1,518 research outputs found
Estimating oil concentration and flow rate with calibrated vessel-mounted acoustic echo sounders
As part of a larger program aimed at evaluating acoustic techniques for mapping the distribution of subsurface oil and gas associated with the Deepwater Horizon-Macondo oil spill, observations were made on June 24 and 25, 2010 using vessel-mounted calibrated single-beam echo sounders on the National Oceanic and Atmospheric Administration ship Thomas Jefferson. Coincident with visual observations of oil at the sea surface, the 200-kHz echo sounder showed anomalously high-volume scattering strength in the upper 200 m on the western side of the wellhead, more than 100 times higher than the surrounding waters at 1,800-m distance from the wellhead, and weakening with increasing distance out to 5,000 m. Similar high-volume scattering anomalies were not observed at 12 or 38 kHz, although observations of anomalously low-volume scattering strength were made in the deep scattering layer at these frequencies at approximately the same locations. Together with observations of ocean currents, the acoustic observations are consistent with a rising plume of small (\u3c 1-mm radius) oil droplets. Using simplistic but reasonable assumptions about the properties of the oil droplets, an estimate of the flow rate was made that is remarkably consistent with those made at the wellhead by other means. The uncertainty in this acoustically derived estimate is high due to lack of knowledge of the size distribution and rise speed of the oil droplets. If properly constrained, these types of acoustic measurements can be used to rapidly estimate the flow rate of oil reaching the surface over large temporal and spatial scales
Regulación de la multiplicación celular en escherichia coli por el AMP cíclico
Fil: De Robertis, E. M. F.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Linux Based Ethernet Communication for Xilinx FPGAs
This article presents the implementation of an Ethernet communication platform for use on Xilinx FPGAs. The proposed solution relies on a synthesized embedded system to provide network data transfer and control capabilities, for use with synthesizable electronic devices. Most TCP/IP stack services and protocols were implemented and the design is flexible to allow adaptation and/or expansion for different application scenarios. Currently this platform is being used on the development of a FPGA based JTAG controller, with remote access. The embedded system hardware requires a MicroBlaze softcore microprocessor running a Petalinux operating system.info:eu-repo/semantics/publishedVersio
Oxygen abundance in the Sloan Digital Sky Survey
We present two samples of \hii galaxies from the Sloan Digital Sky Survey
(SDSS) spectroscopic observations data release 3. The electron
temperatures() of 225 galaxies are calculated with the photoionized \hii
model and of 3997 galaxies are calculated with an empirical method. The
oxygen abundances from the methods of the two samples are determined
reliably. The oxygen abundances from a strong line metallicity indicator, such
as , , , and , are also calculated. We compared oxygen
abundances of \hii galaxies obtained with the method, method,
method, method, and method. The oxygen abundances derived with
the method are systematically lower by 0.2 dex than those derived
with the method, consistent with previous studies based on \hii
region samples. No clear offset for oxygen abundance was found between
metallicity and , and metallicity. When we studied the relation
between N/O and O/H, we found that in the metallicity regime of \zoh > 7.95,
the large scatter of the relation can be explained by the contribution of small
mass stars to the production of nitrogen. In the high metallicity regime, \zoh
> 8.2, nitrogen is primarily a secondary element produced by stars of all
masses.Comment: 7 pages, 3 figures. A&A accepte
Status of the Cylindical-GEM project for the KLOE-2 Inner Tracker
The status of the R&D on the Cylindrical-GEM (CGEM) detector foreseen as
Inner Tracker for KLOE-2, the upgrade of the KLOE experiment at the DAFNE
phi-factory, will be presented. The R&D includes several activities: i) the
construction and complete characterization of the full-size CGEM prototype,
equipped with 650 microns pitch 1-D longitudinal strips; ii) the study of the
2-D readout with XV patterned strips and operation in magnetic field (up to
1.5T), performed with small planar prototypes in a dedicated test at the H4-SPS
beam facility; iii) the characterization of the single-mask GEM technology for
the realization of large-area GEM foils.Comment: 4 pages, 10 figures, Presented at Vienna Conference on
Instrumentation (Feb 15-20, 2010, Vienna, Austria). Submitted to the
Proceeding
The Extinction and Distance of Maffei 1
We have obtained low- and high-resolution spectra of the core of the
highly-reddened elliptical galaxy Maffei 1. From these data, we have obtained
the first measurement of the Mg2 index, and have measured the velocity
dispersion and radial velocity with improved accuracy. To evaluate the
extinction, a correlation between the Mg2 index and effective V-I colour has
been established for elliptical galaxies. Using a new method for correcting for
effective wavelength shifts, we find A_V = 4.67 +/- 0.19 mag, which is lower by
0.4 mag than previously thought. To establish the distance, the Fundamental
Plane for elliptical galaxies has been constructed in I. The velocity
dispersion of Maffei 1, measured to be 186.8 +/- 7.4 km/s, in combination with
modern wide-field photometry in I, leads to a distance of 2.92 +/- 0.37 Mpc.
The Dn-sigma relation, which is independently calibrated, gives 3.08 +/- 0.85
Mpc and 3.23 +/- 0.67 Mpc from photometry in B and K`, respectively. The
weighted mean of the three estimates is 3.01 +/- 0.30 Mpc. The distance and
luminosity make Maffei 1 the nearest giant elliptical galaxy. The radial
velocity of Maffei 1 is +66.4 +/- 5.0 km/s, significantly higher than the
accepted value of -10 km/s. The Hubble distance corresponding to the mean
velocity of Maffei 1, Maffei 2 and IC342 is 3.5 Mpc. Thus, it is unlikely that
Maffei 1 has had any influence on Local Group dynamics
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