Merger histories in warm dark matter structure formation scenarios     

Alexander Knebe  Julien E. G. Devriendt  Asim Mahmood  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2002,329(4):813-828

Observations on galactic scales seem to be in contradiction with recent high-resolution N -body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy haloes. In this paper, we explore a different approach that consists of filtering the dark matter power spectrum on small scales, thereby altering the formation history of low-mass objects. The physical motivation for damping these fluctuations lies in the possibility that the dark matter particles have a different nature, i.e. are warm (WDM) rather than cold. We show that this leads to some interesting new results in terms of the merger history and large-scale distribution of low-mass haloes, compared with the standard CDM scenario. However, WDM does not appear to be the ultimate solution, in the sense that it is not able to fully solve the CDM crisis, even though one of the main drawbacks, namely the abundance of satellites, can be remedied. Indeed, the cuspiness of the halo profiles still persists, at all redshifts, and for all haloes and sub-haloes that we investigated. Despite the persistence of the cuspiness problem of DM haloes, WDM seems to be still worth taking seriously, as it alleviates the problems of over-abundant sub-structures in galactic haloes and possibly the lack of angular momentum of simulated disc galaxies. WDM also lessens the need to invoke strong feedback to solve these problems, and may provide a natural explanation of the clustering properties and ages of dwarfs.  相似文献   

Balance characteristics of multivariate background error covariances and their impact on analyses and forecasts in tropical and Arctic regions   总被引：4，自引：0，他引：4  

Yaodeng Chen  Syed R. H. Rizvi  Xiang-Yu Huang  Jinzhong Min  Xin Zhang 《Meteorology and Atmospheric Physics》2013,121(1-2):79-98

For variational data assimilation, the background error covariance matrix plays a crucial role because it is strongly linked with the local meteorological features, and is especially dominated by error correlations between different analysis variables. Multivariate background error (MBE) statistics have been generated for two regions, namely the Tropics (covering Indonesia and its neighborhood) and the Arctic (covering high latitudes). Detailed investigation has been carried out for these MBE statistics to understand the physical processes leading to the balance (defined by the forecasts error correlations) characteristics between mass and wind fields for the low and high latitudes represented by these two regions. It is found that in tropical regions, the unbalanced (full balanced) part of the velocity potential (divergent part of wind) contributes more to the balanced part of the temperature, relative humidity, and surface pressure fields as compared with the stream function (rotational part of wind). However, the exact opposite happens in the Arctic. For both regions, the unbalanced part of the temperature field is the main contributor to the balanced part of the relative humidity field. Results of single observation tests and six-hourly data assimilation cycling experiments are consistent with the respective balance part contributions of different fields in the two regions. This study provides an understanding of the contrasting dynamical balance relationship that exists between the mass and wind fields in high- and low-latitude regions. The study also examines the impact of MBE on Weather Research and Forecasting model forecasts for the two regions.  相似文献   

Geology and Genesis of Barite Deposits of Lasbela and Khuzdar Districts, Balochistan, Pakistan   总被引：1，自引：0，他引：1  

Syed Nayyer AHSAN  Khalil Ahmed MALLICK 《Resource Geology》1999,49(2):105-111

Abstract: Geology and genesis of the sediment-hosted barite deposits in the Lasbela and Khuzdar districts of Balochistan, Pakistan have been studied and described. Hot solutions generated in rifting environments during the initial stage of separation of the continental crustal block related to the Gondwanaland fragmentation subsequently reposed in Jurassic rocks, most probably played an important role on barite formation.
Paragenetic relationships indicate that the period of barite mineralization was distinctly later than that of zinc-lead sulphide mineralization in the Lasbela and Khuzdar districts. The barite deposits occur on top and in peripheral to the zinc-lead sulphides. The earliest barite mineralization took place in the clastic rock sequence of the lower Spingwar Formation as cross cutting veins. Younger mineralization as stratabound-replacement type occurred within the platform limestones of Loralai Formation, just above the Spingwar Formation. The youngest mineralization as stratiform is hosted within black shales, mudstones and argillaceous limestones of Anjira Formation at the top of Loralai Formation. In the light of the evidences gathered from field and laboratory investigations a genetic model has been deduced.  相似文献   

