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The traditional chemical cross-linking method is based on the formation of covalent bonds between molecules to connect three-dimensional networks to enhance the strength of hydrogels. Although this method can significantly improve the mechanical properties, it also has many problems, such as irreversibility and fatigue. Therefore, the design and preparation of supramolecular hydrogels with high mechanical properties and good temperature resistance have very important research significance and practical value. This paper prepared a supramolecular gel with both temperature resistance and mechanical properties through hydrophobic association and hydrogen bonding, and evaluated its thermal stability, rheology, temperature resistance and pressure plugging ability. The results showed that the supramolecular gel had excellent thermal stability, and there was strong physical entanglement between its three-dimensional network structures, which made it difficult to be destroyed by increasing temperature. The excellent rheological properties of supramolecular gels enable them to maintain good viscoelastic changes in the linear viscoelastic region within the strain range of 0.1-30%. When the strain was greater than 30%, the supramolecular gel began to undergo different degrees of sol-gel phase transition, which showed that the energy storage modulus of supramolecular gel decreased. In addition, the energy storage modulus of supramolecular gel was always greater than the loss modulus in the whole frequency scanning range, and there was no intersection between the two gel and the gel always showed high elasticity. Meanwhile, the supramolecular gel still had good structure and strength after high temperature aging. Its tensile and compressive properties did not change significantly, but the color of the gel surface changed slightly, which could maintain good structural stability under high temperature environment. Supramolecular gel particles could be used as plugging materials for drilling fluid, and had excellent plugging ability of formation fractures and pores. The plugging ability of 1mm aperture plate model was up to 6.3MPa, and the plugging ability of 1mm seam width was up to 4.9MPa. Therefore, the development and application of supramolecular gel plays an important supporting role in drilling fluid plugging.

Amphiphilic nanosheets have gained great attractions in diverse applications owing to its unprecedented performances. In this paper, amphiphilic molybdenum disulfide (CTAB-MoS2) nanosheets were pre...

In this study, 1H low-field NMR was used to compare the liquid absorption-release behaviour of superabsorbent polymers (SAPs) in Portland cement (PC) paste, NaOH-activated slag (SH-AAS) paste, and water glass-activated slag (WG-AAS) paste. The liquid absorption of SAPs in the PC paste was lower than that in the SH-AAS paste and the WG-AAS paste. The liquid release was also faster, which was mainly due to the higher Ca2+ concentration in the pore fluid of the PC system. In the AAS system, although the Ca2+ concentration in the pore fluid was low, the Na+ concentration was much higher than that in the PC system due to the activator. The Ca2+ in the PC system is an important factor affecting the swelling of SAPs, while in the AAS system, the swelling limitation of SAPs is the result of the combined effects of Ca2+ and Na+, with Na+ being dominant.

The formation of the dominant channel of water is a severe problem for most of the oilfields. Recently, gel and nanoparticles regarded as conformance water materials have attracted more attention to control water-cut and enhance oil recovery (EOR) in many water invasion reservoirs. However, nanogel particles possessing synergic properties of nanoparticles and gel are currently unavailable, which causes barrier to EOR. Here, high viscosity α-starch nanogel particles were synthesized to play the synergistic role of gel and nanoparticles economically. The average diameter of nanogel particles was 30 nm with dispersion viscosity of 250 mPa·s at 90°. Through flooding experiments, we demonstrated both light and heavy oil recovery rates reached around 30%. The nanogel particles promotes to displace oil droplets from the rock surface due the creation of the structural disjoining pressure. Also, its high viscosity properties help to drag oil clusters out of the oil phase.

In the present study, alkali-activated slag (AAS) pastes were prepared using slag and water glass with different modulus, and the effect of a modulus of water glass on the volume change of ...

C(-A)-S-H (CaO(-Al2O3)-SiO2-H2O) gel is the main product and source of strength in alkali-activated slag systems. Previous studies on C-A-S-H have focused mostly on the characterization of the structure and composition of the products. In this study, synthetic C-A-S-H particles with a similar composition as gels produced by alkali-activated slag were prepared by a hydrothermal method and were added to the alkali-activated slag systems, and the synthetic can be regarded as a chemical intensifiers of hardening (CIH). The effects of the synthetic C-A-S-H on the hydration process, the early-stage mechanical properties, and the microstructure of the alkali-activated slag were investigated by hydration heat tests, scanning electron microscopy (SEM), mercury intrusion porosimetry tests (MIP), and other methods. The results showed that the synthetic C-A-S-H shortened the setting time, promoted the formation of an acceleration period at an early stage, and increased the hydration heat released during the acceleration period. The synthetic C-A-S-H improved the flexural and compressive strength of the alkali-activated slag to a certain extent and the improvements in the flexural strength were more significant than the improvements in the compressive strength; the flexural strength of the sample with the added 3% synthetic C-A-S-H with 3-d curing increased by 16.25%. Microstructure analysis indicated the synthetic C-A-S-H also reduced the porosity of the alkali-activated slag-hardened paste and optimized the pore size distribution. This study of the early-stage performance provides a new approach and predictions for the late-stage performance and in-depth modification mechanisms of alkali-activated slag systems.

