42 research outputs found
A Strong Upper Limit on the Pulsed Radio Luminosity of the Compact Object 1RXS J141256.0+792204
The ROSAT X-ray source 1RXS J141256.0+792204 has recently been identified as
a likely compact object whose properties suggest it could be a very nearby
radio millisecond pulsar at d = 80 - 260pc. We investigated this hypothesis by
searching for radio pulsations using the Westerbork Synthesis Radio Telescope.
We observed 1RXS J141256.0+792204 at 385 and 1380MHz, recording at high time
and frequency resolution in order to maintain sensitivity to millisecond
pulsations. These data were searched both for dispersed single pulses and using
Fourier techniques sensitive to constant and orbitally modulated periodicities.
No radio pulsations were detected in these observations, resulting in pulsed
radio luminosity limits of L_400 ~ 0.3 (d/250pc)^2 mJy kpc^2 and L_1400 ~ 0.03
(d/250pc)^2 mJy kpc^2 at 400 and 1400MHz respectively. The lack of detectable
radio pulsations from 1RXS J141256.0+792204 brings into question its
identification as a nearby radio pulsar, though, because the pulsar could be
beamed away from us, this hypothesis cannot be strictly ruled out.Comment: To appear in A&A. 3 page
The Geometry of PSR B0031-07
PSR B0031-07 is well known to exhibit three different modes of drifting
sub-pulses (mode A, B and C). It has recently been shown that in a
multifrequency observation, consisting of 2700 pulses, all driftmodes were
visible at low frequencies, while at 4.85 GHz only mode-A drift or non-drifting
emission was detected. This suggests that modes A and B are emitted in
sub-beams, rotating at a fixed distance from the magnetic axis, with the mode-B
sub-beams being closer to the magnetic axis than the mode-A sub-beams. Diffuse
emission between the sub-beams can account for the non-drifting emission. Using
the results of an analysis of simultaneous multifrequency observations of PSR
B0031-07, we set out to construct a geometrical model that includes emission
from both sub-beams and diffuse emission and describes the regions of the radio
emission of PSR B0031-07 at each emission frequency for driftmodes A and B.
Based on the vertical spacing between driftbands, we have determined the
driftmode of each sequence of drift. To restrict the model, we calculated
average polarisation and intensity characteristics for each driftmode and at
each frequency. The model reproduces the observed polarisation and intensity
characteristics, suggesting that diffuse emission plays an important role in
the emission properties of PSR B0031-07. The model further suggests that the
emission heights of this pulsar range from a few kilometers to a little over 10
kilometers above the pulsar surface. We also find that the relationships
between height and frequency of emission that follow from curvature radiation
and from plasma-frequency emission could not be used to reproduce the observed
frequency dependence of the width of the average intensity profiles.Comment: 15 pages, 9 figures, 8 tables, accepted for publication in A&
Multi-telescope timing of PSR J1518+4904
PSR J1518+4904 is one of only 9 known double neutron star systems. These
systems are highly valuable for measuring the masses of neutron stars,
measuring the effects of gravity, and testing gravitational theories. We
determine an improved timing solution for a mildly relativistic double neutron
star system, combining data from multiple telescopes. We set better constraints
on relativistic parameters and the separate masses of the system, and discuss
the evolution of PSR J1518+4904 in the context of other double neutron star
systems. PSR J1518+4904 has been regularly observed for more than 10 years by
the European Pulsar Timing Array (EPTA) network using the Westerbork, Jodrell
Bank, Effelsberg and Nancay radio telescopes. The data were analysed using the
updated timing software Tempo2. We have improved the timing solution for this
double neutron star system. The periastron advance has been refined and a
significant detection of proper motion is presented. It is not likely that more
post-Keplerian parameters, with which the individual neutron star masses and
the inclination angle of the system can be determined separately, can be
measured in the near future. Using a combination of the high-quality data sets
present in the EPTA collaboration, extended with the original GBT data, we have
constrained the masses in the system to m_p1.55 msun (95.4%
confidence), and the inclination angle of the orbit to be less than 47 degrees
(99%). From this we derive that the pulsar in this system possibly has one of
the lowest neutron star masses measured to date. From evolutionary
considerations it seems likely that the companion star, despite its high mass,
was formed in an electron-capture supernova.Comment: 11 pages, 8 figures, accepted by A&
Carbogen-induced changes in rat mammary tumour oxygenation reported by near infrared spectroscopy
We have evaluated the ability of steady-state, radially-resolved, broad-band near infrared diffuse reflectance spectroscopy to measure carbogen-induced changes in haemoglobin oxygen saturation (SO2) and total haemoglobin concentration in a rat R3230 mammary adenocarcinoma model in vivo. Detectable shifts toward higher saturations were evident in all tumours (n = 16) immediately after the onset of carbogen breathing. The SO2 reached a new equilibrium within 1 min and remained approximately constant during 200–300 s of administration. The return to baseline saturation was more gradual when carbogen delivery was stopped. The degree to which carbogen increased SO2 was variable among tumours, with a tendency for tumours with lower initial SO2 to exhibit larger changes. Tumour haemoglobin concentrations at the time of peak enhancement were also variable. In the majority of cases, haemoglobin concentration decreased in response to carbogen, indicating that increased tumour blood volume was not responsible for the observed elevation in SO2. We observed no apparent relationship between the extent of the change in tumour haemoglobin concentration and the magnitude of the change in the saturation. Near infrared diffuse reflectance spectroscopy provides a rapid, non-invasive means of monitoring spatially averaged changes in tumour haemoglobin oxygen saturation induced by oxygen modifiers. © 1999 Cancer Research Campaig
The location of silver in frog epidermis after treatment by ranvier's method, and possible implication of the flask cells in transport
Stent Design, Restenosis and Recurrent Stroke After Carotid Artery Stenting in the International Carotid Stenting Study
Hyperbaric oxygen enhances the effects of meta-iodobenzylguanidine (MIBG) on energy metabolism and lipid peroxidation in the human neuroblastoma cell line SK-N-BE(2C)
In this paper we report the effects of the combination of MIBG (a structural analogue of norepinephrine, used in its radio iodinated form for the diagnosis and therapy of neuroblastoma) and hyperbaric oxygen on the human neuroblastoma cell line SK-N-BE(2c). Exposure of the neuroblastoma cells to hyperbaric oxygen conditions enhanced the effects of MIBG on cell proliferation, lipid peroxidation and energy metabolism of the cell line. Cell proliferation and energy metabolism were further decreased and lipid peroxidation further increased. Enhancement of the effects of MIBG by HBO may provide an explanation for the positive effects on the cumulative survival curve observed when stage IV neuroblastoma patients were treated with the combination of [131I] MIBG and HB
PuMa, a digital pulsar machine
We have designed and constructed PuMa, a pulsar machine that has both
a baseband recording and a digital filterbank mode. Its design is
based on the use of digital signal processors (DSPs). Their operation
is controlled by software, which makes PuMa reconfigurable, flexible
and easy to operate. The maximum number of channels in the digital
filterbank mode is 32 768 over a bandwidth of 80 MHz. This makes PuMa
suitable for pulsar observations at low sky frequencies. The maximum
bandwidth in baseband recording mode is two times 10 MHz. The machine
was installed at the Westerbork Synthesis Radio Telescope in The
Netherlands in 1998. We discuss in some detail PuMa's technical
properties and capabilities. Recent observations, a sample of which
are presented here, demonstrate its capabilities and that it
is performing up to its
specifications