The NAIAD experiment for WIMP searches at Boulby mine and recent results     

B. Ahmed  G. J. Alner  H. Araujo  J. C. Barton  A. Bewick  M. J. Carson  D. Davidge  J. V. Dawson  T. Gamble  S. P. Hart  R. Hollingworth  A. S. Howard  W. G. Jones  M. K. Joshi  V. A. Kudryavtsev  T. B. Lawson  V. Lebedenko  M. J. Lehner  J. D. Lewin  P. K. Lightfoot  I. Liubarsky  R. Lüscher  J. E. McMillan  B. Morgan  G. Nicklin  S. M. Paling  R. M. Preece  J. J. Quenby  J. W. Roberts  M. Robinson  N. J. T. Smith  P. F. Smith  N. J. C. Spooner  T. J. Sumner  D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702

The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented.  相似文献   

Implications of Kali-Hindon inter-stream aquifer water balance for groundwater management in western Uttar Pradesh     

Rashid Umar  M. Muqtada A. Khan  Izrar Ahmed  Shakeel Ahmed 《Journal of Earth System Science》2008,117(1):69-78

The Kali-Hindon inter-stream region extends over an area of 395 km² within the Ganga-Yamuna interfluve. It is a fertile tract for sugarcane cultivation. Groundwater is a primary resource for irrigation and industrial purposes. In recent years, over-exploitation has resulted in an adverse impact on the groundwater regime. In this study, an attempt has been made to calculate a water balance for the Kali-Hindon inter-stream region. Various inflows and outflows to and from the aquifer have been calculated. The recharge due to rainfall and other recharge parameters such as horizontal inflow, irrigation return flow and canal seepage were also evaluated. Groundwater withdrawals, evaporation from the water table, discharge from the aquifer to rivers and horizontal subsurface outflows were also estimated. The results show that total recharge into the system is 148.72 million cubic metres (Mcum), whereas the total discharge is 161.06 Mcum, leaving a deficit balance of −12.34 Mcum. Similarly, the groundwater balance was evaluated for the successive four years. The result shows that the groundwater balance is highly sensitive to variation in rainfall followed by draft through pumpage. The depths to water level are shallow in the canal-irrigated northern part of the basin and deeper in the southern part. The pre-monsoon and post-monsoon water levels range from 4.6 to 17.7 m below ground level (bgl) and from 3.5 to 16.5 m bgl respectively. It is concluded that the groundwater may be pumped in the canal-irrigated northern part, while withdrawals may be restricted to the southern portion of the basin, where intense abstraction has led to rapidly falling water table levels.  相似文献   

Extensional tectonic origin of gneissosity and related structures of the Feiran–Solaf metamorphic belt, Sinai, Egypt     

A. Fowler  I. Hassan 《Precambrian Research》2008,164(3-4):119-136

The Feiran–Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S₁, and is almost everywhere parallel to lithological layering, S₀. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S₀. S₁ formed by coaxial pure shear flattening strain (Z normal to S₀, i.e. vertical; with X and Y both extensional and lying in S₁). This strain also produced chocolate tablet boudinage of some layers and S₁-concordant sills and veins. S₁ has a strong stretching lineation L₁ with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L₁-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F₁ folds with hinges parallel to the stretching lineation. F₁ fold asymmetry variations do not support previous models involving macroscopic F₁ folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran–Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia.  相似文献   

Hydrogeological framework and water balance studies in parts of Krishni–Yamuna interstream area, Western Uttar Pradesh, India     

Izrar Ahmed  Rashid Umar 《Environmental Geology》2008,53(8):1723-1730

The Krishni–Yamuna interstream area is a micro-watershed in the Central Ganga Plain and a highly fertile track of Western Uttar Pradesh. The Sugarcane and wheat are the major crops of the area. Aquifers of Quaternary age form the major source of Irrigation and municipal water supplies. A detailed hydrogeological investigation was carried out in the study area with an objective to assess aquifer framework, groundwater quality and its resource potential. The hydrogeological cross section reveals occurrence of alternate layers of clay and sand. Aquifer broadly behaves as a single bodied aquifer down to the depth of 100 m bgl (metre below ground level) as the clay layers laterally pinch out. The depth to water in the area varies between 5 and 16.5 m bgl. The general groundwater flow direction is from NE to SW with few local variations. An attempt has been made to evaluate groundwater resources of the area. The water budget method focuses on the various components contributing to groundwater flow and groundwater storage changes. Changes in ground water storage can be attributed to rainfall recharge, irrigation return flow and ground water inflow to the basin minus baseflow (ground water discharge to streams or springs), evapotranspiration from ground water, pumping and ground water outflow from the basin. The recharge is obtained in the study area using Water table fluctuation and Tritium methods. The results of water balance study show that the total recharge in to the interstream region is of the order of 185.25 million m³ and discharge from the study area is of the order of 203.24 million m³, leaving a deficit balance of −17.99 million m³. Therefore, the present status of groundwater development in the present study area has acquired the declining trend. Thus, the hydrogeological analysis and water balance studies shows that the groundwater development has attained a critical state in the region.  相似文献   

Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh,India, Vietnam,and Nepal     

A. van Geen  K. Radloff  Z. Aziz  Z. Cheng  M.R. Huq  K.M. Ahmed  B. Weinman  S. Goodbred  H.B. Jung  Y. Zheng  M. Berg  P.T.K. Trang  L. Charlet  J. Metral  D. Tisserand  S. Guillot  S. Chakraborty  A.P. Gajurel  B.N. Upreti 《Applied Geochemistry》2008

