# Mechanical Engineering Commons™

Articles 1 - 30 of 216

## Full-Text Articles in Mechanical Engineering

Influence Of Naoh Concentration On Transfer Process Of Graphene, Francisco Saldana, Chengyu Wen, George Patrick Watson Sep 2019

#### Influence Of Naoh Concentration On Transfer Process Of Graphene, Francisco Saldana, Chengyu Wen, George Patrick Watson

##### Protocols and Reports

The process of transferring a monolayer of graphene using two diﬀerent concentrations of sodium hydroxide (NaOH) solution unto a silicon dioxide (SiO2) coated Si chip using electrochemistry was performed. The transfer process is crucial for the delamination of a continuous graphene monolayer ﬁlm from copper foil. After examining and inspecting the integrity of the graphene monolayer, it was observed that the lower concentration to NaOH led to slower rate of hydrogen bubble generation; this condition was found to be less destructive and yielded a graphene ﬁlm with fewer visible tears.

Reactive Ion Etching Selectivity Of Si/Sio2: Comparing Of Two ﬂuorocarbon Gases Chf3 And Cf4, Meiyue Zhang, Pat Watson Mar 2019

#### Reactive Ion Etching Selectivity Of Si/Sio2: Comparing Of Two ﬂuorocarbon Gases Chf3 And Cf4, Meiyue Zhang, Pat Watson

##### Protocols and Reports

Two reactive ion etching (RIE) processes were studied to show the relative etch selectivity between SiO2 and Si using two ﬂuorocarbon gases, CF4 and CHF3. Results show that CHF3 gives better selectivity (16:1) over CF4 (1.2 :1). On the other hand, the etch rate of SiO2 of CF4 is approximately 52.8 nm/min, faster than CHF3 (32.4 nm/min).

Modeling And Control For Robotic Assistants: Single And Multi-Robot Manipulation, Monroe David Kennedy Jan 2019

#### Modeling And Control For Robotic Assistants: Single And Multi-Robot Manipulation, Monroe David Kennedy

##### Publicly Accessible Penn Dissertations

As advances are made in robotic hardware, the complexity of tasks they are capable of performing also increases. One goal of modern robotics is to introduce robotic platforms that require very little augmentation of their environments to be effective and robust. Therefore the challenge for a roboticist is to develop algorithms and control strategies that leverage knowledge of the task while retaining the ability to be adaptive, adjusting to perturbations in the environment and task assumptions. This work considers approaches to these challenges in the context of a wet-lab robotic assistant. The tasks considered are cooperative transport with limited communication ...

#### Atomic Force Microscopy-Based Investigation Of Plastic Deformation Mechanisms In Disordered Nanoparticle Packings, Joel Allen Lefever

##### Publicly Accessible Penn Dissertations

Understanding the plastic deformation mechanisms of disordered materials is a longstanding and complex problem in condensed matter physics and materials science. In particular, the elementary plastic rearrangement in a disordered material is believed to be the shear transformation zone, a localized cooperative motion of a handful of constituents. Although observed in mesoscale systems, the shear transformation zone has never been identified in an experiment at the nanoscale. In the present work, atomic force microscopy is used to probe the mechanical response of thin films of disordered nanoparticle packings that have been deposited by spin-coating and layer-by-layer deposition. Results demonstrate that ...

#### Examination Of Callaway-Holland-Based Thermal Conductivity Calculation For Nano-Phononic Crystals, Ruiyuan Ma

##### Publicly Accessible Penn Dissertations

Phononic crystals are periodic structured materials whose frequency spectrum is characterized by band gaps, which are regions in frequency space where acoustic or elastic waves cannot propagate. Nano scale phononic crystals have shown promise for reducing thermal conductivity and improving the thermoelectric figure of merit. Correctly calculating the thermal conductivity of nano phononic crystals has become increasingly important due to the growing research interest in the thermal properties of these materials. A widely used expression to calculate thermal conductivity, presented by Klemens and expressed in terms of the relaxation time by Callaway and Holland, originates from the Boltzmann transport equation ...

