10,747 research outputs found
Non-equilibrium of Ionization and the Detection of Hot Plasma in Nanoflare-heated Coronal Loops
Impulsive nanoflares are expected to transiently heat the plasma confined in
coronal loops to temperatures of the order of 10 MK. Such hot plasma is hardly
detected in quiet and active regions, outside flares. During rapid and short
heat pulses in rarified loops the plasma can be highly out of equilibrium of
ionization. Here we investigate the effects of the non-equilibrium of
ionization (NEI) on the detection of hot plasma in coronal loops.
Time-dependent loop hydrodynamic simulations are specifically devoted to this
task, including saturated thermal conduction, and coupled to the detailed
solution of the equations of ionization rate for several abundant elements. In
our simulations, initially cool and rarified magnetic flux tubes are heated to
10 MK by nanoflares deposited either at the footpoints or at the loop apex. We
test for different pulse durations, and find that, due to NEI effects, the loop
plasma may never be detected at temperatures above ~5 MK for heat pulses
shorter than about 1 min. We discuss some implications in the framework of
multi-stranded nanoflare-heated coronal loops.Comment: 22 pages, 7 figures, accepted for publicatio
Isogrid design handbook
Handbook has been published which presents information needed for design of isogrid triangular integral-stiffened structures. It develops equations, methods, and graphs to handle wide variety of loadings, materials, and geometry. Handbook is divided into seven sections. Handbook may be used by marine and civil engineers and by students and designers without access to computers
Radio polarization maps of shell-type SNRs II. Sedov models with evolution of turbulent magnetic field
Polarized radio emission has been mapped with great detail in several
Galactic supernova remnants (SNRs), but has not yet been exploited to the
extent it deserves. We have developed a method to model maps of the Stokes
parameters for shell-like SNRs during their Sedov evolution phase. At first,
3-dimensional structure of a SNR has been computed, by modeling the
distribution of the magnetohydrodynamic parameters and of the accelerated
particles. The generation and dissipation of the turbulent component of
magnetic field everywhere in SNR are also considered taking into account its
interaction with accelerated particles. Then, in order to model the emission,
we have used a generalization of the classical synchrotron theory, valid for
the case in which the magnetic field has ordered and disordered components.
Finally, 2-dimensional projected maps have been derived, for different
orientations of SNR and of interstellar magnetic field with respect to the
observer. An important effect to consider is the Faraday rotation of the
polarization planes inside the SNR interior. In this paper we present details
of the model, and describe general properties of the images.Comment: accepted in MNRA
ISS and TPD study of the adsorption and interaction of CO and H2 on polycrystalline Pt
The adsorption and interaction of CO and H2 on polycrystalline Pt has been studied using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). The ISS results indicate that the initial CO adsorption on Pt takes place very rapidly and saturates the Pt surface with coverage close to a monolayer. ISS also shows that the CO molecules adsorb at an angular orientation from the surface normal and perhaps parallel to the surface. A TPD spectrum obtained after coadsorbing C-12 O-16 and C-13 O-18 on Pt shows no isotopic mixing, which is indicative of molecular CO adsorption. TPD spectra obtained after coadsorbing H2 and CO on polycrystalline Pt provides evidence for the formation of a CO-H surface species
Turbulent transport of heat and momentum in a boundary layer subject to deceleration, suction and variable wall temperature
The relationship between the turbulent transport of heat and momentum in an adverse pressure gradient boundary layer was studied. An experimental study was conducted of turbulent boundary layers subject to strong adverse pressure gradients with suction. Near-equilibrium flows were attained, evidenced by outer-region similarity in terms of defect temperature and defect velocity profiles. The relationship between Stanton number and enthalpy thickness was shown to be the same as for a flat plate flow both for constant wall temperature boundary conditions and for steps in wall temperature. The superposition principle used with the step-wall-temperature experimental result was shown to accurately predict the Stanton number variation for two cases of arbitrarily varying wall temperature. The Reynolds stress tensor components were measured for strong adverse pressure gradient conditions and different suction rates. Two peaks of turbulence intensity were found: one in the inner and one in the outer regions. The outer peak is shown to be displaced outward by an adverse pressure gradient and suppressed by suction
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