Coccolithophore biomineralization: New questions, new answers.

Coccolithophores are unicellular phytoplankton that are characterized by the presence intricately formed calcite scales (coccoliths) on their surfaces. In most cases coccolith formation is an entirely intracellular process - crystal growth is confined within a Golgi-derived vesicle. A wide range of coccolith morphologies can be found amongst the different coccolithophore groups. This review discusses the cellular factors that regulate coccolith production, from the roles of organic components, endomembrane organization and cytoskeleton to the mechanisms of delivery of substrates to the calcifying compartment. New findings are also providing important information on how the delivery of substrates to the calcification site is co-ordinated with the removal of H(+) that are a bi-product of the calcification reaction. While there appear to be a number of species-specific features of the structural and biochemical components underlying coccolith formation, the fluxes of Ca(2+) and a HCO3(-) required to support coccolith formation appear to involve spatially organized recruitment of conserved transport processes.

Coccolithophore biomineralization: New questions, new answers.

Coccolithophores are unicellular phytoplankton that are characterized by the presence intricately formed calcite scales (coccoliths) on their surfaces. In most cases coccolith formation is an entirely intracellular process - crystal growth is confined within a Golgi-derived vesicle. A wide range of coccolith morphologies can be found amongst the different coccolithophore groups. This review discusses the cellular factors that regulate coccolith production, from the roles of organic components, endomembrane organization and cytoskeleton to the mechanisms of delivery of substrates to the calcifying compartment. New findings are also providing important information on how the delivery of substrates to the calcification site is co-ordinated with the removal of H(+) that are a bi-product of the calcification reaction. While there appear to be a number of species-specific features of the structural and biochemical components underlying coccolith formation, the fluxes of Ca(2+) and a HCO3(-) required to support coccolith formation appear to involve spatially organized recruitment of conserved transport processes.

NleH effectors interact with Bax inhibitor-1 to block apoptosis during enteropathogenic Escherichia coli infection

<p>The human pathogens enteropathogenic (EPEC) and enterohemorrhagic Escherichia coli and the related mouse pathogen Citrobacter rodentium subvert a variety of host cell signaling pathways via their plethora of type III secreted effectors, including triggering of an early apoptotic response. EPEC-infected cells do not develop late apoptotic symptoms, however. In this study we demonstrate that the NleH family effectors, homologs of the Shigella effector kinase OspG, blocks apoptosis. During EPEC infection, NleH effectors inhibit elevation of cytosolic Ca(2+) concentrations, nuclear condensation, caspase-3 activation, and membrane blebbing and promote cell survival. NleH1 alone is sufficient to prevent procaspase-3 cleavage induced by the proapoptotic compounds staurosporine, brefeldin A, and tunicamycin. Using C. rodentium, we found that NleH inhibits procaspase-3 cleavage at the bacterial attachment sites in vivo. A yeast two-hybrid screen identified the endoplasmic reticulum six-transmembrane protein Bax inhibitor-1 (BI-1) as an NleH-interacting partner. We mapped the NleH-binding site to the N-terminal 40 amino acids of BI-1. Knockdown of BI-1 resulted in the loss of NleH's antiapoptotic activity. These results indicate that NleH effectors are inhibitors of apoptosis that may act through BI-1 to carry out their cytoprotective function.</p>

