Department of Mechanical Engineering

The vast capabilities of autonomous underwater vehicles (AUVs)—such as in assisting scientific research, conducting military tasks, and repairing oil pipelines—are limited by high operating costs and the relative inaccessibility of power in the open ocean. Wave powered AUV charging stations may address these issues. With projected increases in usage of AUVs globally in the next five years, AUV charging stations can enable less expensive and longer AUV missions. This paper summarizes the design process and investigates the feasibility of a wave powered, mobile AUV charging station, including the choice of a wave energy converter and AUV docking station as well as the ability to integrate the charging station with an autonomous surface vehicle. The charging station proposed in this paper meets many different commercial, scientific, and defense needs, including continuous power availability, data transmission capabilities, and mobility. It will be positioned as a hub for AUV operations, enabling missions to run autonomously with no support ship. The potential market for this design is very promising, with an estimated $1.64 million market size just for AUV technologies by 2025.

This study focuses on solving the numerical challenges of imposing absorbing boundary conditions for dynamic simulations in the material point method (MPM). To attenuate elastic waves leaving the computational domain, the current work integrates the Perfectly Matched Layer (PML) theory into the implicit MPM framework. The proposed approach introduces absorbing particles surrounding the computational domain that efficiently absorb outgoing waves and reduce reflections, allowing for accurate modeling of wave propagation and its further impact on geotechnical slope stability analysis. The study also includes several benchmark tests to validate the effectiveness of the proposed method, such as several types of impulse loading and symmetric and asymmetric base shaking. The conducted numerical tests also demonstrate the ability to handle large deformation problems, including the failure of elasto-plastic soils under gravity and dynamic excitations. The findings extend the capability of MPM in simulating continuous analysis of earthquake-induced landslides, from shaking to failure.

BACKGROUND: Focal ablation techniques are integral in the surgical intervention of diseased tissue, where it is necessary to minimize damage to the surrounding parenchyma and critical structures. Irreversible electroporation (IRE) and high-frequency IRE (H-FIRE), colloquially called pulsed-field ablation (PFA), utilize high-amplitude, low-energy pulsed electric fields (PEFs) to nonthermally ablate soft tissue. PEFs induce cell death through permeabilization of the cellular membrane, leading to loss of homeostasis. The unique nonthermal nature of PFA allows for selective cell death while minimally affecting surrounding proteinaceous structures, permitting treatment near sensitive anatomy where thermal ablation or surgical resection is contraindicated. Further, PFA is being used to treat tissue when tumor margins are not expected after surgical resection, termed margin accentuation. This review explores both the theoretical foundations of PFA, detailing how PEFs induce cell membrane destabilization and selective tissue ablation, the outcomes following treatment, and its clinical implications across oncology and cardiology. CONCLUSIONS: Clinical experience is still progressing, but reports have demonstrated that PFA reduces complications often seen with thermal ablation techniques. Mounting oncology data also support that PFA produces a robust immune response that may prevent local recurrences and attenuate metastatic disease. Despite promising outcomes, challenges such as optimizing field delivery and addressing variations in tissue response require further investigation. Future directions include refining PFA protocols and expanding its application to other therapeutic areas like benign tissue hyperplasia and chronic bronchitis.

Endothelial cell damage after cold preservation and reperfusion injury causes deterioration of the endothelial barrier and ultimately results in edema, leading to transplant failure. Here, a vascular microphysiological system (MPS) is introduced as a testbed to investigate the combinational effect of thermal and fluid perturbations (i.e., wall shear stress) on human endothelial barrier function. Two methods of organ storage are compared: isochoric supercooling (ISC) preservation, which prevents ice formation at subzero temperatures; and, the standard clinical protocol of static cold storage (SCS) at 4 °C. Integrating electrical impedance measurements on chip allow real-time monitoring and quantification of barrier function during preservation and reperfusion protocols. Isochoric supercooling preservation enables longer periods of preservation with superior recovery of barrier function during reperfusion, and has lower metabolic activities compared to static cold storage. Genomic analysis reveals injury and recovery mechanisms at the molecular level for the different preservation and reperfusion conditions. The multifunctional vascular microphysiological system provides a physiologically relevant in vitro model recapitulating ischemia-reperfusion injury to the endothelium. The vascular MPS has potential for optimizing organ preservation protocols, ultimately improving organ transplant viability.

Photonic surfaces designed with specific optical characteristics are becoming increasingly crucial for novel energy harvesting and storage systems. The design of these surfaces can be achieved by texturing materials using lasers. The optimal adjustment of laser fabrication parameters to achieve target surface optical properties is an open challenge. Thus, we develop a surrogate-based optimization approach. Our framework employs the Random Forest algorithm to model the forward relationship between the laser fabrication parameters and the resulting optical characteristics. During the optimization process, we use a greedy, prediction-based exploration strategy that iteratively selects batches of laser parameters to be used in experimentation by minimizing the predicted discrepancy between the surrogate model's outputs and the user-defined target optical characteristics. This strategy allows for efficient identification of optimal fabrication parameters without the need to model the error landscape directly. We demonstrate the efficiency and effectiveness of our approach on two synthetic benchmarks and two specific experimental applications of photonic surface inverse design targets. By calculating the average performance of our algorithm compared to other state of the art optimization methods, we show that our algorithm performs, on average, twice as well across all benchmarks. Additionally, a warm starting inverse design technique for changed target optical characteristics enhances the performance of the introduced approach.