Interfacial Wave Dynamics Of Core-Annular Flow Of Two Fluids, Mohammed Asaduzzaman Jan 2018

#### Interfacial Wave Dynamics Of Core-Annular Flow Of Two Fluids, Mohammed Asaduzzaman

##### Publicly Accessible Penn Dissertations

In core-annular flow of two different fluids, for a set of suitable flow conditions, various shapes of saturated waves such as bamboo, snake and corkscrew waves are observed. Some of the dominant parameters such as thickness ratio of the fluid, Reynolds number, viscosity ratio, density ratio, interfacial surface tension, and the direction of gravitational forces determine the final shape of the saturated wave and their ultimate stability in a nonlinear regime.

When the flow rate ratio is high, it is sometimes difficult to determine the differences between the final shape of the waves for up-flow and down-flow. For some combinations ...

#### Understanding And Improving The Environmental Dependent Tribology And Thermal Stability Of Hydrogenated Amorphous Carbon By Using Silicon And Oxygen As Dopants, James Hilbert

##### Publicly Accessible Penn Dissertations

Hydrogenated amorphous carbon (a-C:H) films are a class of non-crystalline materials composed of hydrogen and carbon bonded in both sp2 and sp3 configurations. These films are notable for their high hardness (10–16 GPa), low roughness, chemical inertness, and good tribological performance (low friction and wear). This combination of favorable properties has led to promising applications in diverse fields, including automotive and aerospace components, biomedical devices, and computer hard drives. However, a-C:H becomes unstable above 150 °C, preventing its use in important technological applications, such as heat assisted magnetic recording (HAMR) disk drives. Also, the low friction and ...

#### Flow Behavior And Instabilities In Viscoelastic Fluids: Physical And Biological Systems, Boyang Qin

##### Publicly Accessible Penn Dissertations

The flow of complex fluids, especially those containing polymers, is ubiquitous in nature and industry. From blood, plastic melts, to airway mucus, the presence of microstructures such as particles, proteins, and polymers, can impart nonlinear material properties not found in simple fluids like water. These rheological behaviors, in particular viscoelasticity, can give rise to flow anomalies found in industrial settings and intriguing transport dynamics in biological systems.

The first part of my work focuses on the flow of viscoelastic fluids in physical systems. Here, I investigate the flow instabilities of viscoelastic fluids in three different geometries and configurations. Realized in ...

Condensation And Mobility Studies Of Fluid Interfaces, Paul Barclay Jan 2018

#### Condensation And Mobility Studies Of Fluid Interfaces, Paul Barclay

##### Publicly Accessible Penn Dissertations

Condensation is of central importance in a broad range of areas in nature and industry. Aerosol-cloud interactions, a currently a significant open question in climate modeling, and water harvesting mechanisms on organisms such as cacti, beetles, and spiders, are natural processes that are rely on condensation. Condensation is an effective method for transferring heat due to the latent heat required for a fluid to change phase from a gas to a liquid. Improvements in condensation processes would have an impact in a variety of industrial areas such as thermal management, environmental control, microelectronics, desalination, and power generation. Dropwise condensation is ...

Technical Report On: Towards Reactive Control Of Simplified Legged Robotics Maneuvers, Jeff Duperret, D. E. Koditschek Oct 2017

#### Technical Report On: Towards Reactive Control Of Simplified Legged Robotics Maneuvers, Jeff Duperret, D. E. Koditschek

##### Technical Reports (ESE)

This technical report provides proofs and calculations for the paper "Towards Reactive Control of Simplified Legged Robotics Maneuvers," as well as implementation notes and a discussion on robustness.