Ferulates and lignin structural composition in cork

The structure of lignin and suberin, and ferulic acid (FA) content in cork from Quercus suber L. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Cork(sap)), and milled-cork lignins (MCL) from Cork and Cork(sap) were isolated. Suberin composition was determined by GC-MS/FID, whereas the polymers structure in Cork, Corksap, and MCL was studied by Py-TMAH and 2D-HSQC-NMR. Suberin contained 94.4% of aliphatics and 3.2% of phenolics, with 90% of omega-hydroxyacids and alpha,omega-diacids. FA represented 2.7% of the suberin monomers, overwhelmingly esterified to the cork matrix. Py-TMAH revealed significant FA amounts in all samples, with about 3% and 6% in cork and cork lignins, respectively. Py-TMAH and 2D-HSQC-NMR demonstrated that cork lignin is a G-lignin (>96% G units), with a structure dominated by beta-O-4' alkyl-aryl ether linkages (80% and 77% of all linkages in MCL and MCLsap, respectively), followed by phenylcoumarans (18% and 20% in MCL and MCLsap, respectively), and smaller amounts of resinols (ca. 2%) and dibenzodioxocins (1%). HSQC also revealed that cork lignin is heavily acylated (ca. 50%) exclusively at the side-chain gamma-position. Ferulates possibly have an important function in the chemical assembly of cork cell walls with a cross-linking role between suberin, lignin and carbohydrates.

Purifica����o, caracteriza����o e efeitos imunomodulat��rio e antiproliferativo de uma lectina do fungo Clavaria cristata (Holmsk.) Pers

A 140,0 kDa lectin was purified and characterized from the mushroom Clavaria cristata. The purification procedures from the crude extract of the mushroom comprised gel filtration chromatography on Sephacryl s200 and ion exchange on Resource Q column. The purified lectin agglutinated all types of human erythrocytes with preference for trypsinized type O erythrocytes. The haemagglutinating activity is dependent of Ca 2+ ions and was strongly inhibited by the glycoprotein bovine submaxillary mucin (BSM) up to the concentration of 0, 125 mg/mL. The C. cristata lectin (CcL) was stable in the pH range of 2,5-11,5 and termostable up to 80 ��C. CcL molecular mass determined by gel filtration on a Superose 6 10 300 column was approximately 140,3 kDa. SDS polyacrilamide gel electrophoresis revealed a single band with a molecular mass of approximately 14,5 kDa, when the lectin was heated at 100 ���C in the presence or absence of ��-mercaptoethanol. CcL induced activation of murine peritoneal macrophages in vitro resulting in the release of nitric oxide (NO), reaching the maximum production at 24 h. In experimental paw oedema model in mice, CcL showed proinflammatory activity being able to induce oedema formation. Cell viability of HepG2, MDA 435 e 3T3 cell lines was examined after 72 h of incubation with CcL in different concentrations (0,5-50 ��g/mL). CcL inhibited HepG2 cells growth with an IC50 value of 50 ��g/mL. In the present work, the observed immunomodulatory and antiproliferative effects indicate CcL as a possible immunomodulator compound, interfering in the macrophages immune response, taking possible anti-parasitic, anti-tumoral effects or diagnostic and/or therapeutic

Isotope characterisation of deep aquifers in the Gwda catchment, northern Poland

We present the results of isotope measurements (�� 18 O, �� D, �� 13 C DIC and 14 C) and chemical analyses (TDS, TOC, HCO 3��� , SO 42��� , Cl ��� , NO 3��� , NH 4+ , Ca 2+ , Mg 2+ Na + and K + ) conducted on groundwater samples collected from deep Cenozoic aqui- fers. These aquifers are the basic source of drinking water at numerous localities within the study area in northern Po- land. Most of the �� 18 O determinations are characterised by low variability (i.e., > 70 per cent of �� 18 O are between ���9.5��� and ���9.2���). In most cases tritium activity was not detected or its content slightly exceeded the uncertainty of measure- ment (from ��0.3 T.U. to �� 0.5 T.U.). On average, 14 C activity is twice higher than that under similar conditions and in hydrogeological systems. The �� 13 C DIC values fall within the ���13.6��� to ���12.8��� range. A slight variability is observed when considering all isotope and chemical data within the study area and under these hydrogeological conditions. In general, the results of isotope and chemical analyses seem to be homogeneous, indicating the presence of closely similar groundwaters in the system, irrespective of geological formation. It is likely that there is a significant hydraulic connec- tion between shallow and deep aquifers in the Gwda catchment, which indicates the potential for seepage of pollutants from shallow Pleistocene to deep Miocene aquifers. This can endanger the latter by e.g., high concentrations of NO 3��� , SO 42��� and Cl ��� ions from shallow aquifers within the Gwda catchment.

