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Aerospace Engineering

Erosion Mechanisms in the Hall Effect Thruster

Wednesday, September 19, 2018; 4:30 PM - 5:30 PM
220 Hammond Building
Speaker: Mitchell L. R. Walker from Georgia Institute of Technology

Electric propulsion devices are rapidly replacing traditional chemical rockets on government and commercial spacecraft.  Electric propulsion devices possess a combination of high specific impulse and high thrust efficiency that drastically reduce the mass of propellant required to perform a specific mission.  Satellite operators leverage these characteristics to reduce the mass and related size of a spacecraft while maintaining its payload capability.  Thus, the same on-orbit capability is achieved at a significantly lower launch cost.  Concurrently, NASA uses electric propulsion to execute missions that are not possible with chemical rockets.  The drawback of electric propulsion is that the thrust level is limited by the electrical power available on the spacecraft.  Thus, the required operational life of contemporary electric propulsion devices is thousands of hours. The Hall effect thruster (HET) is a type of electric propulsion that has a high thrust density.  HETs are routinely flown on geosynchronous spacecraft.  Currently, HET development requires expensive, high-risk, ground-based qualification tests that exceed 7,000 hours to demonstrate the necessary on-orbit lifetime.  To date, modeling efforts have been unable to predict the dominant failure mechanism observed in HET qualification tests.  In particular, how quickly is the ceramic HET discharge channel eroded by the accelerated plasma? In response to this issue, the Air Force Office of Scientific Research (AFOSR) has initiated a research program to study plasma-wall interactions.  This presentation discusses an AFOSR-sponsored effort to develop a fundamental understanding of how the HET discharge plasma erodes the boron-nitride discharge channel.  This knowledge will facilitate our ability to predict HET lifetime and will influence the design of future high-power HETs.

Hosted by: Michelle Barnyak,  Aerospace Engineering  (mlf1@psu.edu)

Biomedical Engineering

Red Blood Cell Released ATP in Disturbed Blood Flow-Initiated Vascular Inflammation and Atherosclerosis

Thursday, September 20, 2018; 12:05 PM - 1:20 PM
158 Willard Building
Speaker: Dr. Ping Nian He from Penn State

Vascular inflammation and atherosclerosis are implicated in many cardiovascular diseases. While the systemic risk factors such as hyperlipidemia are exposed to entire vasculature under pathological conditions, the atherosclerotic plaques often preferentially develop at sites with disturbed flow, indicating a role of hemodynamic forces in atherogenesis. For decades, endothelial cell (EC) responses to the changes in wall shear stress (WSS) have been the main focus of the flow dynamics related studies, which basically consider the circulating blood as a cell-free fluid and completely overlooked the impact of mechanical force-activated blood cells on the vascular walls. Our recent studies conducted in intact venules provided the first experimental evidence that changes in blood flow alter EC function through both WSS and flow dynamics-triggered ATP release from RBCs, and that the released ATP via RBC pannexin 1 (Panx1) channels alters EC barrier integrity and vascular permeability. These observations led us to hypothesize that the RBC-released ATP during blood flow changes plays a significant role in site-specific vascular vulnerability and synergistically contributes to the initiation and progression of vascular inflammation and atherosclerosis in the presence of systemic risk factors. Two hypercholesterolemia mouse models with blood cell specific deletion of Panx1 (ApoE-/-Panx1-/- and AAV-PCSK9DYPanx1-/- fed with high fat diet) were developed to investigate the role of RBC-released ATP in high fat diet-induced site-specific plaque formation and atherosclerotic progression in major arteries. Our study found reduced leukocyte adhesion in venules and about 40-60% reduction of atherosclerotic plaque formation in mouse aorta at regions of disturbed flow with RBC Panx1 deletion. Our results indicate an important role of RBC released ATP in the site-specific vascular pathogenesis. We are in the process of establishing collaborations to develop computational models of shear stress effects on RBCs and the distribution of RBC released ATPs during blood flow pattern changes. We aim to provide new mechanistic insight into mechanical force-initiated vascular pathogenesis with both experimental evidence and computational support.

Hosted by: Jenna Sieber,  Biomedical Engineering  (jns5431)

Engineering Science and Mechanics

Study of the Anterior Cruciate Ligament-My Cross to Bear

Wednesday, September 19, 2018; 3:35pm - 4:25pm
114 EES Building
Speaker: Professor Patrick Smolinski from University of Pittsburgh

The anterior cruciate ligament (ACL) is the most often injured ligament in the knee and is a common activity related injury. In the United States, it is estimated that 100,000-200,000 ACL injuries occur and over 100,000 ACL reconstructions are performed annually. Although ACL reconstruction has been performed for nearly 100 years, and is now a very common arthroscopic surgery, there is not agreement on methods of the reconstruction. Moreover, there are still unresolved issues in ACL reconstruction with long term results generally leading to joint arthritis. Due to its complex mechanical behavior, the study of the knee is still an active area of research. This is also true of the ACL which has an irregular morphology with a composite construction and nonlinear material properties. This talk will give an overview of the knee function and anatomy and then discuss the anterior cruciate ligament, its function, anatomy and mechanisms of injury. Aspects of ACL reconstruction surgery will also be discussed. A variety of examples of the application of engineering and technology to study aspects of ACL anatomy, function and reconstruction will be presented. This will include both experimental and computational studies. Bio sketch