Predictive synthesis of aqueous organic solutions with desired liquid-solid phase equilibria could drive progress in industrial chemistry, cryopreservation, and beyond, but is limited by the predictive power of current solution thermodynamics models. In particular, few analytical models enable accurate liquidus and eutectic prediction based only on bulk thermodynamic properties of the pure components, requiring instead either direct measurement or costly simulation of solution properties. In this work, we demonstrate that a simple modification to the canonical ideal solution theory accounting for the entropic effects of dissimilar molecule sizes can transform its predictive power. Incorporating a Flory-style entropy of mixing term that includes both the mole and volume fractions of each component, we derive size-dependent equations for the ideal chemical potential and liquidus temperature, and use them to predict the binary phase diagrams of water and 10 organic solutes of varying sizes. We show that size-dependent prediction outperforms the ideal model in all cases, reducing average error in the predicted liquidus temperature by 59% (to 5.6 K), eutectic temperature by 45% (to 9.7 K), and eutectic composition by 43% (to 4.7 mol%), as compared to experimental data. Furthermore, by retaining the ideal assumption that the enthalpy of mixing is zero, we demonstrate that, for aqueous organic solutions, much of the deviation from ideality that is typically attributed to molecular interactions may in fact be explained by simple entropic size effects. These results suggest an underappreciated dominance of mixing entropy in these solutions, and provide a simple approach to predicting their phase equilibria.

The absence of affordable and deployable large-scale energy storage poses a major barrier to providing zero-emission energy on demand for societal decarbonization. High temperature thermal energy storage is one promising option with low cost and high scalability, but it is hindered by the inherent complexity of simultaneously satisfying all of the material requirements. Here we design a class of ceramic-carbon composites based on co-optimizing mechanical, electrical, and thermal properties. These composites demonstrate stability in soak-and-hold tests and direct self-heating up to 1,936 °C and 750 thermal cycles from 500 to 1,630 °C without degradation. This thermal performance derives from their composition and microstructural design as verified by in situ high-temperature transmission electron microscopy and X-ray diffraction. They offer both higher energy density and lower cost than conventional storage technologies with a projected system Levelized Cost of Storage below the U.S. Department of Energy’s 2030 target 5 ¢/kWh (electric).

Ultrafast near-field optical nanoscopy has emerged as a powerful platform to characterize low-dimensional materials. While analytical and numerical models have been established to account for photoexcited carrier dynamics, quantitative evaluation of the associated pulsed laser heating remains elusive. Here, we decouple the photocarrier density and temperature increase in near-field nanoscopy by integrating the two-temperature model (TTM) with finite-difference time-domain (FDTD) simulations. These results reveal that the electron-phonon coupling in a silicon film after femtosecond laser excitation is most pronounced within approximately 3 ps─substantially shorter than the photocarrier decay time scale at tens of picoseconds. Moreover, the coupled TTM-FDTD method indicates that ultrafast laser heating can cause up to a 14% variation in the near-field signal at a 220 μJ/cm2 pump pulse fluence. Our numerical results are further validated by transient experiments, highlighting the potential of this method for investigations of carrier and thermal phenomena in emerging nanomaterials and nanodevices.

This study evaluates the effectiveness of isochoric impregnation during isochoric cold storage in extending the shelf life of strawberries. Strawberries in two different impregnation solutions-(1) sucrose solution and (2) sucrose solution containing calcium chloride (CaCl2) and ascorbic acid (AA)-were first stored in an isochoric chamber at -2 °C/48 MPa for 1 week, followed by refrigeration at 4 °C for 3 weeks. For comparison, strawberries were also immersed in each solution for 1 week at 4 °C then refrigerated at 4 °C for 3 weeks. Additionally, a control group of fresh strawberries was stored at 4 °C for 4 weeks. The quality of the strawberries was assessed at 1-week intervals throughout the storage period. Isochoric cold storage effectively inhibited microbial growth and reduced the weight loss of the strawberries compared to refrigerated storage. Also, isochoric cold storage resulted in strawberries that retained their color attributes, whereas refrigeration led to a significant change in their color attributes. Isochoric impregnated strawberries in the sucrose solution containing CaCl2 and AA showed better mechanical properties and higher nutrient contents (anthocyanins and ascorbic acid) than those impregnated in the sucrose solution, impregnated in the solutions at 4 °C, and refrigerated with no impregnation (control). The results demonstrated that isochoric cold storage in a solution containing sucrose, CaCl2, and ascorbic acid effectively maintained the quality of the strawberries, as indicated by parameters such as firmness, color retention, and reduced microbial growth. This method extended the strawberries shelf life by up to 4 weeks.

The continuing developments in semiconductor device technologies have prompted the need for advanced nanoscale processing techniques. Laser chemical processing offers significant advantages, including spatial selectivity, high localization, minimal material damage, and fast operation. Pulsed laser-induced dissociation of gas species serves as an essential process step, contributing to doping, etching, and other chemical modifications of semiconductor materials. However, the mechanisms behind the laser-gas interactions and subsequent surface modifications remain elusive. Here, we demonstrate ultraviolet picosecond laser-induced atomic layer etching of silicon in a gaseous chlorine environment, achieving self-limited etching with a precision of 0.93 nm/cycle. Through in situ optical emission spectroscopy, we elucidate the transition energy states of laser-excited products during chlorination. Complementing our experimental findings, we perform numerical modeling that reveals the complex spatiotemporal dynamics of chlorine species, encompassing their generation, recombination, diffusion, and transient surface reaction with the silicon substrate. Our study demonstrates optical diagnostics of laser-induced chlorination in atomic layer etching, which can provide valuable insights into ultrafine chemical nanostructuring of semiconductor materials.