661 research outputs found
Radio Properties of the Auroral Ionosphere, Final Report (Phase I)
It has been found in recent years that a study of the fluctuations
in the signals received from radio stars affords a powerful means of
investigating the irregular structure of the ionosphere. In 1955 studies
of this type, using frequencies of 223 Me and 456 Me, were initiated
at the Geophysical Institute, with a view to investigating the smallscale
structure of the highly disturbed auroral ionosphere. The purpose
of this report is to present a complete description of the initial experimental
arrangement. Further developments of the equipment and some
results of analysis of the data have been presented in Quarterly Progress
Reports covering the period since 1 June 1956,
The report is divided into three sections. Section I contains a
description of the basic philosophy of the experiment with an elementary
discussion of the various parameters involved. Section II contains a
brief description of the actual field installation, and Section III is
devoted to the electronic design features.
The diagrams pertaining to each section are located at the end of
the section.Air Force Contract No. AF 30(635)-2887
Project No. 5535 - Task 45774
Rome Air Development Center, Griffiss Air Force Base
Rome, New YorkABSTRACT AND GENERAL INTRODUCTION -- [SECTION I] Investigation of the Ionosphere Using Extra- Terrestrial Radio Sources : 1.1 Introduction ; 1.2 Extra-Terrestrial Sources ; Apparent Positions ; 1.3 Instrumental Techniques for the Study of Radiation from Radio Stars ; Interferometer Methods ; Advantages of the Phase-Switch Interferometer ; Interferometer Parameters ; 1.5 Limitations on Accuracy -- References -- [SECTION II] The Field Installation : 2.1 Introduction ; 2.2 The Radio Telescope Towers ; 2.3 The Antennas ; 2.4 Acknowledgements -- [SECTION III] Electronic Design of Phase-Switch Interferometers : 3.1 Introduction ; 3.2 223 Mc Phase-Switch Equipment ; 3.3 456 Mc Phase-Switch Equipment ; 3.4 Auxiliary EquipmentYe
A Study of Giant Pulses from PSR J1824-2452A
We have searched for microsecond bursts of emission from millisecond pulsars
in the globular cluster M28 using the Parkes radio telescope. We detected a
total of 27 giant pulses from the known emitter PSR J1824-2452A. At wavelengths
around 20 cm the giant pulses are scatter-broadened to widths of around 2
microseconds and follow power-law statistics. The pulses occur in two narrow
phase-windows which correlate in phase with X-ray emission and trail the peaks
of the integrated radio pulse-components. Notably, the integrated radio
emission at these phase windows has a steeper spectral index than other
emission. The giant pulses exhibit a high degree of polarization, with many
being 100% elliptically polarized. Their position angles appear random.
Although the integrated emission of PSR J1824-2452A is relatively stable for
the frequencies and bandwidths observed, the intensities of individual giant
pulses vary considerably across our bands. Two pulses were detected at both
2700 and 3500 MHz. The narrower of the two pulses is 20 ns wide at 3500 MHz. At
2700 MHz this pulse has an inferred brightness temperature at maximum of 5 x
10^37 K. Our observations suggest the giant pulses of PSR J1824-2452A are
generated in the same part of the magnetosphere as X-ray emission through a
different emission process to that of ordinary pulses.Comment: Accepted by Ap
The Contribution of the Smectic-Nematic Interface to the Surface Energy
The contribution of the smectic-nematic interface to the surface energy of a
nematic liquid crystal sample is analyzed. By means of a simple model it is
shown that the surface energy depends on the thickness of the region over which
the transition smectic-nematic takes place. For perfectly flat substrates this
thickness is of the order of the correlation length entering in the transition.
An estimate of this contribution shows that it is greater than the one arising
from the nematic-substrate interaction. Moreover, it is also shown that the
surface energy determined in this way presents a non-monotonic behavior with
the temperature.Comment: 10 pages, revte
An improved solar wind electron-density model for pulsar timing
Variations in the solar wind density introduce variable delays into pulsar
timing observations. Current pulsar timing analysis programs only implement
simple models of the solar wind, which not only limit the timing accuracy, but
can also affect measurements of pulsar rotational, astrometric and orbital
parameters. We describe a new model of the solar wind electron density content
which uses observations from the Wilcox Solar Observatory of the solar magnetic
field. We have implemented this model into the tempo2 pulsar timing package. We
show that this model is more accurate than previous models and that these
corrections are necessary for high precision pulsar timing applications.Comment: Accepted by ApJ, 13 pages, 4 figure
Voltage dependent director of a homeotropic negative liquid crystal cell
Copyright © 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 93 (2008) and may be found at http://link.aip.org/link/?APPLAB/93/031909/1Thin layers of obliquely (60° to normal) thermally evaporated SiOx lead to homeotropic alignment of a nematic liquid crystal (LC) having negative dielectric anisotropy. Under application of an ac voltage the director, as characterized by the fully leaky waveguide technique, is found to realign with a voltage controlled tilt along the evaporation direction. This behavior is in complete contrast with that of a LC having positive dielectric anisotropy and may have important implications for modern LC display technology
Kinetics studies of the polymerization and analysis of the mechanical behavior of the adhesive hysol EA-9321
Simultaneous Absolute Timing of the Crab Pulsar at Radio and Optical Wavelengths
The Crab pulsar emits across a large part of the electromagnetic spectrum.
Determining the time delay between the emission at different wavelengths will
allow to better constrain the site and mechanism of the emission. We have
simultaneously observed the Crab Pulsar in the optical with S-Cam, an
instrument based on Superconducting Tunneling Junctions (STJs) with s time
resolution and at 2 GHz using the Nan\c{c}ay radio telescope with an instrument
doing coherent dedispersion and able to record giant pulses data. We have
studied the delay between the radio and optical pulse using simultaneously
obtained data therefore reducing possible uncertainties present in previous
observations. We determined the arrival times of the (mean) optical and radio
pulse and compared them using the tempo2 software package. We present the most
accurate value for the optical-radio lag of 255 21 s and suggest the
likelihood of a spectral dependence to the excess optical emission asociated
with giant radio pulses.Comment: 8 pages; accepted for publication in Astronomy and Astrophysic
{Interstellar Plasma Weather Effects in Long-term Multi-frequency Timing of Pulsar B1937+21
We report here on variable propagation effects in over twenty years of
multi-frequency timing analysis of pulsar PSR B1937+21 that determine
small-scale properties of the intervening plasma as it drifts through the sight
line. The phase structure function derived from the dispersion measure
variations is in remarkable agreement with that expected from the Kolmogorov
spectrum, with a power law index of , valid over an inferred
scale range of 0.2--50 A.U. The observed flux variation time scale and the
modulation index, along with their frequency dependence, are discrepant with
the values expected from a Kolmogorov spectrum with infinitismally small inner
scale cutoff, suggesting a caustic-dominated regime of interstellar optics.
This implies an inner scale cutoff to the spectrum of
meters. Our timing solutions indicate a transverse velocity of 9 km sec
with respect to the solar system barycenter, and 80 km sec with respect
to the pulsar's LSR. We interpret the frequency dependent variations of DM as a
result of the apparent angular broadening of the source, which is a sensitive
function of frequency (). The error introduced by this in
timing this pulsar is 2.2 s at 1 GHz. The timing error introduced by
``image wandering'' from the slow, nominally refractive scintillation effects
is about 125 nanosec at 1 GHz. The error accumulated due to positional error
(due to image wandering) in solar system barycentric corrections is about 85
nanosec at 1 GHz.Comment: Accepted for publication in the Astrophysical Journa
- …