Penn Engineering Events

MEAM Seminar: "Data-driven Discovery of Governing Physical Laws in Engineering, Physics, and Biology"
2019-04-23 10:30 - 12:00 (America/New_York) | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
A major challenge in the study of dynamical systems is that of model discovery: turning data into models that are not just predictive, but provide insight into the nature of the underlying dynamical system that generated the data. This problem is made more difficult by the fact that many systems of interest exhibit parametric dependencies and diverse behaviors across multiple time scales. We introduce a number of data-driven strategies for discovering nonlinear multiscale dynamical systems and their embeddings from data. We consider two canonical cases: (i) systems for which we have full measurements of the governing variables, and (ii) systems for which we have incomplete measurements. For systems with full state measurements, we show that the recent sparse identification of nonlinear dynamical systems (SINDy) method can discover governing equations with relatively little data and introduce a sampling method that allows SINDy to scale efficiently to problems with multiple time scales and parametric dependencies. Specifically, we can discover distinct governing equations at slow and fast scales. For systems with incomplete observations, we show that the Hankel alternative view of Koopman (HAVOK) method, based on time-delay embedding coordinates, can be used to obtain a linear model and Koopman invariant measurement system that nearly perfectly captures the dynamics of nonlinear quasiperiodic systems. We introduce two strategies for using HAVOK on systems with multiple time scales. Together, our approaches provide a suite of mathematical strategies for reducing the data required to discover and model nonlinear multiscale systems.

PSOC Spring 2019 Seminar Series: Shreyas Rao , Ph.D.
2019-04-22 12:00 - 13:00 | Room 337, Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States

PICS Seminar: "Topology, Geometry, and Fracture in Networked Materials: A Tale of Scales"
2019-04-19 14:00 - 15:00 | Raisler Lounge (Room 225), Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
The skeleton of many natural and artificial structures may be abstracted as networks of nonlinearly interacting elements. Examples include rubber, gels, soft tissues, and lattice materials. Understanding the multiscale nature of deformation and failure of networked structures hold key for uncovering origins of fragility in many complex systems including biological tissues and enables designing novel materials.
I will start by an overview of our prior work on modeling polymer chains with sacrificial bonds and hidden length; a topological feature that was previously hypothesized to be responsible for increased toughness and fracture resistance in animal bone. Our model combines nonlinear entropic elasticity with transition state theory for bond breakage and formation to predict rate dependence and time dependent healing in these systems in the quasi-1D limit. I will then introduce an extension of this model to a discrete 2D setting (at the scale of 10s of microns) that enables exploring interplay of topological and geometrical features such as coordination number, cross linking density, and disorder with mechanical deformation and fracture. Specifically, we identify a non-monotonic rate dependence of the reaction force and dissipated energy as well as a transition in mode of failure from diffusive to localized with increased pulling rate. Furthermore, we show that networks with small-world architectures, balancing clustering and average path length, may lead to an optimum fracture toughness.
To generalize our results to larger scales relevant for engineering and material science applications, I will discuss our recent efforts in adopting an extended version of the Quasi-Continuum (QC) method to studying polymer networks across scales. In regions of high interest, for example near defects or cracks, each polymer chain is idealized using the worm like chain model. Away from these imperfections, the network structure is computationally homogenized, using Hill-Mandell’s principle, to yield an anisotropic material tensor consistent with the underlying network structure. Dynamic adaptivity provides a seamless transition across the two models. Overall, the proposed method provides a multi-resolution capability by retaining explicit representation of small scale heterogeneities and topological features, where they matter near the crack tips, while still accurately accounting for bulk elasticity and loading. We show several examples verifying our approach and illustrate the potential of the method for testing the influence of small scale features in controlling the macroscopic response. We discuss the implications of our findings for the analysis and design of tough networks.

