基于信息筛选和拉依达准则识别地下水主要组分水化学异常的方法研究

地下水水化学组分的异常值识别是获取水化学背景值的重要的一环,以往提出的基于水化学各组分内在联系的计算背景值的水化学图法及Durov图法在柳江盆地的研究中均取得了良好的效果,但是水化学图法的计算步骤繁多,过程复杂,对采样精度要求严格.因此,为简化计算过程,快速识别异常,本文借鉴英国地调局识别异常的方法,以沙颍河流域为研究区,针对该区浅层地下水水质资料,利用信息筛选法替代水化学图法,对研究区内水化学主要组分进行异常识别,并将不同识别方法的识别效果进行对比分析.结果表明,尽管存在两种方法单独识别出的异常数据较多,但是水化学图法+拉依达准则和信息筛选法+拉依达准则对地下水主要组分的异常识别效果均较好,异常识别后的剩余数据的阈值范围较为一致,信息筛选法能够在大尺度区域内精度较低条件下,有效地替代水化学图法快速识别出异常值.     

从色觉、科学仪器、测不准原理看非决定论

通过对色觉、科学仪器、测不准原理的分析,认为认识在感性阶段是客主体相互作用的结果.感官的生物学意义在于对客体的区别.这种区别是相对准确的,而不是与客体严格一一对应的.科学仪器是人感官的延伸.色觉与其它感官和科学仪器同是人类认识工具.测不准问题是与认识工具直接相关,与客主体相互影响密不可分的,它在宏观上和微观上同时存在,它不是非决定论的理论依据.     

USING MARYLAND'S STREAM CORRIDOR ASSESSMENT SURVEY TO PRIORITIZE WATERSHED RESTORATION EFFORTS1

ABSTRACT: The Stream Corridor Assessment survey has been developed by the Maryland Department of Natural Resources as a watershed management tool to identify environmental problems and to help prioritize restoration opportunities on a watershed basis. Potential environmental problems commonly identified during the survey include: stream channel alterations, excessive bank erosion, exposed pipes, inadequate stream buffers, fish migration blockages, trash dumping sites, near stream construction, pipe outfalls, and unusual conditions. In addition, the survey records information on the location of potential wetlands creation sites and collects data on the general condition of instream and riparian habitats. Over the past several years, in collaboration with the Maryland Conservation Corps, watershed associations, and local governments, more than 3,293 km (2,046 miles) of Maryland streams have been surveyed. Overall, the survey has proven to be a cost effective starting point for many watershed restoration efforts.     

Communication Strategy of Transboundary Air Pollution Findings in a US–Mexico Border XXI Program Project

From 1996 to 1997, the US Environmental Protection Agency (EPA) and the Texas Natural Resource Conservation Commission (TNRCC) conducted an air quality study known as the Lower Rio Grande Valley Transboundary Air Pollution Project (TAPP). The study was a US–Mexico Border XXI program project and was developed in response to local community requests on a need for more air quality measurements and concerns about the health impact of local air pollutants; this included concerns about emissions from border-dependent industries in Mexico, known as maquiladoras. The TAPP was a follow-up study to environmental monitoring done by EPA in this area in 1993 and incorporated scientific and community participation in development, review of results, and public presentation of findings. In spite of this, critical remarks were leveled by community activists against the study's preliminary “good news” findings regarding local air quality and the influence of transboundary air pollution. To resolve these criticisms and to refine the findings to address these concerns, analyses included comparisons of daily and near real-time measurements to TNRCC effects screening levels and data from other studies along with wind sector analyses. Reassessment of the data suggested that although regional source emissions occurred and outliers of elevated pollutant levels were found, movement of air pollution across the border did not appear to cause noticeable deterioration of air quality. In spite of limitations stated to the community, the TAPP was presented as establishing a benchmark to assess current and future transboundary air quality in the Valley. The study has application in Border XXI Program or other air quality studies where transboundary transport is a concern since it involved interagency coordination, public involvement, and communication of scientifically sound results for local environmental protection efforts.     

A GIS-BASED MODELING APPROACH FOR EVALUATING GROUNDWATER VULNERABILITY TO PESTICIDES1

ABSTRACT: The Attenuation Factor (AF), a screening model, was used to evaluate the relative degree of vulnerability of groundwater to pesticide contamination in Louisa County, Virginia. For evaluating the contamination potential of pesticides, three scenarios of pesticide leaching represented by high, moderate, and low cases of degradation and sorption in the soil were considered. Data layers were overlaid within a Geographic Information System (GIS) for spatial computation of AF for the actual and 2m groundwater depths. This spatial database was divided into five contamination potential categories namely high, medium, low, very low, and unlikely, based on the numerical values of the AF for each cell (119 ha). The results for the three most mobile pesticides are presented in this paper. The performance of the AF model was evaluated by comparing its predicted results with the field data from an experimental watershed. The AF model was able to identify most of the frequently detected pesticides in the watershed. A sensitivity analysis was also performed. The results of this study provide information about the potential groundwater threat by pesticides to the citizens ahd decision-makers in the County and can be used for formulating an appropriate land use management plan to protect the groundwater quality.     

模具在工件反挤压过程中的变形模拟研究

模具在金属塑性成形过程中起着十分重要的作用。就一般而言,模具在金属成形过程中的变形被忽略,将之视为刚性体。然而在金属精密成形中,模具的变形对成形件的尺寸精度将产生较大的影响。利用SuperForm软件针对模具在工件挤压过程中的变形进行了有限元数值模拟,对这一问题作了初步分析与探讨,为工厂实际生产的工艺制定、模具设计提供理论参考与依据。     

硅碳比对机床铸件性能的影响

在一定的碳当量的条件下 ,提高硅碳比 (Si/C) ,可以提高机床铸件的抗拉强度、硬度及硬度均匀性 ,降低残留应力 ,改善铸造性能和机加工性能 ,降低废品率。从而达到提高机床的刚度和精度稳定性的目的     

Down's syndrome screening in multiple pregnancies using alpha-fetoprotein and free beta hCG

Second-trimester distributions of the free beta human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP) levels in 420 twin and 19 triplet pregnancies were measured and compared with the distributions in 6661 singleton pregnancies. On average, the levels of both analytes were twice as high in twins and over three times as high in triplets. Eight sets of twins discordant for Down's syndrome showed elevated levels of free beta hCG and reduced levels of AFP after correction of the multiple of the median for the presence of a twin pregnancy. Screening for Down's syndrome using the twin correction of the multiple of the median is expected to achieve a 51 per cent detection rate at a 5 per cent false-positive rate using these two markers.     

Prenatal cystic fibrosis carrier screening: Factors in a woman's decision to decline testing

Among 2207 women eligible to be screened for cystic fibrosis (CF) carrier status during pregnancy, 325 (15 per cent) declined to be tested. Of these, 260 (80 per cent) answered a questionnaire soliciting their reasons for not participating. The main factor was opposition to termination of pregnancy, with 43 per cent being against termination for any reason and another 11 per cent against termination of a CF fetus. Other reasons given were partner's disapproval or non-participation (10 per cent), perceived risk of a CF child being low (7 per cent), the error rate of the test (6 per cent), and the generation of unacceptable levels of anxiety (5 per cent). Eleven women (4 per cent) said that they did not wish to be tested during pregnancy, but only six of these would have accepted screening at another time.