Biomedical subjects

JF Lynch

Publications and source records attributed to JF Lynch.

6 recordsLinked to original sources

PubMed2000

Tomographic inversion for sediment parameters in shallow water

This article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources. The experimental data used for the inversions are SUS charge explosions acquired on a vertical hydrophone array during the Shelf Break Primer Experiment conducted south of New England in the Middle Atlantic Bight in August 1996. The SUS signals were analyzed for their time-frequency behavior using wavelets. The group speed dispersion curves were obtained from the wavelet scalogram of the SUS signals. A genetic algorithm (GA) was used for the inversion of sound speeds in the water column and compressional wave speeds in the sediment layers. The variations in the sound speeds in the water column were represented using empirical orthogonal functions (EOFs). A range-independent normal mode routine was used to construct the replica fields corresponding to the parameters. Comparison of group speeds for modes 1 to 9 and for a range of frequencies 8 to 200 Hz was used to arrive at the best parameter fit. An efficient hybrid optimization scheme using the GA and a Levenberg-Marquardt algorithm is presented. Linear perturbation methods were also used to "fine tune" the inversions and to obtain resolution and variance estimates. Analysis was also done to compute the degree of convergence of each of the parameters by explicitly calculating the Hessian matrices numerically. A posteriori estimation of mean and covariance was also done to obtain error estimates. Group speeds for the inverted sound speed fields provide an excellent match to the experimental data. The inverted sediment compressional speed profile compares well with in situ measurements.

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PubMed2000

Acoustic field variability induced by time evolving internal wave fields

A space- and time-dependent internal wave model was developed for a shallow water area on the New Jersey continental shelf and combined with a propagation algorithm to perform numerical simulations of acoustic field variability. This data-constrained environmental model links the oceanographic field, dominated by internal waves, to the random sound speed distribution that drives acoustic field fluctuations in this region. Working with a suite of environmental measurements along a 42-km track, a parameter set was developed that characterized the influence of the internal wave field on sound speed perturbations in the water column. The acoustic propagation environment was reconstructed from this set in conjunction with bottom parameters extracted by use of acoustic inversion techniques. The resulting space- and time-varying sound speed field was synthesized from an internal wave field composed of both a spatially diffuse (linear) contribution and a spatially localized (nonlinear) component, the latter consisting of solitary waves propagating with the internal tide. Acoustic simulation results at 224 and 400 Hz were obtained from a solution to an elastic parabolic equation and are presented as examples of propagation through this evolving environment. Modal decomposition of the acoustic field received at a vertical line array was used to clarify the effects of both internal wave contributions to the complex structure of the received signals.

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PubMed2000

Modeling mode arrivals in the 1995 SWARM experiment acoustic transmissions

As part of the Shallow Water Acoustics in a Random Medium (SWARM) experiment, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. A 400-Hz acoustic tomography source was moored some 32-km shoreward of this array, such that an acoustic path was created that was anti-parallel to the primary propagation direction for shelf-generated internal wave solitons. The presence of these soliton internal waves in the acoustic waveguide causes significant coupling of energy between propagating acoustic modes, creating fluctuations in modal intensities and modal peak arrival times, as well as time spreading of the pulses. Two methods by which acoustic propagation and scattering in soliton-filled waveguides can be modeled are presented here in order to understand and explain the scattering observed in the SWARM field data. The first method utilizes the Preisig and Duda [IEEE J. Ocean. Eng. 22, 256-269 (1997)] Sudden Interface Approximation (SIA) to represent the solitons. The second method, which is computationally slower, uses a finely meshed, "propagated" thermistor record to simulate the solitons in the SWARM experiment waveguide. Both numerical methods are found to generate scattering characteristics that are similar to the SWARM field data.

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PubMed2000

Acoustic normal mode fluctuation statistics in the 1995 SWARM internal wave scattering experiment

In order to understand the fluctuations imposed upon low frequency (50 to 500 Hz) acoustic signals due to coastal internal waves, a large multilaboratory, multidisciplinary experiment was performed in the Mid-Atlantic Bight in the summer of 1995. This experiment featured the most complete set of environmental measurements (especially physical oceanography and geology) made to date in support of a coastal acoustics study. This support enabled the correlation of acoustic fluctuations to clearly observed ocean processes, especially those associated with the internal wave field. More specifically, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. Tomography sources of 224 Hz and 400 Hz were moored 32 km directly shoreward of this array, such that an acoustic path was constructed that was anti-parallel to the primary, onshore propagation direction for shelf generated internal wave solitons. These nonlinear internal waves, produced in packets as the tide shifts from ebb to flood, produce strong semidiurnal effects on the acoustic signals at our measurement location. Specifically, the internal waves in the acoustic waveguide cause significant coupling of energy between the propagating acoustic modes, resulting in broadband fluctuations in modal intensity, travel-time, and temporal coherence. The strong correlations between the environmental parameters and the internal wave field include an interesting sensitivity of the spread of an acoustic pulse to solitons near the receiver.

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PubMed1998

Hereditary Factors in Gynecologic Cancer.

Cancer predisposition in some families is known to be the result of germ-line mutations. The most noteworthy hereditary gynecologic cancer syndromes include hereditary breast-ovarian cancer (HBOC) syndrome, wherein BRCA1 and BRCA2 germ-line mutations have been identified, and hereditary nonpolyposis colorectal cancer (HNPCC) of the Lynch syndrome II variant, wherein hMSH2, hMLH1, hPMS2, hMSH3, and hMSH6 germ-line mutations have been identified. DNA testing for specific cancer-associated germ-line mutations is now available for HBOC and HNPCC syndrome family members who are in the direct line of inheritance. Genetic counseling is mandatory prior to DNA testing and at the time of disclosure of findings. A patient found to be negative for the family's particular cancer-associated germ-line mutation can revert to general population screening recommendations. When a deleterious mutation is identified, the physician is able to predict a patient's lifetime susceptibility to breast and ovarian carcinomas in the HBOC syndrome or the cancers which characterize the Lynch syndrome II variant of HNPCC, particularly carcinomas of the colon, endometrium, and ovary. Management strategies can be offered which are designed to take advantage of the natural history of that distinct hereditary cancer syndrome. We discuss the unfolding developments concerning familial and heritable susceptibilities, molecular genetics, and possible carcinogenic co-factors of the three most common gynecologic cancers: carcinomas of the uterine cervix, endometrium, and ovary. We offer rationales for management based on current epidemiologic and clinical data and emerging technologies.

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PubMed1996

The Lynch Syndrome: Melding Natural History and Molecular Genetics to Genetic Counseling and Cancer Control.

Hereditary nonpolyposis colorectal cancer (HNPCC), also referred to as Lynch syndromes I and II, is an autosomal, dominantly inherited disorder that accounts for approximately 5% of all colorectal cancers. While colorectal cancer is the most frequently occurring malignancy in HNPCC, other types of cancer occur with increased statistical significance. A better understanding of its natural history, particularly early age of onset and the pattern of multiple primary cancer excess, is essential for the diagnosis and management of HNPCC.

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