应用核磁共振技术分析干盐湖地区地下卤水空间分布特征——以昆特依干盐湖为例   总被引：3，自引：1，他引：2  

杨修猛  刘文玉  韩凤清  韩继龙  HUSSAIN Syed Asim  年秀清  毛庆飞  严维德 《湖泊科学》2018,30(1):220-233

昆特依干盐湖位于柴达木盆地西北部,为特大型综合盐类矿床.大盐滩是昆特依干盐湖内最大的盐滩,地下赋存有一定量的卤水矿床,但该矿床的水文地质条件差,主要卤水矿层含水性弱,开采难度大.核磁共振找水方法作为当今世界上唯一的直接找水地球物理新方法,具有高分辨力、高效率、信息量丰富和解的唯一性等优点,本文运用该方法对昆特依干盐滩地区地下卤水空间分布特征进行研究,通过对核磁共振数据进行处理与反演,结合已有的地质与钻井资料,对测点进行综合地质-地球物理解释,获得以下认识:1)大盐滩0~130 m深度范围内,共存在3个卤水含水层,主要呈扁平状或漏斗状、近似层状展布,W1为晶间潜卤水层,渗透系数较大,颗粒较粗,单位体积含水量为0.4%~2.7%,W2和W3为晶间承压卤水层,渗透系数较小,颗粒较粗,单位体积含水量分别为0.2%~1.1%和0.1%~0.8%;2)大盐滩地区存在两个卤水富集区,分别为研究区西南部沉积盆地中心的Ⅰ号富卤区和盆地东北部的Ⅱ号富卤区;3)根据区域内卤水富集分布以及构造情况,划定大盐滩向斜沉积中心、大盐滩北侧F1~F8及遥F6断裂发育区和冷湖构造带为区域内主要的找矿找水远景区;4)GMR核磁共振系统在干盐滩地区理论探测深度为130 m,该系统不仅可以有效地探测自由水,而且可以依据束缚水的分布解译地下各类含水盐类矿物和含水黏土矿物的存在与分布.  相似文献   

Assessment of village-wise groundwater draft for irrigation: a field-based study in hard-rock aquifers of central India     

R. K. Ray  T. H. Syed  Dipankar Saha  B. C. Sarkar  A. K. Patre 《Hydrogeology Journal》2017,25(8):2513-2525

Extracted groundwater, 90% of which is used for irrigated agriculture, is central to the socio-economic development of India. A lack of regulation or implementation of regulations, alongside unrecorded extraction, often leads to over exploitation of large-scale common-pool resources like groundwater. Inevitably, management of groundwater extraction (draft) for irrigation is critical for sustainability of aquifers and the society at large. However, existing assessments of groundwater draft, which are mostly available at large spatial scales, are inadequate for managing groundwater resources that are primarily exploited by stakeholders at much finer scales. This study presents an estimate, projection and analysis of fine-scale groundwater draft in the Seonath-Kharun interfluve of central India. Using field surveys of instantaneous discharge from irrigation wells and boreholes, annual groundwater draft for irrigation in this area is estimated to be 212 × 10⁶ m³, most of which (89%) is withdrawn during non-monsoon season. However, the density of wells/boreholes, and consequent extraction of groundwater, is controlled by the existing hydrogeological conditions. Based on trends in the number of abstraction structures (1982–2011), groundwater draft for the year 2020 is projected to be approximately 307 × 10⁶ m³; hence, groundwater draft for irrigation in the study area is predicted to increase by ～44% within a span of 8 years. Central to the work presented here is the approach for estimation and prediction of groundwater draft at finer scales, which can be extended to critical groundwater zones of the country.  相似文献   