CBE Seminar: "Lipid-like Materials for RNA Delivery: A How-to Guide for Hacking Gene Expression"
2019-04-17 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States

MEAM/MSE Special Seminar: "Scalable Functional Phase Change Materials for Displays and Photonic Non-von Neumann Computing"
2019-04-17 11:00 - 12:00 | Reading Room, LRSM, 3231 Walnut Street, Philadelphia, PA, 19104, United States
In electronics, doping silicon results in one of the most versatile functional materials ever employed. The pursuit of such functional materials in the optical domain is an area of great interest in the photonics community. I hope to convince you that whatever route photonics takes, a class of materials known as phase change materials, will play a key role in its commercialization. These materials can be addressed electrically, and whilst this can be used to control optical signals on photonic circuits this can also be used to create displays and smart windows. In this talk, I hope to give an overview of these applications of these materials with a view towards their near-term applications in displays, and their longer-term potential in integrated photonic memories to photonic machine-learning hardware components, with a few of our recent results in this area.

MEAM Seminar: "Wrinkles, Spaghetti, and Knots"
2019-04-16 10:30 - 12:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Buckling, twisting and fracture are ubiquitous phenomena that, despite having been studied for centuries, still pose many interesting conceptual and practical challenges. In this talk, I will summarize recent theoretical and experimental work that aims to understand the role of curvature and torsion in wrinkle pattern selection, fragmentation cascades and knots. First, we will show how changes in curvature can induce phase transitions and topological defects in the wrinkling patterns on curved elastic surfaces. Thereafter, we will revisit an observation by Feynman who noted that dry spaghetti appears to fragment into at least three (but hardly ever two) pieces when placed under large bending stresses. Using a combination of experiments, simulations and analytical scaling arguments, we will demonstrate how twist can be used to control binary fracture of brittle elastic rods. Finally, in the last part, we will try to shed some light on how topology and torsion affect the stability of knots.

The Joy of Being Faculty: How I Devised My Research Program
2019-04-12 16:00 - 17:00 | Heilmeier Hall (Room 100), Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
This professional development workshop is designed to provide Penn Engineering graduate students and postdocs with a richer understanding of what it is like to pursue a career in academia from those that have navigated the process successfully.
Deputy Dean Kathleen J. Stebe (SEAS) will lead this extemporaneous panel discussions with a mix of both tenured and tenure-track professors from Penn Engineering.

CIS Seminar: " Deep Learning for Network Biomedicine"
2019-04-11 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Abstract:

Large datasets are being generated that can transform biology and medicine. New machine learning methods are necessary to
unlock these data and open doors for scientific discoveries. In this talk, I will argue that, in order to advance science,
machine learning models should not be trained in the context of one particular dataset. Instead, we should be developing
methods that can integrate rich, heterogeneous data and knowledge into multimodal networks, enhance these networks to reduce
biases and uncertainty, and learn over the networks.

My talk will focus on two key aspects of this goal: deep learning and network science for multimodal networks. I will first
show how we can move beyond prevailing deep learning methods, which treat network features as simple variables and ignore
interactions between entities. Further, I will present an algorithm that learns deep models by embedding multimodal networks
into compact embedding spaces whose geometry is optimized to reflect the interactions, the essence of multimodal networks.
These deep models set sights on new frontiers, including the prediction of protein functions in specific human tissues,
modeling of drug combinations, and repurposing of old drugs for new diseases. Beyond such predictive ability, a hallmark of
science is to achieve a holistic understanding of the world. I will discuss how we can blend network algorithms with rigorous
statistics to harness biomedical networks at the scale of billions of interactions. These methods revealed, among others, how
Darwinian evolution changes molecular networks, providing evidence for a longstanding hypothesis in biology. In all studies, I
collaborated closely with experimental biologists and clinical scientists to give insights and validate predictions made by our
methods. I will conclude with future directions for contextual models of rich interaction data which open up new avenues for science.

MSE Seminar: "Nanoscience and Quantum Information Science at the Center for Functional Nanomaterials, a National Scientific User Facility"
2019-04-11 10:45 - 11:45 | Auditorium, LRSM Building, 3231 Walnut Street, Philadelphia, PA, 19104, United States

CBE and Physics Joint Seminar: "Structuring Matter Over Multiple Length Scales Using the Self-assembly of Colloidal Particles"
2019-04-10 16:00 - 17:00 | David Rittenhouse Lab, A4, 209 South 33rd Street, Philadelphia, PA, 19104, United States

