Sum Of Mineral Research Articles

Suspended sediment in lowland rivers – towards identifying the ratios of mineral and organic components and their variation during the year

Abstract Concentrations of suspended sediment transported by rivers are influenced by interactions between multiple drivers that act on a range of spatial and temporal scales. Such levels vary over the year, as well as across multi-year periods. Most conventional approaches to determining suspended load are based upon analyses of total suspended sediment concentration (SSC), i.e., the sum of mineral and organic matter. This approach makes it difficult, if not impossible, to determine the impact of multiple environmental factors on changes in suspension concentration precisely. The present paper focuses on the mineral and organic components of suspended sediment with the aim of determining how our knowledge of the share of each individual component can improve interpretations of SSC fluctuations during a hydro-logical year. The analysis conducted (personal and other researchers’ results) has shown that mineral and organic suspensions demonstrate mutually incompatible opposite trends under influence of environmental factors. This analysis of organic components identifies clear seasonal trends, which indicates that organic suspensions of autogenous origin have a strong influence on the dynamics of changes in suspension concentration; such analyses are rarely included in assessments of SSC dynamics.

Fatigue damage distribution and reliability assessment of grid mooring system for fish cage

This paper investigates the evolution of fatigue damage distribution with the loading cycle and predicts the annual fatigue damage distribution and system reliability of the grid mooring system under fatigue limit state for fish cage, employing the generalized probability density evolution method (GPDEM). A series of the hydrodynamic analysis for the grid mooring system of fish cage are performed to obtain the fatigue damage of the grid mooring system considering the long term environmental loading. The GPDEM equation is solved to determine the evolution of probability distribution of fatigue damage in term of the loading cycles, and the probability distribution of the annual fatigue damage of mooring lines is evaluated through the combination of the GPDEM and the virtual stochastic process model. In addition, the system reliability assessment of the grid mooring system under fatigue limit state is performed by the equivalent extreme-value event method. The results indicate that the probability distribution of the fatigue damage of the mooring component becomes more asymmetrical and platykurtic with the increase of the loading cycle and the annual fatigue damage distribution of the components in the grid mooring system can be estimated by the GPDEM from a stochastic point of view without any approximations or any asymptotic distributions. And it is necessary to conduct the uncertainty quantification of the Miner's sum at failure for the system reliability prediction of the grid mooring system under fatigue limit state to ensure the safety of fish farm.

Sustained effects of atmospheric [CO2] and nitrogen availability on forest soilCO2efflux

Soil CO2 efflux (Fsoil ) is the largest source of carbon from forests and reflects primary productivity as well as how carbon is allocated within forest ecosystems. Through early stages of stand development, both elevated [CO2] and availability of soil nitrogen (N; sum of mineralization, deposition, and fixation) have been shown to increase gross primary productivity, but the long-term effects of these factors on Fsoil are less clear. Expanding on previous studies at the Duke Free-Air CO2 Enrichment (FACE) site, we quantified the effects of elevated [CO2] and N fertilization on Fsoil using daily measurements from automated chambers over 10 years. Consistent with previous results, compared to ambient unfertilized plots, annual Fsoil increased under elevated [CO2] (ca. 17%) and decreased with N (ca. 21%). N fertilization under elevated [CO2] reduced Fsoil to values similar to untreated plots. Over the study period, base respiration rates increased with leaf productivity, but declined after productivity saturated. Despite treatment-induced differences in aboveground biomass, soil temperature and water content were similar among treatments. Interannually, low soil water content decreased annual Fsoil from potential values - estimated based on temperature alone assuming nonlimiting soil water content - by ca. 0.7% per 1.0% reduction in relative extractable water. This effect was only slightly ameliorated by elevated [CO2]. Variability in soil N availability among plots accounted for the spatial variability in Fsoil , showing a decrease of ca. 114 g C m(-2) yr(-1) per 1 g m(-2) increase in soil N availability, with consistently higher Fsoil in elevated [CO2] plots ca. 127 g C per 100 ppm [CO2] over the +200 ppm enrichment. Altogether, reflecting increased belowground carbon partitioning in response to greater plant nutritional needs, the effects of elevated [CO2] and N fertilization on Fsoil in this stand are sustained beyond the early stages of stand development and through stabilization of annual foliage production.