Estudos de Durabilidade Frente ao Ataque ��cido de Comp��sitos Portland-Pol��mero para Cimenta����o de Po��os de Petr��leo

Portland-polymers composites are promising candidates to be used as cementing material in Northeastern oil wells of Brazil containing heavy oils submitted to steam injection. In this way, it is necessary to evaluate its degradation in the commonly acidizind agents. In addition, to identify how aggressive are the different hostile environments it is an important contribution on the decision of the acidic systems to be used in. It was investigated the performance of the Portland-polymer composites using powdered polyurethane, aqueous polyurethane, rubber tire residues and a biopolymer, those were reinforced with polished carbon steel SAE 1045 to make the electrochemical measurements. HCl 15,0 %, HCl 6,0 % + HF 1,5 % (soft mud acid), HCl 12,0 % + HF 3,0 % (regular mud acid) and HAc 10 % + HF 1,5 % were used as degrading environment and electrolytes. The more aggressive acid solution to the plain Portland hardened cement paste was the regular mud acid, that showed loss of weight around 23.0 %, followed by the soft mud acid, the showed 11.0 %, 15.0 % HCl with 7,0 % and, at last the 10.0 % HAc plus HF 1.5 % with just 1.0 %. The powdered polyurethane-composite and the aqueous polyurethane one showed larger durability, with reduction around 87.0 % on the loss of weight in regular mud acid. The acid attack is superficial and it occurs as an action layer, where the degraded layer is responsible for the decrease on the kinetic of the degrading process. This behavior can be seen mainly on the Portland- aqueous polyurethane composite, because the degraded layer is impregnated with chemically modified polymer. The fact of the acid attack does not have influence on the compressive strength or fratography of the samples, in a general way, confirms that theory. The mechanism of the efficiency of the Portland-polymers composites subjected to acid attack is due to decreased porosity and permeability related with the plain Portland paste, minor quantity of Ca+2, element preferentially leached to the acidic solution, wave effect and to substitute part of the degrading bulk for the polymeric one. The electrolyte HAc 10 % + HF 1,5 % was the least aggressive one to the external corrosion of the casing, showing open circuit potentials around +250 mV compared to -130 mV to the simulated pore solution to the first 24 hours immersion. This behavior has been performed for two months at least. Similar corrosion rates were showed between both of the electrolytes, around 0.01 &#956;A.cm-2. Total impedance values, insipient arcs and big polarization resistance capacitive arcs on the Nyquist plots, indicating passivity process, confirm its efficiency. In this way, Portlandpolymers composites are possible solutions to be succeed applied to oilwell cementing concomitant submitted to steam injection and acidizing operation and the HAc 10,0 % + HF 1,5 % is the less aggressive solution to the external corrosion of the casing

I. Quantal effects in biochemical cooperativity and a proposed mechanism for the differentiation of calcium signaling in synaptic plasticity. II. Evolutionary algorithms for the optimization of methods in computational chemistry

<p>In Part 1 of this thesis, we propose that biochemical cooperativity is a fundamentally non-ideal process. We show quantal effects underlying biochemical cooperativity and highlight apparent ergodic breaking at small volumes. The apparent ergodic breaking manifests itself in a divergence of deterministic and stochastic models. We further predict that this divergence of deterministic and stochastic results is a failure of the deterministic methods rather than an issue of stochastic simulations.</p> <p>Ergodic breaking at small volumes may allow these molecular complexes to function as switches to a greater degree than has previously been shown. We propose that this ergodic breaking is a phenomenon that the synapse might exploit to differentiate Ca$^{2+}$ signaling that would lead to either the strengthening or weakening of a synapse. Techniques such as lattice-based statistics and rule-based modeling are tools that allow us to directly confront this non-ideality. A natural next step to understanding the chemical physics that underlies these processes is to consider \textit{in silico} specifically atomistic simulation methods that might augment our modeling efforts.</p> <p>In the second part of this thesis, we use evolutionary algorithms to optimize \textit{in silico} methods that might be used to describe biochemical processes at the subcellular and molecular levels. While we have applied evolutionary algorithms to several methods, this thesis will focus on the optimization of charge equilibration methods. Accurate charges are essential to understanding the electrostatic interactions that are involved in ligand binding, as frequently discussed in the first part of this thesis.</p>

