21,227 research outputs found
Literature review on pickling inhibitors and cadmium electroplating processes
Because introduction of hydrogen during bright-cadmium electroplating of high strength steels causes hydrogen-stress cracking, a program was undertaken to evaluate various processes and materials. Report describes effectiveness of inhibitors for reducing hydrogen absorption by steels
Impulsive Heating of Solar Flare Ribbons Above 10 MK
The chromospheric response to the input of flare energy is marked by extended
extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are
usually explained as the result of heating and bremsstrahlung emission from
accelerated electrons colliding in the dense chromospheric plasma. We present
evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon
flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class
event using data from Atmospheric Imaging Assembly (AIA) on board of Solar
Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and
differential emission measure of the flaring regions and investigate the
evolution of the plasma in the flaring ribbons. The ribbons were visible at all
SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 \AA\ filters,
sensitive to temperatures of 8 MK and 12 MK. Time evolution of the emission
measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak
time. The presence of hot plasma in the lower atmosphere is further confirmed
by RHESSI imaging spectroscopy analysis, which shows resolved sources at 11-13
MK associated with at least one ribbon. We found that collisional beam heating
can only marginally explain the necessary power to heat the 10 MK plasma at the
ribbons.Comment: 21 pages, 15 figure
Magnetic fields and spiral arms in the galaxy M51
(Abridged) We use new multi-wavelength radio observations, made with the VLA
and Effelsberg telescopes, to study the magnetic field of the nearby galaxy M51
on scales from 200\pc to several \kpc. Interferometric and single dish data
are combined to obtain new maps at \wwav{3}{6} in total and polarized emission,
and earlier \wav{20} data are re-reduced. We compare the spatial distribution
of the radio emission with observations of the neutral gas, derive radio
spectral index and Faraday depolarization maps, and model the large-scale
variation in Faraday rotation in order to deduce the structure of the regular
magnetic field. We find that the \wav{20} emission from the disc is severely
depolarized and that a dominating fraction of the observed polarized emission
at \wav{6} must be due to anisotropic small-scale magnetic fields. Taking this
into account, we derive two components for the regular magnetic field in this
galaxy: the disc is dominated by a combination of azimuthal modes, , but
in the halo only an mode is required to fit the observations. We disuss
how the observed arm-interarm contrast in radio intensities can be reconciled
with evidence for strong gas compression in the spiral shocks. The average
arm--interam contrast, representative of the radii r>2\kpc where the spiral
arms are broader, is not compatible with straightforward compression: lower
arm--interarm contrasts than expected may be due to resolution effects and
\emph{decompression} of the magnetic field as it leaves the arms. We suggest a
simple method to estimate the turbulent scale in the magneto-ionic medium from
the dependence of the standard deviation of the observed Faraday rotation
measure on resolution. We thus obtain an estimate of 50\pc for the size of
the turbulent eddies.Comment: 21 pages, 18 figures (some at lower resolution than submitted
version), accepted for publication in MNRA
Benchmark calculations for reduced density-matrix functional theory
Reduced density-matrix functional theory (RDMFT) is a promising alternative
approach to the problem of electron correlation. Like standard density
functional theory, it contains an unknown exchange-correlation functional, for
which several approximations have been proposed in the last years. In this
article, we benchmark some of these functionals in an extended set of molecules
with respect to total and atomization energies. Our results show that the most
recent RDMFT functionals give very satisfactory results compared to more
involved quantum chemistry and density functional approaches.Comment: 17 pages, 1 figur
The supernova-regulated ISM. I. The multi-phase structure
We simulate the multi-phase interstellar medium randomly heated and stirred
by supernovae, with gravity, differential rotation and other parameters of the
solar neighbourhood. Here we describe in detail both numerical and physical
aspects of the model, including injection of thermal and kinetic energy by SN
explosions, radiative cooling, photoelectric heating and various transport
processes. With 3D domain extending 1 kpc^2 horizontally and 2 kpc vertically,
the model routinely spans gas number densities 10^-5 - 10^2 cm^-3, temperatures
10-10^8 K, local velocities up to 10^3 km s^-1 (with Mach number up to 25).
The thermal structure of the modelled ISM is classified by inspection of the
joint probability density of the gas number density and temperature. We confirm
that most of the complexity can be captured in terms of just three phases,
separated by temperature borderlines at about 10^3 K and 5x10^5 K. The
probability distribution of gas density within each phase is approximately
lognormal. We clarify the connection between the fractional volume of a phase
and its various proxies, and derive an exact relation between the fractional
volume and the filling factors defined in terms of the volume and probabilistic
averages. These results are discussed in both observational and computational
contexts. The correlation scale of the random flows is calculated from the
velocity autocorrelation function; it is of order 100 pc and tends to grow with
distance from the mid-plane. We use two distinct parameterizations of radiative
cooling to show that the multi-phase structure of the gas is robust, as it does
not depend significantly on this choice.Comment: 28 pages, 22 figures and 8 table
Omega time transmissions and receiving requirements
A short history is given of the development of dual VLF time transmission techniques. The theory of time recovery from the relative phase of the dual frequency transmission is presented. The transmission and receiving requirements for cycle identification and cycle ambiguity resolution are described. Finally, an experiment to test the capability of time transmission of the OMEGA system is propose
Geometric approach to Fletcher's ideal penalty function
Original article can be found at: www.springerlink.com Copyright Springer. [Originally produced as UH Technical Report 280, 1993]In this note, we derive a geometric formulation of an ideal penalty function for equality constrained problems. This differentiable penalty function requires no parameter estimation or adjustment, has numerical conditioning similar to that of the target function from which it is constructed, and also has the desirable property that the strict second-order constrained minima of the target function are precisely those strict second-order unconstrained minima of the penalty function which satisfy the constraints. Such a penalty function can be used to establish termination properties for algorithms which avoid ill-conditioned steps. Numerical values for the penalty function and its derivatives can be calculated efficiently using automatic differentiation techniques.Peer reviewe
Running Reconnaissance of French Maritime Pine for the British Army
The best thing about this story is, it\u27s true. All the dates, places, people and facts are real and can be verified upon examination. For that reason it may have a little more interest for those people who do not •Care particularly how a forest reconnaissance is run, but who might be interested to know how two Americans came to be attached with the British for ten months and what they did :in that time
A review of the literature on pickling inhibitors and cadmium electroplating processes to minimize hydrogen absorption by ultrahigh-strength steels
Literature review on pickling inhibitors and cadmium electroplating processes to minimize hydrogen absorption by ultrahigh strength steel
Review of literature on hydrogen embrittlement
Hydrogen embrittlement in high strength iron-base and nickel-base alloys and titaniu
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