Nepea and the nepeids (trilobites,Middle Cambrian,Australia)∗     

A. A. Öpik 《Australian Journal of Earth Sciences》2013,60(2):339-341

Nepea narinosa Whitehouse, 1939, is as yet the only known species of the Nepeidae and Nepeacea. It is based on fragmentary material unsuitable for conclusive interpretation. The census of Nepeidae as yet unpublished includes five genera and twelve species, confined to the Middle and early Upper Cambrian of Australia. All nepeids have cedariform posterior sutures, free cheeks fused into a unit, a preglabellar boss, forked ocular ridges and a pustulose test. Nepea narinosa is distinguished by its very long intergenal spines and pointed, falcate palpebral lobes provided with a doublure.  相似文献   

Effects of basin activities and land use on water quality trends in Tahtali Basin, Turkey   总被引：1，自引：1，他引：0  

Şebnem Elçi  Pelin Selçuk 《Environmental Earth Sciences》2013,68(6):1591-1598

Bi-weekly water quality data from seven monitoring stations located within Tahtali Watershed, ?zmir, Turkey and digital land use/land cover data of the same watershed are analyzed in this study. To examine the changes in land use associated with urbanization, the satellite images of the main pool of the Tahtali reservoir prior to filling and subsequent to filling, respectively, are analyzed. Aerial photos of the basin taken in 1995 (October) are compared with images taken in 2005 (November) from the IKONOS satellite through use of several GIS techniques. New residential buildings, greenhouses, and industrial buildings are presented in separate layers, and changes in basin activities are quantified. The effects of urbanization on the water quality are investigated through statistical analysis. The seasonal Kendall test is applied to the water quality parameters monitored bi-weekly at seven stations within the basin for the duration 1997–2005. There was no trend in phosphorus, but there was a negative trend in boron and nitrate and a positive trend in the parameters of biological oxygen demand (BOD) and chemical oxygen demand (COD). The improvement in nitrate concentrations is attributed to the new regulations on the use of fertilizers in greenhouses. However, increase of BOD and COD concentrations is related to the growing settlement areas and industrial zones, which point to the insufficient wastewater treatment within the basin. Soil erosion within the basin is also quantified by the universal soil loss equation using available maps. Estimated total soil loss rate increased about 2.5 times that of 1995 when the changed land use composition in 2005 is considered in the calculations.  相似文献   

Using sewage sludge as a sealing layer to remediate sulphidic mine tailings: a pilot-scale experiment, northern Sweden   总被引：1，自引：0，他引：1  

Peter Nason  Lena Alakangas  Björn Öhlander 《Environmental Earth Sciences》2013,70(7):3093-3105

At the Kristineberg mine, northern Sweden, sulphidic mine tailings were remediated in an 8-year pilot-scale experiment using sewage sludge to evaluate its applicability as a sealing layer in a composite dry cover. Sediment, leachate water, and pore gas geochemistry were collected in the aim of determining if the sludge was an effective barrier material to mitigate acid rock drainage (ARD) formation. The sludge was an effective barrier to oxygen influx as it formed both a physical obstruction and functioned as an organic reactive barrier to prevent oxygen to the underlying tailings. Sulphide oxidation and consequential ARD formation did not occur. Sludge-borne trace elements accumulated in a reductive, alkaline environment in the underlying tailings, resulting in an effluent drainage geochemistry of Cd, Cu, Pb and Zn below 10 μg/L, high alkalinity (810 mg/L) and low sulphate (38 mg/L). In contrast, the uncovered reference tailings received a 0.35-m deep oxidation front and typical ARD, with dissolved concentrations of Cd, Zn and sulphate, 20.8 μg/L, 16,100 μg/L and 1,390 mg/L, respectively. Organic matter degradation in the sludge may be a limiting factor to the function of the sealing layer over time as 85 % loss of the organic fraction occurred over the 8-year experimental period due to aerobic and anaerobic degradation. Though the cover may function in the short to medium term (100 years), it is unlikely to meet the demands of a long-term remedial solution.  相似文献   

