Scholarly Works, Mechanical Engineering

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Research articles, presentations, and other scholarship


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  • Layered control for cooperative locomotion of two quadrupedal robots: Centralized and distributed approaches
    Kim, Jeeseop; Fawcett, Randall T.; Kamidi, Vinay R.; Ames, Aaron D.; Akbari Hamed, Kaveh (Institute of Electrical and Electronics Engineers, 2023)
    This paper presents a layered control approach for real-time trajectory planning and control of robust cooperative locomotion by two holonomically constrained quadrupedal robots. A novel interconnected network of reduced-order models, based on the single rigid body (SRB) dynamics, is developed for trajectory planning purposes. At the higher level of the control architecture, two different model predictive control (MPC) algorithms are proposed to address the optimal control problem of the interconnected SRB dynamics: centralized and distributed MPCs. The distributed MPC assumes two local quadratic programs that share their optimal solutions according to a one-step communication delay and an agreement protocol. At the lower level of the control scheme, distributed nonlinear controllers are developed to impose the full-order dynamics to track the prescribed reduced-order trajectories generated by MPCs. The effectiveness of the control approach is verified with extensive numerical simulations and experiments for the robust and cooperative locomotion of two holonomically constrained A1 robots with different payloads on variable terrains and in the presence of disturbances. It is shown that the distributed MPC has a performance similar to that of the centralized MPC, while the computation time is reduced significantly.
  • Engineered live bacteria as disease detection and diagnosis tools
    Tanniche, Imen; Behkam, Bahareh (2023-10-24)
    Sensitive and minimally invasive medical diagnostics are essential to the early detection of diseases, monitoring their progression and response to treatment. Engineered bacteria as live sensors are being developed as a new class of biosensors for sensitive, robust, noninvasive, and in situ detection of disease onset at low cost. Akin to microrobotic systems, a combination of simple genetic rules, basic logic gates, and complex synthetic bioengineering principles are used to program bacterial vectors as living machines for detecting biomarkers of diseases, some of which cannot be detected with other sensing technologies. Bacterial whole-cell biosensors (BWCBs) can have wide-ranging functions from detection only, to detection and recording, to closed-loop detection-regulated treatment. In this review article, we first summarize the unique benefits of bacteria as living sensors. We then describe the different bacteria-based diagnosis approaches and provide examples of diagnosing various diseases and disorders. We also discuss the use of bacteria as imaging vectors for disease detection and image-guided surgery. We conclude by highlighting current challenges and opportunities for further exploration toward clinical translation of these bacteria-based systems.
  • Interfacial Dynamics in Dual Channels: Inspired by Cuttlebone
    Huang, Matthew; Frohlich, Karl; Esmaili, Ehsan; Yang, Ting; Li, Ling; Jung, Sunghwan (MDPI, 2023-10-01)
    The cuttlebone, a chambered gas-filled structure found in cuttlefish, serves a crucial role in buoyancy control for the animal. This study investigates the motion of liquid-gas interfaces within cuttlebone-inspired artificial channels. The cuttlebone’s unique microstructure, characterized by chambers divided by vertical pillars, exhibits interesting fluid dynamics at small scales while pumping water in and out. Various channels were fabricated with distinct geometries, mimicking cuttlebone features, and subjected to different pressure drops. The behavior of the liquid-gas interface was explored, revealing that channels with pronounced waviness facilitated more non-uniform air-water interfaces. Here, Lyapunov exponents were employed to characterize interface separation, and they indicated more differential motions with increased pressure drops. Channels with greater waviness and amplitude exhibited higher Lyapunov exponents, while straighter channels exhibited slower separation. This is potentially aligned with cuttlefish’s natural adaptation to efficient water transport near the membrane, where more straight channels are observed in real cuttlebone.