2019 Heilmeier Lecture: "Cell-Matrix Interactions in Cancer and Fibrosis: Multiscale Chemo-Mechanical Models"
2019-04-10 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Cell invasion into the surrounding matrix from nonvascularized primary tumors is the main mechanism by which cancer cells migrate to nearby blood vessels and metastasize to eventually form secondary tumors. This process is mediated by an intricate coupling between intracellular forces and extracellular forces that depend on the stiffness of the surrounding stroma and the alignment of matrix fibers. A multiscale model is used to elucidate the two-way feedback loop between stress-dependent cell contractility and matrix fiber realignment and strain stiffening, which enables the cells to polarize and enhance their contractility to break free from the tumor and invade into the matrix. Importantly, Dr. Shenoy’s model can be used to explain how morphological and structural changes in the tumor microenvironment, such as elevated rigidity and fiber alignment prior to cell invasion, are prognostic of the malignant phenotype. The model also predicts how the alignment of matrix fibers can recruit macrophages, which are among the first responders of the innate immune system following organ injury and are crucial for repair, resolution, and re-establishing homeostasis of damaged tissue. In this talk, Shenoy will discuss how the deformation of the nucleus during migration can lead to changes in the spatial organization of chromosomes and their intermingling which can result in genetic mutations and genomic instability. He will also discuss how targeting extracellular matrix mechanics, by preventing or reversing tissue stiffening or interrupting the cellular response in cancer and fibrosis, is a therapeutic approach with clinical potential.

CIS Seminar: "Towards a New Synthesis of Reasoning and Learning"
2019-04-09 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
This talk discusses the role of logical reasoning in statistical machine learning. While their unification has been a long-standing and crucial open problem, automated reasoning and machine learning are still disparate fields within artificial intelligence. I will describe recent progress towards their synthesis in three facets.
I start with a very practical question: how can we enforce logical constraints on the output of deep neural networks to incorporate symbolic knowledge? Second, I explain how circuits developed for tractable logical reasoning can be turned into statistical models. When brought to bear on a variety of machine learning tasks, including discrete density estimation and simple image classification, these probabilistic and logistic circuits yield state-of-the-art results. In a third facet, I argue for high-level representations of uncertainty, such as probabilistic programs, probabilistic databases, and statistical relational models. These pose unique challenges for inference that can only be overcome by high-level reasoning about their first-order structure to exploit symmetry and exchangeability.

MEAM Seminar: "Integrating Manufacturing and Topological Optimization for the Design of Architected Materials and Components"
2019-04-09 10:30 - 12:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Topology optimization has long been touted as a powerful tool capable of discovering innovative solutions to engineering design problems. It has been used to design ‘structures’ characterized at a range of length scales, from tens of microns (material architectures) to decameters (structures), for performance properties governed by a range of physics. Despite its tremendous potential as a design tool, topology optimized solutions are typically suboptimal when considering real-world operating conditions, design objectives, and manufacturing processes, and thus may require significant post-processing and re-design which is both detrimental and time consuming. This talk will review the topology optimization methodology and discuss our efforts at overcoming these shortcomings, with a particular emphasis on providing the design engineer geometric control to enable design for manufacturability. Several design examples will be presented including architected materials, components and devices that are fabricated through additive manufacturing, machining or 3D weaving, and optimized for mechanical, fluidic, and/or thermal properties.

Doctoral Dissertation Defense: "Hyperpolarized Carbon-13 Magnetic Resonance Imaging as a Tool for Assessing Lung Transplantation Outcomes"
2019-04-08 13:00 - 15:00
The Department of Bioengineering at the University of Pennsylvania and Dr. Rahim Rizi are pleased to announce the Doctoral Dissertation Defense of Sarmad Siddiqui.

The public is welcome to attend.

Location: Donner Auditorium, Basement HUP.

The Joy of Being Faculty: How to Apply for a Faculty Position
2019-04-05 16:00 - 17:00 | Heilmeier Hall (Room 100), Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States

BE Grace Hopper Lecture: Powering tumor cell migration through heterogeneous microenvironments
2019-04-04 15:30 - 16:30 | Glandt Forum, Singh Center for Nanotechnology, 3205 Walnut Street, Philadelphia, PA, 19104, United States
To move through tissues, cancer cells must navigate a complex, heterogeneous network of fibers in the extracellular matrix. This network of fibers also provides chemical, structural and mechanical cues to the resident cells. In this talk, I will describe my lab’s efforts to understand the forces driving cell movements in the tumor microenvironment. Combining tissue engineering approaches, mouse models, and patient samples, we create and validate in vitro systems to understand how cells navigate the tumor stroma environment. Microfabrication and native biomaterials are used to build mimics of the paths created and taken by cells during metastasis. Using these platforms, we have described a role for a balance between cellular energetics, cell and matrix stiffness, and confinement in determining migration behavior. Moreover, we have extended this work into investigating the role of the mechanical microenvironment in tumor angiogenesis to show that mechanics guides vessel growth and integrity. I will discuss the mechanical influences at play during tumor progression and the underlying biological mechanisms driving angiogenesis and metastatic cell migration as a function of the ECM with an eye towards potential therapeutic avenues.

