Increase In Ca Concentration Research Articles

English

Bell pepper (Capsicum annuum L.) experiences significant loss during postharvest handling. This study aimed to provide an alternative postharvest handling technology for the vegetable. The factor studied was Ca CaCl2 at 4 levels: 0% (distilled water), 3, 6 and 9%. Weight loss and total soluble solids were determined at an interval of 3 days whereas total chlorophyll, Fe, ascorbic acid and Ca content were determined at an interval of 4 days. Shelf life elapsed when fruit lost 25% of their initial weight. Calcium CaCl2 reduced weight loss by up to 16.7%, increased Ca content by up to 252.7%, maintained total soluble solids by up to 11.8%,  total chlorophyll by up to 23.3%, Fe by up to 10.1%, ascorbic acid by up to 13.9% and Ca content by up to 13.7% and extended shelf life by up to 3 days. Calcium CaCl2 at 6% was the best treatment and therefore can be used by bell pepper growers, retailers and consumers to maintain postharvest quality of bell pepper. Key words: Chemical treatment, fruit vegetable, fresh weight loss, ascorbic acid.

Effect of Ca content on biomineralization of Mg-Ca alloys

The mechanical and physical properties of biodegradable Mg-based alloys make them suitable for temporary orthopaedic implants. However, processing them in such a way that it degrades at the required rate in physiological environment is a challenge. Among the possible methods, in situ formation of calcium phosphate (CaP) during service to control the degradation rate is least explored. The CaP formation can be improved by enhancing the biomineralization of Mg alloys. The present work investigates the effect of Ca concentration (0, 0.5, 1, and 2 wt.%) on the biomineralization of Mg-Ca alloys. Optical microscopy observations and X-ray diffraction analysis showed that Mg-xCa (x = 0.5, 1 & 2 wt. %) alloys were composed of two phases, α-Mg and Mg2Ca. The electrochemical corrosion test in biomimetic NaCl solution and immersion test in simulated body fluid shows that the corrosion rate increases as Ca content increases. The studies reveal that a low calcium content single-phase microstructure is preferred over a multiphase morphology for promoting biomineralization.

Therapeutic Strategies and Metal-Induced Oxidative Stress: Application of Synchrotron Radiation Microbeam to Amyotrophic Lateral Sclerosis in the Kii Peninsula of Japan.

A series of extensive gene-environment studies on amyotrophic lateral sclerosis (ALS) and Parkinsonism–dementia complex (PDC) in Guam Island, USA, and the Kii Peninsula of Japan, including Auyu Jakai, West New Guinea, have led us to hypothesize that a prolonged low calcium (Ca) and magnesium (Mg) intake, especially over generation, may cause oxidative stress to motor and nigral neurons by an increased uptake of environment metallic elements, i.e., aluminum (Al), manganese (Mn), and iron (Fe). Otherwise, 5–10% of total ALS cases are familial ALS (fALS), of which 20% of the fALS cases linked to a point mutation of Cu/Zn superoxide dismutase (SOD1). In the vicinity of the Kii Peninsula, about 7% of the ALS cases are also linked to the SOD1 mutation. Using synchrotron radiation (SR) microbeam, conglomerate inclusion (SOD1 aggregates) within a spinal motor neuron of the fALS case in the vicinity revealed a loss of copper (Cu) in contrast to extremely high contents of Zinc (Zn) and Ca. That means an exceptionally low Cu/Zn ratio with an increased Ca content, indicating the abnormalities of the active site of SOD1 protein of the fALS. Furthermore, sALS in the southernmost high incidence areas of the Kii Peninsula showed a low Cu/Zn ratio within a motor neuron, suggesting a fragility of SOD1 proteins. From the perspective of gene–environment interactions, the above two research trends may show a common oxidative stress underlying the neuronal degenerative process of ALS/PDC in the Kii Peninsula of Japan. Therefore, it is a crucial point for the prospect of therapeutic strategy to clarify a role of transition metals in the oxidative process in both ALS/PDC, including ALS elsewhere in the world. This paper reviews a history of the genetic epidemiological studies, especially from the aspect of gene–environment interaction, on ALS/PDC in the Kii and Guam high incidence foci and the results of a series of analytical research on trace metallic elements within neurons of both sALS and fALS cases, especially using a synchrotron radiation (SR) microbeam of Spring-8 and Photon Factory of Japan. The SR microbeam is an ideal X-ray source, which supplies an extremely high brilliance (high-intensity photon) and tunability (energy variability) to investigate trace metallic elements contained in biological specimens at the cellular level, even more without any damages. This research will provide a valuable information about the mechanism of oxidative stress involved in neuronal cell death in ALS and related neurodegenerative disorders. To elucidate the physicochemical mechanism of the oxidative process in neuronal degeneration, it will shed a new light on the therapeutic strategies for ALS/PDC in near future.

