17,261 research outputs found
Gravitomagnetic Effects
The paper summarizes the most important effects in Einsteinian
gravitomagnetic fields related to propagating light rays, moving clocks and
atoms, orbiting objects, and precessing spins. Emphasis is put onto the
gravitational interaction of spinning objects. The gravitomagnetic field lines
of a rotating or spinning object are given in analytic form.Comment: 7 pages, 3 figures, Proc. Hyper Symposium, Paris 200
Presenters or Patients? A Crucial Distinction in Individual Health Assessments
Individual health assessments (IHAs) for asymptomatic individuals provide a challenge to traditional distinctions between patient care and non-medical practice. They may involve undue radiation exposure, lead to false positives, and involve high out-of-pocket costs for recipients. A recent paper (Journal of the American College of Radiology 13(12): 1447–1457.e1, 2016) has criticised the use of IHAs and argued that recipients should be classified as ‘presenters’, not ‘patients’, to distinguish it from regular medical care. I critique this classificatory move, on two grounds: one, it is conceptually suspect. Two, it obviates the medical ethics framework for IHAs, potentially exposing recipients of IHAs to lower standards of oversight and protection. Responsible regulation of IHAs will be easier to ethically justify if those seeking IHAs are considered patients and not merely presenters
Apparatus and method for determining the position of a radiant energy source
The position of a terrestrial RF source is determined from a geostationary, synchronous satellite by scanning the beam of a narrow beam width antenna in first and second orthogonal directions over a region including the source. The peak level of energy transduced by the antenna in each of the scanning directions is detected and correlated with the scanning position of the beam by feeding the output of a detector responsive to the transduced signal to an indicator of an X-Y recorder. The X and Y axes of the recorder are scanned in synchronism with the beam being respectively scanned in the first and second directions to form X and Y traces on which are indicated the detected peak position in each of the scanning directions. The source position is determined from an intersection of lines drawn parallel to the X and Y axes and including the detected peak position of each trace
Arnold diffusion for a complete family of perturbations with two independent harmonics
We prove that for any non-trivial perturbation depending on any two
independent harmonics of a pendulum and a rotor there is global instability.
The proof is based on the geometrical method and relies on the concrete
computation of several scattering maps. A complete description of the different
kinds of scattering maps taking place as well as the existence of piecewise
smooth global scattering maps is also provided.Comment: 23 pages, 14 figure
Application of PN and avalanche silicon photodiodes to low-level optical
New approaches to the discovery of other planetary systems require very sensitive and stable detection techniques in order to succeed. Two methods in particular, the astrometric and the photometric methods, require this. To begin understanding the problems and limitations of solid state detectors regarding this application, preliminary experiments were performed at the National Bureau of Standards and a low light level detector characterization facility was built. This facility is briefly described, and the results of tests conducted in it are outlined. A breadboard photometer that was used to obtain stellar brightness ratio precision data is described. The design principles of PN and avalanche silicon photodiodes based on low light level measuring circuits are discussed
Discovery of the 2010 Eruption and the Pre-Eruption Light Curve for Recurrent Nova U Scorpii
We report the discovery by B. G. Harris and S. Dvorak on JD 2455224.9385
(2010 Jan 28.4385 UT) of the predicted eruption of the recurrent nova U Scorpii
(U Sco). We also report on 815 magnitudes (and 16 useful limits) on the
pre-eruption light curve in the UBVRI and Sloan r' and i' bands from 2000.4 up
to 9 hours before the peak of the January 2010 eruption. We found no
significant long-term variations, though we did find frequent fast variations
(flickering) with amplitudes up to 0.4 mag. We show that U Sco did not have any
rises or dips with amplitude greater than 0.2 mag on timescales from one day to
one year before the eruption. We find that the peak of this eruption occurred
at JD 2455224.69+-0.07 and the start of the rise was at JD 2455224.32+-0.12.
From our analysis of the average B-band flux between eruptions, we find that
the total mass accreted between eruptions is consistent with being a constant,
in agreement with a strong prediction of nova trigger theory. The date of the
next eruption can be anticipated with an accuracy of +-5 months by following
the average B-band magnitudes for the next ~10 years, although at this time we
can only predict that the next eruption will be in the year 2020+-2.Comment: Astronomical Journal submitted, 36 pages, 3 figures, full table
On Orbital Period Changes in Nova Outbursts
We propose a new mechanism that produces an orbital period change during a
nova outburst. When the ejected material carries away the specific angular
momentum of the white dwarf, the orbital period increases. A magnetic field on
the surface of the secondary star forces a fraction of the ejected material to
corotate with the star, and hence the binary system. The ejected material thus
takes angular momentum from the binary orbit and the orbital period decreases.
We show that for sufficiently strong magnetic fields on the surface of the
secondary star, the total change to the orbital period could even be negative
during a nova outburst, contrary to previous expectations. Accurate
determinations of pre- and post-outburst orbital periods of recurrent nova
systems could test the new mechanism, in addition to providing meaningful
constraints on otherwise difficult to measure physical quantities. We apply our
mechanism to outbursts of the recurrent nova U Sco.Comment: Accepted for publication in MNRA
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