545 research outputs found
STUDIES IN THE METABOLISM OF CRASSULACEAN PLANTS: THE EFFECT OF TEMPERATURE UPON THE CULTURE OF EXCISED LEAVES OF BRYOPHYLLUM CALYCINUM
Evidence for a change in the nuclear mass surface with the discovery of the most neutron-rich nuclei with 17<Z <25
The results of measurements of the production of neutron-rich nuclei by the
fragmentation of a 76-Ge beam are presented. The cross sections were measured
for a large range of nuclei including fifteen new isotopes that are the most
neutron-rich nuclides of the elements chlorine to manganese (50-Cl, 53-Ar,
55,56-K, 57,58-Ca, 59,60,61-Sc, 62,63-Ti, 65,66-V, 68-Cr, 70-Mn). The enhanced
cross sections of several new nuclei relative to a simple thermal evaporation
framework, previously shown to describe similar production cross sections,
indicates that nuclei in the region around 62-Ti might be more stable than
predicted by current mass models and could be an indication of a new island of
inversion similar to that centered on 31-Na.Comment: 4 pages, 3 figures, to be published in Physical Review Letters, 200
Production cross sections from 82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line
Production cross sections for neutron-rich nuclei from the fragmentation of a
82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions
of 126 neutron-rich isotopes of elements 11 <= Z <= 32 were scanned using an
experimental approach of varying the target thickness. Production cross
sections with beryllium and tungsten targets were determined for a large number
of nuclei including several isotopes first observed in this work. These are the
most neutron-rich nuclides of the elements 22 <= Z <= 25 (64Ti, 67V, 69Cr,
72Mn). One event was registered consistent with 70Cr, and another one with
75Fe. The production cross sections are correlated with Qg systematics to
reveal trends in the data. The results presented here confirm our previous
result from a similar measurement using a 76Ge beam, and can be explained with
a shell model that predicts a subshell closure at N = 34 around Z = 20. This is
demonstrated by systematic trends and calculations with the Abrasion-Ablation
model that are sensitive to separation energies.Comment: 13 pages, 11 figures, accepted to Phys.Rev.
Conceptual and Numerical Analysis of Active Wingtip Vortex Cancellation in Propeller-Driven Electric Aircraft
As battery and electric motor technology continues to advance rapidly, propeller-driven electric aircraft are likely to become a significant part of the aviation market in the near future. One proposed design configuration for electric aircraft involves using large, wingtip- mounted propellers to actively cancel wingtip vortices, a method called active wingtip vortex cancellation (AWVC). By reclaiming part of the kinetic energy that would otherwise be lost to tip vortex formation, drag is decreased. In addition, the induced spanwise flow and upwash from the propeller causes the spanwise lift distribution to remain more uniform at the wingtips, increasing lift. Previous wind tunnel testing of this configuration characterized a significant increase in lift and decrease in drag, particularly in low-aspect-ratio configurations. This paper builds on that research by examining several test cases with a 3D, transient, viscous, sliding mesh CFD analysis in an effort to validate numerical methods for future conceptual design studies. In addition, many practical considerations regarding the implementation of this design are analyzed. Geometry from the aforementioned wind tunnel literature was reconstructed and analyzed. CFD indicated an 18.1% increase in lift and 5.1% increase in net thrust was possible solely through the phenomenon of AWVC. Furthermore, this CFD analysis matched wind tunnel data to within approximately 1%, validating the CFD approach for the analysis of more exotic configurations involving active wingtip vortex cancellation
Production cross sections of neutron rich isotopes from a 82Se beam
Production cross sections for neutron-rich nuclei from the fragmentation of a
82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions
of 122 neutron-rich isotopes of elements were determined by
varying the target thickness. Production cross sections with beryllium and
tungsten targets were determined for a large number of nuclei including several
isotopes first observed in this work. These are the most neutron-rich nuclides
of the elements (64Ti, 67V, 69Cr, 72Mn). One event was
registered consistent with 70Cr, and another one with 75Fe. A one-body Qg
systematics is used to describe the production cross sections based on thermal
evaporation from excited prefragments. The current results confirm those of our
previous experiment with a 76Ge beam: enhanced production cross sections for
neutron-rich fragments near Z=20.Comment: Talk given at the 11th International Conference on Nucleus-Nucleus
Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear
in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS
Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40
The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.Comment: 4 pages, 2 figure
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