含钾矿物中钾的释放及其与溶液环境中离子种类的关系

通过室内试验研究探讨5种含K矿物中K在不同溶液中的释放规律(释放量和释放速率).结果表明,不同含K矿物中K释放速率和释放量的顺序均表现为:黑云母>蛭石>金云母≥白云母>钾长石,不同K矿物释K速率在酸溶液中差异最大,其次在钙和钠盐溶液中,在水中的速率差异最小,这主要是受其矿物本身结构的影响.不同离子对含K矿物中非交换态K释放的促进作用差异显著:H~+>>Ca~(3+)>Na~+>H_2O>NH_4~+.随矿物K有效性增加,H~+和Ca~(2+)对矿物K释放的促进作用越大,而且H~+较Ca~(2+)对黑云母、金云母和长石中的K有更突出的促释作用.此外,Ca~(2+)较Na~+显著促进了黑云母和蛭石中K的释放,但对其他矿物中K释放的影响两者无显著差异.NH~+_4则显著抑制了各种矿物中K的释放,对黑云母和蛭石的抑制作用更强于对金云母和白云母的作用.     

四苯硼钠溶液中含钾矿物非交换态钾的释放特性研究

含钾矿物的全钾含量、非交换态钾总量以及非交换态钾的释放速率因矿物种类而异,且3种参数之间没有必然的相关性。供试5种含钾矿物非交换态钾总量由高到低的顺序是:金云母 5.19% 黑云母3.08% 蛭石2.01% 白云母1.18% 钾长石0.24%,占各矿物全钾的比例分别为:58.4% 、99.7% 、62.5% 、14.2% 和4.98% ,平均达48%。选择较弱提取力的四苯硼钠溶液进行非交换态钾的释放特性研究,5种矿物非交换态钾3d释放累积量顺序为:黑云母 蛭石 金云母 白云母 钾长石;非交换态钾平均释放速率也表现为同样的顺序。上述5种矿物在弱提取力的四苯硼钠溶液中释放3 d,非交换态钾的平均释放速率分别为5.99、2.34、0.52、0.22和0.17 mg/(kgmin),差异明显。如何根据非交换态钾的释放量和释放速率来综合评价矿物钾的生物有效性是未来研究中需要明确的问题。     

Laboratory Dissolution Studies of Rocks from the Borrowdale Volcanic Group (English Lake District)

Laboratory studies were conducted to investigate the rates ofrelease of Na, Mg, Al, Si, K, Ca and Fe from 10 samples of metamorphosed igneous rock of the Borrowdale Volcanic Group (BVG), consisting mainly of plagioclase feldspars, chlorite andquartz, with minor amounts of hornblende, epidote and carbonates.Experiments were performed using freshly-prepared rock pieces (ca. 12 mm cubes), in batch mode, but with frequent changes of the solution phase so that accumulation of dissolved solutes wasminimised. The initial element release rates were relatively high, but declined with time to reach approximate (pseudo-) steady state conditions. Element release rates declined withpH in the pH range 2–7, the dependence upon pH decreasing in the order Al ～ Fe > Si > Mg ～ Ca > K ～ Na. Thepseudo-steady state rates for Si were comparable to steady state values for single minerals. Calcium showed the greatestsample-to-sample variation (more than 100-fold). Rock dissolutionwas far from stoichiometric, with Ca and Mg being present in thesolution phase in proportions greater than in the rock, and Al and Si in lower proportions. In some samples the release rates ofMg and Ca were equal, while in others the Ca rate was up to 100times that of Mg. The rate of release of Ca is correlated with the carbonate content of the rocks. The results indicate that the main source of Ca in the faster-dissolving samples is calcite, while the highest release rates of Mg are consistent with dissolution of dolomite. Aluminium, Si and Fe are probablyreleased predominantly from chlorite. The results are discussed in terms of the supply of base cations to stream waters drainingcatchments underlain by rocks of the BVG.     

