Microstructure-based numerical modeling of the mechanical behavior of Mg alloys

Dentro de los materiales estructurales, el magnesio y sus aleaciones están siendo el foco de una de profunda investigación. Esta investigación está dirigida a comprender la relación existente entre la microestructura de las aleaciones de Mg y su comportamiento mecánico. El objetivo es optimizar las aleaciones actuales de magnesio a partir de su microestructura y diseñar nuevas aleaciones. Sin embargo, el efecto de los factores microestructurales (como la forma, el tamaño, la orientación de los precipitados y la morfología de los granos) en el comportamiento mecánico de estas aleaciones está todavía por descubrir. Para conocer mejor de la relación entre la microestructura y el comportamiento mecánico, es necesaria la combinación de técnicas avanzadas de caracterización experimental como de simulación numérica, a diferentes longitudes de escala. En lo que respecta a las técnicas de simulación numérica, la homogeneización policristalina es una herramienta muy útil para predecir la respuesta macroscópica a partir de la microestructura de un policristal (caracterizada por el tamaño, la forma y la distribución de orientaciones de los granos) y el comportamiento del monocristal. La descripción de la microestructura se lleva a cabo mediante modernas técnicas de caracterización (difracción de rayos X, difracción de electrones retrodispersados, así como con microscopia óptica y electrónica). Sin embargo, el comportamiento del cristal sigue siendo difícil de medir, especialmente en aleaciones de Mg, donde es muy complicado conocer el valor de los parámetros que controlan el comportamiento mecánico de los diferentes modos de deslizamiento y maclado. En la presente tesis se ha desarrollado una estrategia de homogeneización computacional para predecir el comportamiento de aleaciones de magnesio. El comportamiento de los policristales ha sido obtenido mediante la simulación por elementos finitos de un volumen representativo (RVE) de la microestructura, considerando la distribución real de formas y orientaciones de los granos. El comportamiento del cristal se ha simulado mediante un modelo de plasticidad cristalina que tiene en cuenta los diferentes mecanismos físicos de deformación, como el deslizamiento y el maclado. Finalmente, la obtención de los parámetros que controlan el comportamiento del cristal (tensiones críticas resueltas (CRSS) así como las tasas de endurecimiento para todos los modos de maclado y deslizamiento) se ha resuelto mediante la implementación de una metodología de optimización inversa, una de las principales aportaciones originales de este trabajo. La metodología inversa pretende, por medio del algoritmo de optimización de Levenberg-Marquardt, obtener el conjunto de parámetros que definen el comportamiento del monocristal y que mejor ajustan a un conjunto de ensayos macroscópicos independientes. Además de la implementación de la técnica, se han estudiado tanto la objetividad del metodología como la unicidad de la solución en función de la información experimental. La estrategia de optimización inversa se usó inicialmente para obtener el comportamiento cristalino de la aleación AZ31 de Mg, obtenida por laminado. Esta aleación tiene una marcada textura basal y una gran anisotropía plástica. El comportamiento de cada grano incluyó cuatro mecanismos de deformación diferentes: deslizamiento en los planos basal, prismático, piramidal hc+ai, junto con el maclado en tracción. La validez de los parámetros resultantes se validó mediante la capacidad del modelo policristalino para predecir ensayos macroscópicos independientes en diferentes direcciones. En segundo lugar se estudió mediante la misma estrategia, la influencia del contenido de Neodimio (Nd) en las propiedades de una aleación de Mg-Mn-Nd, obtenida por extrusión. Se encontró que la adición de Nd produce una progresiva isotropización del comportamiento macroscópico. El modelo mostró que este incremento de la isotropía macroscópica era debido tanto a la aleatoriedad de la textura inicial como al incremento de la isotropía del comportamiento del cristal, con valores similares de las CRSSs de los diferentes modos de deformación. Finalmente, el modelo se empleó para analizar el efecto de la temperatura en el comportamiento del cristal de la aleación de Mg-Mn-Nd. La introducción en el modelo de los efectos non-Schmid sobre el modo de deslizamiento piramidal hc+ai permitió capturar el comportamiento mecánico a temperaturas superiores a 150_C. Esta es la primera vez, de acuerdo con el conocimiento del autor, que los efectos non-Schmid han sido observados en una aleación de Magnesio. The study of Magnesium and its alloys is a hot research topic in structural materials. In particular, special attention is being paid in understanding the relationship between microstructure and mechanical behavior in order to optimize the current alloy microstructures and guide the design of new alloys. However, the particular effect of several microstructural factors (precipitate shape, size and orientation, grain morphology distribution, etc.) in the mechanical performance of a Mg alloy is still under study. The combination of advanced characterization techniques and modeling at several length scales is necessary to improve the understanding of the relation microstructure and mechanical behavior. Respect to the simulation techniques, polycrystalline homogenization is a very useful tool to predict the macroscopic response from polycrystalline microstructure (grain size, shape and orientation distributions) and crystal behavior. The microstructure description is fully covered with modern characterization techniques (X-ray diffraction, EBSD, optical and electronic microscopy). However, the mechanical behaviour of single crystals is not well-known, especially in Mg alloys where the correct parameterization of the mechanical behavior of the different slip/twin modes is a very difficult task. A computational homogenization framework for predicting the behavior of Magnesium alloys has been developed in this thesis. The polycrystalline behavior was obtained by means of the finite element simulation of a representative volume element (RVE) of the microstructure including the actual grain shape and orientation distributions. The crystal behavior for the grains was accounted for a crystal plasticity model which took into account the physical deformation mechanisms, e.g. slip and twinning. Finally, the problem of the parametrization of the crystal behavior (critical resolved shear stresses (CRSS) and strain hardening rates of all the slip and twinning modes) was obtained by the development of an inverse optimization methodology, one of the main original contributions of this thesis. The inverse methodology aims at finding, by means of the Levenberg-Marquardt optimization algorithm, the set of parameters defining crystal behavior that best fit a set of independent macroscopic tests. The objectivity of the method and the uniqueness of solution as function of the input information has been numerically studied. The inverse optimization strategy was first used to obtain the crystal behavior of a rolled polycrystalline AZ31 Mg alloy that showed a marked basal texture and a strong plastic anisotropy. Four different deformation mechanisms: basal, prismatic and pyramidal hc+ai slip, together with tensile twinning were included to characterize the single crystal behavior. The validity of the resulting parameters was proved by the ability of the polycrystalline model to predict independent macroscopic tests on different directions. Secondly, the influence of Neodymium (Nd) content on an extruded polycrystalline Mg-Mn-Nd alloy was studied using the same homogenization and optimization framework. The effect of Nd addition was a progressive isotropization of the macroscopic behavior. The model showed that this increase in the macroscopic isotropy was due to a randomization of the initial texture and also to an increase of the crystal behavior isotropy (similar values of the CRSSs of the different modes). Finally, the model was used to analyze the effect of temperature on the crystal behaviour of a Mg-Mn-Nd alloy. The introduction in the model of non-Schmid effects on the pyramidal hc+ai slip allowed to capture the inverse strength differential that appeared, between the tension and compression, above 150_C. This is the first time, to the author's knowledge, that non-Schmid effects have been reported for Mg alloys.