Hydrogeochemical assessment of surface and groundwater resources of Korba coalfield,Central India: environmental implications     

Rambabu Singh  Tajdarul H. Syed  Suresh Kumar  Manoj Kumar  A. S. Venkatesh 《Arabian Journal of Geosciences》2017,10(14):318

The present study assesses the impact of coal mining on surface and groundwater resources of Korba Coalfield, Central India. Accordingly, water samples collected from various sources are analyzed for major ions, trace elements, and other mine effluent parameters. Results show that the groundwater samples are slightly acidic, whereas river water and mine water samples are mildly alkaline. Elevated concentrations of Ca²⁺, Na⁺, HCO₃ ^?, and SO₄ ^2? alongside the molar ratios (Ca²⁺+Mg²⁺)/(SO₄ ^2?+HCO₃ ^?) <1 and Na⁺/Cl^? >1 suggest that silicate weathering (water-rock interaction) coupled with ion exchange are dominant solute acquisition processes controlling the chemistry of groundwater in the study area. The overall hydrogeochemistry of the area is dominated by two major hydrogeochemical facies (i.e., Ca–Cl–SO₄ and Ca–HCO₃). Analysis of groundwater and river water quality index (GRWQI) elucidates that majority (82%) of samples are of “excellent” to “good” category, and the remaining 12% are of “poor” quality. Similarly, the effluent water quality index (EWQI) indicates that 6 out of 8 samples belong to excellent quality. Concentration of trace element constituents such as As, Zn, Cu, Cr, and Cd is found to be well within the stipulated limits for potable use, except for Fe, Mn, and Pb. Suitability of water samples for irrigation purpose, established using standard tools like Wilcox and USSL diagrams, reveal “excellent to permissible” category for majority of the samples. The present study also substantiates the effectiveness of the measures implemented for the treatment of mine effluent water.  相似文献   

Benthic foraminiferal response to changes in mining pattern: a case study from the Zuari estuary,Goa, India     

Syed Mohammad Saalim  R. Saraswat  T. Suokhrie  S. R. Bhadra  S. R. Kurtarkar  R. Nigam 《Environmental Earth Sciences》2017,76(20):706

Being sensitive to environmental changes, foraminifera have been extensively used to monitor pollution level in the marine environment, including the effect of mining in coastal areas. In the Goa state of India, the rejects from opencast mining on land largely find their way to the estuaries, as washout during monsoon. Additionally, the Mormugao Port at the mouth of the Zuari estuary is the hub of activities due to the transport of ore from hinterland areas by barges and its subsequent loading for export. On the directive of the Supreme Court of India, all the mining-related activities abruptly stopped throughout India, including that in Goa in 2012, and got reinstated in 2015. Therefore, it provided a fit case to test the effectiveness of benthic foraminifera as an indicator of environmental impact due to mining activities. A total of ten surface sediment samples from five locations in Zuari estuary were collected from a depth range of 4.5–8.5 m in the years of 2013 and 2016 and were analyzed for both the living (stained) and dead benthic foraminifera. The year 2013 represents a time interval immediately after the closure of extensive mining activity, and the sampling during 2016 represents minimal mining. The living benthic foraminiferal abundance was higher (19–54/g sediment) during 2013 and decreased substantially during 2016 (3–22/g sediment), suggesting an adverse effect of activities associated with mine closure on benthic foraminifera. Additionally, the relative abundance of Ammonia was also significantly low during the year 2016. The temporal variation in dead foraminifera was, however, different than that of the living foraminifera. The differential response was attributed to the terrigenous dilution as a result of change in sedimentation rate. Therefore, we conclude that living foraminifera correctly incorporate the changes in mining pattern and may be used as an effective tool to monitor the impact of mining. We further suggest that the potential counter effect of terrigenous dilution on total and living benthic foraminiferal population should be considered while interpreting temporal variations in foraminiferal abundance in marginal marine settings.  相似文献   