Enzymatic and structural characterization of new PLA2 isoform isolated from white venom of Crotalus durissus ruruima

This work reports the structural and enzymatic characterization of a new sPLA2 from the white venom of Crotalus durissus ruruima, nominated PLA2A. The homogeneity of the PLA2A fraction and its molecular mass were initially evaluated by SDS-PAGE and confirmed by MALDI-TOF spectrometry, indicating a molecular mass of 14,299.34 Da. Structural investigation, through circular dichroism spectroscopy, revealed that PLA2A has a high content of alpha helix and beta-turn structures, 45.7% and 35.6% respectively. Its amino acid sequence, determined by Edman degradation and de novo amino acid sequencing, exhibited high identity to PLA2 Cdt F15 from Crotalus durissus terrificus. The enzymatic investigation, conducted using the synthetic substrate 4-nitre-3-(octanoyloxy)benzoic acid, determined its V(max) (7.56 nmoles/min) and K(M) (2.76 mM).Moreover, PLA2A showed an allosteric behavior and its enzymatic activity was dependent on Ca(2+). Intrinsic fluorescence measurements suggested that Ca(2+) induced a significant increase of PLA2A fluorescence, whereas its replacement for Mg(2+), Mn(2+), Sn(2+) and Cd(2+) apparently induced no structural modifications. The optimal pH and temperature for the enzymatic activity of PLA2A were 8.4 and 40 degrees C, respectively, and the minimal concentration of p-BPB and crotapotin that significantly inhibited such activity was 0.75 mM and 0.4 mu M, respectively. In addition, PLA2A showed a significant antibacterial effect that was not strictly dependent on the enzymatic activity of such sPLA2. (c) 2008 Elsevier Ltd. All rights reserved.

Carbono da biomassa microbiana em solo com aplica����o de dejetos de su��nos em sistema de plantio direto e convencional.

A aplica����o de dejetos de su��nos em solos cultivados pode alterar suas caracter��sticas qu��micas, f��sicas e biol��gicas. Estes estudos s��o importantes para compreens��o e recomenda����o de pr��ticas conservacionistas de uso do solo, que visam minimizar os efeitos da produ����o agr��cola nos recursos naturais. O objetivo deste trabalho foi avaliar o carbono da biomassa microbiana (CBM) do solo, em tr��s profundidades, ap��s a aplica����o de cinco doses de dejetos l��quidos de su��nos (DLS) em sistema de plantio direto (SPD) e convencional (SPC). O experimento foi instalado em 1997, na Esta����o Experimental do Instituto Agron��mico do Paran��, em Palotina, Paran��, em Latossolo Vermelho distrof��rrico de textura argilosa. Os tratamentos foram a aplica����o de 0, 30, 60, 90 e 120 m3 ha-1 ano-1 de dejetos de su��nos no solo cultivado em SPD ou SPC, em delineamento experimental de blocos casualizados, com tr��s repeti����es. Em outubro de 2015, ap��s o cultivo de aveia (Avena strigosa), foram coletadas amostras de solo, nas profundidades de 0-10 cm, 10-20 cm e 20-40 cm, para determina����o dos atributos qu��micos e do CBM. O DLS apresentou em g L-1 58,20 de massa seca; 5,52 N; 3,97 P; 1,4 K; 3,32 Ca; 2,16 Mg; 0,01 Cu; 0,23 Zn; 0,06 Mn; densidade de 1,01 g cm-3 e condutividade de 10,72 mS cm-1. O CBM foi avaliado pelo m��todo de fumiga����o-extra����o. O teor de carbono nos extratos foi quantificado por titula����o com sulfato ferroso amoniacal, ap��s a oxida����o do dicromato de pot��ssio por digest��o sulf��rica. O CBM foi calculado utilizando um fator de corre����o Kc de 0,33. A an��lise de vari��ncia foi realizada a 5% de probabilidade e, quando significativo pelo teste F, as m��dias foram comparadas pelo teste de Tukey. O CBM, com a aplica����o de DLS no SPD, apresentou valores m��dios de 457, 355 e 284 micrograma C-CBM g solo nas profundidades de 0-10, 10-20 e 20-40 cm, respectivamente. No SPC, o CBM, com a aplica����o de DLS, apresentou valores m��dios de 400, 284 e 253 micrograma C-CBM g solo, respectivamente, nas mesmas profundidades. N��o houve efeito significativo das doses de DLS sobre o CBM nas profundidades 0-10, 10-20 e 20-40 cm, tanto sob SPD quanto SPC. Os valores de CBM foram maiores no SPD quando comparados com SPC na profundidade de 0-10 cm e 10-20 cm, n��o diferindo entre si na profundidade de 20-40 cm. Houve intera����o significativa entre as doses de DLS e SPD sobre o CBM, somente na adi����o das doses de 0 e 120 m3 ha-1 ano-1 DLS na profundidade de 10-20 cm.