La casa de Norman Foster en Hampstead: tecnología y domesticidad

Entre 1978 y 1979, Norman y Wendy Foster proyectan su propia vivienda en el barrio londinense de Hampstead. El proyecto más personal de los Foster permite —como en tantos otros casos— rastrear los referentes, obsesiones, sueños y frustraciones de sus autores. Este proyecto representa el primer y único intento de aplicación en el campo de la arquitectura doméstica de un modelo, denominado por Reyner Banham “la nave bien servida”, que utiliza la integración de sistemas como principal estrategia proyectual. Los 18 meses de intenso trabajo reflejan, a través de las múltiples opciones desarrolladas, la evolución de la obra de la pareja de arquitectos, que avanza desde el funcionalismo fabril de la “nave bien servida”, hacia el expresionismo tecnológico del denominado High-Tech. En los motivos del fracaso del proyecto, que no llegaría a construirse, subyacen los debates y conflictos —entre arquitectura e ingeniería, prefabricación y artesanía, expresionismo y funcionalismo— en los que el estudio se encuentra inmerso a finales de los años 70, y que precipitarán una nueva forma de entender la relación entre arquitectura y tecnología. | Between 1978 and 1979 Norman and Wendy Foster design their own home in the London neighbourhood of Hampstead. The most personal project of the Fosters allows us —as in many other cases— to trace the references, obsessions, dreams and frustrations of its creators. This project represents a unique attempt to apply the “well-serviced shed” concept —as described by Reyner Banham— to the domestic realm. A concept based in the use of systems integration as the main project strategy. The 18 months of intense work show, through the various options developed, the evolution of the production of the couple of architects, from the industrial functionalism of the “well-serviced shed”, towards the technological expressionism of the so-called High-Tech movement. In the reasons behind the failure of this unbuilt project, one can read the debates and conflicts —between architecture and engineering, prefabrication and craftsmanship, expressionism and functionalism— in which the practice is immerse by the end of the 1970s. A series of events that will precipitate a new way of understanding the relationship between architecture and technology.