Assessment of the Applicability of Ca-Based Sorbents for Arsenic Removal from Flue Gases

Arsenic is one of the most hazardous compounds released into the atmosphere from coal conversion processes. One possibility to limit its amount in the flue gas is to inject dusty sorbents directly into the flue gas duct. The aim of this study was to analyze the removal efficiency of gaseous forms of As on selected Ca-based materials, with a focus on sorbents based on waste materials versus traditionally used sorbents. Coal combustion byproducts, waste (such as filter cake, fly ash, and gypsum), sedimentary rocks (dolomite and limestone), and chemical reagents like Ca(OH)2, Fe2O3, and Mg(OH)2 were examined in the quartz retort in a heated furnace where the temperature of the sorbent bed was 120 °C. The source of Asgas was the direct combustion of coal at 1200 °C. Among the tested materials, calcined limestone, calcined dolomite, Fe2O3, Mg(OH)2, and Ca(OH)2 were the most effective (removal efficiency: 85–98%). In the case of waste materials, the highest efficiency was obtained for filter cakes. However, because of their high content of toxic elements, they could be used as sorbent only after thermal preparation at 250 °C. Furthermore, the analyses showed that an increased Ca concentration in the sorbent may promote Asgas adsorption more than the development of the sorption surface area.

CO conversion over LaFeO3 perovskite during chemical looping processes: Influences of Ca-doping and oxygen species

As a critical intermediate substance or a target product, CO plays a vital role in the chemical looping processes. The control of CO conversion is significant since chemical looping processes with various target products have different requirements for CO content. In the present work, the CO oxidation behaviors with different oxygen species were investigated experimentally and theoretically with Ca-substituted lanthanum ferrite (LaFeO3) as the oxygen carrier to regulate the CO conversion. The results showed that the CO2 yield increased significantly when the adsorbed oxygen species was removed, suggesting that the lattice oxygen was the active oxygen species. It was consistent with the calculation result that the energy barrier of CO oxidation with lattice oxygen was lower than that with surface adsorbed oxygen. Moreover, the CO2 yield increased with the increase of Ca concentration, indicating that Ca doping was favorable for lattice oxygen migration and further promoted CO oxidation.

Copper mobilization via seawater-volcanic rock interactions: New experimental constraints for the formation of the iron oxide Cu-Au (IOCG) mineralization

The involvement of modified seawater and/or basinal brine in IOCG mineralization was documented by numerous geologic studies. Still, this process remains poorly understood. In this study, we reacted seawater with andesite and basalt, the most common arc volcanic rocks, at 150 and 240 °C and water vapor-saturated pressure to assess the Cu leaching capacity and fluid evolution due to the seawater-volcanic rock interactions. The experimental results show that Mg, Fe, Al, and SO42− in the modified seawater decreased significantly, accompanied by an increased Ca concentration. The fluid pH also decreased from 8.3 of the initial seawater to ∼7.5 and ∼7.0 after 150 and 240 °C experiments, respectively. The incongruent calcsilicate (e.g., plagioclase) dissolution and anhydrite precipitation were observed in the reacted rock samples. Thermodynamic modeling confirmed the trends of those concentration changes but predicted several alteration minerals that were not observed in the experiments. Our experiments show that Cu-leaching efficiency is much higher from the andesite than from the basalt, also higher at 240 °C than at 150 °C. The andesite contains more Cu than the basalt samples, and abundant Cu-rich (average 106 ppm) plagioclase-hosted silicate melt inclusions and Cu-bearing (average 59 ppm) groundmass are identified in the original andesite sample but not in the original basalt sample, which is considered to be the cause of the Cu-leaching differences between the two rock samples. The δ34S value of resultant fluids is dominated by seawater sulfate with a minor contribution of magmatic sulfur from the rock. Thermodynamic modeling combined with recent experimental studies show that deposition of Cu sulfides is the most effective when Cu-bearing fluids react with early-stage pyrite. Our results suggest that the seawater/(brine)-volcanic rock reactions at 150–250 °C can produce Cu-bearing fluids, which in turn can form IOCG deposits, and that Cu mineralization with sulfides zonation can result from replacement reactions between the Cu-bearing fluids and Fe-rich minerals in precursor iron ore bodies.

