573 research outputs found
WHOI acoustic telemetry project interim report 12/1/88 - 6/1/89
This interim report covers the progress of the acoustic telemetry project
during the period 12/1/88 to 5/15/89. In general, the work followed the
format specified in WHOI proposal No. 5674.1. The major exception was
the deletion of the transmitter array development task and a corresponding
funding decrease from 170,000. In addition, the period for the
funding was extended to June 30, partly due to a two month delay in project
startup.
The telemetry project was centered around the construction, programming
and testing of a digital receiver prototype capable of supporting future
signal processing algorithms in real-time over ocean acoustic channels. The
baseline receiver consists of a two-channel analog quadrature demodulator,
and interface to a multiprocessor receiver for digital signal processing.
The software developed includes routines for command and control of the
analog demodulator, data handling and formatting, and minimal software
to digitally implement an incoherent MFSK demodulator, synchronizer and
data decoder. Data storage and display programs were also completed to
facilitate the performance analysis of the unit during testing.
The system was tested in Woods Hole harbor at data rates up to 4800
bits/sec. The acoustic channel was time-dispersive Rayleigh fading, and
performance close to theoretical expectations was achieved. We are confident
that the system error behavior is arising from channel-caused effects and
known deficiencies in system performance, such as excessive synchronizer
steady-state jitter.Funding was provided by the Office of Naval Research
under contract Number N00014-86-K-0751, and
by the Charles Stark Draper Laboratory Inc
Design study for a moored surface-scanning sonar
This report contains the results of a design study for a surface scanning sonar instrument capable of long-term deployment on
ocean moorings. The instrument is intended to sample the bubble field just below the ocean's surface and compute the
backscattered intensity and Doppler velocity in small unit volumes. The principal motivation for the development of such an
instrument is to enhance the study of upper ocean processes by utilizing the ability of the sonar to detect surface waves and
Langmuir circulation. Important design parameters for the instrument are investigated and a detailed design proposed. Key technical
issues such as the trade-offs among spatial resolution, temporal resolution, velocity precision, total range, and power are discussed.
The azimuthal motion of the instrument on a mooring is considered as a potential problem, and possible solutions are discussed.
Matlab functions used for the investigations are included in an appendix.Funding was provided by a grant from the Webster Foundation to the
Woods Hole Oceanographic Institution
Ocean acoustical ray-tracing : Software Ray
A new computer program for accurate calculation of acoustic ray paths through a range-varing ocean sound channel has been
written. It is based on creating a model of the speed of sound in the ocean, consistent with input data, that produces the smoothest
possible wavefronts. This scheme eliminates "false caustics" from the wavefront. It may be useful in calculating an approximate
solution to the full wave equation at megameter ranges.Funding was provided by the Office of Naval Research under contract N00014-86-C-0358 and the
Office of Naval Technology under contract N00014-90-C-0098
Inversion of surficial sediment thickness from under-ice acoustic transmission measurement
Author Posting. © Acoustical Society of America, 2021. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 149(1), (2021): 371, https://doi.org/10.1121/10.0003328.The under-ice acoustic transmission experiment of 2013, conducted under ice cover in the Fram Strait, was analyzed for bottom interactions for the purpose of developing a model of the seabed. Using the acoustic signals, as well as data from other sources, including cores, gravimetric, refraction, and seismic surveys, it was deduced that the seabed may be modeled as a thin surficial layer overlaid on a deeper sediment. The modeling was based on the Biot–Stoll model for acoustic propagation in porous sediments, aided by more recent developments that improve parameter estimation and depth dependence due to consolidation. At every stage, elastic and fluid approximations were explored to simplify the model and improve computational efficiency. It was found the surficial layer could be approximated as a fluid, but the deeper sediment required an elastic model. The full Biot–Stoll model, while instrumental in guiding the model construction, was not needed for the final computation. The model could be made to agree with the measurements by adjusting the surficial layer thickness.The fieldwork was performed under funding from the Research Council of Norway through the UNDER-ICE (Grant No. 226373) project and ENGIE E&P Norway providing additional support. This analysis was supported by the United States Office of Naval Research, Ocean Acoustics Program.2021-07-1
