James M. Stephens

Nonuniform Effective Temperatures in Ising Models on Tangled Chains

Abstract Exact solutions are presented for the partition function of a tangled Ising chain in a magnetic field. The tangled geometry introduces additional bonds at knots that couple otherwise distant pairs of spins across (not along) the chain. These additional bonds are introduced as a form of perfectly correlated disorder, and then their effects on the spin correlation are studied.

Source characterization study 2007: The three‐dimensional primary field of a seismic airgun array.

During September 2007 the Littoral Acoustic Demonstration Center collected acoustic and related data from three moored arrays and ship‐deployed hydrophones spanning the full water column to measure the 3‐D acoustic field of a seismic airgun array. A seismic source vessel shot a series of lines to give detailed angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total energy spectra, one‐third octave band, and source directivity analyses are measures used to characterize the field. Three‐dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Three‐dimensional visualizations are being developed using a visualization cave and software for 2‐D cave emulation. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]

The source characterization study 2007: A detailed three dimensional acoustic field measurement of a seismic airgun array.

In September 2007 the Littoral Acoustic Demonstration Center (LADC) collected acoustic and related data from three moored arrays and ship‐deployed hydrophones spanning the full water column to measure the three‐dimensional acoustic field of a seismic airgun array. The seismic source vessel shot a series of lines to give a detailed angle and range information concerning the field. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, and one‐third octave band analyses are measures used to characterize the field. Three dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Both the direct and indirect fields are characterized. Moveout analysis is done to delineate arrivals and to detect ducted and interface waves. [Research supported by the International Association of Oil and Gas Producers.]

Environmental acoustic recording system (EARS) buoys for marine animal acoustics.

EARS buoys were developed as autonomous, moored, underwater recording systems by the Naval Oceanographic Office (NAVOCEANO) to make long‐term ocean ambient noise measurements. When the Littoral Acoustic Demonstration Center (LADC) was formed as a consortium of university and U.S. Navy scientists in 2001, the buoys were capable of measuring up to 1000 Hz for 1 yr. LADC added listening to sperm whales to its noise and propagation measurements. NAVOCEANO quickly modified the buoys to measure up to 5859 Hz for 36 days. The buoys, moored at depths from 550 to 950 m in the Gulf of Mexico, produced exceptionally clear recordings of sperm whale echolocation and coda clicks and recordings of other whales. EARS Generation 2 buoys are now capable of recording one channel to 96 kHz, or four channels to 25 kHz, for more than 13 days on four 120 Gbyte notebook disk drives. Experiments in the Gulf of Mexico and the Ligurian Sea have targeted both sperm and beaked whales. Audio results and visualizations of these recordi...

Experimental design for acoustic characterization of a seismic exploration airgun array

The Littoral Acoustic Demonstration Center (LADC) (participating institutions given in author list) is scheduled to perform an experiment in the Gulf of Mexico to characterize the underwater acoustic field of a seismic exploration airgun array. The design is constrained by the array lengths and hydrophone spacings of the ten four‐channel LADC calibrated environmental acoustic recording system (EARS) buoys available for the measurements. Placement of the EARS arrays is determined to achieve best the design goals, given the constraints. The fixed mooring EARS hydrophone depths will vary from 100 to 1171 m, and near‐surface ship‐deployed phones will be used for shallower depths. Straight‐line source boat paths of varying length and spacing have been calculated that redundantly fill all solid angle bins whose size is determined by small uncertainties in the array location and orientation [Robert Laws (2006), private communication]. Shot spacing is also a factor. Care is taken to have nearby shots to the EARS ...

Time and frequency analysis of seismic airgun calibration data from an environmental acoustic recording system (EARS) buoy

In the summer of 2003 two Environmental Acoustic Recording System (EARS) buoys were deployed in the northern Gulf of Mexico by the Littoral Acoustic Demonstration Center. The buoys were collocated and recorded ambient noise and seismic airgun array shots up to approximately 25 kHz. The gains and hydrophone sensitivities were set such that one EARS buoy could record the seismic shots without clipping and the other could record ambient noise. The M/V Kondor towed an airgun array on parallel linear tracks with horizontal closest points of approach to the buoy of 0, 500, 1000, 2000, and 5000 m, giving experimental data for a wide range of horizontal distances (up to 7 km) and arrival angles. The raw data were calibrated using the EARS system parameters to produce calibrated pressure time series for each shot. These data are analyzed in both the time and frequency domains. Maximum pressures for each shot as well as sound exposure levels (pressure squared integrated over time for 200 ms in this case) are presen...