  • Experimental and theoretical model for the origin of coiling of cellular protrusions around fibers
    Sadhu, Raj Kumar; Hernandez-Padilla, Christian; Eisenbach, Samo Penič; Zhang, Lixia; Vishwasrao, Harshad D.; Behkam, Bahareh; Konstantopoulos, Konstantinos; Shroff, Hari; Iglič, Aleš; Peles, Elior; Nain, Amrinder S.; Gov, Nir S. (Nature Research, 2023-09-12)
    Protrusions at the leading-edge of a cell play an important role in sensing the extracellular cues during cellular spreading and motility. Recent studies provided indications that these protrusions wrap (coil) around the extracellular fibers. However, the physics of this coiling process, and the mechanisms that drive it, are not well understood. We present a combined theoretical and experimental study of the coiling of cellular protrusions on fibers of different geometry. Our theoretical model describes membrane protrusions that are produced by curved membrane proteins that recruit the protrusive forces of actin polymerization, and identifies the role of bending and adhesion energies in orienting the leading-edges of the protrusions along the azimuthal (coiling) direction. Our model predicts that the cell’s leading-edge coils on fibers with circular cross-section (above some critical radius), but the coiling ceases for flattened fibers of highly elliptical cross-section. These predictions are verified by 3D visualization and quantitation of coiling on suspended fibers using Dual- View light-sheet microscopy (diSPIM). Overall, we provide a theoretical framework, supported by experiments, which explains the physical origin of the coiling phenomenon.
  • Unified Learning from Demonstrations, Corrections, and Preferences during Physical Human-Robot Interaction
    Mehta, Shaunak A.; Losey, Dylan P. (ACM, 2023)
    Humans can leverage physical interaction to teach robot arms. This physical interaction takes multiple forms depending on the task, the user, and what the robot has learned so far. State-of-the-art approaches focus on learning from a single modality, or combine multiple interaction types by assuming that the robot has prior information about the human?s intended task. By contrast, in this paper we introduce an algorithmic formalism that unites learning from demonstrations, corrections, and preferences. Our approach makes no assumptions about the tasks the human wants to teach the robot; instead, we learn a reward model from scratch by comparing the human?s inputs to nearby alternatives. We first derive a loss function that trains an ensemble of reward models to match the human?s demonstrations, corrections, and preferences. The type and order of feedback is up to the human teacher: we enable the robot to collect this feedback passively or actively. We then apply constrained optimization to convert our learned reward into a desired robot trajectory. Through simulations and a user study we demonstrate that our proposed approach more accurately learns manipulation tasks from physical human interaction than existing baselines, particularly when the robot is faced with new or unexpected objectives.
  • High-Frequency Dielectrophoresis Reveals That Distinct Bio-Electric Signatures of Colorectal Cancer Cells Depend on Ploidy and Nuclear Volume
    Duncan, Josie L.; Bloomfield, Mathew; Swami, Nathan; Cimini, Daniela; Davalos, Rafael V. (MDPI, 2023-09-01)
    Aneuploidy, or an incorrect chromosome number, is ubiquitous among cancers. Whole-genome duplication, resulting in tetraploidy, often occurs during the evolution of aneuploid tumors. Cancers that evolve through a tetraploid intermediate tend to be highly aneuploid and are associated with poor patient prognosis. The identification and enrichment of tetraploid cells from mixed populations is necessary to understand the role these cells play in cancer progression. Dielectrophoresis (DEP), a label-free electrokinetic technique, can distinguish cells based on their intracellular properties when stimulated above 10 MHz, but DEP has not been shown to distinguish tetraploid and/or aneuploid cancer cells from mixed tumor cell populations. Here, we used high-frequency DEP to distinguish cell subpopulations that differ in ploidy and nuclear size under flow conditions. We used impedance analysis to quantify the level of voltage decay at high frequencies and its impact on the DEP force acting on the cell. High-frequency DEP distinguished diploid cells from tetraploid clones due to their size and intracellular composition at frequencies above 40 MHz. Our findings demonstrate that high-frequency DEP can be a useful tool for identifying and distinguishing subpopulations with nuclear differences to determine their roles in disease progression.
