Lamellar Shape Research Articles

Lamellar magnetism and exchange bias in billion-year-old metamorphic titanohematite with nanoscale ilmenite exsolution lamellae – III. Atomic-magnetic basis for experimental results

SUMMARY Lamellar magnetism is a source of remanent magnetization in natural rocks different from common bulk magnetic moments in ferrimagnetic minerals. It has been found to be a source for a wide class of magnetic anomalies with extremely high Koenigsberger ratio. Its physical origin are uncompensated interface moments in contact layers of nanoscale ilmenite lamellae inside an hematite host, which also generate unusual low-temperature (low-T) magnetic properties, such as shifted low-T hysteresis loops due to exchange bias. The atomic-magnetic basis for the exchange bias discovered in the hematite-ilmenite system is explored in a series of papers. In this third article of the series, simple models are developed for lamellae interactions of different structures when samples are either cooled in zero-field, or field-cooled in 5 T to temperatures below the ordering temperature of ilmenite. These models are built on the low-temperature measurements described earlier in Paper II. The important observations include: (i) the effects of lamellar shapes on magnetic coupling, (ii) the high-T acquisition of lamellar magnetism and low-T acquisition of magnetization of ilmenite lamellae, (iii) the intensity of lamellar magnetism and the consequent ilmenite magnetism in populations of randomly oriented crystals, (iv) lattice-preferred orientation of the titanohematite host crystal populations and (v) the effects of magnetic domain walls in the host on hysteresis properties. Based on exemplary growth models of lamellae with different geometries and surface couplings we here provide simple models to assess and explain the different observations listed above. Already the simplified models show that the shapes of the edges of ilmenite lamellae against their hematite hosts can control the degree of low-T coupling between ilmenite, and the lamellar magnetic moments. The models also explain certain features of the low-T exchange bias in the natural samples and emphasize the role of lattice-preferred orientation upon the intensity of remanent magnetization. The inverse link between ilmenite remanence and exchange-bias shift in bimodal low-T ilmenite lamellae is related to different densities of hematite domain walls induced by the clusters of ilmenite lamellae.

Effects of heating temperature on pore structure evolution of briquette coals

Coal and gas outburst disasters mainly occur in geological structure belts, whose outburst coals are cataclastic, granular, or mylonitic microstructures, and their texture is loose, with mostly broken grain and pieces, so that it they hardly meet the laboratory specimen requirements. Consequently, briquettes are usually prepared at room temperature to study the mechanisms of coal and gas outburst in coal mines. In the present study, we employed a novel method of heating on briquette coal samples to investigate the effect of heating temperature on the strength and pore and fracture structure of briquette coals, and to determine the suitable heating temperature for briquette forming processes. A rock mechanics test system, MTS-815, scanning electron microscopy, nuclear magnetic resonance, and specific surface area and aperture analyzer measurements were used to analyze the mechanical parameters, morphology, and pore size distribution of briquette coal samples at different heating temperatures. The results indicate that the uniaxial compressive strength and elastic modulus of briquette coal first increased and then decreased. The pore size distribution and morphology of the briquette coal samples changed after heating. The smooth intact lamellar shape changed to a rough fractured lamellar shape, and the pores changed from unobvious micropores to observable mesopores and macropores. With an increase in the heating temperature, the transverse relaxation time spectra of the briquette coal samples decreased gradually, and both the porosity of the mesopores and macropores first increased, decreased, and then increased again. The pore diameter distributions of the five tested briquette coal samples had similar pore structures, excluding the sample heated to 600 °C. With an increase in heating temperature, pore volume, specific surface area, and average pore diameter of the briquette coal samples first decreased and then increased. The present study provides a novel method that can be applied in physical simulations aimed at preventing future disasters caused by coal and gas outburst in coal mines.

Analysis of defects in a twin roll cast Mg‐Y‐Zn magnesium alloy

AbstractTwin roll casting (TRC) enables the production of magnesium strips in an economic manner. TRC has enormous potential for the production of thin strip material from magnesium alloys. However, a range of defects may arise during casting. Internal and surface defects also influence the final properties of TRC strips. In this work, the magnesium alloy Mg‐6.8Y‐2.5Zn‐0.4Zr (WZ73) containing long‐period stacking ordered (LPSO) structures was twin roll cast with different process parameters, and the defects that arose were investigated. In particular, defects such as surface bleeds, center‐line segregations and deformation segregations in the mid‐thickness of the strip were observed and analyzed with regard to the TRC parameters applied. The latter may have developed due to the solidification of solute‐rich liquid in the center of the strip. X‐ray diffraction analysis was carried out to determine the phase compositions within the casting defects. A (Mg,Zn)3Y phase was found to precipitate in a blocky or lamellar shape within large, plate‐like LPSO phases. Wavy lines resulting from high specific rolling forces can be avoided if specific rolling force does not exceed a value of 8 kN/mm. Casting speed of 1.5 m/min has proven to be favorable to prevent the occurrence of center‐line segregation.