Enhanced ferroelectric and piezoelectric characteristics in Ca-substituted BaTi0.88Zr0.12O3ceramics

In this work, Ba[Formula: see text]Ca[Formula: see text]Ti[Formula: see text]Zr[Formula: see text]O3 ([Formula: see text]= 0.00–0.25) ceramics were prepared by a solid-state reaction method, and the variation of dielectric, ferroelectric and piezoelectric characteristics has been investigated together with the structure evolution. The crystal structure varies from rhombohedral to tetragonal at room-temperature and the morphotropic phase boundary (MPB) is determined around [Formula: see text]= [Formula: see text]0.10, where the significantly enhanced ferroelectric and piezoelectric properties are achieved. With the increase of Ca content, the system gradually evolves into a relaxor ferroelectric. This work provides useful guidance for future research on lead-free piezoelectric materials.

Nanosecond Pulsed Electric Field (nsPEF): Opening the Biotechnological Pandora's Box.

Nanosecond Pulsed Electric Field (nsPEF) is an electrostimulation technique first developed in 1995; nsPEF requires the delivery of a series of pulses of high electric fields in the order of nanoseconds into biological tissues or cells. They primary effects in cells is the formation of membrane nanopores and the activation of ionic channels, leading to an incremental increase in cytoplasmic Ca concentration, which triggers a signaling cascade producing a variety of effects: from apoptosis up to cell differentiation and proliferation. Further, nsPEF may affect organelles, making nsPEF a unique tool to manipulate and study cells. This technique is exploited in a broad spectrum of applications, such as: sterilization in the food industry, seed germination, anti-parasitic effects, wound healing, increased immune response, activation of neurons and myocites, cell proliferation, cellular phenotype manipulation, modulation of gene expression, and as a novel cancer treatment. This review thoroughly explores both nsPEF’s history and applications, with emphasis on the cellular effects from a biophysics perspective, highlighting the role of ionic channels as a mechanistic driver of the increase in cytoplasmic Ca concentration.

Effect of calcium doping on structural, magnetic and magneto-caloric properties of La0.55CaxSr0.45-xMnO3 manganites

Effect of calcium (Ca) doping on structural, magnetic and magnetocaloric properties of calcium-strontium doped lanthanum manganite La0.55CaxSr0.45-xMnO3 (x = 0.00, 0.05, 0.1, 0.25) prepared by solid state reaction technique has been reported in this paper. Room temperature XRD measurements reveal rhombohedral structure for all the samples. Microstructural analysis have been done by the field emission scanning electron microscopy and elemental compositions are determined by energy dispersive X-ray diffractometer. It is observed that the lattice parameters as well as Mn-O-Mn bond angle are decreased with increasing Ca content which has changed the magnetic and magnetocaloric properties and tuned Curie temperature (TC) toward the room temperature. Magnetization measurement as a function of temperature reveals a reduction of magnetic saturation and decrease in Curie temperature from 354 K to 311 K with increase in Ca content from 0.00 to 0.25, respectively. A second order ferromagnetic to paramagnetic phase transition is noticed from their Arrots plots. The magnetocaloric effect is calculated in terms of entropy change and relative cooling power from the isothermal magnetization measurements around TC using Maxwell’s thermodynamic relations. The maximum entropy change and relative cooling power are observed to be decreased while TC shifted toward the room temperature with increase in Ca content in our studied polycrystalline manganite.

