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1.
Data from 2907 transcervical CVS cases performed on singleton pregnancies were reviewed retrospectively and villus sample size was correlated with cytogenetic results, placental location, maternal age at the expected date of confinement (EDC), gestational age at the time of sampling, birth weight, gestational age at the time of delivery, and pregnancy outcome. No correlation was noted between villus sample size and maternal age, gestational age at sampling, gestational age at delivery, birth weight, or pregnancy outcome. An inverse correlation between villus sample size and percentage of abnormal cytogenetic findings was statistically significant (X2 = 8·53, p <0·01). The percentage of small samples was greater when the placenta was anterior, lateral, or fundal than when the placenta was posterior. 相似文献
2.
本文讨论了在高纬度地区公司所起的作用,它被概念化为以社会和经济为媒介的生态系统,同时指出了商业环境里其他的一些重要的社会参与者.我们列举了高纬地区企业行为的三个案例并对其中各种共性进行了讨论.特别的,我们认为有必要对商业理论和实践进行革新,以使其不只是停留在社会与经济概念的组织恢复力上,而要把高纬地区的生态恢复力也包括到商业管理的目标之中.同时我们也认为区域生态系统的恢复力应该成为衡量企业可持续管理的一个有意义的指标,企业高层可以据此制定和修改企业的管理策略.最后,文章在结尾处呼吁对高纬地区内的跨国公司和国内公司的作用制定更为详细的研究议程. 相似文献
3.
Carl Folke Stephen Polasky Johan Rockstrm Victor Galaz Frances Westley Michle Lamont Marten Scheffer Henrik
sterblom Stephen R. Carpenter F. Stuart Chapin III Karen C. Seto Elke U. Weber Beatrice I. Crona Gretchen C. Daily Partha Dasgupta Owen Gaffney Line J. Gordon Holger Hoff Simon A. Levin Jane Lubchenco Will Steffen Brian H. Walker 《Ambio》2021,50(4):834
The COVID-19 pandemic has exposed an interconnected and tightly coupled globalized world in rapid change. This article sets the scientific stage for understanding and responding to such change for global sustainability and resilient societies. We provide a systemic overview of the current situation where people and nature are dynamically intertwined and embedded in the biosphere, placing shocks and extreme events as part of this dynamic; humanity has become the major force in shaping the future of the Earth system as a whole; and the scale and pace of the human dimension have caused climate change, rapid loss of biodiversity, growing inequalities, and loss of resilience to deal with uncertainty and surprise. Taken together, human actions are challenging the biosphere foundation for a prosperous development of civilizations. The Anthropocene reality—of rising system-wide turbulence—calls for transformative change towards sustainable futures. Emerging technologies, social innovations, broader shifts in cultural repertoires, as well as a diverse portfolio of active stewardship of human actions in support of a resilient biosphere are highlighted as essential parts of such transformations. 相似文献
4.
A comprehensive review of climate adaptation in the United States: more than before, but less than needed 总被引:2,自引:0,他引:2
Rosina Bierbaum Joel B. Smith Arthur Lee Maria Blair Lynne Carter F. Stuart Chapin III Paul Fleming Susan Ruffo Missy Stults Shannon McNeeley Emily Wasley Laura Verduzco 《Mitigation and Adaptation Strategies for Global Change》2013,18(3):361-406
We reviewed existing and planned adaptation activities of federal, tribal, state, and local governments and the private sector in the United States (U.S.) to understand what types of adaptation activities are underway across different sectors and scales throughout the country. Primary sources of review included material officially submitted for consideration in the upcoming 2013 U.S. National Climate Assessment and supplemental peer-reviewed and grey literature. Although substantial adaptation planning is occurring in various sectors, levels of government, and the private sector, few measures have been implemented and even fewer have been evaluated. Most adaptation actions to date appear to be incremental changes, not the transformational changes that may be needed in certain cases to adapt to significant changes in climate. While there appear to be no one-size-fits-all adaptations, there are similarities in approaches across scales and sectors, including mainstreaming climate considerations into existing policies and plans, and pursuing no- and low-regrets strategies. Despite the positive momentum in recent years, barriers to implementation still impede action in all sectors and across scales. The most significant barriers include lack of funding, policy and institutional constraints, and difficulty in anticipating climate change given the current state of information on change. However, the practice of adaptation can advance through learning by doing, stakeholder engagements (including “listening sessions”), and sharing of best practices. Efforts to advance adaptation across the U.S. and globally will necessitate the reduction or elimination of barriers, the enhancement of information and best practice sharing mechanisms, and the creation of comprehensive adaptation evaluation metrics. 相似文献
5.
6.
Investigation of titanium liquid/gas diffusion layers in proton exchange membrane electrolyzer cells
Stuart M. Steen III Jingke Mo Zhenye Kang Gaoqiang Yang 《International Journal of Green Energy》2017,14(2):162-170
In a proton exchange membrane electrolyzer cell (PEMEC), liquid/gas diffusion layer (LGDL) is expected to transport electrons, heat, and reactants/products to and from the catalyst layer with minimum voltage, current, thermal, interfacial, and fluidic losses. In addition, carbon materials, which are typically used in PEM fuel cells (PEMFCs), are unsuitable in PEMECs due to the high ohmic potential and highly oxidative environment of the oxygen electrode. In this study, a set of titanium gas diffusion layers with different thicknesses and porosities are designed and examined coupled with the development of a robust titanium bipolar plate. It has been found that the performance of electrolyzer improves along with a decrease in thickness or porosity of the anode LGDL of titanium woven meshes. The ohmic resistance of anode LGDL and contact resistance between anode LGDL and the anode catalyst play dominant roles in electrolyzer performance, and better performance can be obtained by reducing ohmic resistance. Thin titanium LGDLs with straight-through pores and optimal pore morphologies are recommended for the future developments of low-cost LGDLs with minimum ohmic/transport losses. 相似文献
7.