Design and Fatigue Performance of Large Utility-Scale Wind Turbine Blades

Aeroelastic design and fatigue analysis of large utility-scale wind turbine blades have been performed to investigate the applicability of different types of materials in a fatigue environment. The blade designs used in the study are developed according to an iterative numerical design process for realistic wind turbine blades, and the software tool FAST is used for advanced aero-servo-elastic simulations. Elementary beam theory is used to calculate strain time series from these simulations, and the material fatigue is evaluated using established methods. Following wind turbine design standards, the fatigue evaluation is based on a turbulent wind load case. Fatigue damage is estimated based on 100% availability and a site-specific annual wind distribution. Rainflow cycle counting and Miner's sum for cumulative damage prediction is used together with constant life diagrams tailored to actual material S-N data. Material properties are based on 95% survival probability, 95% confidence level, and additional material safety factors to maintain conservative results. Fatigue performance is first evaluated for a baseline blade design of the 10 MW NOWITECH reference wind turbine. Results show that blade damage is dominated by tensile stresses due to poorer tensile fatigue characteristics of the shell glass fiber material. The interaction between turbulent wind and gravitational fluctuations is demonstrated to greatly influence the damage. The need for relevant S-N data to reliably predict fatigue damage accumulation and to avoid nonconservative conclusions is demonstrated. State-of-art wind turbine blade trends are discussed and different design varieties of the baseline blade are analyzed in a parametric study focusing on fatigue performance and material costs. It is observed that higher performance material is more favorable in the spar-cap construction of large blades which are designed for lower wind speeds.

Microbial immobilization and mineralization of dissolved organic nitrogen from forest floors

Dissolved organic nitrogen (DON) plays a key role in the N cycle of many ecosystems, as DON availability and biodegradation are important for plant growth, microbial metabolism and N transport in soils. However, biodegradation of DON (defined as the sum of mineralization and microbial immobilization) is only poorly understood. In laboratory incubations, biodegradation of DON and dissolved organic carbon (DOC) from Oi and Oa horizons of spruce, beech and cypress forests ranged from 6 to 72%. Biodegradation of DON and DOC was similar in most samples, and mineralization of DON was more important than microbial immobilization. Nitrate additions (0–10 mg N L −1) never influenced either DON immobilization by microorganisms or mineralization. We conclude that soil microorganisms do not necessarily prefer mineral N over DON for meeting their N demand, and that biodegradation of DON seems to be driven by the microbial demand for C rather than N. Quantifying the dynamics of DON in soils should include consideration of both C and N demands by microbes.

Enhancement of pyrene mineralization in soil by wood-decaying fungi

The mineralization of [14C]pyrene in sterilized and non-sterile soil was investigated using the wood-decaying fungi Kuehneromyces mutabilis and Agrocybe aegerita in a period of 63 days. In sterilized soil 5.1% and 1.5% of the pyrene was mineralized to 14CO2 by K. mutabilis and by A. aegerita, respectively. In non-sterile soil, 27.3% of pyrene was mineralized by indigenous soil microflora including a Mycobacterium gilvum strain. During soil inoculation with fungi the mineralization was higher (47.7% for K. mutabilis and 38.5% for A. aegerita). For a mass balance analysis the soil was extracted with toluene and methanolic KOH (humic acid extraction). Considering the sum of mineralization and formation of bound residues (non-extractable radioactivity), about 50% (sterilized soil) and 75% (non-sterile soil) of pyrene were eliminated by K. mutabilis. In comparison with indigenous soil microflora, K. mutabilis enhanced pyrene elimination up to 42%.

