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991.
A programmable microcomputer-based sonar echo processor has been developed and field tested to process echo data in real time. The device was designed for use in fisheries acoustics and to analyze echoes from the sea floor. The instrument simultaneously performs the functions "echo integration" and "echo peak detection' on the sonar signal. The "echo integration" circuitry measures the relative acoustic energy of the echo while the "echo peak detection' electronics measure the probability density function (PDF) of the peak of the echo envelope. Each process is gated so the echoes may be processed in many short time intervals. In fisheries applications, estimates can be made of fish density (fish per unit volume), average backscattering cross section, and a combination of fish size and behavior. When using the device to analyze bottom echoes, it is possible to measure both the returned energy from the bottom sediment interfaces and the microrelief characteristics. The durability, flexibility, computer link, and floppy-disk data-storage features of the system are discussed. Data are presented of the processed echoes from biological organisms and the ocean bottom from a recent research cruise on the Atlantic Ocean near Cape Hatteras, NC. The biological results illustrated the organisms to be clearly divided into two separate spatial distributions-an observation not obvious from a standard echogram which was simultaneously used. The results from the bottom showed both 1) the difference in sub-bottom structure between two locations and 2) changes in microrelief of the water-bottom interface between another pair of locations. 相似文献
992.
The propagation of dense electron beams and the interaction with the ambient plasmas are studied by using two-dimensional electrostatic simulations. When the width of the beam is of the order of electron gyro-radius, the beam electrons move across the magnetic field lines and the beam-plasma interaction becomes prominent with the reduced beam density. When the width of the beam is of the order of ion gyro-radius, the propagation of beam electrons is possible only with the formation of the ion channel. However, since the time scale of the ionic motion is much longer than that of the electronic motion, most of the beam electrons return back to the original beam injection region 相似文献
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D. Schwan F. Bertoldi S. Cho M. Dobbs R. Guesten N. W. Halverson W. L. Holzapfel E. Kreysa T. M. Lanting A. T. Lee M. Lueker J. Mehl K. Menten D. Muders M. Myers T. Plagge A. Raccanelli P. Schilke P. L. Richards H. Spieler M. White 《New Astronomy Reviews》2003,47(11-12):933
The APEX-SZ experiment is a sky survey designed to discover galaxy clusters via the Sunyaev–Zel’dovich effect at millimeter wavelengths. We describe the components of the instrument, including the 12 m Atacama Pathfinder Experiment telescope, optics, Transition-edge sensor bolometer array and SQUID readout. APEX-SZ will begin observations in 2004. 相似文献
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We previously described the genomic structure of the cytochrome P450 1A (CYP1A) gene from the hermaphroditic fish Rivulus marmoratus [Kim, I.-C., Kim, Y.J., Yoon, Y.-D, Kawamura, S., Lee, Y.-S., Lee, J.-S., 2004a. Cloning of cytochrome P450 1A (CYP1A) genes from the hermaphroditic fish Rivulus marmoratus and the Japanese medaka Oryzias latipes. Mar. Environ. Res. 58, 125–129]. To further characterize R. marmoratus CYP1A, we cloned the cDNA sequence of a CYP1A gene from this species and also expressed its recombinant protein in an E. coli system. We exposed R. marmoratus to 4-nonylphenol, and found a small induction of CYP1A mRNA in the treated animals. In this paper, we discuss the characteristics of R. marmoratus CYP1A gene as well as its potential use in a biomonitoring assay. 相似文献
999.
CHEN Weifeng CHEN Peirong XU Xisheng & ZHANG Min The State Key Laboratory of Mineral Deposit Research Department of Earth Sciences Nanjing University Nanjing China 《中国科学D辑(英文版)》2005,48(12):2104-2117
The South China, including Yangzi Craton and the Cathaysian Block, belongs to the southern part of East Asia continent. It borders Pacific plate on the east side and Qinling-Dabie Orogen on the north side. During the middle-late Cretaceous, a number of downfaulted red basins (the terrestrial sedimentary basins in Fig. 1) and volcanic- sedimentary basins had been developed in South China[1,2], in which the con-temporaneous basaltic rocks were generally distributed (Fig. 1). Although the … 相似文献
1000.
The polarity of the interplanetary magnetic field observed by the Mariner IV spacecraft is compared to the polarity of the photospheric magnetic field observed with the solar magnetograph at Mt. Wilson Observatory. Unlike the results obtained from observations during the flight of IMP-I, these polarities are not well correlated when the photospheric polarity is determined from data along a narrow latitudinal strip. It is suggested that the structure of the interplanetary field is often related to major features in the photospheric field that are observed over a broad range of solar latitudes. 相似文献