Offshore sand sources for beach replenishment: Potential borrows on the continental shelf of the Eastern Gulf of Mexico     

Charles W. Finkl Jr.  Syed M. Khalil  Jeffrey L. Andrews 《Marine Georesources & Geotechnology》2013,31(2):155-173

Erosion of sandy beaches is a worldwide problem that elicits innovative geoengineer‐ing techniques to reduce adverse impacts of shoreline retreat. Beach replenishment has emerged as the “soft”; shore‐stabilization technique of choice for mitigating beach erosion. This method of shore protection involves the addition of sand to the littoral sediment budget for sacrificial purposes. Because inland sand sources are often uneconomical or impractical to use, and known nearshore sources are limited, finding adequate quantities of suitable sand on the inner continental shelf is often vital to beach replenishment projects. The technical studies of survey and materials analysis that identify and delineate usable sand sources are sometimes almost as expensive as small‐project dredging, pumping, and placing the sand on the beach as fill. Inadequate quantity or substandard quality of shelf sand, as well as often‐prohibitive overhead expenses, thus compel shoreline managers to seek suitable sand sources offshore.

In the study area off the central‐west coast of Florida, offshore potential borrow areas (PBAs) were identified on the basis of studies conducted in reconnoitory and detailed phases. Sophisticated state‐of‐the‐art equipment used in this investigation provided more detailed subbottom mapping information than is normally obtained with conventional seismic equipment. An example of sand exploration studies was incorporated in a 215‐km² survey of offshore areas by conducting bathymetric surveys and subbottom seismic profiling, collecting jet probes, grab samples, and vibrocores, and analyzing sediment grading in subsamples from vibrocores. These combined analyses indicated that at least 8.8 ×10⁶ m³ of sand is available in potential borrow areas from 7.0 to 12 km offshore in water depths of 8.0 to 11.5 m. In the PBAs, mean grain size of sand falls into the range 0.13–0.53 mm, sorting averages 0.65–1.31ø, and the overall silt content varies from 3.9–8.5%. High silt contents (13–19%) mapped in some areas make these sedimentary deposits unsuitable as fill for artificial beach renourishment.  相似文献   

Coulomb stress evolution in Northeastern Caribbean over the past 250 years due to coseismic, postseismic and interseismic deformation   总被引：5，自引：0，他引：5  

Syed Tabrez Ali  rew M. Freed  Eric Calais  David M. Manaker  William R. McCann 《Geophysical Journal International》2008,174(3):904-918

  相似文献   

Earthquake hazards and community resilience in Baluchistan   总被引：5，自引：3，他引：2  

Syed Ainuddin  Jayant Kumar Routray 《Natural Hazards》2012,63(2):909-937

Resilience is widely used from a variety of research perspectives; however, community resilience in particular is applied to a number of natural hazards and disasters-related studies, programs, and activities. It is also acknowledged that its measurement is cumbersome but not impossible. The prime objective of this paper is to measure the community resilience of an earthquake-prone area in Baluchistan. The article presents the concept of resilience, its approaches, selection of indicators, formulation of subjective assessment method for weighting the indicators, and finally, developing the community resilience index. For the community resilience measurement, a survey was conducted among 200 households in two earthquake risk zones of Quetta city, using simple random sampling method. The overall composite community resilience index revealed that the resilience is low in both the zones??A and B. However, it is revealed that there is a significant difference between the zones when compared against the components and indicators. Community resilience components such as economic, institutional, and physical have received higher index values in Zone B as compared to Zone A. Based on the findings, it is recommended to improve the socioeconomic, institutional, and structural (housing) conditions of the community by raising the community awareness and preparedness, implementing building codes, and providing income-generating activities in order to enhance the community resilience to cope up with earthquake hazards in the future.  相似文献