Fick's law

Packaging is an intermediary between the produced food products and the customer, which maintains the quality of the product and provides the information required by the customer. The primary function of packaging is to preserve the nutritional quality of products and extend their shelf life. Conventional packaging materials, such as polyethylene, polypropylene, and polystyrene, are derived from petroleum-based sources and are widely utilized in food packaging due to their advantageous properties, including high durability, lightweight nature, cost-effectiveness, ease of manufacturing, and low water vapor permeability. However, degradation of these synthetic materials is very slowly in the environment, leading to significant ecological pollution. In response to this issue, there has been growing interest in the use of biopolymer materials as a sustainable alternative to non-biodegradable, petroleum-derived packaging. Biodegradable biopolymers offer several benefits, such as environmental degradability and lower production costs compared to synthetic polymers. Additionally, in certain applications, biopolymers can enhance product shelf life and quality, making them a promising solution for sustainable packaging.

There are different methods for estimation of soil infiltration equations' coefficients depending on irrigation system. In this study, seasonal variations of the Philip equation coefficients (PEC) were investigated in three different soil textures including loam, sandy loam and sandy clay loam soils. The PEC , s were calculated using four following mehods: Rawls, one-point Shepard, Clemmens and adjusted Weibo methods. The advance phase was simulatied using SURFACE software. The results showed that the Rawls and adjusted Weibo methods estimated the advance phase more accurate than the others in the three soil textures. The sorptivity coefficient (S) at the fourth irrigation was compared with the first one and it showed that S decreased to 85, 10 and 82 percent for Clemmens, one-point Shepard and adjusted Weibo methods, in loamy soil, respectively. Similarly, it decreased to 74, 54 and 65 for the sandy clay loam soil from first to fourth irrigation event. The result showed no trend for transmisivity coefficient (A). Sensitivity analysis remarked that the S was more affected by inflow discharge in one-point Shepard and adjusted Weibo methods than the two others, and also it was affected by hydraulic conductivity in Rawls method.

Nesta monografia a partir da equação da continuidade de nêutrons para um grupo de energia e uma dimensão obtemos, aplicando a lei de Fick, a equação de difusão de nêutrons e, aplicando o operador de média espacial, a equação de balanço nodal. Utilizamos uma das primeiras técnicas empregadas para a solução da equação de difusão de nêutrons, o método de diferenças finitas de malha fina, que consiste em aproximar a derivada do fluxo de nêutrons em um determinado ponto, pela diferença entre valores discretos da função fluxo de nêutrons. Esta é uma técnica de excelente acurácia, desde respeitada a condição de que o comprimento da malha deve ser menor do que o menor comprimento de difusão. Utilizada, inclusive, para obter valores de referência para validar outras técnicas de solução.
Escrevendo a equação de difusão de nêutrons na forma matricial, passamos a ter um problema de autovalor e autovetor, onde estamos interessados em determinar tanto o fator de multiplicação efetivo (o maior autovalor), quanto o fluxo médio de nêutrons nas malhas (o autovetor associado). Por último foi criado um programa em linguagem Fortran para resolver esse problema de autovalor e autovetor iterativamente, onde foi utilizado o Método das Potências Normalizado para o cálculo do fator de multiplicação e o algoritmo de Thomas para o cálculo do fluxo de nêutrons.

Nesta dissertação o Método de Diferenças Finitas de Malha Grossa Analítico (DFMGA) é usado para resolver a equação de difusão de nêutrons tridimensional e em dois grupos de energia. No DFMGA o perfil de fuga transversal é representado por um polinômio do segundo grau e os coeficientes de difusão nas faces do nodo são obtidos resolvendo-se analiticamente a equação de difusão de nêutrons integrada transversalmente, a qual depende do perfil de fuga transversal. Com isto, as densidades de corrente médias nas faces dos nodos podem ser escritas em função destes coeficientes de difusão nas faces e de fluxos médios, da mesma forma que é feito no Método de Diferenças Finitas Clássico. Sendo assim, pode-se resolver qualquer problema de autovalor (na Teoria da Difusão de Nêutrons) usando as mesmas ferramentas computacionais que são utilizadas no Método de Diferenças Finitas Clássico. O programa computacional desenvolvido, que faz uso do DFMGA, foi validado utilizando três benchmarks, benchmark IAEA 3D, LRA 3D e LMW 3D, através da comparação do fator de multiplicação efetivo e da distribuição da densidade de potência calculados, com os resultados de referência deste benchmark. Os resultados dos testes do processo de validação se mostraram dentro do que é esperado para cálculos nodais de malha grossa.

In this study, effective diffusion coefficient of drying clay of ceramics drying clay ceramics have been studied. In this study, the effects of temperature (40-60-80 °C), relative humidity (30-50-70%) and air velocity (1-2-3 ms-1) on the drying behavior of clay ceramics were investigated. A full factorial design of experiments on a cubic sample was performed. In each trial mass and volume reduction using balance and camera was registered and the drying curve was plotted. Effective diffusion coefficient of moisture using drying curves were calculated using the newly developed algorithm of firefly. In this algorithm, the goal is to reduce the error between the analytical values and experimental values. Statistical analysis and analysis of variance showed that in calculation of the effective diffusion coefficient the velocity, temperature and humidity are independent of each other. The greatest impact on the effective diffusion coefficient is respectively related to the temperature, velocity and environment humidity. The comparison between this study and other studies show that 97% similarity and applicability of this method in calculating the effective diffusion coefficient of the ceramic drying processes.