The Penn Baxter Face Database, Naomi T. Fitter, Katherine J. Kuchenbecker Mar 2017

#### The Penn Baxter Face Database, Naomi T. Fitter, Katherine J. Kuchenbecker

##### Departmental Papers (MEAM)

The Penn Baxter Face Database is composed of Baxter robot face images designed in a variety of expressions and colors. Each of these images was photographed on the physical Baxter robot and assessed by internet raters (N = 568) in an Amazon Mechanical Turk survey. Raters assessed the pleasantness and energeticness of each robot face and also shared how safe and pleased each face made them feel. This project was published in our ICSR 2016 paper entitled “Designing and Assessing Expressive Open-Source Faces for the Baxter Robot.” After hearing of interest from other researchers, we previously released our Baxter face database ...

An Investigation Of Lsf-Ysz Conductive Scaffolds For Infiltrated Sofc Cathodes, Yuan Cheng, Tae-Sik Oh, Rachel Wilson, Raymond J. Gorte, John M. Vohs Jan 2017

#### An Investigation Of Lsf-Ysz Conductive Scaffolds For Infiltrated Sofc Cathodes, Yuan Cheng, Tae-Sik Oh, Rachel Wilson, Raymond J. Gorte, John M. Vohs

##### Departmental Papers (CBE)

Porous compostites of Sr-doped LaFeO3 (LSF and yttria-stabilized zirconia (YSZ) were investigated as conductive scaffolds for infiltrated SOFC cathodes with the goal of producing scaffolds for which only a few perovskite infiltration steps are required to achieve sufficient conductivity. While no new phases form when LSF-YSZ composites are calcined to 1623 K, shifts in the lattice parameters indicate Zr can enter the perovskite phase. Measurements on dense, LSF-YSZ composites show that the level of Zr doping depends on the Sr:La ration. Because conductivity of undoped LSF increases with Sr content while both the iconic and electronic conductivities of ...

Modification Of Lsf-Ysz Composite Cathodes By Atomic Layer Deposition, M. Rahmanipour, Yuan Cheng, Tzia M. Onn, A. Donazzi, John M. Vohs, Raymond J. Gorte Jan 2017

#### Modification Of Lsf-Ysz Composite Cathodes By Atomic Layer Deposition, M. Rahmanipour, Yuan Cheng, Tzia M. Onn, A. Donazzi, John M. Vohs, Raymond J. Gorte

##### Departmental Papers (CBE)

composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La0.8Sr0.2FeO3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO2, La2O3, Fe2O3, or La2O3-Fe2O3 codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe2O3 and 523 K for ZrO2 and La2O3 were determined to be 0.024 ...

##### Publicly Accessible Penn Dissertations

Understanding the mechanism of the load bearing and force transmission throughout fibrous biological structures can help decode complex physiological and pathological phenomena and provide insight into possible therapeutic solutions. Fibrous structures are characterized by one-dimensional fibers stabilized by cross-linking proteins and molecules. Preferentially aligned fibers form well-organized parallel bundles, whereas randomly distributed fibers create isotropic three-dimensional networks. Tendons, composed of staggered arrangements of collagen fibrils, and axonal cytoskeleton in neurons, composed of alternate rows of microtubules, are two instances of structures with aligned fibers. Collagen fibrous networks which make up the extracellular matrix (ECM) of connective tissues are an example ...

Jan 2017

#### Grasping, Perching, And Visual Servoing For Micro Aerial Vehicles, Justin Thomas

##### Publicly Accessible Penn Dissertations

Micro Aerial Vehicles (MAVs) have seen a dramatic growth in the consumer market because of their ability to provide new vantage points for aerial photography and videography. However, there is little consideration for physical interaction with the environment surrounding them. Onboard manipulators are absent, and onboard perception, if existent, is used to avoid obstacles and maintain a minimum distance from them. There are many applications, however, which would benefit greatly from aerial manipulation or flight in close proximity to structures. This work is focused on facilitating these types of close interactions between quadrotors and surrounding objects. We first explore high-speed ...

Jan 2017

#### Quantitiative Modeling Of Oxygen Precipitation In Silicon, Yi Yang

##### Publicly Accessible Penn Dissertations

The vast majority of modern microelectronic devices are fabricated on single-crystal silicon wafers, which are produced predominantly by the Czochralski (CZ) melt-growth process. Important metrics that ultimately influence the quality of the silicon wafers include the concentration of impurities and the distribution of lattice defects (collectively known as microdefects). This thesis provides a multiscale quantitative modeling framework for describing physics of microdefects formation in silicon crystals, with particular emphasis on oxide precipitates.