Hosted by: Dr. Akhlesh Lakhtakia,  Engineering Science and Mechanics  (814 865-4523)

Fluid Dynamics Research Consortium

Fluid Dynamics and Local Scour around Complex In-Stream Structures

Thursday, September 20, 2018; 9:00 AM
22 Deike Building
Speaker: Yuncheng Xu from Department of Civil and Environmental Engineering, The Pennsylvania State University

Abstract: In-stream structures play a significant role in flow resistance, sediment transport, invertebrate habitats and other biogeochemical functionalities of rivers and streams. Typical natural and engineered in-stream structures include large woody debris, engineered log jams, rock vanes and weirs. They are often used in engineering practice to restore impaired and disturbed rivers. River restoration is a billion-dollar industry which has impacts on our daily life. All the physical and ecological functions of these structures depend on the flow processes around and inside them. However, due to geometrical complexity and interstitial space within, the flow process is often very complex. In previous studies, these porous complex structures are often simplified as solid cylinders or blocks due to technical limitations in experiments and numerical models. The first part of this talk will demonstrate how much geometrical details is necessary to resolve the hydrodynamics around these complex structures, and the consequences of simplifications in terms of wake dynamics and mixing processes. The second part will show the progress made in simulating sediment transport and local scour around these structures with an immersed boundary method. Since wall shear stress is of critical importance to the motion of sediment particles, our new immersed boundary method utilizes a y+-adaptive strategy which produces much smoother and well-behaved wall shear. The use of immersed boundary method makes it possible to simulate scour around complex structures, and thus its application for real-world projects. Preliminary example simulations will be demonstrated and discussed.  Biography: Yuncheng Xu is a Ph.D. candidate in the Department of Civil & Environmental Engineering at Pennsylvania State University. He got his bachelor’s degree in Engineering Mechanics and master’s degree in Agricultural Engineering from China Agricultural University. He started working with Dr. Xiaofeng Liu since 2014. His doctoral thesis topic is about simulating hydrodynamics and morphodynamics around complex in-stream structures. He specializes in computational hydraulics and developing numerical models in OpenFOAM.


Hosted by: Dr. Ying Pan,  Fluid Dynamics Research Consortium  (yyp5033@psu.edu)

Mechanical and Nuclear Engineering

Distributed Schemes for Networked Stochastic Optimization and Nash Games

Monday, September 17, 2018; 4:00pm-5:00pm
125 Reber Building
Speaker: Jinlong Lei from Penn State Industrial Engineering

There are a broad range of optimization and equilibrium problems in networks, arising in power grids, wireless communication networks, and sensor networks. Such networked problems are complicated by various challenges such as uncertainty and nonconvexity. This talk will focus on the following research questions: (i) How to deal with uncertainty in networked settings? (ii) How may such problems be solved in limited communication regimes? (iii) How such problems be solved asynchronously? In this presentation, we show that these challenges can be addressed by a combination of distributed and Monte-Carlo sampling algorithms, asynchronous fixed-point iterations, quantization methods, etc. We present several schemes: (i) We propose a stochastic approximation-based distributed primal-dual algorithm to solve the distributed stochastic convex optimization problem and prove a.s. convergence along with the asymptotic normality and efficiency; (ii) We then present a variable sample-size stochastic gradient method with increasing batch-sizes to solve the stochastic nonconvex optimization, prove a.s. convergence to stationary points, and establish the oracle and iteration complexity bounds; (iii) Our third scheme is a distributed quantized algorithm for solving networked linear equations, where we obtain the exponential convergence with a minimal bit rates statement; (iv) Finally, we design an asynchronous inexact proximal best response scheme for potential stochastic Nash games, where a.s. and mean convergence are shown under suitable conditions on the inexactness sequences.

Hosted by: Hosam Fothy,  Mechanical Engineering  (hkf2@psu.edu)

How to Start and Grow a Business Out of Grad School

Tuesday, September 18, 2018; 3:35 pm
135 Reber Building
Speaker: Jeremy Frank from KFC Technologies

Jeremy Frank will discuss the pitfalls and failures (and how to overcome them!) on the path to building a successful company out of graduate research.

Hosted by: Mary Frecker,  Mechanical Engineering  (amb52@psu.edu)

The International Nuclear Nonproliferation Regime

Thursday, September 20, 2018; 4:00pm-5:00pm
135 Reber Building
Speaker: Katherine Bachner from Brookhaven National Laboratory

The lecture will introduce students to the international nuclear nonproliferation regime at a high level, focusing on safeguards and security. It will touch upon key historical moments that have driven nonproliferation as it exists today, the development of essential legal instruments used by the international community to fight further proliferation, diplomatic tensions that exist surrounding the nuclear ‘haves’ versus ‘have-nots’, and as time permits, will include an overview on the logic of nuclear deterrence.

Hosted by: Kenan Unlu,  Mechanical Engineering  (amb52@psu.edu)

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