El trabajo consistio en, primer lugar, utilizar dos tipos diferentes carbones vegetales nacionales y comparar el grado de dureza alcanzada por un acero hipoeutectoide despues de aplicado un tratamiento termoquimico superficial. En segundo lugar, cementar brocas comerciales utilizadas para perforar materiales blandos. Se trataron 10 probetas de acero AISI 1018, introducidas en dos (2) cajas metalicas; una con carbon de mangle (rizophora mangle) y la otra con carbon de nance (byrsonima crassifolia) pulverizado. En la cementacion con mangle se alcanzaron durezas promedio de 44.38 RWC, mientras que con el carbon de nance presentaron durezas del orden de 45.27 RWC. y la profundidad de penetracion de la templabilidad fue del orden de 0.05 mm. Finalmente, brocas ferrosas fueron cementadas con mezclas a base de carbon vegetal de mangle y de carbonato de sodio al 10% en peso, y sometidas a ensayos controlados de perforacion. Las brocas cementadas fueron capaces de perforar mas de 10 orificio...

In this study, a new metho simulation of dilute polymer suspensio function is employed to generate an equ polymer suspension in the inception of flow configuration based on the conve agreement between the results demonstr The main advantage of the proposed me

Importance of this paper: Agricultural soil is an important source of atmospheric N 2 O. Soil compaction created by tractor trac is favourable for N 2 O production in soil due to its eect on soil aeration. The high input of mineral nitrogen (a common practice of conventional agricultural) to the compacted soil would emit N 2 O emission more vigorously. In this paper, we have presented the result of four year long ®eld research investigating the eect of soil compaction on N 2 O emission in relation to factors of potential explanatory importance. Since agricultural modernisation (with increased tractor trac) is taking place worldwide , such investigation will have important implications for the global N 2 O budget. This paper may also provide a scienti®c basis for encouraging ecological agriculture that causes the least soil compaction.

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH4 consumption rates during the two years (mean 0.43 and 0.49 mg m-2 h-1), and at different sites (mean 0.36 to 0.57 mg m-2 h-1). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH4, and C and N status of soils regulates the strength of the sink in the long term.

Background and objectives: The increase of irrigation efficiency is a technique applied to water conservation; therefore, appropriate and productive management and the application of efficient methods in order to maintain enough water in the soil for optimum utilization of scarce water resources is necessary in the long run. The use of super-absorbent polymers offers effective ways of saving water in agriculture. However, before selecting a suitable polymer, determining of an appropriate model is essential.
Materials and Methods: In this study, the water absorption model was evaluated by two super-absorbent polymers from polyacrylamide family, abbreviated as T-A200 and T-A100. The experiment was carried out with four replicates and water absorption was recorded by the polymers in different times until reaching the equilibrium swelling (stable inflation), as instantaneous and cumulative. After testing the free swelling, the absorption kinetics of fluid (the changes in the absorption of water by the gel time) was determined by immersion in water. After that the result was presented by a graph that depicted the changes in the ratio of absorbed solvent in time to this solvent in equilibrium in time. Also, the trend of solvent absorption by the two polymers in time measured. To determine the mechanism of penetration, the mentioned model used and the values of n and k were calculated.
Results: The results showed that the fluid absorption in heterogeneous environments such as gels was associated with significant deformation. The graph shows that in all cases n was less than 5.0, and therefore the mechanism of transfer of the solvent into the polymer network follows the Fick's law.
Conclusion: the appropriate super-absorbent polymers in agriculture must be able to absorb maximum amount of water at the minimum time; therefore, doing so will prevent from the loss of rainfall or irrigation water applied. To prove it, the model should follow the Fick diffusion which penetration rate is lower than the speed of molecular relaxation, and only diffusion phenomena is effective through the transfer of ground-penetrating, so, molecular relaxation phenomenon does not affect on the transfer of ground-penetrating. Consequently, after any deformation or swelling, the polymers quickly reached a new balance and stresses will quickly vanish; therefore, it does not have any effect on the speed of penetrating component. In this study, the penetration of the fluid into the polymer followed the Fick model. Hence, this model would certainly be recommended to periodic swelling ability in agricultural purposes.

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH4 consumption rates during the two years (mean 0.43 and 0.49 mg m-2 h-1), and at different sites (mean 0.36 to 0.57 mg m-2 h-1). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH4, and C and N status of soils regulates the strength of the sink in the long term.

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH4 consumption rates during the two years (mean 0.43 and 0.49 mg m-2 h-1), and at different sites (mean 0.36 to 0.57 mg m-2 h-1). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH4, and C and N status of soils regulates the strength of the sink in the long term.

Importance of this paper: Agricultural soil is an important source of atmospheric N 2 O. Soil compaction created by tractor trac is favourable for N 2 O production in soil due to its eect on soil aeration. The high input of mineral nitrogen (a common practice of conventional agricultural) to the compacted soil would emit N 2 O emission more vigorously. In this paper, we have presented the result of four year long ®eld research investigating the eect of soil compaction on N 2 O emission in relation to factors of potential explanatory importance. Since agricultural modernisation (with increased tractor trac) is taking place worldwide , such investigation will have important implications for the global N 2 O budget. This paper may also provide a scienti®c basis for encouraging ecological agriculture that causes the least soil compaction.