The corrosion characteristics and mechanism of directionally solidified Mg-3Zn-xCa alloys

An investigation into the corrosion characteristics and mechanism of directionally solidified (DSed) Mg-3Zn-xCa (x = 0, 0.2, 0.5, 0.8 wt.%) alloys in 0.9 wt.% NaCl solution is presented. The DSed microstructure consists of columnar dendrites and eutectics distributed in the interdendritic region. The primary dendritic arm spacing (PDAS) and the volume fraction (fv) of the secondary phases are under the significant impact of the content of Ca. The corrosion rates evaluated using electrochemical measurements and immersion tests are accelerated monotonously with the increase of Ca content in DSed alloys. The corrosion resistance of the DSed alloys is significantly affected by the corrosion products film (CPF) and the secondary phases. The corrosion products of DSed Mg-3Zn alloy contain Mg(OH)2 and ZnO. The existence of ZnO greatly enhances the corrosion resistance of DSed Mg-3Zn alloy. As for the DSed alloys containing Ca content, a relatively protective CPF without deep pits can form on the surface of DSed Mg-3Zn-0.2Ca specimen during the corrosion. The fv of the secondary phases dominates the corrosion rate of the DSed Mg-Zn-Ca alloys. The corrosion of DSed Mg-3Zn-xCa alloys initiates as a result of micro-galvanic coupling between the cathodes of secondary phases and α-Mg matrix anode. Then, the corrosion gradually extends longitudinally with the breakdown of CPF.

Reaction mechanism between MgO crucible and AerMet100 steel during vacuum induction melting

AerMet100 steel has strict composition and inclusion requirements. Therefore, its reaction with MgO refractory during vacuum induction melting cannot be ignored. In this study, the reaction mechanism between the MgO refractory and AerMet100 steel during the refining stage was investigated using a MgO crucible. The influence of the MgO crucible on AerMet100 steel composition and inclusions under refining vacuum pressures of 50–100 and 5–10 Pa was compared. The results indicate that SiO2, Al2O3, and MgO in the crucible decompose and are reduced by C in the liquid steel, which results in the increase of Si, dissolved Al (Als), and dissolved Mg (Mgs) content in the liquid steel. The increase of Ca content is due to the reduction of CaO in the crucible by C in the liquid steel. The reaction of Al2O3 inclusions and Mgs in the liquid steel is the primary generation method of MgO·Al2O3 spinel inclusions. As the Mgs content in the liquid steel increases, Al2O3 inclusions transform into MgO·Al2O3 spinel inclusions along the path Al2O3 + Mgs → Al2O3 with a small amount of MgO + Mgs → MgO·Al2O3 spinel. In contrast, the vacuum pressure of 50–100 Pa is more effective at controlling the composition and inclusions of AerMet100 steel and is a more appropriate choice for the refining vacuum pressure.

Hydroxyapatite nanoparticles promote mitochondrial-based pyroptosis via activating calcium homeostasis and redox imbalance in vascular smooth muscle cells

Hydroxyapatite nanoparticles (HAP) have been widely used in various fields because of their natural biological origin and functional properties. The emerging evidence on their toxicities has attracted research interest. HAP-induced vascular smooth muscle cell (VSMC) damage is a key step in vascular calcification (VC), particularly in patients with chronic kidney disease. However, the injury effects and mechanism of action of HAP on VSMCs have not been extensively investigated. This study comprehensively characterized commercially available HAP and investigated its adverse biological effects in cultured A7R5 cells. In vitro experiments revealed that internalized HAP was localized in lysosomes, followed by the release of Ca2+ owing to the low pH microenvironment. Upon Ca2+ homeostasis, Ca2+ enters the mitochondria, leading to the simultaneous generation of reactive oxygen species (ROS). ROS subsequently attack mitochondrial transmembrane potentials, promote mitochondrial ROS production, and oxidize mitochondrial DNA (Ox-mtDNA). Mitochondrial permeability-transition pores open, followed by the release of more Ox-mtDNA from the mitochondria into the cytosol due to the redox imbalance. This activates NLRP3/caspase-1/gasdermin D-dependent pyroptosis and finally excretes inflammatory factors to induce VC; an antioxidant could rescue this process. It has been suggested that HAP could induce an imbalance in intracellular Ca2+ homeostasis in A7R5 cells, followed by the promotion of mitochondrial dysfunction and cell pyroptosis, finally enhancing VC. To detect the in vivo toxicity of HAP, mice were treated with Cy7-labelled HAP NPs for 24 h. In vivo results also demonstrated that HAP accumulated in the kidneys, accompined with increased Ca concentration, upregulated oxidative stress-related factor and kidney damage. Overall, our research elucidates the mechanism of calcium homeostasis and redox imbalance, providing insights into the prevention of HAP-induced cell death.

