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  • Communications and Radar  (9)
  • *Protons  (1)
  • Cytoplasm/metabolism  (1)
  • Fluctuations  (1)
  • Geosciences (General)  (1)
  • 2005-2009  (12)
  • 1
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    Sound scattering by several zooplankton groups. I. Experimental determination of dominant scattering mechanisms (2008)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 1998. 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 103 (1998): 225-235, doi:10.1121/1.421469.
    Description: The acoustic scattering properties of live individual zooplankton from several gross anatomical groups have been investigated. The groups involve (1) euphausiids (Meganyctiphanes norvegica) whose bodies behave acoustically as a fluid material, (2) gastropods (Limacina retroversa) whose bodies include a hard elastic shell, and (3) siphonophores (Agalma okeni or elegans and Nanomia cara) whose bodies contain a gas inclusion (pneumatophore). The animals were collected from ocean waters off New England (Slope Water, Georges Bank, and the Gulf of Maine). The scattering properties were measured over parts or all of the frequency range 50 kHz to 1 MHz in a laboratory-style pulse-echo setup in a large tank at sea using live fresh specimens. Individual echoes as well as averages and ping-to-ping fluctuations of repeated echoes were studied. The material type of each group is shown to strongly affect both the overall echo level and pattern of the target strength versus frequency plots. In this first article of a two-part series, the dominant scattering mechanisms of the three animal types are determined principally by examining the structure of both the frequency spectra of individual broadband echoes and the compressed pulse (time series) output. Other information is also used involving the effect on overall levels due to (1) animal orientation and (2) tissue in animals having a gas inclusion (siphonophores). The results of this first paper show that (1) the euphausiids behave as weakly scattering fluid bodies and there are major contributions from at least two parts of the body to the echo (the number of contributions depends upon angle of orientation and shape), (2) the gastropods produce echoes from the front interface and possibly from a slow-traveling circumferential (Lamb) wave, and (3) the gas inclusion of the siphonophore dominates the echoes, but the tissue plays a role in the scattering and is especially important when analyzing echoes from individual animals on a ping-by-ping basis. The results of this paper serve as the basis for the development of acoustic scattering models in the companion paper [Stanton et al., J. Acoust. Soc. Am. 103, 236–253 (1998)].
    Description: This work was supported by the National Science Foundation Grant No. OCE- 9201264, the U.S. Office of Naval Research Grant Nos. N00014-89-J-1729 and N00014-95-1-0287, and the MIT/ WHOI Joint Graduate Education Program.
    Keywords: Bioacoustics ; Acoustic wave scattering ; Fluctuations
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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    PAPER (OA)
  • 2
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    Mechanism of Na+/H+ antiporting (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-08-11
    Description: Na+/H+ antiporters are central to cellular salt and pH homeostasis. The structure of Escherichia coli NhaA was recently determined, but its mechanisms of transport and pH regulation remain elusive. We performed molecular dynamics simulations of NhaA that, with existing experimental data, enabled us to propose an atomically detailed model of antiporter function. Three conserved aspartates are key to our proposed mechanism: Asp164 (D164) is the Na+-binding site, D163 controls the alternating accessibility of this binding site to the cytoplasm or periplasm, and D133 is crucial for pH regulation. Consistent with experimental stoichiometry, two protons are required to transport a single Na+ ion: D163 protonates to reveal the Na+-binding site to the periplasm, and subsequent protonation of D164 releases Na+. Additional mutagenesis experiments further validated the model.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Arkin, Isaiah T -- Xu, Huafeng -- Jensen, Morten O -- Arbely, Eyal -- Bennett, Estelle R -- Bowers, Kevin J -- Chow, Edmond -- Dror, Ron O -- Eastwood, Michael P -- Flitman-Tene, Ravenna -- Gregersen, Brent A -- Klepeis, John L -- Kolossvary, Istvan -- Shan, Yibing -- Shaw, David E -- New York, N.Y. -- Science. 2007 Aug 10;317(5839):799-803.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉D. E. Shaw Research, New York, NY 10036, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17690293" target="_blank"〉PubMed〈/a〉
    Keywords: Aspartic Acid/metabolism ; Binding Sites ; Computer Simulation ; Crystallization ; Cytoplasm/metabolism ; Escherichia coli/growth & development/*metabolism ; Escherichia coli Proteins/*chemistry/*metabolism ; Hydrogen Bonding ; Hydrogen-Ion Concentration ; Ion Transport ; *Models, Biological ; Models, Molecular ; Mutagenesis ; Periplasm/metabolism ; Protein Conformation ; Protein Structure, Secondary ; *Protons ; Sodium/*metabolism ; Sodium-Hydrogen Antiporter/*chemistry/*metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 3
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    Spaceborne Doppler Radar Measurements of Rainfall: Correction of Errors Induced by Pointing Uncertainties (2005)
    In:  Other Sources
    Details
    Publication Date: 2018-06-11
    Description: In this paper a sea surface radar echo spectral analysis technique to correct for the rainfall velocity error caused by radar-pointing uncertainty is presented. The correction procedure is quite straightforward when the radar is observing a homogeneous rainfall field. When nonuniform beam filling (NUBF) occurs and attenuating frequencies are used, however, additional steps are necessary in order to correctly estimate the antenna-pointing direction. This new technique relies on the application of the combined frequency-time (CFT) algorithm to correct for uneven attenuation effects on the observed sea surface Doppler spectrum. The performance of this correction technique was evaluated by a Monte Carlo simulation of the Doppler precipitation radar backscatter from high-resolution 3D rain fields (either generated by a cloud resolving numerical model or retrieved from airborne radar measurements). The results show that the antenna-pointing-induced error can, indeed, be reduced by the proposed technique in order to achieve 1 m s(exp -1) accuracy on rainfall vertical velocity estimates.
