Macro Porosity Research Articles

Mineralogical and compositional changes in bones exposed on soil surfaces in Amboseli National Park, Kenya: diagenetic mechanisms and the role of sediment pore fluids

Bones exposed on tropical savannah grasslands of Amboseli National Park, Kenya undergo extensive post-mortem alteration within 40 years. A combined analytical approach involving TEM microscopy, trace metal analysis, FTIR spectroscopy, and petrographic analysis has revealed a complex, dynamic diagenetic environment operating within exposed bones, driven by evaporative transport of soil water from the bone/soil interface to the upper exposed surface of the bone. This process results in extensive bone/soil-water interaction, and is responsible for increases in the concentrations of trace elements such as Ba and La of 100 – >1000% within 15 years. The maximum and mean size of bone crystallites increases with continued exposure. This change in mean crystallite length is correlated positively with increases in bone crystallinity, which in turn is associated with degradation of the bone protein. Microbial decomposition is rarely observed in the Amboseli bones, but where present resulted in severe dissolution–reprecipitation of bone mineral. Many bones showed extensive permineralization of the larger vascular spaces with calcite and barite and, to a lesser extent, crandallite. Permineralization of unburied bones may account for 95% reduction in macro (micron–millimeter scale) porosity in the bone within 2 years of death. We produce a model for pre-burial diagenesis of bone in arid tropical environments that highlights extensive alteration of bone chemistry within 1–40 years post-mortem.

O tráfego de máquinas agrícolas e as propriedades físicas, hídricas e mecânicas de um Latossolo dos Cerrados

No Brasil, o tráfego contínuo e inadequado de rodados de máquinas e a ação da soleira dos implementos sobre áreas agrícolas na região dos Cerrados têm provocado alterações dos atributos físicos e mecânicos dos solos. Com este entendimento, este estudo teve por objetivo avaliar a influência do rodado traseiro e da soleira de implementos agrícolas, usualmente utilizados na região dos Cerrados, sobre a compressibilidade de um Latossolo Vermelho distrófico típico. Os ensaios foram realizados em parcelas preparadas com arado de discos, arado de aivecas, grade aradora e semeadora/adubadora, que, desde novembro de 1994 até à data da amostragem, novembro de 1999, estiveram sob o sistema plantio direto. As alterações na compressibilidade foram avaliadas pela quantificação das pressões de preconsolidação, assim como por algumas propriedades físicas e hídricas (densidade do solo, porosidade e condutividade hidráulica do solo saturado) no momento do preparo e depois da colheita. No momento do preparo, logo depois da passada do rodado e antes que o implemento mobilizasse o solo, o solo foi avaliado em superfície (SP - 0,00 a 0,05 m) e na profundidade média de trabalho (PMT - 0,24 a 0,27 m). A influência da soleira dos implementos foi avaliada logo depois do corte, na profundidade de trabalho abaixo da soleira de cada implemento (PT-SI). Depois da colheita, as amostragens foram repetidas, o que permitiu verificar a influência dos tráfegos subseqüentes. A intensidade de tráfego do rodado e a ação da soleira dos implementos alteraram a compressibilidade, a densidade do solo, a porosidade e condutividade hidráulica do solo saturado do Latossolo Vermelho distrófico nas profundidades: superficial (SP), profundidade média de trabalho (PMT) e profundidade de corte dos implementos (PT-SI). De maneira geral, a passada do rodado traseiro aumentou os valores de pressão de preconsolidação (sigmap) do solo na superfície (SP), enquanto o tráfego subseqüente, necessário ao cultivo, elevou esses valores em subsuperfície, tanto na PMP como em PT-SI. A passada do rodado elevou e reduziu a densidade do solo (Ds) e a macroporosidade, respectivamente, tendo sido o arado de aivecas o implemento que mais modificou essas propriedades. As soleiras dos órgãos ativos do arado de discos e da grade aradora foram as que mais elevaram a pressão de preconsolidação (sigmap), consolidando, portanto, a estrutura do solo na profundidade PT-SI. Com exceção da semeadora/adubadora, a soleira dos órgãos ativos dos demais implementos avaliados reduziram significativamente a condutividade hidráulica do solo saturado (Ks) na profundidade PT-SI, tendo o arado de aivecas se mostrado o implemento mais impactante, seguido da grade aradora e arado de discos.

