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《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(4):295-302
Pulpwood has been imported to Norway since the beginning of the 20th century. However, exotic plant species hitchhiking with pulpwood were not observed before c.1985. Prior to this the imported timber was debarked, and the chances that diaspores would have attached to a debarked log (compared to a log with bark) are very small. A greenhouse germination experiment based on 385 dm2 of sifted bark from the holds of nine Estonian pulpwood ships yielded 3187 seeds of 201 species of vascular plants, few of which were typical of coniferous forests. Approximately 39% of the hitchhiking seeds did not germinate until after a period of cold treatment. Most of the species germinated in low densities, and those occurring in greater numbers are common and widespread in Norway. Six species were new to Norway: Agrostis clavata, Androsace filiformis, Bidens radiata, Carex montana, Melica picta, and Ranunculus cassubicus. During the last 20 years, pulpwood has been imported to Norway from many countries around the world, e.g. Russia, Scotland, Canada, and Zaire. While the present data do not indicate any immediate threat from aggressively invasive exotics, in order to avoid the introduction of non-native species and reduce the potential for biological invasion, timber should ideally be debarked prior to importation. 相似文献
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The paper presents a comprehensive multi-objective hydrodynamic optimisation procedure and its application to the early design of a floating liquefied natural gas (LNG) terminal for improved seakeeping and wave attenuation characteristics on its lee side. Genetic algorithms are used to find the Pareto optima designs followed by multi-objective decision making procedures to select the optimum design among them. The paper addresses the definition of the relevant optimisation problem and the set-up and interface of relevant software tools, presents results of systematic studies with respect to the minimisation of the motion responses and wave elevation on the leeward side of free-floating terminals and concludes with analysis and critical review of the obtained results and their impact on terminal design. 相似文献
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Roderick J. Mclntosh Boubacar Hama Diaby Tér’ba Togola 《Natural Resources Research》1997,6(2):111-129
There is a civilization at risk. In the middle of West Africa, just south of the Sahara, where the Niger River spills into
a vast floodplain (the Middle Niger), an indigenous urban civilization emerged around two thousand years ago. The story of
that civilization is just beginning to be uncovered from the thousands of tells (ancient settlement mounds) that litter the
Middle Niger, but archaeologists have until recently been loosing the race with the looters who plunder these sites for ancient
statues and bronze art. The nation of Mali, and the local community of Jenne at the epicenter of this looting recently invented
effective shields for the remains of this civilization, protections against local looters in the employ of a syndicate of
wealthy European antiquities dealers. In the person of the new, democratically-elected archaeologist-President, the nation
has articulated a vision of Mali’s future linked to the preservation of its past. The government has promulgated effective
regulations and education programs, and initiated with the United States the world’s first bilateral import ban between a
major “source” and a major “market” nation. This 1993 bilateral accord has become a prototype for many nations. In that same
year, Mali established a Cultural Mission at Jenne to reinforce local pride in a local past. This local pride, in only a short
period, has turned into a total protection of some 200 sites within a ten-kilometer radius of Jenne. These indigenous actions
have, in less than a decade, transformed the nonrenewable archaeological resources of the Jenne region from surely one of
the world’s most endangered, to a case study in local and national protection 相似文献
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演化经济地理学认为,地方产业演化是路径依赖的,新的产业从本地现有关联产业中衍生出来。这个理论以地方具备同等优势的创造能力为前提,而创造能力本身对地方条件有着较高的要求。现实条件下,发展中地区开发先进工业,相比依赖本地现有产业基础自主创造的发展路径,紧密跟随并积极参与发达经济体开辟的先进制造业产品市场、主动吸收知识溢出、进行学习合作型创造或是一条更可行的道路。以2000—2015年中国561个海关报关国内地区代码划分的地区行政单元高技术出口产业地理演化为研究对象,验证了这一假设。结论显示：本地技术关联水平对地方高技术产业地理演化主要在近期产生影响,进口产品的知识溢出表现出中长期的促进作用,且地方技术水平的差异对地方利用知识溢出效果并无显著影响。这一结论证明发展中地区可以通过紧随前沿、学习合作打破本地路径锁定,实现路径跳跃。 相似文献
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从进口集中度、进口来源国稳定性、运输通道风险和进口量占世界比例四个指标入手,构建了海外石油供应风险评价方法,定量评价了2000年至2017年中国海外石油供应风险变化趋势,结果显示,过去17年,中国海外石油供应风险整体呈不断增长趋势。通过分析中国海外石油供应风险不断提高的原因,研判未来中国海外石油供应风险趋势,提出了提高中国石油供应安全的对策建议：一是努力提高核能、太阳能、水电、风能等新能源供应比例,力争到2030年将石油消费量控制在总能源消费的13%以内;二是全力保障中东石油供应安全,持续推进中俄石油资源合作,巩固、提升中亚石油资源供应能力,加强与非洲、东南亚、南美等地的石油合作;三是平衡多渠道来源,到2025年,力争进口来源实现中东1/4,俄罗斯及中亚1/4,美洲1/4,非洲及东南亚等地1/4,真正实现中国石油资源供应安全。 相似文献
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BM Macey KW Christison J de Goede L Hutchings CD van der Lingen 《African Journal of Marine Science》2016,38(2):269-273
Catches of South African sardine Sardinops sagax have declined in recent years from about 200 000 t harvested annually during the period 2002–2006 to less than 100 000 t. Consequently, some companies are now importing sardine from sources elsewhere in the world to meet local demand for canned sardine and bait. This importation has the potential for the introduction of sardine pathogens, in particular the pilchard herpesvirus (PHV), which could have a negative impact on the currently small South African sardine population. The aims of the current study were to determine whether PHV is present in the local sardine population and to assess the extent to which sardine is being imported into the country and whether imported fish are from countries where the virus is known to be endemic. Fish sampled from South Africa’s western (n = 150), southern (n = 182) and eastern (n = 96) putative stocks of S. sagax were analysed for the presence of PHV using real-time quantitative polymerase chain reaction (qPCR). The origin and amount of potentially infected material imported into South Africa during the period 2010–2014 was also assessed. None of the South African sardine collected during this study tested positive for PHV, suggesting that active PHV was not prevalent in the local population of S. sagax at the time of this study. Between 56 000 and 71 000 t of frozen sardine was imported annually into South Africa from countries where S. sagax occurs, including some from areas (Australia and New Zealand) where sardine infection by PHV is known to be endemic. Hence, it is plausible that the PHV pathogen, capable of perpetuating infections in local sardine populations, could be imported into South Africa along with the importation of frozen sardine. Should local sardine be naïve to the virus, as suggested by this study, then the population is at risk of infection and precautions against such must be taken. 相似文献
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以中国361个地级行政区为空间单元,运用核密度、空间自相关、空间计量回归方法,研究中国跨境进口电商企业的时空特征及其影响因素。结果表明：①2004—2018年间中国跨境进口电商企业从“萌芽期”“发展期”到“平缓期”呈阶段性发展;企业分布涉及城市不断增加,从东部向中部逐步扩散,多中心化更加明显,大城市带动周边城市发展范围扩大。②跨境进口电商企业在全国范围内呈现“东多西少,南多北少”的分布特征,城市层面具有较强的集聚特点,形成“两大两小”不同分布模式的跨境进口电商企业集聚区。③跨境进口电商企业的空间分布是多因素共同作用的结果,集聚经济、交通运输水平、网络设施水平、物流发展水平对此影响较大。 相似文献
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