Penn Engineering Events

CBE Seminar: "No Equations, No Variables, No Space, No Time: Data and the Modeling of Complex Systems”
2021-09-08 15:30 - 16:30 (America/New_York) | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Abstract
Obtaining predictive dynamical equations from data lies at the heart of science and engineering modeling, and is the linchpin of our technology. In mathematical modeling, one typically progresses from observations of the world (and some serious thinking!) first to equations for a model, and then to the analysis of the model to make predictions. Good mathematical models give good predictions (and inaccurate ones do not), but the computational tools for analyzing them are the same: algorithms that are typically based on closed form equations.
While the skeleton of the process remains the same, today we witness the development of mathematical techniques that operate directly on observations data, and appear to circumvent the serious thinking that goes into selecting variables and parameters and deriving accurate equations. The process then may appear to the user a little like making predictions by “looking in a crystal ball”. Yet the “serious thinking” is still there and uses the same – and some new – mathematics: it goes into building algorithms that jump directly from data to the analysis of the model (which is now not available in closed form) so as to make predictions. Our work here presents a couple of efforts that illustrate this ”new” path from data to predictions. It really is the same old path, but it is traveled by new means.

MEAM Seminar: "The Role of Manipulation Primitives in Building Dexterous Robotic Systems"
2021-09-07 10:00 - 11:30 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
In this talk I will illustrate four different perspectives that we as a community have embraced to study robotic manipulation: 1) controlling a simplified model of the mechanics of interaction with an object; 2) using haptic feedback such as force or tactile to control the interaction with an environment; 3) planning sequences or trajectories of manipulation actions to achieve long-horizon goals; and 4) using visual cues to guide manipulation actions. These are complementary perspectives, and building general dexterous robotic manipulation systems requires integrating them. I will discuss the key role that manipulation primitives play at integrating these perspectives. In particular I will present recent work on tactile dexterity to embed tactile feedback into the mechanics models of frictional contact, and on planning with visual affordances to execute dexterous long-term behavior on novel objects. I will illustrate this work in the context of a dual-arm dexterous robotic system.

BE Seminar: "Synthetic Biochemistry: Engineering Molecules and Pathways for Precision Medicine" (Michael Lin)
2021-09-02 15:30 - 16:30 | Moore 216, 200 S. 33rd Street, Philadelphia, PA, 19104, United States
Update 9/2/21: Unfortunately due to the flooding in Philadelphia we will not be able to hold this seminar on campus. Check your email for the zoom link or contact ksas@seas.upenn.edu.
The most effective medicines are those that target the earliest causes of disease, rather than later manifestations. Engineering of biomolecules is a promising but underexplored approach to precisely detecting or targeting disease causes. I will present our work to develop a novel approach to treating cancer by detecting the signaling abnormalities that give rise to cancer. Interestingly, this effort involves biomolecular engineering at multiple scales: proteins, pathways, and viruses. I will also discuss how our work has translated serenditously to developing treatments for SARSCoV2.

BE Doctoral Dissertation: "From '-omics' to biomarkers and mechanisms in Parkinson's disease: Growth hormone receptor and GPNMB" (Maria E. Diaz Ortiz)
2021-09-02 13:00 - 14:00 | https://upenn.zoom.us/j/96715197752
The Department of Bioengineering at the University of Pennsylvania and Dr. Alice S. Chen-Plotkin are pleased to announce the Doctoral Dissertation Defense of Maria E. Diaz Ortiz.

Title: From ‘-omics’ to biomarkers and mechanisms in Parkinson’s disease: Growth hormone receptor and GPNMB
Date/Time: Thursday, September 2nd from 1-2 PM EST
Zoom Link: https://us02web.zoom.us/j/83054658861?pwd=[REDACTED]

ODEI Spotlight: SAC Fall Activities Fair Day 3
2021-09-02 12:00 - 16:00
This is an opportunity to get to know more about the many undergraduate student organizations that exist at Penn. In addition to the in-person events being hosted 8/31-9/2 on College Green, groups will be available to connect virtually from 6-8pm these same days via PennClubs.com.