Posidonia oceanica (L.) Delile in its westernmost biogeographical limit (northwestern Alboran Sea): Meadows characterisation, phenology and flowering events

Posidonia oceanica is a Mediterranean endemic seagrass species that forms meadows covering ca. 2.5���4.5 millions of hectares, representing ca.25 % of the infralittoral and shallow circalittoral (down to 50m) bottoms of the Mediterranean. This seagrass is considered a habitat-engineer species and provides an elevated number of ecosystem services. In addition the Marine Strategy Framework Directive (MSFD, 2008/56/EC) includes seagrass like elements to evaluate the ���Good Environmental Status��� of the European coasts. Information about their phenological characteristic and structure of the meadows is needed for indicator estimations in order to establish their conservation status. The studied meadows are located in the westernmost limit of the P. oceanica distribution (North-western Alboran Sea) in the vecinity of the Strait of Gibraltar, an Atlantic-Mediterranean water transition area. Four sites were selected from East to West: Paraje Natural de Acantilados de Maro-Cerro Gordo (hereafter Maro), Special Area of Conservation ���Calahonda��� (hereafter Calahonda), Site of Community Importance Estepona (hereafter Estepona) and Punta Chullera (hereafter Chullera) where P. oceanica present their westernmost meadows. Phenological data were recorded from mid November to mid December in P. oceanica patches located at 2 ��� 3 m depth. At each site three types of patches (patch area <1m2, small patches; 1-2 m2, medium patches and >2 m2, large patches) were sampled. At each patch and site, 3 quadrants of 45 x 45 cm were sampled for shoot and inflorescences density measurements. In each quadrant, 10 random shoots were sampled for shoot morphology (shoot height and number of leaves). Shoot and inflorescences densities were standardized to squared meters. All the studied P. oceanica meadows develop on rocks and they present a fragmented structure with a coverage ranging between ca. 45% in Calahonda and Estepona and ca. 31% in Maro. The meadows of Chullera are reduced to a few small - medium patches with areas ranging between 0.5-1.5 m2 (Fig. 1). The meadows of Chullera and Estepona presented similar values of shoot density (ca. 752 ��� 662 shoots m-2, respectively) and leaf height (ca. 25 cm). Similarly, the Calahonda and Maro meadows also showed similar values of shoot density (ca. 510 ��� 550 shoots m-2, respectively) but displaying lower values than those of sites located closer to the Strait of Gibraltar. Regarding patch sizes and leaf height, the longest leaves (ca. 25 cm) were found in medium and large patches, but the number of leaves per shoot were higher in the small and the medium size patches (ca. 6.3 leaves per shoot). Flowering was only detected at the Calahonda meadows with maximum values of ca. 330 inflorescences m-2 (115.2 �� 98.2 inflorescences m-2, n= 9; mean �� SD) (Fig.1). Inflorescence density was not significant different among patches of different sizes. In the Alboran Sea and unlike the studied meadows, extensive beds of P. oceanica occur at the National Park of Cabo de Gata (northeastern Alboran Sea), but from east to west (Strait of Gibraltar), meadows are gradually fragmenting and their depth range decrease from 30m to 2m depth between Cabo de Gata and Chullera, respectively. Probably, the Atlantic influence and the characteristic oceanographic conditions of the Alboran Sea (i.e., higher turbidity, higher water turbulence) represent a developmental limiting factor for P. oceanica at higher depths. Similarities between the meadows located closer to Strait of Gibraltar (Chullera and Estepona) were detected as well as between those more distant (Calahonda and Maro). The first ones showed higher values of shoot densities and leaf heights than the formers, which could be relating to the higher hydrodynamic exposure found at Chullera and Estepona meadows. Regarding flowering events, sexual reproduction in P. oceanica is not common in different locations of the Mediterranean Sea. The available information seems to indicate that flowering represent an irregular event and it is related to high seawater temperature. In fact, the flowering episodes that occurred in Calahonda in November 2015, match with the warmest year ever recorded. This is the third flowering event registered in these meadows located close to the westernmost distributional limit of P. oceanica (M��laga, Alboran Sea), which could indicates that these meadows presents a healthy status. Furthermore, the absence of significant differences in relation to inflorescence density between patches of different sizes may be indicating that the fragmentation does not necessarily influence on the flowering of this seagrass species.