A INFLUÊNCIA DO STRESS NA EXPRESSÃO CLÍNICA DA ASMA INFANTIL

A asma é a doença crônica mais freqüente na infância e o stress é considerado um dos agentes desencadeantes e agravantes do broncoespasmo nesses pacientes. O objetivo deste trabalho foi investigar a influência do stress na expressão clínica da asma e sua associação com as crises em crianças. Para verificar a presença de stress, utilizou-se a Escala de Stress Infantil (LIPP E LUCARELLI, 1998) e por meio de um questionário aplicado aos pais, observou-se freqüência de sintomas e crises de asma, as alterações do sono, o absenteísmo escolar, as limitações à prática de atividade física, a freqüência de uso de broncodilatador, as condutas dos pais durante as crises de asma, os fatores associados ao desencadeamento das crises, o poder aquisitivo e o grau de instrução do chefe da família. Observou-se que as crianças com asma estavam mais estressadas que as crianças do grupo controle, principalmente aquelas com maior gravidade da doença. Os resultados indicam que a presença de stress pode intensificar a freqüência de sintomas da asma, a limitação à atividade física, o absenteísmo escolar e as interrupções do sono. O maior tempo de diagnóstico de asma implicou em menor ocorrência de stress, sugerindo a existência de um fator de adaptação à doença. Conclui-se que o stress é um fator importante no desencadeamento e agravamento das crises de asma nas crianças e observa-se a necessidade de maiores pesquisas na aérea para aprofundar os conhecimentos sobre esse assunto.

A INFLUÊNCIA DO STRESS NA EXPRESSÃO CLÍNICA DA ASMA INFANTIL

A asma é a doença crônica mais freqüente na infância e o stress é considerado um dos agentes desencadeantes e agravantes do broncoespasmo nesses pacientes. O objetivo deste trabalho foi investigar a influência do stress na expressão clínica da asma e sua associação com as crises em crianças. Para verificar a presença de stress, utilizou-se a Escala de Stress Infantil (LIPP E LUCARELLI, 1998) e por meio de um questionário aplicado aos pais, observou-se freqüência de sintomas e crises de asma, as alterações do sono, o absenteísmo escolar, as limitações à prática de atividade física, a freqüência de uso de broncodilatador, as condutas dos pais durante as crises de asma, os fatores associados ao desencadeamento das crises, o poder aquisitivo e o grau de instrução do chefe da família. Observou-se que as crianças com asma estavam mais estressadas que as crianças do grupo controle, principalmente aquelas com maior gravidade da doença. Os resultados indicam que a presença de stress pode intensificar a freqüência de sintomas da asma, a limitação à atividade física, o absenteísmo escolar e as interrupções do sono. O maior tempo de diagnóstico de asma implicou em menor ocorrência de stress, sugerindo a existência de um fator de adaptação à doença. Conclui-se que o stress é um fator importante no desencadeamento e agravamento das crises de asma nas crianças e observa-se a necessidade de maiores pesquisas na aérea para aprofundar os conhecimentos sobre esse assunto.

A family of fibrinogen-related proteins that precipitates parasite-derived molecules is produced by an invertebrate after infection

After infection with the digenetic trematode Echinostoma paraensei, hemolymph of the snail Biomphalaria glabrata contains lectins comprised of 65-kDa subunits that precipitate polypeptides secreted by E. paraensei intramolluscan larvae. Comparable activity is lacking in hemolymph of uninfected snails. Three different cDNAs with sequence similarities to peptides derived from the 65-kDa lectins were obtained and unexpectedly found to encode fibrinogen-related proteins (FREPs). These FREPs also contained regions with sequence similarity to Ig superfamily members. B. glabrata has at least five FREP genes, three of which are expressed at increased levels after infection. Elucidation of components of the defense system of B. glabrata is relevant because this snail is an intermediate host for Schistosoma mansoni, the most widely distributed causative agent of human schistosomiasis. These results are novel in suggesting a role for invertebrate FREPs in recognition of parasite-derived molecules and also provide a model for investigating the diversity of molecules functioning in nonself-recognition in an invertebrate.

