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921.
922.
The motion and the drift force of a floating OWC (oscillating water column) wave energy device in regular waves are studied taking account of the oscillating surface-pressure due to the pressure drop across the duct of the air chamber. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine-type Green function while the outer problem with the Kelvin-type Green function. The added mass, wave damping and excitation coefficients as well as the motion and drift force of the OWC device are calculated for various values of parameter related to the pressure drop. 相似文献
923.
The Cenozoic shelf margin of the Amazon Mouth Basin is characterized by a thick prograding prism of siliciclastic sediments.
This prism, composed mainly of Upper Miocene and younger sediments, overlies a Lower Tertiary carbonate shelf. Two tectonic–sedimentary
models for the area were developed with the aid of new deep-reflection seismic data. Gravitational tectonics dominate the
regional geological framework. Tensional stresses are created near the shelf margin, and compressional features dominate at
the base of the slope. The morphology of this compressional zone is closely associated with the St. Paul Fracture Zone and
the boundary between continental and oceanic crusts.
Received: 20 August 1996 / Revision received: 11 June 1998 相似文献
924.
925.
926.
Astronomy Letters - The formation of the rubidium resonance lines is considered by taking into account the effects of departures from local thermodynamic equilibrium (LTE). A rubidium model atom... 相似文献
927.
Gabriella Sch?ll-Barna Attila Demény Gábor Serlegi Szilvia Fábián Pál Sümegi István Fórizs Bernadett Bajnóczi 《Journal of Paleolimnology》2012,47(1):87-100
Geochemical records of bivalve shells have been increasingly studied in the last decade to obtain information on climate conditions.
In this paper we present stable isotope compositions of living and prehistoric shells of freshwater mussels (Unionidae) and
their relationships with climate conditions in a shallow lake environment of Lake Balaton, West-Central Hungary. Physical
conditions and stable oxygen isotope compositions of lake water samples were monitored where living bivalves were collected.
Comparisons between seasonal variations in ambient temperature, water composition and within-shell isotopic variations indicate
that the shells of Unio pictorum do reflect local changes at high resolution and thus can be used to study past conditions. Additionally, shells covering
the last two decades were gathered at several locations along the lake in order to determine spatial and temporal variations
in the shells’ isotopic compositions as a function of weather conditions. As an application, prehistoric shells collected
in archaeological excavations were analysed in order to study past environmental variations. Climate variations during the
Late Copper Age (5460–4870 cal. yr BP) have been assumed on the basis of geomorphological and archaeozoological observations
at the site Balatonkeresztúr-Réti-dűlő (south of Lake Balaton), that suggested increasing humidity as a cause of changes in
settlement location and domestic livestock husbandry. Stable carbon and oxygen isotope compositions of prehistoric bivalve
shells were analyzed from excavations representing five archaeological subphases (Boleráz subphase, 5460–5310 cal. yr BP;
two transitional subphases around 5310 cal. yr BP; Early Classic subphase, 5310–5060 cal. yr BP; Late Classic subphase, 5040–4870 cal.
yr BP). The analyses revealed significant negative C and O isotope shifts in the transitional subphases relative to the earlier
and later subphases. The isotopic variations indicate that the local climate became relatively wet and possibly cold around
5310 cal. yr BP, then it returned to drier (and likely warmer) conditions during the Classic subphases. This interpretation
is in agreement with previous studies on climate changes related to the “5.3 ky event” in the European continental area and
the North Atlantic Region, indicating an Atlantic influence in the Carpathian Basin. 相似文献
928.
The LOw Frequency ARray (LOFAR) is a next-generation radio telescope which uses thousands of stationary dipoles to observe celestial phenomena. These dipoles are grouped in various ‘stations’ which are centred on the Netherlands with additional ‘stations’ across Europe. The telescope is designed to operate at frequencies from 10 to 240 MHz with very large fractional bandwidths (25?–?100 %). Several ‘beam-formed’ observing modes are now operational and the system is designed to output data with high time and frequency resolution, which are highly configurable. This makes LOFAR eminently suited for dynamic spectrum measurements with applications in solar and planetary physics. In this paper we describe progress in developing automated data analysis routines to compute dynamic spectra from LOFAR time–frequency data, including correction for the antenna response across the radio frequency pass-band and mitigation of terrestrial radio-frequency interference (RFI). We apply these data routines to observations of interplanetary scintillation (IPS), commonly used to infer solar wind velocity and density information, and present initial science results. 相似文献
929.
R. Burrows I.A. Walkington N.C. Yates T.S. Hedges J. Wolf J. Holt 《Applied Ocean Research》2009,31(4):229-238
With concerns mounting over the UK’s energy future and the effects of climate change, it will soon become paramount that all viable sources of renewable energy are fully exploited. This study has examined the scope for reliable and fully predictable tidal electricity generation from the conjunctive operation of 5 major estuary barrages on the West Coast of the UK in an attempt to establish the potential scale of the extractable resources. Two levels of investigation have been undertaken: simple 0-D (‘two-tank’) modelling of barrage energy generation under different operational modes, using the hydraulic characteristics of turbine performance; and 2-D modelling of tidal hydrodynamics over a wide sea area in a computational grid incorporating the barrages with turbines and sluices. It has been demonstrated that more than 33TWh per year of electricity should be attainable, from 22GW of installed capacity, this representing close to 10% of present UK demand. 相似文献
930.
Ground temperature, pressure and wind speed monthly averages in the area of the Italian Station at Terra Nova Bay, Antarctica, were analyzed for the period 1987–1991 by means of a network of nine AWS (automatic weather stations). Spatial configurations of temperature show a well-defined, relatively warm island in the area of Terra Nova Bay, between Drygalsky and Campbell ice tongues, throughout the year. A second warm island is present to the north along the coast, between Aviator and Mariner ice tongues, for most of the year. From February to March a rapid drop in temperature is observed at all stations. A strong thermal gradient develops during February, March, April and October, November, December, between the coastal region and inner highlands. The baric configuration follows the elevation of the area. Annual average pressure and temperature as functions of stations altitude show linear trends. Severe katabatic wind episodes are recorded at all stations, with wind speed exceeding 25 ms–1 and direction following the orographic features of the inner areas. Co-occurrences of these episodes were observed for stations located along stream lines of cold air drainage. The autocorrelation function of maximum wind speed time series shows wind persistence of 2–3 days and wind periodicity of about one week. 相似文献