Choice chamber experiments to test the attraction of postflexion Rhabdosargus holubi larvae to water of estuarine and riverine origin     

Nicola C. James  Paul D. Cowley  Alan K. Whitfield  Horst Kaiser 《Estuarine, Coastal and Shelf Science》2008

Although the recruitment of larvae and juveniles of marine fishes into estuaries has been well documented, little is known about the factors governing the immigration of estuary-associated marine fishes into estuaries. Fishes have a well-developed sense of smell and it has been suggested by several workers that olfactory cues of freshwater or estuarine origin serve as stimuli, attracting larvae and juveniles of estuary-associated species into estuaries. Attraction of postflexion Rhabdosargus holubi larvae to estuary and river water from the Kowie estuarine system, South Africa, was measured using a rectangular choice chamber. In experiments, conducted during peak recruitment periods, larvae selected estuary and river water with a significantly higher frequency than sea water. This study, the first to assess the possible role of olfaction in the recruitment process of an estuary-associated marine fish species, demonstrates that larvae are able to recognise water from different origins, probably based on odour.  相似文献   

Holocene aeolian dynamics in the European sand‐belt as indicated by geochronological data     

Johann Friedrich Tolksdorf  Knut Kaiser 《Boreas: An International Journal of Quaternary Research》2012,41(3):408-421

Aeolian sands are widespread in the European sand‐belt. While there is a consensus about the timing of increased aeolian activity and, in contrast, of surface stabilization during the Lateglacial, knowledge about Holocene aeolian dynamics is still very sparse. It is generally assumed that aeolian processes have been closely connected to human activities since at least the Neolithic period. A compilation of 189 luminescence dates from aeolian sands of Holocene age and 301 ¹⁴C‐dates from palaeo‐surfaces, comprising palaeosols, buried peats and archaeological features from the whole sand‐belt, is plotted as histograms and kernel density plots and divided into sub‐phases by cluster analysis. This is also done separately for the dates from the areas west and east of the river Elbe. Our results show that aeolian activity did not cease with the end of the Younger Dryas but continued in the whole European sand‐belt until the Mid‐Atlantic (c. 6500 a BP), presenting evidence of vegetation‐free areas at least at the local scale. During the subsequent time period evidence of aeolian sedimentation is sparse, and surface stabilization is indicated by a cluster of palaeo‐surfaces ascribed to the early Subboreal (c. 5000 cal. a BP). The agglomeration of luminescence ages around 4000 years is probably connected with intensified land use during the Late Neolithic. Younger phases of aeolian sedimentation are indicated by clusters of luminescence ages around 1800 years, a group of luminescence ages from the Netherlands and NW Germany around 900 years, and a group of ages around 680 years in Germany. Among the dates from palaeo‐surfaces, clusters were identified around 2700, 1300 and 900 cal. a BP as well as around 690 cal. a BP in the western part and 610 cal. a BP in the eastern part of the sand‐belt. The clusters within the luminescence ages and the ¹⁴C‐dates coincide with phases where increased human impact can be deduced from archaeological and historical sources as well as from environmental history.  相似文献   

Modelling of a medium-term dynamics in a shallow tidal sea, based on combined physical and neural network methods     

Agnieszka Herman  Ralf Kaiser  Hanz D. Niemeyer 《Ocean Modelling》2007,17(4):277-299

The paper presents an approach towards a medium-term (decades) modelling of water levels and currents in a shallow tidal sea by means of combined hydrodynamic and neural network models. The two-dimensional version of the hydrodynamic model Delft3D, forced with realistic water level and wind fields, is used to produce a two-year-database of water levels and currents in the study area. The linear principal component analysis (PCA) of the results is performed to reveal dominating spatial patterns in the analyzed dataset and to significantly reduce the dimensionality of the data. It is shown that only a few principal components (PCs) are necessary to reconstruct the data with high accuracy (over 95% of the original variance). Feed-forward neural networks are set up and trained to effectively simulate the leading PCs based on water level and wind speed and direction time series in a single, arbitrarily chosen point in the study area. Assuming that the spatial modes resulting from the PCA are ‘universally’ applicable to the data from time periods not modelled with Delft3D, the trained neural networks can be used to very effectively and reliably simulate temporal and spatial variability of water levels and currents in the study area. The approach is shown to be able to accurately reproduce statistical distribution of water levels and currents in various locations inside the study area and thus can be viewed as a reliable complementary tool e.g., for computationally expensive hydrodynamic modelling. Finally, a detailed analysis of the leading PCs is performed to estimate the role of tidal forcing and wind (including its seasonal and annual variability) in shaping the water level and current climate in the study area.  相似文献   

