119 research outputs found
Big Bang Nucleosynthesis Constraints on Primordial Magnetic Fields
We reanalyze the effect of magnetic fields in BBN, incorporating several
features which were omitted in previous analyses. We find that the effects of
coherent magnetic fields on the weak interaction rates and the electron
thermodynamic functions (\rhoe, \Pe, and \drhoedt ) are unimportant in
comparison to the contribution of the magnetic field energy density in BBN. In
consequence the effect of including magnetic fields in BBN is well approximated
numerically by treating the additional energy density as effective neutrino
number. A conservative upper bound on the primordial magnetic field,
parameterized as , is (). This bound can be stronger than the conventional bound coming from
the Faraday rotation measures of distant quasars if the cosmological magnetic
field is generated by a causal mechanism.Comment: Latex, 20 pages, 3 uuencoded figures appende
Multiple solutions and corresponding power output of a nonlinear bistable piezoelectric energy harvester
We examine multiple responses of a vibrational energy harvester composed of a vertical
beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while
mechanical vibrational energy is converted to electrical power through a piezoelectric
patch. The mechanical resonator can be described by single or double well potentials
depending on the gravity force from the tip mass. By changing the tip mass we examine the
appearance of various solutions and their basins of attraction. Identification of
particular solutions of the energy harvester is important as each solution may provide a
different level of power output
Testing The Friedmann Equation: The Expansion of the Universe During Big-Bang Nucleosynthesis
In conventional general relativity, the expansion rate H of a
Robertson-Walker universe is related to the energy density by the Friedmann
equation. Aside from the present day, the only epoch at which we can constrain
the expansion history in a model-independent way is during Big-Bang
Nucleosynthesis (BBN). We consider a simple two-parameter characterization of
the behavior of H during BBN and derive constraints on this parameter space,
finding that the allowed region of parameter space is essentially
one-dimensional. We also study the effects of a large neutrino asymmetry within
this framework. Our results provide a simple way to compare an alternative
cosmology to the observational requirement of matching the primordial
abundances of the light elements.Comment: 18 pages, Final version to be published in Phys. Rev.
Oesophageal cancer among the Turkomans of northeast Iran
A Caspian Littoral Cancer Registry survey in the early 1970s established northern Iran as one of the highest oesophageal cancer incidence regions of the world. To verify this, an oesophageal cancer survey was carried out between 1995 and 1997 in the Turkoman Plain at the southeastern corner of the Caspian Sea. Oesophageal balloon cytology screening was carried out on 4192 asymptomatic adults above age 30 years in one town and three adjoining villages with a total population of 20 392 people at risk. Oesophagoscopy was performed on 183 patients with abnormal cytological findings. The discovery of two asymptomatic small squamous cell cancers and one ‘carcinoma- suspect’ implied a prevalence ranging from 47.7 per 100 000 to 71.5 per 100 000. During a 1-year active surveillance, 14 patients were found with clinically advanced oesophageal squamous cell cancer, yielding age-standardized incidence rates of 144.09 per 100 000 for men and 48.82 per 100 000 for women. The very high frequency of oesophageal cancer reported for northern Iran 25 years ago stands confirmed. Differences in incidence rates, then and now, can be attributed to survey methods used and diagnostic criteria applied, but not to socioeconomic factors, which have remained relatively stable. Oesophageal balloon cytology is a practical method of mass screening for oesophageal cancer in Iran. © 2000 Cancer Research Campaig
Solar Neutrino Constraints on the BBN Production of Li
Using the recent WMAP determination of the baryon-to-photon ratio, 10^{10}
\eta = 6.14 to within a few percent, big bang nucleosynthesis (BBN)
calculations can make relatively accurate predictions of the abundances of the
light element isotopes which can be tested against observational abundance
determinations. At this value of \eta, the Li7 abundance is predicted to be
significantly higher than that observed in low metallicity halo dwarf stars.
Among the possible resolutions to this discrepancy are 1) Li7 depletion in the
atmosphere of stars; 2) systematic errors originating from the choice of
stellar parameters - most notably the surface temperature; and 3) systematic
errors in the nuclear cross sections used in the nucleosynthesis calculations.
Here, we explore the last possibility, and focus on possible systematic errors
in the He3(\alpha,\gamma)Be7 reaction, which is the only important Li7
production channel in BBN. The absolute value of the cross section for this key
reaction is known relatively poorly both experimentally and theoretically. The
agreement between the standard solar model and solar neutrino data thus
provides additional constraints on variations in the cross section (S_{34}).
