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781.
Steen Smidt-Jensen Anne-Marie Lind Michael Permin Julia M. Zachary Claes Lundsteen John Philip 《黑龙江环境通报》1993,13(8):723-740
We report cytogenetic results from a randomized Danish chorionic villus sampling (CVS) and amniocentesis (AC) study including 2928 placental and 1075 amniotic fluid specimens processed in the same laboratory. The results are presented in groups comparing CVS with amniocentesis and transabdominal (TA) CVS with transcervical (TC) CVS as randomized. More abnormalities and more ambiguous diagnostic problems were found in placental tissues than in amniotic cells. There were no diagnostic errors and no incorrect sex predictions. Mosaicism was detected in 1 per cent of all cases of CVS (discordancies included). When confirmation studies were done, 90 per cent were found to be confined to the placenta. Eight cases (0.7 per cent) of mosaicism/pseudomosaicism were seen in amniotic fluid specimens, and two cases of five with confirmation studies were confirmed in the fetus. The rate of mosaicism/pseudomosaicism in CVS and AC specimens differed (P <0.05). The rate of pseudomosaicism in cultures of villi and amniotic fluid cells was 0.5 and 0.6 per cent, respectively. Single-cell aneuploidy was observed in 1.8 per cent of villi and 1.4 per cent of amniotic fluid cell specimens. Maternal cell contamination (MCC) was seen more often after TC sampling (4.5 per cent) compared with TA sampling (1.5 per cent), but posed no problems in interpretation. Compared with the processing of cultured specimens, the short-term method of preparation of villi in our laboratory doubled the technicians' workload. For practical and economic reasons we have ceased the routine use of short-term preparations. 相似文献
782.
Two approaches are frequently mentioned in proposals to use tropical forest maintenance as a carbon offset. One is to set up, specific reserves, funding the establishment, demarcation, and guarding of these units. Monitoring, in this case, consists of the relatively straightforward process of confirming that the forest stands in question continue to exist. In Amazonia, where large expanses of tropical forest still exist, the reserve approach has the logical weakness of being completely open to “leakage”: with the implantation of any given reserve, the people who would have been deforesting in the reserve area will probably continue to clear the same amount of forest somewhere else in the region. The second approach is through policy changes aimed at reducing the rate of clearing, but not limited to specific reserves or areas of forest. This second approach addresses more fundamental aspects of the tropical deforestation problem, but has the disadvantages of not assuring the permance of forest and of not resulting in a visible product that can be convincingly credited, to the existence of the project. In order for credit to be assigned to policy change projects, functioning models of the deforestation process must be developed that are capable of producing seenarios with and without different policy changes. This requires understanding the process of deforestation, which depends on monitoring in order to have information as a time series. Information is needed both from satellite imagery and from on-the-ground observations on who occupies the land and why the observed changes occur. Monitoring must be done by individual property if causal factors are to be identified reliably; this is best achieved using a database in a Geographical, Information System (GIS) that includes property boundaries. Once policy changes are made in practice, not only deforestation but also the policies themselves must be monitored. Deerees and laws are not the same as changes in practice; the initiation and continued application of changes must therefore be confirmed regularly. The value of carbon benefits from Amazonia depends directly on the credibility and transparency of monitoring. The great potential value of carbon maintenance in Amazonia should provide ample reason for Amazonian countries to strengthen and increase the transparency of their monitoring efforts. 相似文献
783.
