, we derive a cluster distance no smaller than ∼4.69 kpc and show that the characteristics of these MSPs are very similar to their counterparts in the Galactic disc. We find no evidence in favour of an intermediate mass black hole at the centre of the cluster. Finally, we describe the orbital behaviour of four ‘black widow’ systems. Two of them, 47 Tuc J and O, exhibit orbital variability similar to that observed in other such systems, while for 47 Tuc I and R the orbits seem to be remarkably stable. It appears therefore that not all ‘black widows’ have unpredictable orbital behaviour
River bedform inception by flow unsteadiness: a modal and nonmodal analysis
River bedforms arise as a result of morphological instabilities of the stream-sediment interface. Dunes and antidunes constitute the most typical patterns, and their occurrence and dynamics are relevant for a number of engineering and environmental applications. Although flow variability is a typical feature of all rivers, the bedform-triggering morphological instabilities have generally been studied under the assumption of a constant flow rate. In order to partially address this shortcoming, we here discuss the influence of (periodic) flow unsteadiness on bedform inception. To this end, our recent one-dimensional validated model coupling Dressler's equations with a refined mechanistic sediment transport formulation is adopted, and both the asymptotic and transient dynamics are investigated by modal and nonmodal analyses
Long-term observations of the pulsars in 47 Tucanae - II. Proper motions, accelerations and jerks
This paper is the second in a series where we report the results of the
long-term timing of the millisecond pulsars (MSPs) in 47 Tucanae with the
Parkes 64-m radio telescope. We obtain improved timing parameters that provide
additional information for studies of the cluster dynamics: a) the pulsar
proper motions yield an estimate of the proper motion of the cluster as a whole
(, ) and the motion of the pulsars
relative to each other. b) We measure the second spin-period derivatives caused
by the change of the pulsar line-of-sight accelerations; 47 Tuc H, U and
possibly J are being affected by nearby objects. c) For ten binary systems we
now measure changes in the orbital period caused by their acceleration in the
gravitational field of the cluster. From all these measurements, we derive a
cluster distance no smaller than 4.69 kpc and show that the
characteristics of these MSPs are very similar to their counterparts in the
Galactic disk. We find no evidence in favour of an intermediate mass black hole
at the centre of the cluster. Finally, we describe the orbital behaviour of the
four "black widow" systems. Two of them, 47 Tuc J and O, exhibit orbital
variability similar to that observed in other such systems, while for 47 Tuc I
and R the orbits seem to be remarkably stable. It appears, therefore, that not
all "black widows" have unpredictable orbital behaviour.Comment: 21 pages in journal format, 9 figures, 4 tables, accepted for
publication in MNRAS, several clarifications made and typos fixe
Long-term observations of the pulsars in 47 Tucanae. I. A study of four elusive binary systems
For the past couple of decades, the Parkes radio telescope has been regularly
observing the millisecond pulsars in 47 Tucanae (47 Tuc). This long-term timing
program was designed to address a wide range of scientific issues related to
these pulsars and the globular cluster where they are located. In this paper,
the first of a series, we address one of these objectives: the characterization
of four previously known binary pulsars for which no precise orbital parameters
were known, namely 47 Tuc P, V, W and X (pulsars 47 Tuc R and Y are discussed
elsewhere). We determined the previously unknown orbital parameters of 47 Tuc V
and X and greatly improved those of 47 Tuc P and W. For pulsars W and X we
obtained, for the first time, full coherent timing solutions across the whole
data span, which allowed a much more detailed characterization of these
systems. 47 Tuc W, a well-known tight eclipsing binary pulsar, exhibits a large
orbital period variability, as expected for a system of its class. 47 Tuc X
turns out to be in a wide, extremely circular, 10.9-day long binary orbit and
its position is ~3.8 arcmin away from the cluster center, more than three times
the distance of any other pulsar in 47 Tuc. These characteristics make 47 Tuc X
a very different object with respect to the other pulsars of the cluster.Comment: Accepted for publication by MNRAS, 18 pages, 11 figure
Internal gas models and central black hole in 47 Tucanae using millisecond pulsars
Despite considerations of mass loss from stellar evolution suggesting
otherwise, the content of gas in globular clusters seems poor and hence its
measurement very elusive. One way of constraining the presence of ionized gas
in a globular cluster is through its dispersive effects on the radiation of the
millisecond pulsars included in the cluster. This effect led Freire et al. in
2001 to the first detection of any kind of gas in a globular cluster in the
case of 47 Tucanae. By exploiting the results of 12 additional years of timing,
as well as the observation of new millisecond pulsars in 47 Tucanae, we
revisited this measurement: we first used the entire set of available timing