Among the most prevalent microdefects found in silicon crystals are nanoscale voids and oxide precipitates. Oxide precipitates, in particular, are critically important because they provide gettering sites for ...

#### Constitutive Modeling Of Viscoplastic Porous Single Crystals And Polycrystals: Macroscopic Response And Evolution Of The Microstructure, Dawei Song

##### Publicly Accessible Penn Dissertations

\noindent Porosity can have a significant effect on the overall constitutive behavior of many materials, especially when it serves to relax kinematic constraints imposed by the underlying matrix behavior. In this study, we investigate the multiscale, finite-strain response of viscoplastic porous single crystals and porous polycrystals. For these materials, the presence of voids leads to highly nonlinear dilatational behavior for loads with a large hydrostatic component, even though the matrix material itself is essentially incompressible.

\vspace*{15pt}

\noindent In this study, we employ the recently developed fully optimized second-order" homogenization approach, along with an iterated homogenization procedure, to obtain accurate ...

Actuation, Sensing And Control For Micro Bio Robots, Denise Wong Jan 2017

#### Actuation, Sensing And Control For Micro Bio Robots, Denise Wong

##### Publicly Accessible Penn Dissertations

The continuing trend in miniaturization of technology, advancements in micro and nanofabrication and improvements in high-resolution imaging has enabled micro- and meso-scale robots that have many applications. They can be used for micro-assembly, directed drug delivery, microsurgery and high-resolution measurement. In order to create microrobots, microscopic sensors, actuators and controllers are needed. Unique challenges arise when building microscale robots. For inspiration, we look toward highly capable biological organisms, which excel at these length scales. In this dissertation we develop technologies that combine biological components and synthetic components to create actuation, sensing and assembly onboard microrobots. For actuation, we study the ...

The Penn Hand-Clapping Motion Dataset, Naomi T. Fitter, Katherine J. Kuchenbecker Nov 2016

#### The Penn Hand-Clapping Motion Dataset, Naomi T. Fitter, Katherine J. Kuchenbecker

##### Departmental Papers (MEAM)

The Penn Hand-Clapping Motion Dataset is composed of inertial measurement unit (IMU) recordings from the hand motions of 15 naïve people. Each of these individuals participated in an experiment during which they were asked to pantomime various sequences of 10 different motions: back five, clap, double, down five, front five, lap pat, left five, right five, right snap, and up five. The examined motions comprise most typical actions from hand-clapping games like “Pat-a-cake” and “Slide.” This project was published in our IROS 2016 paper entitled “Using IMU Data to Demonstrate Hand-Clapping Games to a Robot.” After hearing of interest from ...

A Scalable Strategy For Open Loop Magnetic Control Of Microrobots Using Critical Points, Luis Guerrero-Bonilla, Subhrajit Bhattacharya, Vijay Kumar May 2016

#### A Scalable Strategy For Open Loop Magnetic Control Of Microrobots Using Critical Points, Luis Guerrero-Bonilla, Subhrajit Bhattacharya, Vijay Kumar

##### Departmental Papers (MEAM)

A novel scalable strategy for open loop control of ferromagnetic microrobots on a plane using a scalable array of electromagnets is presented. Instead of controlling the microrobot directly, we create equilibrium points in the magnetic force field that are stable and attractive on the plane in which the microrobot is to be controlled. The microrobot moves into these equilibrium points rapidly in presence of low viscous forces, and thus controlling the equilibrium points let us control the microrobot precisely. An unit/cell in the array of electromagnets allows precise control of the microrobot in the unit/cell’s domain. Motion ...