Soil properties and grape yield of vineyard as affected by sawdust addition in a semi-arid region

Due to its high organic matter content, sawdust can be used for soil amendment. This study investigated the effect of sawdust obtained from a furniture industry (Yildiz Integre Akhisar flakeboard) on grape yield and loam texture soil (Typic Xerofluvent) properties of a vineyard located in Saruhanlı District, Manisa, Turkey. In the trial, three groups with dry sawdust (10 t ha-1, 20 t ha-1; 30 t ha-1) was added to plots of vineyard while 0 t ha-1 or without sawdust addition was set up as a control group. All the 4 treatments were replicated three times (4×3). Sawdust addition resulted in significant increase (p <0.05) of soil organic matter, total nitrogen, electrical conductivity (EC), available Na, Ca, Mg, Fe, Zn, P, K, and Mn contents, moisture, saturation percentage, field capacity, wilting point, available water and aggregation percentage values compared with control group. Also, the soil pH, bulk density, and dispersion percentage significantly decreased with sawdust addition. However, there was no significant change in lime, available Cu contents, structure stability index, aggregate stability of the soil with sawdust addition. Compared with control group, addition of 20 t ha-1 and 30 t ha-1 of dry sawdust significantly increased the grape yield of the vineyard. The highest yield of 4.23 t ha-1 was recorded with 30 t ha-1 sawdust addition. Sawdust can be used as a soil amendment given its positive effects on some soil properties and grape yield of the vineyard. It is suggested that nitrogen immobilization from the soil by microorganisms due to sawdust’s high C/N ratio is a key consideration for its future use.

Enrichment of drinking water with Ca and Mg by a fluidized bed recarbonization reactor: a case study of Devičie, Slovak Republic.

A low content of Ca and Mg in drinking water causes increased health risks. To increase the Ca and Mg contents in the drinking water supplied to the inhabitants of the village of Devičie, a prototype of a fluidized bed recarbonization reactor (RRF) was proposed and tested. A half-burnt dolomite (HBD) was used for the recarbonization. In the RRF, the HBD is kept in buoyancy with the help of water circulation. The capacity of the circulation pump is up to 5 m3 h-1 and the volume of discharged concentrate, which is added directly to the water source, is up to 0.2 m3 h-1. The volume of water circulated between the reactor and the circulating tank is many times higher than the volume of discharged water. In 24 h, the Ca and Mg contents stabilized at an equilibrium value of 80 mg L-1 for Ca and 120 mg L-1 for Mg, which corresponded to the equilibrium of formation and removal of ions from the system. The concentrate was diluted with the water in the reservoir at a ratio of 1:10, and it achieved the desired increase in Mg and Ca contents by more than 10 and 6 mg L-1, respectively.