Environmental Acoustic Recording System (EARS) in the Gulf of Mexico

The Littoral Acoustic Demonstration Center (LADC) was formed in early 2001 to utilize Environmental Acoustic Recording System (EARS) buoys developed by the Naval Oceanographic Office (NAVOCEANO) which has provided technical guidance and support to LADC. The purpose of LADC is to make environmental measurements, which is not part of the mission of NAVOCEANO. This chapter describes the Gulf of Mexico marine mammal measurements and related data analysis of LADC. LADC has also used the buoys to characterize the three-dimensional acoustic field of a seismic airgun array and to analyze the noise due to nearby storms. LADC is a consortium of scientists from universities and the U.S. Navy. The following institutions are or have been represented: initially, the University of New Orleans, the University of Southern Mississippi, and the Naval Research Laboratory-Stennis Space Center; and then the University of Louisiana at Lafayette, the Applied Research Laboratories at the University of Texas at Austin, and Oregon State University. The scientists are listed in the first section of the chapter. A technical overview of EARS technology is given in Sect. 6.2. The current Generation 2 EARS buoys can record four channels of up to 25 kHz each or one channel up to 96 kHz.

Three-dimensional primary acoustic field characterization for a seismic airgun array

The Littoral Acoustic Demonstration Center conducted the Source Characterization Study in 2007 (SCS07) to measure the 3-D acoustic field of a seismic airgun array in the Gulf of Mexico. Three moorings with sensitive and desensitized hydrophones at different depths were deployed as well as hydrophones suspended from a ship, while a seismic source vessel shot specified lines. Hydrophone positions were measured. Peak pressures, RMS sound pressure levels (SPL), sound exposure levels, total shot energy spectra, one-third octave band analyses, and source directivity studies are used to characterize the field. Summary results are first calculated for each hydrophone. These are then combined to give isopleths for azimuthal cuts at 0, 45, 90 degrees, etc., for the spatial domain measures. Plots for each solid angle bin give these and frequency measures analyzed versus range. Zero-to-peak pressures directly under the array go from 210 dB for depths less than 200 m down to 195 dB at 1200 m. At 2000 m horizontal rang...

The measured 3-D primary acoustic field of a seismic airgun array

The Littoral Acoustic Demonstration Center has conducted an experiment to measure the 3-D acoustic field of a seismic airgun array in the Gulf of Mexico. A seismic source vessel shot specified lines to give solid angle and range information. Hydrophone positions were measured by an ultra-short baseline (USBL) acoustic system while the source ship was turning between lines. An acoustic Doppler current profiler measured currents so the positions could be modeled between USBL measurements. The position locations were refined by using information from the acoustic arrival times on the hydrophones. Peak pressures, sound exposure levels, total shot energy spectra, one-third octave band analyses, and source directivity studies are used to characterize the field. One third octave band analysis shows received levels up to 180 dB re 1 µP for emission angles from 0 degrees (vertically down) up to 45 degrees for horizontal ranges up to 200 m at endfire, between 10 Hz and 200 Hz. The levels decrease with increasing fr...

Experimental determination of the three‐dimensional primary field of a seismic airgun array.

The Littoral Acoustic Demonstration Center (LADC) recorded acoustic and related data on three moored arrays and ship‐deployed hydrophones, which together spanned the full water column to measure the 3‐D acoustic field of a seismic airgun array, in September 2007. The seismic source vessel shot specified lines to give detailed solid angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, one‐third octave band analyzes, and source directivity studies are used to characterize the field. Three‐dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Longer lines were shot for propagation analyzes. Source signatures from NUCLEUS and GUNDALF are used in propagation modeling. [Research supported by the Joint Industry Programme through the International Association of Oil a...