508 research outputs found
Bounds on Relic Neutrino Masses in the Z-burst Model
Neutrinos from far-away sources annihilating at the Z resonance on relic
neutrinos may give origin to the extreme-energy cosmic rays (EECR). If
``Z-bursts'' are responsible for the EECR events, then we show that the
non-observation of cosmic ray events at energies above 2 x 10^20 eV by the
AGASA Collaboration implies a lower bound around 0.3 eV on the relic neutrino
mass. Since this mass exceeds the mass-squared differences inferred from
oscillation physics, the bound in fact applies to all three neutrino masses.
Together with the upper bound provided by comparisons of the CMB anisotropy
with large-scale structure, this bound leaves only a small interval for
neutrino masses around 0.3 eV, if Z-bursts are to explain the existing EECR
events.Comment: 19 pages, including 4 figure
Evaluating on-line health information for patients with polymyalgia rheumatica: a descriptive study
BACKGROUND: The Internet is increasingly used to access health information, although the quality of information varies. The aim of this study was to evaluate the readability, and quality of websites about polymyalgia rheumatica (PMR). METHODS: Three UK search engines (Google, Yahoo and Bing) were searched for the term 'polymyalgia rheumatica'. After deleting duplicates, the first 50 eligible websites from each were evaluated. Readability was assessed using the Flesch Reading Ease and 'Simple Measure of Gobbledygook (SMOG) Readability' indicators. Credibility was assessed using a previously published Credibility Indicator. RESULTS: Of the 52 unique websites identified, the mean (standard deviation) Flesch Reading Ease and SMOG Readability scores were 48 (15) and 10 (2), respectively. The mean (SD) Credibility Indicator was 2 (1). Fifty (96%) of websites were accurate. Website design and content was good, with an average of 68 and 64% respectively, of the assessed criteria being met. CONCLUSIONS: Most websites about PMR require a higher readability age than is recommended. Thus whilst websites are often well designed and accurate this study suggests that their content could be refined and simplified to maximise patient benefit
Electromagnetic Cascades and Cascade Nucleosynthesis in the Early Universe
We describe a calculation of electromagnetic cascading in radiation and
matter in the early universe initiated by the decay of massive particles or by
some other process. We have used a combination of Monte Carlo and numerical
techniques which enables us to use exact cross sections, where known, for all
the relevant processes. In cascades initiated after the epoch of big bang
nucleosynthesis -rays in the cascades will photodisintegrate He,
producing He and deuterium. Using the observed He and deuterium
abundances we are able to place constraints on the cascade energy deposition as
a function of cosmic time. In the case of the decay of massive primordial
particles, we place limits on the density of massive primordial particles as a
function of their mean decay time, and on the expected intensity of decay
neutrinos.Comment: compressed and uuencoded postscript. We now include a comparison with
previous work of the photon spectrum in the cascade and the limits we
calculate for the density of massive particles. The method of calculation of
photon spectra at low energies has been improved. Most figures are revised.