  • Scale modeling of thermo-structural fire tests
    Gangi, Michael J.; Lattimer, Brian Y.; Case, Scott W. (Wiley, 2023-03)
    Standard methods for fire resistance testing require large-scale assemblies and are typically conducted on specialized furnaces at considerable cost. This research focused on developing a scaling methodology for a reduced-scale fire resistance test that reduces the size of the test article while maintaining the same thermal and structural response exhibited in the large-scale test. The developed scaling methodology incorporates uniform geometric scaling, Fourier number time scaling, and furnace boundary condition matching. The scaling laws were experimentally validated with fire exposure tests on gypsum wallboard samples at three scales (full-scale, 1/2-scale, and 1/6-scale). In the tests, samples were exposed to a full-scale equivalent of 60-min of ASTM E119 fire curve exposure on a reduced-scale horizontal furnace, and the temperature rise through the thickness profile was measured. Models were created to calculate the modified fire curves for the smaller-scale tests. Experimental results show that on the exposed surface, the 1/2-scale absolute temperature was within 1.7% of full-scale, while the 1/6-scale temperature was within 2.5%. While the time-dependent properties of burning and cracking caused visual differences in these gypsum tests, modeling and temperature measurements demonstrated that the test results were thermally similar. The good similarity of temperatures is achievable in fire exposure tests of non-combustible gypsum wallboard down to 1/6-scale.
  • Phononic Bandgap Programming in Kirigami By Unique Mechanical Input Sequencing
    Khosravi, Hesameddin; Li, Suyi (Wiley, 2023-04)
    This study investigates the programming of elastic wave propagation bandgaps in periodic and multi-stable metamaterials by intentionally and uniquely sequencing its constitutive mechanical bits. To this end, stretched kirigami is used as a simple and versatile testing platform. Each mechanical bit in the stretched kirigami can switch between two stable equilibria with different external shapes (aka. "(0)" and "(1)" states). Therefore, by designing the sequence of (0) and (1) bits, one can fundamentally change the underlying periodicity and thus program the phononic bandgap frequencies. This study develops an algorithm to identify the unique periodicities generated by assembling "n-bit strings" consisting of n mechanical bits. Based on a simplified geometry of these n-bit strings, this study also formulates a theory to uncover the rich mapping between input sequencing and output bandgaps. The theoretical prediction and experiment results confirm that the (0) and (1) bit sequencing is effective for programming the phonic bandgap frequencies. Moreover, one can additionally fine-tune the bandgaps by adjusting the global stretch. Overall, the results of this study elucidate new strategies for programming the dynamic responses of architected material systems.
  • Design, development, and analysis of the lower body of next-generation 3D-printed humanoid research platform: PANDORA
    Fuge, Alexander J.; Herron, Connor W.; Beiter, Benjamin C.; Kalita, Bhaben; Leonessa, Alexander (Cambridge University Press, 2023-04)
    The main contribution of this paper is the design and development of the lower body of PANDORA (3D-Printed Autonomous humaNoid Developed for Open-source Research Applications), a new humanoid robotic platform implementing additive manufacturing techniques. The three joint configurations (hip, knee, and ankle) along with the major three structural parts (pelvis, thigh, and shin) of the lower body are discussed. The use of 3D printing and PLA+ material makes the robot an affordable solution for humanoid robotics research that gives a high power-to-weight ratio by significantly reducing the number of parts, as well as manufacturing and assembly time. The range of motion of the lower body of PANDORA has been investigated and is found to be comparable to a human lower body. Further, finite element analysis has been performed on the major parts of the lower body of PANDORA to check the structural integrity and to avoid catastrophic failures in the robot. The use of in-house developed actuators and robot electronics reduces the overall cost of the robot and makes PANDORA easily accessible to the research communities working in the field of humanoids. Overall, PANDORA has the potential for becoming popular between researchers and designers for investigating applications in the field of humanoid robotics, healthcare, and manufacturing, just to mention a few. The mechanical designs presented in this work are available open source to lower the knowledge barrier in developing and conducting research on bipedal robots.
