Long-Term Soft X-Ray Variability of Active Galaxies. I. Mrk 926

We present a detailed analysis of the soft X-ray (0.1–2.4 keV) emission of the Seyfert 1 galaxy Mrk 926 in order to investigate its long-term variation. The X-ray data were obtained from the ROSAT-PSPC archives. The light curves show a gradual decrease of brightness for a time scales of 36months with the exception of a single flare event superimposed on the gradual variation of brightness. The light variations for three different energy bands and the hardness ratios were investigated to search for correlations; no correlation was confirmed. In order to compare spectral variations during the flare event with other periods, the spectral parameters were determined. Results of our analysis are discussed within the framework of the accretion disk phenomenon. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-Speed x-ray Jets Associated with the 18 June 1999 Limb Flares

Peculiar high-speed X-ray jets associated with the 18 June 1999 limb flares have directly been observed with the soft X-ray Telescope (SXT) aboard Yohkoh. The jets have a much shorter lifetime (within 200 s) and a much larger velocity (∼ 1700 km s⁻¹) than the previously reported jets. Judged from their large velocity, the kinetic energy of the jets is approximately one order of magnitude larger than the thermal energy content, which is far different from the jets previously reported by other researchers. Here we present the preliminary results and discuss the particular features of the jets. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013324126229     

Impacts of Coagulation Pretreatment on MF Filtration and a Comparative Study of Different Membrane Module Types

Changes in the regulatory requirements and the forthcoming Disinfectant/Disinfection By-Products （D/DBP） Rule will require that drinking water treatment facilities be operated to achieve maximum removals of particles and disinfectant tolerant microorganisms as well as natural organic matter （NOM）. For drinking water production, the use of membrane filtration processes such as microfiltration and ultrafiltration （MF/UF） alone to satisfy the turbidity, particle and microorganism removal a requirement of the surface water treatment regulation （SWTR） is not enough. MF/UF treatment processes can achieve only nominal （10 percent） removal of disinfection by-products （DBP） precursors （James, et al., 1995）. On the other hand, too fast fouling can make the filtration processes more difficult to carry on. To solve these problems, many authors have been interested in installing coagulation pretreatment before membrane filtration to improve membrane performance. However, previous studies reported conflicting results. Some supported the effectiveness of coagulation pretreatment, while others contended that coagulation aggravated membrane performance. This research aims to identify the effects of coagulation pretreatment on membrane filtration through a pilot study using PVDF membrane in combination with analyzing the rationale of coagulation. Another objective of this research was to evaluate the different impacts on membrane performance of using different membrane modules （the submerged module and pressured module）. The results showed that coagulation pretreatment greatly improved the membrane performance, extending the filtration time as well as reducing the permeated organic level, and that the submerged module is much more efficient than the pressured module.     

Ionomeric electroactive polymer artificial muscle for naval applications

Specialized propulsors for naval applications have numerous opportunities in terms of research, design, and fabrication of an appropriate propulsor. One of the most important components of any propulsor is the actuator that provides the mode of locomotion. ionomeric electroactive polymer may offer an attractive solution for locomotion of small propulsors. A common ionomeric electroactive polymer, ionic polymer-metal composites (IPMCs) give large true bending deformations under low driving voltages, operate in aqueous environments, are capable of transduction, and are relatively well understood. IPMC fabrication and operation are presented to further elucidate the use of the material for a propulsor. Various materials, including IPMCs, are investigated and a simplified propulsor model is explored.     

Simultaneous identification of parameter,initial condition,and boundary condition in groundwater modelling

In this paper, we perform an inverse method to simultaneously estimate aquifer parameters, initial condition, and boundary conditions in groundwater modelling. The parameter estimation is extended to a complete inverse problem that makes the calibrated groundwater flow model more realistic. The adjoint state method, the gradient search method, and the least square error algorithm are combined to build the optimization procedure. Horizontal two‐dimensional groundwater flow in a confined aquifer is exemplified to demonstrate the correlation between unknowns, the contribution of observation, as well as the suitability of applying the inverse method. The correlation analysis shows the connection between storage coefficient and initial condition. Besides, transmissivity and boundary conditions are also highly correlated. More observations at different location and time are necessary to provide sufficient information. A time series of unsteady head is requested for estimation of storage coefficient and initial condition. Observation near boundary is very effective for boundary condition estimation. The observation at pumping well mostly contributes to the estimation of transmissivity. According to all observations, it is possible to identify parameters, initial condition, and boundary condition simultaneously. Furthermore, the results not only illustrate the traditional assumption of known boundary condition but also initial condition, which may cause an incorrect estimation. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance evaluation of ultrafine cement as a grout for reservoir impermeability improvement

Acta Geotechnica - Although Ordinary Portland Cement (OPC) has been widely used as one of the significant grouting materials, there are many drawbacks to its application in the field. In this...     

Performance Analysis of ANN Prediction for Groundwater Level Considering Regional-Specific Influence Components

Groundwater level (GWL) varies periodically or non-periodically with various factors including precipitation, river stage (RS) change, sea level, and dewatering activities. In this study, the effect of influence components on the prediction of GWL using an artificial neural network (ANN) was investigated. Six regions with different hydrologic and geologic conditions were collected and adopted in the investigation using various input combinations. In urban areas with a high surface paved ratio, GWL was mainly affected by RS. In rural areas, the permeability of ground showed a significant impact on GWL. For such cases, the moving average (MA) was a suitable component as it could reflect both time lag and the effect of preceding precipitation. It was shown that site-specific influence component should be firstly identified and introduced into input for more enhanced and reliable prediction of GWL using ANN. The effect of learning data length (LDL) was less significant. In urban and rural areas, the introduction of RS and MA into ANN input significantly improved the prediction performance, respectively, which was consistent with the correlation analysis of GWL influence components.     

Life span of a landslide dam on mountain valley caught on seismic signals and its possible early warnings

Landslides - Outburst flooding after a landslide dam breach causes global fatalities and devastation. Information on the timing, magnitude, and location of the landslide dam is crucial to hazard...     

Reverse fault slip through soft rock and sand strata by centrifuge modeling tests

The devastating damage after the 1999 Chi-Chi and 1999 Izmit earthquakes has greatly motivated soil–reverse fault interaction studies. However, most centrifuge modeling studies have employed a single homogeneous soil layer during testing, which does not represent in situ conditions. Indeed, while geological conditions vary spatially, engineering soils are often underlain by soft rocks. Therefore, four centrifuge models were developed to evaluate the effect of soft rock layers on the ground surface and subsurface deformation. Sand–cement mixtures of varying thicknesses with a uniaxial compressive strength of 0.975 MPa, simulating extremely soft rock, were overlain by pluviated sandy soil. The model thickness was 100 mm, corresponding to 8 m in the prototype scale when spun at 80 g. Every model was subjected to a vertical offset of 50 mm/4 m (0.5 H; H: total sedimentary deposit thickness) along a reverse fault with a 60° dip. The results indicate that the presence of a soft rock stratum results in the creation of a horst profile at the ground surface. Additionally, the thinner the soil layer on top of the soft rock stratum is, the longer and higher the horst created at the ground surface. Consequently, the fault deformation zone lengthens proportionally with the increasing thickness ratio of the soft rock. Furthermore, the presence of soft rock as an intermediary stratum between bedrock and soil causes the deformation zone boundary on the hanging wall side to move in the direction of fault movement.