CIS Seminar: "Making Parallelism Pervasive with the Swarm Architecture"
2019-04-04 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Abstract:
Parallelism is critical to achieve high performance in modern computer systems. Unfortunately, most programs scale poorly beyond a few cores, and those that scale well often require heroic implementation efforts. This is because current architectures squander most of the parallelism available in applications and are too hard to program.
I will present Swarm, a new architecture that exploits far more parallelism than conventional multicores and is almost as easy to program as a sequential thread. Swarm programs consist of tiny tasks, as small as tens of instructions each. Synchronization is implicit: the programmer specifies a total or partial order on tasks. This eliminates the correctness pitfalls of explicit synchronization (e.g. deadlock and data races). Swarm hardware uncovers parallelism by speculatively running tasks out of order, even thousands of tasks ahead of the earliest active task. Its speculation mechanisms build on decades of prior work, but Swarm is the first to scale to hundreds of cores due to its new programming model, distributed structures, and distributed protocols. Swarm also incorporates new techniques to reduce data movement, harness nested parallelism, and combine speculative and non-speculative parallelism.
Swarm achieves efficient near-linear scaling to hundreds of cores on challenging irregular applications. These span a broad set of domains, including graph analytics, machine learning, databases, simulation, and more. Swarm even accelerates applications that are often deemed sequential. It outperforms state-of-the-art software-only parallel algorithms by one to two orders of magnitude, and sequential implementations by up to 600x at 256 cores.

MSE Seminar: “Integrated Lithium Niobate Photonics”
2019-04-04 10:45 - 11:45 | Auditorium, LRSM Building, 3231 Walnut Street, Philadelphia, PA, 19104, United States

MedTech Panel Series, Part 1: Executives - "From bench to boardroom"
2019-04-03 18:00 - 19:00
Presented by the students of BE 370 (Medical Device Development): Come to the MedTech Panel Series to hear about these experiences and more from some of the most successful founders and CEOs in the industry! Our panelists will share their stories on how they took innovation from the bench to the boardroom and built multi-million dollar companies.
This event will be held on campus. RSVP for details at: https://bit.ly/2Ydlfl5.

CBE Seminar: "C4E-Computational Chemistry of Compounds for Catalysis and Energy"
2019-04-03 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States

Doctoral Dissertation Defense: Tissue Engineered Nigrostriatal Pathway for Treatment of Parkinson's Disease
2019-04-02 15:00 - 17:00
Location TBD

MEAM Seminar: "Additive Manufacturing and Architected Materials"
2019-04-02 10:30 - 12:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Material properties are governed by the chemical composition and spatial arrangement of constituent elements. Over the past decade, the field of architected materials has sought to design, fabricate, and demonstrate materials with performance that is fundamentally controlled by geometry at multiple length-scales rather than chemical composition alone. There have been many advancements ranging from the maturation of additive manufacturing technologies which can be used to realize these materials, to inverse design methods such as topology optimization, and even includes unique new material feedstocks which make up the structures. This presentation will touch on all aspects of the architected materials realization process as well as evaluate performance of some of those materials. Specifically, we have demonstrated designer properties of these architected materials in polymers, metals, ceramics and combinations thereof. In addition to novel properties such as ultra-stiff lightweight materials, negative stiffness, and negative thermal expansion, I will present multifunctional architected materials with energy storage capability and architectures that respond to external fields. Many of these architected materials derived from advanced design and optimization methods which we have been developing and were fabricated with custom additive manufacturing techniques. These include projection microstereolithography (PµSL), direct ink writing (DIW), electrophoretic deposition (EPD), volumetric additive manufacturing (VAM), computed axial lithography (CAL), and diode-based additive manufacturing (DiAM) to name a few. New materials including graphene aerogel, carbon fiber composites, and printed glass will also be touched upon.