Fine Structure of Solar Radio Bursts Observed at Decametric and Hectometric Waves     

G. P. Chernov  M. L. Kaiser  J.-L. Bougeret  V. V. Fomichev  R. V. Gorgutsa 《Solar physics》2007,241(1):145-169

The analysis of WIND/WAVES RAD2 spectra with fine structure in the form of different fibers in 14 events covering 1997?–?2005 is carried out. A splitting of broad bands of the interplanetary (IP) type II bursts into narrow band fibers of different duration is observed. The instantaneous-frequency bandwidth of fibers is stable: 200?–?300 kHz for slow-drifting fibers in type II bursts, and 700?–?1000 kHz for fast-drifting fibers in type II?+?IV (continuum). Intermediate drift bursts (IDB or fiber bursts) and zebra patterns with variable frequency drift of stripes, typical for the metric range, were not found. Comparison of spectra with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO C2) images shows a connection of the generation of the fiber structures with the passage of shock fronts through narrow jets in the wake of Coronal Mass Ejections (CME). Therefore the most probable emission mechanism of fibers in IP type II bursts appears to be resonance transition radiation (RTR) of fast particles at the boundary of two media with different refractive indices. The same mechanism is also valid for striae in the type III bursts. Taking into account a high-density contrast in the CME wake and the actually observed small-scale inhomogeneities, the effectiveness of the RTR mechanism in IP space must be considerably higher than in the meter or decimeter wavelengths. For the most part the fibers in the type IV continuum at frequencies of 14?–?8 MHz were seen as the direct expansion of similar fine structure (as fibers or “herringbone” structure) in the decametric range observed with the Nançay and IZMIRAN spectrographs.  相似文献   

A Severance Tax Revenue Forecast Model for Louisiana     

Mark J. Kaiser  Yunke Yu 《Natural Resources Research》2012,21(2):245-264

Most states levy severance taxes on the value of natural resources when they are severed or extracted from the ground or subsurface. In Louisiana, severance tax on oil and gas production contributes to the majority of mineral revenue in the state, and over the last decade, has ranged between $400 million and $1.1 billion, or between 5 and 9% of annual state revenue. The purpose of this article is to develop a forecast model for severance tax revenue to better understand the severance tax regime and to assist in state budgeting and planning purposes. We couple an oil and gas production model with empirical relationships describing historical severance tax receipts to perform the forecast. We demonstrate that oil production correlations are robust, but that in recent years, unconventional gas production from the Haynesville shale has led to a significant departure from historic trends. We estimate that cumulative oil and gas severance tax revenues during 2011–2015 will range from $1.0 to $2.1 billion for oil and $1.3–$1.9 billion for gas. Louisiana is transforming into a gas-producing state, and more attention needs to be paid to tax design and the impact of exemptions on future severance revenue receipts.  相似文献   

Analysis of a giant lightning storm on Saturn     

G. Fischer  W.S. Kurth  M.L. Kaiser  A. Lecacheux  D.A. Gurnett 《Icarus》2007,190(2):528-544

On January 23, 2006, the Cassini/RPWS (Radio and Plasma Wave Science) instrument detected a massive outbreak of SEDs (Saturn Electrostatic Discharges). The following SED storm lasted for about one month and consisted of 71 consecutive episodes. It exceeded all other previous SED observations by Cassini as well as by the Voyagers with regard to number and rate of detected events. At the same time astronomers at the Earth as well as Cassini/ISS (Imaging Science Subsystem) detected a distinctive bright atmospheric cloud feature at a latitude of 35° South, strongly confirming the current interpretation of SEDs being the radio signatures of lightning flashes in Saturn's atmosphere. In this paper we will analyze the main physical properties of this SED storm and of a single small SED storm from 2005. The giant SED storm of 2006 had maximum burst rates of 1 SED every 2 s, its episodes lasted for 5.5 h on average, and the episode's periodicity of about 10.66 h exactly matched the period of the ISS observed cloud feature. Using the low frequency cutoff of SED episodes we determined an ionospheric electron density around ¹⁰⁴ cm⁻³ for the dawn side of Saturn.  相似文献   

