6,693 research outputs found
Damage to metallic samples produced by measured lightning currents
A total of 10 sample disks of 2024-T3 aluminum and 4130 ferrous steel were exposed to rocket-triggered lightning currents at the Kennedy Space Center test site. The experimental configuration was arranged so that the samples were not exposed to the preliminary streamer, wire-burn, or following currents that are associated with an upward-initiated rocket-triggered flash but which are atypical of naturally initiated lightning. Return-stroke currents and continuing currents actually attaching to the sample were measured, augmented by close-up video recordings of approximately 3 feet of the channel above the sample and by 16-mm movies with 5-ms resolution. From these data it was possible to correlate individual damage spots with streamer, return-stroke, and continuing currents that produced them. Substantial penetration of 80-mil aluminum was produced by a continuing current of submedian amplitude and duration, and full penetration of a 35-mil steel sample occurred under an eightieth percentile continuing current. The primary purpose of the data acquired in these experiments is for use in improving and quantifying the fidelity of laboratory simulations of lightning burnthrough
The Sandia transportable triggered lightning instrumentation facility
Development of the Sandia Transportable Triggered Lightning Instrumentation Facility (SATTLIF) was motivated by a requirement for the in situ testing of a munitions storage bunker. Transfer functions relating the incident flash currents to voltages, currents, and electromagnetic field values throughout the structure will be obtained for use in refining and validating a lightning response computer model of this type of structure. A preliminary shakedown trial of the facility under actual operational conditions was performed during summer of 1990 at the Kennedy Space Center's (KSC) rocket-triggered lightning test site. A description is given of the SATTLIF, which is readily transportable on a single flatbed truck of by aircraft, and its instrumentation for measuring incident lightning channel currents and the responses of the systems under test. Measurements of return-stroke current peaks obtained with the SATTLIF are presented. Agreement with data acquired on the same flashes with existing KSC instrumentation is, on average, to within approximately 7 percent. Continuing currents were measured with a resolution of approximately 2.5 A. This field trial demonstrated the practicality of using a transportable triggered lightning facility for specialized test applications
A Comprehensive Method of Estimating Electric Fields from Vector Magnetic Field and Doppler Measurements
Photospheric electric fields, estimated from sequences of vector magnetic
field and Doppler measurements, can be used to estimate the flux of magnetic
energy (the Poynting flux) into the corona and as time-dependent boundary
conditions for dynamic models of the coronal magnetic field. We have modified
and extended an existing method to estimate photospheric electric fields that
combines a poloidal-toroidal (PTD) decomposition of the evolving magnetic field
vector with Doppler and horizontal plasma velocities. Our current, more
comprehensive method, which we dub the "{\bf P}TD-{\bf D}oppler-{\bf F}LCT {\bf
I}deal" (PDFI) technique, can now incorporate Doppler velocities from
non-normal viewing angles. It uses the \texttt{FISHPACK} software package to
solve several two-dimensional Poisson equations, a faster and more robust
approach than our previous implementations. Here, we describe systematic,
quantitative tests of the accuracy and robustness of the PDFI technique using
synthetic data from anelastic MHD (\texttt{ANMHD}) simulations, which have been
used in similar tests in the past. We find that the PDFI method has less than
error in the total Poynting flux and a error in the helicity flux
rate at a normal viewing angle ) and less than and
errors respectively at large viewing angles (). We compare our
results with other inversion methods at zero viewing angle, and find that our
method's estimates of the fluxes of magnetic energy and helicity are comparable
to or more accurate than other methods. We also discuss the limitations of the
PDFI method and its uncertainties.Comment: 56 pages, 10 figures, ApJ (in press
The Interrelation of Soft and Hard X-ray Emission During Solar Flares
The objective of this project is to determine the characteristics of flare energy transport processes through the study of soft X-rays, hard X-rays, and their interrelationships through analysis of Yohkoh SXT, HXT, and BCS data, and comparison with theoretical models. The personnel involved in the research include SSL Assistant Research Physicists Dr. Peng Li and Dr. James McTiernan
Photospheric Electric Fields and Energy Fluxes in the Eruptive Active Region NOAA 11158
How much electromagnetic energy crosses the photosphere in evolving solar
active regions? With the advent of high-cadence vector magnetic field
observations, addressing this fundamental question has become tractable. In
this paper, we apply the "PTD-Doppler-FLCT-Ideal" (PDFI) electric field
inversion technique of Kazachenko et al. (2014) to a 6-day HMI/SDO vector
magnetogram and Doppler velocity sequence, to find the electric field and
Poynting flux evolution in active region NOAA 11158, which produced an X2.2
flare early on 2011 February 15. We find photospheric electric fields ranging
up to V/cm. The Poynting fluxes range from to
ergscms, mostly positive, with the largest contribution to
the energy budget in the range of -
ergscms. Integrating the instantaneous energy flux over
space and time, we find that the total magnetic energy accumulated above the
photosphere from the initial emergence to the moment before the X2.2 flare to
be ergs, which is partitioned as and
ergs, respectively, between free and potential energies.
Those estimates are consistent with estimates from preflare non-linear
force-free field (NLFFF) extrapolations and the Minimum Current Corona
estimates (MCC), in spite of our very different approach. This study of
photospheric electric fields demonstrates the potential of the PDFI approach
for estimating Poynting fluxes and opens the door to more quantitative studies
of the solar photosphere and more realistic data-driven simulations of coronal
magnetic field evolution.Comment: 51 pages, 10 figures, accepted by ApJ on August 11, 201
Business Enterprise Value in Shopping Malls: An Empirical Test
This paper discusses the economic basis for the existence of business enterprise value in a shopping mall. The existence of business enterprise value in a mall is then tested by examining the rent paid by existing tenants on a lease renewal vs. that paid by new tenants for otherwise identical space. The hypothesis that there is no difference in rents between renewals and new tenants can be rejected. This suggests that with each lease renewal there is a marginal increase in business enterprise value component of the rents. Proposed federal regulations for the appraisal of federally related transactions, the uniform standards of professional appraisal practice, and real property tax law call for separation of the value of intangibles (which include business value) from tangible personal property and from real property. Thus the business value portion of the mall rental should not be capitalized into the value of the real estate. Because income from lease renewals included business value, the leases must be adjusted before they can be used as an indication of market rent.
- …