Because a large fraction of the world's carbon exists in the soil of boreal forests, understanding how soil temperature and moisture affect soil respiration is vital for predicting soil response to climate change. We measured soil respiration and CO 2 concentrations within soils of floodplain and upland forests in interior Alaska from 1996 to 1997. At each site, a 0.10-ha-area shelter was constructed that prevents summer precipitation from infiltrating into the soil. Measurements of soil profile CO 2 , soil respiration, soil temperature, and soil moisture were made inside (treatment) and outside (control) the sheltered areas through two growing seasons and the winter of 1996-1997. Sheltered soils had decreased profile concentrations and surface flux of CO 2. At the upland control site, individual flux rates ranged from 0.10 to 0.95 g•m-2 •h-1 in the summer and at sites under the shelter from 0.10 to 0.53 g•m-2 •h-1. Rates at the floodplain control site ranged from 0.11 to 1.45 g•m-2 •h-1 and under the shelter from 0.11 to 0.55 g•m-2 •h-1. Fick's Law could predict surface CO 2 flux when the CO 2 concentration gradient within the profile accurately represented the soil surface gradient and biological sources and sinks of the gas did not overwhelm flux calculations. Résumé : Étant donné qu'une fraction importante du carbone dans le monde se trouve dans le sol des forêts boréales, il est vital de comprendre de quelle façon la température et l'humidité du sol affectent la respiration du sol pour prédire la réaction du sol à un changement climatique. Nous avons mesuré la respiration du sol et les concentrations de CO 2 dans le sol de forêts situées sur une plaine alluviale et sur un plateau de l'intérieur de l'Alaska de 1996 à 1997. À chaque endroit, un abri d'une superficie de 0,10 ha a été construit pour empêcher les précipitations estivales de s'infiltrer dans le sol. Les mesures du CO 2 dans le profil de sol, de la respiration, de la température et de l'humidité du sol ont été prises à l'intérieur (traitement) et à l'extérieur (témoin) des sites couverts pendant deux saisons de croissance et pendant l'hiver 1996-1997. Les sols protégés avaient des concentrations de CO 2 dans le profil et un flux de CO 2 en surface plus faibles. Pendant l'été sur le plateau, les taux individuels de flux variaient de 0,10 à 0,95 g•m-2 •h-1 dans les zones témoins et de 0,10 à 0,53 g•m-2 •h-1 dans les zones sous abri. Sur la plaine alluviale, les taux variaient de 0,11 à 1,45 g•m-2 •h-1 dans les zones témoins et de 0,11 à 0,55 g•m-2 •h-1 dans les zones sous abri. La loi de Fick pouvait prédire le flux de CO 2 en surface lorsque le gradient de concentration de CO 2 dans le profil représentait fidèlement le gradient à la surface du sol et que les sources et les puits biologiques de CO 2 ne venaient pas fausser les calculs de flux. [Traduit par la Rédaction] Billings et al. 1783

Because a large fraction of the world's carbon exists in the soil of boreal forests, understanding how soil temperature and moisture affect soil respiration is vital for predicting soil response to climate change. We measured soil respiration and CO2 concentrations within soils of floodplain and upland forests in interior Alaska from 1996 to 1997. At each site, a 0.10-ha-area shelter was constructed that prevents summer precipitation from infiltrating into the soil.

Long-term records of the methane uptake by five different aerated soils in South-West Germany and spot measurements in Western Europe, North America, and North-West Africa are presented. A good correlation between the methane uptake rate and soil permeability, obtained from parallel 222Radon flux and concentration measurements of methane and 222Radon in soil air indicates, that methane consumption in aerated soils is mainly controlled by the gas transport resistance within the soil. Soil temperature is found to be of minor influence on the methane flux from the atmosphere into the soil. The soils investigated were classified with respect to the three major soil texture classes - coarse, medium, and fine - representing soils with low, medium, and high gas transport resistance, respectively. Average methane uptake rates for each soil texture class were determined and extrapolated to fit into the scheme of the NASA-GISS global digital data set of soil types (Staub et al., 1987). Assumi...

A 6-year record of soil respiration and C0 2 concentration measurements in various soils with different plant cover is presented. The effect of temperature and soil-moisture content is discussed; for this, 222 Rn-ftux and concentration measurements are used to trace gas transport in the unsaturated soil zone. The C0 2 production in the soil is strongly correlated with the subsoil temperature. Q 10-values vary between 1.4 and 2.7, depending on mean annual temperature and precipitation. Soil respiration is reduced not only by extremely dry but also by extremely wet soil conditions. This is probably due to an evolution adaptation of soil microorganism to the long-time mean meteorological situation. The regional mean annual cycle of soil respiration representative for the Rhine Valley area near Heidelberg is deduced from spot measurements in this region. Minimum soil respiration occurs in February; the maximum C0 2 production is in June and July. A steep increase of the respiration curve in spring is followed by a slow decrease from summer to winter. Even during the coldest winter months, soil respiration does not reach zero, but makes up 10% to 15% of the maximum respiration rate. The regional annual mean value of the soil C0 2 production is 6 mmol m-2 h-1 ; the summer mean value is 9 mmol m-2 h-1 .