In this study, superabsorbent polymers (SAPs) and two expansive additives (a MgO-based expansion agent and gypsum) were studied to possibly mitigate the shrinkage of AAS (alkali-activated slag) systems. To this end, an experimental study was carried out to evaluate the effect of SAPs and the expansive additives on the setting time, compressive strength, autogenous shrinkage, and total shrinkage of AAS. SAPs prolonged the setting time of AAS and decreased the compressive strength, while the expansive additives shortened the setting time of AAS. When gypsum was used as an expansive additive, the shortest initial setting time of AAS was less than 10 min. SAPs have a significant effect in reducing the autogenous shrinkage of AAS, and a better result was achieved when used together with the MgO-based expansion agent as the SAPs promoted the consumption of MgO. The 1H low-field NMR results showed that when the SAPs and gypsum were used together, the absorption capacity of the SAPs decreased, and part of the absorbed liquid was rapidly released back into the mortar matrix. However, for the total shrinkage, the SAPs were less effective. SAPs increased the mass loss of the AAS mortar upon drying, which may increase the drying shrinkage of AAS and counteract part of the reduction in autogenous shrinkage.

Based on the analytical 1H low-field nuclear magnetic resonance (NMR) technique, we developed a novel method and corresponding model to analyze the hydration degree (αt) of cement in cement paste under different curing conditions. The hydration degree can be calculated quantitatively based on the transverse relaxation time (T2) distributions using NMR measurements. The T2 distributions of the cement paste samples with the water/cement (W/C) ratios of 0.25, 0.35 and 0.45 under standard curing, steam curing at 40 °C and steam curing at 60 °C were obtained. The αt of cement was studied by the hydration heat method and portlandite (CH) quantitative measurements. The results show that the intensity-weighted T2 value of non-surface water peaks ( T 2 ¯ ) has a significant correlation with αt that can be expressed by an exponential equation. In this paper, the derivation of this exponential equation is given, and the effects of W/C ratio and curing condition on its parameters are analyzed.

Copper slag (CS) is an industrial by-product of copper metal smelting. In the present study, two alkaline activators (sodium silicate (SS) and sodium hydroxide (SH)) were used to develop different samples of alkali-activated CS cementitious material, respectively. The mechanical performance of alkali-activated CS cured with the standard and steam programs were investigated. The results indicate that the steam program was more suitable. In particular, SS was more effective than SH in improving the compressive strength, i.e., the highest 28 day compressive strength of CS activated with SS was 30.3 MPa; SH achieved only 4.7 MPa. Furthermore, the effect of SS and SH on the microscopic properties of alkali-activated CS were studied. The C–S–H in the CS activated with SS was mostly amorphous and had a higher degree of polymerization. By contrast, in the CS activated with SH, some reaction products are network structure, which was composed of plate-shaped plombierite with high crystallinity. The drastically different structures and degrees of polymerization of the reaction products resulted in different matrix densities, which affected the compressive strength.

Fractured-vuggy carbonate reservoir played a significant role in unconventional reservoirs, but it was difficult to be developed due to its complex reservoir types. Therefore, it was crucial to find a suitable development program to enhance oil recovery. In this work, a two-dimensional visual physical model of fractured-vuggy reservoir was designed and fabricated according to actual geological data and injection-production characteristics of a representative fractured-vuggy carbonate reservoir, Tahe Oilfield in China. Nitrogen flooding experiment, nitrogen flooding under the high gas energy experiment, nitrogen flooding under strong bottom water energy experiment and foam assisted nitrogen gas flooding experiment were carried out respectively by using two-dimensional visual model. The flow behaviors and the main mechanisms for enhanced oil recovery were revealed by analyzing the oil displacement performance in the visual physical model. Experiment results showed that the gas cap energy and the bottom water energy played a synergistic effect in the nitrogen flooding. The stronger the bottom water energy was, the larger the gas spread area was, and the increase of oil recovery would be very high. If the gas injection rate was too strong, the dominant gas flow channel would be formed prematurely, and the oil recovery was little increase. In addition, foam could effectively control the gas mobility, delay the formation of gas channeling. Meanwhile, the oil recovery of foam assisted nitrogen gas flooding was higher 12% than that of nitrogen flooding. Therefore, the mechanism for improving the degree of development was obtained mainly through gravity differentiation to form the secondary gas top and realize the development of the remaining oil.