Processing and preliminary interpretation of noisy high-resolution seismic reflection/refraction data across the active Ostler Fault zone,South Island,New Zealand     

Fiona M. Campbell  A. Kaiser  H. Horstmeyer  A.G. Green  F. Ghisetti  A.R. Gorman  M. Finnemore  D.C. Nobes 《Journal of Applied Geophysics》2010,70(4):332-342

In an attempt to understand the structure of active faults as they emerge from bedrock into shallow semi-consolidated and unconsolidated sediments, we have recorded a comprehensive high-resolution seismic reflection/refraction data set across the Ostler Fault zone on the central South Island of New Zealand. This fault zone, which absorbs 1–2 mm/yr of compression associated with oblique convergence of the Pacific and Australian tectonic plates, consists of a series of surface-rupturing N–S trending, west-dipping reverse faults that offset a thick sequence of Quaternary glacial outwash and late Neogene fluvio-lacustrine sediments of the Mackenzie Basin. Our study focuses on a region of the basin where two non-overlapping fault segments are separated by a transfer zone. Deformation in this area is accommodated by offsets on multiple small faults and by folding in their hanging walls. The seismic data with source and receiver spacing of 6 and 3 m and nominal CMP fold of 60 was acquired along twelve 1.2 km long lines orthogonal to fault strike and an additional 1.6 km long tie-line parallel to fault strike. The combination of active deformation and shallow glacial outwash sediments results in particularly complicated seismic data, such that application of relatively standard processing schemes yields only poor quality images. We have designed a pre- and post-stack reflection/refraction processing scheme that focuses on minimising random and source-generated noise, determining appropriate static corrections and resolving contrasting reflection dips. Application of this processing scheme to the Ostler Fault data provides critical information on fault geometry and offset and on sedimentary structures from the surface to ～ 800 m depth. Our preliminary interpretation of one of the lines includes complex deformation structures with folding and multiple subsidiary fault splays on either side of a ～ 50° west-dipping primary fault plane.  相似文献   

The variation of cosmogenic Kr and Xe in a core from Estherville mesosiderite: direct evidence that the lunar¹³¹Xe anomaly is a depth effect     

Wulf A. Kaiser  R.S. Rajan 《Earth and Planetary Science Letters》1973,20(2):286-294

Kr and Xe were measured by a stepwise heating technique in three samples of a drill core in the “Minnesota” fragment of the Estherville mesosiderite. The cosmogenic⁷⁸Kr/⁸³Kr decreased from the “top” sample to the “bottom” sample(“top” = 0.163 ± 0.005, “bottom” = 0.151 ± 0.005) while the cosmogenic¹³¹Xe/¹²⁶Xe ratio increased(“top” = 5.58 ± 0.35, “bottom” = 6.92 ± 0.17). Cosmic-ray track studies have shown that the “top” sample was indeed closer to the preatmospheric surface than the “bottom” sample by ～ 10 cm. This is the first direct evidence, in a sample of known geometry, that the cosmogenic¹³¹Xe/¹²⁶Xe ratio increases as a function of depth, and as such, confirms the hypothesis that the lunar¹³¹Xe anomaly is a bona fide depth effect due to resonance neutron capture in¹³⁰Ba.  相似文献   

Kinetics of suprathermal hydrogen atom reactions with saturated hydrides in planetary and satellite atmospheres     

Richard J MortonRalf I Kaiser 《Planetary and Space Science》2003,51(6):365-373

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The effects of thermal conduction on the intracluster medium of the Virgo cluster     

Edward C. D. Pope  Georgi Pavlovski  Christian R. Kaiser  Hans Fangohr 《Monthly notices of the Royal Astronomical Society》2005,364(1):13-28

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