Porous Hydroxyapatite and Glass Reinforced Hydroxyapatite for Controlled Release of Sodium Ampicillin

Porous Hydroxyapatite and Glass Reinforced Hydroxyapatite for Controlled Release of Sodium Ampicillin

The Ideal Soil: III. Fitness of Edaphic Variables to Achieve Sustenance in Agroecosystems

ABSTRACT In the agroecosystems, the soil plays a leading role in establishing systems of sustainable agriculture. Therefore, edaphic attributes related to functions that soil renders to crops have been proposed as potentially useful to infer whether those functions are suitable to diagnose or the adopted management system led to sustainability. Those attributes are: Bulk density (Bd); Macroporosity (MPo); Optimal Hydric Interval (OHI); Aggregates stability (As); Relative Aggregates stability (rAs); Rooting depth (Rd); pH; Available Phosphorus (P); Active Nitrogen (acN); and Seal Infiltration (Iseal). The potential fitness of some of those attributes, linked with functions that soils must render to crops, is studied here. All the studied lots are located in Argiudolls, in the Province of Santa Fe, in Reconquista (NE), Hipatia (center-east) and San Jorge (center-west). The variation in the value of the attributes in different soils, which are exposed to contrasting management systems, is analysed. These contrasting management systems are: (a) Never cultivated (Nat); (b) With more than 20 years of conventional till (C-till); (c) In agriculture/artificial prairie rotation (R); and (d) Cultivated for several years in direct drill (DD). Later those values are compared with their critical threshold (CT) values based on regional experience and on specific bibliography. The most sensible variables have been OHI, Iseal, P, acN and pH. C-till causes degradation of all the measured attributes, taking the soils far from their natural states and therefore from the Ideal Soil, while on the other hand, DD causes less soil degradation: After 6 years of DD practice only Mpo, Bd and rAs, in some cases, reached the Ideal Soil values. The use of the Ideal Soil concept to assess and detect the CTs of the main attributes may guide scientific research as much as the agricultural practices to improve unfavorable soil properties. However, when scanning the fit attributes and knowing their CT values, only a qualitative or half-quantitative agronomic judgment can be made. In order to do that, the diverse attributes must be integrated in a mathematical, dynamic model, which simulates the multiple interactions that occur among soils, atmosphere and crops in the North Pampean Region. This evolves to complement the analytic-reductionist approach that has guided this research, with the holistic and systemic one.

Effect of process parameters on the characteristics of porous calcium phosphate ceramics for bone tissue scaffolds.

Porous hydroxyapatite (HA) has already been widely used as a bone substitute due to its similarity with the mineral part of the bone. In this work, cylindrical tablets with micro and macro porosity were produced from stoichiometric and deficient hydroxyapatites by using naphthalene as porosifier agent. The influence of the processing parameters such as Ca/P ratio of start material, calcination temperature, and naphthalene content on the characteristics of porous calcium phosphate tablets was evaluated. Three mineral phases-HA, alpha-TCP (alpha tri-calcium phosphate), and beta-TCP (beta tricalcium phos-phate)-with variable contents were identified by x-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR). Image analysis and density measurements were used to characterize sample porosity. As expected, the total porosity of the calcinated material is not dependent on the stoichiometry of the precursor hydroxyapatite. For calcium-deficient hydroxyapatite, the increase in naphthalene content contributes to stabilize alpha-TCP phase, altering the relative phases content.

Caracterização estatística de variáveis físicas do solo

The objective of this study was to characterize statistically the properties bulk density of soil, density of particles, total porosity, micro porosity, macro porosity and saturated hydraulic conductivity based on the verification of the adjustment of a series of data to the statistical distribution, aiming to indicate the best representation form and values to be adopted for these variables, so that they can be used in operations of agricultural practices. The studied area is part of the Experimental Station of IAC, in Piracicaba , Estado de São Paulo; and the soil is an oxisol, texture sandy clay. We can be conclude that outliers values were not detected and that the variables in study can be represented by the normal probability density function (Distribution of Gauss), using their parameters for their representations, except for the saturated hydraulic conductivity variable, which cannot be described by the normal probability density function and, therefore, considering this function usually distributed can lead to erroneous conclusions.

