Optical and magnetic pulsations     

S. Åsheim  K. Aarsnes 《Planetary and Space Science》1984,32(6):735-744

Based on data from the PULSAUR-rocket (1980) and ground observations, a correlation study between optical and magnetic pulsations has been carried out. By use of All-Sky TV along with the measured flux of electrons we have also simulated the ground magnetic field. The simulation is based on a model of pulsating currents caused by conductivity changes in the ionosphere. Our simulated field well represents the observed field. The time delay between the optical and magnetic signal is discussed in relation to our model, and so is the lack of correlation between the high frequency component of the two types of pulsations.  相似文献   

Effect of porous medium heterogeneity on water flow: a stochastic hydrofacies approach     

Mohammad?H.?MakkawiEmail author 《Hydrogeology Journal》2004,12(5):481-487

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A low-scattering approximation for the hydrodynamic interactions of small wave-power devices     

Åge Kyllingstad 《Applied Ocean Research》1984,6(3):132-139

This paper concerns mathematical modelling of the hydrodynamic interaction forces between small vertically axisymmetric wave-power devices. The model takes into account small-body approximations for the first order scattered waves but neglects multiple scattering. Further, the local wave fields are neglected, making the model inapplicable for very closely spaced bodies.The model, which is called the low-scattering approximation, comprises analytical formulae for the forces in any of the translation modes surge, sway and heave. It requires, however, that the following isolated-body parameters are known or externally supplied: the added mass and the force coefficients for both heave and surge motion.Comparison with accurate numerical results of a two-buoy system indicates that the present approach is fairly good even when the buoy diameter is as large as 1/6 of the wavelength and the buoy spacing is as small as 5 buoy radii.  相似文献   

On the evaluation of natural illumination from radiometric measurements of solar radiation     

Anders Ångström  A. J. Drummond 《Theoretical and Applied Climatology》1962,12(1):41-46

Summary A new method is described for deriving values of the natural illumination of direct solar radiation from measurements of the latter, integrally with regard to wavelength and, simultaneously, in well-defined spectral regions. The basic equations are presented and graphical comparisons between data so computed and observed analyzed. The degree of prediction of individual short-period values of direct illumination flux (e. g. half-hourly intervals), established for wide ranges of solar height and turbidity, is of the same order as the accuracy generally expected in such series of carefully conducted measurement programs. This technique of employing radiometric rather than photometric measurements is thus shown to have a general application.

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Zusammenfassung Es wird eine neue Methode zur Berechnung von Werten der natürlichen Beleuchtungsst?rke durch die direkte Sonnenstrahlung aus Messungen der letzteren abgeleitet, und zwar gleichzeitig für das gesamte Spektrum und für genau abgegrenzte Spektralbereiche. Es werden die Grundgleichungen angegeben und graphische Vergleiche zwischen den so berechneten und den beobachteten Werten durchgeführt. Einzelwerte des direkten Lichtstromes über kurze Zeiten (z. B. Halbstundenintervalle), die für gro?e Bereiche von Sonnenh?he und Trübung berechnet wurden, haben denselben Genauigkeitsgrad, wie man ihn bei sorgf?ltig ausgeführten Me?programmen gew?hnlich erwartet. Damit ist erwiesen, da? die Methode, Strahlungsmessungen statt Lichtmessungen zu verwenden, allgemein angewendet werden kann.

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Résumé Les auteurs exposent ici une nouvelle méthode permettant de calculer l'intensité lumineuse naturelle du rayonnement solaire direct au moyen de la mesure de ce dernier. Cette méthode permet le calcul aussi bien pour la totalité du spectre que pour certaines bandes délimitées. Les auteurs indiquent les équations de base et donnent des comparaisons graphiques entre des valeurs observeés et calculées de cette manière. Les valeurs isolées du flux lumineux direct regu en des laps de temps brefs (par exemple dúne demie-heure), valeurs calculées pour de grands intervalles aussi bien de la hauteur du soleil que du trouble atmosphérique, donnent le même degré déxactitude que celui quón peut attendre de mesures directés effectées soigneusement. On a ainsi démontré que la méthode qui consiste à utiliser des mesures du rayonnement au lieu de la luminosité peut être utilisée de fa?on trés g&&ale.