Long-term records of the methane uptake by five different aerated soils in SouthWest Germany and spot measurements in Western Europe, North America, and NorthWest Africa are presented. A good correlation between the methane uptake rate and soil permeability, obtained from parallel 2Z2Radon flux and concentration measurements of methane and 22ZRadon in soil air indicates, that methane consumption in aerated soils is mainly controlled by the gas transport resistance within the soil. Soil temperature is found to be of minor influence on the methane flux from the atmosphere into the soil. The soils investigated were classified with respect to the three major soil texture classes coarse, medium, and fine-representing soils with low, medium, and high gas transport resistance, respectively. Average methane uptake rates for each soil texture class were determined and extrapolated to fit into the scheme of the NASA-GISS global digital data set of soil types (Staub et al., 1987). Assuming that the observed relation between methane uptake rate and soil permeability (soil texture) is valid for all kinds of aerated soils, methane uptake rates are estimated on a regional and global scale. From this parameterization we calculate a global CH 4 soil sink in the range of 9.0 to 55.9 Tg CHa/a with a best estimate of 28.7 Tg CH4/a. This corresponds to about 7% of the total global destruction rate by OH radicals.

Long-term records of the methane uptake by five different aerated soils in SouthWest Germany and spot measurements in Western Europe, North America, and NorthWest Africa are presented. A good correlation between the methane uptake rate and soil permeability, obtained from parallel 2Z2Radon flux and concentration measurements of methane and 22ZRadon in soil air indicates, that methane consumption in aerated soils is mainly controlled by the gas transport resistance within the soil. Soil temperature is found to be of minor influence on the methane flux from the atmosphere into the soil. The soils investigated were classified with respect to the three major soil texture classes coarse, medium, and fine-representing soils with low, medium, and high gas transport resistance, respectively. Average methane uptake rates for each soil texture class were determined and extrapolated to fit into the scheme of the NASA-GISS global digital data set of soil types (Staub et al., 1987). Assuming that the observed relation between methane uptake rate and soil permeability (soil texture) is valid for all kinds of aerated soils, methane uptake rates are estimated on a regional and global scale. From this parameterization we calculate a global CH 4 soil sink in the range of 9.0 to 55.9 Tg CHa/a with a best estimate of 28.7 Tg CH4/a. This corresponds to about 7% of the total global destruction rate by OH radicals.

Evidence is accumulating that land use changes and other human activity during the past 100 to 200 years have contributed to decreased CI~ oxidation in the soil. Recent studies have documented the effect of land use change on ~ oxidation in a variety of ecosystems. Increased N additions to temperate forest soils in the northeastern United States decreased CI-L uptake by 30 to 60%, and increased N fertilization and conversion to cropland in temperate grasslands decreased CI-L uptake by 30 to 75%. Using these data, we made a series of calculations to estimate the impact of land use and management changes which have altered soil the CI-L sink in temperate forest and grassland ecosystems. Our study indicates that as the atmospheric mixing ratio of CH 4 has increased during the past 150 y, the temperate CH 4 sink has risen from approximately 8 Tg y.t to 27 Tg y-t, assuming no loss of land cover to cropland conversion. The net effect of intensive land cover changes and extensive chronic disturbance (i.e., increased atmospheric N deposition) to these ecosystems have resulted in about 30% reduction in the CI-L sink relative to the soil sink assuming no disturbance to any of the temperate ecosystems. This will impact the global CH 4 budget even more as atmospheric CI-I 4 concentrations increase and as a result of further disturbance to other biomes. Determining the reasons for the decreased CI-I 4 uptake due to land disturbance is necessary to understand the role of CI-L uptake in conjunction with the increasing atmospheric CI-L concentrations. Without accounting for this approximately 20 Tg y.t temperate soil sink, the atmospheric CH 4 concentration would be increasing about 1.5 times the current rate.

Methane oxidation in soil cores from a mixed hardwood-coniferous forest varied relatively little as a function of incubation temperatures from -1 to 30 degrees C. The increase in oxidation rate was proportional to T (in kelvins). This relationship was consistent with limitation of methane transport through a soil gas phase to a subsurface zone of consumption by diffusion. The Q(10) for CO(2) production, 3.4, was substantially higher than that for methane oxidation, 1.1, and indicated that the response of soil respiration to temperature was limited by enzymatic processes and not diffusion of either organic substrates or molecular oxygen. When grown under conditions of phase-transfer limitation, cultures of Methylomonas rubra showed a minimal response to temperature changes between 19 and 38 degrees C, as indicated by methane oxidation rates; in the absence of phase-transfer limitations, M. rubra oxidized methane at rates strongly dependent on temperature.

