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1. Influence of multi-walled carbon nanotubes on the hydration products of ordinary Portland cement paste

   https://doi.org/https://doi.org/10.1016/j.cemconres.2020.106197  

   Jiaxin Chen, Ange-Therese Akono (November 2020, Cement and concrete research)

   null (Ed.)

   We elucidate the mechanisms by which multi-walled carbon nanotubes (MWCNTs) influence the microstructure, fracture behavior, and hydration of cement paste. We disperse MWCNTs using a multi-step approach that involves high-energy pre-dispersion using ultrasonic energy followed by low-energy dispersion using un-hydrated cement particles. In turn, the low-energy dispersion step involves high-shear mixing and mechanical stirring. High-resolution environmental scanning electron microscopy of cement+0.2 wt% MWCNT, cement+0.5 wt% MWNCT, and of cement+1 wt% MWCNT show that MWCNTs bridge air voids, thereby refining the pore size and strengthening the C-S-H matrix. The fracture toughness increased by 9.38% with the addition of 0.2 wt% multi-walled carbon nanotubes, and by 14.06% with the addition of 0.5 wt% multi-walled carbon nanotubes and ligament bridging was the dominant toughening mechanism. Moreover, for all reinforcement levels, MWCNTs induced a conversion of low-density C-S-H into high-density C-S-H along with a drastic drop in the capillary porosity: adding 0.1–0.5 wt% MWCNT resulted in a 200% increase in the volume fraction of high-density C-S-H. Thus, our experiments show that MWCNT enhances the mechanical properties and transport properties by: (i) promoting high-density C-S-H formation, (ii) promoting calcium hydroxide formation, (iii) filling microscopic air voids, (iv) reducing the capillary porosity, (v) increasing the fraction of small gel pores (1.2–2 nm in size), and (vi) by bridging microcracks. 

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2. Measuring and Simulating the Transient Packing Density During Ultrasound Directed Self‐Assembly and Vat Polymerization Manufacturing of Engineered Materials

   https://doi.org/10.1002/admt.202301950  

   Noparast, Soheyl; Guevara_Vasquez, Fernando; Francoeur, Mathieu; Raeymaekers, Bart (June 2024, Advanced Materials Technologies)

   Abstract Ultrasound‐directed self‐assembly (DSA) uses ultrasound waves to organize and orient particles dispersed in a fluid medium into specific patterns. Combining ultrasound DSA with vat photopolymerization (VP) enables manufacturing materials layer‐by‐layer, wherein each layer the organization and orientation of particles in the photopolymer is controlled, which enables tailoring the properties of the resulting composite materials. However, the particle packing density changes with time and location as particles organize into specific patterns. Hence, relating the ultrasound DSA process parameters to the transient local particle packing density is important to tailor the properties of the composite material, and to determine the maximum speed of the layer‐by‐layer VP process. This paper theoretically derives and experimentally validates a 3D ultrasound DSA model and evaluates the local particle packing density at locations where particles assemble as a function of time and ultrasound DSA process parameters. The particle packing density increases with increasing particle volume fraction, decreasing particle size, and decreasing fluid medium viscosity is determined. Increasing the particle size and decreasing the fluid medium viscosity decreases the time to reach steady‐state. This work contributes to using ultrasound DSA and VP as a materials manufacturing process. 

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3. Longitudinal Monostatic Acoustic Effective Bulk Modulus and Effective Density Evaluation of Underground Soil Quality: A Numerical Approach

   https://doi.org/10.3390/app11010146  

   Jin, Yuqi; Choi, Tae-Youl; Neogi, Arup (January 2021, Applied Sciences)

   null (Ed.)

   In this study, we introduce a novel method using longitudinal sound to detect underground soil voids to inspect underwater bed property in terms of effective bulk modulus and effective density of the material properties. The model was simulated in terms of layered material within a monostatic detection configuration. The numerical model demonstrates the feasibility of detecting an underground air void with a spatial resolution of about 0.5 λ and can differentiate a soil firmness of about 5%. The proposed technique can overcome limitations imposed by conventional techniques that use spacing-consuming sonar devices and suffer from low penetration depth and leakage of the transverse sound wave propagating in an underground fluid environment. 

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4. Properties of Voids and Void Galaxies in the TNG300 Simulation

   https://doi.org/10.3847/1538-4357/ad18b4  

   Curtis, Olivia; McDonough, Bryanne; Brainerd, Tereasa G (February 2024, The Astrophysical Journal)

   Abstract We investigate the properties of voids and void galaxies in theTNG300simulation. Using a luminous galaxy catalog and a spherical void-finding algorithm, we identify 5078 voids at redshiftz= 0. The voids cover 83% of the simulation volume and have a median radius of 4.4h⁻¹Mpc. We identify two populations of field galaxies based on whether the galaxies reside within a void (“void galaxies”; 75,220 objects) or outside a void (“nonvoid galaxies”; 527,454 objects). Within the voids, mass does not directly trace light. Instead, the mean radial underdensity profile as defined by the locations of void galaxies is systematically lower than the mean radial underdensity profile as defined by the dark matter (i.e., the voids are more “devoid” of galaxies than they are of mass). Within the voids, the integrated underdensity profiles of the dark matter and the galaxies are independent of the local background density (i.e., voids-in-voids versus voids-in-clouds). Beyond the void radii, however, the integrated underdensity profiles of both the dark matter and the galaxies exhibit strong dependencies on the local background density. Compared to nonvoid galaxies, void galaxies are on average younger, less massive, bluer in color, less metal enriched, and have smaller radii. In addition, the specific star formation rates of void galaxies are ∼20% higher than nonvoid galaxies and, in the case of galaxies with central supermassive black holes withM_BH≳ 3 × 10⁶h⁻¹M_⊙, the fraction of active void galaxies is ∼25% higher than active nonvoid galaxies. 

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5. Enhanced Instantaneous Elastography in Tissues and Hard Materials Using Bulk Modulus and Density Determined without Externally Applied Material Deformation

   https://doi.org/10.1109/TUFFC.2019.2950343  

   Jin, Yuqi; Walker, Ezekiel; Krokhin, Arkadii; Heo, Hyeonu; Choi, Tae-Youl; Neogi, Arup (October 2019, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control)

   —Ultrasound is a continually developing technology that is broadly used for fast, non-destructive mechanical property detection of hard and soft materials in applications ranging from manufacturing to biomedical. In this study, a novel monostatic longitudinal ultrasonic pulsing elastography imaging method is introduced. Existing elastography methods require an acoustic radiational or dynamic compressive externally applied force to determine the effective bulk modulus or density. This new, passive M-mode imaging technique does not require an external stress, and can be effectively utilized for both soft and hard materials. Strain map imaging and shear wave elastography are two current categories of M-mode imaging that show both relative and absolute elasticity information. The new technique is applied to hard materials and soft material tissue phantoms for demonstrating effective bulk modulus and effective density mapping. As compared to standard techniques, the effective parameters fall within 10% of standard characterization methods for both hard and soft materials. As neither the standard A-mode imaging technique nor the presented technique require an external applied force, the techniques are applied to composite heterostructures and the findings presented for comparison. The presented passive M-mode technique is found to have enhanced resolution over standard A-mode modalities. 

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