703 research outputs found
Relationships between cell population kinetics and radiation resistance in pocket mice /Heteromyidae - Perognathus/
Relationships between cell population kinetics and radiation resistance in pocket mic
The Evaluation of V_{ud}, Experiment and Theory
The value of the V_{ud} matrix element of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix can be derived from nuclear superallowed beta decays, neutron decay, and
pion beta decay. We survey current world data for all three. Today, the most
precise value of V_{ud} comes from the nuclear decays; however, the precision
is limited not by experimental error but by the estimated uncertainty in
theoretical corrections. Experimental uncertainty does limit the neutron-decay
result, which, though statistically consistent with the nuclear result, is
approximately a factor of three poorer in precision. The value obtained for
leads to a result that differs at the 98% confidence level from the
unitarity condition for the CKM matrix. We examine the reliability of the small
calculated corrections that have been applied to the data, and assess the
likelihood of even higher quality nuclear data becoming available to confirm or
deny the discrepancy. Some of the required experiments depend upon the
availability of intense radioactive beams. Others are possible today.Comment: 21 pages, 1 figure, LaTe
High temperature /800 to 1600 F/ magnetic materials
Tests of magnetic materials from 800 to 1600
Calculated corrections to superallowed Fermi beta decay: New evaluation of the nuclear-structure-dependent terms
The measured -values for superallowed nuclear
-decay can be used to obtain the value of the vector coupling constant
and thus to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. An
essential requirement for this test is accurate calculations for the radiative
and isospin symmetry-breaking corrections that must be applied to the
experimental data. We present a new and consistent set of calculations for the
nuclear-structure-dependent components of these corrections. These new results
do not alter the current status of the unitarity test -- it still fails by more
than two standard deviations -- but they provide calculated corrections for
eleven new superallowed transitions that are likely to become accessible to
precise measurements in the future. The reliability of all calculated
corrections is explored and an experimental method indicated by which the
structure-dependent corrections can be tested and, if necessary, improved.Comment: Revtex4, one figur
Isospin-mixing corrections for fp-shell Fermi transitions
Isospin-mixing corrections for superallowed Fermi transitions in {\it
fp}-shell nuclei are computed within the framework of the shell model. The
study includes three nuclei that are part of the set of nine accurately
measured transitions as well as five cases that are expected to be measured in
the future at radioactive-beam facilities. We also include some new
calculations for C. With the isospin-mixing corrections applied to the
nine accurately measured values, the conserved-vector-current hypothesis
and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are
tested.Comment: 13 pages plus five tables. revtex macro
Superallowed 0+ to 0+ nuclear beta decays: A new survey with precision tests of the conserved vector current hypothesis and the standard model
A new critical survey is presented of all half-life, decay-energy and
branching-ratio measurements related to 20 0+ to 0+ beta decays. Compared with
our last review, there are numerous improvements: First, we have added 27
recently published measurements and eliminated 9 references; of particular
importance, the new data include a number of high-precision Penning-trap
measurements of decay energies. Second, we have used the recently improved
isospin symmetry-breaking corrections. Third, our calculation of the
statistical rate function now accounts for possible excitation in the daughter
atom. Finally, we have re-examined the systematic uncertainty associated with
the isospin symmetry-breaking corrections by evaluating the radial-overlap
correction using Hartree-Fock radial wave functions and comparing the results
with our earlier calculations, which used Saxon-Woods wave functions; the
provision for systematic uncertainty has been changed as a consequence. The new
corrected Ft values are impressively constant and their average, when combined
with the muon liftime, yields the up-down quark-mixing element of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix, V_{ud} = 0.97425(22). The unitarity
test on the top row of the matrix becomes |V_{ud}|^2 + |V_{us}|^2 + |V_{ub}|^2
= 0.99995(61). Both V_{ud} and the unitarity sum have significantly reduced
uncertainties compared with our previous survey, although the new value of
V_{ud} is statistically consistent with the old one. From these data we also
set limits on the possible existence of scalar interactions, right-hand
currents and extra Z bosons. Finally, we discuss the priorities for future
theoretical and experimental work with the goal of making the CKM unitarity
test even more definitive.Comment: 36 pages, 11 tables, 9 figure
Inclusive neutrino scattering off deuteron from threshold to GeV energies
Background: Neutrino-nucleus quasi-elastic scattering is crucial to interpret
the neutrino oscillation results in long baseline neutrino experiments. There
are rather large uncertainties in the cross section, due to insufficient
knowledge on the role of two-body weak currents. Purpose: Determine the role of
two-body weak currents in neutrino-deuteron quasi-elastic scattering up to GeV
energies. Methods: Calculate cross sections for inclusive neutrino scattering
off deuteron induced by neutral and charge-changing weak currents, from
threshold up to GeV energies, using the Argonne potential and
consistent nuclear electroweak currents with one- and two-body terms. Results:
Two-body contributions are found to be small, and increase the cross sections
obtained with one-body currents by less than 10% over the whole range of
energies. Total cross sections obtained by describing the final two-nucleon
states with plane waves differ negligibly, for neutrino energies
MeV, from those in which interaction effects in these states are fully
accounted for. The sensitivity of the calculated cross sections to different
models for the two-nucleon potential and/or two-body terms in the weak current
is found to be weak. Comparing cross sections to those obtained in a naive
model in which the deuteron is taken to consist of a free proton and neutron at
rest, nuclear structure effects are illustrated to be non-negligible.