Experiments were conducted to determine the eects of various carbon substrates on the oxidation of atmospheric CH 4 by an alpine tundra soil. Acetate, formate, methanol, trimethylamine and yeast extract were tested. Acetate and formate (500 mg C (g d.w.) À1) stimulated CH 4 oxidation rates from 300 to 1192.8 (297.2) and 1036.8 (233.6) pg C (g d.w.) À1 h À1 , respectively. In contrast, methanol did not cause an increase in maximal CH 4 oxidation rates, but methanol-treated soil maintained peak rates of CH 4 oxidation longer than control soil. In parallel with the CH 4 data, acetate additions stimulated acetate utilization, whereas methanol did not stimulate methanol utilization in the soil. This indicates that the mechanism by which acetate stimulates soil CH 4 oxidation may not be the same as that by which methanol sustains soil CH 4 oxidation. Growth of methanotrophs on acetate has not been reported previously. Therefore, these data indicate that either there is a novel strain of methanotroph in this soil, or that acetate stimulates atmospheric CH 4 oxidation by increasing methanogenesis, which in turn increases the supply of methane to the methane oxidizers in this soil.

Studies were done to assess the effects of soil moisture manipulations on CH R oxidation in soils from a dry alpine tundra site. When water was added to these soils there was a stimulation of CH R oxidation. This stimulation of CH R oxidation took time to develop. One to three days after water additions no stimulation was observed. Nine days after rewetting, CH R oxidation was greatly stimulated. This time delay suggests that methanotrophs grew in response to water additions, or that they take a long time to recover from metabolically inactive resting stages.

NH 4 ؉ inhibition kinetics for CH 4 oxidation were examined at near-atmospheric CH 4 concentrations in three upland forest soils. Whether NH 4 ؉-independent salt effects could be neutralized by adding nonammoniacal salts to control samples in lieu of deionized water was also investigated. Because the levels of exchangeable endogenous NH 4 ؉ were very low in the three soils, desorption of endogenous NH 4 ؉ was not a significant factor in this study. The K m(app) values for water-treated controls were 9.8, 22, and 57 nM for temperate pine, temperate hardwood, and birch taiga soils, respectively. At CH 4 concentrations of <15 l liter ؊1 , oxidation followed first-order kinetics in the fine-textured taiga soil, whereas the coarse-textured temperate soils exhibited Michaelis-Menten kinetics. Compared to water controls, the K m(app) values in the temperate soils increased in the presence of NH 4 ؉ salts, whereas the V max(app) values decreased substantially, indicating that there was a mixture of competitive and noncompetitive inhibition mechanisms for whole NH 4 ؉ salts. Compared to the corresponding K ؉ salt controls, the K m(app) values for NH 4 ؉ salts increased substantially, whereas the V max(app) values remained virtually unchanged, indicating that NH 4 ؉ acted by competitive inhibition. Nonammoniacal salts caused inhibition to increase with increasing CH 4 concentrations in all three soils. In the birch taiga soil, this trend occurred with both NH 4 ؉ and K ؉ salts, and the slope of the increase was not affected by the addition of NH 4 ؉. Hence, the increase in inhibition resulted from an NH 4 ؉-independent mechanism. These results show that NH 4 ؉ inhibition of atmospheric CH 4 oxidation resulted from enzymatic substrate competition and that additional inhibition that was not competitive resulted from a general salt effect that was independent of NH 4 ؉ .

El trabajo consistió en, primer lugar, utilizar dos tipos diferentes carbones vegetales nacionales y comparar el grado de dureza alcanzada por un acero hipoeutectoide después de aplicado un tratamiento termoquímico superficial. En segundo lugar, cementar brocas comerciales utilizadas para perforar materiales blandos. Se trataron 10 probetas de acero AISI 1018, introducidas en dos (2) cajas metálicas; una con carbón de mangle (rizophora mangle) y la otra con carbón de nance (byrsonima crassifolia) pulverizado. En la cementación con mangle se alcanzaron durezas promedio de 44.38 RW C , mientras que con el carbón de nance presentaron durezas del orden de 45.27 RW C. y la profundidad de penetración de la templabilidad fue del orden de 0.05 mm. Finalmente, brocas ferrosas fueron cementadas con mezclas a base de carbón vegetal de mangle y de carbonato de sodio al 10% en peso, y sometidas a ensayos controlados de perforación. Las brocas cementadas fueron capaces de perforar más de 10 orificios en lámina de acero de 4.76 mm de espesor, contrario a las brocas no tratadas, las cuales se mostraron ineficientes al realizar la mínima perforación posible.

NH4+ inhibition kinetics for CH4 oxidation were examined at near-atmospheric CH4 concentrations in three upland forest soils. Whether NH4+-independent salt effects could be neutralized by adding nonammoniacal salts to control samples in lieu of deionized water was also investigated. Because the levels of exchangeable endogenous NH4+ were very low in the three soils, desorption of endogenous NH4+ was not a significant factor in this study. The Km(app) values for water-treated controls were 9.8, 22, and 57 nM for temperate pine, temperate hardwood, and birch taiga soils, respectively. At CH4 concentrations of &lt;/=15 &mgr;l liter-1, oxidation followed first-order kinetics in the fine-textured taiga soil, whereas the coarse-textured temperate soils exhibited Michaelis-Menten kinetics. Compared to water controls, the Km(app) values in the temperate soils increased in the presence of NH4+ salts, whereas the Vmax(app) values decreased substantially, indicating that there was a mixture of...

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH 4 consumption rates during the two years (mean 0.43 and 0.49 mg m 2 h 1 ), and at different sites (mean 0.36 to 0.57 mg m 2 h 1 ). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH 4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH 4 , and C and N status of soils regulates the strength of the sink in the long term.