Various filtering algorithms used to eliminate outliers in velocity time series obtained by ADVs (acoustic Doppler velocimeter)     

Ömer Köse 《Arabian Journal of Geosciences》2013,6(7):2691-2697

The correct measurement of velocities in rivers is important for the true determination of discharge, erosion, scouring, and sediment transport processes. With the goal of increased accuracy, the use of acoustic Doppler velocimeters (ADVs) is increasing in hydrological measurements in rivers, lakes, and laboratories. ADVs are extensively used in the USA. ADVs have advantages when compared with classical measurement devices; however, one must be careful while using an ADV because their sampling approach creates a large number of extreme values by sending signals into the flow, measuring the velocities of particles moving with the water and assuming that these particles move with same velocity as the water. To calculate unbiased statistical properties, outliers must be removed from the time series. This study explains the methods used to filter velocity time series collected with ADVs and investigates the effects of these filters on the statistical characteristics of the filtered time series.  相似文献   

Neogene basin development around Söke-Kuşadası (western Anatolia) and its bearing on tectonic development of the Aegean region     

Ömer Feyzi Gürer  Mustafa Bozcu  Kamil Yılmaz  Yücel Yımaz 《Geodinamica Acta》2013,26(1-3):57-69

The AMS study has been performed on various types of the basement – Variscan granitic and surrounding – Mesozoic sedimentary rocks in the Velká Fatra Mountains, Tatric Superunit of the Central Western Carpathians. The Velká Fatra Mts. provides good opportunity for AMS study because of composite S-type and I-type granite character of pluton and clear relations to Mesozoic sedimentary rocks in the cover and nappe positions. The granitic massif consists of the three types of weakly magnetic peraluminous granites (350 – 340 Ma in age), ranging from two-mica granites to biotite granodiorites in composition and carrying accessory monazite and ilmenite; whereby they resemble common S-type and/or Ilmenite Series granite. This pre-existing granitic body was intruded by relatively young (304 Ma old) metaluminous to subaluminous, strongly magnetic (due to magnetite) tonalitic intrusion of the I-type and/or Magnetite Series granite. In all S-types investigated as well as in the I-type tonalite body, the magnetic fabrics are not uniform, but slightly variable within a body and differing from body to body. The magnetic fabrics in all granitic rocks can be classified as mostly magmatic in origin, only subordinately affected by ductile deformation. The Alpine overprint of the magnetic fabric of the Variscan granite frequent in the central areas of the Central Western Carpathians was only weak in the Velká Fatra Mts. and the magnetic fabrics of these granites thus mostly comprise the original Variscan magmatic fabrics. On the other hand, in the marginal parts of the Velká Fatra Mts. the magnetic fabrics in granites are locally conformable to the deformational magnetic fabrics in surrounding sedimentary rocks (Mesozoic in age) thus indicating at least local effects of the Alpine deformation. The magnetic fabrics in Mesozoic sedimentary rocks covering the crystalline basement are partially (Cover Formation) to entirely (Nappe Units) deformational in origin.  相似文献   

Ion–Cyclotron Resonance Frequency Interval Dependence on the O VI Ion Number Density in the North Polar Coronal Hole 1.5R–3R Region     

Özgür Gültekin  Emine Rızaoǧlu  K. Gediz Akdeniz 《Journal of Astrophysics and Astronomy》2013,34(4):349-355

The frequency intervals in which O VI ions get in resonance with ion–cyclotron waves are calculated using the kinetic model, for the latest six values found in literature on O VI ion number densities in the 1.5R–3R region of the NPCH. It is found that the common resonance interval is 1.5 kHz to 3 kHz. The R-variations of wave numbers necessary for the above calculations are evaluated numerically, solving the cubic dispersion relation with the dielectric response derived from the quasi-linear Vlasov equation for the left-circularly polarized ion-cyclotron waves.  相似文献   