Interaction of Coatomer with Aminoglycoside Antibiotics: Evidence That Coatomer Has at Least Two Dilysine Binding Sites

Coatomer is the soluble precursor of the COPI coat (coat protein I) involved in traffic among membranes of the endoplasmic reticulum and the Golgi apparatus. We report herein that neomycin precipitates coatomer from cell extracts and from purified coatomer preparations. Precipitation first increased and then decreased as the neomycin concentration increased, analogous to the precipitation of a polyvalent antigen by divalent antibodies. This suggested that neomycin cross-linked coatomer into large aggregates and implies that coatomer has two or more binding sites for neomycin. A variety of other aminoglycoside antibiotics precipitated coatomer, or if they did not precipitate, they interfered with the ability of neomycin to precipitate. Coatomer is known to interact with a motif (KKXX) containing adjacent lysine residues at the carboxyl terminus of the cytoplasmic domains of some membrane proteins resident in the endoplasmic reticulum. All of the antibiotics that interacted with coatomer contain at least two close amino groups, suggesting that the antibiotics might be interacting with the di-lysine binding site of coatomer. Consistent with this idea, di-lysine itself blocked the interaction of antibiotics with coatomer. Moreover, di-lysine and antibiotics each blocked the coating of Golgi membranes by coatomer. These data suggest that certain aminoglycoside antibiotics interact with di-lysine binding sites on coatomer and that coatomer contains at least two of these di-lysine binding sites.

Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences

Geological, geophysical, and geochemical data support a theory that Earth experienced several intervals of intense, global glaciation (“snowball Earth” conditions) during Precambrian time. This snowball model predicts that postglacial, greenhouse-induced warming would lead to the deposition of banded iron formations and cap carbonates. Although global glaciation would have drastically curtailed biological productivity, melting of the oceanic ice would also have induced a cyanobacterial bloom, leading to an oxygen spike in the euphotic zone and to the oxidative precipitation of iron and manganese. A Paleoproterozoic snowball Earth at 2.4 Giga-annum before present (Ga) immediately precedes the Kalahari Manganese Field in southern Africa, suggesting that this rapid and massive change in global climate was responsible for its deposition. As large quantities of O2 are needed to precipitate this Mn, photosystem II and oxygen radical protection mechanisms must have evolved before 2.4 Ga. This geochemical event may have triggered a compensatory evolutionary branching in the Fe/Mn superoxide dismutase enzyme, providing a Paleoproterozoic calibration point for studies of molecular evolution.

The biotic crisis and the future of evolution

The biotic crisis overtaking our planet is likely to precipitate a major extinction of species. That much is well known. Not so well known but probably more significant in the long term is that the crisis will surely disrupt and deplete certain basic processes of evolution, with consequences likely to persist for millions of years. Distinctive features of future evolution could include a homogenization of biotas, a proliferation of opportunistic species, a pest-and-weed ecology, an outburst of speciation among taxa that prosper in human-dominated ecosystems, a decline of biodisparity, an end to the speciation of large vertebrates, the depletion of “evolutionary powerhouses” in the tropics, and unpredictable emergent novelties. Despite this likelihood, we have only a rudimentary understanding of how we are altering the evolutionary future. As a result of our ignorance, conservation policies fail to reflect long-term evolutionary aspects of biodiversity loss.

Illite and hydrocarbon exploration

Illite is a general term for the dioctahedral mica-like clay mineral common in sedimentary rocks, especially shales. Illite is of interest to the petroleum industry because it can provide a K-Ar isotope date that constrains the timing of basin heating events. It is critical to establish that hydrocarbon formation and migration occurred after the formation of the trap (anticline, etc.) that is to hold the oil. Illite also may precipitate in the pores of sandstone reservoirs, impeding fluid flow. Illite in shales is a mixture of detrital mica and its weathering products with diagenetic illite formed by reaction with pore fluids during burial. K-Ar ages are apparent ages of mixtures of detrital and diagenetic end members, and what we need are the ages of the end members themselves. This paper describes a methodology, based on mineralogy and crystallography, for interpreting the K-Ar ages from illites in sedimentary rocks and for estimating the ages of the end members.

