14,896 research outputs found
Fast fluctuations of soft X-rays from active regions
A selection of short lived small soft X-ray bursts is studied using data from the Hard X-ray Imaging Spectrometer (HXIS), and the results are compared with the data from the Hard X-Ray Burst Spectrometer (HXRBS) with a view to understanding conditions at the onset of flares. Short-lived events provide an opportunity to study the radiation from the primary energy transfer process without confusion from the slowly-varying thermal X-ray emission which characterizes the decay of a large flare. The fast decay of the soft X-rays, only a few tens of seconds, suggests that they occur in the dense chromosphere. The results indicate that the short events may be signatures of several different phenomena, depending on their characteristics. Some events occur in association with reverse-drift type III bursts and simultaneous flaring elsewhere on the Sun, thus suggesting dumping of particles accelerated at a remote site. Some events have hard X-ray bursts and normal type III bursts associated with them, while others have neither. The latter events place strong constraints on the nonthermal electron population present
Cost/benefit analysis of advanced materials technology candidates for the 1980's, part 2
Cost/benefit analyses to evaluate advanced material technologies projects considered for general aviation and turboprop commuter aircraft through estimated life-cycle costs, direct operating costs, and development costs are discussed. Specifically addressed is the selection of technologies to be evaluated; development of property goals; assessment of candidate technologies on typical engines and aircraft; sensitivity analysis of the changes in property goals on performance and economics, cost, and risk analysis for each technology; and ranking of each technology by relative value. The cost/benefit analysis was applied to a domestic, nonrevenue producing, business-type jet aircraft configured with two TFE731-3 turbofan engines, and to a domestic, nonrevenue producing, business type turboprop aircraft configured with two TPE331-10 turboprop engines. In addition, a cost/benefit analysis was applied to a commercial turboprop aircraft configured with a growth version of the TPE331-10
SU(3) quasidynamical symmetry underlying the Alhassid--Whelan arc of regularity
The first example of an empirically manifested quasi dynamical symmetry
trajectory in the interior of the symmetry triangle of the Interacting Boson
Approximation model is identified for large boson numbers. Along this curve,
extending from SU(3) to near the critical line of the first order phase
transition, spectra exhibit nearly the same degeneracies that characterize the
low energy levels of SU(3). This trajectory also lies close to the
Alhassid-Whelan arc of regularity, the unique interior region of regular
behavior connecting the SU(3) and U(5) vertices, thus offering a possible
symmetry-based interpretation of that narrow zone of regularity amidst regions
of more chaotic spectra.Comment: 4 pages, LaTeX, 5 eps figure
Fatigue testing a plurality of test specimens and method
Described is a fatigue testing apparatus for simultaneously subjecting a plurality of material test specimens to cyclical tension loading to determine the fatigue strength of the material. The fatigue testing apparatus includes a pulling head having cylinders defined therein which carry reciprocating pistons. The reciprocation of the pistons is determined by cyclical supplies of pressurized fluid to the cylinders. Piston rods extend from the pistons through the pulling head and are attachable to one end of the test specimens, the other end of the test specimens being attachable to a fixed base, causing test specimens attached between the piston rods and the base to be subjected to cyclical tension loading. Because all the cylinders share a common pressurized fluid supply, the breaking of a test specimen does not substantially affect the pressure of the fluid supplied to the other cylinders nor the tension applied to the other test specimens
Emergent Collectivity in Nuclei and Enhanced Proton-Neutron Interactions
Enhanced proton-neutron interactions occur in heavy nuclei along a trajectory
of approximately equal numbers of valence protons and neutrons. This is also
closely aligned with the trajectory of the saturation of quadrupole
deformation. The origin of these enhanced p-n interactions is discussed in
terms of spatial overlaps of proton and neutron wave functions that are
orbit-dependent. It is suggested for the first time that nuclear collectivity
is driven by synchronized filling of protons and neutrons with orbitals having
parallel spins, identical orbital and total angular momenta projections,
belonging to adjacent major shells and differing by one quantum of excitation
along the z-axis. These results may lead to a new approach to symmetry-based
theoretical calculations for heavy nuclei.Comment: 6 pages, 4 figure
0+ states in the large boson number limit of the Interacting Boson Approximation model
Studies of the Interacting Boson Approximation (IBA) model for large boson
numbers have been triggered by the discovery of shape/phase transitions between
different limiting symmetries of the model. These transitions become sharper in
the large boson number limit, revealing previously unnoticed regularities,
which also survive to a large extent for finite boson numbers, corresponding to
valence nucleon pairs in collective nuclei. It is shown that energies of 0_n^+
states grow linearly with their ordinal number n in all three limiting
symmetries of IBA [U(5), SU(3), and O(6)]. Furthermore, it is proved that the
narrow transition region separating the symmetry triangle of the IBA into a
spherical and a deformed region is described quite well by the degeneracies
E(0_2^+)=E(6_1^+), E(0_3^+)=E(10_1^+), E(0_4^+)=E(14_1^+), while the energy
ratio E(6_1^+) /E(0_2^+) turns out to be a simple, empirical, easy-to-measure
effective order parameter, distinguishing between first- and second-order
transitions. The energies of 0_n^+ states near the point of the first order
shape/phase transition between U(5) and SU(3) are shown to grow as n(n+3), in
agreement with the rule dictated by the relevant critical point symmetries
resulting in the framework of special solutions of the Bohr Hamiltonian. The
underlying partial dynamical symmetries and quasi-dynamical symmetries are also
discussed.Comment: 6 pages, 4 postscript figures, LaTeX. To appear in the Proceedings of
the International Conference on Nuclear Physics and Astrophysics: From Stable
Beams to Exotic Nuclei (Cappadocia, 2008
- …