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101.
Niel Hens Christel Faes Marc Aerts Ziv Shkedy Koen Mintiens Hans Laevens Frank Boelaert 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):498-513
Modeling infectious diseases data is a relatively young research area in which clustering and stratification are key features.
It is not unlikely for these data to have missing values. If values are missing completely at random, the analysis on the
complete cases is valid. However, in practice this assumption is usually not fulfilled. This article shows the effect of ignoring
missing data in modeling the force of infection of the bovine herpesvirus-1 in Belgian cattle and proposes the use of weighted
generalized estimating equations with constrained fractional polynomials as a flexible modeling tool. 相似文献
102.
Wang L Lord H Morehead R Dorman F Pawliszyn J 《Journal of agricultural and food chemistry》2002,50(22):6281-6286
Membrane extraction with sorbent interface (MESI) has been applied to monitor plant fragrance volatiles emitted into indoor air. The main components of the MESI system are a membrane module and a trap, which can be connected directly to a GC or GC-MS for simultaneous multicomponent extraction and monitoring. A polydimethylsiloxane (PDMS) membrane and two different traps, PDMS and Tenax, as well as a DC current supply for trap desorption have been applied in this research. After the membrane module is placed in contact with the plant, the MESI/GC-MS provides semicontinuous characterization of volatile compounds emitted. The MESI device has been applied to monitor the biogenic volatile organic compounds released during the first 8 h after a branch was cut from a Eucalyptus dunnii tree. The study demonstrates that the MESI system is a simple and useful tool for monitoring changes in emission processes as a function of time. 相似文献
103.
The effects of artificial rain of various acidities were studied in a lysimeter experiment. Lysimeters, 29 cm in diameter, and 40 cm deep contained a Gleyed Dystric Brunisol. Natural structure, stratification and original vegetation were maintained. Artificial rain was produced from groundwater with “high” concentrations of neutral salts and from rainwater with lower concentrations. pH levels of 6, 4, 3 and 2 were established by adding H2SO4. Effects of dilution with given amounts of acid were examined by comparing the effects of 50 mm “rain” month?1 of pH 3 and pH 2 with 500 mm “rain” month?1 of pH 4 and pH 3, respectively. The study continued for 5 yr. Totals of 1250 or 12500 mm “rain” were applied in addition to a natural input of 2773 mm. Increased input of SO4 2? increased the output of SO4 2? but, as concentration increased, sorption of SO4 2? in the soil also increased. Concentrations of base cations in the leachate increased parallel to the output of SO4 2?. However, significant effects on leaching of base cations and on the content of exchangeable cations in the soil, was only found in the pH 2 treatment with 1250 mm of “rain” and in the pH 4 and pH 3 treatment with 12500 mm of “rain”. 相似文献
104.
Nitrous oxide (N2O) release by Streptomyces nitrosporeus in a sandy loam soil as affected by pO2, pH and amount of easily decomposable organic carbon In model experiments under defined conditions (80%WHC, 300 μg nitrate-N g?1 dry soil, 30°C) the effect of pO2, pH and addition of easily decomposable organic matter on nitrous oxide production by Streptomyces nitrosporeus DSM 40023 from a sterilized sandy loam soil was studied. This streptomycete reduces nitrate to N2O but not to N2. The strain was inoculated into a sterilized sandy loam soil (pH 6), enriched with nitrate and incubated at approximately 20 and 10% (v/v) O2 for 26 days. In another series of experiments the pH was increased with NaOH-solution up to pH 7 or the soil was enriched with pulverized leaves (1%) to increase mineralization activity and the demand for electron acceptors. In the headspace the concentration of O2, CO2 and N2O was analysed by GC. The soil concentration of NO3?, NO2? and NH4+ was measured as well as the pH value. The population density was determined by the plate count method. At a decreased oxygen concentration of about 2.5% (v/v) in the headspace, S. nitrosporeus increased the release of N2O. In the experiments with an initial oxygen concentration of approximately 20% (v/v) this threshold of about 2.5% /(v/v) O2 was hardly reached and consequently only little N2O was produced. Apparently, S. nitrosporeus uses O2 in preference to nitrate, which is characteristical of nitrate respiration. A pH increase from pH 6 to 7 reduced the lag phase significantly and increased the rate of oxygen consumption, CO2 release and N2O production. Maximum nitrous oxide production was reached after 13 days. The result indicated that streptomycetes like S. nitrosporeus may use nitrate alternativly to O2 to maintain energy conservation (ATP synthesis) with the release of N2O. So far, nothing is known about the role of streptomycetes in contributing to N2O production in natural soils. 相似文献
105.
106.
畜禽粪便固液分离技术特点及效率评估 总被引:1,自引:3,他引:1
该文对常用畜禽粪便固液分离技术进行分析,评估出各分离技术的优缺点、适用对象、分离效果和性价比,为企业选择粪便固液分离设备提供参考。研究结果表明:重力分离技术成本最低,分离粒径小于1 mm的有机物效果最好,但分离后固相含水率过高(90%),一般作为其他技术的预处理。筛分技术对于分离大粒径的有机颗粒物最有效,投资相对小,运行费用低;但对氮磷等营养元素分离效率较低,分离后的固相的含水率偏高,分离产物可用于固态发酵。压滤技术提高了磷元素的分离效率和固相含水率,但运营成本也增加,分离产物可用于有机肥生产。沉淀离心技术对去除细小颗粒最为有效,并能够去除氮磷元素,但运营成本太高,在中国推广难度大。絮凝剂能和大多数的分离技术结合使用从而提高分离效率。所有固液分离技术都不能分离畜禽粪便中的挥发性脂肪酸,因此也不能有效去除液相中的生化需氧量和臭味。多种分离技术的联合使用,在提高营养物质的分离效率的同时,降低固相的含水率将是未来技术发展的主要方向。 相似文献
107.
108.
Effects of thiopental sedation on learning and memory 总被引:1,自引:0,他引:1
A G Osborn J P Bunker L M Cooper G S Frank E R Hilgard 《Science (New York, N.Y.)》1967,157(788):574-576
Subjects who were administered thiopental showed a loss of memory for events discussed while they were under sedation. We tested the subjects for recognition memory of pictures and recall of associated pairs of letters and words, and found that the subsequent memory loss was correlated with the concentration of thiopental in the venous blood at the time the material was learned. Retention did not appear to be state-dependent because the subject, while under sedation, could recall material learned prior to sedation, and because recall was not facilitated by reinstatement of the sedation. 相似文献
109.
Hellal F Hurtado A Ruschel J Flynn KC Laskowski CJ Umlauf M Kapitein LC Strikis D Lemmon V Bixby J Hoogenraad CC Bradke F 《Science (New York, N.Y.)》2011,331(6019):928-931
Hypertrophic scarring and poor intrinsic axon growth capacity constitute major obstacles for spinal cord repair. These processes are tightly regulated by microtubule dynamics. Here, moderate microtubule stabilization decreased scar formation after spinal cord injury in rodents through various cellular mechanisms, including dampening of transforming growth factor-β signaling. It prevented accumulation of chondroitin sulfate proteoglycans and rendered the lesion site permissive for axon regeneration of growth-competent sensory neurons. Microtubule stabilization also promoted growth of central nervous system axons of the Raphe-spinal tract and led to functional improvement. Thus, microtubule stabilization reduces fibrotic scarring and enhances the capacity of axons to grow. 相似文献
110.
Frank P 《Science (New York, N.Y.)》1954,119(3102):823-824