宇宙核素地学研究的理论基础与应用模型   总被引：1，自引：0，他引：1  

李英奎  Jon Harbor  刘耕年  周力平  崔之久 《水土保持研究》2005,12(4):139-145

宇宙核素是宇宙射线与地表物质相互作用的产物，具有蜕变、中子捕获和介子反应三种形成机制。宇宙核素产生率随深度的变化而变化，同时还受纬度、高度和时间等因素的影响，其浓度变化与表面的暴露时间和侵蚀速率密切有关。宇宙核素的应用模型主要基于单一核素和核素对，单一核素方法只能解决一个未知因素，但核素浓度-深度分布曲线可用于复杂问题的解决。核素对方法可以解决具有多种未知因素的复杂状况，实际应用中主要基于核素比值变化曲线的分析。另外，基于核素对还可以解决埋藏年龄等问题。  相似文献   

Histological structures of cooked rice grain     

Ogawa Y  Glenn GM  Orts WJ  Wood DF 《Journal of agricultural and food chemistry》2003,51(24):7019-7023

Raw and cooked whole grain sections of milled, medium grain California rice were compared for gross histological and morphological features using fluorescence and scanning electron microscopy (SEM). Cooked and raw grains were compared and the differences were assessed by autofluorescence of the cell walls and correlating fluorescence to SEM images. Milled, raw grains contain fine cracks throughout the endosperm. Cooked grains have wider, more defined cracks, suggesting that they serve as channels for water migration into the grain during cooking. Water penetrates unequally into the grain during cooking: low water penetration produces dense regions with minimal starch gelatinization, and high water penetration produces large voided areas. The voids occur in the transverse orientation of the grain and are the main of cause grain expansion during cooking.  相似文献   

Empirical predictions of plant material C and N mineralization patterns from near infrared spectroscopy, stepwise chemical digestion and C/N ratios     

Sander Bruun  Bo Stenberg  Jon Gudmundsson  Lars S. Jensen  Jesper Luxhøi  Anders Pedersen 《Soil biology & biochemistry》2005,37(12):2283-2296

Prediction of carbon (C) and nitrogen (N) mineralization patterns of plant litter is desirable for both agronomic and environmental reasons. Near infrared reflectance (NIR) spectroscopy has recently been introduced in decomposition studies to characterize biochemical composition. The purpose of the current study was to use empirical techniques to predict C and N mineralization patterns of a wide range of plant materials incubated under controlled temperature and moisture conditions. We hypothesized that the richness of information in the NIR spectra would considerably improve predictions compared to traditional stepwise chemical digestion (SCD) or C/N ratios. Initially, we fitted a number of empirical functions to the observed C and N mineralization patterns. The best functions fitted with R²=0.990 and 0.949 to C and N, respectively. The fractions of C and N mineralized at different points in time were then either predicted directly with regression functions or indirectly by prediction of the parameters of the empirical functions fitted to incubation data. In both cases, partial least squares (PLS) regressions were used and predictions were validated by cross-validations. We found that the NIR spectra (best R²=0.925) were able to predict C mineralization patterns marginally better than the SCD fractions (best R²=0.911), but considerably better than the C/N ratios (best R²=0.851). In contrast, N mineralization was better predicted by SCD fractions (best R²=0.533) than the C/N ratio (best R²=0.497), which was better than NIR predictions (best R²=0.446). Although the predictions with the NIR spectra were only slightly better for C and worse for N mineralization compared to SCD fractions, NIR spectroscopy still holds advantages, as it is a much less laborious and cheaper analytical method. Furthermore, exploration of the applications of NIR spectroscopy in decomposition studies has only just begun, and offers new ways to gain insights into the decomposition process.  相似文献   

Sorption and vapor transmission properties of uncompressed and compressed microcellular starch foam     

Glenn GM  Klamczynski AP  Takeoka G  Orts WJ  Wood D  Widmaier R 《Journal of agricultural and food chemistry》2002,50(24):7100-7104

Microcellular starch foams (MCFs) are made by a solvent-exchange process and consist of a porous matrix with pores generally ranging from approximately 2 microm to submicrometer size. MCF may potentially be useful as a slow-release agent for volatile compounds because of its ability to sorb chemicals from the atmosphere and to absorb liquids into its porous structure, and because it can be compressed to form a starch plastic. MCF made of high-amylose corn and wheat starches was prepared with or without 2% (w/w) silicone oil (SO) or palmitic acid (PA). The MCF was loaded with 1% of various volatile compounds with vapor pressures ranging from 0.02 to 28 mm. The MCF depressed the vapor pressure from 0.37 to 37% compared to a control containing no MCF. Incorporating SO or PA in the matrix of the MCF had little effect on sorption of volatiles. Compressing MCF at 1.4, 6.9, and 69 MPa made a starch plastic with varying porosity. The vapor transmission rate of various volatile compounds through MCF was positively correlated to the vapor pressure of the test compound but was inversely proportional to the compression force used to form the starch plastic. The results indicate that uncompressed and compressed MCFs could be effective slow-release agents for a variety of volatile compounds, especially if used together.  相似文献   

Agricultural Sediment Reduction by Giant Cane and Forest Riparian Buffers     

Jon E. Schoonover  Karl W. J. Williard  James J. Zaczek  Jean C. Mangun  Andrew D. Carver 《Water, air, and soil pollution》2006,169(1-4):303-315