Influence of Prescribed Burning on Nitrogen Mineralization and Nitrification in Grassland

The seasonal dynamics of gross nitrogen (N) mineralization, nitrification, and mineral nitrogen consumption rates were studied with the 15N pool dilute technique in burned and unburned Leymus chinensis (Trin.) Tzvel. (Chinese Wildryegrass) grasslands. Gross N mineralization is the gross rate of the process of the conversion of organic N to the form during decomposition before N immobilization by microbes. Similarly, gross nitrification is the gross rate of the conversion of and organic N to before N immobilization by microbes, and consumption is sum of mineral N losses by biological or nonbiological processes. Results indicated that gross mineralization and nitrification rates, and consumption rates, and soil concentrations of were higher in burned grassland areas than in unburned areas in April and May and that all were lower or similar compared to unburned areas in September. The soil concentrations of indicated no difference between burned and unburned areas in April and May, but burned areas had higher in July and September. Results indicate that prescribed burning in spring could benefit the renewal of grasslands of northeast China through mobilization of soil N pools.

Consorciação de plantas de cobertura antecedendo o milho em plantio direto: I - Dinâmica do nitrogênio no solo

A dinâmica do N no solo é um assunto ainda pouco estudado no Sul do Brasil, principalmente no sistema plantio direto. O presente estudo avaliou a dinâmica do N no solo durante o ciclo do milho, em sucessão à aveia preta (AP) (Avena strigosa Schieb), ervilhaca comum (EC) (Vicia sativa L.) e nabo forrageiro (NF) (Raphanus sativus L. var. oleiferus Metzg.), em cultivos solteiros e consorciados. O trabalho foi realizado nos anos agrícolas de 1998/99 e 1999/00, em área do Departamento de Solos da Universidade Federal de Santa Maria (RS) em um Argissolo Vermelho distrófico arênico (Hapludalf). Utilizou-se o delineamento experimental de blocos inteiramente ao acaso, com quatro repetições. Os tratamentos foram os seguintes: 100 % AP (80 kg ha-1 de sementes), 100 % EC (80 kg ha-1), 100 % NF (14 kg ha-1), 15 % AP + 85 % EC, 45 % AP + 55 % EC e 30 % AP + 70 % NF. Além desses, foram utilizados dois tratamentos em pousio invernal onde cresceu a vegetação espontânea da área. Num tratamento, o milho foi cultivado sem adubação nitrogenada e, no outro, o milho foi adubado com 180 kg ha-1 de N-uréia. A partir de 10 dias do manejo das plantas de cobertura, avaliou-se a quantidade de N mineral do solo, nas camadas de 0-5, 5-15, 15-30, 30-60 e 60-90 cm, em nove épocas. A soma das quantidades de N mineral das cinco camadas de solo no tratamento com ervilhaca solteira foi superior à dos tratamentos em pousio e aveia solteira. Ao final do primeiro mês, a diferença em favor da ervilhaca foi de aproximadamente 30 kg ha-1 de N. Nos tratamentos com nabo forrageiro, as quantidades de N mineral foram inferiores às da ervilhaca solteira e próximas às dos consórcios de aveia e ervilhaca. Os resultados deste trabalho evidenciaram que a consorciação de aveia e ervilhaca provocou uma diminuição na quantidade de N mineral do solo em relação à ervilhaca solteira, tendo sido esse efeito proporcional à participação de aveia no consórcio. Verificou-se também que o potencial de perdas de N por lixiviação foi maior após a ervilhaca solteira do que após a aveia e o nabo solteiros e os consórcios de aveia e ervilhaca.

The time-dependent effect of the biological component of 137Cs soil contamination

Abstract In investigations of the long-term development of the population dose in the highly contaminated regions of the Commonwealth of Independence States it was found that the external dose has not decreased as strongly as expected since 1992. Further investigations have shown that, contrary to expectations, no linear correlation can be observed between soil contamination and measured area dose rate. As a contribution towards clarifying these issues, the area dose rate and the soil contamination including the plant fraction were investigated in the Korma district, Belarus. It was found that it is necessary to cover and average over larger areas in order to determine from ground contamination the long-term development of the external dose commitment. This means that for this purpose the introduction of an “effective” surface contamination (sum of mineral and organic contamination components) is necessary. The phenomena observed are described in a model, which permits an analytical calculation of the contamination profile in soil taking migration and transfer effects into account. The differences observed between the measured soil contamination and the resulting external doses or the directly measured dose rate can be explained by the proposed model. Moreover, their long-term development can be calculated. The results show that a time decade after the accident the biological part of the “effective” soil contamination becomes dominant and cannot be neglected.