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With 3 Figures

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Dedicated to Dr.W. M?rikofer on the occasion of his 70th birthday.  相似文献   

Analysis of subsurface magnetic features of the southeast of Al-Muwayh quadrangle,Saudi Arabia,using aeromagnetic data     

Mansour?A.?Al-GarniEmail author 《Arabian Journal of Geosciences》2016,9(2):155

Aeromagnetic data have been utilized to investigate the subsurface features of the southeast of Al-Muwayh quadrangle. Several techniques have been comprehensively used in an integrative way to reach the goals. Local phase and normalized standard deviation filters are used in this study as edge detectors, showing the possible occurrences of structural lineaments/faults in the quadrangle. Magnitude magnetic transform filters are used to produce anomalies that are closer to the true horizontal position of magnetic sources to enhance the interpretation. Among these transforms, a transform which has been used as edge detectors and the other two transforms are used to show the shallow and the shallowest magnetic sources within the study area. Tilt angle is mainly used to delineate the main magnetic contacts (faults), their locations, and their expected depths. The integration between these different filters show clearly the possible occurrences of edges (contacts/faults), the direction of these lineaments, the source locations of magnetic anomalies, the shallow and the shallowest causative targets, and the location and the depths of the main faults deduced from the tilt angle approach.  相似文献   

Study of the relationship between African ITCZ variability and an extreme heat wave on Egypt in summer 2015     

Y.?Y.?HafezEmail author  M.?Almazroui 《Arabian Journal of Geosciences》2016,9(6):476

An extreme heat wave hit Egypt in summer 2015. Abnormal hot weather conditions existed over Egypt for the entire summer season. The present paper investigates the relationship between the intertropical convergence zone (ITCZ) over Africa and a scorching heat wave that existed over Egypt in summer 2015. The National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data of mean surface air temperature for the domain of Egypt for the summer season from 1948 to 2015 were used in this study. In addition, data of the daily maximum and daily minimum temperature used for the summer season of the year 2015 were also used. Time cross-section analysis of the daily operational data of geopotential height at level 500 hPa over Egypt from 1 June to 31 August 2015 was done. Moreover, the African ITCZ, both the western and the eastern ITCZ, data for summer of 2015 were used for the said period. The time series, time cross-section, anomaly, and correlation coefficient techniques were used to analyze the datasets. The results revealed that a new climate change record of heat wave over Egypt existed in summer 2015. Moreover, there is an outstanding significant positive correlation between the abrupt shift of African ITCZ position and heat wave occurrence over Egypt in summer 2015. In particular, the southerly movement of the eastern African ITCZ controls the weather over Egypt and led to the extreme heat wave in summer 2015.  相似文献   

Environmental assessment of heavy metal contamination in bottom sediments of Al-Kharrar lagoon,Rabigh, Red Sea,Saudi Arabia     

Mohamed?YoussefEmail author  Abdelbaset?El-Sorogy 《Arabian Journal of Geosciences》2016,9(6):474

In order to assess the pollution levels of selected heavy metals, 45 bottom sediment samples were collected from Al-Kharrar lagoon in central western Saudi Arabia. The concentrations of the heavy metals were recorded using inductively coupled plasma-mass spectrometer (ICP-MS). The results showed that the concentrations of Pb and Cd exceeded the environmental background values. However, the heavy metal contents were less than the threshold effect level (TEL) limit. The concentrations of heavy metals in lagoon bottom sediments varied spatially, but their variations showed similar trends. Elevated levels of metals were observed in the northern and southern parts of the lagoon. Evaluation of contamination levels by the sediment quality guidelines (SQG) of the US-EPA revealed that sediments were non-polluted-moderately to heavily polluted with Pb; non-polluted to moderately polluted with Cu; and non-polluted with Mn, Zn, Cd, and Cr. The geoaccumulation index showed that lagoon sediments were unpolluted with Cd, Mn, Fe, Hg, Mo, and Se; unpolluted to moderately polluted with Zn and Co; and moderately polluted with Pb, Cr, Cu, and As. The high enrichment factor values for Pb, As, Cu, Cr, Co, and Zn (>2) indicate their anthropogenic sources, whereas the remaining elements were of natural origins consistent with their low enrichment levels. The values of CF indicate that the bottom sediments of Al-Kharrar lagoon are moderately contaminated with Mn and Pb.  相似文献   