The sediment filtering capabilities of giant cane (Arundinaria gigantea (Walt.) Chapm.) and forest riparian buffers were compared in a southern Illinois, USA non tile drained agricultural watershed. Giant cane, a bamboo species, serves as important wildlife habitat throughout its native range in the southeastern and lower midwestern United States. Overland flow samples were collected at the field edge and at 3.3 m, 6.6 m, and 10.0 m within the riparian buffers during 19 precipitation events over a 1-year period. On an annual basis, significant sediment reductions occurred by 3.3 m and 6.6 m in the cane and forest buffers, respectively. The giant cane buffer reduced incoming sediment mass by 94% within the first 3.3 m, while the forest buffer reduced sediment by 86% over 6.6 m. Within 10.0 m of the field edge, the cane and forest buffers reduced sediment mass by 100% and 76%, respectively. On a seasonal basis, the cane buffer outperformed the forest buffer. During each of the four seasons, the cane buffer reduced sediment masses within 3.3 m of the field edge, while the forest buffer showed initial reductions occurring at 6.6 m during the summer, fall, and winter. No detectable reductions occurred during the spring in the forested buffer. Reductions in sediment concentrations were less evident compared to mass basis, indicating that infiltration may be a more important sediment reduction mechanism than particle settling. Both the forest and giant cane buffers had relatively high measured soil infiltration rates. Study results indicate that giant cane is an appropriate species to include in riparian buffer restoration designs for sediment control.  相似文献   

Effects of a chromated-copper-arsenate wood preservative on the growth of a pentachlorophenol degrading bacterium     

A. James Wall  Glenn W. Stratton 《Water, air, and soil pollution》1995,82(3-4):723-737

A chromated-copper-arsenate (CCA) wood preservative was tested for toxic effects on the growth of a bacterial culture (Flavobactenum sp. ATCC 53874) capable of biodegrading pentachlorophenol, another wood preservation chemical. Both a commercially available CCA preparation and a laboratory-prepared CCA solution were tested. Each had an inhibitory effect on the growth of Flavobacterium at diluted CCA levels as low as 1.0×10^?4 to 1.0×10^?5% wt vol^?1. The commercial formulation was generally more toxic. EC₅₀ values calculated after 96 hr of incubation were 1.2 ×10^?4% wt vol^?1 for the commercial material (containing 0.15/0.097/0.14 μg mL^?1 of Cr/Cu/As, respectively) and 3.8×10^?4% for the laboratory solution (containing 0.51/0.31/0.49 μg mL^?1 of Cr/Cu/As, respectively). CCA toxicity increased during the first 7 to 8 days and then slowly decreased for the balance of the 21 day incubation period. Biodegradation of pentachlorophenol residues in contaminated soil will be negatively affected by the presence of CCA as a co-contaminant.  相似文献   

State park contributions to natural area protection in Texas,USA     

E.Glenn Carls  A.K. Ludeke 《Biological conservation》1984,28(2):95-110

The continuing alteration of global ecosystems has put a high premium on the development of a system of representative conservation reserves. In addition to existing national parks and reserves, and a developing international system of biosphere reserves, state and provincial parks can serve to strengthen the network of protected natural areas. An analysis of Texas state parks shows that they are a viable supplement to national park areas in the state. The level of resource protection within the parks is generally high, and they contribute to the representation of the state's eight natural regions and several subregions.  相似文献   

Rust-proofing wheat for a changing climate     

Sukumar Chakraborty  Jo Luck  Grant Hollaway  Glenn Fitzgerald  Neil White 《Euphytica》2011,179(1):19-32

This paper offers projections of potential effects of climate change on rusts of wheat and how we should factor in a changing climate when planning for the future management of these diseases. Even though the rusts of wheat have been extensively studied internationally, there is a paucity of information on the likely effects of a changing climate on the rusts and their influence on wheat production. Due to the lack of published empirical research we relied on the few published studies of other plant diseases, our own unpublished work and relevant information from the vast literature on rusts of wheat to prepare this overview. Three broad areas of potential risks from a changing climate were described: increased loss from wheat rusts, new rust pathotypes evolving faster and the reduced effectiveness of rust resistances. Increased biomass of wheat crops grown in the presence of elevated CO₂ concentrations and higher temperatures will increase the leaf area available for attack by the pathogen leading to increased inoculum production. If changed weather conditions were to accelerate the life cycle of a pathogen, the increased inoculum can lead to severe rust epidemics in many environments. Likewise should the effects of climate change result in more conducive conditions for rust development there will also be a corresponding increase in the rate of evolution of new pathotypes which could increase the rate of appearance of new virulences. The effectiveness of some rust resistance genes is influenced by temperature and crop development stage. Climate change may directly or indirectly influence the effectiveness of some resistance genes but this can not be ascertained due to a complete lack of knowledge. Since disease resistance breeding is a long term strategy it is important to determine if any of the important genes may become less effective due to climate change. Studies must be made to acquire new information on the rust disease triangle to increase the adaptive capacity of wheat under climate change. Leadership within the Borlaug Global Rust Initiative (BGRI) is needed to broker research on rust evolution and the durability of resistance under climate change.  相似文献   

Epidemiology. New estimates scale back scope of HIV/AIDS epidemic     

Cohen J 《Science (New York, N.Y.)》2007,318(5855):1360-1361

  相似文献   

Infectious diseases. Global fund pulls Myanmar grants     

Cohen J 《Science (New York, N.Y.)》2005,309(5739):1312

  相似文献