Liming in soils with plinthic materials of the Brazilian Savanna: potentials and limitations

The expansion of agriculture has been taking place in marginal soils with low productive potential, such as Plinthosols. The liming can increase the economic and environmental sustainability of agriculture. However, there are no studies on the dissolution or recommendation of limestone for Plinthosols. The objective was to evaluate the effect of limestone doses on the chemical attributes of three soils with different gravel contents (ironstone concretions). The soils were collected (0-20 cm layer) in native areas of the central region of the Brazilian Savanna. They were classified as Red-Yellow Latosol (RYO) and two Concretionary Pétric Plinthosol (with 29% [CPP-29] and 72.8% [CPP-72] of soil volume with gravel). A factorial scheme (3x6) with the three soils (RYO, CPP-29, and CPP-72), six limestone doses, and four replications. The evolution of pH was verified at 10, 20, 30, and 40 days after the beginning of incubation (DAI), and determined the chemical attributes (Al, H+Al, Ca, Mg, BS, V%, P, and K) at 40 DAI. The doses to reach pH 6 were 1.4 t ha-1 for RYO, 3.9 t ha-1 for CPP-29, and 2.7 t ha-1 for CPP-72. Al3+ neutralization was 100% with doses above 3.5, 2.5 and 0.5 t ha-1 for CPP-29, CPP-72, RYO. There was a significant increase in Ca and Mg contents in all soils. However, the Soil CPP-72 did not reach a critical level for Ca (&gt;2.41 cmolc dm-3) and Mg (&gt;0.91 cmolc dm-3) for Plinthosols with higher plinthite content. Thus, we recommend using agricultural practices that increase the capacity of the soil to retain and recycle nutrients.

Effect of the Ca2Mg6Zn3 Phase on the Corrosion Behavior of Biodegradable Mg-4.0Zn-0.2Mn-xCa Alloys in Hank's Solution.

The effect of the Ca2Mg6Zn3 phase on the corrosion behavior of biodegradable Mg-4.0Zn-0.2Mn-xCa (ZM-xCa, x = 0.1, 0.3, 0.5 and 1.0 wt.%) alloys in Hank’s solution was investigated with respect to phase spacing, morphology, distribution and volume fraction. With the increase in Ca addition, the volume fraction of the Ca2Mg6Zn3 phase increased from 2.5% to 7.6%, while its spacing declined monotonically from 43 μm to 30 μm. The Volta potentials of secondary phases relative to the Mg matrix were measured by using scanning kelvin probe force microscopy (SKPFM). The results show that the Volta potential of the intragranular spherical Ca2Mg6Zn3 phase (+109 mV) was higher than that of the dendritic Ca2Mg6Zn3 phase (+80 mV). It is suggested that the Ca2Mg6Zn3 acted as a cathode to accelerate the corrosion process due to the micro-galvanic effect. The corrosion preferred to occur around the spherical Ca2Mg6Zn3 phase at the early stage and developed into the intragranular region. The corrosion rate increased slightly with increasing Ca content from 0.1 wt.% to 0.5 wt.% because of the enhanced micro-galvanic corrosion effect. The decrease in the phase spacing and sharp increase in the secondary phase content resulted in a dramatic increase in the corrosion rate of the ZM-1.0Ca alloy.

Structural, elastic and magnetic properties of Ca doped copper ferrite nanoparticles

Calcium doped Copper ferrite (CaxCu1-xFe2O4, x = 0.0, 0.1, 0.2, 0.3) nanoparticles were prepared by co-precipitation method. The effect of calcium doping in structural, elastic and magnetic properties of copper ferrite were explored by X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared (FTIR), and Vibrating Sample magnetometer (VSM). X-ray diffraction verified the single phase cubic spinel structure and hematite phase also present in x = 0.02 with the space group Fd3m. The average crystallite size ranged in 44–58 nm and increased with increasing Ca concentration. Scanning electron microscope images showed that the ferrite particles seem in spherical shape with agglomeration. The Fourier transform infrared spectrum showed the two main absorption bands of spinel structure in the wavenumber scale of 476–576 cm−1 assigned to the stretching vibration of A and B sites. The three types of moduli of elasticity, Poisson's ratio, velocities of elastic waves and Debye temperature estimated using FTIR. Vibrating Sample magnetometer exhibited the room temperature ferromagnetic behavior and coercivity decreases with Ca concentration while saturation magnetization increases.

