3,281 research outputs found
Automated analysis of blood pressure measurements (Korotkov sound)
Automatic system for noninvasive measurements of arterial blood pressure is described. System uses Korotkov sound processor logic ratios to identify Korotkov sounds. Schematic diagram of system is provided to show components and method of operation
Apparatus and method for processing Korotkov sounds
A Korotkov sound processor, used in a noninvasive automatic blood measuring system where the brachial artery is occluded by an inflatable cuff, is disclosed. The Korotkoff sound associated with the systolic event is determined when the ratio of the absolute value of a voltage signal, representing Korotkov sounds in the range of 18 to 26 Hz to a maximum absolute peak value of the unfiltered signals, first equals or exceeds a value of 0.45. Korotkov sound associated with the diastolic event is determined when a ratio of the voltage signal of the Korotkov sounds in the range of 40 to 60 Hz to the absolute peak value of such signals within a single measurement cycle first falls below a value of 0.17. The processor signals the occurrence of the systolic and diastolic events and these signals can be used to control a recorder to record pressure values for these events
A MERLIN Observation of PSR B1951+32 and its associated Plerion
In an investigative 16 hour L band observation using the MERLIN radio
interferometric array, we have resolved both the pulsar PSR B1951+32 and
structure within the flat spectral radio continuum region, believed to be the
synchrotron nebula associated with the interaction of the pulsar and its `host'
supernova remnant CTB 80. The extended structure we see, significant at
4.5 , is of dimensions 2.5" 0.75", and suggests a sharp bow
shaped arc of shocked emission, which is correlated with similar structure
observed in lower resolution radio maps and X-ray images. Using this MERLIN
data as a new astrometric reference for other multiwavelength data we can place
the pulsar at one edge of the HST reported optical synchrotron knot, ruling out
previous suggested optical counterparts, and allowing an elementary analysis of
the optical synchrotron emission which appears to trail the pulsar. The latter
is possibly a consequence of pulsar wind replenishment, and we suggest that the
knot is a result of magnetohydrodynamic (MHD) instabilities. These being so, it
suggests a dynamical nature to the optical knot, which will require high
resolution optical observations to confirm.Comment: 12 pages, 2 figures. Accepted for publication in ApJ
Implications of the Optical Observations of Neutron Stars
We show that observations of pulsars with pulsed optical emission indicate
that the peak flux scales according to the magnetic field strength at the light
cylinder. The derived relationships indicate that the emission mechanism is
common across all of the observed pulsars with periods ranging from 33ms to 385
ms and ages of 1000-300,000 years. It is noted that similar trends exist for
ray pulsars. Furthermore the model proposed by Pacini (1971) and
developed by Pacini and Salvati (1983,1987) still has validity and gives an
adequate explanation of the optical phenomena.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Antimatter research in Space
Two of the most compelling issues facing astrophysics and cosmology today are
to understand the nature of the dark matter that pervades the universe and to
understand the apparent absence of cosmological antimatter. For both issues,
sensitive measurements of cosmic-ray antiprotons and positrons, in a wide
energy range, are crucial. Many different mechanisms can contribute to
antiprotons and positrons production, ranging from conventional reactions up to
exotic processes like neutralino annihilation. The open problems are so
fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that
experiments in this field will probably be of the greatest interest in the next
years. Here we will summarize the present situation, showing the different
hypothesis and models and the experimental measurements needed to lead to a
more established scenario.Comment: 10 pages, 7 figures, Invited talk at the 18th European Cosmic Ray
Symposium, Moscow, July 2002, submitted to Journal of Physics
Collective excitations in electron-hole bilayers
We report a combined analytic and Molecular Dynamics analysis of the
collective mode spectrum of an electron-hole (bipolar) bilayer in the strong
coupling quasi-classical limit. A robust, isotropic energy gap is identified in
the out-of-phase spectra, generated by the combined effect of correlations and
of the excitation of the bound dipoles; the in-phase spectra exhibit a
correlation governed acoustic dispersion for the longitudinal and transverse
modes. Strong nonlinear generation of higher harmonics of the fundamental
dipole oscillation frequency and the transfer of harmonics between different
modes is observed. The mode dispersions in the liquid state are compared with
the phonon spectrum in the crystalline solid phase, reinforcing a coherent
physical picture.Comment: 4 pages, 5 figure
Measurement of 0.25-3.2 GeV antiprotons in the cosmic radiation
The balloon-borne Isotope Matter-Antimatter Experiment (IMAX) was flown from Lynn Lake, Manitoba, Canada on 16–17 July 1992. Using velocity and magnetic rigidity to determine mass, we have directly measured the abundances of cosmic ray antiprotons and protons in the energy range from 0.25 to 3.2 GeV. Both the absolute flux of antiprotons and the antiproton/proton ratio are consistent with recent theoretical work in which antiprotons are produced as secondary products of cosmic ray interactions with the interstellar medium. This consistency implies a lower limit to the antiproton lifetime of ∼10 to the 7th yr
Correlational Origin of the Roton Minimum
We present compelling evidence supporting the conjecture that the origin of
the roton in Bose-condensed systems arises from strong correlations between the
constituent particles. By studying the two dimensional bosonic dipole systems a
paradigm, we find that classical molecular dynamics (MD) simulations provide a
faithful representation of the dispersion relation for a low- temperature
quantum system. The MD simulations allow one to examine the effect of coupling
strength on the formation of the roton minimum and to demonstrate that it is
always generated at a sufficiently high enough coupling. Moreover, the
classical images of the roton-roton, roton-maxon, etc. states also appear in
the MD simulation spectra as a consequence of the strong coupling.Comment: 7 pages, 4 figure
Unpulsed UBV Optical Emission from the Crab Pulsar
Based on observations of the Crab pulsar using the TRIFFID high speed imaging
photometer in the UBV bands using the Special Astrophysical Observatory's 6m
telescope in the Russian Caucasus, we report the detection of pronounced
emission during the so-called `off' phase of emission. Following de-extinction,
this unpulsed component of emission is shown to be consistent with a power law
with an exponent of alpha = -0.60 +/- 0.37, the uncertainty being dominated by
the error associated with the independent CCD photometry used to reference the
TRIFFID data. This suggests a steeper power law form than that reported
elsewhere in the literature for the total integrated spectrum, which is
essentially flat with alpha ~ 0.1, although the difference in this case is only
significant at the ~ 2 sigma level. Deeper reference integrated and TRIFFID
phase-resolved photometry in these bands in conjunction with further
observations in the UV and R region would constrain this fit further.Comment: 26 pages, 2 figures, uses aasms4.sty, accepted for publication in the
Astrophysical Journa
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