Using archival ASCA and ROSAT observations of RE 0751+14, X- ray energy spectra, pulse profiles and the results of pulse timing
analysis are presented. The energy spectra are well-fitted by a blackbody model at low energy and a Raymond-Smith model at
high energy, together with a partial covering absorber. A fluorescence emission line at 6.4 keV with an equivalent width ∼
220 eV was resolved for the first time.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
We present CCD BV and JHKs 2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting
magnitude of V∼19 mag. The star-count method showed that the centre of the cluster lies at α2000=04h09m36s, δ2000=49°28′43″ and its angular size is r=10 arcmin. The optical and near-infrared two-colour diagrams revealed the colour excesses in the direction of the cluster
as E(B−V)=0.68±0.06, E(J−H)=0.21±0.02 and E(J−Ks)=0.33±0.04 mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age
Main-Sequences (ZAMS) provided an average distance modulus of (m−M)0=10.80±0.13 mag, which can be translated into a distance of 1440±80 pc. Finally, using Padova isochrones we determined the
metallicity and age of the cluster as Z=0.015±0.004 ([M/H]=−0.10±0.10 dex) and log (t/yr)=8.40±0.04, respectively. 相似文献
The necessity of estimating the degree and spatial extent of positive impacts with regard to protecting communities and properties
through potential flood control projects can be considered one of the main reasons for performing flood modeling. This paper
presents an overall systematic approach based on the simulation of some extreme event conditions, using a hydrological model
to generate the resulting river flows and then using a hydraulic modeling exercise to decide upon floodplain evolution in
the case-study area, Bostanli river basin, which has been under the threat of flooding for many years. The potential serviceability
of the planned Bostanli Dam in the study area was examined by using the HEC-HMS and HEC-RAS modeling tools, both integrated
with GIS functions for spatial operations. The results indicate that the dam construction as planned would have a somewhat
positive impact as a potential flood control measure, since it seems to decrease the flood peaks of 68.9 and 158.7 m3/s (that would potentially be generated by 100- and 500-year storm events under current conditions) to 65.5 and 150.7 m3/s (when the dam is in operation), respectively. However, this seems to contribute little to the overall flood mitigation
performance in the basin. 相似文献
In this study, the relationship between the hourly changes of the ionospheric critic frequency values of F2 layers in low latitudes and geomagnetic activity is examined by using statistical methods. The ionospheric critical frequency data has been taken from the Manila (121.1° E, 14.7° N) ionosonde station. In order to investigate the effect of sun activity on ionospheric critical frequency, the data of 1981 when the sun was active and of 1985 when the sun was less active has been used. According to the Granger causality test results, on 5 % significance level, a causality relationship from disturbance storm time (Dst) index values to ionospheric critical frequency values direction has been observed. However, a causality relationship from ionospheric critical frequency values to Dst values has not been observed. From the results of cause-and-effect analysis, it is evaluated that the effect of a shockwave occurring in geomagnetic activity on ionospheric critical frequency continues along 72 h, that is, geomagnetic activity has a long-term effect on ionospheric critical frequency. The response of ionospheric critical frequency to geomagnetic activity substantially depends on seasons. This response is more observed especially in equinox period when the sun is active and in winter months. The increase in geomagnetic activity causes ionospheric critical frequency to decrease in night hours and increase in day hours. The same relationship has not been observed exactly, though observed very little in winter months, for 1985 when the sun was less active. 相似文献
The study is a deterministic-based approach on landslide susceptibility. The purpose of the paper is to create quantitative susceptibility maps by joining the one-dimension infinite slope stability model with a raster-based GIS (ILWIS) and taking into account the spatial distribution of input parameters. A landslide-prone area, with relative homogeneous geology and geomorphology, located in the Subcarpathian sector of the Prahova River, Romania, was selected for the study. There are frequent problems caused by active landslides in the studied area, especially in years with heavy precipitation, often causing destruction of houses and roads situated on the slopes (1992, 1997, and 2005). Detailed surveys covering a 7-year period provided the necessary input data on slope parameters, hydrological components, and the geotechnical background. Two simulations were used: one on dry soil conditions and one on fully saturated soil conditions. A third test was based on the level of the groundwater table mapped in summer 2008. Detailed analyses were particularly focused on landslides to compare predicted results with actual results using field measurements. The model is very suitable for use in raster GIS because it can calculate slope instability on a pixel basis, each raster cell being considered individually. The drawback of the model is the highly detailed data of input parameters. Despite this disadvantage, in conclusion, the usefulness of slope stability models on a large-scale basis was emphasized under infinitely high failure plain conditions and lithological homogeneity. 相似文献
Using the continuation method we prove that the circular and the elliptic symmetric periodic orbits of the planar rotating
Kepler problem can be continued into periodic orbits of the planar collision restricted 3-body problem. Additionally, we also
continue to this restricted problem the so called “comet orbits”.
An erratum to this article can be found at 相似文献
We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's
astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations,
covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that
with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σE(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σE(B-V) ≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA
this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales
within the framework of the GAIA mission.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The distribution of spotless flares (SFs) covering the time interval between 1947 and 1990 was investigated. The (11 – 20°)
latitude zone was found as the most prolific region for the occurrence of SFs. The longitudinal distribution of SFs occurred
most frequently at six or more places on the solar surface. In addition, the asymmetry of SF activity on the solar disk was
also studied in this paper. The variation of the asymmetry was compared with other solar activity manifestations. The existence
of secondary maxima of SFs appears to be an important result of our analysis. A one-year shift was found when the number of
events was plotted versus the year. 相似文献
In the context of major outcomes of a steadily changing climate, extreme climatic conditions and the associated events in various forms of weather-related natural disasters, e.g. droughts, floods, and heat waves, are more frequently experienced on the global scale in recent years. In support of this argument, there are adequate numbers of explicit signals over such a persistent outlook, which is greatly illustrated by historical data and observations. This study, which is mainly oriented to investigating the drought behaviour in Thracian, Aegean and Mediterranean transects of Turkey's major river basins, is actually inspired by the foreseen potential of using annual maximum drought severity series (based on drought definition through the standardized precipitation index (SPI)) within a framework that resembles the use of flood discharge directly from flow measurements in a river basin. To this end, a series of spatial analyses were employed to identify different aspects of flood appearance in the study extent, including trend views on annual average drought severity series, shifts in the starting time of the annually most severe flood periods, and changes in spatial coverage views of average drought conditions under different drought severity categories. The framework of the analytical approaches depends greatly on validated international datasets and open-source computational algorithms. The results from the analyses that were conducted in two consecutive periods of 1958–1980 and 1981–2004 revealed that Turkey's western and southern river basin systems seemed to have experienced quite different behaviours between the two periods in terms of drought severity magnitudes, drought durations and annual occurrence times.