Lost fishing gear and litter at Gorringe Bank (NE Atlantic)

Studies concerning marine litter have received great attention over the last several years by the scientific community mainly due to their ecological and economic impacts in marine ecosystems, from coastal waters to the deep ocean seafloor. The distribution, type and abundance of marine litter in Ormonde and Gettysburg, the two seamounts of Gorringe Bank, were analyzed from photo and video imagery obtained during ROV-based surveys carried out at 60���3015 m depths during the E/V Nautilus cruise NA017. Located approximately 125 nm southwest of Portugal, Gorringe Bank lays at the crossroad between the Atlantic and the Mediterranean and is therefore characterized by an intense maritime traffic and fishing activities. The high frequency of lost or discarded fishing gear, such as cables, longlines and nets, observed on Gorringe Bank suggests an origin mostly fromfishing activities,with a clear turnover in the type of litter (mostly metal, glass and to amuch lesser extent, plastic) with increasing depth. Litter was more abundant at the summit of Gorringe Bank (ca. 4 items��km���1), decreasing to less than 1 item��km���1 at the flanks and to ca. 2 items��km���1 at greater depths. Nevertheless, litter abundance appeared to be lower than in continental margin areas. The results presented herein are a contribution to support further actions for the conservation of vulnerable habitats on Gorringe Bank so that they can continue contributing to fishery productivity in the surrounding region.

Evaluation of the throughfall and stemflow nutrient contents in mixed and pure plantations of Acacia mangium, Pseudosamenea guachapele and Eucalyptus grandis.

