The Spectrum and Dips of RE 0751+14: A Joint Evaluation of ROSAT and ASCA Archival Data

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.     

Asteroseismic modelling of the solar-like star β Hydri

We present the results of modelling the subgiant star β Hydri using seismic observational constraints. We have computed several grids of stellar evolutionary tracks using the Aarhus STellar Evolution Code (ASTEC, Christensen-Dalsgaard in Astrophys. Space Sci. 316:13, 2008a), with and without helium diffusion and settling. For those models on each track that are located at the observationally determined position of β Hydri in the Hertzsprung-Russell (HR) diagram, we have calculated the oscillation frequencies using the Aarhus adiabatic pulsation package (ADIPLS, Christensen-Dalsgaard in Astrophys. Space Sci. 316:113, 2008b). Applying the near-surface corrections to the calculated frequencies using the empirical law presented by Kjeldsen et al. (Astrophys. J. 683:L175, 2008), we have compared the corrected model frequencies with the observed frequencies of the star. We show that after correcting the frequencies for the near-surface effects, we have a fairly good fit for both l=0 and l=2 frequencies. We also have good agreement between the observed and calculated l=1 mode frequencies, although there is room for improvement in order to fit all the observed mixed modes simultaneously.     

CCD BV and 2MASS photometric study of the open cluster NGC 1513

We present CCD BV and JHK _s 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 α ₂₀₀₀=04 ^h 09 ^m 36 ^s , δ ₂₀₀₀=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−K _s )=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.     

南海神狐海域水合物三相混合层测井评价方法研究

天然气水合物降压试采过程中,水合物、游离气和水的三相混合层中的游离气首先被采出,从而提高降压效率,促进水合物分解;因此利用岩心刻度测井的方法开展南海神狐海域水合物三相混合层测井评价方法研究,对水合物矿体储量计算以及产业化开采具有重要意义.三相混合层与水合物层相比,其密度和中子孔隙度值均减小,纵波速度明显下降;与气层相比...     

Effect of degree of saturation on mechanical behaviour of unsaturated soils and its elastoplastic simulation

The two stress-state variable approach has been widely used in interpreting unsaturated soil behaviour. However this approach cannot take into account the effect of degree of saturation or water contents on the stress–strain behaviour and strength of unsaturated soils. The triaxial test results presented in this paper show that even if the same path of net stress and suction is followed, the stress–strain relation and strength are different due to different degrees of saturation. When other conditions are the same, the higher the degree of saturation for the soil sample is, the higher the stress ratio corresponding to a given axial strain will be. This effect can be modeled by using an elasto-plastic constitutive model coupling hydraulic and mechanical behaviour of unsaturated soils. Comparisons between the predicted and measured results are presented, which demonstrate that the model can quantitatively simulate the influence of the degree of saturation on stress–strain behaviour and strength of unsaturated soils.     

A combined hydrologic and hydraulic modeling approach for testing efficiency of structural flood control measures

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.     

Radium-traced nutrient outwelling from the Subei Shoal to the Yellow Sea: Fluxes and environmental implication

The Subei Shoal is the largest sandy ridge in the southern Yellow Sea and is important source for nutrient loading to the sea. Here, the nutrient fluxes in the Subei Shoal associated with eddy diffusion and submarine groundwater discharge（SGD） were assessed to understand their impacts on the nutrient budget in the Yellow Sea. Based on the analysis of 223 Ra and 224 Ra in the field observation, the offshore eddy diffusivity mixing coefficient and SGD were estimated to be 2.3×10⁸ cm     

Ecological risk assessment and ecological security pattern optimization in the middle reaches of the Yellow River based on ERI+MCR model

The middle reaches of the Yellow River represent an important area for the protection and development of the Yellow River Basin. Most of the area of the river basin is within the Loess Plateau, which establishes it as a fragile ecological environment. Firstly, using high-resolution data of land use in the watershed from the past 30 years, landscape ecological risk(LER) sample units are defined and an ecological risk index(ERI) model is constructed. Kriging interpolation is used to display the LE...     

The effect of the geomagnetic activity to the hourly variations of ionospheric foF2 values at low latitudes

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.