A Saccharomyces cerevisiae homolog of the human adrenoleukodystrophy transporter is a heterodimer of two half ATP-binding cassette transporters.

The adrenoleukodystrophy protein (ALDP) and the 70-kDa peroxisomal membrane protein (PMP70) are half ATP-binding cassette (ABC) transporters in the human peroxisome membrane. ALDP and PMP70 share sequence homology and both are implicated in genetic diseases. PXA1 and YKL741 are Saccharomyces cerevisiae genes that encode homologs of ALDP and PMP70. Pxa1p, a putative ortholog of ALDP, is involved in peroxisomal beta-oxidation of fatty acids while YKL741 is an open reading frame found by the yeast genome sequencing project. Here we designate YKL741 as PXA2 and show that its protein product, Pxa2p, like Pxa1p, is associated with peroxisomes but not required for their assembly. Yeast strains carrying gene disruption of PXA1, PXA2, or both have similar and, in the case of the latter, nonadditive phenotypes. We also find that the stability of Pxa1p, but not Pxa2p, is markedly reduced in the absence of the other. Finally, we find that Pxa1p and Pxa2p coimmuno-precipitate. These genetic and physical data suggest that Pxa1p and Pxa2p heterodimerize to form a complete peroxisomal ABC transporter involved in fatty acid beta-oxidation. This result predicts the presence of similar heterodimeric ABC transporters in the mammalian peroxisome membrane.

The 37/40-kilodalton autoantigen in insulin-dependent diabetes mellitus is the putative tyrosine phosphatase IA-2.

Major targets for autoantibodies associated with the development of insulin-dependent diabetes mellitus (IDDM) include tryptic fragments with a molecular mass of 37 kDa and/or 40 kDa of a pancreatic islet cell antigen of unknown identity. The assay identifying autoantibodies against the 37/40-kDa antigen in human sera is based on the immunoprecipitation of 35S-labeled rat insulinoma cell proteins with sera from IDDM patients, followed by limited trypsin digestion of the immunoprecipitated material. To identify cDNA clones coding for the 37/40-kDa antigen, we have screened a cDNA expression library from rat insulinoma cells with a serum from an IDDM patient that precipitated the 37/40-kDa antigen in our assay. Among the cDNA products that reacted with the IDDM serum, we identified one cDNA clone whose open reading frame encodes a protein with a predicted mass of 105 kDa that we termed "ICA105" for 105-kDa islet cell antibody. The deduced amino acid sequence has high homology to a recently cloned putative tyrosine phosphatase IA-2 from human and mouse cDNA libraries. Translation of the cDNA in vitro results in a polypeptide with the expected molecular mass of 105 kDa. The evidence that ICA105 is indeed the precursor of the 37/40-kDa tryptic fragments is based on the following three results: (i) Sera from IDDM patients containing autoantibodies to the 37/40-kDa antigen precipitate the in vitro translated polypeptide, whereas sera from healthy subjects as well as sera from IDDM patients not reactive with the 37/40-kDa antigen do not precipitate the cDNA product. (ii) Immunoprecipitation of the in vitro translated protein with sera containing autoantibodies to the 37/40-kDa antigen followed by limited trypsin digestion of the precipitated proteins results in a 40-kDa polypeptide. (iii) The protein derived from our cDNA but not from an unrelated control cDNA clone can block immunoprecipitation of the 37/40-kDa antigen from a labeled rat insulinoma cell extract. The availability of the cloned 37/40-kDa antigen should facilitate the identification of individuals at risk of IDDM with increased accuracy. Furthermore, the identification of the 37/40-kDa antigen as the putative tyrosine phosphatase IA-2 is of relevance in elucidating the role of this antigen in the development of IDDM.