parameters in order to measure the dynamical properties of the cluster and the
three-dimensional position of the pulsars. Then we applied and tested various
gas distribution models: assuming a constant gas density, we confirmed the
detection of ionized gas with a number density of cm,
larger than the previous determination (at 2 uncertainty). Models
predicting a decreasing density or following the stellar distribution density
are highly disfavoured. We are also able to investigate the presence of an
intermediate mass black hole in the centre of the cluster, showing that is not
required by the available data, with an upper limit for the mass at
M.Comment: 14 pages, 10 figures, accepted for publication in MNRA
Piecewise planar underwater mosaicing
A commonly ignored problem in planar mosaics, yet often present in practice, is the selection of a reference homography reprojection frame where to attach the successive image frames of the mosaic. A bad choice for the reference frame can lead to severe distortions in the mosaic and can degenerate in incorrect configurations after some sequential frame concatenations. This problem is accentuated in uncontrolled underwater acquisition setups as those provided by AUVs or ROVs due to both the noisy trajectory of the acquisition vehicle - with roll and pitch shakes - and to the non-flat nature of the seabed which tends to break the planarity assumption implicit in the mosaic construction. These scenarios can also introduce other undesired effects, such as light variations between successive frames, scattering and attenuation, vignetting, flickering and noise. This paper proposes a novel mosaicing pipeline, also including a strategy to select the best reference homography in planar mosaics from video sequences which minimizes the distortions induced on each image by the mosaic homography itself. Moreover, a new non-linear color correction scheme is incorporated to handle strong color and luminosity variations among the mosaic frames. Experimental evaluation of the proposed method on real, challenging underwater video sequences shows the validity of the approach, providing clear and visually appealing mosaic
A performance score of the quality of inpatient diabetes care is a marker of clinical outcomes and suggests a cause-effect relationship between hypoglycaemia and the risk of in-hospital mortality
Aims: To build a tool to assess the management of inpatients with diabetes mellitus and to investigate its relationship, if any, with clinical outcomes. Materials and methods: A total of 678 patients from different settings, Internal Medicine (IMU, n = 255), General Surgery (GSU, n = 230) and Intensive Care (ICU, n = 193) Units, were enrolled. A work-flow of clinical care of diabetes was created according to guidelines. The workflow was divided into five different domains: (a) initial assessment; (b) glucose monitoring; (c) medical therapy; (d) consultancies; (e) discharge. Each domain was assessed by a performance score (PS), computed as the sum of the scores achieved in a set of indicators of clinical appropriateness, management and patient empowerment. Appropriate glucose goals were included as intermediate phenotypes. Clinical outcomes included: hypoglycaemia, survival rate and clinical conditions at discharge. Results: The total PS and those of initial assessment and glucose monitoring were significantly lower in GSU with respect to IMU and ICU (P <.0001). The glucose monitoring PS was associated with lower risk of hypoglycaemia (OR = 0.55; P <.0001), whereas both the PSs of glucose monitoring and medical therapy resulted associated with higher in-hospital survival only in the IMU ward (OR = 6.67 P =.001 and OR = 2.38 P =.03, respectively). Instrumental variable analysis with the aid of PS of glucose monitoring showed that hypoglycaemia may play a causal role in in-hospital mortality (P =.04). Conclusions: The quality of in-hospital care of diabetes may affect patient outcomes, including glucose control and the risk of hypoglycaemia, and through the latter it may influence the risk of in-hospital mortality
Radio pulsations from the -ray millisecond pulsar PSR J2039-5617
The predicted nature of the candidate redback pulsar 3FGL\,J2039.65618 was
recently confirmed by the discovery of -ray millisecond pulsations
(Clark et al. 2020, hereafter Paper\,I), which identify this -ray
source as \msp. We observed this object with the Parkes radio telescope in 2016
and 2019. We detect radio pulsations at 1.4\,GHz and 3.1\,GHz, at the 2.6ms
period discovered in -rays, and also at 0.7\,GHz in one 2015 archival
observation. In all bands, the radio pulse profile is characterised by a single
relatively broad peak which leads the main -ray peak. At 1.4\,GHz we
found clear evidence of eclipses of the radio signal for about half of the
orbit, a characteristic phenomenon in redback systems, which we associate with
the presence of intra-binary gas. From the dispersion measure of
\,pc\,cm we derive a pulsar distance of \,kpc
or \,kpc, depending on the assumed Galactic electron density model.
The modelling of the radio and -ray light curves leads to an
independent determination of the orbital inclination, and to a determination of
the pulsar mass, qualitatively consistent to the results in Paper\,I.Comment: 18 pages, accepted for publication on MNRA
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