Glenn E. Palomaki B.S. James E. Haddow George J. Knight Nicholas J. Wald Anne Kennard Jacob A. Canick Devereux N. Saller Jr Miriam G. Blitzer Lois H. Dickerman Rachel Fisher Dagmar Hansmann Manfred Hansmann David A. Luthy Anne M. Summers Philip Wyatt 《黑龙江环境通报》1995,15(8):713-723
Nine centres collaborated to examine the feasibility of a screening method for trisomy 18 that was based on assigning individual risk, using a combination of maternal age and measurements of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG). Second-trimester measurements of these analytes were obtained from 94 trisomy 18 pregnancies. In the 89 pregnancies without an associated open defect, the median levels for AFP, uE3, and hCG were 0.65, 0.43 and 0.36 multiples of the unaffected population median, respectively. The strongest individual predictor of risk for trisomy 18 was uE3, followed by hCG, AFP, and maternal age, in that order. Using a method of individual risk estimation that is based on the three markers and maternal age, 60 per cent of pregnancies associated with trisomy 18 would be detected at a risk cut-off level of 1:100, with a false-positive rate of about 0.2 per cent. One in nine pregnancies identified as being at increased risk for trisomy 18 would be expected to have an affected pregnancy. This risk-based screening method is more efficient than an existing method that is based on fixed analyte cut-off levels. Even though the birth prevalence of trisomy 18 is low, prenatal screening can be justified when performed in conjunction with Down syndrome screening and when a high proportion of women offered amniocentesis have an affected fetus. 相似文献
784.
How Climate and Vegetation Influence the fire Regime of the Alaskan Boreal Biome: The Holocene Perspective 总被引:2,自引:0,他引:2
Feng Sheng Hu Linda B. Brubaker Daniel G. Gavin Philip E. Higuera Jason A. Lynch T. Scott Rupp Willy Tinner 《Mitigation and Adaptation Strategies for Global Change》2006,11(4):829-846
We synthesize recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal
ecosystems. At the millennial time scale, the most robust feature of these records is an increase in fire occurrence with
the establishment of boreal forests dominated by Picea mariana: estimated mean fire-return intervals decreased from ≥300 yrs to as low as ∼80 yrs. This fire-vegetation relationship occurred
at all sites in interior Alaska with charcoal-based fire reconstructions, regardless of the specific time of P. mariana arrival during the Holocene. The establishment of P. mariana forests was associated with a regional climatic trend toward cooler/wetter conditions. Because such climatic change should
not directly enhance fire occurrence, the increase in fire frequency most likely reflects the influence of highly flammable
P. mariana forests, which are more conducive to fire ignition and spread than the preceding vegetation types (tundra, and woodlands/forests
dominated by Populus or Picea glauca). Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where
fire frequency increased around 4000 calibrated years before present (BP) without an apparent increase in the abundance of
P. mariana. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime
and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial
array of regional fire regimes was non-static through the Holocene. However, the patterns and causes of the spatial variation
remain largely unknown. Advancing our understanding of climate-fire-vegetation interactions in the Alaskan boreal biome will
require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, and improved knowledge
of how sedimentary charcoal records fire events.
In this paper, charcoal refers to macroscopic (≥180 μm) as opposed to microscopic (< 180 μm) particles unless indicated otherwise.
Radiocarbon ages were converted to calibrated years before AD 1950 using the atmospheric calibration data set (Stuiver et
al. 1998). 相似文献
785.
786.
Bob Crabtree Philip Leat John Santarossa 《Journal of Environmental Planning and Management》1993,36(2):187-198
This paper identifies criteria for efficient public utilization of designated wildlife sites. It describes a survey of the major wildlife sites in Scotland in order to determine the site management objectives and extent to which sites are utilized by visitors. Substantial differences were found to exist between organizations as regards site management objectives, promotion and the provision of visitor facilities. Explanations for the apparent variability in efficiency of site utilization are discussed in terms of organization ideology, funding and structure. It is argued that trusts funded through membership may be best able to reconcile the benefits from current site utilization with the conservation of long‐term use and existence values. 相似文献
787.
788.