  • Actin Filaments Couple the Protrusive Tips to the Nucleus through the I-BAR Domain Protein IRSp53 during the Migration of Cells on 1D Fibers
    Mukherjee, Apratim; Ron, Jonathan Emanuel; Hu, Hooi Ting; Nishimura, Tamako; Hanawa-Suetsugu, Kyoko; Behkam, Bahareh; Mimori-Kiyosue, Yuko; Gov, Nir Shachna; Suetsugu, Shiro; Nain, Amrinder Singh (Wiley-VCH, 2023-03)
    The cell migration cycle, well-established in 2D, proceeds with forming new protrusive structures at the cell membrane and subsequent redistribution of contractile machinery. Three-dimensional (3D) environments are complex and composed of 1D fibers, and 1D fibers are shown to recapitulate essential features of 3D migration. However, the establishment of protrusive activity at the cell membrane and contractility in 1D fibrous environments remains partially understood. Here the role of membrane curvature regulator IRSp53 is examined as a coupler between actin filaments and plasma membrane during cell migration on single, suspended 1D fibers. IRSp53 depletion reduced cell-length spanning actin stress fibers that originate from the cell periphery, protrusive activity, and contractility, leading to uncoupling of the nucleus from cellular movements. A theoretical model capable of predicting the observed transition of IRSp53-depleted cells from rapid stick-slip migration to smooth and slower migration due to reduced actin polymerization at the cell edges is developed, which is verified by direct measurements of retrograde actin flow using speckle microscopy. Overall, it is found that IRSp53 mediates actin recruitment at the cellular tips leading to the establishment of cell-length spanning fibers, thus demonstrating a unique role of IRSp53 in controlling cell migration in 3D.
  • Role of Secondary Ions on the i-v Characteristics of Oxyfuel Flame Subject to an Electric Field
    Untaroiu, Alexandrina; Rahman, S. M. Mahbobur; Martin, Christopher R. (ASME, 2023-07)
    Recent use of ion currents as a sensing strategy in the mechanized oxyfuel cutting process motivated a series of studies which revealed that the steel work piece contributes secondary ions in addition to the primary ions classically identified in the oxyfuel flame. In this work, we present a computational model that has linked carbon-related chemi-ions as a source of secondary ions in preheating stage of oxyfuel cutting process subject to electric bias voltages. The flames' response to the electric field at different positive and negative polarities manifested a better understanding of the physical behavior of current-voltage (i-v) relationship. While copper surface exhibits stable and repeatable i-v characteristics, sporadically enhanced current was observed in positive saturation regime for steel surface, and this is believed to be due to the presence of secondary chemi-ions. To this extent, a source term of gaseous carbon has been assigned to mimic the 'work surface' reactions. The hypothesis is that since carbon is an important element, it will be diffusing out of the steel surface and evaporate into the flame.
  • Modeling liquid droplet impact on a micropillar-arrayed viscoelastic surface via mechanically averaged responses
    Li, Yang; Cheng, Jiangtao (Taylor & Francis, 2023)
    Droplet impact on a substrate is an intriguing phenomenon that widely exists in our daily life and a broad range of industrial processes. However, droplet impact dynamics on soft textured surfaces are less explored and the underlying mechanisms remain elusive. Here, we report numerical simulation of droplet impact dynamics on a micropillar-arrayed soft surface using BASILISK, which involves a multiscale geometric domain containing the micropillars and droplet that are in the order of mu m and mm, respectively. As such, the volume of fluid (VOF) method is coupled with the finite volume method (FVM) to build the fluid fields and track their interface. From a conceptual point of view, the micropillared substrate is formed by imposing interstitial gaps into the otherwise intact soft material, whose viscoelastic properties can be quantified by gap density epsilon. Via a five-parameter generalized Maxwell model, the viscoelastic properties of the micropillared substrate can be approximated by its equivalent elastic response in the Laplace-Carson (LC) space, and the averaged bulk strain of the micropillared substrate in the real space is obtained by the inverse LC transform. Moreover, through parametric studies of splash extent, it turns out that for a specific epsilon, the splash is dramatically intensified with increasing impact velocity U-i. The splash also turns more violent with increasing ambient pressure P-a, which is evidenced by a larger splash angle of 114.44 degrees between the ejected sheet and the horizontal substrate at 5 atm. Conversely, the splash becomes more depressed with increasing surface tension sigma. Overall, the splash magnitudes of our simulations agree well with those predicted by the Kelvin-Helmholtz instability theory. By leveraging the LC transform in the fluid-viscoelastic solid interactions, our simulation methodology captures the main features of droplet impact dynamics on microstructured viscoelastic surfaces by means of the mechanically averaged responses while avoiding the predicament of domain scale inconsistency.
