3,630 research outputs found
Stratospheric column NO2 measurements from three Antarctic sites
The significance of stratospheric odd-nitrogen compounds in Antarctic ozone depletion studies has prompted an increase in Antarctic activities. Although several species are being studied, work has concentrated on the acquisition of NO2 data. Ground-based measurements of stratospheric column NO2 have been made at Arrival Heights, Antarctica, since spring 1982, with some gaps in the data base. Additional data has been acquired since February 1986 at Pole Station and Halley Bay, thus providing a chain of stations across the continent. The technique used is that of absorption spectroscopy in several wavelength regions, although here only those measurements are reported in the 430 to 450 nm region where strongly structured absorption been determined experimentally. However, theory features due to NO2 are identified in scattered sunlight in the zenith sky. Operation of a moon-tracking system at Arrival Heights has provided some additional data during the polar night. Previous analyses have shown that the NO2 column observed from the ground is strongly influenced by the season, and by the location of the site with respect to that of the polar vortex. The column amount correlates strongly with stratospheric temperature at about 70 mbar. The present data set further illustrates these features, and demonstrates both the strengths and qualifications apparent in the technique
A Tale of Two Tilings
What do you get when you cross a crystal with a quasicrystal? The surprising
answer stretches from Fibonacci to Kepler, who nearly 400 years ago showed how
the ancient tiles of Archimedes form periodic patterns.Comment: 3 pages, 1 figur
Frictional Resistance to a Ship's Passage through Converging Ice
Presents formulae to estimate the pressure developed in a converging ice field and to calculate the resulting frictional resistance to a ship attempting to navigate through such ice. The icebreaker-tanker Manhattan is used as an example. It is shown that the power necessary to navigate in ice which is failing in compression would be prohibitive
Perverse Nudges: Minimum Payments and Debt Paydown in Consumer Credit Cards
Credit card minimum payments can act as an “anchor” that causes consumers to pay less of their debt than they otherwise would, leading to higher balances and interest costs, lower credit card scores, increased bankruptcy risks, and in the aggregate, suboptimally high levels of debt in the macro-economy. Policy “nudges,” which aim to increase the monthly amount that individuals pay on their credit card debt, have had mixed results.https://repository.upenn.edu/pennwhartonppi/1018/thumbnail.jp
Propagating Wave Phenomena Detected in Observations and Simulations of the Lower Solar Atmosphere
We present high-cadence observations and simulations of the solar
photosphere, obtained using the Rapid Oscillations in the Solar Atmosphere
imaging system and the MuRAM magneto-hydrodynamic code, respectively. Each
dataset demonstrates a wealth of magneto-acoustic oscillatory behaviour,
visible as periodic intensity fluctuations with periods in the range 110-600 s.
Almost no propagating waves with periods less than 140s and 110s are detected
in the observational and simulated datasets, respectively. High concentrations
of power are found in highly magnetised regions, such as magnetic bright points
and intergranular lanes. Radiative diagnostics of the photospheric simulations
replicate our observational results, confirming that the current breed of
magneto-hydrodynamic simulations are able to accurately represent the lower
solar atmosphere. All observed oscillations are generated as a result of
naturally occurring magnetoconvective processes, with no specific input driver
present. Using contribution functions extracted from our numerical simulations,
we estimate minimum G-band and 4170 Angstrom continuum formation heights of 100
km and 25 km, respectively. Detected magneto-acoustic oscillations exhibit a
dominant phase delay of -8 degrees between the G-band and 4170 Angstrom
continuum observations, suggesting the presence of upwardly propagating waves.
More than 73% of MBPs (73% from observations, 96% from simulations) display
upwardly propagating wave phenomena, suggesting the abundant nature of
oscillatory behaviour detected higher in the solar atmosphere may be traced
back to magnetoconvective processes occurring in the upper layers of the Sun's
convection zone.Comment: 13 pages, 9 figures, accepted into Ap
The Velocity Distribution of Solar Photospheric Magnetic Bright Points
We use high spatial resolution observations and numerical simulations to
study the velocity distribution of solar photospheric magnetic bright points.
The observations were obtained with the Rapid Oscillations in the Solar
Atmosphere instrument at the Dunn Solar Telescope, while the numerical
simulations were undertaken with the MURaM code for average magnetic fields of
200 G and 400 G. We implemented an automated bright point detection and
tracking algorithm on the dataset, and studied the subsequent velocity
characteristics of over 6000 structures, finding an average velocity of
approximately 1 km/s, with maximum values of 7 km/s. Furthermore, merging
magnetic bright points were found to have considerably higher velocities, and
significantly longer lifetimes, than isolated structures. By implementing a new
and novel technique, we were able to estimate the background magnetic flux of
our observational data, which is consistent with a field strength of 400 G.Comment: Accepted for publication in ApJL, 12 pages, 2 figure
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