Ontogenetic Changes in Vulnerability of the Prawn <Emphasis Type="Italic">Fenneropenaeus indicus</Emphasis> to UV-B Radiation Help Explain Ontogenetic Habitat Shifts     

Gopikrishna?Mantha  Ali?M.?Al-Aidaroos  Mohsen?M.?O.?El-Sherbiny  Sathianeson?Satheesh  Sambhu?Chithambaran  Carlos?M.?DuarteEmail author 《Estuaries and Coasts》2016,39(3):839-845

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Dating mafic–ultramafic intrusions by ion-microprobing contact-melt zircon: examples from SW Sweden     

Anders Scherstén  Hans Årebäck  David Cornell  Paul Hoskin  Anton Åberg  Richard Armstrong 《Contributions to Mineralogy and Petrology》2000,139(1):115-125

Zircons from anatectic melts of the country rocks of three Proterozoic mafic–ultramafic intrusions from the Sveconorwegian Province in SW Sweden were microanalyzed for U–Th–Pb and rare earth elements. Melting and interaction of the wall rocks with the intrusions gave rise to new magmas that crystallized zircon as new grains and overgrowths on xenocrysts. The ages of the intrusions can be determined by dating this newly crystallized zircon. The method is applied to three intrusions that present different degrees of complexity, related to age differences between intrusion and country rocks, and the effects of post-intrusive metamorphism. By careful study of cathodoluminescent images and selection of ion probe spots in zircon grains, we show that this approach is a powerful tool for obtaining accurate and precise ages. In the contact melts around the 916?±?11?Ma Hakefjorden Complex, Pb-loss occurred in some U-rich parts of xenocrystic zircon due to the heat from the intrusion. In back-veins of the 1624?±?6?Ma Olstorp intrusion we succeeded in geochemically distinguishing new magmatic from xenocrystic zircon despite small age differences. At Borås the mafic intrusion mixed with country rock granite to form a tonalite in which new zircon grew at 1674?±?8?Ma. Reworking of zircon occurred during 930+33/–34?Ma upper amphibolite facies Sveconorwegian metamorphism. Pb-loss was the result of re-equilibration with metamorphic fluids. REE-profiles show consistent differences between xenocrystic, magmatic, and metamorphic zircon in all cases. They typically differ in Lu/La_N, Ce/Ce*, and Eu/Eu*, and igneous zircon with marked positive Ce/Ce* and negative Eu/Eu* lost its anomalies during metamorphism.  相似文献   

Abundance, Sources and Speciation of Trace Elements in Humus-Rich Streams Affected by Acid Sulphate Soils   总被引：3，自引：0，他引：3  

Mats Åström  Nina Corin 《Aquatic Geochemistry》2000,6(3):367-383

The behaviour of trace elements (Al, As, Cd, Co, Cr,Cu, Fe, Mn, Ni, V, Zn) was studied in five humus-richstreams (dissolved organic carbon = 14–40 mg/L)impacted by acid sulphate soils developed in marinesulphide-bearing fine-grained sediments. During heavyrainfalls in autumn, on which the study focusses, themetals Al, Cd, Co, Cu, Mn, Ni and Zn are extensivelyleached from these acidic soils (pH = 2.5–4.5), whileAs, Cr, Fe and V are not leached more strongly fromthis soil type than from areas of till and peat. Aspeciation experiment, based on anion and cationexchange of the stream waters in the field, showedthat (1) the metals Al, Cd, Co, Mn, Ni and Zn aretransported in the streams mainly as inorganiccations, (2) Cu exists mainly in cationic form but isalso to a significant extent associated with dissolvedhumic substances, (3) Fe occurs mainly in the anionicfraction explained by organic coating on colloidal Feoxyhydoxides and (4) the hydrochemistry of As, Cr andV is complex as these elements may exist in severalunquantified anionic fractions and to a minor extentin cationic species/forms. Whereas the proportion ofacid sulphate soils in the catchments had a largeimpact on concentrations levels of several elements inthe stream waters, these soils did not have a largeaffect on the speciation of elements in water.  相似文献