Multiple geographies of the Arab Internet   总被引：1，自引：0，他引：1  

Barney Warf  Peter Vincent 《Area》2007,39(1):83-96

The Arab world plays a relatively minor role in the rapidly changing geographies of global cyberspace. This paper explores the multiple geographies of the Arab Internet. First, it addresses Internet penetration rates, which averaged 7.8 per cent in 2006, although these varied widely among and within the region's countries. Between 2000 and 2006, the number of users jumped by 830 per cent, indicating these geographies are in rapid flux. It then examines the telecommunications infrastructure of the Middle East and North Africa, including fixed and mobile telephone networks and Internet cafes. Third, it turns to the reasons why the Internet has experienced relatively late adoption among Arab countries, including the dominance of the Latin alphabet, high access costs reflecting state-owned telecommunications monopolies, low Arab literacy rates, and restrictive gender relations that keep the proportion of female users low. The paper pays special attention both to government censorship of the Arab Internet as well as resistance to such controls and attempts to utilize the Internet counter-hegemonically. Finally, it explores the impacts of the Internet on some Arab societies, including the opening of discursive communities of politics, the Palestinian–Israeli conflict, Iraq and electronic commerce.  相似文献   

Characteristics of seasonal and spatial variations of primary production over the southeastern Bering Sea shelf   总被引：3，自引：1，他引：3  

TaeKeun Rho  Terry E. Whitledge 《Continental Shelf Research》2007,27(20):2556-2569

In situ primary production data collected during 1978–1981 period and 1997–2000 period were combined to improve understanding of seasonal and spatial distribution of primary production in the southeastern Bering Sea. Mean daily primary production rates showed an apparent seasonal cycle with high rates in May and low rates in summer over the entire shelf of the southeastern Bering Sea except for oceanic region due to lack of data. There was also an increasing trend of primary production rates in the fall over the inner shelf and the middle shelf. There was a decreasing trend of primary production rates between late April and mid-May over the inner shelf while there was an abrupt increase between late April and mid-May over the middle shelf and the outer shelf. In the shelf break region, there was an increasing pattern in late May. These suggest that there was a gradual progression of the development of the spring phytoplankton bloom from the inner shelf toward the shelf break region. There was also a latitudinal variability of primary production rate over the middle shelf, probably due to either spatial variations of the seasonal advance and retreat of sea ice or horizontal advection of saline water in the bottom layer. Annual rates of primary production across the southeastern Bering Sea shelf were 121, 150, 145, 110, and 84 g C m⁻² yr⁻¹ in the inner shelf, the middle shelf, the outer shelf, the shelf break, and oceanic region, respectively. High annual rates of primary production over the inner shelf can be attributed to continuous summer production based on regenerated nitrogen and/or a continuous supply of nitrogen at the inner front region, and to fall production. There were some possibilities of underestimation of annual primary production over the entire shelf due to lack of measurement in early spring and fall, which may be more apparent over the shelf break and oceanic region than the inner shelf, the middle, and the outer shelf. This study suggests that the response of primary production by climate change in the southeastern Bering Sea shelf can be misunderstood without proper temporal and seasonal measurement.  相似文献   

Textural attributes, mineralogy and provenance of sand dune fields in the greater Al Ain area, United Arab Emirates     

Mohamed M. Abu-Zeid  Ashraf R. Baghdady  Hassan A. El-Etr 《Journal of Arid Environments》2001,48(4):475

Sand dunes and interdune sediments around Al Ain city have markedly high carbonate contents which increase towards Jabal Hafit mountain and the Arabian Gulf coast. The dunes are composed predominantly of well-sorted fine sands, consisting of unstrained quartz and carbonate grains together with minor proportions of chert and feldspars. Scanning electron microscope (SEM) examination reveals that quartz grains display various mechanically- and chemically-formed surface textures. The heavy minerals are dominated by opaques and pyroxenes with minor tourmaline, garnet, rutile, epidote, monazite, zircon, hornblende and staurolite.Interdune sediments consist of fine and very fine, poorly- to extremely poorly-sorted sands together with small concentrations of gravel, silt and clay. The light sand fractions compositionally resemble those of dunes but contain, in addition, gypsum, anhydrite, halite and celestite. Percentages of pyroxenes are higher whereas those of zircon, tourmaline and rutile are lower than in dunes. X-ray diffractometry reveals that the clay fractions consist solely of palygorskite. Generally, interdune sediments are much less mature texturally and mineralogically than dune sands; the maturity of both types of sediments decreases toward the NE of the study area.Sand dunes in the various districts of the greater Al Ain area are genetically related. Also, there is a partial genetic relationship between the dunes and interdune sediments; both are mainly multicyclic. Their major parts were brought mainly by the dominant north-west (El Shamal) winds from older dune fields in other localities in U.A.E., Qatar and El-Rub El-Khali. Local contributions to the dune fields from Jabal Hafit mountain, the Oman Mountains and the calcareous coast of the Arabian Gulf were, in cases, significant. Also, authigenesis by groundwater under highly evaporitic conditions played a major role in the formation of interdune sediments through the genesis of the clay and some nonclay minerals.  相似文献   