草酸对土壤和矿物中钾素的释放规律研究

Oxalic acid plays an important role in improving the bioavailability of soil nutrients. Batch experiments were employed to examine the influences of oxalic acid on extraction and release kinetics of potassium （K） from soils and minerals along with the adsorption and desorption of soil K^＋. The soils and minerals used were three typical Chinese soils, black soil （Mollisol）, red soil （Ultisol）, and calcareous alluvial soil （Entisol）, and four K-bearing minerals, biotite, phlogopite, muscovite, and microcline. The results showed that soil K extracted using 0.2 mol L^-1 oxalic acid was similar to that using 1 mol L^-1 boiling HNO3. The relation between K release （y） and concentrations of oxalic acid （c） could be best described logarithmically as y = a ＋ blogc, while the best-fit kinetic equation of K release was y = a ＋ b√t, where a and b are the constants and t is the elapsed time. The K release for minerals was ranked as biotite 〉 phlogopite 〉〉 muscovite 〉 microcline and for soils it was in the order： black soil 〉 calcareous alluvial soil 〉 red soil. An oxalic acid solution with low pH was able to release more K from weathered minerals and alkaline soils. Oxalic acid decreased the soil K^＋ adsorption and increased the soil K^＋ desorption, the effect of which tended to be greater at lower solution pH, especially in the red soil.     

Über die Einwirkung heterotropher Mikroorganismen auf die Zersetzung silikatischer Minerale

The effect of heterotrophic microorganisms upon the degradation of silicate minerals The purpose of the present work was to study the weathering activity of yeasts and filamentous fungi on various silicate minerals. Culture experiments were carried out on samples of amphibolite, biotite, and orthoclase. Finely ground powder was incubated with pure cultures of 5 yeast strains and 11 filamentous fungi in a glucose-mineral salts-solution at room temperature over a period of 12 weeks. Changes in pH as well as in concentrations of K, Ca, Mg, Fe, Al, and Si in the culture solutions were determined at various intervals.-All fungal strains tested lowered the pH of the culture liquid with or without minerals added from 5.7 to values as low as 1.6. This acidification was brought about by the microbial production of organic acids, especially of gluconic acid. The lowest pH values were found in flasks containing biotite. Acidification in flasks with orthoclase was less pronounced. The pH values found in flasks containing amphibolite were similar to those produced in cultures without mineral powder. From biotite, up to 62% K, 33% Mg, 29% Fe, 59% Al, and 6% Si were released. The solubilizing activity on orthoclase was less effective, and least that on amphibolite.-The importance of acidity and the chelating capacity of the microbially produced organic acids as well as the chemical and structural properties of the mineral with respect to weathering are discussed. The results show that heterotrophic microorganisms like yeasts and filamentous fungi may effectively attack silicate minerals and rocks.     

富钾植物籽粒苋(Amaranthus spp.)对土壤矿物钾的吸收利用研究

运用土培、石英砂培、有机酸释钾实验及矿物X衍射分析研究了不同基因型籽粒苋(Amaranthusspp.)对土壤矿物钾的吸收利用及其机制。结果表明,籽粒苋能有效地利用土壤和云母(黑云母和金云母)中的钾;籽粒苋品种R104、CX4对钾的吸收量高于一般型品种(CX77);籽粒苋根系能引起云母矿物向蛭石转化;籽粒苋根系分泌物中的草酸比一般有机酸具有更高的释放矿物中钾素的能力。     

Effect of natural organic soil solutes on weathering rates of soil minerals

The rate at which minerals in the soil weather is affected by pH and concentration of organic solutes (DOC). The rates of release of Al, Ca, Fe, K, Mg, Na, P and Si from a mineral soil sample to solutions of natural organic solutes and HCI (control) were determined at pH 3 and 4 for up to 17 weeks. Soil solutions were collected by centrifuging materials of O horizons from various soil types under four tree species (spruce, birch, oak, beech) and passed through a cation-exchange resin to yield H⁺-saturated organic solutes. The acceleration of the elements' release by the organic solutes was shown directly by the relative ligand effect (RLE), that is, the release rate in the organic solute solution divided by the release rate in the HCI solution (control) at the same pH. The RLE was greater at pH 4 than at pH 3, and it decreased for the elements in the order Fe > Ca > Mg > Al ≈ Si > K ≈ Na. This indicates that natural organic solutes are more important weathering agents at higher than lower pH and for weathering of mafic minerals rich in Ca, Fe and Mg than of felsic minerals such as K- and Na-feldspars. For all elements and at both pHs, RLE was strongly correlated with the concentration of DOC, which was also closely correlated with titratable acidity of the organic solutes. The important effect of soil type and tree species in producing weathering-promoting organic solutes therefore seems to be expressed through the concentration and not the composition of the organic soil solutes.     