Response of acid forest soils to helicopter liming in the Monongahela National Forest, West Virginia

AbstractTypical of soils in humid climates, soils in the Monongahela National Forest (MNF) in West Virginia are acidic because of leaching of base cations, uptake of Ca and Mg by vegetation, and release of organic acids by organic matter (OM) decomposition. Soil acidity has increased because of anthropogenic acid deposition causing declines in forest health. In anticipation of a large‐scale liming project in the MNF, soils at 10 sites were sampled and analyzed in 2009. In 2018, lime was applied by helicopter to a total of 323 ha at a rate of 10 Mg ha−1. One year after liming, soils were resampled and analyzed in 2019 representing five limed and five unlimed areas using the same procedures. The objectives were to determine whether unlimed soils had changed between 2009 and 2019 and to evaluate changes in soils resulting from liming in 2019 for pH, acidity, and Al and Ca concentrations. In O and A horizons, unlimed soils had changed only slightly in the 10‐yr interval. Liming increased soil pH in O horizons from 4.6 to 5.9. Liming reduced acidity values by 73% and Al concentrations by 80% in O horizons. Liming increased Ca concentrations by at least three times in O and A horizons. Based on first‐year results, liming had a significant effect on soil properties of O and A horizons. Future sampling at 3 and 5 yr after liming will help to evaluate further changes in soils as a result of liming and under reduced acid deposition rates.

Compressive fatigue behaviors of ultra-high performance concrete containing coarse aggregate

In this work, the uniaxial compressive fatigue behaviors of ultra-high performance concrete containing coarse aggregate (UHPC-CA) were investigated, towards a better understanding of the role of CA on its fatigue responses. Upon the constant amplitude fatigue tests performed at three stress levels (i.e. S = 0.7, 0.8, and 0.9), the emphases were focused on the effects of CA content (10%, 20%, and 30%) on the failure pattern, deformation characteristics, fatigue life, failure mechanism, and damage evolution. The results showed that compared to the UHPC specimen free of CA, the crack propagation, strain development, and fatigue life of UHPC-CA specimens are largely affected by the CA incorporation, due to the introduction of weak interfacial transition zones and the interference of fiber distribution. As a result, the risk of premature fatigue failure of UHPC-CA will be generally amplified as the CA content increases. Furthermore, inspired by the experimental observation that the fatigue failure strain of UHPC-CA stably approaches the descending branch of the monotonic stress-strain curve, a modified model based on the strain development instead of highly scattered fatigue life was proposed to estimate the nonlinear evolution of the fatigue damage. The good agreements with independent test results demonstrated the applicability of the model, representing a compromise between accuracy and practicability.

Implications of Major and Trace Element Migration in Altered Granites for Hydrothermal Alteration and Granite-Related Uranium Mineralization in the Sanjiu Ore Field, South China

The recently discovered Sanjiu ore field (SJOF) is a granite-related uranium ore field located in the middle of Zhuguangshan (South China). The relationship between hydrothermal alteration of granite and uranium mineralization in the SJOF is crucial yet understudied. In this study, the major- and trace-element contents of granite samples (fresh granite, altered granite, and tectonites) with different uranium contents were analyzed by using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma–mass spectrometry (ICP–MS). The analytical results show a relative increase in Si, S, Ca, Pb, Mo, and Sb content in altered granites and tectonites, relative to fresh granites. During the mineralization stage, the increase of the aforementioned elements is related to various hydrothermal alterations (e.g., silicification, carbonation, sulfation, etc.) and newly formed minerals (e.g., microfine crystalline quartz veins; calcite agglomerates or fine veins; and metal sulfides, such as pyrite). There is a concomitant relative decrease in Na, K, Al, Fe, Mg, and other elemental contents that may be due to mineralogical alteration processes, such as biotite to chlorite, feldspar-group minerals to clay minerals, and redox of Fe-bearing minerals. The LREE/HREE ratio in altered granites decreases significantly with the increase in uranium content, suggesting that a low LREE/HREE ratio may be a prospecting indicator. The normalized trace-element patterns of mineralized granite (ore) and the relatively high U content of fresh granite imply that granitic rocks may be the primary uranium source in the SJOF. The uranium mineralization is mainly concentrated in the redox zone that occurs at a depth of 100−300 m. The redox zone is characterized by the most developed hydrothermal alterations and enrichment of trace elements, including W, Mo, Sb, Li, and the HREE.