  • A general Metal-Ion-Modification route for preparing hydrophobic paper and tableware from lignocellulose fibers
    Nayanathara, R. M. Oshani; Leng, Weiqi; Liyanage, Senal D.; Wang, Xiang; Wang, Lu; Wang, Jinwu; Tian, Zhenhua; Pittman, Charles U.; Gwaltney, Steven R.; Zhang, Xuefeng (Elsevier, 2023-03)
    Inherent hydrophilicity and poor water resistance prevent using lignocellulosic materials as green plastic al- ternatives to fossil fuel-based plastics. Here, we report a facile metal-ion-modification (MIM) route, swelling with aqueous metal ion solutions, and drying to convert conventional hydrophilic paper and wood pulp into biode- gradable hydrophobic paper and tableware without the addition of hydrophobic sizing chemicals/materials. Metal ions such as Fe3+ and Zr4+ can coordinate with pulp fibers' polar groups (i.e., OH, C-O, and COOH) that induce self-assembly of their surface fibrillated "hairy" cellulose nanofibrils to form a more compact structure with fewer available OH groups for water sorption. This decreases the surface energy of pulp fibers and increases their hydrophobicity and water resistance. Only similar to 3 mg of metal ions is needed to induce the wettability tran- sition in 1 g of kraft pulp, resulting in hydrophobic paper and tableware with water contact angles (WCAs) of 120-140 degrees. The coordinated Fe3+ and Zr4+ are stable, with negligible metal leaching during use, allowing the hydrophobic paper and tableware to be used for food packaging. This MIM technique can be integrated into the existing paper-making process for the scalable production of hydrophobic papers and tableware, providing an alternative route for developing sustainable and biodegradable plastic counterparts.
  • A Real-Time Underwater Acoustic Telemetry Receiver With Edge Computing for Studying Fish Behavior and Environmental Sensing
    Yang, Yang; Elsinghorst, Robbert; Martinez, Jayson J.; Hou, Hongfei; Lu, Jun; Deng, Zhiqun Daniel (IEEE, 2022-09)
    Underwater acoustic telemetry has emerged as a powerful tool for practical applications, including resource exploration, environmental monitoring, and aquatic animal tracking. However, current acoustic telemetry systems lack the capability to transmit the collected data continuously in real time, primarily because the acoustic networking bandwidth is limited. Retrieval of the recorded measurements from the deployed receivers usually must be manual, leading to long delays in data retrieval and processing, high operational costs associated with the required manpower, and safety risks for the operators. In addition, there is no efficient way to continuously assess the status of the acoustic telemetry system, including the acoustic transmitters and receivers. Here, we describe the design, implementation, and field validation of a cloud-based, real-time, underwater acoustic telemetry system with edge computing for estimating fish behavior and monitoring environmental parameters. The system incorporates microcontrollers for edge computing and connects to a cloud-based service that further post-processes the transmitted data stream to derive behavior and survival information of tagged animals. The developed system has been demonstrated to have significantly improved performance over the benchmark system because of the integration of edge computing, with a greatly reduced energy consumption of 0.014 W resulting in the energy used by the acoustic modem being reduced by over 300 times. This work opens up new design opportunities for future real-time and multifunctional underwater acoustic systems.