The generation of phytoplankton patchiness by mesoscale current patterns   总被引：1，自引：0，他引：1  

Katja Fennel 《Ocean Dynamics》2001,52(2):58-70

 Elken et al. (1994) suggested that phytoplankton patchiness can be generated by mesoscale eddies in light-limited, nutrient-replete environments. This hypothesis is explored using two ecological models of different physical complexity. The model results support the idea that the coupling of mesoscale eddy circulation and phytoplankton growth leads to differential growth rates and thus generates variability in phytoplankton distributions. The specific circulation of a cyclonic eddy isolates a phytoplankton population in its core. Due to the reduced vertical mixing, a higher growth rate is supported in the core, and phytoplankton concentrations increase compared to the surrounding environment. A one-dimensional model is used to explore the hypothesis in general and to perform sensitivity studies. A more realistic simulation uses a coupled three- dimensional model for the western Baltic Sea. Starting from vertically and horizontally homogeneous distributions for nutrients and plankton, the models generate patchiness due to the proposed mechanism. The described mechanism may apply for other mesoscale variable environments during light-limited growth periods as well, e.g., the frontal region of the Southern Ocean. Received: 31 March 2001 / Accepted: 31 August 2001  相似文献   

福州市温泉区地面沉降监测与沉降规律分析     

黄国烟 《测绘工程》1996,5(3):59-63

应用精密水准测量方法，于１９９３年在温泉区取得三个周期的观测成果，结合以往资料进行综合分析，得出初步结论。并为福州市地下热水开采的控制、预防及减轻因沉降产生的地灾害方面提出有益的建议。  相似文献   

春小麦单叶气孔行为及蒸腾作用的模拟   总被引：1，自引：0，他引：1  

郑海雷  黄子琛 《高原气象》1992,1(4):423-430

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地震活动期小汤山温泉的水文地球化学效应     

王基华  金晓微 《地震研究》1992,15(2):205-209

本文介绍了自1987年5月开始观测以来,小汤山温泉溶解H_2、CH_4及电导率在地震活动期的变化特征,并对小汤山(以下统称为井)的映震能力进行了初步讨论。  相似文献   

用褶积积分和低通滤波方法处理沂水泉氡观测资料   总被引：1，自引：0，他引：1  

张昭栋  靖继才  高玉斌  张铸钢 《高原地震》1992,(3)

多年来的观测分析表明,影响沂水泉氧值变化的最大干扰是降雨。由于这种干扰存在着滞后效应,所以用一般相关分析难以将这种影响排除干净。本文采用褶积积分方法较好地排除了降雨对沂水泉氧观测的影响。并用低通滤波方法,探讨了沂水泉氧的长趋势变化。  相似文献   

甘肃省春季沙尘暴强弱年份大气环流特征对比分析   总被引：4，自引：0，他引：4  

俞亚勋  赵建华 《干旱气象》2003,21(3):48-57

文中使用NCEP/NCAR1955～2000年全球月平均再分析网格点资料(2.5°×2.5°纬度/经度)和甘肃省区域性沙尘暴过程资料,分别选取了甘肃省5个春季典型沙尘暴年份和5个春季非沙尘暴年份,对其气候平均的大尺度环流场和有关物理量场的动力和热力结构差异进行了对比分析。初步探讨了甘肃省春季沙尘暴发生与全球海温异常的关系。分析结果表明,甘肃省春季沙尘暴年和非沙尘暴年大尺度高低空环流场和有关物理量场差异明显,从而揭示了沙尘暴形成的大尺度环流以及动力和热力因子影响的事实,以期对我国西北地区沙尘暴气候成因有更全面深入的了解,为沙尘暴短期气候预测提供理论依据和强信号。  相似文献   

小口子泉水氡映震范围及能级研究     

訾少刚  延海军  梅浩  吕俊强  赵静 《内陆地震》2007,21(4):342-347

介绍了银川基准台小口子泉的概况以及水氡观测情况。研究了自1990以来银川台小口子泉周边地区300 km范围内ML4.0以上地震与银川台水氡资料的映震情况。通过对典型震例深入研究,总结了小口子泉水氡与周边地区地震活动的对应关系,探讨了小口子泉水氡对周边地区地震的对应范围和对应的震级范围。小口子泉水氡异常对该泉点西北方向的地震反映灵敏,且都是低值异常。  相似文献