El trabajo consistió en, primer lugar, utilizar dos tipos diferentes carbones vegetales nacionales y comparar el grado de dureza alcanzada por un acero hipoeutectoide después de aplicado un tratamiento termoquímico superficial. En segundo lugar, cementar brocas comerciales utilizadas para perforar materiales blandos. Se trataron 10 probetas de acero AISI 1018, introducidas en dos (2) cajas metálicas; una con carbón de mangle (rizophora mangle) y la otra con carbón de nance (byrsonima crassifolia) pulverizado. En la cementación con mangle se alcanzaron durezas promedio de 44.38 RW C , mientras que con el carbón de nance presentaron durezas del orden de 45.27 RW C . y la profundidad de penetración de la templabilidad fue del orden de 0.05 mm. Finalmente, brocas ferrosas fueron cementadas con mezclas a base de carbón vegetal de mangle y de carbonato de sodio al 10% en peso, y sometidas a ensayos controlados de perforación. Las brocas cementadas fueron capaces de perforar más de 10 orificios en lámina de acero de 4.76 mm de espesor, contrario a las brocas no tratadas, las cuales se mostraron ineficientes al realizar la mínima perforación posible.

NH4+ inhibition kinetics for CH4 oxidation were examined at near-atmospheric CH4 concentrations in three upland forest soils. Whether NH4+-independent salt effects could be neutralized by adding nonammoniacal salts to control samples in lieu of deionized water was also investigated. Because the levels of exchangeable endogenous NH4+ were very low in the three soils, desorption of endogenous NH4+ was not a significant factor in this study. The Km(app) values for water-treated controls were 9.8, 22, and 57 nM for temperate pine, temperate hardwood, and birch taiga soils, respectively. At CH4 concentrations of &lt;/=15 &mgr;l liter-1, oxidation followed first-order kinetics in the fine-textured taiga soil, whereas the coarse-textured temperate soils exhibited Michaelis-Menten kinetics. Compared to water controls, the Km(app) values in the temperate soils increased in the presence of NH4+ salts, whereas the Vmax(app) values decreased substantially, indicating that there was a mixture of...

Recently, atmospheric CH 4 concentration has risen dramatically, apparently due to human activities. Since CH 4 is involved in several atmospheric processes that regulate Earth's climate, it is important that we understand the factors that control its atmospheric concentration. One such factor is biological CH 4 consumption in well-drained soils. Although this sink may comprise nearly one-tenth of the annual destruction of atmospheric CH 4 , we know relatively little about it. I conducted a research project to investigate the influences of CH 4 supply, soil moisture, dissolved salts, and NH 4 + -fertilizer on the activity of soil CH 4 oxidizers.

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH 4 consumption rates during the two years (mean 0.43 and 0.49 mg m 2 h 1 ), and at different sites (mean 0.36 to 0.57 mg m 2 h 1 ). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH 4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH 4 , and C and N status of soils regulates the strength of the sink in the long term.

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH 4 consumption rates during the two years (mean 0.43 and 0.49 mg m 2 h 1 ), and at different sites (mean 0.36 to 0.57 mg m 2 h 1 ). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH 4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH 4 , and C and N status of soils regulates the strength of the sink in the long term.

SummaryÐChanges in land use and management of tropical systems are considered to be major factors in the recent upsurge in increases in atmospheric nitrous oxide (N 2 O) and methane (CH 4 ). Studies were initiated in western Puerto Rico grasslands to determine the eect of plowing, or liming and fertilizing an acid Oxisol on the soil±atmosphere exchanges of N 2 O and CH 4 . Weekly ®eld¯ux measurements and ®eld manipulation and laboratory studies were conducted over 22 months during 1993±1995. We found that N 2 O emissions from an Oxisol acidi®ed to pH 4 were generally lower than from pH 6 Oxisol soils that were used as reference controls. Plowing the grasslands did not change mean N 2 O emission rates from either pH soil. Liming the acidi®ed Oxisol to pH 6 tended to increase N 2 O emissions to the rates from the undisturbed grassland. Fertilizing the acidi®ed grassland increased N 2 O emissions but much less than when these soils were both limed and fertilized. Short-term ®eld studies employing nitri®cation inhibitors in which we measured nitric oxide (NO) and N 2 O emissions, demonstrated that nitri®cation rates generally control N 2 O emissions; thus these were lower in unlimed soil. It is likely that NO was produced through the chemical decomposition of nitrite, which in turn, was a product of biological nitri®cation. Soil consumption of atmospheric CH 4 in the acidi®ed Oxisol was about onefourth of that in the pH 6 reference soil. Liming did not restore CH 4 consumption in the acid soil to rates comparable to those in the reference Oxisol. We conducted a laboratory induction study to determine if incubation of these limed or unlimed acidi®ed soils with high concentrations of CH 4 could induce methanotrophic activity. Comparable uptake rates to the control soils were not induced by these incubations. These studies illustrate that management of soil can considerably aect the soil±atmosphere exchange of such trace gases as N 2 O and CH 4 which can aect global atmospheric properties. Published by

Methane oxidation in soil cores from a mixed hardwood-coniferous forest varied relatively little as a function of incubation temperatures from -1 to 30 degrees C. The increase in oxidation rate was proportional to T (in kelvins). This relationship was consistent with limitation of methane transport through a soil gas phase to a subsurface zone of consumption by diffusion. The Q(10) for CO(2) production, 3.4, was substantially higher than that for methane oxidation, 1.1, and indicated that the response of soil respiration to temperature was limited by enzymatic processes and not diffusion of either organic substrates or molecular oxygen. When grown under conditions of phase-transfer limitation, cultures of Methylomonas rubra showed a minimal response to temperature changes between 19 and 38 degrees C, as indicated by methane oxidation rates; in the absence of phase-transfer limitations, M. rubra oxidized methane at rates strongly dependent on temperature.