Carbon dioxide uptake of hardened cement pastes and hardened cement pastes mixed with fly ash during carbonation cycles were investigated. The volume changes of that two series of hardened pastes on carbonation cycles were measured by the helium pycnometer. For further discussion, samples were analyzed by X-ray diffraction with RIR (Reference Intensity Ratio) method. The pH changes of those leaching solutions were also mentioned. Results showed the final trend of carbon dioxide uptake of two sample series was nearly the same, which was decreased to the identical uptake level. But there were differences in the volume changes of the two sample series. For the cement pastes, the volume change increased rapidly and then changed to gentle gradually. The volume change increased first, then reduced steadily as for the mixed pastes. However, the volume of hardened cement pastes was still expanded after 24-hour carbonation. Different trends of the volume changes might be due to the carbonation of not only the calcium hydroxide but the C-S-H (Calcium-Silicate-Hydrate).

Compared with the traditional water-based fracturing fluid, the water-based clean fracturing fluid had the advantages of low friction, easy flowback and no residue. A kind of erucic amide propyl betaine (EAPB) was synthesized by using erucic acid and N, N-dimethyl-1,3-propanediamine as raw materials, and a clean fracturing fluid was furtherly constructed by combining EAPB with organic acid. The composition of the fracturing fluid system was determined according to the viscosity change of the system. Meanwhile, the temperature resistance, salt resistance, sand-carrying performance and micelle-breaking properties of the system were studied. The results showed that the optimum molar ratio of EAPB to sodium salicylate (NaSal) in fracturing fluid system was 50:9. The zero-shear viscosity could reach up to 129 Pa·s at 25 ℃. When the shear rate was 170 s−1 and the temperature was 80 ℃, the viscosity could keep above 60 mPa·s after continuous one-hour shearing. Furthermore, it had good sand-carrying and micelle-breaking performance. There was easy flowback and no residue after the micelle-breaking, which did low damage to the formation and achieved the effect of increasing oil and gas production. In addition, the average permeability damage rate of the fracturing fluid to the natural core of the reservoir in the target block was 6.07 %. This showed that the fracturing fluid system had the characteristics of low damage, which could effectively reduce the secondary damage after fracturing and play a certain role in reservoir protection. Therefore, it could be used as a clean fracturing fluid. The research results could provide guidance and reference for the fracturing fluid system in oilfield application.

Fractured-vuggy carbonate reservoirs are becoming the key to oil reserves, but their complex reservoir structure and connectivity make it difficult to be developed. In this work, a visual physical model representing an underground river reservoir in two-dimensional fractured-vuggy reservoir was designed and fabricated to study gas channeling characteristics of nitrogen and foam flooding. In order to further study the influence of the porous media on gas channeling characteristics of foam and nitrogen gas flooding, the visual physical model was filled with 2 mm transparent glass beads and the effects of glass beads on different types of nitrogen and foam flooding gas channeling were studied. Experimental results showed that the synergistic action of gas and water and the bottom water energy were the important factors affected gas channeling. Furthermore, foam could effectively control gas mobility, delay formation of gas channeling. In terms of enhanced oil recovery, the recovery efficiency of foam flooding was 35% higher than nitrogen flooding in the horizontal model. In addition, the glass beads in fractured-vuggy of underground river reservoirs could change the flow direction of the fluid and cause a certain flow resistance, foam was more easily to occur gas channeling in the longitudinal model filled with glass beads. The oil recovery by foam in the longitudinal model filled with glass beads was lower 12% than that in the longitudinal model. Therefore, determined the factors that influence gas channeling had a practical value for enhancing oil recovery in fractured-vuggy reservoirs.

Differential protection has been the main protection of transformer for a long time. The key and difficult problem is how to prevent the differential protection misoperation caused by inrush current. In recent years, there has been a lot of sympathetic inrush accidents caused by misoperation of transformer differential protection, affecting the safe and stable operation of power system. This paper established the simulation model of inrush current and, analysis of sympathetic inrush mechanism. At the same time, the fundamental reasons of differential protection misoperation caused by the sympathetic inrush were found out. And relevant methods and measures of preventing the sympathetic inrush misoperation in the transformer differential protection are put forward.

Traditionally, the optimization of a turbomachinery engine casing for tip clearance has involved either two-dimensional transient thermomechanical simulations or three-dimensional mechanical simulations. This paper illustrates that three-dimensional transient whole-engine thermomechanical simulations can be used within tip clearance optimizations and that the efficiency of such optimizations can be improved when a multifidelity surrogate modeling approach is employed. These simulations are employed in conjunction with a rotor suboptimization using surrogate models of rotor-dynamics performance, stress, mass and transient displacements, and an engine parameterization.