MSE Thesis Defense: "An In Situ Study of Resistance Degradation and Switching of Bulk Yttria-Stabilized Zirconia and Strontium Titanate Single Crystals"
2021-09-01 16:00 - 17:00

BE Doctoral Dissertation: "Adaptation of Maternal Skeletal Mechano-responsiveness, Osteocyte Microenvironment, and Bone Marrow Adipocytes in Response to Reproduction and Lactation" (Yihan Li)
2021-09-01 13:00 - 15:00 | https://upenn.zoom.us/j/96715197752
The Department of Bioengineering at the University of Pennsylvania and Dr. X. Sherry Liu are pleased to announce the Doctoral Dissertation Defense of Yihan Li.

Title: “Adaptation of Maternal Skeletal Mechano-responsiveness, Osteocyte Microenvironment, and Bone Marrow Adipocytes in Response to Reproduction and Lactation”

Date: September 1, 2021
Time: 1:00 PM
The public is welcome to attend via the Zoom link below:
https://upenn.zoom.us/j/7602733549

ODEI Spotlight: SAC Fall Activities Fair Day 2
2021-09-01 12:00 - 16:00

ODEI Spotlight: SAC Fall Activities Fair
2021-08-31 12:00 - 16:00
This is an opportunity to get to know more about the many undergraduate student organizations that exist at Penn. In addition to the in-person events being hosted 8/31-9/2, groups will be available to connect virtually from 6-8pm these same days via PennClubs.com.

PSOC Webinar: Kuangzheng (Peter) Zhu
2021-08-30 12:00 - 12:30 | https://upenn.zoom.us/j/96715197752
Zoom Meeting Waiting Room (email discher@seas for entry)

https://upenn.zoom.us/j/95100409935?pwd=[REDACTED]

Meeting ID: 951 0040 9935
Passcode: [REDACTED]

PSOC@Penn Summer Webinars 2021
Contact manu@seas.upenn.edu with any questions

BE Doctoral Dissertation: "Biophysical dynamics of RGS-LOV proteins as systems for light-induced membrane recruitment" (Ivan Kuznetsov)
2021-08-30 10:00 - 12:00 | Room 307, Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
The Department of Bioengineering at the University of Pennsylvania and
Dr. Brian Chow are pleased to announce the Doctoral Dissertation Defense of Ivan Kuznetsov.
Title: Biophysical dynamics of RGS-LOV proteins as systems for light-induced membrane recruitment
Date: August 30, 2021
Time: 10:00 AM
Location: Levine 307 and via zoom at the link below:

https://upenn.zoom.us/j/93272141232?pwd=[REDACTED]
Abstract:
Light–oxygen–voltage sensitive (LOV) domains represent a ubiquitous family of blue-light photoreceptors. Recently, we reported BcLOV4, a LOV protein from B. cinerea, which demonstrates a light-induced protein-lipid interaction with the plasma membrane. Previous work demonstrated preliminary characterization of BcLOV4 but stopped short of demonstrating its applications as an optogenetic tool. Here, we report a 3D non-linear finite element model of the cell-wide spatiotemporal dynamics of BcLOV4 membrane recruitment. Inputs were data from single cells unique in morphology and initial absolute protein concentration, as opposed to fitting an idealized cell to population data. All necessary BcLOV4 biophysical parameters were measured with recombinant protein or in HEK cells. The model outperforms existing (2D and/or linear) approaches and recapitulates observed complexities, including cell-geometric effects on recruitment efficiency and inter-instrument diffractive effects. It also highlights underappreciated determinants of signaling magnitude, contrast, and spatial confinement – such as the nonlinearity introduced by finite membrane-binding sites, outsized role of rebinding kinetics, and impact of excitation volume on the signaling impulse response. By capturing both intrinsic biophysical contributions of the optogenetic tools and extrinsic contributions of the optical hardware, this framework improves understanding of how to spatiotemporally shape signaling.
The biophysical and computational study of BcLOV4 suggest that it has great utility as a generalizable modality for optogenetic tool development. We leverage this to construct a multitude of BcLOV4-based tools, focusing primarily on Rho GTPases, specifically Rac1 and RhoA. We demonstrate that these tools can generate physiologically relevant downstream signaling, including cell motility and, in the case of RhoA, YAP-TEAD-dependent transcriptional activity. This work sets the groundwork for a BcLOV4-based optogenetic toolkit for accurate dissection of mechanotransduction.