Macro porosity prediction of SG iron castings considering microstructure formation

Some macro- and micro- phenomena and their interaction during solidification of spheroidal graphite (SG) iron castings, including the nucleation and growth of microstructure, gray-to-white transition, latent heat and volume change from various phase formation, and so on, were considered in the porosity prediction of the castings. With modeling microstructure formation, the volume expansion and contraction resulted from temperature drop and phase formation of graphite, austenite, and carbide were calculated. Based on the judgment of the hot spots and feeding relationship, a method to predict macro porosity of the castings has been developed and has been applied to a real hub and brake housing SG iron castings. The results were verified with the production, and compared with commercial softwares. The process of the hub casting was improved as well. It seems that the proposed method is applicable for predicting macro porosity of real SG iron castings.

Polylactide membranes in the treatment of segmental diaphyseal defects: Animal model experiments in the rabbit radius, sheep tibia, Yucatan minipig radius, and goat tibia

Resorbable polymeric membranes have many potential applications in the treatment of bone loss. A resorbable membrane can be fabricated to have: (1) a custom in vivo life span, (2) specific mechanical attributes, (3) an optimal micro or macro porosity for nutritional diffusion or vascular ingrowth, and (4) carrier properties for the timed delivery of drugs, organic compounds, or inorganic substances, or cells. Because the polylactide class of polymers has a proven record of human biocompatibility as well as a wide range of synthetic characteristics, polylactide membranes have been studied for their utility in regenerating diaphyseal bone defects. Using a variety of animal models, the basic mechanism of bone regeneration has been elucidated. A resorbable membrane functions by: (1) exclusion of nonosseous tissues, (2) maintenance of an intramedullary canal, and (3) the provision of an extralumenal scaffold for periosteum regeneration and revascularization. Microporous membranes have been studied in small defects which do not require stabilization-the rabbit and minipig radius models where the ulna is left intact (1-4 cm diaphyseal defects). Larger defects (4-7 cm middiaphysis) have been studied in the sheep and goat tibia where intramedullary (IM) nailing or double plate stabilization was used. So far the parameters of polylactide composition, biocompatibility, porosity, adjunctive internal fixation, and the suitability of membranes as chemical delivery devices have been investigated in these animal models. Large defects successfully treated with polylactide membranes suggest that the optimum construct will be a perforated, thin, microporous membrane used to span an appropiately stabilized defect.

An Estimate of Eros's Porosity and Implications for Internal Structure

Earth-based spectral measurements and NEAR Shoemaker magnetometer, X-ray, and near-infrared spectrometer data are all consistent with Eros having a bulk composition and mineralogy similar to ordinary chondrite meteorites (OC). By comparing the bulk density of 433 Eros (2.67±0.03 g/cm3) with that of OCs (3.40 g/cm3), we estimate the total porosity of the asteroid to be 21–33%. Macro (or structural) porosity, best estimated to be ∼20%, is constrained to be between 6 and 33%. We conclude that Eros is a heavily fractured body, but we find no evidence that it was ever catastrophically disrupted and reaccumulated into a rubble pile.

