Isolation, identification and toxicity of three strains of Heterocapsa (Dinophyceae) in a harmful event in Fujian, China.

Heterocapsa is a genus of dinoflagellates including species that can form harmful algae blooms (HABs) and cause deleterious ecological effects. To date two species ( H circularisquama and H bohaiensis) are known to be toxic. Here we isolated three strains of Heterocapsa from a multi-species dinoflagellate bloom in the aquaculture area of Fujian, China in June, 2019 that caused mass mortality of farmed abalone. Morphological analysis using light, transmission electron and scanning electron microscopy along with phylogenetic analyses with small (SSU) and large (LSU) subunit rRNA and internal transcribed spacer (ITS) gene sequences showed that these strains were H. cf. niei H. horiguchii, and H. cf. pygmaea, respectively. Furthermore, rabbit erythrocyte assay revealed hemolytic activity in all three strains in cell density dependent fashion, and only in the presence of light. In addition, the strains caused significant mortality of Artemia salina, and the toxicity was also cell density dependent. The Heterocapsa cultures and toxicity information obtained in this study expanded our knowledge of toxic species of Heterocapsa, and will facilitate further investigating the mechanism of their toxicity and developing monitoring tools for their blooms in the future.

Permeability and Equivalent Circuit Model of Ionically Conductive Mortar Using Electrochemical Workstation.

Ionically conductive mortar is a new Portland cement-based construction material prepared by permeating electrolyte solution into porous mortar specimen. The conductive mechanism of ionically conductive mortar is the directional movement of internal free ions under external electric field. Because of the strong electrochemical properties of ionically conductive mortar, electrochemical workstation was used to test the performance of ionically conductive mortar. The open-circuit potential during the permeation process of ionically conductive mortar was tested. The results show that the change of open-circuit potential can effectively reflect the permeability rate of the samples with different porosity and electrolyte mass fraction. Besides the permeation of specimen, electrochemical workstation was also used to test the EIS (electrochemical impedance spectroscopy) of permeated specimens with different porosity, concentration of electrolyte solution, and different kinds of electrolyte solution. The quasi-Randles circuit model was then used to establish an equivalent circuit of ionically conductive mortar. Finally, the relation between parameter of circuit and the porosity or electrolyte solution was established. The test results show that solution resistance of the equivalent circuit and real resistivity of specimens is linearly correlated. This shows the equivalent circuit can effectively reflect the real resistivity of ionically conductive mortar, and the variation of electronic component parameters of equivalent circuit conforms to the conductive mechanism of ionically conductive mortar.

The Influence of Water/Cement Ratio and Air Entrainment on the Electric Resistivity of Ionically Conductive Mortar.

Ionically-conductive mortar can be used for indoor radiant heating partition walls. In these applications, mortar blocks are soaked in electrolyte solutions of CuSO4. The surfaces of the block are coated with sealant and epoxy resin afterwards to prevent evaporation. The mortar block becomes a heating element due to ionic conduction if a voltage is applied to the electrodes in the block. Its electrical conductivity depends on the dispersion of the electrolyte, and hence on the porosity of the mortar. The test specimens in this study were divided into four groups according to the different air entrainment agents, including aluminum powder and hydrogen peroxide as well as two air-entraining agents, SJ-2 and K12. Each group was manufactured with water/cement ratios in the range of 0.5 to 0.9. The test results showed that the conductivity of the mortar was strongly influenced by the air-entrainment and the water cement ratios. The volumetric electric resistivity and the associated microstructures of the mortar were investigated. The test results showed that the specimens made with aluminum powder and a water⁻cement ratio of 0.65⁻0.75 had high porosity. The porosity of those specimens was further increased by adding two different air-entraining agents. The specimens with aluminum powder and SJ-2, along with a water⁻cement ratio of 0.7 appeared to be the optimum mixture. Its resistivity was 19.37 Ω·m at 28 days under 25.31% porosity. The experimental results indicate that an ionically-conductive mortar can be produced by combining different air-entrainment agents with variable water-cement ratios to meet a specified electrical heating requirement.