Launching into SEAS: Underrepresented @ Penn Engineering
2021-08-28 13:00 - 14:00
Launching into SEAS: Underrepresented @ Penn Engineering
Date: Saturday, August 28th
Time: 1 p.m. – 2 p.m.
Location: Skirkanich Hall – Berger Auditorium
Are you eager to get involved in the SEAS community? Interested in learning more about minority student organizations? Want to meet upperclassmen and fellow engineering students?
Join the Underrepresented Student Advisory Board in Engineering (USABE) and the Office of Diversity, Equity, and Inclusion (ODEI) in an NSO preceptorial panel featuring upperclassmen from identity organizations in SEAS. Participants will gain insightful advice on navigating their first semester in SEAS and learn about resources to support their academic, professional, and social development. Grab-and-go lunch will be provided at the end of the event!
Register for the event here. Please reach out to Shriya Karam and/or Fahmida Lubna for more information.

BE Doctoral Dissertation Defense: "Engineering Novel High-Resolution Bioelectronic Interfaces from MXene Nanomaterials" (Brendan Murphy)
2021-08-24 15:00 - 17:00 | https://upenn.zoom.us/j/96715197752
The Department if Bioengineering at the University of Pennsylvania and Drs. Brian Litt and Flavia VItale are pleased to announce the Doctoral Dissertation Defense of Brendan Murphy.

Title: Engineering Novel High-Resolution Bioelectronic Interfaces from MXene Nanomaterials
Date: August 24, 2021
Time: 3:00pm

The public is welcome to attend via Zoom:
https://us06web.zoom.us/j/9948619859

MEAM Seminar: "Deep Learning and Uncertainty Quantification: Methodologies and Applications"
2021-08-24 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Uncertainty is ubiquitous in physical and engineering science because of the lack of knowledge, inaccuracy in measurements, objective stochastic nature. “You cannot be certain about uncertainty”. Uncertainty quantification plays an essential role in decision making, solutions of partial differential equations, optimal design, etc. However, quantifying the uncertainty is not trivial in computational science. The difficulty of uncertainty quantifications increases dramatically with for instance, the dimensionality of the problems, the type of noise in the data, the complexity of black box functions where the data is obtained (large scale simulations, expensive experiments), etc. Moreover, with the knowledge of physics, how to quantify uncertainty with only a few numbers of data should be considered properly.
Uncertainty quantification and its interactions with deep learning is a recently emerging interdisciplinary area that leverages the power of statistical methods, machine learning models, numerical methods and data-driven approach to provide reliable inference for quantities of interest in natural science and engineering problems. Given the fast growth in deep learning, probabilistic methods and the large volume of data available across different research areas (computer visions, natural language processing, decision making), we aim in taking advantage of these recent advances to propose novel methodologies to solve problems where uncertainty quantification plays important roles.
This talk will highlight our recent process on the interaction between deep learning and uncertainty quantifications in the aspects of methodologies and applications. On the methodology side, solutions regarding partial differential equations (forward problems) and system identifications (inverse problems) will be discussed with robust uncertainty estimations. Active learning and data acquisition will also be covered in the presence of uncertainty. Equipped with the methodologies we have developed, we will briefly discuss some applications of such uncertainty quantification techniques in real-world problems such as cardiac flow activation mapping, optimal design as well as analysis for high dimensional data.

PSOC Webinar: Mai Wang
2021-08-23 12:00 - 12:30 | https://upenn.zoom.us/j/96715197752

BE Doctoral Dissertation Defense: "A Computational Study of the Influence of Cortical Processes on the Olfactory Bulb" (David Kersen)
2021-08-20 15:00 - 17:00 | Room 337, Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
The Department of Bioengineering at the University of Pennsylvania and Drs. Vijay Balasubramanian and Minghong Ma proudly announce the Doctoral Dissertation Defense of David Kersen.