Visual Servoing Of Quadrotors For Perching By Hanging From Cylindrical Objects, Justin Thomas, Giuseppe Loianno, Kostas Daniilidis, Vijay Kumar Jan 2016

#### Visual Servoing Of Quadrotors For Perching By Hanging From Cylindrical Objects, Justin Thomas, Giuseppe Loianno, Kostas Daniilidis, Vijay Kumar

##### Departmental Papers (MEAM)

This paper addresses vision-based localization and servoing for quadrotors to enable autonomous perching by hanging from cylindrical structures using only a monocular camera. We focus on the problems of relative pose estimation, control, and trajectory planning for maneuvering a robot relative to cylinders with unknown orientations. We first develop a geometric model that describes the pose of the robot relative to a cylinder. Then, we derive the dynamics of the system, expressed in terms of the image features. Based on the dynamics, we present a controller which guarantees asymptotic convergence to the desired image space coordinates. Finally, we develop an ...

Particle, Polymer & Phase Dynamics In Living Fluids, Alison E. Koser Jan 2016

#### Particle, Polymer & Phase Dynamics In Living Fluids, Alison E. Koser

##### Publicly Accessible Penn Dissertations

Flocks of birds, schools of fish, and jams in traffic surprisingly mirror the collective motion observed in the microscopic wet worlds of living microbes, such as bacteria. While these small organisms were discovered centuries ago, scientists have only recently examined the dynamics and mechanics of suspensions that contain these swimming particles. I conduct experiments with the model organism and active colloid, the bacterium Escherichia coli, and use polymers, particles, and phase-separated mixtures to probe the non-equilibrium dynamics of bacterial suspensions. I begin by examining the hydrodynamic interactions between swimming E. coli and particles. For dilute suspensions of bacteria in Newtonian ...

Passive Stability And Actuation Of Micro Aerial Vehicles, Matthew Piccoli Piccoli Jan 2016

#### Passive Stability And Actuation Of Micro Aerial Vehicles, Matthew Piccoli Piccoli

##### Publicly Accessible Penn Dissertations

Micro Aerial Vehicles (MAVs) have increased in popularity in recent years. The most common platform, the quadrotor, has surpassed other MAVs like traditional helicopters and ornithopters in popularity mainly due to their simplicity. Yet the quadrotor design is a century old and was intended to carry people. We set out to design a MAV that is designed specifically to be a MAV, i.e. a vehicle not intended to carry humans as a payload. With this constraint lifted the vehicle can continuously rotate, which would dizzy a human, can sustain larger forces, which would damage a human, or can take ...

Jan 2016

#### Path Planning For Persistent Surveillance Applications Using Fixed-Wing Unmanned Aerial Vehicles, James F. Keller

##### Publicly Accessible Penn Dissertations

This thesis addresses coordinated path planning for ﬁxed-wing Unmanned Aerial Vehicles

(UAVs) engaged in persistent surveillance missions. While uniquely suited to this mission,

ﬁxed wing vehicles have maneuver constraints that can limit their performance in this role.

Current technology vehicles are capable of long duration ﬂight with a minimal acoustic

footprint while carrying an array of cameras and sensors. Both military tactical and civilian

safety applications can beneﬁt from this technology. We make three main contributions:

C1 A sequential path planner that generates a C2 ﬂight plan to persistently acquire a

covering set of data over a user designated area ...

Jan 2016

#### Continuum And Computational Modeling Of Flexoelectricity, Sheng Mao

##### Publicly Accessible Penn Dissertations

Flexoelectricity refers to the linear coupling of strain gradient and electric polarization. Early studies of this subject mostly look at liquid crystals and biomembranes. Recently, the advent of nanotechnology revealed its importance also in solid structures, such as flexible electronics, thin films, energy harvesters, etc. The energy storage function of a flexoelectric solid depends not only on polarization and strain, but also strain-gradient. This is our basis to formulate a consistent model of flexoelectric solids under small deformation. We derive a higher-order Navier equation for linear isotropic flexoelectric materials which resembles that of Mindlin in gradient elasticity. Closed-form solutions can ...