Ukrainian economy on the verge of recession. OSW Commentary No. 96, 2012-11-21

In the third quarter of 2012, Ukraine’s economy recorded negative growth (-1.3%) for the first time since its 2009 economic crisis. Q4 GDP is projected to suffer a further decline, bringing Ukraine into formal recession. In addition to the worsening macroeconomic indicators, Ukraine is also facing a series of concomitant economic problems: a growing trade deficit, industrial decline, shrinking foreign exchange reserves, and the weakening of the hryvnia. Poor economic growth is expected to result in lower than projected budget revenues, which in turn could lead to the sequestration of the budget in December. The decline evident across the key economic indicators in the second half of 2012 brings to a close a period of relative economic stability and two years of economic growth, which had been seen as a significant personal achievement of President Viktor Yanukovych and the ruling Party of Regions. The health of the Ukrainian economy largely depends on the state of the country’s export- -oriented industries. The current economic forecasts for foreign markets are not very optimistic. It is impossible to determine whether the current economic downturn is likely to be merely temporary or whether it heralds the onset of a prolonged economic crisis. The limited capacity to deal with the growing economic problems may mean that Kiev will need to seek financial support from abroad. This is particularly significant with regard to external debt servicing, since in 2013 Ukraine will need to pay back around 9 billion USD, including over 5.5 billion USD to the International Monetary Fund. In order to overcome the recession and stabilise public finances, the government may be forced to take a series of unpopular measures, including raising the price of natural gas and utilities. These measures have been stipulated by the IMF as a condition of further financial assistance and the disbursement of the 12 billion USD stabilisation loan granted to Ukraine in July 2010. The only alternative for Western loans and economic reforms appears to be financial support from Russia. The price for Moscow’s help might however turn out to be very high, and precipitate a turn in Kiev’s foreign policy towards a gradual re-integration of former Soviet republics under Moscow-led geopolitical projects.

Balkan Pitfalls. ACES Working Papers, 2011

The Western Balkans are becoming increasingly mired in political conflicts, social disquiet, ethnic disputes, and state fragilities that can precipitate a new phase of regional instability. At the same time, the major international players may be unprepared and ill equipped to manage or resolve the emerging conflicts. While the U.S. and NATO have scaled down their presence in the region, the EU’s capabilities and effectiveness are coming under closer scrutiny.

Data compilation of ESOP

The work in this sub-project of ESOP focuses on the advective and convective transforma-tion of water masses in the Greenland Sea and its neighbouring areas. It includes observational work on the sub-mesoscale and analysis of hydrographic data up to the gyre-scale. Observations of active convective plumes were made with a towed chain equipped with up to 80 CTD sensors, giving a horizontal and vertical resolution of the hydrographic fields of a few metres. The observed scales of the penetrative convective plumes compare well with those given by theory. On the mesoscale the structure of homogeneous eddies formed as a result of deep convection was observed and the associated mixing and renewal of the intermediate layers quantified. The relative importance and efficiency of thermal and haline penetrative convection in relation to the surface boundary conditions (heat and salt fluxes and ice cover) and the ambient stratification are studied using the multi year time series of hydro-graphic data in the central Greenland Sea. The modification of the water column of the Greenland Sea gyre through advection from and mixing with water at its rim is assessed on longer time scales. The relative contributions are quantified using modern water mass analysis methods based on inverse techniques. Likewise the convective renewal and the spreading of the Arctic Intermediate Water from its formation area is quantified. The aim is to budget the heat and salt content of the water column, in particular of the low salinity surface layer, and to relate its seasonal and interannual variability to the lateral fluxes and the fluxes at the air-sea-ice interface. This will allow to estimate residence times for the different layers of the Greenland Sea gyre, a quantity important for the description of the Polar Ocean carbon cycle.

Chemical composition and solubility of ocean phosphatized rocks in seawater

In order to elucidate possibility of limestone phosphatization during contact with seawater two sets of experiments were carried out: that of solubility of natural phosphates in seawater and that of deposition of phosphorus onto calcareous phase. Concentration of phosphorus in seawater used for solubility experiments varied from 39 to 338 µ/l, temperature was 5.5-17.5°C and pH 7.8-7.9. The lowest solubility was characteristic of ancient crystallized samples. The deposition experiments showed that in case when concentration of dissolved phosphate in seawater reaches 3 mg/l it might be sorbed on solid CaCO3 phase without forming its own mineral. The latter is able to form rapidly but only if magnesium is not present in solution. In magnesium-free water calcium phosphates precipitate when concentration of dissolved phosphorus is higher than 0.9-1.2 mg/l. These results show that phosphatization of limestones in marine environment takes place during their contact with pore water but not with marine bottom water.