The title is “A computational study of the influence of cortical processes on the olfactory bulb”

Date: August 20,2021
Time: 3:00pm

The zoom link is:
https://upenn.zoom.us/j/98075290445?pwd=[REDACTED]

MEAM Seminar: "Metal and Air Generate Power for Robots"
2021-08-17 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
In many cases, the size and weight of energy storage technologies required to power robotic systems are too large or massive for a robot to carry, leading to limited operational times and long recharging times over which the robot remains unused. Computer-free autonomous decision making based on environmental cues provides exciting alternatives to classic control systems for robots and smart materials. Although this functionality has been studied in microswimmers and active colloids where energy in the surrounding liquid is prevalent, there are no devices that can provide sufficient power from environmental chemicals to move and steer larger scale robots and vehicles in dry environments.
In this talk, I will show a new approach for powering robots and electronics by electrochemically scavenging energy from metal surfaces. This approach overcomes energy storage scaling laws by allowing robots and electronics to extract energy from large volumes of energy dense material without having to carry the material on-board. Next, we demonstrated an environmentally controlled voltage source (ECVS) that, when directly attached to electric motors on a vehicle, can increase the energy available to the vehicle and provide computer-free autonomous navigation toward chemical fuels in the environment and away from hazards. The ECVS uses electrochemistry to extract power from the chemical fuels, and the vehicle avoids hazards that reduce the output voltage or electrochemical kinetics.
These works present a new method to simultaneously steer and power vehicles and robots without computers by directly responding to a wide variety of chemical fields in their environment using electrochemistry.

PSOC Webinar: Aayush Kant & Xingyu Chen
2021-08-16 12:00 - 13:00 | https://upenn.zoom.us/j/96715197752
Zoom Meeting Waiting Room (email discher@seas for entry)

https://upenn.zoom.us/j/95100409935?pwd=[REDACTED]

Meeting ID: 951 0040 9935
Passcode: [REDACTED]

PSOC@Penn Summer Webinars 2021
Contact manu@seas.upenn.edu with any questions
Aayush Kant 12:00-12:30 PM
Xingyu Chen 12:30-1:00 PM

MEAM Seminar: "Accelerated Design of Heterogeneous Materials for Improved Failure Characteristics"
2021-08-10 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Nature provides countless examples of the use of heterogeneity to enhance the failure properties of materials. Many biological materials, such as bone, marine shells, and fish scales, are extremely resilient to fracture and failure. These often consist of regions that are highly mineralized and stiff and regions of biopolymers that are extremely soft. In practice, combining such disparate materials in synthetic systems is fraught with difficulties, such as poor interfacial adhesion. However, as we show in our work, other types of heterogeneities lead to similar enhancements to failure characteristics, including voids (inspired by bamboo) and spatial variations in fiber orientation (inspired by many materials, such as aorta). With the rise of 3D printing technology, it is possible to arbitrarily place materials with spatially-varying microstructure to mimic biological materials, ultimately with the goal of achieving comparable improvements to failure properties in synthetic materials.
In this talk, I will discuss three different types of heterogeneities that can be easily introduced to enhance failure characteristics. First, inspired by the microstructure of the Mantis shrimp club, we show how process defects that are intrinsic to extrusion-based additive approaches (voids and weak interfaces) can be spatially arranged in a helical (Bouligand) pattern to produce complex crack patterns and enhanced energy absorption. Next, we show how arrangements of voids (inspired by conch shells) can deflect cracks and enhance energy dissipation during fracture. Finally, we show how spatial variations in fiber orientation (inspired by aorta) can be produced using direct ink writing (DIW), leading to soft composites with high toughness and fatigue threshold.
Heterogeneities in materials, and the 3D printing processes used to create them, introduce a large number of parameters into the material design process, such as infill layer angle, fiber orientation, void placement, etc. Bio-inspiration provides a starting point and some basic intuition about how to design heterogeneous materials for improved failure properties, but it cannot guarantee optimal failure properties. I will therefore conclude the talk with a discussion of the use of Bayesian optimization for the acceleration of the design of architected heterogeneous materials with optimal failure properties. This will include the use of Bayesian optimization to design optimal architectures for energy dissipation using arrangements of voids inspired by conch shells. The second example uses a multi-fidelity Bayesian optimization approach to accelerate the design of heterogeneous triangular lattices with maximal energy absorption during compressive loading.

