2,353 research outputs found
A Micro-glitch in the Millisecond Pulsar B1821-24 in M28
We report on the observation of a very small glitch observed for the first
time in a millisecond pulsar, PSR B1821-24 located in the globular cluster M28.
Timing observations were mainly conducted with the Nancay radiotelescope
(France) and confirmation comes from the 140ft radiotelescope at Green Bank and
the new Green Bank Telescope data. This event is characterized by a rotation
frequency step of 3 nHz, or 10^-11 in fractional frequency change along with a
short duration limited to a few days or a week. A marginally significant
frequency derivative step was also found. This glitch follows the main
characteristics of those in the slow period pulsars, but is two orders of
magnitude smaller than the smallest ever recorded. Such an event must be very
rare for millisecond pulsars since no other glitches have been detected when
the cumulated number of years of millisecond pulsar timing observations up to
2001 is around 500 for all these objects. However, pulsar PSR B1821-24 is one
of the youngest among the old recycled ones and there is likely a correlation
between age, or a related parameter, and timing noise. While this event happens
on a much smaller scale, the required adjustment of the star to a new
equilibrium figure as it spins down is a likely common cause for all glitches.Comment: Accepted by ApJ Letters, 5 pages, 2 figures, LaTex (uses
emulateapj.sty
The level of specialist assessment of adult asthma is influenced by patient age
SummaryBackgroundLate onset asthma is associated with more severe disease and higher morbidity than in younger asthma patients. This may in part relate to under recognition of asthma in older adults, but evidence on the impact of patient age on diagnostic assessment of asthma in a specialist setting is sparse.AimTo examine the impact of patient age on the type and proportion of diagnostic tests performed in patients undergoing specialist assessment for asthma.MethodsData from a clinical population consisting of all patients consecutively referred over a 12 months period to a specialist clinic for assessment of asthma were analysed.ResultsA total of 224 patients with asthma or suspected asthma were referred during the 12 month period; 86 adults aged <35 years, 95 aged 35–55 years and 43 aged >55 years. Symptom characteristics were similar, but adults >35 years had a lower lung function than younger adults, and were more frequently smokers. However, a regression analysis showed that older age was associated with a lower likelihood of diagnostic assessment with a reversibility test, a bronchial challenge test, or measurement of exhaled NO, independently of a known diagnosis of asthma, smoking habits and lung function at referral.ConclusionA lower level of diagnostic assessment was observed already after the age of 35 years, indicating a risk for under diagnosis of asthma at an earlier patient age than previously thought
γ-H2AX foci as in vivo effect biomarker in children emphasize the importance to minimize x-ray doses in paediatric CT imaging
Objectives: Investigation of DNA damage induced by CT x-rays in paediatric patients versus patient dose in a multicentre setting.
Methods: From 51 paediatric patients (median age, 3.8 years) who underwent an abdomen or chest CT examination in one of the five participating radiology departments, blood samples were taken before and shortly after the examination. DNA damage was estimated by scoring gamma-H2AX foci in peripheral blood T lymphocytes. Patient-specific organ and tissue doses were calculated with a validated Monte Carlo program. Individual lifetime attributable risks (LAR) for cancer incidence and mortality were estimated according to the BEIR VII risk models.
Results: Despite the low CT doses, a median increase of 0.13 gamma-H2AX foci/cell was observed. Plotting the induced gamma-H2AX foci versus blood dose indicated a low-dose hypersensitivity, supported also by an in vitro dose-response study. Differences in dose levels between radiology centres were reflected in differences in DNA damage. LAR of cancer mortality for the paediatric chest CT and abdomen CT cohort was 0.08 and 0.13% respectively.
Conclusion: CT x-rays induce DNA damage in paediatric patients even at low doses and the level of DNA damage is reduced by application of more effective CT dose reduction techniques and paediatric protocols
New Pulsars from an Arecibo Drift Scan Search
We report the discovery of pulsars J0030+0451, J0711+0931, and J1313+0931
that were found in a search of 470 square degrees at 430 MHz using the 305m
Arecibo telescope. The search has an estimated sensitivity for long period, low
dispersion measure, low zenith angle, and high Galactic latitude pulsars of ~1
mJy, comparable to previous Arecibo searches. Spin and astrometric parameters
for the three pulsars are presented along with polarimetry at 430 MHz. PSR
J0030+0451, a nearby pulsar with a period of 4.8 ms, belongs to the less common
category of isolated millisecond pulsars. We have measured significant
polarization in PSR J0030+0451 over more than 50% of the period, and use these
data for a detailed discussion of its magnetospheric geometry. Scintillation
observations of PSR J0030+0451 provide an estimate of the plasma turbulence
level along the line of sight through the local interstellar medium.Comment: 21 pages, 4 figures, Accepted for Publication in Ap
Size of the Vela Pulsar's Emission Region at 13 cm Wavelength
We present measurements of the size of the Vela pulsar in 3 gates across the
pulse, from observations of the distribution of intensity. We calculate the
effects on this distribution of noise in the observing system, and measure and
remove it using observations of a strong continuum source. We also calculate
and remove the expected effects of averaging in time and frequency. We find
that effects of variations in pulsar flux density and instrumental gain,
self-noise, and one-bit digitization are undetectably small. Effects of
normalization of the correlation are detectable, but do not affect the fitted
size. The size of the pulsar declines from 440 +/- 90 km (FWHM of best-fitting
Gaussian distribution) to less than 200 km across the pulse. We discuss
implications of this size for theories of pulsar emission.Comment: 51 pages, 10 figures. To appear in ApJ. Also available at
http://www.physics.ucsb.edu/~cgwinn/pulsar/size_14.p
Detection of Signals from Cosmic Reionization using Radio Interferometric Signal Processing
Observations of the HI 21cm transition line promises to be an important probe
into the cosmic dark ages and epoch of reionization. One of the challenges for
the detection of this signal is the accuracy of the foreground source removal.
This paper investigates the extragalactic point source contamination and how
accurately the bright sources ( ~Jy) should be removed in order to
reach the desired RMS noise and be able to detect the 21cm transition line.
Here, we consider position and flux errors in the global sky-model for these
bright sources as well as the frequency independent residual calibration
errors. The synthesized beam is the only frequency dependent term included
here. This work determines the level of accuracy for the calibration and source
removal schemes and puts forward constraints for the design of the cosmic
reionization data reduction scheme for the upcoming low frequency arrays like
MWA,PAPER, etc. We show that in order to detect the reionization signal the
bright sources need to be removed from the data-sets with a positional accuracy
of arc-second. Our results also demonstrate that the efficient
foreground source removal strategies can only tolerate a frequency independent
antenna based mean residual calibration error of in amplitude
or degree in phase, if they are constant over each days of
observations (6 hours). In future papers we will extend this analysis to the
power spectral domain and also include the frequency dependent calibration
errors and direction dependent errors (ionosphere, primary beam, etc).Comment: accepted by ApJ; 12 pages, 10 figure
- …