Assessing the vulnerability of food crop systems in Africa to climate change     

Andrew Challinor  Tim Wheeler  Chris Garforth  Peter Craufurd  Amir Kassam 《Climatic change》2007,83(3):381-399

Africa is thought to be the region most vulnerable to the impacts of climate variability and change. Agriculture plays a dominant role in supporting rural livelihoods and economic growth over most of Africa. Three aspects of the vulnerability of food crop systems to climate change in Africa are discussed: the assessment of the sensitivity of crops to variability in climate, the adaptive capacity of farmers, and the role of institutions in adapting to climate change. The magnitude of projected impacts of climate change on food crops in Africa varies widely among different studies. These differences arise from the variety of climate and crop models used, and the different techniques used to match the scale of climate model output to that needed by crop models. Most studies show a negative impact of climate change on crop productivity in Africa. Farmers have proved highly adaptable in the past to short- and long-term variations in climate and in their environment. Key to the ability of farmers to adapt to climate variability and change will be access to relevant knowledge and information. It is important that governments put in place institutional and macro-economic conditions that support and facilitate adaptation and resilience to climate change at local, national and transnational level.  相似文献   

Full-scale structural monitoring using an integrated GPS and accelerometer system   总被引：2，自引：0，他引：2  

Xiaojing Li  Linlin Ge  Eliathamby Ambikairajah  Chris Rizos  Yukio Tamura  Akihito Yoshida 《GPS Solutions》2006,10(4):233-247

Accurate in situ measurement of the full-scale structural responses, especially tall buildings, under severe loading conditions is an important requirement for validating their design, evaluating their construction as well as facilitating their maintenance. Traditionally such response has been measured using accelerometers. However, it is impossible to measure the static and quasi-static components of motion with acceleration sensors. An integrated system comprising of RTK-GPS and accelerometers has been developed with the objective of assessing full-scale structural responses by exploiting the complementary characteristics of GPS and accelerometer sensors. The data used in this paper were obtained from GPS and accelerometer sensors installed on a 108-m-high steel tower in Tokyo, together with other sensors such as anemometer and strain gauge. The seismic and wind-induced responses of the tower were analyzed using the Fast Fourier Transformation (FFT) and compared to results from finite element modeling (FEM). In order to study the system reliability, the correlated signals were extracted by applying a digital filtering technique. Then the filtered data sets were converted to displacement (in the case of accelerometer data) and acceleration (in the case of GPS data) through double integration and double differentiation, respectively, for the purpose of direct comparison and to further fuse data from the two different sensors. The results agree with each other very well, although the static and quasi-static components are missing from the accelerometer-derived results. The redundancy of the monitoring system therefore has been achieved.  相似文献   

A real-time meteorological-based troposphere (RMT) correction with integrity bound for long baseline DGPS     

Yujie Zhang  Chris G. Bartone 《GPS Solutions》2006,10(1):73-73

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A note on a property of pulasting stars     

Chris Koen 《Astrophysics and Space Science》1987,132(1):53-56

An explanation for the observed correlation between the ratio (relative amplitude of flux variation)/(relative amplitude of radius variation) and the period of radial pulsation in cepheids is proposed. If the explanation is correct, correlations may be expected for other classes of pulsating stars with the general functional form determined by physical conditions in the atmosphere.  相似文献   

The Oxford–Dartmouth Thirty Degree Survey – I. Observations and calibration of a wide-field multiband survey     

Emily C. MacDonald  Paul Allen  Gavin Dalton  Leonidas A. Moustakas  Catherine Heymans  Edward Edmondson  Chris Blake  Lee Clewley  Molly C. Hammell  Ed Olding  Lance Miller  Steve Rawlings  Jasper Wall  Gary Wegner  Christian Wolf 《Monthly notices of the Royal Astronomical Society》2004,352(4):1255-1272

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Herbicides implicated as the cause of severe mangrove dieback in the Mackay region, NE Australia: consequences for marine plant habitats of the GBR World Heritage Area     

Duke NC  Bell AM  Pederson DK  Roelfsema CM  Bengtson Nash S 《Marine pollution bulletin》2005,51(1-4):308-324