LATERITIC DEEP WEATHERING OF GRANITE

Chemical and mineralogical analyses of two representative laterite profiles developed from granite in south-western Australia have shown that several depth zones defined by particular mineral suites and geochemistry may be recognized. These zones are not simply related to the conventional morphological pallid, mottled, and ferruginous zones. Changes in geochemistry in both profiles can be related to the stability of the major mineral species and to the common isomorphous substitutions occurring in them. Ca, Na, and Mg, which are mainly present in plagioclase feldspars and ferromagnesian minerals, are removed during the earliest stage of alteration of the parent granite. K, Mn, Zn, and residual Ca, Na, Mg, and Sr decrease as microcline and micas alter to kaolin. Al and Fe are most abundant in the surface zones which contain secondary sesquioxide minerals.     

METAL-COMPLEX FORMATION BY LICHEN COMPOUNDS

The formation of soluble complexes, frequently coloured, when solid lichen compounds were shaken with water suspensions of biotite, granite, and basalt indicated that chemical weathering had occurred. The formation of colourless complexes and the adsorption of the dissolved lichen compound or complex by the silicate phase complicate the interpretation of the spectrophotometric analysis data. Lichen compounds invariably released greater amounts of Ca than of Mg, Fe, and Al from the silicates and, for each lichen compound, the release of Ca was usually greater from biotite than from granite or basalt. Release of cations from the silicate materials resulted largely from metal-complex formation rather than from reactions directly involving hydrogen ions. Citric, salicylic, and phydroxy-benzoic acids and EDTA, used as control organic acids, usually released considerably greater amounts of cations from the silicates than did the lichen compounds, consistent with the higher water solubility of the control organic acids. Similar amounts of Fe, Al, Ca, and Mg were released from the silicates by solutions of the lichen compounds and by solid lichen compounds. Lichen compounds are sufficiently soluble in water to form soluble metal complexes and to effect chemical weathering of minerals and rocks.     

Genesis and dynamics of an oxic dystrochrept and a typic haploperox from ultrabasic rock in the tropical rain forest climate of south-east Brazil

Oxisols are a product of long and intense weathering. Their actual characteristics can neither be traced back to a certain climatic period, nor do they reveal the present soil-forming factors. In this paper, therefore, a reconstruction of the soil genesis of a strongly weathered Oxisol is attempted by comparing the present mineralogical status and the recent dynamics of selected elements with a nearby Inceptisol from the same catena. The parent rock of both soils is serpentinized dunite with nepheline-syenitic veins; the soil moisture regime is udic. Chemical and mineralogical parameters, as well as the concentration of elements in the soil solution of a Typic Haploperox and an Oxic Dystrochrept from the same catena were analyzed for one year. The dynamics of Si and Mg strongly depended on the state of weathering. In the saprolite of the Dystrochrept, Si is partially removed and partially fixed by the formation of quartz and mixed layer minerals. Mg is first fixed in mixed layer minerals, but is during consecutive weathering leached from the transition zone from saprolite to the oxic horizon. Due to the high redox potential, Fe is not soluble, forming goethite in the upper part of the saprolite. Al is also not removed and is finally fixed in kaolinite. In the weathered upper part of both profiles the concentration of Al, Si, Mg and Fe in the soil solution is too low to perceive a further weathering. The present dynamics of Fe, Al, Mg and Si and the mineralogical status of the Dystrochrept indicate that these processes are similar to those that have led to the formation of the Haploperox. The soils, therefore, developed exclusively by the relative enrichment of Al and Fe, the partial loss of Si and the almost complete loss of Mg. Desilification and ‘laterisation’ are hence processes occurring also presently under a tropical rain forest climate.     