Restoring mechanism of mechanical properties of recycled polyethylene pellet moldings by a\xa0repelletizing treatment using a twin-screw extruder

To develop material-recycling processes for used plastic products, it is necessary to design new material-recycling techniques to optimize the mechanical properties of the recycled plastics since the mechanical properties of recycled plastic products are normally deteriorated. In this study, we suggest one of the approaches that is a repelletizing treatment for improving the mechanical properties of recycled-polyethylene moldings using a twin-screw extruder. The results of the tensile test revealed the significant effect of the repelletizing treatment on the tensile performance of the recycled-polyethylene moldings. The tensile performance of the repelletized recycled-polyethylene moldings was significantly higher than that of the original recycled-polyethylene moldings under specific repelletizing conditions. The analysis of the polymeric structures revealed the significant effect of the repelletizing treatment on the secondary and higher-order structures such as the lamellar shape, aggregation of the crystal domains, amorphousness, and polyethylene chain conformation in the recycled-polyethylene moldings. The repelletizing treatment increased the tensile performances by optimizing the internal structure of the recycled-polyethylene moldings. The results confirmed the efficacy of the repelletizing treatment to optimize the mechanical performance of the recycled-polymer materials, thereby facilitating the reuse of waste plastics as value-added materials for various industrial applications.

Alterations in gills and intestine of Danio rerio after exposure to acaricide yoksorrun-5EC (hexythiazox): histopathologic and morphometric evaluation

In this study, histopathological and morphological changes in gill and intestinal tissue of zebra fish exposed to acaricide yoksorrun were aimed to determine. Yoksorrun was applied to the experimental groups as 0.01 mL/L, 0.02 mL/L, and 0.03 mL/L. Histopathological findings which showed a parallel increase with the amount of exposure in the gill were determined. In the gills, disruption of lamellae shape, shortening and breakage of primary and secondary lamellae, edema, fusion, and separation in the secondary lamellae epithelium, hyperplasia were observed. In the intestine tissue of some groups, advanced necrosis at the tip of the villi and deterioration of the overall integrity of the villi in these regions, epithelial hyperplasia, increasing in eosinophilic cells in the submucosa, and dissolution in muscle fibers of tunica muscularis were observed. In the morphometric analysis of the gills, a significant decrease in gas exchange (PAGE) percentages (p < 0.0001) was observed in the experiment group compared to the control group. Compared to the control group, a significant decrease in the interlamellar distance and secondary lamellar length measurements of the gills and a significant increase in the secondary lamellar width measurement were observed. In basal epithelial thickness measurement, the result was insignificant between the groups. According to the results of the morphometric analysis of the intestine, a significant decrease in musculus externa was observed only in the group 2. In total wall thickness, there was a significant thinning (p < 0.0001) in all experimental groups. There was a significant shortening of the villi length (p < 0.0001) and a significant increase (p < 0.0001) in the villus width only in the group 2 and group 3. A significant increase in epithelial thickness after application was observed (p < 0.0001) in all groups compared to the control group. Based on the findings, it was decided that the living in the aquatic ecosystem would be adversely affected by this acaricide if exposed.

Synergistic effect of pH solution and photocorrosion of ZnO particles on the photocatalytic degradation of Rhodamine B

This research aims to study the synergistic effect of pH solution and photocorrosion of ZnO particles on the photodegradation of Rhodamine B (RhB) dye. The stability of ZnO particles was investigated by zeta potential measurement. The structure, morphology and photocatalytic activity of ZnO were analysed by X-ray diffraction, scanning electron microscope and ultraviolet–visible spectrophotometer, respectively. The ZnO particles were highly crystalline with a bandgap energy of 3.23 eV. The surface charges of particles were found to be pH-sensitive, where they were more negative under alkaline condition, i.e., −11.1, −5.3 and −38.2 mV at pH 3, 7 and 11, respectively. ZnO particles that dissolved in pH 3 solution produce Zn2+ ions, while precipitation of Zn(OH) 4 2− was observed in pH 11 solution, resulting in morphology change of ZnO from rod shape to lamellar shape . The synergistic effect of photocorrosion and dissolution of ZnO particles in acidic solution reduced RhB dye removal efficiency from ~90% at pH 7 to ~70% at pH 3. In alkaline solution, ZnO particles displayed remarkable reusability as it still recorded a 94.8% degradation efficiency after five successive cycles.

