Effect of Fine Aggregate Particle Characteristics on Mechanical Properties of Fly Ash-Based Geopolymer Mortar

This research aimed to investigate the effect of fine aggregate particles on mechanical properties of fly ash-based geopolymer mortar. In this work, seven kinds of river sand particles were designed based on different fine aggregate characteristics. The fineness modulus was adopted to quantitatively describe the gradation of sands. The fluidity, compressive, flexural, and tensile strengths of geopolymer mortar with different sand gradations were analyzed by laboratory tests. Furthermore, the composition and morphology of fly ash-based geopolymer mortar was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reasonable gradation range and filling effect of sand were obtained. The results show that fluidity and compressive and flexural strengths of geopolymer mortar both improve with the increase of the fineness modulus, while specific surface area and voidage are opposite. The tensile strength of mortar largely lies on the interface properties between the geopolymer binder and fine aggregates. When the pass rate of the key sieving size 1.18 mm is 75–95%, the pass rate of the key sieving size 0.15 mm is 15–25%, the fineness modulus is 2.2–2.6 and the appropriate filling coefficient of geopolymer paste is around 1.0–1.15, the comprehensive performance of geopolymer mortar is the best. This research paper could provide a basis for the design of geopolymer mortar based on fly ash, and it is of great significance for its popularization and application.

Conductive Heat Transfer Prediction of Plain Socks in Wet State

In this study, an algebraic model and its experimental verification was carried out to investigate the effect of moisture content on the heat loss that takes place due to conduction of sock fabrics. The results show that increasing moisture content in the studied socks caused a significant increase in their conductive heat loss. Plain knitted socks with different fiber composition were wetted to a saturated level, and then their moisture content was reduced stepwise. When achieving the required moisture content, the socks samples were characterized by the Alambeta testing instrument for heat transfer. Three different existing modified mathematical models for the thermal conductivity of wet fabrics were used for predicting thermal resistance of socks under wet conditions. The results from both ways are in very good agreement for all the socks at a 95% confidence level. In the above-mentioned models, the prediction of thermal resistance presents newly a combined effect of the real filling coefficient and thermal conductivity of the so-called “wet” polymers instead of dry polymers. With these modifications, the used models predicted the thermal resistance at different moisture levels. Predicted thermal resistance is converted into heat transfer (due to conduction) with a significantly high coefficient of correlation.

Scale production of conductive cotton yarns by sizing process and its conductive mechanism

Conductive yarn is an important component and connector of electronic and intelligent textiles, and with the development of high-performance and low-cost conductive yarns, it has attracted more attention. Herein, a simple, scalable sizing process was introduced to prepare the graphene-coated conductive cotton yarns. The electron conductive mechanism of fibers and yarns were studied by the percolation and binomial distribution theory, respectively. The conductive paths are formed due to the conductive fibers' contact with each other, and the results revealed that the connection probability of the fibers in the yarn (p) is proportional to the square of the fibers filling coefficient (φ) as p ∝ φ2. The calculation formula of the staple spun yarn resistance can be derived from this conclusion and verified by experiments, which further proves the feasibility of produce conductive cotton yarns by sizing process.

Design and verification of 5-channel 1.5T knee joint receiving coil based on wearable technology

BACKGROUND: Over the past 20 years, magnetic resonance receiving coil technology has developed rapidly. The traditional, commercial knee joint coil has a fixed mechanical structure. To meet the imaging needs of most patients, it is necessary to ensure that the mechanical geometry of the coil is as large as possible. Therefore, different quality images can be obtained by filling coefficients under loads of knees of different sizes. Lufkin et al. [1] have demonstrated that the signal-to-noise ratio (SNR) of coil imaging is directly proportional to its filling coefficient, which is S/N≈QL*η. Thus, the pursuit of an optimal coil filling coefficient is an important way to improve the coil imaging quality. OBJECTIVE: This study combines wearable concepts and coil development techniques and applies flexible and elastic materials to coil designs. METHODS: We used an elastic material instead of the traditional fixed mechanical structure to develop a 1.5T 5-channel knee joint receiving coil that can be attached to knee joints of different sizes within a certain range, allowing the coil to achieve a maximum filling coefficient under the loads of knees of different sizes. RESULTS: Compared to commercial 8-channel knee coils, the phantom test and clinical knee joint imaging demonstrated that the SNR of the developed coil increased by four times in the shallow layer and two times in the deep layer, under different load conditions. CONCLUSION: This high SNR performance demonstrates potential for the realization of high resolution and fast imaging sequences in knee imaging.

Specific Features of Thermal Performance of the Arc Steel Furnace in Unstable Properties Conditions of Burden Materials

In the production of steel in a state-of-the art arc furnace, there are two serious issues, resulting from a decrease in bulk density of burden materials, and an increase in non-ferrous metals concentration. The paper presents the analysis results of changes in the chemical composition of iron-containing materials related with an increase in the content of non-ferrous metals: copper, tin, lead, antimony and unspecified metals in a given steel grade and a decrease in the bulk density of burden materials. A method of reducing impurities by means of using pellets produced from natural raw materials, that are pure in terms of impurities, is presented. A method of setting up charging of burden materials with different bulk density, using the filling coefficient of the furnace operating volume, is proposed. Combined burden materials that include various types of scrap and non-ferrous metals of iron-ore pellets, that are pure in terms of impurities, will ensure high-quality steel production.

Novel method on thermal resistance prediction and thermo-physiological comfort of socks in a wet state

The present study proposes a novel method to measure the thermal resistance and comfort properties of various sock samples under wet conditions. Theoretically, comfort properties are responsible for transporting moisture by our body with different rates. Therefore, plain socks with different fiber composition were wetted to a saturated level and after getting the required moisture content, the sock samples were characterized by Alambeta (for thermal resistance and thermal absorptivity) and Permetest instruments for relative water vapor permeability in the wet state. In addition, various skin models were utilized to make a comparison of thermal resistance in the dry state. Two different models were modified for analyzing the thermal resistance under wet conditions. According to the models used, the prediction of thermal resistance is a combined effect of the filling coefficient and thermal conductivity of wet polymers instead of dry polymers. With these modifications, the used models predicted the thermal resistance at different moisture levels with a significant correlation ( R2) value, that is, 0.84–0.97.

EXPERIMENTAL STUDY OF IMPACT OF PERCUSSIVE PULSE FORM ON SINKING PROCESS OF HOLLOW ROD ELEMENTS INTO SOILS

The work has experimental nature and it is aimed to development of vibro-percussion method of pipe-cover sinking during trenchless constructions of underground utilities. The maid idea of the research is the determination of regularities of filling inner tube hollow by soil at different forms of percussive pulse. Theoretical dependences of impact of percussion energy structure (form of percussion pulse) on efficiency of hollow rod element advance in the solid at different stages of insertion. Dimensionless parameter – filling coefficient is used for quantitative evaluation of filling rate by soil. Influence of pipe diameter on incrementation of length of soil core-sample for different percussive machines with the same percussive energy is shown. Stand and method of field test operation at various soil condition and interpretation of obtained data and its comparison with previous results obtained by the authors of the work and foreign researchers are represented.