Wavelet regression model as an alternative to neural networks for monthly streamflow forecasting   总被引：3，自引：0，他引：3  

Özgür Kişi 《水文研究》2009,23(25):3583-3597

The accuracy of the wavelet regression (WR) model in monthly streamflow forecasting is investigated in the study. The WR model is improved combining the two methods—the discrete wavelet transform (DWT) model and the linear regression (LR) model—for 1‐month‐ahead streamflow forecasting. In the first part of the study, the results of the WR model are compared with those of the single LR model. Monthly flow data from two stations, Gerdelli Station on Canakdere River and Isakoy Station on Goksudere River, in Eastern Black Sea region of Turkey are used in the study. The comparison results reveal that the WR model could increase the forecast accuracy of the LR model. In the second part of the study, the accuracy of the WR model is compared with those of the artificial neural networks (ANN) and auto‐regressive (AR) models. On the basis of the results, the WR is found to be better than the ANN and AR models in monthly streamflow forecasting. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Investigation of liquefaction and pore water pressure development in layered sands     

Pelin Tohumcu Özener  Kutay Özaydın  Mehmet M. Berilgen 《Bulletin of Earthquake Engineering》2009,7(1):199-219

This paper presents the results of shaking table model tests which were carried out to investigate the pore water pressure generation and related liquefaction mechanism in layered sand deposits. The experiments were performed on uniform sand columns, silt interlayered sand columns and two layered sand columns deposited at various relative densities and subjected to different input excitations. During the experiments excess pore water pressures were measured by pore pressure transducers installed at three different depths and, surface settlements and thickness of water film developed under less permeable inclusions were measured by a digital camera. The experimental results are discussed and compared to demonstrate the effects of relative density, input acceleration and presence of a silt seam on the generation of excess pore water pressure in sand deposits subjected to dynamic loading. The results showed that the presence of a less permeable silt interlayer within the sand deposit and existence of a loose sand layer underlying dense sand deposits can have significant effect on the pore water pressure generation mechanism.  相似文献   

The most metal-poor galaxies     

D. Kunth  G. Östlin 《Astronomy and Astrophysics Review》2000,10(1-2):1-79

Summary. Metallicity is a key parameter that controls many aspects in the formation and evolution of stars and galaxies. In this review we focus on the metal deficient galaxies, in particular the most metal-poor ones, because they play a crucial r?le in the cosmic scenery. We first set the stage by discussing the difficult problem of defining a global metallicity and how this quantity can be measured for a given galaxy. The mechanisms that control the metallicity in a galaxy are reviewed in detail and involve many aspects of modern astrophysics: galaxy formation and evolution, massive star formation, stellar winds, chemical yields, outflows and inflows etc. Because metallicity roughly scales as the galactic mass, it is among the dwarfs that the most metal-poor galaxies are found. The core of our paper reviews the considerable progress made in our understanding of the properties and the physical processes that are at work in these objects. The question on how they are related and may evolve from one class of objects to another is discussed. While discussing metal-poor galaxies in general, we present a more detailed discussion of a few very metal-poor blue compact dwarf galaxies like IZw18. Although most of what is known relates to our local universe, we show that it pertains to our quest for primeval galaxies and is connected to the question of the origin of structure in the universe. We discuss what do QSO absorption lines and known distant galaxies tell us already? We illustrate the importance of star-forming metal-poor galaxies for the determination of the primordial helium abundance, their use as distance indicator and discuss the possibility to detect nearly metal-free galaxies at high redshift from Ly emission. Received 19 August 1999 / Published online: 15 February 2000  相似文献   

Late Pleistocene–Holocene environmental change in eastern Turkey: multi‐proxy palaeoecological data of vegetation and lake‐catchment changes          下载免费PDF全文

Demet Bİltekİn  Kürşad Kadİr Erİş  Memet Namık Çağatay  Sena Akçer Ön  Dİcle Bal Akkoca 《第四纪科学杂志》2018,33(5):575-585

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