Holocene stratigraphy-of the Lower Ganges-Brahmaputra River delta in Bangladesh     

Sirajur Rahman KHAN  Md Badrul ISLAM 《Frontiers of Earth Science》2008,2(4):393-399

Major part of the Holocene Ganges-Brahmaputra delta occupies the southern and southwestern part of Bangladesh with a smaller part extending beyond the international boundary in the west. Five facies assemblages are documented in the lower deltaic plain in five different depositional environments: levee or levee complex, bil or depression, abandoned meander belt, interdistributary plain and estuarine plain. The thickness of the Holocene sediments ranges from 30 m to 70 m in the deltaic plain, usually floored by the Pleistocene stiff clays, with the exception of the abandoned meander belt deposit where Holocene channel sand deposited directly on the Pleistocene sand. Radiocarbon dates indicate that low-rate sedimentation has occurred in the northern part, where 4-6 m thick sediments were deposited since the mid-Holocene, whereas 10-30 mthick sediments were deposited in the southern part during the same span of time. In addition, significant coastal subsidence (3 mm/a on average), added by sea-level rise (1.5 mm/a, conservative rate) occurs in the study area, which serves as a negative factor in degrading the coastal plain of Bangladesh in the future, while taking into consideration the weaker sedimentation in the area.  相似文献   

Multicriteria decision analysis in water resources management: the malnichara channel improvement   总被引：2，自引：2，他引：0  

R. K. Chowdhury  R. Rahman 《International Journal of Environmental Science and Technology》2008,5(2):195-204

Multicriteria decision analysis tool is used in many water resources and environmental management projects. The Malnichara is one of the natural channels in Sylhet city (Bangladesh) responsible for storm runoff conveyance to the downstream Surma river. The channel is found to be encroached at many locations of the city and found to be very vulnerable. The authority has taken decision to improve natural channels by a traditional approach, e.g. constructing box culvert. In most cases, stakeholders’ participation is ignored in such type of decision making. Hence, efforts were made to evaluate three common alternatives viz. sodding natural channel, lined natural channel and box culvert for the channel improvement. The channel is hydrologically divided into two parts: the upper portion (Choukidekhi-Kanishail) and the lower portion (Kanishail-Topoban). Both parts were separately analyzed. Small groups of stakeholders were interviewed for the selection of criteria and for the assignment of weighed factor and scores. Experts’ opinions were also taken through consultation. Nine criteria from four categories such as technical, economic, environment and social aspects were selected. The relative performances of alternatives were evaluated using the weighed sum technique of multicriteria decision analysis. It was found that the sodding natural channel is the best alternative for both portions of the channel. However, the choice is very sensitive to the social criteria.  相似文献   

Application of artificial neural networks in regional flood frequency analysis: a case study for Australia   总被引：4，自引：3，他引：1  

K. Aziz  A. Rahman  G. Fang  S. Shrestha 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(3):541-554

Regional flood frequency analysis (RFFA) is widely used in practice to estimate flood quantiles in ungauged catchments. Most commonly adopted RFFA methods such as quantile regression technique (QRT) assume a log-linear relationship between the dependent and a set of predictor variables. As non-linear models and universal approximators, artificial neural networks (ANN) have been widely adopted in rainfall runoff modeling and hydrologic forecasting, but there have been relatively few studies involving the application of ANN to RFFA for estimating flood quantiles in ungauged catchments. This paper thus focuses on the development and testing of an ANN-based RFFA model using an extensive Australian database consisting of 452 gauged catchments. Based on an independent testing, it has been found that ANN-based RFFA model with only two predictor variables can provide flood quantile estimates that are more accurate than the traditional QRT. Seven different regions have been compared with the ANN-based RFFA model and it has been shown that when the data from all the eastern Australian states are combined together to form a single region, the ANN presents the best performing RFFA model. This indicates that a relatively larger dataset is better suited for successful training and testing of the ANN-based RFFA models.  相似文献   

Timeline analysis and wavelet multiscale analysis of the AKARI All-Sky Survey at 90 μm     

Lingyu Wang  Michael Rowan-Robinson  Issei Yamamura  Hiroshi Shibai  Rich Savage  Seb Oliver  Matthew Thomson  Nurur Rahman  Dave Clements  Elysandra Figueredo  Tomotsugu Goto  Sunao Hasegawa  Woong-Seob Jeong  Shuji Matsuura  Thomas G. Müller  Takao Nakagawa  Chris P. Pearson  Stephen Serjeant  Mai Shirahata  Glenn J. White 《Monthly notices of the Royal Astronomical Society》2008,387(2):601-615

We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio  (S/N) > 5  for a single detector row is  1.1 ± 0.1 Jy  which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.  相似文献   

Seismological model parameters for northeastern and its surrounding region of India          下载免费PDF全文