Herbicides, particularly diuron, were correlated with severe and widespread dieback of the dominant mangrove, Avicennia marina (Forsk.) Vierh. var. eucalyptifolia (Val.) N.C. Duke (Avicenniaceae), its reduced canopy condition, and declines in seedling health within three neighbouring estuaries in the Mackay region of NE Australia. This unusual species-specific dieback, first observed in the early 1990s, had gotten notably worse by 2002 to affect >30 km(2) of mangroves in at least five adjacent estuaries in the region. Over the past century, agricultural production has responded well to the demands of increasing population with improvements in farm efficiency assisted by significant increases in the use of agricultural chemicals. However, with regular and episodic river flow events, these chemicals have sometimes found their way into estuarine and nearshore water and sediments where their effects on marine habitats have been largely unquantified. Investigations over the last three years in the Mackay region provide compelling evidence of diuron, and possibly other agricultural herbicides, as the most likely cause of the severe and widespread mangrove dieback. The likely consequences of such dieback included declines in coastal water quality with increased turbidity, nutrients and sediment deposition, as well as further dispersal of the toxic chemicals. The implications of such findings are immense since they describe not only the serious deterioration of protected and beneficial mangrove habitat but also the potential for significant direct and indirect effects on other highly-valued estuarine and marine habitats in the region, including seagrass beds and coral reefs of the Great Barrier Reef lagoon. This article reviews all key findings and observations to date and describes the essential correlative and causative evidence.  相似文献   

新疆叶城晚新生代山前盆地演化与高原北缘的隆升—Ⅰ地层学与岩石学证据   总被引：21，自引：2，他引：19  

郑洪波  KatherineButcher 《沉积学报》2002,20(2):274-281

叶城晚新生代山前盆地的岩性主要由中新世的细粒泥岩和砂岩（乌恰群）,上新世的砂岩夹薄层砾岩（阿图什组）及上新世－更新世的粗粒砾岩（西域组）构成。中新世的沉积以细颗粒泥砂岩为主,表明物源区较远,古流域坡度较小,搬运距离较长。古流向分析显示物源区位于南和偏南方,此时昆仑山的地势起伏尚不大。到上新世的阿图什组沉积时,开始出现砾石沉积,反映西昆仑山已经开始有规模地隆升。西域砾岩的沉积标志着作为物源区的西昆仑山民有相当的高度,随着山系的隆升,基底岩石被暴露和剥蚀。  相似文献   

Implications for unified schemes from the quasar fraction and emission-line luminosities in radio-selected samples     

Jennifer A. Grimes  Steve Rawlings  Chris J. Willott 《Monthly notices of the Royal Astronomical Society》2004,349(2):503-517

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On the redshift cut-off for steep-spectrum radio sources   总被引：1，自引：0，他引：1  

Matt J. Jarvis  Steve Rawlings  Chris J. Willott  Katherine M. Blundell  Steve Eales  Mark Lacy 《Monthly notices of the Royal Astronomical Society》2001,327(3):907-917

We use three samples (3CRR, 6CE and 6C*) selected at low radio frequency to constrain the cosmic evolution in the radio luminosity function (RLF) for the 'most luminous' steep-spectrum radio sources. Though intrinsically rare, such sources give the largest possible baseline in redshift for the complete flux-density-limited samples currently available. Using parametric models to describe the RLF, incorporating distributions in radio spectral shape and linear size, as well as the usual luminosity and redshift, we find that the data are consistent with a constant comoving space density between     and     . We find that this model is favoured over a model with similar evolutionary behaviour to that of optically selected quasars (i.e., a roughly Gaussian distribution in redshift) with probability ratios of     and     for spatially flat cosmologies with     and     respectively. Within the uncertainties, this evolutionary behaviour may be reconciled with the shallow decline preferred for the comoving space density of flat-spectrum sources by Dunlop & Peacock and Jarvis & Rawlings, in line with the expectations of unified schemes.  相似文献   

I _C and R_C band time-series observations of some bright ultracool dwarfs     

Chris Koen 《Monthly notices of the Royal Astronomical Society》2005,360(3):1132-1142

The results of more than 100 h of CCD photometric monitoring of 10 L dwarfs and two T dwarfs are presented. Reasonable evidence is shown for I _C band variability in DENIS 0255−4700, DENIS 1705−0516 and 2M 2104−1037. Substantial brightening of the T dwarf binary ε Indi Bab was observed over the course of 3.6 h; it is unlikely that this could have been caused by surface spots. No unequivocal variability could be detected in the R _C band.  相似文献