The Effect of Electron Beam Welding on the Microstructure and Microhardness of 3D-Printed Products from Titanium Alloy Ti–6Al–4V

The microstructure of double-sided welded joints of 3D-printed items made of titanium alloy Ti‒6Al–4V by the electron-beam freeform fabrication (EBF3) method has been investigated using the methods of X-ray diffraction analysis, optical metallography, and scanning and transmission electron microscopy. It is found that columnar epitaxial growth of primary β grains with transverse dimensions close to the sizes of primary β grains in the base material occurs in the process of electron-beam welding with a double-sided welded joint. Inside the primary β grains, there are grains of the α-phase with a lamellar shape inherited from the α' martensite, which is formed in the course of transformation β → α'. As in the printed samples, there is a nanocrystalline α"-phase in the metal of the welded joint inside grains of the α-phase and in interlayers of the β-phase. However, the density of particles of this phase in the metal of the welded joint is higher than in the base material. In the metal of the welded joint, tensile macrostresses and elastic residual microstrains also increase. The microhardness of the metal of the welded joint is greater than the microhardness of the base material.

Production of WC–15Co Ultrafine-Grained Hard Alloy from Powder Obtained by the Electroerosive Dispersion of VK15 Alloy Wastes in Water

In this paper we study the possibility of producing a WC–15Co ultrafine-grained hard alloy (HA) from a powder obtained by the electroerosive dispersion (EED) of wastes of a VK15 HA in water. As a result of the EED of the alloy in the oxygen-containing liquid, the carbon concentration in the resulting powder decreases from 5.3 to 2.3%. When the powder is heated to 900°C in a vacuum, the carbon content drops to 0.2% due to the presence of oxygen. The resulting powder includes WC, W2C, and Co phases. The particles have a dendritic structure consisting of newly formed tungsten-containing grains and cobalt interlayers. In this study, the controlled removal of oxygen and the replacement of carbon in the powder were performed under heating in a CO atmosphere to t = 900°C. The processed powder has the required phase composition (WC + Co) and contains 5.3% carbon. The particles retain their spherical shape after carbon replenishment. The WC grains in the particles acquire a lamellar configuration, the space between which is filled with cobalt. The average grain diameter was found to be smaller than that in the initial alloy. As a result of sintering the powder in vacuum at 1390°C, a WC–15Co ultrafine-grained HA is obtained, the average diameter of WC grains in which is 0.44 μm, which is several times smaller than that in the initial alloy (1.8 μm). In this case, most of the grains retain their lamellar shape. Due to the fineness and 15% cobalt content, the resulting alloy has high hardness (1620 HV), fracture toughness (13.2 MPa m1/2), and strength (1920 MPa). In terms of the set of characteristics, this material is not inferior to analogs obtained by other methods.

Исследование процессов усталостного и коррозионно-усталостного разрушения псевдо- титанового сплава

The paper describes the results of fatigue and corrosion-fatigue tests of the pseudo α titanium alloy PT-3V, which is actively used in nuclear engineering for the manufacture of heat exchange equipment for modern nuclear power plants. Alloy PT-3V has an inhomogeneous coarse-crystalline structure with precipitates of β-phase particles along the grain boundaries of the lamellar shape. It is shown that smooth specimens tested according to the bending-with-rotation loading scheme do not show a noticeable decrease in the cyclic fatigue life when exposed to a neutral corrosive environment (3 % aqueous NaCl solution). However, specimens with a notch (stress concentrator) tested according to the cantilever bending loading scheme demonstrate sensitivity to the action of a corrosive environment at the stages of initiation and growth of fatigue cracks, as evidenced by a significant decrease in the number of cycles before crack initiation, as well as before specimen failure, in comparison with tests in air. Fractographic analysis of fractures of smooth specimens and specimens with a concentrator after fatigue and corrosion-fatigue tests has been carried out. The main stages of the initiation and growth of fatigue cracks are revealed. It has been established that a decrease in the resistance to the initiation and propagation of corrosion-fatigue cracks during testing of notched specimens may be due to the effect of hydrogen embrittlement, accelerated by stress concentration.