Tauhidur Rahman 《地震科学（英文版）》2012,25(4):323-338

A point source seismological model is used in this study to model the available strong motion accelerograms recorded by 17 events and to calculate three seismological model parameters, the source, path, and quality factor. Due to the paucity of recorded events, this is the first time these model parameters have been obtained for the northeastern and its surrounding region of India. The quality factors of the horizontal and vertical components of recorded events with corresponding standard deviations are Q_H(f) = 188.55f^0.94, σ₁ value (25, 0.025) and Q_V(f) = 169.76f^0.93, σ₁ value (20, 0.03), respectively. The source parameter stress drop values (μσ) vary within 124–180 bars for the subduction region and 80–169 bars for the active region. The Kappa factors for the horizontal and vertical components of recorded events on the soft rock site are 0.06 and 0.05, respectively. These seismological model parameters obtained in this study will be useful for future work deriving a ground motion attenuation relation based on a spectral model. Finally, these results are useful for seismic hazard assessment of a region having sparsely recorded events.  相似文献   

Designing Iron‐Amended Biosand Filters for Decentralized Safe Drinking Water Provision     

Chicgoua Noubactep  Emile Temgoua  Mohammad A. Rahman 《洁净——土壤、空气、水》2012,40(8):798-807

There are ongoing efforts to render conventional biosand filters (BSF) more efficient for safe drinking water provision. One promising option is to amend BSF with a reactive layer containing metallic iron (Fe⁰). The present communication presents some conceptual options for efficient Fe⁰‐amended BSF in its fourth generation. It is shown that a second fine‐sand layer should be placed downwards from the Fe⁰‐reactive layer to capture dissolved iron. This second fine‐sand layer could advantageously contain adsorbing materials (e.g. activated carbons, wooden charcoals). An approach for sizing the Fe⁰‐reactive layer is suggested based on 3 kg Fe⁰ per filter. Working with the same Fe⁰ load will ease comparison of results with different materials and the scaling up of household BSF to large scale community slow sand filters (SSF).  相似文献   

Geochemistry of subsurface Late Quaternary ironstones in Rajshahi and Bogra Districts,Bangladesh: implications for genetic and depositional conditions     

Rahman  Md. Sazzadur  Hossain  Ismail  Biswas  Pradip Kumar  Rahim  Md. Abdur  Hasan  A. S. M. Mehedi  Adham  Md. Ibrahim 《中国地球化学学报》2019,38(3):404-413

The present study deals with the geochemistry of Late Quaternary ironstones in the subsurface in Rajshahi and Bogra districts, Bangladesh with the lithological study of the boreholes sediments. Major lithofacies of the studied boreholes are clay, silty clay, sandy clay, fine to coarse grained sand, gravels and sands with (fragmentary) ironstones. The ironstones contain major oxides, Fe₂O₃* (* total Fe) (avg. 66.6 wt%), SiO₂ (avg. 15.3 wt%), Al₂O₃ (avg. 4.0 wt%), MnO (avg. 7.7 wt%), and CaO (avg. 3.4 wt%). These geochemical data imply that the higher percentage of Fe₂O₃* along with Al₂O₃ and MnO indicate the ironstone as goethite and siderite, which is also validated by XRD data. A comparatively higher percentage of SiO₂ indicates the presence of relative amounts of clastic quartz and manganese-rich silicate or clay in these rocks. These ironstones also have significant amounts of MnO (avg. 7.7 wt%) suggesting their depositional environments under oxygenated condition. Chemical data of these ironstones suggest that the source rock suffered deep chemical weathering and iron was mostly carried in association with the clay fraction and organic matter. Iron concretion was mostly formed by bacterial build up in swamps and marshes, and was subsequently embedded in clayey mud. Within the coastal environments, the water table fluctuates and goethite and siderite with mud and quartz became dry and compacted to form ironstone.

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Number Counts,Confusion, Mapping Issues,and Sky Coverage Analysis for Radio Continuum Surveys through Emu Early Science,EMU-ASKAP,and WODAN Especially for Cosmology Science Goals     

ur Rahman  Syed Faisal  Iqbal  M. J. 《Astronomy Reports》2019,63(7):515-526

In this study, we discuss the challenges radio astronomers face while observing radio continuum sources. We consider issues related to rms noise, confusion, position accuracy, shot noise and how these issues affect observation results, data analysis and the science goals we are trying to achieve. We mainly focus on the Evolutionary Map of the Universe (EMU-ASKAP) sky survey, EMU Early science survey and Westerbork Observations of the Deep APERTIF Northern sky (WODAN). The study will also be useful for future surveys like with possible continuum surveys through MeerKAT (e.g., MIGHTEE) and SKA-1. The late time Integrated Sachs-Wolfe (ISW) effect detection is one of the major areas of research related to dark energy cosmology. We will particularly discuss how technical, data analysis and mapping issues, affect galaxy over/under density dependent science goals like the detection of the late time Integrated Sachs-Wolfe (ISW) effect through wide-field radio continuum surveys.

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The first electric field pulse of cloud and cloud-to-ground lightning discharges     

Noor Azlinda Ahmad  M. Fernando  Z.A. Baharudin  M. Rahman  V. Cooray  Ziad Saleh  Joseph R. Dwyer  Hamid K. Rassoul 《Journal of Atmospheric and Solar》2010,72(2-3):143-150

In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as ‘small’, ‘medium’ and ‘large’, depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.  相似文献   

Assessment of trace elements of groundwater and their spatial distribution in Rangpur district,Bangladesh     

A. R. M. Towfiqul Islam  Shuanghe Shen  Md. Bodrud-Doza  M. Atiqur Rahman  Samiran Das 《Arabian Journal of Geosciences》2017,10(4):95

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