Site selection for a radio astronomy observatory in Turkey: atmospherical, meteorological, and radio frequency analyses     

?brahim Kü?ük  ?pek üler  ?ükriye ?z  Sedat Onay  Ali R?za ?zdemir  Mehmet Gül?en  Mikail Sar?kaya  Nazl? Derya Dag?tekin  Ferhat Fikri ?zeren 《Experimental Astronomy》2012,33(1):1-26

Selecting the future site for a large Turkish radio telescope is a key issue. The National Radio Astronomy Observatory is now in the stage of construction at a site near Karaman City, in Turkey. A single-dish parabolic radio antenna of 30?C40 m will be installed near a building that will contain offices, laboratories, and living accommodations. After a systematic survey of atmospheric, meteorological, and radio frequency interference (RFI) analyses, site selection studies were performed in a predetermined location in Turkey during 2007 and 2008. In this paper, we described the experimental procedure and the RFI measurements on our potential candidate??s sites in Turkey, covering the frequency band from 1 to 40 GHz.  相似文献   

Potential impact of climate change on ecosystems of the Barents Sea Region     

Hedwig Roderfeld  Eleanor Blyth  Rutger Dankers  Geir Huse  Dag Slagstad  Ingrid Ellingsen  Annett Wolf  Manfred A. Lange 《Climatic change》2008,87(1-2):283-303

The EU project BALANCE (Global Change Vulnerabilities in the Barents region: Linking Arctic Natural Resources, Climate Change and Economies) aims to assess vulnerability to climate change in the Barents Sea Region. As a prerequisite the potential impact of climate change on selected ecosystems of the study area has to be quantified, which is the subject of the present paper. A set of ecosystem models was run to generate baseline and future scenarios for 1990, 2020, 2050 and 2080. The models are based on data from the Regional Climate Model (REMO), driven by a GCM which in turn is forced by the IPCC-B2 scenario. The climate change is documented by means of the Köppen climate classification. Since the multitude of models requires the effect of climate change on individual terrestrial and marine systems to be integrated, the paper concentrates on a standardised visualisation of potential impacts by use of a Geographical Information System for the timeslices 2050 and 2080. The resulting maps show that both terrestrial and marine ecosystems of the Barents region will undergo significant changes until both 2050 and 2080.  相似文献   

Transient dissolution patterns on stressed crystal surfaces     

Daniel Koehn  Dag Kristian Dysthe 《Geochimica et cosmochimica acta》2004,68(16):3317-3325

We present an experimental investigation on the dissolution of uniaxially stressed crystals of NaClO₃ in contact with brine. The crystals are immersed in a saturated fluid, stressed vertically by a piston and monitored constantly in situ with a CCD camera. The experiments are temperature-controlled and uniaxial shortening of the sample is measured with a high-resolution capacitance analyzer. Once the crystal is stressed it develops dissolution grooves on its free surface. The grooves are oriented with their long axis perpendicular to the direction of compressive stress and the initial distance between the parallel grooves is in accordance with the Asaro-Tiller-Grinfeld instability. We observe a novel, transient evolution of this roughness: The grooves on the crystal surface migrate upwards (against gravity), grow in size and the inter-groove distance increases linearly with time. During the coarsening of the pattern this switches from a one-dimensional geometry of parallel grooves to a two-dimensional geometry with horizontal and vertical grooves. At the end of the experiment one large groove travels across the crystal and the surface becomes smooth again. Uniaxial shortening of the crystal by pressure solution creep decays exponentially with time and shows no long term creep within the range of the resolution of the capacitance analyzer (accuracy of 100nm over a period of 14 days). This indicates that, while active, the fast transient processes on the free surface increase the solution concentration and thereby significantly slow down or stop pressure solution at the top of the crystal. This novel feedback mechanism can explain earlier results of cyclic pressure solution creep and demands development of a more complex theory of pressure-solution creep including processes that act on free surfaces.  相似文献   