C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O) have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O)/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH)2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH)2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali-activated materials.

Terrestrial planetary bodies such as Mars and the Moon are known to harbor volcanic terrain with enclosed lava tube conduits and caves. The shielding from cosmic radiation that they provide makes them a potentially hospitable habitat for life. This motivates the need to explore such lava tubes and assess their potential as locations for future human outposts. Such exploration will likely be conducted by autonomous mobile robots before humans, and this paper proposes a novel mechanism for constructing maps of lava tubes using a multi-robot platform. A key issue in mapping lava tubes is the presence of fine sand that can be found at the bottom of most tubes, as observed on earth. This fine sand makes robot odometry measurements highly prone to errors. To address this issue, this work leverages the ability of a multi-robot system to measure the relative motion of robots using laser range finders. Mounted on each robot is a 2D laser range finder attached to a servo to enable 3D scanning. The lead robot has an easily recognized target panel that allows the follower robot to measure both the relative distance and orientation between robots. First, these measurements are used to enable 2D (SLAM) of a lava tube. Second, the 3D range measurements are fused with the 2D maps via ICP algorithms to construct full 3D representations. This method of 3D mapping does not require odometry measurements or fine-scale environment features. It was validated in a building hallway system, demonstrating successful loop closure and mapping errors on the order of 0.63 m over a 79.64 m long loop. Error growth models were determined experimentally that indicate the robot localization errors grow at a rate of 20 mm per meter travelled, although this is also dependent on the relative orientation of robots localizing each other. Finally, the system was deployed in a lava tube located at Pisgah Crater in the Mojave Desert, CA. Data was collected to generate a full 3D map of the lava tube. Comparison with known measurements taken between two ends of the lava tube indicates the mapping errors were on the order of 1.03 m after the robot travelled 32 m.

We describe a two-chip micro-scale time-resolved fluorescence analyzer integrating excitation, detection, and filtering. A new 8×8 array of drivers realized in standard low-voltage 0.35-μm complementary metal-oxide semiconductor is bump-bonded to AlInGaN blue micro-pixellated light-emitting diodes (micro-LEDs). The array is capable of producing sample excitation pulses with a width of 777 ps (FWHM), enabling short lifetime fluorophores to be investigated. The fluorescence emission is detected by a second, vertically-opposed 16 × 4 array of single-photon avalanche diodes (SPADs) fabricated in 0.35-μm high-voltage CMOS technology with in-pixel time-gated photon counting circuitry. Captured chip data are transferred to a PC for further processing, including histogramming, lifetime extraction, calibration and background/noise compensation. This constitutes the smallest reported solid-state microsystem for fluorescence decay analysis, replacing lasers, photomultiplier tubes, bulk optics, and discrete electronics. The system is demonstrated with measurements of fluorescent colloidal quantum dot and Rhodamine samples.

The relatively high shrinkage of the alkali-activated slag (AAS) has restricted its application as a widely-used building material. This research attempts to study the effect of a hydrothermally synthesized C-A-S-H gel, which has a similar composition to that of the main AAS product, on the shrinkage performance of the AAS. The C-A-S-H nano-particles were mixed into AAS mortars in a proportion ranging from 1 wt % to 5 wt % using two different methods, and the drying and autogenous shrinkage ratio of modified AAS mortars were measured at various ages. The effect of C-A-S-H on their microstructures was also characterized. Results obtained indicated that the addition of C-A-S-H gel to AAS mortars had reduced their drying and autogenous shrinkage, with the addition of 3 wt % reaching the maximum reduction. However, the added amount was not directly proportional to the decrease of shrinkage, the proportion of early-stage drying shrinkage of AAS mortars was greater than that of autogenous shrinkage, the dispersion method was slightly better than the dry mixing method in both shrinkage reduction. MIP results suggested that the addition of C-A-S-H gel had reduced the total porosity and the average pore size of AAS mortars, optimized their pore structure distribution, and significantly reduced the volume of mesopores (&lt, 0.05 &micro, m) which resulted in high shrinkage, while the adding method had no significant effect on the pore size distribution of AAS mortars. SEM results showed that the addition of C-A-S-H gel can reduce the crack width of mortars, obtain a dense and uniform matrix structure, increase the density, and effectively suppress both shrinkage deformation of the system, whereas the adding method has no obvious effect on the crack width of the mortar. This research provides a novel approach of the AAS shrinkage reduction and structure refinement, shedding lights on nano-material modification of the AAS.