Using the standard solar model of Bahcall, and recent solar neutrino data, we
can exclude systematic S_{34} variations of the magnitude needed to resolve the
BBN Li7 problem at > 95% CL. Additional laboratory data on
He3(\alpha,\gamma)Be7 will sharpen our understanding of both BBN and solar
neutrinos, particularly if care is taken in determining the absolute cross
section and its uncertainties. Nevertheless, it already seems that this
``nuclear fix'' to the Li7 BBN problem is unlikely; other possible solutions
are briefly discussed.Comment: 21 pages, 3 ps figure
Quantifying uncertainties in primordial nucleosynthesis without Monte Carlo simulations
We present a simple method for determining the (correlated) uncertainties of
the light element abundances expected from big bang nucleosynthesis, which
avoids the need for lengthy Monte Carlo simulations. Our approach helps to
clarify the role of the different nuclear reactions contributing to a
particular elemental abundance and makes it easy to implement
energy-independent changes in the measured reaction rates. As an application,
we demonstrate how this method simplifies the statistical estimation of the
nucleon-to-photon ratio through comparison of the standard BBN predictions with
the observationally inferred abundances.Comment: 22 pages (RevTeX) incl. 8 figures (epsf); Changes: Figs. 5 & 6
combined + typo in Footnote 1 corrected + several stylistic changes; to
appear in Phys. Rev.
Constraining Strong Baryon-Dark Matter Interactions with Primordial Nucleosynthesis and Cosmic Rays
Self-interacting dark matter (SIDM) was introduced by Spergel & Steinhardt to
address possible discrepancies between collisionless dark matter simulations
and observations on scales of less than 1 Mpc. We examine the case in which
dark matter particles not only have strong self-interactions but also have
strong interactions with baryons. The presence of such interactions will have
direct implications for nuclear and particle astrophysics. Among these are a
change in the predicted abundances from big bang nucleosynthesis (BBN) and the
flux of gamma-rays produced by the decay of neutral pions which originate in
collisions between dark matter and Galactic cosmic rays (CR). From these
effects we constrain the strength of the baryon--dark matter interactions
through the ratio of baryon - dark matter interaction cross section to dark
matter mass, . We find that BBN places a weak upper limit to this ratio . CR-SIDM interactions, however, limit the possible DM-baryon cross
section to ; this rules out an energy-independent
interaction, but not one which falls with center-of-mass velocity as or steeper.Comment: 17 pages, 2 figures; plain LaTeX. To appear in PR
Regular and chaotic vibration in a piezoelectric energy harvester
We examine regular and chaotic responses of a vibrational energy harvester composed of a vertical beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric patch. The mechanical resonator can be described by single or double well potentials depending on the gravity force from the tip mass. By changing the tip mass we examine bifurcations from single well oscillations, to regular and chaotic vibrations between the potential wells. The appearance of chaotic responses in the energy harvesting system is illustrated by the bifurcation diagram, the corresponding Fourier spectra, the phase portraits, and is confirmed by the 0–1 test. The appearance of chaotic vibrations reduces the level of harvested energy
Targeting Primitive Chronic Myeloid Leukemia Cells by Effective Inhibition of a New AHI-1BCR-ABL-JAK2 Complex
This is a pre-copyedited, author-produced version of an article accepted for publication in JNCI: Journal of the National Cancer Institute following peer review. The version of record Chen, M., et al. (2013). "Targeting Primitive Chronic Myeloid Leukemia Cells by Effective Inhibition of a New AHI-1–BCR-ABL–JAK2 Complex." JNCI: Journal of the National Cancer Institute 105(6): 405-423. is available online at: https://doi.org/10.1093/jnci/djt006This work was funded by the Canadian Cancer Society (grant 700289), in part by the Canadian Institutes of Health Research, the Leukemia & Lymphoma Society of Canada, and the Cancer Research Society (XJ), the Canadian Cancer Society Research Institute (AE, XJ, CE), Cancer Research UK Programme grant C11074/A11008 (TLH), the Glasgow Experimental Cancer Medicine Centre, which is funded by Cancer Research UK and by the Chief Scientist’s Office (Scotland), and Cancer Research UK grant C973/A9894 (JP, JS). M. Chen was supported by a fellowship from Lymphoma Foundation Canada, and P. Gallipoli was supported by Medical Research Council grant G1000288. X. Jiang was a Michael Smith Foundation for Health Research Scholar
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