Resistance to cropping pressure of two New Zealand soils with contrasting mineralogy

Changes in soil properties in response to cropping pressure were measured in 2 mineralogically contrasting New Zealand topsoils. Waiareka clay (Vertic Haplustoll) with >65% smectite clay was compared with Wakanui silt loam (Aquic Haplustept), which contains about 20% mixed or illite clays. Soil properties (0–10 cm) were assessed by changes in organic carbon (C) and nitrogen (N), pH, cation exchange capacity, Olsen P, microbial C, soil respiration, microbial functional evenness, mineralisable N, bulk density, unsaturated hydraulic conductivity, readily available and total available water, macro porosity and total porosity, particle density, and particle size distribution. Additional samples of the Waiareka clay soil were taken at 10–20 cm depth. Cropping pressure was estimated using a scale based on the number of years in crop v. those in pasture. The organic and biological status of the Waiareka pasture soil (0–10 cm) was greater than that of the Wakanui pasture, with contents of 5.1% organic C, 0.43% total N, 1429 microbial C (µg/cm3), and 123 mineralisable N (µg/cm3), compared with values of 4.0%, 0.31%, 795 µg/cm3, and 89 µg/cm3, respectively. Total and macroporosity, and total and readily available water, were also greater on the Waiareka pasture soil compared with the Wakanui pasture soil. Under cropping pressure, the Waiareka soil had marked declines in organic matter C and N, microbial C and soil respiration, microbial functional evenness, macroporosity, and available water. In contrast, the Wakanui silt loam showed little response to cropping pressure; mineralisable N declined slightly and particle density increased under cropping. We concluded that the initial properties of a soil were not good predictors of subsequent resistance to cropping pressure; and that soils with initially high status have the potential for proportionally greater decline.

Macroporous biphasic calcium phosphate ceramics: influence of macropore diameter and macroporosity percentage on bone ingrowth

Synopsis A total of 60 cylindrical 6×6 mm samples of a macroporous biphasic calcium phosphate (MBCP) ceramic were impla nted into a distal femoral site in 30 rabbits. These samples represented six kinds of implants with two different macropore diamete rs and three different macroporosity percentages. Analysis of backscattered electron images of implant surfaces analysed by a factorial design method showed that implants with 565 μm pore size provided more abundant newly formed bone both in peripheral and deep pores than those with 300 μm pore size. No significant differences were found between implants with 40 and 50% macroporosi ty, suggesting that the influence of macropore size on bone ingrowth was greater than that of macroporosity percentage. MBCP implan ts with 565 μm pore diameter and 40% macroporosity represented the optimal association for homogeneous and abundant bone ingrowth.

Efeito de sistemas de manejo nas propriedades físicas de um latossolo vermelho-escuro

Este trabalho foi realizado em 1995 na área experimental da Universidade de Cruz Alta, UNICRUZ, Cruz Alta - RS, com o objetivo de avaliar a influência de diferentes sistemas de manejo do solo nas propriedades físicas de um latossolo vermelho-escuro distrófico, bem como no rendimento de grãos da cultura da soja. O delineamento experimental utilizado foi o de blocos ao acaso com quatro repetições. Os sistemas de manejo do solo foram: (1) plantio direto contínuo -PDC; (2) plantio direto e escarificação de acordo com a necessidade (sistema dinâmico) - PDSD; (3) plantio direto no verão com escarificação no outono/inverno - PD V; (4) plantio convencional: escarificador mais grade niveladora - PCEG; e, (S) plantio convencional: arado de discos mais grade niveladora - PCAG. Determinou-se o espaço poroso (porosidade total, macro e microporosidade) e a densidade do solo. As amostras foram coletadas em dois pontos por parcela nas profundidades de 0-7, 7-14 e 14-21 cm. A densidade do solo foi maior nas profundidades de 0-7 cm e 7- l4cm para o tratamento PDC que diferiu dos demais tratamentos à exceção ao tratamento PDSD. A porosidade lote e a microporosidade foram menores nos tratamentos PDC e PDSD, nas profundidades de 0-7, 7-14 e 14-21 cm, quando comparados aos tratamentos P D V, PCEG e PCAG. Para a microporosidade, apenas na profundidade de 7-14cm encontrou-se diferença significativa entre os valores, onde o tratamento PDC diferiu com valor superior apenas do tratamento PCAG. O rendimento de grãos de soja não diferiu entre os sistemas de manejo do solo utilizados.

