1,645 research outputs found
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
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
Analysis of Economic Depreciation for Multi-Family Property
This paper uses a hedonic pricing model and National Council of Real Estate Investment Fiduciaries data to estimate economic depreciation for multi-family real estate. The findings indicate that investment grade multi-family housing depreciates approximately 2.7% per year in real terms based on total property value. This implies a depreciation rate for just the building of about 3.25% per year. With 2% inflation, this suggests a nominal depreciation rate of about 5.25% per year. Converted into a straight-line depreciation rate that has the same present value, this suggests a depreciable life of 30.5 years - as compared to 27.5 years allowed under the current tax laws. Thus, these laws are slightly favorable to multi-family properties by providing a tax depreciation rate that exceeds economic depreciation, which is in part due to inflation that has been less than expected during the past decade.
On the beta function and the neutrix product of distributions
The Beta function B(x,n) and the related Beta functions B(x ±, n) and B±(x,n) are defined as distributions and a number of neutrix products of distributions are evaluated
A Clinical Masquerader: Squamous Cell Carcinoma of the Eyelid Previously Diagnosed as an Eye Bump
Malignant eyelid tumors are often difficult to diagnose at early stage growth, and can be clinically challenging. Due to the high prevalence of periocular skin cancers, clinicians must be very attentive in their assessment of skin lesions amongst their patients. This case report highlights an early non-healing eyelid lesion transforming into squamous cell carcinoma. An 83-year-old male with no history of malignancy presented with a non-healing and rapidly growing lesion of the left lower eyelid. He first noticed this lesion one-month prior and was treated with oral antibiotics without improvement by his primary care provider. Our slit lamp examination of the left eyelid revealed a large ulcerated mass with white mucoid discharge draining from the center of the lesion. After an oculoplastics referral, the patient was diagnosed with squamous cell carcinoma confirmed by biopsy. Computed tomography(CT) showed no metastasis or invasion to deep layer tissue. The management decision in this case required exenteration of the left eye socket followed by radiation therapy. This case illustrates the clinical course and invasive nature of periocular squamous cell carcinoma. It can present in a variety of different appearances, but are mostly painless, hyperkeratotic lesions that progressively change and ulcerate. An extensive history and careful clinical examination are vital in order to detect malignancy in a timely manner
Pair Analytics: Capturing Reasoning Processes in Collaborative Visual Analytics
Studying how humans interact with abstract, visual representations of massive amounts of data provides knowledge about how cognition works in visual analytics. This knowledge provides guidelines for cognitive-aware design and evaluation of visual analytic tools. Different methods have been used to capture and conceptualize these processes including protocol analysis, experiments, cognitive task analysis, and field studies. In this article, we introduce Pair Analytics: a method for capturing reasoning processes in visual analytics. We claim that Pair Analytics offers two advantages with respect to other methods: (1) a more natural way of making explicit and capturing reasoning processes and (2) an approach to capture social and cognitive processes used to conduct collaborative analysis in real-life settings. We support and illustrate these claims with a pilot study of three phenomena in collaborative visual analytics: coordination of attention, cognitive workload, and navigation of analysis
Calculation of the entropy of binary hard sphere mixtures from pair correlation functions
This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/97/3/10.1063/1.463103.We evaluate the entropy of several binary hard sphere fluid mixtures using two approximate expressions that require as input only the pair correlation functions,g αβ(r). An approximation based on the incompressible limit is found to be accurate for medium to high density fluids
Phased Array Feed Calibration, Beamforming and Imaging
Phased array feeds (PAFs) for reflector antennas offer the potential for
increased reflector field of view and faster survey speeds. To address some of
the development challenges that remain for scientifically useful PAFs,
including calibration and beamforming algorithms, sensitivity optimization, and
demonstration of wide field of view imaging, we report experimental results
from a 19 element room temperature L-band PAF mounted on the Green Bank
20-Meter Telescope. Formed beams achieved an aperture efficiency of 69% and
system noise temperature of 66 K. Radio camera images of several sky regions
are presented. We investigate the noise performance and sensitivity of the
system as a function of elevation angle with statistically optimal beamforming
and demonstrate cancelation of radio frequency interference sources with
adaptive spatial filtering.Comment: 19 pages, 13 figure
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