PSOC Webinar: Benjamin Emert & Kuangzheng (Peter) Zhu
2021-08-09 12:00 - 13:00 | https://upenn.zoom.us/j/96715197752
Join Zoom Meeting:
https://upenn.zoom.us/j/99334915941?pwd=[REDACTED]
Meeting ID: 993 3491 5941
Passcode: [REDACTED]
PSOC@Penn Summer Webinars 2021
Contact manu@seas.upenn.edu with any questions
Benjamin Emert 12:00-12:30 PM
Peter Zhu 12:30-1:00 PM

MEAM Seminar: "A Differential Homogenization Framework for Precipitation Strengthened Metals"
2021-08-06 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Precipitation-strengthened alloys are a commercially important class of materials because their mechanical properties can be altered by changing the microstructure through heat-treatment. Specifically, precipitates are introduced into the bulk (matrix) material to interact with dislocations and affect their mobility. It is known that the size, shape, orientation and stiffness of the precipitates, which can be altered during the age-hardening process, have a strong influence on the alloy and its plastic behavior. In this talk, I will discuss a differential homogenization framework that has been developed to model elasto-viscoplastic particulate composites which exhibit hardening at the local scale. The new homogenization estimates incorporate the second moments of the local hardening fields and improve on existing formulations which only take into account the first moment. First, we’ll consider the simple case of linear viscoelasticity and show that by using differential equations instead of difference equations, the new formulation is more robust than earlier incremental approaches and recovers exact results for certain classes of composites. Next, we provide estimates for creeping single crystals with elastic particles and find that neglecting the elasticity of the crystal, an assumption which is typically made, can lead to an overestimation of the effective creep-rate. Last, we examine the role of microstructure on the effective workhardening of precipitation-strengthened crystals. We focus on the interplay between crystallographic and morphological anisotropy and how these can reduce the overall anisotropy, as well as how the choice of the crystal matrix(either FCC or HCP) leads to markedly different work-hardening behavior.

MEAM PhD Thesis Defense: "Controlled Levitation of Nanostructured Thin Films for Sun-Powered Near-Space Flight"
2021-08-03 12:00 - 13:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Earth’s mesosphere is the least studied part of our atmosphere. The data it contains within itself can help develop more comprehensive and accurate models of the atmosphere and can help us understand our climate better. The main challenge before scientists is the inaccessibility of this region. The pressure is not high enough for aircraft and balloons and it is too high for satellites. There are remote sensing methods as well as transient rockets to collect data, though they are expensive and collect data for a few minutes at a time. In this thesis, we present photophoresis or light-driven motion as an alternative flight mechanism for long-duration access to this region.
Photophoretic force has long been studied for micron scale particles. However, in order to leverage photophoresis to levitate large microflyers capable of carrying useful payloads under sunlight, the structure of microflyers need to be ultralight, with areal densities of no more than a few g/m2. Creating a large scale structure with thicknesses that result in temperature difference and weigh only a few g/m2 is a challenge. The approach we present in this thesis is to generate photophoretic force that leverages heat transfer between gas molecules and surface molecules/structure. By altering this heat transfer on either side of a thin disc we can generate large photophoretic forces that can levitate cm-scale samples with several milligrams of payload.
In this work we propose and validate a predictive theoretical framework that accounts for conductive, convective, and radiative heat transfer and determines the temperature of illuminated thin disc microflyers as well as their lift force and payload capacity with sizes ranging from millimeters to centimeters over pressures ranging from 10 to 120 pascals.
We used cheap and fast methods to fabricate cm-scale thin disc microflyers with areal density of ~ 1 g/m2 and test them in vacuum and under variable light intensity. We fabricated four generations of microflyers starting by dropcasting carbon nanotubes onto thin disc-shaped mylar films. Atomic layer deposition and laser micromachining enabled stiffer continuous and porous samples to be created as well. Moreover, we used different microfabrication techniques to improve the performance of microflyers and increase their range of operation. Lastly, we used our validated theoretical model to predict the performance of the microflyers in upper atmosphere under natural sunlight, and we further propose different approaches that can lead to better performance and higher payload carrying capabilities.