Influence of Residual Stress Around Constituent Particles on Recrystallization and Grain Growth in Al-Mn Based Alloy During Annealing

The recrystallization behavior of the homogenized AA3003 aluminum alloy with reduction rate of 20%, 50% and 90% was investigated. The change in the microstructure and dislocation density during annealing was characterized by TEM image analysis and Williamson-Hall plot. It was found that as the reduction rate increased, the microstructure evolves into a lamellar shape parallel to the rolling direction with the increased dislocation density. By applying subsequent annealing process, the dislocation density under the recovery stage was decreased by about 10%, which suggests the dislocation rearrangement. In the meanwhile, the dislocation density under the recrystallization stage was rapidly decreased due to the evolution of recrystallized grains. The effect of particle stimulated nucleation on the recrystallization was discussed in terms of residual stress around the α-Al(Mn, Fe)Si precipitate by solving inhomogeneous inclusion problem under cold rolling.

Effect of hydrogen addition on compression deformation behaviour of Ti–0.3Mo–0.8Ni alloy argon-arc welded joints

The effect of hydrogen addition on compression deformation behaviour of Ti–0.3Mo–0.8Ni alloy argon-arc welded joint has been investigated. Evolution mechanism of hydrogen-induced flow stress was discussed in detail. The results show that with increasing hydrogen content, the stretching and bending extent of fully lamellar microstructures including α lamellas and acicular hydride continued to increase, the morphology of dynamic recrystallization (DRX) grains tended to change from approximately equiaxed to large lamellar shape, and the quantity of DRX grains and recrystallization degree of grains increased obviously. A large number of dislocations concentrated in the vicinity of the hydride. Steady stress was decreased continuously with increasing hydrogen content, while peak stress of the hydrogenated 0.12 wt.% H weld zone was decreased to the minimum value and then increased slowly. A slight decrease in flow stress of the hydrogenated 0.05 wt.% H weld zone was caused by limited increase in the volume fraction of softer β phase. Hydrogen-induced DRX of α phase and improved dislocation movement by strong interaction between the hydride and dislocation directly resulted in a sharp drop in flow stress of the hydrogenated 0.12 and 0.21 wt.% H weld zone. Solute hydrogen also finitely contributed to a sharp drop in flow stress of the hydrogenated 0.12 and 0.21 wt.% H weld zone by promoted local softening, which induced continuous DRX and more movable dislocations to participate in slipping or climbing. The reinforcement effect and plastic deformation of the hydride and solution strengthening of β phase induced by solute hydrogen finally led to the increase in flow stress of the hydrogenated 0.21 wt.% H weld zone in its true strain range from 0 to 0.36.

Pseudacanthus alani, a New Species of Mesoamerican Bess Beetles (Coleoptera: Passalidae) of Oaxaca, Mexico and Nomenclatural Notes for the Genus.

A new species, Pseudacanthus alani n. sp., is described from cloud forest in Oaxaca, Mexico. This species is similar to Pseudacanthus junctistriatus Kuwert 1891 in size, shape of antennal lamella, and the absence of pubescence on abdominal terga, but has larger internal tubercles, an apex of central tubercle that is not free, glabrous elytral humerus, pubescent mesepisternum and mesepimeron and mesosternal scar, and male sexual characters. Photographs are provided of the head, male and female genitalia, and plectrum. Additionally, a taxonomic key to species of Pseudacanthus Kaup 1869 is provided, complemented with photographs of diagnostic characters. Finally, we propose two junior synonyms: Pseudacanthus solidus (Arrow 1907) n. syn. of Pseudacanthus junctistriatus and Pseudacanthus truquii Kuwert 1891 n. syn. of Pseudacanthus mexicanus (Truqui 1857).

