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261.
Abstract

Some problems of weed control in Cuba are discussed and the important weeds listed.  相似文献   
262.
The proper development of the central nervous system depends upon a finely tuned balance between cell proliferation and programmed cell death (PCD). Although PCD was initially believed to depend solely on the inability of certain neurons to obtain access to a limited supply of trophic factors, it has become apparent that the local production of death signals is also critical. In this Viewpoint, we discuss several pathways implicated in the survival of cerebellar granule cells- both pathways that protect from apoptosis and pathways that promote apoptosis-and describe how these disparate pathways converge on the final common mediators of PCD. Information on other important pathways implicated in granule cell survival may be found in the Connections Maps.  相似文献   
263.
Pillow lava rims from the Mesoarchean Barberton Greenstone Belt in South Africa contain micrometer-scale mineralized tubes that provide evidence of submarine microbial activity during the early history of Earth. The tubes formed during microbial etching of glass along fractures, as seen in pillow lavas from recent oceanic crust. The margins of the tubes contain organic carbon, and many of the pillow rims exhibit isotopically light bulk-rock carbonate delta13C values, supporting their biogenic origin. Overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3.5 billion years ago.  相似文献   
264.
Summary After an initial phase of development and programme establishment the activities of the International Potato Center (CIP) grew rapidly from 1981 to 1985, putting emphasis on germplasm distribution, research on diffused-light storage and TPS, and exploration of sources of resistance. Later, strong emphasis was given to genetic resource utilization and field resistance to late blight. The impact of CIP research showed internal rates of return ranging from 26 to 102 percent. At the end of the 1980s CIP's financial resources were cut severely and restructuring the programme was necessary. Through a careful process of prioritizing, programmes are identified which will contribute most to ensuring the continued increase of potato production in developing countries and to continuing the leading role of CIP in potato research.  相似文献   
265.
An MS-based method, combining reversed-phase capillary liquid chromatography (capillary LC) with quadrupole time-of-flight tandem mass spectrometry (nano-ESI Q-TOF MS/MS), was developed with the aim of identifying a set of peptides that can function as markers for peanut allergens. Emphasis was given to the identification of the three major peanut allergens Ara h 1, Ara h 2, and Ara h 3, because these proteins are considered to represent >30% of the total protein content of peanut and are directly relevant for the allergenic potential of this food. The analytical data obtained were used to perform databank searching in combination with de novo sequencing and led to the identification of a multitude of sequence tags for all three peanut allergens. Food processing such as roasting of peanuts is known to affect the stability of proteins and was shown to influence the detection of allergen sequence tags. The analysis of raw and roasted peanuts allowed the identification of five peanut-specific sequence tags that can function as markers of the specific allergenic proteins. For Ara h 1, two peptide markers were proposed, namely, VLEENAGGEQEER (m/z 786.88, charge 2+) and DLAFPGSGEQVEK (m/z 688.85, charge 2+), whereas for Ara h 2 only one peptide, RQQWELQGDR (m/z 439.23, charge 3+), was found to satisfy the required conditions. For Ara h 3, the two specific peptides, SPDIYNPQAGSLK (m/z 695.35, charge 2+) and SQSENFEYVAFK (m/z 724.84, charge 2+), were selected. Other peptides have been proposed as indicative for food processing.  相似文献   
266.
Little is known about how socio-economic factors quantitatively contribute to shaping introductions of exotic species in space and time. Here, we discover that socio-economic, historical and political factors are largely responsible for shaping exotic bird introductions into Europe. We find that the Cold War and its resulting commercial alliances in Eastern vs. Western Europe led to contrasting patterns in the numbers, composition and origin of birds introduced into each of the two European blocs. The isolation of the Eastern European bloc from the west during the Cold War led to a decline in the number of birds introduced, the number of introduction events and the number of bird species established. Birds introduced during the Cold War originated largely from economically allied countries of each of the two blocs. The Cold War provided a hitherto unexpected benefit to the Eastern European bloc by limiting exotic species introductions, and subsequent population establishment, due to its restrictions on international trade. We suggest that work on the factors shaping invasive species establishment, spread and impacts should incorporate a socio-economic context. Given the ongoing increase in human movement and trade in Europe and the integration of most former Eastern European countries to the European Union, clear policies should be urgently established to prevent inflow of exotic species into formerly more isolated regions and reduce the risk of future biotic invasions.  相似文献   
267.
Long‐term contribution of soil loss events depends on both – the magnitude and the occurrence probability – but oftentimes, a limited observation period impedes the assessment of the temporal soil loss distribution. In this research, the event‐based soil loss from two plot locations in Lower Austria (Mistelbach and Pixendorf) was linked with the event‐based rainfall erosivity (EI30) to assess the temporal soil loss distribution using long‐term rainfall data from two meteorological stations in Lower Austria. For both plot locations, a risk analysis was performed to (i) assess the long‐term average annual soil loss and to (ii) evaluate the contribution of incremental erosion events according to different event return periods. The risk analysis showed that in Pixendorf the events <20 years return period dominatingly contribute to long‐term soil loss, because the contribution of the events >20 years return period is progressively reduced through the low occurrence probability. On the contrary, in Mistelbach the soil loss magnitudes of the extreme events overcome the effect of the low occurrence probability, and consequently, the contribution of the extreme events (>20 years return period) is dominant. The spatially variable contribution of the erosion events reveals the need for spatially customized soil conservation strategies. A risk analytical approach may help to allocate the driving events and thus to define proper event design magnitudes for local soil conservation planning. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
268.
德国是近自然林业的发源地,目标树经营法是近自然林业的重要操作方法.长期以来,德国高等院校和林业科研机构对目标树经营法进行了多方位的研究,形成了不同的经营模式,影响较大的有弗莱堡模式、巴伐利亚模式和罗腾堡模式.借鉴德国的经验,文中在进行大量调查研究的基础上,设计了基于湖北实际的目标树经营法.核心内容是:以平均胸径10 c...  相似文献   
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