Cementation of Sand With Enzyme-Induced Carbonate Precipitation (EICP) Using Concrete-Extracted Calcium

Calcium carbonate precipitation and crystallization induced by urease enzyme to solidify soil is known as biocement technology. The uses of waste and cheap materials can make this technology more cost-effective and practical for applications. In this study, calcium ions were obtained by dissolving waste concretes in acidic liquid. Sand columns were treated by enzyme-induced carbonate precipitation (EICP) with either concrete-extracted calcium or reagent calcium for comparison. Compressive strengths, calcium carbonate contents, and microscopic analysis on the treated sand were carried out. It was found that the compressive strength of the former could reach 833 kPa in the dry state and 204 kPa in the wet state after 5 times of EICP treatment, both of which were higher than that of the latter. The calcium carbonate contents could reach 2–3% after 3–5 times of treatment. Based on the scanning electron microscope (SEM) and X-ray diffractometer (XRD) analyses, the crystal type of calcium carbonate produced in sand was calcite. The comparative results showed that the treatment effect using concrete-extracted calcium was similar or better than that using reagent calcium.

Propagation of ultrashort optical pulses in anisotropic optical media with carbon nanotubes

In this paper, we investigate the evolution of electromagnetic waves in a nonlinear anisotropic optical medium with carbon nanotubes (CNTs). Based on Maxwell’s equation, an effective equation is obtained for the vector potential of the electromagnetic field, which takes into account different values of the velocity and polarization with two directions. The dependence of the pulse shape on the crystal type, as well as the angle between the electric field and the CNTs axis is revealed.

Assessing fall velocity-maximum dimension relationships and particle size distributions for snowfall

Snowfall is an atmospheric phenomenon that can cause significant impacts to many aspects of daily life in Missouri. Further, no two snowfall events are exactly the same, as even small differences in environmental characteristics can result in differing snow crystal types dominating the event, which in turn can result in differing impacts from event to event. Therefore, it is necessary to understand snowfall behavior so that better forecasts and in situ analyses may be made. In this study, snowflake maximum dimension and fall velocity measurements were recorded using the OTT Parsivel Laser Disdrometer. In conjunction with distribution of measured maximum dimensions, RAP Analysis soundings were used to determine snow crystal type. From there, the relationships between fall velocity and maximum dimension and the particle size distributions of snowflakes from many snowfall events were analyzed. Observed relationships between fall velocity and maximum dimension were compared with previously derived relationships, and it was found that, in most cases, no single curve represented the relationship in the observed data well, with discrepancies caused by instrumentation error and lack of a single dominant crystal type. To analyze particle size distributions, several distribution functions were fit to the observed distribution using a least-squares regression method in MATLAB. It was found that, overall, the triple Gaussian distribution function performed the best in modeling particle size distributions in snow, but there were some instances where the gamma function modeled the distribution best. Further study, especially with the inclusion of field observations in addition to instrument observations, is necessary to develop a better understanding of these snowfall events.

The effect of calcium fluoride on extracting magnesium from magnesite and calcium carbonate by silicothermal reduction in flowing argon

At present, the production of magnesium is mainly carried out semi-continuously with ferrosilicon as reducing agent under high temperature and high vacuum. In order to continuously produce magnesium, anew method of extracting magnesium from low-grade magnesite and calcium carbonate by silicothermal method in flowing inert gas was proposed. The effects of calcium fluoride(CaF2)on decomposition rate, decomposition kinetics, reduction rate of magnesia and crystal type of dicalcium silicate in reduction slag were investigated in the paper. The experimental results showed that calcium fluoride could accelerate the decomposition of carbonate, and had no side effect on the calcined products. In addition, the analysis results of DTA curves showed that calcium fluoridecould reduce the decomposition reaction activation energy and the reaction temperature of carbonatein the prefabricated pellets. The results of reduction experiments showed that proper calcium fluoridecould promote the reduction rate of magnesia, and in the temperature range of 1250? ~ 1350?, with same timeframe, the corresponding calcium fluoride contents were5%, 3% and 1% respectively when the reduction rate reached the maximum. Excessive calcium fluoride could reduce the reduction rate of magnesia, but it couldpromote the transformation of dicalcium silicate to ? phase in the reduction slag.

Leaf anatomical variation in Desmos Lour. and Dasymaschalon (Hook. f. & Thomson) Dalla Torre & Harms species (Annonaceae)

Nikmah IA, Rugayah R, Chikmawati T. 2020. Leaf anatomical variation in Desmos Lour. and Dasymaschalon (Hook. f. & Thomson) Dalla Torre & Harms species (Annonaceae). Biodiversitas 21: 3317-3330. The relationships between Desmos and Dasymaschalon are debated for along time. Those two genera have high morphological similarities, especially in their generative character (moniliform monocarps). Therefore, sterile specimens of Desmos are difficult to be distinguished from Dasymaschalon. Leaf anatomy in paradermal section of 20 taxa (12 species of Desmos, eight species of Dasymaschalon) have been carried out. The data were used to support the interspecific and intergeneric delimitation of Desmos and Dasymaschalon. Desmos and Dasymaschalon are two distinct genera mainly distinguished based on the anticlinal wall undulation of epidermal cells and supported by variation of the crystal type, and size. The anticlinal wall undulation of Desmos is almost straight to slightly wavy, and never sinuous, meanwhile, Dasymaschalon varies from almost straight to deeply sinusoid. The crystals of Desmos consist of rhombohedric, druse type A, and druse type B crystals, whereas Dasymaschalon has prism, druse type A, druse type B, and drue type C crystals.

Impact of Environmental Conditions on Frost Crystal Structure

Frost crystal type and distribution were characterized in the initial periods of frost growth on an aluminum surface. Experiments were carried out for a range of wall temperatures from [Formula: see text]C to [Formula: see text]C, air temperatures from [Formula: see text]C to [Formula: see text]C, relative humidities from 15% to 85%, and air velocities from 0.5 to 5.0[Formula: see text]m/s. The results showed that frost crystal type was strongly dependent on the wall temperature and humidity. Changing the air temperature shifted the region of some frost crystal types. Decreasing the air temperature from 22 down to either [Formula: see text]C or [Formula: see text]C led to the decrease of feather crystals but increased the region of scroll crystals. Air velocity had smaller impacts on frost crystal type but had a strong influence on the distance between the crystals, particularly at lower air velocities. The results were compared to prior researchers. The results should provide a better understanding of frost morphology during the early stages of frost growth on metal surfaces.

Study of Microstructure and Properties of Laser Cladding Ni60-WC + TiC Composite Coating

As a novel surface strengthen technology laser cladding was widely used in surface engineering. In this work, Ni60 + 25%WC + 10%TiC composite coatings were fabricated on the TC4 by laser cladding technology. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and frictional wear were used in the study of coatings. The results showed that dendrites is the main crystal type in the coatings, there were some bulk type crystal generated in 400 mm/min scanning speed. XRD results showed that some of the metalloceramics phases, such as TiC, VC, WC were formed in the coatings, some of the intermetallic compounds such as AlNi3, Al0.96B0.04Ni3, NiTi and C0.12Fe1.88 also formed, which improving the hardness, and the hardness tests results showed that the hardness of the coatings increased by 300% compared to the substrate, of above 1100 HV0.3. The max friction coefficient in 600 mm/min was 0.39, because of the unmelted TiC and WC particles fallen off from coatings, so the mechanism of the coating was abrasive wear. The friction coefficient is decreased to 0.11 and 0.19 when the scanning speed is 500 mm/min and 400 mm/min, respectively.