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Solar eclipses occur several times a year, but most people will be lucky if they see one total solar eclipse in their lifetime. There are two upcoming total solar eclipses that can be seen from different parts of the United States (August 21, 2017 and April 8, 2024), and they provide teachers with an amazing opportunity to engage students with a remarkable astronomical event. We summarize the science behind eclipses and describe an inexpensive activity for students from third grade up through middle school that will let them use models to see the differences between total, annular, and partial solar eclipses. The activity lets students explore why, during a solar eclipse, people in different areas will see different types of eclipses. The activity can be used as a way to get students excited about astronomy and the upcoming eclipses. We also give ideas for ways that teachers can engage their students during the eclipses.  相似文献   

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Where will new antibiotics come from?   总被引:10,自引:0,他引:10  
There is a constant need for new antibacterial drugs owing to the inevitable development of resistance that follows the introduction of antibiotics to the clinic. When a new class of antibiotic is introduced, it is effective at first, but will eventually select for survival of the small fraction of bacterial populations that have an intrinsic or acquired resistance mechanism. Pathogens that are resistant to multiple drugs emerge around the globe, so how robust are antibiotic discovery processes?  相似文献   

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Polyunsaturated fatty acid synthesis: what will they think of next?   总被引:1,自引:0,他引:1  
Polyunsaturated fatty acids have crucial roles in membrane biology and signaling processes in most living organisms. However, it is only recently that molecular genetic approaches have allowed detailed studies of the enzymes involved in their synthesis. New evidence has revealed a range of pathways in different organisms. These include a complex sequence for synthesis of docosahexaenoic acid (22:6) in mammals and a polyketide synthase pathway in marine microbes.  相似文献   

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This paper reconsiders Stephen Castle’s classic paper Why Migration Policies Fail. Beginning with the so-called migration crisis of 2015 it considers the role of numbers is assessing success or failure. It argues that in the UK public debates about immigration changed with European Union (EU) Enlargement in 2004, when the emphasis shifted from concerns about asylum to concerns about EU mobility. Concerns were exacerbated by the government’s failure to meet its promise to reduce net migration. This policy is hampered by the general problem of definition of “migrant” and the gap between statistical measures and popular usage in which “migration” signifies problematic mobility. In fact, concern about migration has become a placeholder for concerns about globalization and democratic accountability. A new politics of migration must make connections between migrants and citizens, but also between migration and other global processes, particularly outsourcing and the exploitation of labour and resources in the global south.  相似文献   

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The golden age of antimicrobial drug development is a distant memory, and the likelihood of there being another seems slim. In part, this is because the pharmaceutical industry, which has now adopted an unsustainable business model, abandoned the anti-infective sector, and the pipeline is almost empty. The contribution to this crisis of national governments, health agencies and funders also merits discussion. Much of the basis for drug discovery is funded by the public sector, thereby generating intellectual property and leads for drug development that are often not pursued owing to funding gaps. In particular, the cost of testing drug efficacy in clinical trials is beyond the means of most companies and organizations. Lack of a concerted international effort to develop new antimicrobials is particularly alarming at a time when multidrug-resistant bacteria threaten all areas of human medicine globally. Here, the steps that led to this situation are retraced, and some possible solutions to the dilemma are proposed.  相似文献   

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Restoration of coastal habitat fragmented, degraded, or destroyed by development and climate‐related processes such as sea level rise and storm surge usually involves planting native plants to restore habitat structure, but whether and how restored areas benefit taxa other than plants is rarely reported. Installing restoration plantings is one method used to build habitat such as beach dunes where dunes have been lost, potentially creating habitat for dune‐dependent species. We compared use of natural vegetated dunes, open sand gaps, and restoration plantings (habitat treatment) by Perdido Key beach mice (Peromyscus polionotus trissyllepsis) over 3 years using tracking tubes to assess the value of restoration plantings for beach mice. Tubes were monitored in two seasons (early and mid‐summer), and under new and full moon conditions. Mice used restoration plantings less than natural vegetated dunes but more than open sand gaps, which suggests restoration plantings may facilitate movement of mice across fragmented areas. Both season and moon phase influenced the effect of habitat treatment, interactions which may be attributable to perceived risk associated with movement under a combination of different conditions of ambient light, vegetation cover, and habitat novelty. Our results show restoration plantings provide habitat for movement and foraging, and may ameliorate some consequences of sea level rise and storms for beach mice and potentially other dune‐dependent species into the future.  相似文献   