Overbank sediment: a representative sample medium for regional geochemical mapping   总被引：2，自引：0，他引：2  

R.T. Ottesen  J. Bogen  B. Blviken  T. Volden 《Journal of Geochemical Exploration》1989,32(1-3)

In Scandinavia, most fluvial erosion takes place in the Quaternary glacial overburden at a restricted number of small source areas along individual drainage channels. As a consequence, a sample of active stream sediment is representative of only a very limited portion of the drainage area. This restriction makes stream sediment less reliable for regional exploration than generally expected. Overbank (levee or river-plain) sediment produced during large floods is an alternate more representative sampling medium. The sediment suspended during a flood has a much more widespread origin, and when the load is deposited upon the flood plain, nearly horizontal strata are formed and preserved at levels above the ordinary stream channel. A composite sample through a vertical section of such strata represents a great number of sediment sources that have been active at different times and forms an integrated sample of the entire catchment area. Because young sediments overlay older, the uppermost layers will be contaminated by pollutants in industrialized regions, but those at depth may remain pristine and will to a greater extent reflect the natural pre-industrial environment. In regional geochemical mapping, overbank sediment can be sampled at widely spaced sites, keeping costs per unit area low. Examples from Norway (1 sample station per 500 km²) show that overbank sediment produces broad geochemical patterns with high contrasts reflecting the bedrock geochemistry. Some patterns agree with known geological units and metallogenic provinces, but hitherto unknown major structures have also been indicated. A large Mo-deposit missed by a traditional stream survey is readily detected in the overbank sediment. It is concluded that overbank sediment is a promising alternate sample medium that should be tested in other physiographic regions.  相似文献   

On the use of forward scatter techniques in the study of turbulent stratified layers in the troposhere     

Dag T. Gjessing 《Boundary-Layer Meteorology》1973,4(1-4):377-396

This review paper considers the potentials of forward scatter radio techniques as a diagnostic tool in the study of stratified turbulent layers. Seven classes of experimental techniques have been considered (beamswinging, multifrequency, vertical and horizontal field strength correlation, coupling loss, pulse delay and bandwidth measurements). All these techniques with the exception of bandwidth and delay experiments measure directly or indirectly the irregularity spectrum of refractive index. Bandwidt hand delay distributions are determined by the vertical distribution of the refractivity irregularities. Thus for the purpose of obtaining information about a layered structure where our interest is focused on the vertical refractivity distribution rather than on the averaged spectral properties of the structure, the last two categories of experiments appear to represent a powerful tool. If one is interested in the spectral properties, multifrequency and beamswinging experiments are of great potential value whereas other experiments such as that measuring coupling loss are largely influenced by pure refraction effects.  相似文献   

Evaluating Thickness of Bauxite Deposit Using Indicator Geostatistics and Fuzzy Estimation     

Ahmet Dag  Bayram A. Mert 《Resource Geology》2008,58(2):188-195

Evaluating the geological properties of a mineral deposit is a fundamental task for mine planning and it requires an assessment of reserve parameters such as thickness and grade. This paper presents a linguistic model for estimating bauxite thickness within a deposit in a fuzzy environment using indicator geostatistics and fuzzy modeling. The proposed model consists of two main stages: determining the orebody boundary and estimating the thickness. In order to estimate the thickness, a rule‐based fuzzy inference mechanism has been developed based on data statistics. Results and performance of the model have been compared with that of a well‐known conventional technique, geostatistics (kriging), and it is shown that the proposed model has bigger estimation power. In addition, the fuzzy approach is more flexible than the kriging approach. The fuzzy methodology used in the present paper is convenient for modeling reserve parameters.  相似文献   