A Thermoporometry Study of Fumed Silica/aerogel Composites

The porous texture of fumed silica/aerogel composite materials is studied by thermoporometry. The effect of fumed silica (Aerosil) powder in aerogels, added during the sol-gel processing is investigated. The textural change due to the autoclave drying process as a function of the fumed silica/aerogel ratio of the systems is investigated. The meso- and macro porosity of the fumed silica/aerogel composites is mainly influenced by the ratio fumed silica/aerogel and only slightly by the autoclave drying process. Addition of fumed silica powder results in an increase of the mean pore radius of the system and in a decrease of the meso- and macro-pore volume. By contrast, the micro-porosity is hardly affected by the addition of the fumed silica powder; it is only influenced by the autoclave drying process.

Krasnozems - organic-matter

Virgin krasnozems contain about 6% C from 0-15 cm and, while the C content is less at depth, the total C reserves may exceed 200 t ha(-1) to about Im depth. Highest organic matter contents occur where the annual rainfall is 1500 � 200 mm. At higher rainfalls, the C contents are less. There is a negative correlation between organic C and N content and mean annual temperature. Krasnozems contain more C than other soils in the same climate and are comparatively more fertile. Correlations of C contents with clay contents are confounded by the contents of free iron oxides. While data are fragmented, it is evident that the clearing of rainforests and replacement by pastures or other agricultural and horticultural pursuits have led to losses of up to 50% of the organic C over several decades. A simple model illustrates that this is caused by lower inputs of C to the soil in most situations except perhaps long term productive pastures where inputs may be greater than under rainforests. Studies using natural isotopes of C have shown the persistence of some C in krasnozems for hundreds of years. Some of this is particulate organic matter occluded in aggregates but most of it appears to be associated with clays, particularly at depth. The chemistry of organic matter in krasnozems appears similar to that of other soils, although solid state 13C nuclear magnetic resonance has shown more aliphatic materials in krasnozems than other soils, but the reason for this is not clear. There is little information on biota in krasnozems. The deep well structured soils are a good habitat for organisms and their high fertility guarantees a good supply of substrate for fauna and flora. It is important to maintain the organic matter contents of krasnozems to maintain cation exchange capacity, mineralization of N and other elements, to decrease phosphate sorption and to stabilize larger aggregates and thus macro porosity.

EM of a macro defect-free cement

Engineering materials application of silicate or aluminate cements are limited because of their low strength and toughness. These poor properties can be easily attributed to the inherent macro and micro porosity of cement pastes. However in the last decade it has been found that by the addition of a water soluble polymer, high shear mixing and the by application of modest pressure during processing, cement with mechanical properties comparable to most ceramics can be obtained. The water soluble polymer, apart from filling the pores, also act as a rheological aid, reducing the interparticle friction coefficient and providing for optimum particle packing in the microstructure. Although a brief account of the microstructure of this new composite (called Macro Defect Free Cement) has been reported, a close and detailed examination of the cement particle/polymer interface remains to be performed. The aim of this communication is to report the microstructure of a macro defect free cement with particular emphasis on the cement particle/polymer interfaces. Cement nomenclature is used in this report: C= CaO, A= Al2O3, H=H2O

Pilot study of an aggregate abrasion test for breakwater armourstone

The long-term performance of the materials out of which breakwaters and coastal protection works are constructed depends not only on physico-chemical degradation processes but also on the mechanical abrasion resistance of the rock or concrete used. The abrasion of breakwater armourstone affects the armour layer stability directly by causing weight loss from the rock blocks. Another important though unquantified source of stability reduction in the armour layer is the progressive rounding of armour by abrasion leading to poor interlocking between individual blocks and their neighbours (see the discussion of this phenomenon by Dibb et al. 1983). Gupta (1985) and others have demonstrated that there is a relative decrease in aggregate (macro)porosity for rounded compared with angular fragments. Such a decrease in an armour layer porosity due to the rounding of blocks may have a deleterious effect on energy absorbing properties of the layer. The assessment of abrasion resistance is therefore of great interest to the engineer concerned with in-service deterioration of armour layer performance. New quantitative methods for measuring the effects of abrasion on the entire profile of the breakwater armour layer were reported by Latham & Poole (1986). Several standard engineering tests and analytical procedures have been recommended for the assessment of suitability of a particular rock for breakwater core and armour material (Fookes & Poole 1981; Allsop et al. 1985). The test values recommended for acceptance by Allsop et al. are drawn from a list of tests which does not include an abrasion resistance test, although several abrasion