Lee A. McBride III 《Journal of Agricultural and Environmental Ethics》2012,25(4):535-541
In The Agrarian Vision, Thompson argues that a better appreciation of agrarian ideals could lead to a more virtuous, more sustainable way of life. While I agree with Thompson in many respects, there are some aspects of the book that I question and others that I would like to hear Thompson explicate in greater detail. In this paper, I question Thompson’s claim that agrarian farmers and farming communities serve as ideal models of virtuous habits and good character. I challenge Thompson’s use of virtue theory, particularly the notion that farming virtues can be acquired without participating in farming practices. In the end, I make the point that Thompson seems to vacillate between being realistic and being idealistic, which may seriously complicate our notions of responsibility and obligation in practice. 相似文献
8.
H. Barndõk M. Peláez C. Han W. E. Platten III P. Campo D. Hermosilla A. Blanco D. D. Dionysiou 《Environmental science and pollution research international》2013,20(6):3582-3591
This study reports the synthesis and characterization of composite nitrogen and fluorine co-doped titanium dioxide (NF-TiO2) for the removal of contaminants of concern in wastewater under visible and solar light. Monodisperse anatase TiO2 nanoparticles of different sizes and Evonik P25 were assembled to immobilized NF-TiO2 by direct incorporation into the sol–gel or by the layer-by-layer technique. The composite films were characterized with X-ray diffraction, high-resolution transmission electron microscopy, environmental scanning electron microscopy, and porosimetry analysis. The photocatalytic degradation of atrazine, carbamazepine, and caffeine was evaluated in a synthetic water solution and in an effluent from a hybrid biological concentrator reactor (BCR). Minor aggregation and improved distribution of monodisperse titania particles was obtained with NF-TiO2-monodisperse (10 and 50 nm) from the layer-by-layer technique than with NF-TiO2?+?monodisperse TiO2 (300 nm) directly incorporated into the sol. The photocatalysts synthesized with the layer-by-layer method achieved significantly higher degradation rates in contrast with NF-TiO2-monodisperse titania (300 nm) and slightly faster values when compared with NF-TiO2-P25. Using NF-TiO2 layer-by-layer with monodisperse TiO2 (50 nm) under solar light irradiation, the respective degradation rates in synthetic water and BCR effluent were 14.6 and 9.5?×?10?3?min?1 for caffeine, 12.5 and 9.0?×?10?3?min?1 for carbamazepine, and 10.9 and 5.8?×?10?3?min?1 for atrazine. These results suggest that the layer-by-layer technique is a promising method for the synthesis of composite TiO2-based films compared to the direct addition of nanoparticles into the sol. 相似文献
9.
Donald G. Miller III. 《Behavioral ecology and sociobiology》1998,43(2):95-103
This study investigated the consequences of communal gall induction on individual and group fitness in the aphid Tamaliacoweni. The possibilities that kin discrimination and foundress density are factors favoring communal gall occupation were examined.
Clonally produced aphid foundresses were collected to create two treatments: clonal groups and groups of less closely related
individuals. These were confined on suitable host plant tissue to compare their respective propensities towards communal behavior.
There were no significant differences in the frequencies of communal gall occupation; therefore, active kin discrimination
by T.coweni foundresses apparently does not play a role in their communal behavior, within the context of this experiment. In a second
experiment, aphid foundress density on the host plant was manipulated in three treatments and was correlated with the frequency
of communal gall occupation. Individual fitness was inversely related to the mean number of foundresses per gall. These results
suggest that communal gall occupation does not necessarily represent mutual cooperation but may instead be the outcome of
competition for limited gall sites on the host plant. However, natural selection at the clonal level may favor communal gall
occupation under the conditions of resource limitation and high within-group relatedness.
Received: 26 September 1997 / Accepted after revision: 28 March 1998 相似文献
10.
Growth of zooxanthellae in culture with two nitrogen sources 总被引:2,自引:0,他引:2
Physiological characteristics of zooxanthellae were examined under nutrient-saturated conditions created by mixing ammonium
(15NH4) with nitrate (15NO3) to give 0.88 mM total nitrogen. Growth rate varied with the form of nitrogen provided. Ammonium alone resulted in the lowest
C:N and C:chl-a ratios. Although zooxanthellae took up nitrate in the absence of ammonium, ammonium assimilation was 1.3 times higher than
nitrate assimilation. Ammonium strongly inhibited nitrate assimilation. While high-ammonium treatments resulted in the highest
14C incorporation into intermediate compounds, high nitrate levels resulted in the highest 14C incorporation into protein, suggesting that the intermediate compounds are produced prior to the subsequent production of
protein when ammonium is the dominant N source. The enhanced production of intermediate compounds at the expense of carbon
directed to protein synthesis in the presence of ammonium might be analogous to the “host factor” observed in zooxanthellae–host
symbioses, since growth rate is depressed due to low production of protein.
Received: 16 March 2000 / Accepted: 26 August 2000 相似文献