The geothermal model of Mersin (Turkey) region     

Y. Uras  M. Dag 《Geochemistry International》2016,54(6):559-568

The purpose of the study is to present the geothermal model of Mersin (Camili) region geothermal area with its geology, hydrogeology, hydrogeochemistry and isotope hydrology. The 1/25000 scale geology map obtained from the literature research is revised. In order to obtain a geothermal model, geological crosssections are extracted in certain points on the revised geology map. There are 3 hot water outlets. There are MC-1, C-1 and Uclu Cesme deep drillings. MC-1 well is 420 m, approximately 43.6°C temperature and 35 L/s flow rate and C-1 is 150 m, 40.3°C and 35 L/s. There is no exact information about the depth of Uclu Cesme well, but its average temperature is 37.5°C and it has a very low flow rate. Isotope analyses of the water samples obtained from these three wells and the Icme Dere are carried out by using the IRMS method with δ¹⁸O–δ²H (Deuterium) and IAEA method with ³H (Tritium). Radioactive Alpha-Beta determination and Physico-chemical and Bacteriological analyses of MC-1 well are made by using EPA 900.00. δ¹⁸O–δ²H isotope ratios clearly indicate a meteoric origin for the waters. In the light of all this information, the revised 1/25000 scare geology map of Mersin Guneyyolu (Camili) geothermal area is obtained; it is found out that hot waters are of meteoric origin; and the isotope hydrology and hydro-chemical assessment of the area is conducted to shape the geothermal model.  相似文献   

Steepness and asymmetry of extreme waves and the highest waves in deep water     

Dag Myrhaug  Sren Peter Kjeldsen 《Ocean Engineering》1986,13(6)

Traditional wave steepness s=H/L does not define steep asymmetric waves in a random sea uniquey. Three additional parameters characterising single zero-downcross waves in a time series are crest front steepness, vertical asymmetry factor and horizontal asymmetry factor. Results for steepness and asymmetry from zero-downcross analysis of wave data obtained from full scale measurements in deep water on the Norwegian continental shelf in 58 time series are presented. The analysis demonstrates clearly the asymmetry of both “extreme waves” and the highest waves. The period and height of the highest waves are also given together with their correlation to spectral parameters. The measured maximum wave heights are also compared with predicted values of maximum wave heights showing good agreement.  相似文献   

Wind gust spectrum over waves: Effect of wave age     

Dag Myrhaug   《Ocean Engineering》2007,34(2):353-358

The effect of wave age on the wind gust spectrum over wind waves is considered by using the Ochi and Shin [1988. Wind turbulent spectra for design considerations of offshore structures. Proceedings of 20th Offshore Technology Conference, Paper No. 5736, Houston, Texas. pp. 461–467] spectrum together with the wave age dependant Volkov [2001. The dependence on wave age. In: Jones, I.S.F., Toba, Y. (Eds.), Wind Stress Over the Ocean. Cambridge University Press, Cambridge, UK, pp. 206–217] sea surface roughness formula. The wave age independent Charnock [1955. Wind stress on a water surface. Quarterly Journal of Royal Meteorological Society 81, 639–640] sea surface roughness is used as a reference. An example of results demonstrates a clear effect of wave age on the wind gust spectrum.  相似文献   

Mobile layer thickness in sheet flow beneath random waves     

Dag Myrhaug  Lars Erik Holmedal 《Coastal Engineering》2007

The erosion depth and the sheet flow layer thickness represent two characteristic parameters for transport processes in oscillatory sheet flow. Formulas for these parameters under regular waves have been applied to obtain characteristic statistical values under random waves. The applicability of the method for practical purposes is illustrated by two examples using data typical for field conditions at water depths of 70 m (Ekofisk location in the North Sea) and 15 m, respectively. Two fictive storms based on the Dohmen-Janssen and Hanes [Dohmen-Janssen, C.M., Hanes, D.M., 2005. Sheet flow and suspended sediment due to wave groups in a large wave flume. Cont. Shelf Res. 25, 333–347] data from large scale wave flume tests have also been utilized to demonstrate how the return period of the sheet flow layer thickness observed in their experiments can be estimated.  相似文献