546 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
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
Radio disappearance of the magnetar XTE J1810-197 and continued X-ray timing
We report on timing, flux density, and polarimetric observations of the
transient magnetar and 5.54 s radio pulsar XTE J1810-197 using the GBT, Nancay,
and Parkes radio telescopes beginning in early 2006, until its sudden
disappearance as a radio source in late 2008. Repeated observations through
2016 have not detected radio pulsations again. The torque on the neutron star,
as inferred from its rotation frequency derivative f-dot, decreased in an
unsteady manner by a factor of 3 in the first year of radio monitoring. In
contrast, during its final year as a detectable radio source, the torque
decreased steadily by only 9%. The period-averaged flux density, after
decreasing by a factor of 20 during the first 10 months of radio monitoring,
remained steady in the next 22 months, at an average of 0.7+/-0.3 mJy at 1.4
GHz, while still showing day-to-day fluctuations by factors of a few. There is
evidence that during this last phase of radio activity the magnetar had a steep
radio spectrum, in contrast to earlier behavior. There was no secular decrease
that presaged its radio demise. During this time the pulse profile continued to
display large variations, and polarimetry indicates that the magnetic geometry
remained consistent with that of earlier times. We supplement these results
with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the
first 4 years, XTE J1810-197 experienced non-monotonic excursions in f-dot by
at least a factor of 8. But since 2007, its f-dot has remained relatively
stable near its minimum observed value. The only apparent event in the X-ray
record that is possibly contemporaneous with the radio shut-down is a decrease
of ~20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However,
the permanence of the high-amplitude, thermal X-ray pulse, even after the radio
demise, implies continuing magnetar activity.Comment: ApJ, accepted, 12 pages, 9 figure
Surface alignment and anchoring transitions in nematic lyotropic chromonic liquid crystal
The surface alignment of lyotropic chromonic liquid crystals (LCLCs) can be
not only planar (tangential) but also homeotropic, with self-assembled
aggregates perpendicular to the substrate, as demonstrated by mapping optical
retardation and by three-dimensional imaging of the director field. With time,
the homeotropic nematic undergoes a transition into a tangential state. The
anchoring transition is discontinuous and can be described by a double-well
anchoring potential with two minima corresponding to tangential and homeotropic
orientation.Comment: Accepted for publication in Phys. Rev. Lett. (Accepted Wednesday Jun
02, 2010
Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: a case for Caustic Radio Emission?
We report the detection of pulsed gamma-ray emission from the fast
millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20
(J1959+2048) using 18 months of survey data recorded by the \emph{Fermi} Large
Area Telescope (LAT) and timing solutions based on radio observations conducted
at the Westerbork and Nan\c{c}ay radio telescopes. In addition, we analyzed
archival \emph{RXTE} and \emph{XMM-Newton} X-ray data for the two MSPs,
confirming the X-ray emission properties of PSR B1937+21 and finding evidence
() for pulsed emission from PSR B1957+20 for the first time. In
both cases the gamma-ray emission profile is characterized by two peaks
separated by half a rotation and are in close alignment with components
observed in radio and X-rays. These two pulsars join PSRs J0034-0534 and
J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks
in different energy bands. The modeling of the radio and gamma-ray emission
profiles suggests co-located emission regions in the outer magnetosphere.Comment: Accepted for publication in the Astrophysical Journa
Single-run separation of closely related cationic and anionic compounds by CE-ESI-MS: application to the simultaneous analysis of melamine and its analogs in milk
In recent years, two adulteration incidents concerning the addition of melamine, a nitrogen-rich industrial small polar compound, to pet food and infant formula products have occurred in China. These issues prompted laboratories to develop methods for the analysis of melamine and related compounds in a wide variety of food products and ingredients. In this context, a CE-ESI-MS method was developed to simultaneously analyze melamine and its related products (ammeline, ammelide and cyanuric acid) that possess close physico-chemical properties. This method allows the simultaneous analysis of both cations and anions in a single run, using CE to divide the run into two time segments in normal polarity mode. For this purpose, ESI polarity was switched once during the run, increasing sensitivity and data quality. The method was applied to spiked powdered milk and melamine-contaminated powdered milk, with two sample preparation procedures
Single-run separation of closely related cationic and anionic compounds by CE-ESI-MS: application to the simultaneous analysis of melamine and its analogs in milk
In recent years, two adulteration incidents concerning the addition of melamine, a nitrogen-rich industrial small polar compound, to pet food and infant formula products have occurred in China. These issues prompted laboratories to develop methods for the analysis of melamine and related compounds in a wide variety of food products and ingredients. In this context, a CE-ESI-MS method was developed to simultaneously analyze melamine and its related products (ammeline, ammelide and cyanuric acid) that possess close physico-chemical properties. This method allows the simultaneous analysis of both cations and anions in a single run, using CE to divide the run into two time segments in normal polarity mode. For this purpose, ESI polarity was switched once during the run, increasing sensitivity and data quality. The method was applied to spiked powdered milk and melamine-contaminated powdered milk, with two sample preparation procedures
A Bayesian parameter estimation approach to pulsar time-of-arrival analysis
The increasing sensitivities of pulsar timing arrays to ultra-low frequency
(nHz) gravitational waves promises to achieve direct gravitational wave
detection within the next 5-10 years. While there are many parallel efforts
being made in the improvement of telescope sensitivity, the detection of stable
millisecond pulsars and the improvement of the timing software, there are
reasons to believe that the methods used to accurately determine the
time-of-arrival (TOA) of pulses from radio pulsars can be improved upon. More
specifically, the determination of the uncertainties on these TOAs, which
strongly affect the ability to detect GWs through pulsar timing, may be
unreliable. We propose two Bayesian methods for the generation of pulsar TOAs
starting from pulsar "search-mode" data and pre-folded data. These methods are
applied to simulated toy-model examples and in this initial work we focus on
the issue of uncertainties in the folding period. The final results of our
analysis are expressed in the form of posterior probability distributions on
the signal parameters (including the TOA) from a single observation.Comment: 16 pages, 4 figure
Radio Detection of the Fermi LAT Blind Search Millisecond Pulsar J1311-3430
We report the detection of radio emission from PSR J1311-3430, the first
millisecond pulsar discovered in a blind search of Fermi Large Area Telescope
(LAT) gamma-ray data. We detected radio pulsations at 2 GHz, visible for <10%
of ~4.5-hrs of observations using the Green Bank Telescope (GBT). Observations
at 5 GHz with the GBT and at several lower frequencies with Parkes, Nancay, and
the Giant Metrewave Radio Telescope resulted in non-detections. We also report
the faint detection of a steep spectrum continuum radio source (0.1 mJy at 5
GHz) in interferometric imaging observations with the Jansky Very Large Array.
These detections demonstrate that PSR J1311-3430, is not radio quiet and
provides additional evidence that the radio beaming fraction of millisecond
pulsars is very large. The radio detection yields a distance estimate of 1.4
kpc for the system, yielding a gamma-ray efficiency of 30%, typical of
LAT-detected MSPs. We see apparent excess delay in the radio pulsar as the
pulsar appears from eclipse and we speculate on possible mechanisms for the
non-detections of the pulse at other orbital phases and observing frequencies.Comment: 6 pages, 4 figures. ApJ Letters, in pres
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