Our conclusions are substantially unchange
Kiloparsec-Scale Jets in FR I Radio Galaxies and the Gamma-Ray Background
We discuss the contribution of kiloparsec-scale jets in FR I radio galaxies
to the diffuse gamma-ray background radiation. The analyzed gamma-ray emission
comes from inverse-Compton scattering of starlight photon fields by the
ultrarelativistic electrons whose synchrotron radiation is detected from such
sources at radio, optical and X-ray energies. We find that these objects, under
the minimum-power hypothesis (corresponding to a magnetic field of 300 muG in
the brightest knots of these jets), can contribute about one percent to the
extragalactic gamma-ray background measured by EGRET. We point out that this
result already indicates that the magnetic fields in kpc-scale jets of
low-power radio galaxies are not likely to be smaller than 10 muG on average,
as otherwise the extragalactic gamma-ray background would be overproduced.Comment: 18 pages, 3 figures included. ApJ accepte
Propagation of ultra-high energy protons in the nearby universe
We present a new calculation of the propagation of protons with energies
above eV over distances of up to several hundred Mpc. The calculation
is based on a Monte Carlo approach using the event generator
SOPHIA for the simulation of hadronic nucleon-photon interactions and a
realistic integration of the particle trajectories in a random extragalactic
magnetic field. Accounting for the proton scattering in the magnetic field
affects noticeably the nucleon energy as a function of the distance to their
source and allows us to give realistic predictions on arrival energy, time
delay, and arrival angle distributions and correlations as well as secondary
particle production spectra.Comment: 12 pages, 9 figures, ReVTeX. Physical Review D, accepte
Limits on models of the ultrahigh energy cosmic rays based on topological defects
An erratum exists for this article. Please see the description link below for details.Using the propagation of ultrahigh energy nucleons, photons, and electrons in the universal radiation backgrounds, we obtain limits on the luminosity of topological defect scenarios for the origin of the highest energy cosmic rays. The limits are set as a function of the mass of the X particles emitted by the cosmic strings or other defects, the cosmological evolution of the topological defects, and the strength of the extragalactic magnetic fields. The existing data on the cosmic ray spectrum and on the isotropic 100 MeV gamma-ray background limit significantly the parameter space in which topological defects can generate the flux of the highest energy cosmic rays, and rule out models with the standard X-particle mass of 10¹⁶GeV and higher.R. J. Protheroe and Todor Stane
The Lick Planet Search: Detectability and Mass Thresholds
We analyse 11 years of precise radial velocities for 76 solar type stars from
the Lick survey. Eight stars in this sample have previously reported
planetary-mass companions, all with mass (m sin i) less than 8 Jupiter masses
(MJ). For the stars without a detected companion, we place upper limits on
possible companion mass. For most stars, we can exclude companions with m sin i
> 0.7 MJ (a/AU)^1/2 for orbital radii a < 5 AU.
We use our results to interpret the observed masses and orbital radii of
planetary-mass companions. For example, we show that the finite duration of the
observations makes detection of Jupiter mass companions more and more difficult
for orbital radii beyond 3 AU. Thus it is possible that the majority of solar
type stars harbor Jupiter-mass companions much like our own, and if so these
companions should be detectable in a few years.
To search for periodicities, we adopt a "floating-mean" periodogram, which
improves on the traditional Lomb-Scargle periodogram by accounting for
statistical fluctuations in the mean of a sampled sinusoid. We discuss in
detail the normalization of the periodogram, an issue which has been of some
debate in the literature.Comment: To appear in the Astrophysical Journal (50 pages, LaTeX, including 11
figures
Extremely High Energy Neutrinos, Neutrino Hot Dark Matter, and the Highest Energy Cosmic Rays
Extremely high energy (up to 10**(22) eV) cosmic neutrino beams initiate high
energy particle cascades in the background of relic neutrinos from the Big
Bang. We perform numerical calculations to show that such cascades could
contribute more than 10% to the observed cosmic ray flux above 10**(19) eV if
neutrinos have masses in the electron volt range. The required intensity of
primary neutrinos could be consistent with astrophysical models for their
production if the maximum neutrino energy reaches to 10**(22) eV and the
massive neutrino dark matter is locally clustered. Future observations of ultra
high energy cosmic rays will lead to an indirect but practical search for
neutrino dark matter.Comment: 4 latex pages, 3 postscript figures included, uses revtex.sty and
psfig.sty. Submitted to Physical Review Letter
What e-patients want from the doctor-patient relationship: content analysis of posts on discussion boards.
People with long-term conditions are encouraged to take control and ownership of managing their condition. Interactions between health care staff and patients become partnerships with sharing of expertise. This has changed the doctor-patient relationship and the division of roles and responsibilities that traditionally existed, but what each party expects from the other may not always be clear. Information that people with long-term conditions share on Internet discussion boards can provide useful insights into their expectations of health care staff. This paper reports on a small study about the expectations that people with a long-term condition (diabetes) have of their doctors using information gleaned from Internet discussion boards
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