5,970 research outputs found
Observations of ozone production in a dissipating tropical convective cell during TC4
From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times (15:12–17:00 UTC), providing a unique examination of ozone (O3) photochemistry on the edge of a convective cell. Ozone increased at a rate of 1.6–4.6 ppbv/hr between the first and last ascent, resulting cell wide in an increase of (2.1–2.5)×106 moles of O3. This estimate agrees to within a factor of two of our estimates of photochemical lightning O3 production from the WWLLN flashes, from the radar-inferred lightning flash data, and from the OMI NO2 data (1.2, 1.0, and 1.7×106 moles, respectively), though all estimates have large uncertainties. Examination of DC-8 in situ and lidar O3 data gathered around the Gulf that day suggests 70–97% of the O3 change occurred in 2.5–5.1 km layer. A photochemical box model initialized with nearby TC4 aircraft trace gas data suggests these O3 production rates are possible with our present understanding of photochemistry
Spiral Structure Based Limits on the Disk Mass of the Low Surface Brightness Galaxies UGC 6614 and F568-6
Upper limits for the disk mass-to-light ratios for the low surface brightness
galaxies UGC 6614 and F568-6 (Malin 2) are estimated by considering the minimum
velocity perturbations in the HI velocity field that should result from the
spiral structure observed in the R band images. The weak observed response in
the velocity component limits the mass-to-light ratios of the disk
within a scale length to M/L <~ 3 and 6 for UGC 6614 for F568-6 respectively
(in solar units) based upon azimuthal variations observed in the R band images.
These limits are sufficiently strong to require a significant dark matter
component even in the central regions of these galaxies. Our limits furthermore
imply that this dark matter component cannot be in the form of a cold disk
since a cold disk would necessarily be involved in the spiral structure.
However, a more massive disk could be consistent with the observations because
of a non-linear gas response or if the gas is driven by bar-like distortions
instead of spiral structure. To produce the large observed arm/interarm HI
density variations it is likely that the spiral arm potential perturbation is
sufficiently strong to produce shocks in the gas. For a forcing that is greater
than 2% of the axisymmetric force, M/L >~ 1 is required in both galaxies in the
outer regions. These lower limits imply that the stellar surface density is at
least of the same order as the gas surface density. This is consistent with the
large scale morphology of the spiral structure, and the stability of the gas
disk, both which suggest that a moderate stellar component is required to
produce the observed spiral structure. (Shortened abstract)Comment: AAS Latex, Postscript and jpeg Figures, Accepted for publication in
A
Science as It Could Have Been: Discussing the Contingency/Inevitability Problem
This collection of essay explore the different facets of the contingency/necessity debate in the philosophy of scienc
The fermion mass at next-to-leading order in the HTL effective theory
The calculation of the real part of a quasi-particle dispersion relation at
next-to-leading order in the hard thermal loop effective theory is a very
difficult problem. Even though the hard thermal loop effective theory is almost
20 years old, there is only one next-to-leading order calculation of the real
part of a quasi-particle dispersion relation in the literature. In this paper,
we calculate the fermion mass in QED and QCD at next-to-leading order. For QED
the result is M=eT/sqrt{8} * [1-(1.427 \pm 0.02)e/4pi] and for QCD with N_f=2
and N_c=3 we obtain M=gT/sqrt{6} * [1+(1.867 \pm 0.02)g/4pi].Comment: 9 pages, 5 figure
Fe I Oscillator Strengths for the Gaia-ESO Survey
The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale
study of multi-element chemical abundances of some 100 000 stars in the Milky
Way with the ultimate aim of quantifying the formation history and evolution of
young, mature and ancient Galactic populations. However, in preparing for the
analysis of GES spectra, it has been noted that atomic oscillator strengths of
important Fe I lines required to correctly model stellar line intensities are
missing from the atomic database. Here, we present new experimental oscillator
strengths derived from branching fractions and level lifetimes, for 142
transitions of Fe I between 3526 {\AA} and 10864 {\AA}, of which at least 38
are urgently needed by GES. We also assess the impact of these new data on
solar spectral synthesis and demonstrate that for 36 lines that appear
unblended in the Sun, Fe abundance measurements yield a small line-by-line
scatter (0.08 dex) with a mean abundance of 7.44 dex in good agreement with
recent publications.Comment: Accepted for publication in Mon. Not. R. Astron. So
Spatio-temporal patterns of beaked whale echolocation signals in the North Pacific.
At least ten species of beaked whales inhabit the North Pacific, but little is known about their abundance, ecology, and behavior, as they are elusive and difficult to distinguish visually at sea. Six of these species produce known species-specific frequency modulated (FM) echolocation pulses: Baird's, Blainville's, Cuvier's, Deraniyagala's, Longman's, and Stejneger's beaked whales. Additionally, one described FM pulse (BWC) from Cross Seamount, Hawai'i, and three unknown FM pulse types (BW40, BW43, BW70) have been identified from almost 11 cumulative years of autonomous recordings at 24 sites throughout the North Pacific. Most sites had a dominant FM pulse type with other types being either absent or limited. There was not a strong seasonal influence on the occurrence of these signals at any site, but longer time series may reveal smaller, consistent fluctuations. Only the species producing BWC signals, detected throughout the Pacific Islands region, consistently showed a diel cycle with nocturnal foraging. By comparing stranding and sighting information with acoustic findings, we hypothesize that BWC signals are produced by ginkgo-toothed beaked whales. BW43 signal encounters were restricted to Southern California and may be produced by Perrin's beaked whale, known only from Californian waters. BW70 signals were detected in the southern Gulf of California, which is prime habitat for Pygmy beaked whales. Hubb's beaked whale may have produced the BW40 signals encountered off central and southern California; however, these signals were also recorded off Pearl and Hermes Reef and Wake Atoll, which are well south of their known range
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