Sedimentology,three‐dimensional geobody reconstruction and carbon dioxide origin of Pleistocene travertine deposits in the Ballık area (south‐west Turkey)          下载免费PDF全文

Hannes Claes  Jeroen Soete  Koen Van Noten  Hamdy El Desouky  Marcelle Marques Erthal  Frank Vanhaecke  Mehmet Özkul  Rudy Swennen 《Sedimentology》2015,62(5):1408-1445

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Photometry of the magnetic white dwarf SDSS 121209.31+013627.7     

C. Koen  P. F. L. Maxted 《Monthly notices of the Royal Astronomical Society》2006,371(4):1675-1680

The results of 27 h of time series photometry of SDSS 121209.31+013627.7 are presented. The binary period established from spectroscopy is confirmed and refined to 0.061 412 d (88.43 min). The photometric variations are dominated by a brightening of about 16 mmag, lasting a little less than half a binary cycle. The amplitude is approximately the same in V ,  R and white light. A secondary small brightness increase during each cycle may also be present. We speculate that SDSS 121209.31+013627.7 may be a polar in a low state.  相似文献   

I-band time-series observations of five bright ultracool dwarfs     

Chris Koen 《Monthly notices of the Royal Astronomical Society》2004,354(2):378-386

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Model atmosphere and kinematical analyses of early-type stars from the Edinburgh–Cape Survey     

H.R.M. Magee  P.L. Dufton  F.P. Keenan  W.R.J. Rolleston  D. Kilkenny  D. O'Donoghue  C. Koen  R.S. Stobie 《Monthly notices of the Royal Astronomical Society》2001,324(3):747-756

We present high-resolution spectroscopic observations of 21 B-type stars, selected from the Edinburgh–Cape Blue Object Survey. Model atmosphere analyses confirm that 14 of these stars are young, main-sequence B-type objects with Population I chemical compositions. The remaining seven are found to be evolved objects, including subdwarfs, horizontal branch and post-AGB objects. A kinematical analysis shows that all 14 young main-sequence stars could have formed in the disc and subsequently been ejected into the halo. These results are combined with the analysis of a previous subsample of stars taken from the Survey. Of the complete sample, 31 have been found to be young, main-sequence objects, with formation in the disc, and subsequent ejection into the halo, again being found to be a plausible scenario.  相似文献   

Simulation of ionosphere-plasmasphere coupling taking into account ion inertia and temperature anisotropy     

G.V. Khazanov  M.A. Koen  Yu.V. Konikov  I.M. Sidorov 《Planetary and Space Science》1984,32(5):585-598

In this paper we offer a model for the Earth's ionosphere and plasmasphere, allowing for the inertia and anisotropic energy distribution of thermal plasma. A procedure for simultaneous solution of equations of continuity and motion for the O⁺ and H⁺ ions, subject to inertia terms, is described. The model also includes transfer equations for longitudinal and transversal thermal energies. The system of simulating equations and the kinetic equation for superthermal electron spectra are concordantly solved along geomagnetic field lines. Within the framework of the model we developed a study is made of the dynamics of filling of the evacuated plasmaspheric reservoir after a magnetospheric disturbance. It is shown that the filling of the tubes offorce with L ? 3.5 proceeds with supersonic speeds during the first several days and the character of filling differs very much from a diffusion-equilibrium one. The spatio-temporal behavior of electron and ion temperature anisotropy that is formed in the process of filling, is considered. It is found that the value of electron anisotropy can be large. A brief analysis is made of the causes of electron and ion temperature anisotropy.  相似文献   

Late Holocene changes in ultraviolet radiation penetration recorded in an East Antarctic lake     

Elie?VerleyenEmail author  Dominic?A.?Hodgson  Koen?Sabbe  Wim?Vyverman 《Journal of Paleolimnology》2005,34(2):191-202

Late Holocene changes in the ultraviolet radiation (UVR) penetration in a lake in the Larsemann Hills (East Antarctica) were reconstructed using sediment core proxies based on fossil pigments (scytonemins and its derivatives) and siliceous microfossils. The influence of changes in lake depth on the UVR proxy was excluded by applying a correction, based on the non-linear relation between modern scytonemin concentrations and lake depth in a regional reference data set, and the record of past lake depths inferred using a diatom based transfer function in the sediment core. Results showed four well-defined maxima in the UVR proxy during the last 1600–1800 years, centred around 1820–1780, 1580–1490, 790–580 and 680–440 AD. Several mechanisms may account for these observed changes in UVR penetration, including past variability in cloud cover, atmospheric turbidity, ozone column depth, snow cover on the lake ice, DOM concentrations and lake-ice thickness and transparency resulting from temperature fluctuations. Although some gaps remain in our knowledge of scytonemin production in relation to the limnology of Antarctic lakes, the results highlight the importance and potential of the sediments in these highly transparent water bodies as archives of changes in past UVR receipt at the Earth’s surface.  相似文献   