  • The Surface Accelerations Reference— A Large-Scale, Interactive Catalog of Passenger Vehicle Accelerations
    Ali, Gibran; McLaughlin, Shane; Ahmadian, Mehdi (IEEE, 2023-04)
    There is a need for a large-scale, real world, diverse, and context rich vehicle acceleration catalog that can be used to design, analyze, and compare various intelligent transportation systems. This paper fulfills three primary objectives. First, it provides such a catalog through the Surface Accelerations Reference, which is openly available as an interactive analytics tool as well as an open and downloadable dataset. The Surface Accelerations Reference statistically describes the driving profiles of about 3,500 individuals contributing 34 million miles of continuous driving data collected in the Second Strategic Highway Research Program Naturalistic Driving Study (SHRP 2 NDS). These profiles were created by summarizing billions of longitudinal and lateral acceleration epochs experienced by the participants. Second, this paper introduces a standardized methodology for creating such a catalog so that similar acceleration profiles can be produced for other human cohorts or automated driving systems. Finally, the data are used to analyze the effect of roadway speed category on the rates of lateral and longitudinal acceleration epochs at various thresholds. It is observed that, for the median driver, the rates of epochs are up to three orders of magnitude higher on low-speed roads as compared to high-speed roads. This catalog will facilitate intelligent vehicle system designers to compare and tune their systems for safer driving experiences. It will also allow agencies with similar data to create comparable catalogs facilitating safety and behavioral comparisons between populations. Datasets:
  • Qualifying the contribution of fiber diameter on the acrylate-based electrospun shape memory polymer nano/microfiber properties
    Xi, Jiaxin; Shahab, Shima; Mirzaeifar, Reza (Royal Society Chemistry, 2022-10)
    Fibrous shape memory polymers (SMPs) have received growing interest in various applications, especially in biomedical applications, which offer new structures at the microscopic level and the potential of enhanced shape deformation of SMPs. In this paper, we report on the development and investigation of the properties of acrylate-based shape memory polymer fibers, fabricated by electrospinning technology with the addition of polystyrene (PS). Fibers with different diameters are manufactured using four different PS solution concentrations (25, 30, 35, and 40 wt%) and three flow rates (1.0, 2.5, and 5.0 mu L min(-1)) with a 25 kV applied voltage and 17 cm electrospinning distance. Scanning electron microscope (SEM) images reveal that the average fiber diameter varies with polymer concentration and flow rates, ranging from 0.655 +/- 0.376 to 4.975 +/- 1.634 mu m. Dynamic mechanical analysis (DMA) and stress-strain testing present that the glass transition temperature and tensile values are affected by fiber diameter distribution. The cyclic bending test directly proves that the electrospun SMP fiber webs are able to fully recover; additionally, the recovery speed is also affected by fiber diameter. With the combination of the SMP material and electrospinning technology, this work paves the way in designing and optimizing future SMP fibers properties by adjusting the fiber diameter.
  • Corrosion behavior of aluminum alloy in simulated nuclear accident environments regarding the chemical effects in GSI-191
    Wang, Da; Leong, Amanda; Yang, Qiufeng; Zhang, Jinsuo (Korean Nuclear Society, 2022-11)
    Long-term aluminum (Al) corrosion tests were designed to investigate the condition that would generate severe Al corrosion and precipitation. Buffer agents of sodium tetraborate (NaTB), trisodium phosphate (TSP) and sodium hydroxide (NaOH) were adopted. The insulation materials, fiberglass and calcium silicate (Ca-sil), were examined to explore their effects on Al corrosion. The results show that significant precipitates were formed in both NaTB/TSP-buffered solutions at high pH. The precipitates formed in NaTB solution raise more concerns on chemical effects in GSI-191. A passivation layer formed on the surfaces of coupon in solution with the presence of insulations could effectively mitigate Al corrosion. The Fe-enriched intermetallic particles (IPs) embedded in coupon appeared to serve as seeds to readily induce precipitation via providing extra area for heterogeneous Al hydroxide precipitation. X-ray spec-troscopy (EDS) and X-ray diffraction (XRD) analyses indicate that the precipitates are mainly boehmite (g-AlOOH) and no direct evidence confirms the presence of sodium aluminum silicate or calcium phosphate.