Underwater additive manufacturing of Ti-6Al-4V alloy by laser metal deposition: Formability, gran growth and microstructure evolution

No underwater laser additive manufacturing technology has been reported. In this paper, the underwater thin-walled Ti-6Al-4V part was built firstly by underwater laser metal deposition (ULMD), and the formability, grain growth and microstructure transformation were investigated. The stable local dry cavity and the shielding-gas flow layer surrounding the deposited layer formed during the ULMD process utilizing an improved ULMD nozzle, generating the uniform thin-walled part without cracks and pores. Columnar β-grains, growing epitaxially opposite to the heat flow direction, were observed in the whole ULMD part, and the grain size increased firstly and then reduced with increasing the deposition layer, attributed to the comparative growth and decreasing cooling rate. The water cooling effect suppressed the formation of equiaxed β grains that only formed in the top region of ULMD part. For the microstructures of ULMD sample, only acicular martensites α' with different size scales formed in the bottom region, and martensites α' were replaced gradually by α phase with lamellar, lathy and blocky shapes with increasing the building height, except the top region because the absence of multiple thermal cycles. The larger cooling rate promoted the formation of α' martensite and decreased the width of α lath of ULMD part.

Magnesium Silicate Polymer as a Coagulant for Reactive Dye Removal from Wastewater: Considering the Intrinsic pH in Magnesium Silicate Polymer and Coagulation Behavior.

A magnesium silicate polymeric coagulant (MgSiPC), which is an inorganic polymer for dye removal from wastewater, was prepared with different pH by copolymerization. The acidity was a key factor in the preparation of the MgSiPC. In the present research, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to analyze the characterization of optimum coagulants. Additionally, the response surface method (RSM) was applied to optimize the process of coagulation–flocculation. The results of FT-IR and XRD implied that the main components of the MgSiPC with pH 1.50–2.50 were almost the same. SEM images showed that MgSiPCs with pH 1.50–2.50 exhibited different structures including cluster and lamellar shape structure, compact rod-like and network structure, and a kind of irregular geometry shape structure. In the process of coagulation–flocculation, MgSiPCs with pH 1.50–2.50 showed highly efficient coagulation performance. The removal rate of reactive yellow 2(RY2) could reach above 90% at a dosage of 50–70 mg/L and initial pH 12.00, while the removal rate of reactive blue 2 (RB2) could attain above 93% at a dosage of 50–80 mg/L and initial pH 12.00. Moreover, MgSiPCs with pH 2.00 had the highest efficiency. The results of RSM showed that the optimum combination of the MgSiPC’s dosage and initial pH was 62 mg/L and 12.08 for RY2 and 78 mg/L and 12.00 for RB2, respectively. Under optimum experimental conditions, the predicted data from this model were 96% for RY2 and 100% for RB2, which was consistent with the actual experimental data. Therefore, a pH of 2.00 is considered to be the optimal acidity for preparing MgSiPCs.

Computer Simulation of Micro-Mechanic in Pearlitic Steel Wire Drawing

Cold-drawn high-carbon steel wire with pearlite microstructure is one of the most popular raw materials for modern reinforcing ropes. Lamellae thinning, changes in interlamellar interface and metallographic texture, strain localization is the main property-forming phenomena in the wire drawing process. However, the experimental study of these phenomena dynamics is difficult and time-consuming. Drawing process of pearlitic steel wire was investigated. Behavior of pearlite colonies on the surface and the central layer of the wire were researched, based on the multiscale computer simulation. Cementite lamellae orientation in relation to the drawing axis, interlamellar spacing and shape of cementite inclusions were key factors. Regularities of the pearlite colonies reorientation, changing the shape and size of cementite lamellae and strain localization in the ferrite were established on the basis of FEM. It was established that the cementite lamellae, that are parallel to the drawing axis, had the maximum thinning. Interlamellar distance in pearlite colonies with such lamellae changed most intensively. Cementite lamellae, that are perpendicular to the drawing axis, are the most susceptible to fracture. It was found out that for certain values interlamellar distance this effect can be reduced. Intensive reorientation of pearlite colonies in relation to the drawing axis was observed in the case of their location at an angle to the drawing direction. At the same time, there was a significant bending of cementite lamellae and their susceptibility to fragmentation. Estimated values of the wire mechanical properties were compared with a real experiment. The simulation results were verified by metallographic analysis.

Microstructure and Texture Evolution of 0.6 mm Ultra-Thin-Walled Tubes of Magnesium Alloys Fabricated by Multi-Pass Variable Wall Thickness Extrusion (VWTE)

AZ80+0.4%Ce alloy ultra-thin-walled tube with a wall thickness of 0.6 mm was fabricated by multi-pass variable wall thickness extrusion (VWTE) at 693 K. Microsturcture and texture evolution were investigated. The results indicate that the average grain size decreases from ~47 μm of extruded alloy to ~8.9 μm after 5 passes VWTE. The total area reduction of Mg alloy tube is 91 %. Homogeneity of microstructure is improved obviously and the morphology of Mg17Al12 phases in coarse grains and fine DRXed grains exhibit lamellar and granular shapes, respectively. In addition to the microstructure evolution, the VWTEed tubes showed a strong texture of (0001) planes, and the intensity decreased with deformation increasing to 4 passes. After 5p-VWTE, a strong texture characterized by (0001) pole tilting 20 degrees rotated from extrusion direction (ED) towards normal direction (ND).

