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861.
862.
Fast direct GPS P-Code acquisition 总被引:5,自引:0,他引:5
GPS P-Code has a higher chipping rate, better accuracy, and anti-jamming property than C/A code. Traditionally, GPS P-Code acquisition depends on handover from C/A code. This potentially needs long acquisition time. Moreover, when C/A code is not available, it is no longer possible to acquire GPS P-Code through handover from C/A code. The purpose of this paper is to describe a new overlap average method to facilitate hardware design of fast direct P-Code acquisition. It allows the rapid code phase search to acquire GPS P-Code signals, and also decreases the hardware resource requirement. The small size FFT in the proposed methods is very promising for fast FPGA hardware system design using FFT cores. The simulation results and theoretical analysis are included demonstrating the overall performance of the proposed method.
相似文献
Jing PangEmail: Phone: +1-916-2784549Fax: +1-916-2787215 |
863.
864.
Oliver Bujok Viceith Tan Erich Klein Ralf Nopper Reimar Bauer Andreas Engel Marie-Theres Gerhards Armin Afchine Daniel S. McKenna Ulrich Schmidt Frank G. Wienhold Horst Fischer 《Journal of Atmospheric Chemistry》2001,39(1):37-64
A novel fully-automated airborne gas chromatograph for in situmeasurements of long-lived stratospheric tracers hasbeen developed, combining the high selectivity of a megabore PLOTcapillary column with recently developed sampling and separationtechniques. The Gas cHromatograph for theObservation of Stratospheric Tracers (GHOST)has been successfully operated during three STREAM campaigns(Stratosphere TRoposphere Experiment byAirborne Measurement) onboard a Cessna Citation IIaircraft in two different modes: Either N2O andCF2Cl2(CFC-12) or CFC-12 and CFCl3 (CFC-11) have been measuredsimultaneously, with a time resolution of 2 min for both modes.Under flight conditions the instrument precision (1) forthese species is better than 0.9%, and the accuracy(1) is better than 2.0% of the tropospheric values ofall measured compounds. The detection limits (3) arebelow 28 ppb for N2O, 14 ppt for CFC-12, and 8 ppt forCFC-11, respectively, i.e., well below 10 % of the troposphericvalues of all measured compounds. Post-mission optimization of thechromatographic separation showed a possible enhancement of thetime resolution by up to a factor of 2, associated with acomparable increase in precision and detection limit. As test ofactual performance of GHOST results from an in-flight N2Ointercomparison with a tunable diode laser absorptionspectrometer (TDLAS) are presented. They yield an excellentagreement between both instruments. Furthermore, on the basis ofthe hitherto most extensive set of upper tropospheric and lowerstratospheric data, the relative stratospheric N22O lifetime isre-assessed. When referenced to the WMO reference CFC-11 lifetimeof 45 ± 7 years an N2O lifetime of 91 ± 15 yearsis derived, a value substantially smaller than the WMO referencelifetime of 120 years. Moreover, this value implies astratospheric N2O sink strength of 16.3 ± 2.7 Tg (N)yr–1 which is 30% larger than previous estimates. 相似文献
865.
Michael O. Garcia J. M. Rhodes Frank A. Trusdell Aaron J. Pietruszka 《Bulletin of Volcanology》1996,58(5):359-379
The Puu Oo eruption has been remarkable in the historical record of Kilauea Volcano for its duration (over 13 years), volume
(>1 km3) and compositional variation (5.7–10 wt.% MgO). During the summer of 1986, the main vent for lava production moved 3 km down
the east rift zone and the eruption style changed from episodic geyser-like fountaining at Puu Oo to virtually continuous,
relatively quiescent effusion at the Kupaianaha vent. This paper examines this next chapter in the Puu Oo eruption, episodes
48 and 49, and presents new ICP-MS trace element and Pb-, Sr-, and Nd-isotope data for the entire eruption (1983–1994). Nearly
aphyric to weakly olivine-phyric lavas were erupted during episodes 48 and 49. The variation in MgO content of Kupaianaha
lavas erupted before 1990 correlates with changes in tilt at the summit of Kilauea, both of which probably were controlled
by variations in Kilauea's magma supply rate. These lavas contain euhedral olivines which generally are in equilibrium with
whole-rock compositions, although some of the more mafic lavas which erupted during 1990, a period of frequent pauses in the
eruption, accumulated 2–4 vol.% olivine. The highest forsterite content of olivines (∼85%) in Kupaianaha lavas indicates that
the parental magmas for these lavas had MgO contents of ∼10 wt.%, which equals the highest observed value for lavas during
this eruption. The composition of the Puu Oo lavas has progressively changed during the eruption. Since early 1985 (episode
30), when mixing between an evolved rift zone magma and a more mafic summit reservoir-derived magma ended, the normalized
(to 10 wt.% MgO) abundances of highly incompatible elements and CaO have systematically decreased with time, whereas ratios
of these trace elements and Pb, Sr, and Nd isotopes, and the abundances of Y and Yb, have remained relatively unchanged. These
results indicate that the Hawaiian plume source for Puu Oo magmas must be relatively homogeneous on a scale of 10–20 km3 (assuming 5–10% partial melting), and that localized melting within the plume has apparently progressively depleted its incompatible
elements and clinopyroxene component as the eruption continued. The rate of variation of highly incompatible elements in Puu
Oo lavas is much greater than that observed for Kilauea historical summit lavas (e.g., Ba/Y 0.09 a–1 vs ∼0.03 a–1). This rapid change indicates that Puu Oo magmas did not mix thoroughly with magma in the summit reservoir. Thus, except
for variable amounts of olivine fractionation, the geochemical variation in these lavas is predominantly controlled by mantle
processes.