A intercepta����o da chuva pela copa das florestas tem grande relev��ncia no ciclo biogeoqu��mico de nutrientes nos solos de baixa fertilidade sob florestas nativas e plantadas. Entretanto, pouco se sabe sobre as modifica����es na qualidade dessa ��gua e no balan��o hidrol��gico ap��s a intercepta����o pela copa do eucalipto sob condi����es de plantios puros e mistos com leguminosas, no Brasil. Amostras de ��gua de chuva (RF), de precipita����o interna (TF) e de escoamento pelo tronco (SF), foram coletadas e analisadas quimicamente em plantios puros de mangium (esp��cie fixadora de nitrog��nio atmosf��rico - EFN), guachapele (EFN) e eucalipto (esp��cie n��o fixadora de nitrog��nio - ENFN) e consorciados com guachapele e eucalipto, em Serop��dica, Rio de Janeiro. Nove coletores de escoamento pelo tronco (colocados em ��rvores), nove pluvi��metros posicionados ao acaso nos plantios e tr��s fora da influ��ncia deles foram utilizados no monitoramento durante 5,5 meses. A mangium direcionou 33,4% do total precipitado para o seu tronco. Uma estimativa baseada na corre����o da m��dia anual precipitada na ��rea (1.213 mm) indicou uma contribui����o no aporte de nutrientes (kg ha-1) de 8,42; 0,95; 19,04; 6,74; 4,72; e 8,71 kg ha-1 dos elementos N-NH4+, P, K+, Ca+2, Mg+2 and Na+, respectivamente. A precipita����o interna participou com a maior parte da contribui����o, em compara����o com o escoamento pelo tronco. Os maiores aportes de N-NH4+ (15,03 kg ha-1) e K+ (179,43 kg ha-1) foram observados sob as copas de guachapele em plantio puro. Elevada quantidade de Na+ denota influencia do mar pr��ximo �� ��rea experimental. A mangium foi a esp��cie adaptada �� competi����o por ��gua. Comparativamente ao plantio puro de eucalipto, o plantio misto intensificou a lixivia����o de N, Ca e Mg da copa, enquanto o de K e o P aportaram em menores quantidades nesse plantio.

Emiss��o de fluxos foliares, flora����o e ciclagem de nutrientes em clones de copa de Hevea pauciflora.

A fenologia foliar tem sido utilizada como uma caracter��stica importante na sele����o dos clones de Hevea spp., enquanto o teor de nutrientes na serapilheira �� um bom indicador da ciclagem de nutrientes. O objetivo deste trabalho foi verificar o efeito da periodicidade de emiss��o de fluxos foliares na flora����o de copa de Hevea pauciflora, estado nutricional e qualidade da serapilheira. Foram avaliadas 15 plantas de 10 anos de idade dos clones de copa CNS G 112, CNS G 124 e CBA 2. Nas condi����es edafoclim��ticas da Amaz��nia tropical ��mida, a emiss��o de folhas e de flora����o de H. pauciflora ocorre com maior intensidade no segundo semestre (in��cio do per��odo chuvoso). A H. pauciflora apresenta maior ac��mulo de serapilheira que a floresta prim��ria e os teores foliares de 22,18 g kg-1 de N, 1,47 g kg-1 de P, 5,77 g kg-1 de K, 3,79 g kg-1 de Ca, 2,09 g kg-1 de Mg, 16,15 mg kg-1 de B, 6,14 mg kg-1 de Cu, 53,87 mg kg-1 de Fe, 66,20 mg kg-1 de Mn e 48,44 mg kg-1 de Zn podem ser utilizados como refer��ncia para essa esp��cie de seringueira.

Polarization effects in molecular dynamics simulations of glass-formers Ca(NO(3))(2)center dot nH(2)O, n=4, 6, and 8

Thermodynamics, equilibrium structure, and dynamics of glass-forming liquids Ca(NO(3))(2)center dot nH(2)O, n=4, 6, and 8, have been investigated by molecular dynamics (MD) simulations. A polarizable model was considered for H(2)O and NO(3)- on the basis of previous fluctuating charge models for pure water and the molten salt 2Ca(NO(3))(2)center dot 3KNO(3). Similar thermodynamic properties have been obtained with nonpolarizable and polarizable models. The glass transition temperature, T(g), estimated from MD simulations was dependent on polarization, in particular the dependence of T(g) with electrolyte concentration. Significant polarization effects on equilibrium structure were observed in cation-cation, cation-anion, and water-water structures. Polarization increases the diffusion coefficient of H(2)O, but does not change significantly the diffusion coefficients of ions. Viscosity decreases upon inclusion of polarization, but the conductivity calculated with the polarizable model is smaller than the nonpolarizable model because polarization enhances anion-cation interactions.