Microstructure and properties of laser-clad FeNiCoCrTi0.5Nb0.5 high-entropy alloy coating

ABSTRACTFeNiCoCrTi0.5Nb0.5 high-entropy alloy coating is prepared on AISI 1045 steel by laser cladding. The cross-sectional macroscopic morphology, phase, microstructure, microhardness and wear resistance are studied systematically. The results show that FeNiCoCrTi0.5Nb0.5 coating has no porosities, cracks or other defects and is well metallurgically bonded to the substrate. The coating is composed of body-centred cubic (BCC) solid solution, face-centred cubic (FCC) solid solution and hard Laves phase. The solid solution phase and Laves phase distribute uniformly and closely in a lamellar shape to form a fine and dense eutectic structure. The microhardness of FeNiCoCrTi0.5Nb0.5 coating is about three times that of the substrate. Compared with the substrate, the coating has superior wear resistance.

Carbon supported manganese(IV)–cobalt(II/III) oxides nanoparticles for high-performance electrochemical supercapacitors

The carbon supported manganese(IV)–cobalt (II/III) oxides nanoparticles labelled as MnO2–Co3O4/C nanocomposites have been prepared by a simple one-step microwave-assisted heating method using different precursor materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES) have been used for the characterization of morphology, structure and composition of the synthesized nanocomposites, whereas the electrochemical performance of the prepared nanocomposites has been evaluated by using cyclic voltammetry (CV). It was determined that the use of different precursor materials for the synthesis of the carbon supported MnO2 and Co3O4 nanocomposites results in a different morphology of the prepared substances. A high specific capacitance (Cs) of 658.8 F g−1 at a scan rate of 10 mV s−1 in a 1 M Na2SO4 solution has been obtained for the MnO2–Co3O4/C-2 nanocomposite that has a spherical shape of nanoparticles. Moreover, it significantly outperforms the MnO2–Co3O4/C-1 nanocomposite that has a lamellar shape of nanoparticles.

Numerical Simulation of the Influence of Pore Structure on Resistivity, Formation Factor and Cementation Index in Tight Sandstone

AbstractTight sandstone, with severe diagenesis and complex pore structure, differs greatly from conventional sandstone in terms of rock electrical parameters. In subsurface rock electrical experiments, various electrical parameters are confounded and can only be analyzed qualitatively. The lack of quantitative analysis for each individual electrical parameter presents a challenge for the evaluation of oil and gas saturation in tight sandstone. Based on the 2D pore‐throat model and the features of pore structure in the tight sandstone of the Penglaizhen and Shaximiao Formations in the upper and middle Jurassic of the Western Sichuan Depression, this paper presents 3D micro pore‐throat models for three types of tight sandstone. It proposes a finite element‐based rock electrical simulation method to analyze the influence of pore structure parameters, such as throat radius and throat tortuosity, on electrical parameters such as resistivity, formation factor, and cementation index quantitatively. The research revealed the following results: (1) Throats of tight sandstone usually have lamellar or curved lamellar shapes that are slender and narrow. The lamellar throat used in the proposed pore‐throat model is more consistent with the features of tight sandstone than the tubular throat used in the original model. (2) The throat determines the conductivity of tight sandstone. The throat parallel to the electric potential has the greatest influence on conductivity, and the throat perpendicular to the potential has the least influence. (3) In tight sandstone grades I to III, as the porosity decreases, the formation factor increases and the cementation index decreases. (4) The results of the rock electrical simulation are consistent with the results of the rock electrical experiment, which indicates that the proposed rock electrical simulation method of tight sandstone is effective and accurate.

Description of the last instar larva of Peristicta aeneoviridis Calvert, 1909(Odonata: Coenagrionidae).

The larva of Peristicta aeneoviridis Calvert, 1909 is described for the first time, based on material from Misiones Province, Argentina. It differs from the rest of the larvae described for the genus in the shape and coloration of caudal lamellae, femur setae, lacinia teeth and coloration patterns. Additions to the description of the larva of P. forceps Hagen in Selys, 1860 are included.