Asymptotic analysis of the model for distribution of high-tax payers
The z-transform technique is used to investigate the model for distribution
of high-tax payers, which is proposed by two of the authors (K. Y and S. M) and
others. Our analysis shows an asymptotic power-law of this model with the
exponent -5/2 when a total ``mass'' has a certain critical value. Below the
critical value, the system exhibits an ordinary critical behavior, and scaling
relations hold. Above the threshold, numerical simulations show that a
power-law distribution coexists with a huge ``monopolized'' member. It is
argued that these behaviors are observed universally in conserved aggregation
processes, by analizing an extended model.Comment: 5pages, 3figure
Analysis of and workarounds for element reversal for a finite element-based algorithm for warping triangular and tetrahedral meshes
We consider an algorithm called FEMWARP for warping triangular and
tetrahedral finite element meshes that computes the warping using the finite
element method itself. The algorithm takes as input a two- or three-dimensional
domain defined by a boundary mesh (segments in one dimension or triangles in
two dimensions) that has a volume mesh (triangles in two dimensions or
tetrahedra in three dimensions) in its interior. It also takes as input a
prescribed movement of the boundary mesh. It computes as output updated
positions of the vertices of the volume mesh. The first step of the algorithm
is to determine from the initial mesh a set of local weights for each interior
vertex that describes each interior vertex in terms of the positions of its
neighbors. These weights are computed using a finite element stiffness matrix.
After a boundary transformation is applied, a linear system of equations based
upon the weights is solved to determine the final positions of the interior
vertices. The FEMWARP algorithm has been considered in the previous literature
(e.g., in a 2001 paper by Baker). FEMWARP has been succesful in computing
deformed meshes for certain applications. However, sometimes FEMWARP reverses
elements; this is our main concern in this paper. We analyze the causes for
this undesirable behavior and propose several techniques to make the method
more robust against reversals. The most successful of the proposed methods
includes combining FEMWARP with an optimization-based untangler.Comment: Revision of earlier version of paper. Submitted for publication in
BIT Numerical Mathematics on 27 April 2010. Accepted for publication on 7
September 2010. Published online on 9 October 2010. The final publication is
available at http://www.springerlink.co
A Novel Heat Shock Transcription Factor Family in <i>Entamoeba histolytica</i>
The HSTF is a master molecule involved in the transcriptional control of several genes during different types of stress. This transcription factor is a very conserved protein identified in different organisms from bacterial to human. <i>Entamoeba histolytica</i> is the protozoan responsible for the human amoebiasis. This parasite is exposed to different kind of stress as changes in the pH, temperature, drugs, all that situations in where the parasite needs survive. Here we identified and isolated a novel gene family of HSTFs in the protozoan parasite <i>E. histolytica</i>. Three members that we called <i>Ehhstf1</i>, <i>Ehhstf2</i> and <i>Ehhstf3</i> compose this family. Amino acid alignments and domain architecture analysis revealed that the EhHSTFs presents a conserved DNA-binding domain composed of approximately 25 residues. Interestingly this domain is shorter than the domain of the human, mouse and yeast HSTFs. Heterologous antibodies recognized four peptides of 73, 66, 47 and 23 kDa in total extracts from trophozoites growth under normal conditions. The 73, 47 and 23 kDa peptides increased their intensity when the cells were growth at 42°C by 2 h. All results together demonstrate that the amoeba present HSTFs, which may be, controlled the gene expression of this parasite under different stress situations
Smoothed Particle Hydrodynamics simulations of white dwarf collisions and close encounters
The collision of two white dwarfs is a quite frequent event in dense stellar
systems, like globular clusters and galactic nuclei. In this paper we present
the results of a set of simulations of the close encounters and collisions of
two white dwarfs. We use an up- to-date smoothed particle hydrodynamics code
that incorporates very detailed input physics and an improved treatment of the