Conclusion: Contributions of two-body currents in neutrino-deuteron
quasi-elastic scattering up to GeV are found to be smaller than 10%. Finally,
it should be stressed that the results reported in this work do not include
pion production channels.Comment: 30 pages, 17 figures; publishe
Effective Interactions for the Three-Body Problem
The three-body energy-dependent effective interaction given by the
Bloch-Horowitz (BH) equation is evaluated for various shell-model oscillator
spaces. The results are applied to the test case of the three-body problem
(triton and He3), where it is shown that the interaction reproduces the exact
binding energy, regardless of the parameterization (number of oscillator quanta
or value of the oscillator parameter b) of the low-energy included space. We
demonstrate a non-perturbative technique for summing the excluded-space
three-body ladder diagrams, but also show that accurate results can be obtained
perturbatively by iterating the two-body ladders. We examine the evolution of
the effective two-body and induced three-body terms as b and the size of the
included space Lambda are varied, including the case of a single included
shell, Lambda hw=0 hw. For typical ranges of b, the induced effective
three-body interaction, essential for giving the exact three-body binding, is
found to contribute ~10% to the binding energy.Comment: 19 pages, 9 figures, submitted to PR
Large-basis shell-model calculation of 10C->10B Fermi matrix element
We use a shell-model calculation with a two-body effective
interaction derived microscopically from the Reid93 potential to calculate the
isospin-mixing correction for the 10C->10B superallowed Fermi transition. The
effective interaction takes into account the Coulomb potential as well as the
charge dependence of T=1 partial waves. Our results suggest the isospin- mixing
correction , which is compatible with previous
calculations. The correction obtained in those calculations, performed in a
space, was dominated by deviation from unity of the radial
overlap between the converted proton and the corresponding neutron. In the
present calculation this effect is accommodated by the large model space. The
obtained correction is about a factor of four too small to obtain
unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental
data.Comment: 14 pages. REVTEX. 3 PostScript figure
Increased false positive Down syndrome screening in women with sickle cell anemia
ObjectivesThis study seeks to determine whether there is a higher rate of false positive serum screening for Down syndrome in women with sickle cell anemia and, if so, which markers contribute to the false positive screen.MethodsThis is a retrospective cohort study of women who had serum screening between 1998 and 2011. Subjects were women with sickle cell anemia (n = 13), and controls were African American women who did not have that disease (n = 91). The populations were compared using basic inferential statistics.ResultsThe positive screen rate was 38.5% (5/13) in women with sickle cell anemia and 7.7% (7/91) in the control population (odds ratio 7.5, 95% confidence interval 1.6–35.8, P = 0.001). At the average age of the cases (25 years), the expected false positive rate is only 2%. The human chorionic gonadotrophin values were significantly higher in cases than controls (2.00 and 1.30 MoM, P = 0.017), whereas levels of other serum analytes were similar. None of the screen positive results were associated with a fetus or neonate affected by Down syndrome.ConclusionsThe false positive Down syndrome serum screen rate is significantly higher in patients with sickle cell anemia than in African American women without that disease. The human chorionic gonadotrophin values were significantly higher in cases than controls, suggesting that placental factors may contribute to the elevated false positive rate. © 2015 John Wiley & Sons, Ltd.What's already known about this topic? There are no previously published studies on the effect of sickle cell anemia on accuracy of maternal serum genetic screening.What does this study add? Maternal serum second‐trimester genetic screening has a high false positive rate in women with sickle cell anemia.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112238/1/pd4610.pd
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