CIS Seminar: "Towards Human-Level Recognition via Contextual, Dynamic, and Predictive Representations"
2019-03-29 13:00 - 14:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
Abstract:

Existing state-of-the-art computer vision models usually specialize in single domains or tasks, while human-level recognition can be contextual for diverse scales and tasks. This specialization isolates different vision tasks and hinders deployment of robust and effective vision systems. In this talk, I will discuss contextural image representations for different scales and tasks through the lens of pixel-level prediction. These connections, built by the study of dilated convolutions and deep layer aggregation, can interpret convolutional network behaviors and lead to model frameworks applicable to a wide range of tasks. Beyond contextual, I will argue that image representation should also be dynamic and predictive. I will illustrate the case with input-dependent dynamic networks, which lead to new insights into the relationship of zero-shot/few-shot learning and network pruning, and with semantic predictive control, which utilizes prediction for better driving policy learning. To conclude, I will discuss the on-going system and algorithm investigations which couple representation learning and real-world interaction to build intelligent agents that can continuously learn from and interact with the world.

ESE Seminar: "Safety and Robustness Guarantees with Learning in the Loop"
2019-03-29 11:00 - 12:00
In this talk, we present recent progress towards developing learning-based control strategies for the design of safe and robust autonomous systems. Our approach is to recognize that machine learning algorithms produce inherently uncertain estimates or predictions, and that this uncertainty must be explicitly quantified (e.g., using non-asymptotic guarantees of contemporary high-dimensional statistics) and accounted for (e.g., using robust control/optimization) when designing safety critical systems. We focus on the safety constrained optimal control of unknown systems, and show that by integrating modern tools from high-dimensional statistics and robust control, we can provide, to the best of our knowledge, the first end-to-end finite data robustness, safety, and performance guarantees for learning and control. We further show how this approach can be incorporated into an adaptive polynomial-time algorithm with non-asymptotic convergence rate (regret bound) guarantees. As a whole, these results provide a rigorous and contemporary perspective on safe reinforcement learning as applied to continuous control. We conclude with our vision for a general theory of safe learning and control, with the ultimate goal being the design of robust and high performing data-driven autonomous systems.

CIS Seminar: "Improving Security at an Internet Scale: A Data-Driven Approach"
2019-03-28 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
The state of security across the Internet is poor, and it has been so for years. Meanwhile, attacks have become ever more frequent and consequential. How do we actually make meaningful progress? To do so, we must move beyond the folklore that heavily influences Internet security practices today, and establish 1) empirical grounding on how and why security problems manifest the way they do across the Internet, and 2) data-driven methods for improving security at an Internet scale.

In this talk, I will describe my evidence-based and holistic approach to security, illustrated by my work on improving how we remedy security problems (vulnerabilities, misconfigurations, and compromise incidents) for Internet systems. Using a variety of empirical methods, including Internet-wide network measurements, user studies, machine learning, and code analysis, my research systematically identifies how security is managed for Internet systems, factors that contribute to continued vulnerability, and barriers that prohibit the effective remediation of security concerns. Informed by insights from this work, I develop methods and systems for more effective remediation at an Internet scale.

BE Seminar Series: Heterogeneous, Multi-Scale and Patient-Speci C Pharmacodynamic Systems Models for Cancer with Clinical Applications
2019-03-28 13:05 - 13:30 | Room 337, Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
Abstract: Systems models of key signaling pathways in cancer have been extensively used to understand and explore the mechanisms of action of drugs and growth factors on cancer cell signaling. In general, such models predict the effect of mechanical or chemical stimuli (for e.g. drug dosage) in terms of activity of one or more key downstream proteins such as ERK or AKT which are important regulators of cell fate decisions. Although such models are greatly useful and have helped uncover important emergent properties of signaling networks such as ultrasensitivity, bistability and oscillations, they miss many key features that would make them useful in a clinical setting.
1) The predictions of activity of proteins such as ERK or AKT cannot be directly translated into a clinically useful cell fate parameter such as cell kill rate.
2) They don’t work as well when there are multiple biological processes operating under different time and length scales such as receptor based signaling (4-6 hours) and cell cycle (24-48 hours).
3) They cannot incorporate important cellular physics like mechanics of the cell membrane, ECM and the cytoskeleton.
4) The parameter space of such models often exhibits sloppy/stiff character which affect the accuracy of predictions and the robustness of these models. Such analysis are often not done which casts doubt on validity of the predictions.
Here we have developed a multiscale and multiparadigm framework for systems and pharmacodynamic models that helps us address some of the above shortcomings. This framework was used to successfully integrate a single-cell systems model of ErbB receptor mediated Ras-MAPK and PI3K/AKT pathway with tumor suppressor p53 mediated DNA damage response and cell cycle pathway. The integrated model was used in a clinical setting using gene/protein expression data and drug dosage/schedule information from actual patients of prostate adenocarcinoma. Special mathematical techniques were used to develop algorithms that can integrate models of disparate time scales and time resolutions (continuous vs. discrete time).