Enhancement of pyrene mineralization in soil by wood-decaying fungi

The mineralization of [ 14C]pyrene in sterilized and non-sterile soil was investigated using the wood-decaying fungi Kuehneromyces mutabilis and Agrocybe aegerita in a period of 63 days. In sterilized soil 5.1% and 1.5% of the pyrene was mineralized to 14CO 2 by K. mutabilis and by A. aegerita, respectively. In non-sterile soil, 27.3% of pyrene was mineralized by indigenous soil microflora including a Mycobacterium gilvum strain. During soil inoculation with fungi the mineralization was higher (47.7% for K. mutabilis and 38.5% for A. aegerita). For a mass balance analysis the soil was extracted with toluene and methanolic KOH (humic acid extraction). Considering the sum of mineralization and formation of bound residues (non-extractable radioactivity), about 50% (sterilized soil) and 75% (non-sterile soil) of pyrene were eliminated by K. mutabilis. In comparison with indigenous soil microflora, K. mutabilis enhanced pyrene elimination up to 42%.

Fatigue Life of Offshore Steel Structures Under Stochastic Loading

The fatigue life of offshore steel structures under stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation, and in this connection, a comparison between experimental results and results obtained using current codes and specifications. Fatigue test series are performed, with various types of stochastic loadirtg that are realistic in relation to offshore structures. Four different load spectra, with irregularity factors ranging from ∼0.70-1.00, have been applied. The experimental investigation comprises test series on both full‐scale tubular joints and smaller weided test specimens. The materials that have been used until now have been ordinary offshore structural steels, with a yield stress of J. Strain Analysis fy≃360-410MPa. The test series show a significant difference between constant amplitude and variable amplitude fatigue test results. For the welded plate test specimens, approximately 100 fatigue tests have been carried out, and the values of the Miner sum ...

ADVANCED TOOL FOR FAST ASSESSMENT OF FATIGUE UNDER OFFSHORE RADOM WAVE STRESS HISTORIES.

Keywords ASSESSMENT, RANDOM, WELDED, LOADS, RANGE, STRUCTURES, GROWTH, PARTIAL, FATIGUE, WAVES, STEEL, AVERAGE, FRACTURE, EQUATIONS, HISTORY, LIFE, OFFSHORE, STRESS, JOINTS, WEIGHTED, MECHANICS, CRACKS, CORROSION, DAMAGE UNIVERSITY COLLEGE LONDON... Show All

Effect of Load Sequence on the Statistical Fatigue of Composites

Effect of Load Sequence on the Statistical Fatigue of Composites

On the Cumulative Fatigue Damage in Roving Glass Cloth FRP

One and two-stress level fatigue tests have been conducted to investigate the fatigue properties of glass fiber reinforced plastics, especially the relation between cumulative fatigue damage and residual strength. The materials used for the experiment were FRP laminates made of polyester resin and plain woven roving glass cloth. The tests were performed in repeated tension with the minimum value of cyclic stress equal to 5 percent of the cyclic stress amplitude.The tensile strength of the material under fatigue loading decreased with increaing the number of stress cycles, and fatigue failure occured when the residual strength became equal to the maximum value of cyclic stress.The reduction of the residual strength at a given stress level has been determined as a function of number of cycles. The experimental results show that for the high-low stress cumulative damage test the Miner's sum, (n1/N1)+(n2/N2), is greater than unity and for the low-high stress test less than unity.These observations agree both qualitatively and quantitatively with the predicted values of fatigue lives based on the strength reduction theory.