One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.  相似文献   

Geochemistry and mineralogy of arsenic in (natural) anaerobic groundwaters     

J.A. Saunders  M.-K. Lee  M. Shamsudduha  P. Dhakal  A. Uddin  M.T. Chowdury  K.M. Ahmed 《Applied Geochemistry》2008

Here new data from field bioremediation experiments and geochemical modeling are reported to illustrate the principal geochemical behavior of As in anaerobic groundwaters. In the field bioremediation experiments, groundwater in Holocene alluvial aquifers in Bangladesh was amended with labile water-soluble organic C (molasses) and MgSO₄ to stimulate metabolism of indigenous SO₄-reducing bacteria (SRB). In the USA, the groundwater was contaminated by Zn, Cd and SO₄, and contained <10 μg/L As under oxidized conditions, and a mixture of sucrose and methanol were injected to stimulate SRB metabolism. In Bangladesh, groundwater was under moderately reducing conditions and contained ∼10 mg/L Fe and ∼100 μg/L As. In the USA experiment, groundwater rapidly became anaerobic, and dissolved Fe and As increased dramatically (As > 1000 μg/L) under geochemical conditions consistent with bacterial Fe-reducing conditions. With time, groundwater became more reducing and biogenic SO₄ reduction began, and Cd and Zn were virtually completely removed due to precipitation of sphalerite (ZnS) and other metal sulfide mineral(s). Following precipitation of chalcophile elements Zn and Cd, the concentrations of Fe and As both began to decrease in groundwater, presumably due to formation of As-bearing FeS/FeS₂. By the end of the six-month experiment, dissolved As had returned to below background levels. In the initial Bangladesh experiment, As decreased to virtually zero once biogenic SO₄ reduction commenced but increased to pre-experiment level once SO₄ reduction ended. In the ongoing experiment, both SO₄ and Fe(II) were amended to groundwater to evaluate if FeS/FeS₂ formation causes longer-lived As removal. Because As-bearing pyrite is the common product of SRB metabolism in Holocene alluvial aquifers in both the USA and Southeast Asia, it was endeavored to derive thermodynamic data for arsenian pyrite to better predict geochemical processes in naturally reducing groundwaters. Including the new data for arsenian pyrite into Geochemist’s Workbench, its stability field completely dominates in reducing Eh–pH space and “displaces” other As-sulfides (orpiment, realgar) that have been implied to be important in previous modeling exercises and reported in rare field conditions.  相似文献   

Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers     

Kathleen A. Radloff  Anya R. Manning  Brian Mailloux  Yan Zheng  M. Moshiur Rahman  M. Rezaul Huq  Kazi M. Ahmed  Alexander van Geen 《Applied Geochemistry》2008

Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1× or (4) 10× the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.  相似文献   

Distribution of Boron in Some Egyptian Aquatic Environments     

Doaa Hassan Youssef 《Journal of Oceanography》2003,59(5):537-544

Concentrations of boron in seawater (from four regions along the Alexandria coastline, subjected to land disposal), brackish water (Lake Edku) and drains water (e.g. El-Umum Drain) were determined during the period from February to August 2000. Boron was determined spectrophotometrically by a modified curcumin method. For Lake Edku, boron concentration fluctuated between 0.023 and 0.105 mmol/l. There are several factors that affect the concentration of B in the Lake water: (a) effect of the drainage water via El-Khairy and Barsiek Drains, (b) utilization of boron by hydrophytes, and (c) water exchange through the sea-lake connection. It may be concluded that the level of boron in the Lake water cannot be considered a substantial hazard to the Lake organisms. Boron concentration varied from 0.392 to 0.522 mmol/l in seawater samples and from 0.141 to 0.458 mmol/l in the sites where the water from the drains (El-Umum Drain and El-Noubaria Canal) mixed with the seawater. The broader variation of boron (mmol/l)/salinity ratios for seawater samples (0.0106–0.0138) may be due to that the samples were collected from the upper seawater layers, where contributions from land run-off, atmospheric precipitation and differences in the biota affect the concentration. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Preservation of enzymic activity in marine plankton by low-temperature freezing     

S.I. Ahmed  R.A. Kenner  F.D. King 《Marine Chemistry》1976,4(2):133-139

The measurement of enzymic activity in plankton communities is useful in the study of marine ecosystems. Such measurements can lead to a clearer understanding of the biological transformations in plankton communities at a particular time. However, the assays are somewhat time-consuming. To facilitate analysis of large numbers of samples, we have developed a method of quick-freezing of whole cells and of cell-free extracts of the diatom, Skeletonema costatum, followed by storage at ?60°C for up to one week. No loss in either the electron transport system (ETS) or the glutamate dehydrogenase (GDH) activity occurs. Similar conditions of storage can be used for the preservation of ETS activity in the marine copepod Calanus pacificus. Also, no measurable loss in either the GDH or the ETS activity is detectable after the quick-frozen whole cells of S. costatum have been kept frozen for over a year.  相似文献   

Comparison of dissolved and particulate arsenic distributions in shallow aquifers of Chakdaha, India, and Araihazar, Bangladesh     

Jerome Métral  Laurent Charlet  Sara Bureau  Sukumar Basu Mallik  Sudipta Chakraborty  Kazi M Ahmed  MW Rahman  Zhongqi Cheng  Alexander van Geen 《Geochemical transactions》2008,9(1):1

Background  

The origin of the spatial variability of dissolved As concentrations in shallow aquifers of the Bengal Basin remains poorly understood. To address this, we compare here transects of simultaneously-collected groundwater and aquifer solids perpendicular to the banks of the Hooghly River in Chakdaha, India, and the Old Brahmaputra River in Araihazar, Bangladesh.  相似文献