    Keywords: Communications and Radar
    Type: Journal of Atmospheric and Oceanic Technology; Volume 22; Issue 11; 1676-1690
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Second-order multiple-scattering theory associated with backscattering enhancement for a millimeter wavelength weather radar with a finite beam width (2005)
    In:  Other Sources
    Details
    Publication Date: 2018-06-11
    Description: Effects of multiple scattering on reflectivity are studied for millimeter wavelength weather radars. A time-independent vector theory, including up to second-order scattering, is derived for a single layer of hydrometeors of a uniform density and a uniform diameter. In this theory, spherical waves with a Gaussian antenna pattern are used to calculate ladder and cross terms in the analytical scattering theory. The former terms represent the conventional multiple scattering, while the latter terms cause backscattering enhancement in both the copolarized and cross-polarized components. As the optical thickness of the hydrometeor layer increases, the differences from the conventional plane wave theory become more significant, and essentially, the reflectivity of multiple scattering depends on the ratio of mean free path to radar footprint radius. These results must be taken into account when analyzing radar reflectivity for use in remote sensing.
    Keywords: Communications and Radar
    Type: Radio Science; Volume 40
    Format: text
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  • 5
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    Dual-frequency precipitation radar observations in CAMEX-4 and Wakasa Bay Experiments (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: Communications and Radar
    Type: Precipitation Measurement Missions Science Team Meeting; Dec 12, 2005 - Dec 15, 2005; Monterey, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    A Range Compensating Feed Motion Concept for Spaceborne Radar (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Tropical cyclones can cause major loss of both life and property, so that improvements in forecasting motion, intensity, and rainfall are needed. Such forecasting requires accurate measurements of the current state of the cyclone. Ground-based Doppler radars have long been used as an effective means of monitoring severe precipitating storms. Because of the oceanic nature of tropical cyclones, remote monitoring from space is desirable. Recently, the Precipitation Radar (PR) [1] aboard the Tropical Rainfall Measuring Mission (TRMM) [2] satellite has demonstrated an unprecedented capacity for 3-D imaging of precipitating storms. Nonetheless, due to the relatively long TRMM return cycle (less than once per day) the value of PR data has primarily been limited to the understanding of climatological properties of tropical cyclones [3]. The return cycle can be substantially reduced by sensing from a geostationary platform.
    Keywords: Communications and Radar
    Type: IEEE International Symposium on Antennas and Propagation; Jul 03, 2005; Washington, DC; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Time-dependent Second Order Scattering Theory for Weather Radar with a Finite Beam Width (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Multiple scattering effects from spherical water particles of uniform diameter are studied for a W-band pulsed radar. The Gaussian transverse beam-profile and the rectangular pulse-duration are used for calculation. An second-order analytical solution is derived for a single layer structure, based on a time-dependent radiative transfer theory as described in the authors' companion paper. When the range resolution is fixed, increase in footprint radius leads to increase in the second order reflectivity that is defined as the ratio of the second order return to the first order one. This feature becomes more serious as the range increases. Since the spaceborne millimeter-wavelength radar has a large footprint radius that is competitive to the mean free path, the multiple scattering effect must be taken into account for analysis.
    Keywords: Communications and Radar
    Type: International Geoscience and Remote Sensing Symposium (IGARSS); Jul 31, 2006 - Aug 04, 2006; Denver, CO; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Very Long Microstrip Array Feeds of a Membrane Reflector for the Advanced Precipitation Radar (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Very long microstrip arrays have been developed at the Ku- and Ka-band frequencies. Each array having an electrical length of about 110 free-space wavelengths is used to feed a deployable thin-membrane cylindrical reflector for a spaceborne precipitation radar application. These arrays, designed for 0(deg) and 30(deg) beam directions, achieved peak sidelobes of -20 dB and average sidelobes below -30 dB with peak cross-pol levels below -20 dB. Several unique challenges were encountered during the development of these very long arrays, such as the strong coupling between very long power divider lines, the strong leakage radiation from the lengthy transmission lines, and the lack of computer analysis capability of these electrically large arrays.
    Keywords: Communications and Radar
    Type: IEEE Antennas and Propagation Symposium; Jul 05, 2005 - Jul 09, 2005; Washington, DC; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Piezoelectric Polymers Actuators for Precise Shape Control of Large Scale Space Antennas (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Extremely large, lightweight, in-space deployable active and passive microwave antennas are demanded by future space missions. This paper investigates the development of PVDF based piezopolymer actuators for controlling the surface accuracy of a membrane reflector. Uniaxially stretched PVDF films were poled using an electrodeless method which yielded high quality poled piezofilms required for this application. To further improve the piezoperformance of piezopolymers, several PVDF based copolymers were examined. It was found that one of them exhibits nearly three times improvement in the in-plane piezoresponse compared with PVDF and P(VDF-TrFE) piezopolymers. Preliminary experimental results indicate that these flexible actuators are very promising in controlling precisely the shape of the space reflectors.
    Keywords: Communications and Radar
    Type: SPIE Smart Structures and Materials and Nondestruvtive Evaluation and Health Monitoring; Mar 18, 2007 - Mar 22, 2007; San Diego, CA; United States
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    NASA TECHNICAL REPORTS
  • 10
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    Cloud profiling radar for the CloudSat Mission (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The CloudSat Mission is a new satellite mission jointly developed by NASA, JPL, the Canadian Agency, Colorado State University, and the US AirForce to acquire a global data set of vertical cloud structure and its variability.
    Keywords: Communications and Radar
    Type: 2005 IEEE International Radar Conference; May 09, 2005 - May 12, 2005; Arlington, VA; United States
    Format: text
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