Mental maps and travel behaviour: meanings and models     

Els Hannes  Diana Kusumastuti  Maikel León Espinosa  Davy Janssens  Koen Vanhoof  Geert Wets 《Journal of Geographical Systems》2012,14(2):143-165

In this paper, the “mental map” concept is positioned with regard to individual travel behaviour to start with. Based on Ogden and Richards’ triangle of meaning (The meaning of meaning: a study of the influence of language upon thought and of the science of symbolism. International library of psychology, philosophy and scientific method. Routledge and Kegan Paul, London, 1966) distinct thoughts, referents and symbols originating from different scientific disciplines are identified and explained in order to clear up the notion’s fuzziness. Next, the use of this concept in two major areas of research relevant to travel demand modelling is indicated and discussed in detail: spatial cognition and decision-making. The relevance of these constructs to understand and model individual travel behaviour is explained and current research efforts to implement these concepts in travel demand models are addressed. Furthermore, these mental map notions are specified in two types of computational models, i.e. a Bayesian Inference Network (BIN) and a Fuzzy Cognitive Map (FCM). Both models are explained, and a numerical and a real-life example are provided. Both approaches yield a detailed quantitative representation of the mental map of decision-making problems in travel behaviour.  相似文献   

Bulk Transfer Relations for the Roughness Sublayer     

Koen De Ridder 《Boundary-Layer Meteorology》2010,134(2):257-267

In the roughness sublayer (RSL), Monin–Obukhov surface layer similarity theory fails. This is problematic for atmospheric modelling applications over domains that include rough terrain such as forests or cities, since in these situations numerical models often have the lowest model level located within the RSL. Based on empirical RSL profile functions for momentum and scalar quantities, and scaling the height with the RSL height z _*, we derive a simple bulk transfer relation that accounts for RSL effects. To verify the validity of our approach, these relations are employed together with wind speed and temperature profiles measured over boreal forest during the BOREAS experimental campaign to estimate momentum and heat fluxes. It is demonstrated that, when compared with observed flux values, the inclusion of RSL effects in the transfer relations yields a considerable improvement in the estimated fluxes.  相似文献   

The interior structure of Mercury and its core sulfur content     

A. Rivoldini  T. Van Hoolst  O. Verhoeven 《Icarus》2009,201(1):12-30

Depth-dependent interior structure models of Mercury are calculated for several plausible chemical compositions of the core and of the mantle. For those models, we compute the associated libration amplitude, obliquity, tidal deformation, and tidal changes in the external potential. In particular we study the relation between the interior structure parameters for five different mantle mineralogies and two different temperature profiles together with two extreme crust density values. We investigate the influence of the core light element concentration, temperature, and melting law on core state and inner and outer core size. We show that a sulfur concentration above 10 wt% is unlikely if the temperature at the core-mantle boundary is above 1850 K and the silicate shell at least 240 km thick. The interior models can only have an inner core if the sulfur weight fraction is below 5 wt% for core-mantle boundary temperature in the 1850-2200 K range. Within our modeling hypotheses, we show that with the expected precision on the moment of inertia the core size can be estimated to a precision of about 50 km and the core sulfur concentration with an error of about 2 wt%. This uncertainty can only be reduced when more information on the mantle mineralogy of Mercury becomes available. However, we show that the uncertainty on the core size estimation can be greatly reduced, to about 25 km, if tidal surface displacements and tidal variations in the external potential are considered.  相似文献   

Multiple regression of GRB luminosity on light-curve properties     

Chris Koen 《Monthly notices of the Royal Astronomical Society》2009,396(3):1499-1506

Statistical relations between the luminosity L of gamma-ray burster (GRBs) and several of their other observable properties have been discovered. Four of these properties are considered here: the spectral lag; a measure of the light-curve variability; peak energy and the minimum light-curve rise time. Data are taken from a tabulation by Schaefer. Log–log regression of L on various combinations of the four light-curve properties, as well as redshift, is considered, using conventional multiple linear regression, and multiple errors-in-variables regression. Several cases are found in which the regression coefficients of more than one luminosity indicators are significant. In particular, the simultaneous regression of luminosity on peak energy, spectral lag, minimum rise time and redshift is meaningful.  相似文献