Bragg diffraction from crystallized ion plasmas

Single crystals of a one-component plasma were observed by optical Bragg diffraction. The plasmas contained 10(5) to 10(6) single-positive beryllium-9 ions (9Be+) at particle densities of 10(8) to 10(9) per cubic centimeter. In approximately spherical plasmas, single body-centered cubic (bcc) crystals or, in some cases, two or more bcc crystals having fixed orientations with respect to each other were observed. In some oblate plasmas, a mixture of bcc and face-centered cubic ordering was seen. Knowledge of the properties of one-component plasma crystals is required for models of white dwarfs and neutron stars, which are believed to contain matter in that form.     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.     

Sensitivity of boreal forest carbon balance to soil thaw

We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 +/- 0.5 metric ton of carbon per hectare per year (ton C ha-1 year-1) from 1994 to 1997, with a gain of 0.6 +/- 0.2 ton C ha-1 year-1 in moss and wood offset by a loss of 0.8 +/- 0.5 ton C ha-1 year-1 from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool ( approximately 150 tons C ha-1) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.     

Estimating the mass of asteroid 253 mathilde from tracking data during the NEAR flyby

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter.     

福建省明溪县农地土壤重金属的空间分异和潜在生态风险评价

以福建省明溪县农地土壤为研究对象,采集耕层土壤(0-20 cm)样品88个,测定其Cd、Cu和Pb等3种重金属元素含量;利用Arc GIS软件分析其农地土壤重金属空间变异特征;采用Hakanson潜在生态危险指数法评价研究区域农地土壤重金属潜在生态风险与环境污染.结果表明:研究区域土壤重金属Cd、Cu和Pb平均含量分别为0.0119、13.9606和6.8480mg·kg-1,均未超过国家土壤环境质量二级标准.Cd、Cu和Pb等3种重金属含量变异系数为22%-386%,大小排列顺序为CdPbCu;在空间分异上,Cd和Pb元素的空间相关性较强,Cu元素的空间相关性较弱;Cd的高含量区集中于瀚仙镇北部和城关乡东北部,Cu的高含量区位于枫溪、夏坊二乡和盖洋、瀚仙镇,Pb的高含量区则分布在雪峰镇和城关乡以北地带及沙溪乡东部.研究区域中98.86%的样本为低度等级的重金属潜在生态风险(RI平均值为11.03);在生态风险等级分布上,瀚仙镇东北部的重金属潜在生态风险等级较高.     

Microbial characteristics of ectomycorrhizal mat communities in Oregon and California

Summary Specialized ectomycorrhizal fungi form dense mats in forest soils that have different enzyme levels, higher respiration rates, more biomass, different soil fauna, and different soil chemistry compared with adjacent soils not obviously colonized by these mats. In this study, mats formed by two genera of fungi collected in three locations were compared with a wide range of measurements. Per cent moisture, pH, chloroform fumigation-flush C, anaerobic N mineralization, exchangeable ammonium, and respiration, N₂ fixation, and denitrification rates were compared between soils or litter colonized by ectomycorrhizal mat-forming fungi and adjacent non-mat material. Significant differences were observed between the two genera of mat-forming fungi and also between mats formed primarily in mineral soil and those formed in litter. These differences suggest that different mat-forming fungi perform different functions in forest soils and that these fungi function differently in mineral soil compared with litter.Published as Technical Paper 9496, Oregon Agricultural Experiment Station     

Echinococcus granulosus in the Northern Territory,Australia: hydatid disease reported in beef cattle from the region

Hydatid disease in beef cattle has been reported to be widespread throughout Australia, but cattle bred and raised in the Northern Territory were previously believed to be free of the disease. Between 2010 and 2016, 1061 cattle from the Northern Territory were slaughtered at a New South Wales abattoir and inspected for hydatid disease. The proportion of cattle reported infected with hydatid disease was 3.5%. Individual cattle identification numbers indicated that the cattle included in the study had most likely remained within the Northern Territory from birth until immediately prior to slaughter, so were assumed to have become infected within the region. We suspect that the sylvatic cycle of Echinococcus granulosus transmission could be responsible for infection of cattle in this region.