Mikrosonden- und Röntgenbeugungs-Untersuchungen an Tonbelägen von lessivierten Böden aus Löß

Microprobe and x-ray diffraction studies of clay coatings in leached soils derived from loess Point analyses of Si, Al, K, Mg, Ca, Fe, Mn, as well as of Zn and Pb of clay coatings in soil thin sections from illuvial horizons of four leached soils were carried out using an electron microprobe (EMA). The K, Mg, Si, and Al content, the Si/Al-molar ratio of coatings and XRD-analyses indicate that the clay coatings consist mainly of illitic clay minerals. This suggests either a mineral-specific displacement of illite or the formation of illitic clay coatings from migrated smectite or expanded illite (“illitization”) through subsequent K uptake. The clay coatings show, with the exception of Fe, Mn, Zn and Pb, only little variation in their chemical composition within the same horizon. Between the horizons of the investigated soils, however, distinct differences in the total element content, especially in the K content may occur. The strong vertical variation of the K content in clay coatings in some horizons is probably due to acidic conditions and lateral infiltration which lead to an increased weathering of illite and the depletion of K. The EMA results show that Pb is predominantly bound in Fe-Mn-Oxide coatings on the surface of clay minerals or in Fe-Mn-Oxide precipitates within clay coatings. Microanalyses of K depleted clay coatings indicate on the other hand an increased fixation of Zn in expanded illites.     

Composition and properties of poorly ordered minerals in Welsh soils. II. Phosphate adsorption and reactivity towards NaF solution

Eleven horizons of acidic soils developed from Lower Palaeozoic sedimentary rocks in mid Wales contained varying amounts of poorly ordered minerals. In nine of these over 70% of the phosphate adsorption capacity was attributed to poorly ordered minerals. Iron oxide with substituted Al, and a separate Al oxide, together accounted for the phosphate adsorption of the poorly ordered fraction. Aluminium-substitution had no major effect on the adsorption capacity of Fe oxide, but since Al occurred in both active minerals it masked the effect of Fe on phosphate adsorption in simple correlations. The relative contribution of the two mineral forms to phosphate adsorption varied widely between soils. Aluminium as a substituent in Fe oxide and in 'free' oxide form was responsible for the soils' reactivity towards NaF, but no distinction could be made between these poorly ordered forms. For certain horizons both poorly ordered Al and Si were correlated with OH⁻ release, but Al oxides were more important than silicates.     

氮、磷、钾肥与酚对漂洗水稻土硅、铝、铁的活化效应

本研究以四川盆地西缘茶区漂洗水稻土为供试土壤,采用浸提试验探讨尿素（N）、磷酸二氢钙（P）、硫酸钾（K）和邻苯二酚（Phy）对其硅、铝、铁的活化效应（以浸提液硅、铝、铁的浓度表征）,结果表明: 1）各种处理浸提液均以硅的浓度最大,铝次之,铁最小,即活化效应为硅＞铝＞铁; 2）浸提液硅的浓度为NPK+Phy＞NPK P＞Phy＞K CK N处理,说明磷肥通过磷酸根的配位吸附对其活化产生最重要的影响,同时酚类物质也通过弱酸作用促进其活化; 3）浸提液铝的浓度为NPK+Phy＞Phy＞P NPK K N CK处理,说明酚类物质通过与游离铝形成可溶性络合物而对其活化起突出作用,同时磷肥中的钙离子和钾肥中的钾离子也能将强酸性供试土壤中大量交换性铝离子交换而活化; 4）浸提液铁的浓度为NPK+Phy＞Phy＞K P NPK CK N处理,说明酚类物质通过络合溶铁、还原溶铁等作用对其活化做出重大贡献,同时钾肥中的钾离子和磷肥中的钙离子也将土壤胶体吸附的亚铁离子交换而活化; 5）尿素对漂洗水稻土硅、铝、铁均无显著活化效应。综上所述,磷、钾肥和酚类物质是漂洗水稻土中硅、铝、铁活化的重要影响因素。     

Mobilization of aluminium, iron and silicon by Picea abies and ectomycorrhizas in a forest soil