The soil organisms that consume atmospheric CH4 in upland ecosystems have not been identified. Whether these organisms benefit from oxidizing atmospheric CH4 or whether CH4 i& cooxidized fortuitously is uncertain. We investigated the general nutritional physiology of atmospheric CH4 oxidizers occurring in three forest soils by starving them of CH4 for 1-2 months and monitoring their abilities to consume atmospheric CH4 over time. In two Alaskan taiga forest soils, CH4 starvation caused the atmospheric CH4 oxidizers to lose their ability to consume CH4, indicating that they benefitted from oxidizing atmospheric CH4, possibly requiring it for maintenance and growth. In contrast, the organisms in a temperate hardwood forest soil from Massachusetts maintained their ability to consume atmospheric CH4 despite prolonged CH4 deprivation, suggesting that they either cooxidized CH4 fortuitously, or that they used alternative substrates for maintenance and growth. These results may point to diverse nutritional physiologies among atmospheric CH4 oxidizers. «;)

To investigate the consequences of long-term N additions on soil CH 4 dynamics, we measured in situ CH 4 uptake rates, soil profiles and kinetics parameters during the growing season in a temperate deciduous forest in northwestern Pennsylvania (Allegheny College Bousson Environmental Forest). Measurements were made in control and adjacent plots amended with 100 kg N ha −1 year −1 for 8 years. We found that the in situ consumption rates were 0.19±0.02 (mean±SE) for the control and 0.12±0.01 mg CH 4 -C m −2 h −1 for the N treatment, indicating that consumption had been reduced by 35% after 8 years of N amendments. Despite the large difference in rates of consumption, there were no differences in the CH 4 concentration profiles between the control and N-amended plots. Laboratory incubations of CH 4 consumption throughout the soil column (organic horizon and mineral soil depths) showed that rates were greatest in the organic horizon of both control and N-amended soils, although consumption was reduced by 42% in the N-amended plot. However, the rate in the organic horizon was only about 50% the rate measured in organic horizons at other temperate forests. The apparent K m [K m(app) ] value in the organic horizon of the control plot was fourfold less than the K m(app) value in the organic horizon of another temperate forest, but similar to the K m(app) values in adjacent plots amended with N for a decade. Unlike results for other temperate forests, K m(app) values at Bousson generally did not decrease with soil depth. These results indicate that N cycling strongly controls the CH 4 -consuming community, and suggest that alterations of the N cycle due to N deposition or addition may alter rates and the location of CH 4 consumption by soils, even in soils with high N content and cycling rates.

Net transport of atmospheric gases into and out of soil systems is primarily controlled by diffusion along gas partial pressure gradients. Gas fluxes between soil and the atmosphere can therefore be estimated by a generalization of the equation for ordinary gaseous diffusion in porous unsaturated media. Consumption of CH 4 by methylotrophic bacteria in the top several centimeters of soil causes the uptake of atmospheric CH4 by aerated soils. The capacity of the methylotrophs to consume CH 4 commonly exceeds the potential of CH 4 to diffuse from the atmosphere to the consumers. The maximum rate of uptake of atmospheric CI-~ by soil is, therefore, limited by diffusion and can be calculated from soil physical properties and the CH4 concentration gradient. The CH 4 concentration versus depth profile is theoretically described by the equation for gaseous diffusion with homogeneous chemical reaction in porous unsaturated media. This allows for calculation of the in situ rate of CH 4 consumption within specified depth intervals.

El trabajo consistió en, primer lugar, utilizar dos tipos diferentes carbones vegetales y activado para comparar el grado de dureza alcanzada por un acero hipoeutectoide después de aplicado un tratamiento termoquímico superficial que es la cementación. También comparar dos tipos de acero que se recomiendan para cementación y ver cuál de los dos logra una dureza más alta. Se trataron 4 probetas, 2 de acero AISI 1018 y 2 de Acero 7210, introducidas en dos cajas metálicas; una con carbón vegetal pulverizado y la otra con carbón activado. Para medir dureza y comprobar que su centro se mantiene maleable, las probetas fueron rectificadas en escalera a profundidades de 0.03, 0.13 y 0.23 alcanzando durezas en escala Brinell con un promedio 310 HB en el Acero 7210 y 265 HB en el acero AISI 1018. Finalmente se calculó para poder comprobar cuál es el %C que aporta en la atmosfera de cementación cada tipo de carbón sólido. El cálculo brindo que el carbón activado provee de 1,2%C y en el vegetal de 0,6%C en el vegetal.

