46 research outputs found
Recommended from our members
Publisher Correction: Wave energy budget analysis in the Earths radiation belts uncovers a missing energy.
This corrects the article DOI: 10.1038/ncomms8143
Generalized atomic mass law
Least-squares analyses have been performed on a set of atomic masses using standard and generalized semiempirical mass laws. Presumably because of errors in the assumed form of the standard mass law, its least-squares coefficients can be determined at best to an accuracy of about 10%, and masses are predicted with an uncertainty of several Mev/c^2. The standard mass law has been generalized by addition of shell effect and deformation terms. While the least-squares fitting of the generalized mass law is better than for the standard mass law, it is still not possible to predict atomic masses to an accuracy better than a few Mev/c^2. The nuclear deformations and the well depth of the nuclear interaction obtained from the additional mass-law terms are in reasonable agreement with more accurate determinations by other methods. A similar statement applies to the nuclear radius constant as obtained from the least-squares coefficient of the Coulomb energy term. A study has also been made of the effects of additional terms propertional to the absolute value of the isotopic spin, exchange and surface corrections to the Coulomb energy, and the surface correction to the normal isotopic term
Particle-In-Cell Simulations of Sunward and Anti-sunward Whistler Waves in the Solar Wind
Spacecraft observations showed that electron heat conduction in the solar
wind is probably regulated by whistler waves, whose origin and efficiency in
electron heat flux suppression is actively investigated. In this paper, we
present Particle-In-Cell simulations of a combined whistler heat flux and
temperature anisotropy instability that can operate in the solar wind. The
simulations are performed in a uniform plasma and initialized with core and
halo electron populations typical of the solar wind. We demonstrate that the
instability produces whistler waves propagating both along (anti-sunward) and
opposite (sunward) to the electron heat flux. The saturated amplitudes of both
sunward and anti-sunward whistler waves are strongly correlated with their {\it
initial} linear growth rates, , where
for typical electron betas we have . The
correlations of whistler wave amplitudes and spectral widths with plasma
parameters (electron beta and temperature anisotropy) revealed in the
simulations are consistent with those observed in the solar wind. The
efficiency of electron heat flux suppression is positively correlated with the
saturated amplitude of sunward whistler waves. The electron heat flux can be
suppressed by 10--60% provided that the saturated amplitude of sunward whistler
waves exceeds about 1% of background magnetic field. Other experimental
applications of the presented results are discussed
Observations of a Newly "Captured" Magnetosheath Field Line: Evidence for "Double Reconnection"
We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. This region has been routinely sampled for about three months each year for the periods 1999-2001 and 2004-2006. The low-to-mid-energy ion instruments frequently observed dense, magnetosheath-like plasma deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a period of northward interplanetary magnetic field (IMF), shows magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. These results are consistent with the hypothesis that double merging can produce closed field .lines populated by solar wind plasma. Through the use of individual cases such as this and statistical studies of a broader database we seek to understand the morphology of the LLBL as it projects from the sub-solar region into the cusp. We will present preliminary results of our ongoing study
Precise measurement of the W-boson mass with the CDF II detector
We have measured the W-boson mass MW using data corresponding to 2.2/fb of
integrated luminosity collected in proton-antiproton collisions at 1.96 TeV
with the CDF II detector at the Fermilab Tevatron collider. Samples consisting
of 470126 W->enu candidates and 624708 W->munu candidates yield the measurement
MW = 80387 +- 12 (stat) +- 15 (syst) = 80387 +- 19 MeV. This is the most
precise measurement of the W-boson mass to date and significantly exceeds the
precision of all previous measurements combined