Weathering of soil minerals is a key determinant of ground and surface water quality and is also important in pedogenic and rhizosphere processes. The relative importance of biotic and abiotic studies in mineral weathering, however, is poorly understood. We investigated the impact of Picea abies seedlings, an ectomycorrhizal fungus and humic acid on the solubilization of aluminium (Al), iron (Fe) and silicon (Si) in an E horizon forest soil over 10 months. Elemental budgets were constructed based upon losses in drainage water, accumulation in plants and changes in the pools of exchangeable ions. Plants and mycorrhizas or both had a significant effect on the total amounts of Al, Fe and Si mobilized from the soil. Significantly larger amounts of Al and Fe were recovered in plants than those lost in drainage water, whereas the opposite trend was true for Si. The continual addition of dissolved organic matter to the soil in the form of humic acid had an effect only on mobilization of Fe, which increased due to larger plant uptake and an increase in the exchangeable pool. The mobilization of Fe and Si were positively correlated with hyphal length, soil respiration and concentrations of oxalate in the soil solution, and mobilization of Al was strongly correlated with plant weight. Scanning electron microscopy revealed that most fungal hyphae were associated with mineral surfaces with little occupation of cracks and micropores within mineral grains. Evidently ectomycorrhizas have important impacts on mineral dissolution and the chemistry of forest soils.     

Inductively coupled plasma optical emission spectrometric determination of minerals in thyme honeys and their contribution to geographical discrimination

Twenty-four Spanish thyme honey samples were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). Twenty-four minerals were quantified for each honey. The elements Al, As, Ba, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, P, Pb, S, Se, Si, Sr, and Zn were detected in all samples; seven elements are very abundant (Ca, K, Mg, Na, P, S, and Si), and six are not abundant (Al, Cu, Fe, Li, Mn, and Zn). Eleven of them are trace elements (As, Ba, Cd, Co, Cr, Ni, Mo, Pb, Se, Sr, and V) at <1 mg kg(-)(1). Classification of thyme honeys according to their origin (coast, mountains) was achieved by pattern recognition techniques on the mineral data. By means of principal component analysis, a good separation by geographical origin is obtained when scores for the two first principal components are plotted. Classification functions of 11 metals (Al, As, Cr, Cu, K, Li, Mg, Na, P, S, and V) were obtained using stepwise discriminant analysis and applied to classify correctly approximately 100% of the honey samples.     

Microbial degradation of phyllosilicates during simulated podzolization

Perfusion experiments were conducted to study mechanisms in the transformation of phyllosilicates by oxalic acid and other complexing agents synthesized by microorganisms that survived partial sterilization. Those resistant to thymol were mostly non-pigmented Pseudomonas sp. and Bacillus but included a few yeasts. The organic acids formed by the microorganisms dissolved large amounts of mineral elements from samples of granites and granitic sand. Organo-metal complexes were formed with Fe and Al. 70–100% of the dissolved Fe were in complexes stable over a wide range in pH. 10–30% of the dissolved Fe and Al were in very stable anionic complexes that were not exchangeable with strong cationic resins. The acidic compounds that were formed solubilized appreciable amounts of ferromagnesian minerals, mainly biotite, and destroyed primary chlorite and some vermiculite. Under some experimental conditions, illite-vermiculite was transformed into vermiculite and biotite into vermiculite or into a white and brittle residue of Si and Al. Because similar mineral transformations have been shown to occur during podzolization in the field, our experiments are thought to provide a satisfactory model of weathering in that soil-forming process.     

Sesquioxidic components of selected Taiwan soils

Twenty two surface soils, representing six parent materials and four soil groups, were sampled in Taiwan for the present study.Except in the soil derived from volcanic ash, the sesquioxidic components and relatively easily extractable Si were present only in small amounts in the NaOAc and H₂O₂- NaOAc extractable fractions. In addition to Fe, both Si and Al were present in the dithionite-citrate-bicarbonate extracts in considerable amounts, indicating that Si and Al were either present separately or in association with Fe in the sesquioxidic fractions of the soils. The amounts of Si, Al and Fe extracted by the dithionite-citrate-bicarbonate and boiling KOH treatments differed from sample to sample, indicating that they are important variables in the nature of the soils studied.The amounts of the ammonium oxalate-extractable Al and Fe, representing the noncrystalline sesquioxidic products of relatively recent weathering, also differed with parent materials and pedogenic processes. The statistical data indicate that the ammonium oxalate-extractable Al and Fe are related to the contents of organic matter but not to acidity and the contents of clay. The percentage distribution of the extractable Al in the > 2 μm fractions of the selected soil samples ranged from 22.0 to 52.5% and that of the extractable Fe from 11.1 to 38.1%, indicating that the active non-crystalline Al and Fe components in the non-clay fractions deserve close attention in the study of pedogenesis and other soil physicochemical reactions in relation to soil fertility and environmental protection.     