  • Reducing Frost during Cryoimaging Using a Hygroscopic Ice Frame
    Lowery, Adam W.; Ambi, Ashwin; Miller, Lisa M.; Boreyko, Jonathan B. (American Chemical Society, 2022-12)
    Cryomicroscopy is commonly hampered by frost accumulation, reducing the visual clarity of the specimen. Pulling a vacuum or purging with nitrogen gas can greatly reduce the sample chamber's humidity, but at cryogenic temperatures, even minute concentrations of water vapor can still result in frost deposition. Here, a hygroscopic ice frame was created around the specimen to suppress frost growth during cryomicroscopy. Specifically, fluorescently tagged rat brain vessels were frozen on a silicon nitride window with an ice frame, and the luminescence of the fluorescent tag was improved by a factor of 6 compared to a similar specimen in only a nitrogen purge environment. These findings suggest that the simple implementation of a hygroscopic ice frame surrounding the specimen can substantially improve the visual clarity for cryomicroscopy, beyond that of a vacuum or nitrogen purge system.
  • Molecular Weight Distribution of Branched Polymers: Comparison between Monte Carlo Simulation and Flory-Stockmayer Theory
    Wen, Chengyuan; Odle, Roy; Cheng, Shengfeng (MDPI, 2023-04-04)
    It is challenging to predict the molecular weight distribution (MWD) for a polymer with a branched architecture, though such information will significantly benefit the design and development of branched polymers with desired properties and functions. A Monte Carlo (MC) simulation method based on the Gillespie algorithm is developed to quickly compute the MWD of branched polymers formed through step-growth polymerization, with a branched polyetherimide from two backbone monomers (4,4′-bisphenol A dianhydride and m-phenylenediamine), a chain terminator (phthalic anhydride), and a branching agent (tris[4-(4-aminophenoxy)phenyl] ethane) as an example. This polymerization involves four reactions that can be all reduced to a condensation reaction between an amine group and a carboxylic anhydride group. A comparison between the MC simulation results and the predictions of the Flory-Stockmayer theory on MWD shows that the rates of the reactions are determined by the concentrations of the functional groups on the monomers involved in each reaction. It further shows that the Flory-Stockmayer theory predicts MWD well for systems below the gel point but starts to fail for systems around or above the gel point. However, for all the systems, the MC method can be used to reliably predict MWD no matter if they are below or above the gel point. Even for a macroscopic system, a converging distribution can be quickly obtained through MC simulations on a system of only a few hundred to a few thousand monomers that have the same molar ratios as in the macroscopic system.
  • The Ethics of Mandatory Exoskeleton Use in Commercial and Industrial Settings
    Pote, Timothy R.; Asbeck, Nicole V.; Asbeck, Alan T. (IEEE, 2023-04)
    Research shows exoskeletons can reduce muscle activity and decrease the risk of injury for workers. Exoskeletons, therefore, are becoming more prevalent in industrial workplaces, and their use in some circumstances has already been mandated. It is probable that additional employers will mandate the use of exoskeletons as a means of mitigating injuries to their employees. This presents ethical concerns because employers hold power over the employees’ wages and employment. Some employees who are required to wear exoskeletons may not be able to, while others may not wish to. How should workers’ privacy and preferences be weighted? Should employees be prohibited from jobs that use exoskeletons if the exoskeletons do not fit them or if they do not wish to disclose their body’s measurements? Should companies using exoskeletons be permitted to require workers to perform additional work with an exoskeleton? In this paper, we examine these and other ethical considerations related to mandatory exoskeleton use through the Six Pillars of Character framework of the Josephson Institute of Ethics (2002) and the Universal Moral Values for Corporate Codes of Ethics framework by Schwartz (2005). We provide a discussion of possible solutions following ethical tenets, including executing pilot studies before mandatory use policies, offering several self-adjustable models of exoskeletons, and allowing existing workers to transfer jobs if they are ill at ease with new exoskeleton policies. The best course of action may depend on specific individual circumstances.