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We live in interesting times. Recognize that HIPAA will impact nearly everyone in every health care organization and fundamentally change the health care industry. Implementation of HIPAA standards as well as ongoing developments in telemedicine, e-health and the Internet will continue to have a synergistic effect and further transform our industry. Biomedical technology will evolve and combine into ever-larger integrated networks. These networks will extend not only throughout the hospitals but also into the clinics, doctors' offices, and even patients' homes and workplaces. As clinical engineers, we need to stay ahead of the curve, anticipate and be prepared for these developments. We need to understand HIPAA and the implications it has for the technology we manage. We must ensure that the organizations we represent are prepared for what will undoubtedly be an exciting future.  相似文献   

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A macroevolutionary model is developed to account for the “adaptive radiation”; of cheilostome bryozoans that commenced in the Cenomanian after a long phase of low diversity. Living cheilostome species possess one of two types of larvae; planktotrophic (cyphonautes) larvae of relatively long duration, and brooded non‐planktotrophic (coronate) larvae of short duration. Planktotrophic larvae characterize the paraphyletic “malacostegans”; from which “advanced”; cheilostomes with non‐planktotrophic larvae are thought to have evolved monophyletically. Research on other marine invertebrates suggests that gene flow within and between populations is likely to be poorer in species having non‐planktotrophic larvae, and hence the frequency of allopatric and quasi‐sympatric speciation may be greater. Skeletal evidence of larval brooding in the cheilostomes first appears in the late Albian, immediately before their adaptive radiation, and the evolution of non‐planktotrophy with associated increase in speciation rate is proposed to have triggered this radiation.  相似文献   

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In Spain, wild rabbits are essential for some highly endangered species, and, therefore, many actions have been undertaken to increase their populations. In the present study, artificial warrens are provided as a means to increase shelter for native wild rabbit populations in a given area. We evaluate the use of three types of warrens by rabbits and the effect on that use of five habitat characteristics at two spatial scales (500 × 500-m grids and 25-m plots). To evaluate that use, we identified pre-established signs at the entrances to each warren, and based on this, we calculated occupancy rate and activity. Our results indicate that rabbit abundance within a grid is the only variable which simultaneously explains both the greater occupancy and the higher activity in the artificial warrens located in that grid. Some 73.2% of the grids showed signs of rabbit use at the time of the evaluation. However, the pre-existing rabbit populations within the grids were not quantified and, hence, we cannot state that the warrens contributed to an increase in the rabbit abundance. Regarding the habitat, our results reveal that warrens should be situated in grids with food coverage of less than 50%, while the use of each individual refuge is greater where food availability in the immediate surroundings is at least 20% and shelter at least 50%. The tube warrens showed significantly greater rabbit use than the other types while there was little difference between the stone and pallet warrens in terms of use.  相似文献   

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Baas-Becking is famously attributed with the conjecture that ‘everything is everywhere, but the environment selects’. Although this aphorism is largely challenged by microbial biogeographical data, even weak versions of the claim leave unanswered the question about whether all environments that could theoretically support life contain life. In the last decade, the discovery of thermally sterilized habitable environments disconnected from inhabited regions, and habitats within organisms such as the sterile, but habitable human fetal gut, suggest the existence of a diversity of macroscopic habitable environments apparently devoid of actively metabolizing or reproducing life. Less clear is the status of such environments at the micron scale, for example, between colonies of organisms within rock interstices or on and within other substrates. I discuss recent evidence for these types of environments. These environments have practical uses in: (i) being negative controls for understanding the role of microbial processes in geochemical cycles and geological processes, (ii) yielding insights into the extent to which the biosphere extends into all spaces it theoretically can, (iii) suggesting caution in interpreting the results of life detection instrumentation, and (iv) being useful for establishing the conditions for the origin of life and its prevalence on other planetary bodies.  相似文献   

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Photoinhibition in leaves in response to high and/or excess light, consisting of a decrease in photosynthesis and/or photosynthetic efficiency, is frequently equated to photodamage and often invoked as being responsible for decreased plant growth and productivity. However, a review of the literature reveals that photoinhibited leaves characterized for foliar carbohydrate levels were invariably found to possess high levels of sugars and starch. We propose that photoinhibition should be placed in the context of whole-plant source–sink regulation of photosynthesis. Photoinhibition may represent downregulation of the photosynthetic apparatus in response to excess light when (1) more sugar is produced in leaves than can be utilized by the rest of the plant and/or (2) more light energy is harvested than can be utilized by the chloroplast for the fixation of carbon dioxide into sugars.  相似文献   

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