Modelling of sorption experiments and seepage data of an Amazonian Ultisol subsoil under cropping fallow

The results of physico-chemical investigations of an Ultisol subsoil under a 2-year old fallow in eastern Amazonia are presented. Subsoil chemistry was studied using 4 different approaches: i) concentrations of H, Na, K, Ca, Mg, Mn, Al, and Fe in seepage water were measured under field conditions, ii) the equilibrium soil chemistry was studied in sequential batch experiments where the soil was treated with different solutions, iii) results of batch experiments were simulated with a chemical equilibrium model, and iv) the seepage data were calculated using selectivity coefficients obtained by modelling the batch experiments. The model included multiple cation exchange, precipitation/dissolution of Al(OH)₃ and inorganic complexation. Cation selectivity coefficients were pK_x/Ca^sel: X = Na: 0.3, K: 0.8, Mg: ?0.1, and Al: 0.4. The amount of cations sorbed ranged from ?0.2 to 2.0 (K), ?0.7 to 2.3 (Mg), ?1.6 to 1.8 (Ca), ?4.8 to 3.6 (Al) and 0.0 to 8.5 (Na) mmol_c kg^?1. The model predictions were good with values lying within 0.3 pH units (for the pH range 3.7 to 7.2), and 3% of CEC for individual cations. The most important proton buffer reaction seemed to be the dissolution of gibbsite and a large release of Al into the soil solution. When selectivity coefficients obtained by the modelling procedure were used to predict the field data for cation concentrations in the seepage water, they decreased in the following order: Na > K > Ca > Mg > Al. These calculated values were similar to the measured order: Na > Ca > K ≈ Mg > Al. Thus the options for managing these soils should be carefully chosen to avoid soil acidification which may result from inappropriate use of fertilizer during the cropping period.     

Desorption and Transformation of Nitroaromatic (TNT) and Nitramine (RDX and HMX) Explosive Residues on Detonated Pure Mineral Phases

Explosive compounds, including known toxicants 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), are loaded to soils during military training. Their fate in soils is ultimately controlled by soil mineralogical and biogeochemical processes. We detonated pure mineral phases with Composition B, a mixture of TNT and RDX, and investigated the fate of detonation residues in aqueous slurries constructed from the detonated minerals. The pure minerals included Ottawa sand (quartz and calcite), microcline feldspar, phlogopite mica, muscovite mica, vermiculite clay, beidellite (a representative of the smectite clay group), and nontronite clay. Energy-dispersive X-ray spectrometry, X-ray diffraction, and gas adsorption surface area measurements were made of the pristine and detonated minerals. Batch slurries of detonated minerals and deionized water were sampled for 141?days and TNT, RDX, and TNT transformation products were measured from the aqueous samples and from the mineral substrates at day?141. Detonated samples generally exhibited lower gas adsorption surface areas than pristine ones, likely from residue coating, shock-induced compaction, sintering, and/or partial fusion. TNT and RDX exhibited analyte loss in almost all batch solutions over time but loss was greater in vermiculite, beidellite, and phlogopite than in muscovite and quartz. This suggests common phyllosilicate mineral substrates could be used on military training ranges to minimize off-site migration of explosive residues. We present a conceptual model to represent the physical and chemical processes that occurred in our aqueous batches over time.     

Release Kinetics of Si,Al, Fe,and Mn from Acid Soils in the Presence of EGCG

Plant polyphenols can affect soil processes. In the present study, batch experiments were conducted to study the effects of epigallocatechin gallate on the release kinetics of silicon (Si), aluminum (Al), iron (Fe), and manganese (Mn) from acid Anthrosol and Luvisol. The results indicated that the optimal model describing the release kinetics of these elements was a double constant, simple Elovich, or parabolic diffusion equation, and a first-order equation was not suitable. These elements went through an initial rapid-release phase, followed by a slower-release phase. The order of release amounts and rates for Anthrosol was Si > Al > Fe > Mn, but they were different at different phases. However, the order for Luvisol was always Al > Mn > Si > Fe. Meanwhile, the release amount and rate of every element was in the order Luvisol > Anthrosol. The results of this study could help to resolve Al and Mn toxicity in acid soils.