Reclamation of an Ultisol Damaged by Mechanical Land Clearing

AbstractMechanical land clearing in 1972 of a Yurimaguas soil (fine‐loamy siliceous, isohyperthermic Typic Paleudult) located in the Amazon Basin of Peru resulted in compacted soil that was abandoned for continuous crop production in 1974. The purposes of this study were to reclaim this abandoned land for continuous cultivation and to evaluate temporal changes in soil physical properties with time after reclamation treatments began. In February 1980, guinea grass [Panicum maximum L.], which covered the compacted soil, was cut by hand, dried, and burned. The following eight reclamation treatments were imposed: (1) control (no till), planted with a planting stick; (2) rototill (12 kW) and stick planted; (3) rototill (48 kW); (4) chisel plow 25‐cm deep, rototill (48 kW); (5) controlled traffic (i.e., assignment of pathways for foot traffic); (6) bedding with hoe and planted with stick; (7) simulated subsoiling to 25 cm with a tile spade; and (8) mulching (mulch applied when seedlings were 10‐ to 25‐cm high). The following soil physical properties were quantitied several times during the study: infiltration rate, cone index (CI), bulk density (ρb), and the soil‐water characteristic. The crop rotation during the 2‐yr‐long period was rice (Oryza sativa L.)‐soybean [Glycine max (L.) Merr.]‐corn (Zea mays L.)‐soybean‐corn‐rice. Compared to the control treatment, all others decreased ρb and CI and increased infiltration rate, macro porosity, and total porosity in the 0‐ to 15‐cm depth. Only chisel plowing and simulated subsoiling alleviated the detrimental effects of the compacted soil below 15 cm. Infiltration rate at the conclusion of the experiment for the control treatment was 9 mm h−1 compared to 148 mm h−1 for the chisel plow treatment. Yield responses were greater for chiseling and simulated subsoiling. For example, the average relative grain yield for each of the three crops was 100% for chiseling; for no‐till, relative yields were 69, 23, and 20% for rice, soybean, and corn, respectively. We conclude that compacted soils similar to the Yurimaguas series can be reclaimed for continuous cropping by using deep tillage practices such as chisel plowing and subsoiling.

Porous nature of solvent-extracted coals

An investigation has been made into the changes which take place in porosity when coals are partially dissolved in specific solvents. Pore structures were determined by: gas adsorption (N 2 at 77 K and CO 2 at 195 K), densities in mercury and helium, and mercury porosimetry. Six British coals (79.7–88.5% C daf) were extracted with boiling pyridine and one coal (87.0% C daf) with ethylene diamine and a potassium hydroxide/Cellosolve mixture. The development of porosity with increasing pyridine extraction leads to increased microporosity. Residues produced from coals of more than 86.5% C daf have enhanced porosity in all pore regions but those produced from lower-rank coals show diminished macro and transitional porosity. It is suggested that residues are suitable precursors for molecular sieves and activated carbons.

Reactivity of heat-treated coals in air at 500 °C

Twenty one US coals, of widely ranging rank, have been carbonized under controlled conditions to 1000 °C, and the reactivity in air at 500 °C of the resulting chars or cokes has been measured by a gravimetric method. The reactivities lie within a well-defined band when plotted against rank of the parent coal. The lower-rank coal chars are more reactive than those prepared from high-rank coals. In extreme cases, the reactivity found for a Montana lignite char is some 100 times as great as that obtained for a char produced from a Pennsylvania low-volatile coal. Variation of reactivity with heat-treatment temperature (600 to 1000 °C) has been studied for three coals. As heat-treatment temperature increases, there is a decrease in reactivity. Some results are reported on the effects which mineral matter and pore structure have on the reactivity parameter. Chars containing high concentrations of magnesium and calcium impurities are most reactive. The amount of macro and transitional porosity in a char has a marked influence on reactivity.