Received: 8 March 1996 / Accepted: 30 April 1996 相似文献
866.
H. Frank Morrison Yoram Shoham G. Michael Hoversten Carlos Torres-Verdín 《Geophysical Prospecting》1996,44(6):963-986
Sedimentary rocks beneath the Columbia River Basalt Group are recognized as having potential for oil and gas production, but the overlying layered basalts effectively mask seismic reflections from the underlying sediments. Four electromagnetic (EM) methods have been applied on profiles crossing Boylston Ridge, a typical east–west trending anticline of the Yakima Fold Belt, in an attempt to map the resistivity interface between the basalts and the sediments and to map variations in structure and resistivity within the sediments. The EM surveys detected strong variations in resistivity within the basalts, and in particular the continuous magnetotelluric array profiling (EMAP) revealed resistivity lows beneath the surface anticlines. These low resistivity zones probably coincide with fracturing in the core of the anticlines and they appear to correlate well with similar zones of low seismic velocity observed on a nearby seismic profile. The controlled-source EM surveys (in-loop transient, long-offset transient, and variable-offset frequency-domain) were designed in anticipation of relatively uniform high resistivity basalts, and were found to have been seriously distorted by the intrabasalt conductors discovered in the field. In particular, the resistivity sections derived from 1D inversions were found to be inconsistent and misleading. The EMAP survey provided the most information about the subsurface resistivity distribution, and was certainly the most cost-effective. However, both controlled-source and EMAP surveys call for accurate 2D or 3D inversion to accommodate the geological objectives of this project. 相似文献
867.
M. Frank A. Mangini R. Gersonde M. Rutgers van der Loeff G. Kuhn 《International Journal of Earth Sciences》1996,85(3):554-566
High-resolution records of the natural radionuclide230Th were measured in sediments from the eastern Atlantic sector of the Antarctic circumpolar current to obtain a detailed reconstruction
of the sedimentation history of this key area for global climate change during the late Quaternary. High-resolution dating
rests on the assumption that the230Thex flux to the sediments is constant. Short periods of drastically increased sediment accumulation rates (up to a factor of
8) were determined in the sediments of the Antarctic zone during the climate optima at the beginning of the Holocene and the
isotope stage 5e. By comparing expected and measured accumulation rate of230Thex, lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above
were calculated. We show that lateral contributions locally were up to 6.5 times higher than the vertical particle rain rates.
At other locations only 15% of the expected vertical particle rain rate were deposited. 相似文献
868.
Peter C. Burns Frank C. Hawthorne Anne M. Hofmeister Stephanie L. Moret 《Physics and Chemistry of Minerals》1996,23(3):141-150
A complete solid-solution series between cubic (Pm 3 m) KMgF3 and tetragonal (I4/mcm) KCuF3 was synthesized at 730–735 °C in an inert atmosphere. X-ray powder-diffraction at room temperature shows that the transition between the cubic and tetragonal perovskite structures in the series K (Mg1?xCux) F3 occurs at x ~ 0.6. Rietveld structure-refinements were done for selected compositions. In the cubic phase, all parameters are linear with composition up to the transition point. At the transition point, there is a strong discontinuity in the cell volume; this is strongly anisotropic with expansion along the a axes and contraction along the c axis due to a pronounced axial elongation of the (Mg, Cu) F6 octahedron that increases with increasing Cu content. The phase transition is first-order, with a discontinuity of ≈2% in the symmetry-breaking strain at xC. It is proposed that the phase transition in K (Mg, Cu) F3 is due to the onset of the cooperative Jahn-Teller effect. Compositional relationships for lattice vibrations in this solid solution were established using thin-film infrared spectroscopy. A phase transition occurring above 60 mole % KCuF3 is indicated by the appearance of one of the two modes expected for the tetragonal phase; the weaker mode is not resolved below 80 mole % KCuF3. Modes common to both structures vary smoothly and continuously across the binary; however, frequencies do not depend linearly on composition, nor is mode-softening discernable. Two-mode behaviour is observed only for the bending motion of the cubic phase, because this peak alone has non-overlapping end-member components. 相似文献
869.
Although possessing ancient and distinguished histories, the recent urbanization and planning approaches of Madrid, Rome and Athens are relatively unknown to English-speaking planners and urban geographers. This paper reviews the development of each city from the mid-19th century to the present. Special attention is given to the planning instruments developed in each city to guide growth. Each city experienced rapid growth over the past century because of its capital city functions. As a result of strong growth pressures, city planning policies were frequently subverted by private sector interests. Only in the latter part of the 20th century have planning measures become effective in controlling and directing urban growth. 相似文献
870.