Philip M. Fearnside 《Environmental management》1989,13(4):401-423
The Balbina Dam in Brazil's state of Amazonas floods 2360 km2 of tropical forest to generate an average of only 112.2 MW of electricity. The flat topography and small size of the drainage basin make output small. Vegetation has been left to decompose in the reservoir, resulting in acidic, anoxic water that will corrode the turbines. The shallow reservoir contains 1500 islands and innumerable stagnant bays where the water's residence time will be even longer than the average time of over one year. Balbina was built to supply electricity to Manaus, a city that has grown so much while the dam was under construction that other alternatives are already needed. Government subsidies explain the explosive growth, including Brazil's unified tariff for electricity. Alternative power sources for Manaus include transmission from more distant dams or from recently discovered oil and natural gas deposits. Among Balbina's impacts are loss of potential use of the forest and displacement of about one third of the surviving members of a much-persecuted Amerindian tribe: the Waimiri-Atroari. The dam was closed on 1 October 1987 and the first of five generators began operation in February 1989. The example of Balbina points to important ways that the decision-making process could be improved in Brazil and in the international funding agencies that have directly and indirectly contributed to the project. Environmental impact analyses must be completed prior to decisions on overall project implementation and must be free of influence from project proponents. The current environmental impact assessment system in Brazil, as in many other countries, has an undesirable influence on science policy, in addition to failing to address the underlying causes of environmentally destructive development processes and inability to halt irreversible projects like Balbina. 相似文献
789.
Jong Hoon Lee Yasuko Yoshida Philip K. Hopke Richard L. Poirot Paul J. Lioy 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1186-1205
Abstract Source types or source regions contributing to the concentration of atmospheric fine particles measured at Brigantine National Wildlife Refuge, NJ, were identified using a factor analysis model called Positive Matrix Factorization (PMF). Cluster analysis of backward air trajectories on days of high- and low-factor concentrations was used to link factors to potential source regions. Brigantine is a Class I visibility area with few local sources in the center of the eastern urban corridor and is therefore a good location to study Mid-Atlantic regional aerosol. Sulfate (expressed as ammonium sulfate) was the most abundant species, accounting for 49% of annual average fine mass. Organic compounds (22%; expressed as 1.4 × organic carbon) and ammonium nitrate (10%) were the next abundant species. Some evidence herein suggests that secondary organic aerosol formation is an important contributor to summertime regional aerosol. Nine factors were identified that contributed to PM2.5 mass concentrations: coal combustion factors (66%, summer and winter), sea salt factors (9%, fresh and aged), motor vehicle/mixed combustion (8%), diesel/Zn-Pb (6%), incinerator/industrial (5%), oil combustion (4%), and soil (2%). The aged sea salt concentrations were highest in springtime, when the land breeze-sea breeze cycle is strongest. Comparison of backward air trajectories of high- and low-concentration days suggests that Brigantine is surrounded by sources of oil combustion, motor vehicle/mixed combustion, and waste incinerator/industrial emissions that together account for 17% of PM2.5 mass. The diesel/Zn-Pb factor was associated with sources north and west of Brigantine. Coal combustion factors were associated with coal-fired power plants west and southwest of the site. Particulate carbon was associated not only with oil combustion, motor vehicle/mixed combustion, waste incinerator/industrial, and diesel/Pb-Zn, but also with the coal combustion factors, perhaps through common transport. 相似文献
790.
J. R. Philip 《Journal of contaminant hydrology》1998,33(3-4)
The one previous analytical solution to the steady sparging problem in a homogeneous soil was in the boundary-layer approximation that neglects the vertical capillary pressure gradient. The present study gives an analytical solution to the full air-flow equation, with the corresponding boundary-layer solution for comparison. The full solution predicts sparging below the air-injection point, whereas the boundary-layer solution does not. Solutions are expressed both in terms of the dimensionless Kirchhoff potential θ (increasing monotonically with capillary pressure and air saturation also) and the dimensionless Stokes stream function F (mapping the pattern of air flow). Both θ and F show the full solution predicting more effective sparging near the injection point than does the boundary-layer solution. The overall boundary-layer relative error, however, decreases as dimensionless air-injection depth below the undisturbed water-table increases. 相似文献