MEAM Seminar: "Exploiting Interface Patterning for Adhesion Control"
2021-08-03 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Surface force-mediated adhesion, e.g. van der Waals forces, is critical for direct bonding of bulk solids in the absence of an adhesive layer. However, no two surfaces are ideally flat or perfectly conformal due to surface roughness or intentional patterning. When in the adhered state, non-zero surface tractions arise wherever the local separation of the surfaces differs from an intrinsic equilibrium separation, for which surface tractions vanish, hence regions of tensile and compressive loads are induced across the interface. A fundamental understanding of such imperfect adhesion is important and unlocks opportunities to control interfacial strength and toughness in various applications including MEMS/NEMS, micro-transfer printing, and processes to manufacture advanced 3D integrated-circuits. The aim of this work is to understand the fundamentals of direct adhesion of non-conformal surfaces by examining the interplay of (1) the intrinsic adhesive properties of traction-separation relation (TSR), (2) interface geometry, and (3) elastic deformation of the adhered bulk solids. The TSR we adopted accounts for strong repulsion when the interface separation is less than the equilibrium separation, and only the normal surface tractions were considered. The effective TSR properties, including the effective adhesion strength and work of separation, are determined from numerical calculations. Simple closed-form solutions are obtained when assuming rigid bulk solids. A finite element model utilizing cohesive elements in a periodic cell was constructed to study cases with non-uniform deformation in the elastic solids under pure normal separation without shear.

BE Doctoral Dissertation: "Quantitative Methods for Guiding Epilepsy Surgery from Intracranial EEG" (John Bernabei)
2021-08-02 13:30 - 15:30 | Room 337, Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
The Department of Bioengineering at the University of Pennsylvania and Dr. Brian Litt are pleased to announce the Doctoral Dissertation Defense of John Bernabei.

Title: Quantitative methods for guiding epilepsy surgery from intracranial EEG
Date: August 2, 2021
Time: 1:30 PM
Location: 337 Towne Building

The defense will also be available via zoom at the link below:
https://upenn.zoom.us/j/95425194465

PSOC Webinar: Lindsey Fernandez & Mai Wang
2021-08-02 12:00 - 13:00 | https://upenn.zoom.us/j/96715197752
Join Zoom Meeting:
https://upenn.zoom.us/j/99334915941?pwd=[REDACTED]
Meeting ID: 993 3491 5941
Passcode: [REDACTED]
PSOC@Penn Summer Webinars 2021
Contact manu@seas.upenn.edu with any questions
Lindsey Fernandez 12:00-12:30 PM
Mai Wang 12:30-1:00 PM

Climate & Diplomacy: How cities around the world collaborate on science-based climate solutions
2021-07-28 16:15 - 17:15
PIRE REACT Summer Student Program presents a talk for summer student researchers in STEM and their graduate student mentors; all are welcome.
“Climate & Diplomacy: How cities around the world collaborate on science-based climate solutions.” The speaker, Ms. Lolita Jackson, is a Penn Engineering alum and now with Sustainable Dev. Capital, LLP (recent interview in a Scotland-based media forum: https://www.holyrood.com/inside-politics/view,making-change-happen-interview-with-lolita-jackson and PWH bio: https://global.upenn.edu/perryworldhouse/person/lolita-k-jackson).

MEAM Seminar: "Some Investigations of Phase Transitions in Rod-like Macro-molecules and Fibrous Gels"
2021-07-27 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Stress-induced solid-to-solid phase transitions form a large class of phase transitions in nature. They occur in materials that can exhibit different crystal structures under different conditions (stress and temperature), and when the stress and temperature condition changes, the material may undergo a transformation from one phase to another. Despite its considerable potential in application, some fundamental aspects about the basic physical mechanisms of stress-induced solid–solid phase transitions remain poorly understood. In this work we are particularly interested in phase transitions in macromolecules and fibrous gels.
First, we conduct Langevin dynamics calculations on a chain of masses and bistable springs in a viscous fluid and extract a temperature dependent kinetic relation by observing that the dissipation at a phase boundary can be estimated by performing an energy balance. Using this kinetic relation, we solve boundary value problems for a bistable bar immersed in a constant temperature bath and show that the resultant force-extension relation matches very well with the Langevin dynamics results. We estimate the force fluctuations at the pulled end of the bar due to thermal kicks from the bath by using a partition function. We also show rate dependence of hysteresis in cyclic loading of the bar arising from the stick-slip kinetics.
Second, we use a double-well stored energy function in a chemo-elastic model of gels to capture the existence of two phases of the network. We model cyclic compression/decompression experiments on fibrous gels and show that they exhibit propagating interfaces and hysteretic stress-strain curves that have been observed in experiments. We can capture features in the rate-dependent response of these fibrous gels without recourse to finite element calculations.