artificial viscosity. Our simulations have been done using a large number of
particles (~ 4 \times 10^5) and covering a wide range of velocities and initial
distances of the colliding white dwarfs. We discuss in detail when the initial
eccentric binary white dwarf survives the closest approach, when a lateral
collision in which several mass transfer episodes occur is the outcome of the
newly formed binary system, and which range of input parameters leads to a
direct collision, in which only one mass transfer episode occurs. We also
discuss the characteristics of the final configuration and we assess the
possible observational signatures of the merger, such as the associated
gravitational waveforms and the fallback luminosities. We find that the overall
evolution of the system and the main characteristics of the final object agree
with those found in previous studies. We also find that the fallback
luminosities are close to 10^48 erg/s. Finally, we find as well that in the
case of lateral and direct collisions the gravitational waveforms are
characterized by large-amplitude peaks which are followed by a ring-down phase,
while in the case in which the binary white dwarf survives the closest
approach, the gravitational pattern shows a distinctive behavior, typical of
eccentric systems.Comment: 16 pages, 12 figures. Accepted for publication in MNRA
Genome resequencing reveals multiscale geographic structure and extensive linkage disequilibrium in the forest tree Populus trichocarpa
This is the publisher’s final pdf. The article is copyrighted by the New Phytologist Trust and published by John Wiley & Sons, Inc. It can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291469-8137. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.•Plant population genomics informs evolutionary biology, breeding, conservation and bioenergy feedstock development. For example, the detection of reliable phenotype–genotype associations and molecular signatures of selection requires a detailed knowledge about genome-wide patterns of allele frequency variation, linkage disequilibrium and recombination.\ud
•We resequenced 16 genomes of the model tree Populus trichocarpa and genotyped 120 trees from 10 subpopulations using 29 213 single-nucleotide polymorphisms.\ud
•Significant geographic differentiation was present at multiple spatial scales, and range-wide latitudinal allele frequency gradients were strikingly common across the genome. The decay of linkage disequilibrium with physical distance was slower than expected from previous studies in Populus, with r² dropping below 0.2 within 3–6 kb. Consistent with this, estimates of recent effective population size from linkage disequilibrium (N[subscript e] ≈ 4000–6000) were remarkably low relative to the large census sizes of P. trichocarpa stands. Fine-scale rates of recombination varied widely across the genome, but were largely predictable on the basis of DNA sequence and methylation features.\ud
•Our results suggest that genetic drift has played a significant role in the recent evolutionary history of P. trichocarpa. Most importantly, the extensive linkage disequilibrium detected suggests that genome-wide association studies and genomic selection in undomesticated populations may be more feasible in Populus than previously assumed
Blue straggler stars in dwarf spheroidal galaxies
Blue straggler star (BSS) candidates have been observed in all old dwarf
spheroidal galaxies (dSphs), however whether or not they are authentic BSSs or
young stars has been a point of debate. To both address this issue and obtain a
better understanding of the formation of BSSs in different environments we have
analysed a sample of BSS candidates in two nearby Galactic dSphs, Draco and
Ursa Minor. We have determined their radial and luminosity distributions from
wide field multicolour imaging data extending beyond the tidal radii of both
galaxies.
BSS candidates are uniformly distributed through the host galaxy, whereas a
young population is expected to show a more clumpy distribution. Furthermore,
the observed radial distribution of BSSs, normalized to both red giant branch
(RGB) and horizontal branch (HB) stars, is almost flat, with a slight decrease
towards the centre. Such a distribution is at odds with the predictions for a
young stellar population, which should be more concentrated. Instead, it is
consistent with model predictions for BSS formation by mass transfer in
binaries (MT-BSSs). Such results, although not decisive, suggest that these
candidates are indeed BSSs and that MT-BSSs form in the same way in Draco and
Ursa Minor as in globular clusters. This favours the conclusion that Draco and
Ursa Minor are truly 'fossil' galaxies, where star formation ceased completely
more than 8 billion years ago.Comment: 16 pages, 10 figures, MNRAS, in pres
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