To evaluate the CH 4 uptake rate in Japanese deciduous and coniferous evergreen forest soils, the CH 4¯u x and CH 4 concentration in soil gas were measured at seven sites in central Japan. The CH 4 uptake potential was calculated from incubation of soil cores. The CH 4¯u xes at all sites were negative (uptake by the soils) at every sampling time. The CH 4 uptake rate was very high (7.6 mg CH 4 m À2 d À1 ) in one deciduous forest soil. Fluxes were highly correlated to the air temperature except a coniferous forest site. The most active layer of CH 4 uptake in each plot diered with site: subsurface (10±15 cm) at two coniferous forest sites and topsoil (0±5 cm) at the other ®ve sites. The potential of the subsurface layer to oxidize CH 4 made a substantial contribution to soil CH 4 uptake mechanisms, especially when the topsoil had a low ability to oxidize CH 4 . Methane uptake rates were nine times higher than those of previous studies. The soil CH 4 uptake rate on a global scale may be underestimated. 7

In order to better predict soil sinks of methane, we need to examine soil methane¯ux patterns and responses to altered soil moisture regimes. Estimates of the global atmospheric CH 4 budget must also account for¯uxes in the vast boreal region. We measured methane¯uxes into the soil surface, methane concentrations, water content, and temperature in the soil pro®le in two interior Alaskan forests, over two growing seasons. At each site, a 0.10 ha rain-shelter limited summer precipitation from entering the soil. Limiting summer precipitation at the upland site generally increased that site's soil uptake of methane. Average rates of soil methane uptake among upland plots ranged from 0.10 to 0.95 mg m À2 day À1 . At the¯oodplain site, limiting precipitation decreased the soil methane uptake of that site, and the rates here ranged from À0.02 to 0.57 mg m À2 day À1 . Using soil pro®le methane concentrations, we calculated CH 4¯u xes using Fick's Law. Our inability to precisely measure the concentration gradient across the soil surface resulted in calculated¯ux estimates that more likely represent¯uxes within the soil pro®le. Methane sources and sinks in the soil pro®le also confounded the comparison of measured and calculated¯uxes. 7

Carbon dioxide and methane are important greenhouse gases whose exchange rates between soils and the atmosphere are controlled strongly by soil temperature and moisture. We made a laboratory investigation to quantify the relative importance of soil moisture and temperature on fluxes of CO₂ and CH₄ between forest soils and the atmosphere. Forest Poor and mineral soil material were collected from a mixed hardwood forest at the Harvard Forest Long-Term Ecological Research Site (MA) and were incubated in the laboratory under a range of moisture (air-dry  To nearly saturated) and temperature conditions (5 - 25 °C). Carbon dioxide emissions increased exponentially with increasing temperature in forest Poor material, with emissions reduced at the lowest and highest soil moisture contents. The forest Poor Q₁₀ of 2.03 (from 15 - 25 °C) suggests that CO₂ emissions were controlled primarily by soil biological activity. Forest Poor CO₂ emissions were predicted with a multiple polynomial regression model (r²=0.88) of temperature and moisture, but the fit predicting mineral soil respiration was weaker (r²=0.59). Methane uptake was controlled strongly by soil moisture, with reduced Puxes under conditions of very low or very high soil moisture contents. A multiple polynomial model accurately described CH₄ uptake by mineral soil material (r²=0.81), but only weakly (r²=0.45) predicted uptake by forest Poor material. The mineral soil Q₁₀ of 1.11 for CH₄ uptake indicates that methane uptake is controlled primarily by physical processes. Our work suggests that inclusion of both moisture and temperature can improve predictions of soil CO₂ and CH₄ exchanges between soils and the atmosphere. Additionally, global change models need to consider interactions of Temperature and moisture in evaluating efects of global climate change on trace gas fluxes.

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH4 consumption rates during the two years (mean 0.43 and 0.49 mg m-2 h-1), and at different sites (mean 0.36 to 0.57 mg m-2 h-1). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH4 uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH4, and C and N status of soils regulates the strength of the sink in the long term.

Because a large fraction of the world's carbon exists in the soil of boreal forests, understanding how soil temperature and moisture affect soil respiration is vital for predicting soil response to climate change. We measured soil respiration and CO2 concentrations within soils of floodplain and upland forests in interior Alaska from 1996 to 1997. At each site, a 0.10-ha-area shelter was constructed that prevents summer precipitation from infiltrating into the soil.

El trabajo consistió en, primer lugar, utilizar dos tipos diferentes carbones vegetales nacionales y comparar el grado de dureza alcanzada por un acero hipoeutectoide después de aplicado un tratamiento termoquímico superficial. En segundo lugar, cementar brocas comerciales utilizadas para perforar materiales blandos. Se trataron 10 probetas de acero AISI 1018, introducidas en dos (2) cajas metálicas; una con carbón de mangle (rizophora mangle) y la otra con carbón de nance (byrsonima crassifolia) pulverizado. En la cementación con mangle se alcanzaron durezas promedio de 44.38 RW C , mientras que con el carbón de nance presentaron durezas del orden de 45.27 RW C . y la profundidad de penetración de la templabilidad fue del orden de 0.05 mm. Finalmente, brocas ferrosas fueron cementadas con mezclas a base de carbón vegetal de mangle y de carbonato de sodio al 10% en peso, y sometidas a ensayos controlados de perforación. Las brocas cementadas fueron capaces de perforar más de 10 orificios en lámina de acero de 4.76 mm de espesor, contrario a las brocas no tratadas, las cuales se mostraron ineficientes al realizar la mínima perforación posible.