56,814 research outputs found
Stratospheric dynamics
A global circulation model is being used to study the dynamical behavior of stratospheric planetary waves (waves having horizontal wavelengths of tens of thousands of kilometers) forced by growing cyclonic disturbances of intermediate scale, typically with wavelengths of a few thousand kilometers, which occur in the troposphere. Planetary scale waves are the dominant waves in the stratosphere, and are important for understanding the distribution of atmospheric trace constituents. Planetary wave forcing by intermediate scale tropospheric cyclonic disturbances is important for producing eastward travelling planetary waves of the sort which are prominent in the Southern Hemisphere during winter. The same global circulation model is also being used to simulate and understand the rate of dispersion and possible stratospheric climatic feedbacks of the El Chichon volcanic aerosol cloud. By comparing the results of the model calculation with an established data set now in existence for the volcanic cloud spatial and temporal distribution, stratospheric transport processes will be better understood, and the extent to which the cloud modified stratospheric wind and temperature fields can be assessed
A List of Wisconsin Springtails With New Records and Annotations (Hexapoda: Parainsecta: Collembola)
Twenty Collembola species new to Wisconsin were collected from soil at two agricultural sites in southern Wisconsin, including an undescribed species of Isotomidae. The state faunal list now contains 52 species representing seven families
Velocity measurements for a solar active region fan loop from Hinode/EIS observations
The velocity pattern of a fan loop structure within a solar active region
over the temperature range 0.15-1.5 MK is derived using data from the EUV
Imaging Spectrometer (EIS) on board the Hinode satellite. The loop is aligned
towards the observer's line-of-sight and shows downflows (redshifts) of around
15 km/s up to a temperature of 0.8 MK, but for temperatures of 1.0 MK and above
the measured velocity shifts are consistent with no net flow. This velocity
result applies over a projected spatial distance of 9 Mm and demonstrates that
the cooler, redshifted plasma is physically disconnected from the hotter,
stationary plasma. A scenario in which the fan loops consist of at least two
groups of "strands" - one cooler and downflowing, the other hotter and
stationary -- is suggested. The cooler strands may represent a later
evolutionary stage of the hotter strands. A density diagnostic of Mg VII was
used to show that the electron density at around 0.8 MK falls from 3.2 x 10^9
cm^-3 at the loop base, to 5.0 x 10^8 cm^-3 at a projected height of 15 Mm. A
filling factor of 0.2 is found at temperatures close to the formation
temperature of Mg VII (0.8 MK), confirming that the cooler, downflowing plasma
occupies only a fraction of the apparent loop volume. The fan loop is rooted
within a so-called "outflow region" that displays low intensity and blueshifts
of up to 25 km/s in Fe XII 195.12 A (formed at 1.5 MK), in contrast to the
loop's redshifts of 15 km/s at 0.8 MK. A new technique for obtaining an
absolute wavelength calibration for the EIS instrument is presented and an
instrumental effect, possibly related to a distorted point spread function,
that affects velocity measurements is identified.Comment: 42 pages, 15 figures, submitted to Ap
Pump linewidth requirement for optical parametric oscillators
Pumping laser bandwidth requirement for optical parametric oscillator
Dynamics of Energy Transport in a Toda Ring
We present results on the relationships between persistent currents and the
known conservation laws in the classical Toda ring. We also show that
perturbing the integrability leads to a decay of the currents at long times,
with a time scale that is determined by the perturbing parameter. We summarize
several known results concerning the Toda ring in 1-dimension, and present new
results relating to the frequency, average kinetic and potential energy, and
mean square displacement in the cnoidal waves, as functions of the wave vector
and a parameter that determines the non linearity.Comment: 34 pages, 11 figures. Small changes made in response to referee's
comment
Nonequilibrium phase transition on a randomly diluted lattice
We show that the interplay between geometric criticality and dynamical
fluctuations leads to a novel universality class of the contact process on a
randomly diluted lattice. The nonequilibrium phase transition across the
percolation threshold of the lattice is characterized by unconventional
activated (exponential) dynamical scaling and strong Griffiths effects. We
calculate the critical behavior in two and three space dimensions, and we also
relate our results to the recently found infinite-randomness fixed point in the
disordered one-dimensional contact process.Comment: 4 pages, 1 eps figure, final version as publishe
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