PSOC Webinar: Indrajit Tah & David Li
2021-07-26 12:00 - 13:00 | https://upenn.zoom.us/j/96715197752
Join Zoom Meeting:
https://upenn.zoom.us/j/99334915941?pwd=[REDACTED]
Meeting ID: 993 3491 5941
Passcode: [REDACTED]
PSOC@Penn Summer Webinars 2021
Contact manu@seas.upenn.edu with any questions
Indrajit Tah 12:00-12:30 PM
David Li 12:30-1:00 PM

MEAM PhD Thesis Defense: "Lightweight Structures Enabled by Microfabrication"
2021-07-21 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Lightweight structures are the product of the science of making systems as light as possible with constraints, which often refer to being sufficiently strong and stiff. Although the development of lightweight structures was initially driven by the demands for better fuel and material economy, the recent advancements in microfabrication have allowed the manufacture of structures with unprecedented properties. In this work, three strategies of achieving lightweight structures are explored: (1) hollowing, (2) folding, and (3) lightweight composites. The first strategy is demonstrated by creating a hollow atomic force microscopy (AFM) cantilever. We made these hollow cantilevers by conformally depositing a thin layer of alumina on a solid beam and hollowing out the internal mold, resulting in hollow shells with the same overall dimensions but with nanoscale wall thickness. Due to their significantly reduced weight, these hollow cantilevers exhibited comparable resonant frequencies compared to their solid counterparts, but significantly reduced quality factors and spring constants, resulting in increased bandwidth and wear resistance. In the second strategy, we made a self-deployable silicon-based propeller for microflyers with lightweight polymeric film. The propeller can be initially folded and then deployed by the centrifugal force from rotation. The propeller exhibited low weight yet payload capable thrust which is promising for application in micro-aerial vehicles (MAVs). Furthermore, the fabrication techniques we developed allowed controllability on the folding directions which can be beneficial to origami-inspired devices. Lastly, we developed thin composites in the form of millimeter-thick sandwich plates by combining carbon-fiber-based faces with perforated aluminum core. The sandwich constructions allowed improved stiffnesses and strengths without adding excessive mass compared to single-ply carbon-fiber sheets, presenting viability as structural elements for small-scale robotics applications. In addition, these plates can be manufactured to be folded and curved that allows more complex geometries.

MEAM Seminar: "Rheological Behavior and Field Statistics of Suspensions of Rigid Particles in Yield Stress Fluids"
2021-07-20 10:30 - 12:00 | Zoom – Email MEAM for Link, peterlit@seas.upenn.edu
Suspensions of non-Brownian particles in fluids are commonly found in nature (e.g. mud, soils, and debris flows) and in the industry (e.g. paints, food, and cosmetics). Understanding the relations between the microstructure and the effective properties of these materials can provide insight into how they fail or behave during processing. Despite their ubiquity and usefulness, estimating the rheological properties of such suspensions, particularly in the non-dilute regime, remains a challenge. In this talk, I will discuss homogenization techniques to model the rheological behavior of athermal suspensions of hard spheres in both Newtonian and non-Newtonian (viscoplastic) fluids. For the case of Newtonian suspensions, we propose a generalization of the classical homogenization estimates of Ponte Castañeda and Willis (PCW) for the full viscosity tensor. The new estimates make use of an empirical interpolation parameter that is expected to depend on the particle properties (e.g. polydispersivity and size-ratios). Good agreement is found with experimental (rheology) data using polymethyl methacrylate (PMMA) spheres suspended in Glycerol, a viscous fluid. For the case of non-Newtonian suspensions, the generalized PCW estimates are used in combination with a variational linear comparison method to predict the effective nonlinear properties of viscoplastic suspensions. Good agreement is found with experimental data for suspensions of PMMA spheres in Carbopol, a yield-stress fluid. The proposed new theory is found to improve the predictive capabilities of the classical PCW estimates at moderate particle volume fractions. A physical interpretation of the interpolation parameter is offered in terms of the phase averages and the fluctuations of the local fields. Finally, the new estimates are used to generate fully-optimized, second-order homogenization estimates for viscoplastic suspensions under pure and axisymmetric shear. Special attention is devoted to the method’s ability to capture the localized, anisotropic deformation patterns that emerge under pure shear but are absent under axisymmetric shear.