BE Seminar Series: Synchronization is Robust in a Computational Model of Neuronal Network Dynamics and Injury
2019-03-28 12:35 - 13:00 | Room 337, Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
At the macroscale, synchronization between brain regions is believed to be important for memory and attention. Injury, including mild traumatic brain injury, can both increase and decrease synchronization as measured by functional MRI, but these changes are not well understood and are unknown at a smaller spatial scale. Here, we examined how injury affects the synchronization between two clusters of neurons. We used a computational network model consisting of excitatory and inhibitory neurons, derived from Izhikevich integrate-and-fire neurons. We connected two clusters of neurons with different intrinsic firing rates. In this architecture, two distinct clusters of neurons were directionally connected from one upstream cluster to one downstream cluster. The network remodeled according to the rules of spike-timing-dependent plasticity (STDP), resulting in highly synchronized activity between the clusters. We characterized structural subtypes within the network and subsequently explored the functional effects of damaging the network by removing neurons based on their subtype membership.

BE Seminar Series: Applied Topology in Biological Systems
2019-03-28 12:00 - 12:30 | Room 337, Towne Building, 220 South 33rd Street, Philadelphia, PA, 19104, United States
Though rooted in pure mathematics, algebraic topology has recently enabled novel analysis techniques for biological data. Specifically, the method called persistent homology which employs ideas from topology to characterize the voids in a complex network. In this talk, I will briefly introduce persistent homology and give an overview of how we have recently applied this tool to answer questions in neuroscience and semantic learning. Finally, I will provide additional examples of topology in biology and suggest how current research in pure algebraic topology may soon aid in our understanding of complex systems.

ESE Seminar: "Control of Light and Heat for New Energy Applications"
2019-03-28 11:00 - 12:00
Light carries energy and heat, and plays a key role in many energy-conversion processes. The capabilities
to tailor electromagnetic energy transfer at the nanoscale represent important opportunities for novel
energy applications. In this talk I will present two sets of studies integrating experiments and theory. In
the first part, I will discuss how to use near field electromagnetic energy transfer for energy conversion
and photonic refrigeration. I will begin by showing an experiment achieving a 40-fold enhancement of
thermophotovoltaic conversion rates, by reducing the distance between a thermal emitter and a
photovoltaic cell to the nanoscale. This lays the foundation for exploring near-field thermophotovoltaics
for waste heat recovery. I will then show a demonstration of active photonic refrigeration through control
of the chemical potential of photons. This points to a fundamentally new, promising way for solid state
refrigeration by combining nanoscale photonics and optoelectronics.
In the second part, I will discuss how to turn the cold outer space to a thermodynamic resource for passive
cooling and energy efficiency. I will introduce our first demonstration of passive radiative cooling to
below the ambient air temperature under direct sunlight. Next I will show an experiment achieving
passive cooling to 42 ˚C below the ambient temperature, pointing to new regimes of applications such as
food preservation in remote areas. I will also show results of lowering the temperature of a solar absorber
by 13 ˚C while maintaining the sunlight absorption, pointing to significant efficiency improvement for
solar cells. Finally, I will give an overview of my future research directions.

CBE Seminar: "Particle Transport in Soft, Disordered Media"
2019-03-27 15:00 - 16:00 | Wu and Chen Auditorium (Room 101), Levine Hall, 3330 Walnut Street, Philadelphia, PA, 19104, United States