Design Principles For A Family Of Direct-Drive Legged Robots, Gavin Kenneally, Avik De, Daniel E. Koditschek Jan 2016

#### Design Principles For A Family Of Direct-Drive Legged Robots, Gavin Kenneally, Avik De, Daniel E. Koditschek

##### Departmental Papers (ESE)

This letter introduces Minitaur, a dynamically running and leaping quadruped, which represents a novel class of direct-drive (DD) legged robots. We present a methodology that achieves the well-known benefits of DD robot design (transparency, mechanical robustness/efficiency, high-actuation bandwidth, and increased specific power), affording highly energetic behaviors across our family of machines despite severe limitations in specific force. We quantify DD drivetrain benefits using a variety of metrics, compare our machines' performance to previously reported legged platforms, and speculate on the potential broad-reaching value of “transparency” for legged locomotion.

Scalable Scheduling Of Energy Control Systems, Truong X. Nghiem, Rahul Mangharam Oct 2015

#### Scalable Scheduling Of Energy Control Systems, Truong X. Nghiem, Rahul Mangharam

##### Real-Time and Embedded Systems Lab (mLAB)

Peak power consumption is a universal problem across energy control systems in electrical grids, buildings, and industrial automation where the uncoordinated operation of multiple controllers result in temporally correlated electricity demand surges (or peaks). While there exist several different approaches to balance power consumption by load shifting and load shedding, they operate on coarse grained time scales and do not help in de-correlating energy sinks. The Energy System Scheduling Problem is particularly hard due to its binary control variables. Its complexity grows exponentially with the scale of the system, making it impossible to handle systems with more than a few ...

Zirconia-Based Electrolyte Stability In Direct-Carbon Fuel Cells With Molten Sb Anodes, Xiaoliang Zhou, Tae-Sik Oh, John M. Vohs, Raymond J. Gorte Jan 2015

#### Zirconia-Based Electrolyte Stability In Direct-Carbon Fuel Cells With Molten Sb Anodes, Xiaoliang Zhou, Tae-Sik Oh, John M. Vohs, Raymond J. Gorte

##### Departmental Papers (CBE)

Direct carbon fuel cells (DCFC) that use zirconia-based electrolytes and molten Sb anodes have much promise for the efficient conversion of carbonaceous solid fuels into electricity. However, etching of the electrolyte, and ultimately cell failure, has been observed during operation. In this study, we have investigated this etching phenomenon as a function of the electrolyte composition and cell operating conditions and demonstrated that it is not electrochemical in nature, but rather results from reaction between the electrolyte and Sb2O3.

#### Development Of Bond-Order Potentials For Body-Centered-Cubic Transition Metals And Their Application In Atomistic Studies Of Plastic Properties Mediated By Dislocations, Yi-Shen Lin

##### Publicly Accessible Penn Dissertations

ABSTRACT

DEVELOPMENT OF BOND-ORDER POTENTIALS FOR BODY-CENTERED-CUBIC TRANSITION METALS AND THEIR APPLICATION IN ATOMISTIC STUDIES OF PLASTIC PROPERTIES MEDIATED BY DISLOCATIONS

Yi-Shen Lin

Professor Vaclav Vitek

Bond-order potentials (BOPs), based on the tight binding (TB) approach for the evaluation of bonding, are an real-space method. They are eminently suitable for atomistic simulations of extended defects in transition metals in which the bonding is mixed nearly free electron and covalent. The latter requires a rigorous quantum mechanical treatment performed within the TB. In this Thesis, new BOPs were developed for non-magnetic BCC transition metals, V, Nb, Ta, Cr, Mo and W ...

Jan 2015

#### Nanofibrous Disc-Like Angle Ply Structure For Total Disc Replacement In A Small Animal Model, John Thomas Martin

##### Publicly Accessible Penn Dissertations

Low back pain affects 85% of the population and carries a socioeconomic price tag of \$100 billion USD per year. Lumbar intervertebral disc disease is strongly implicated as a causative factor in back pain, as degeneration, which is ubiquitous in the population, leads to loss of normal spine function. For these reasons, our lab has developed disc-like angle ply structures (DAPS) for total disc replacement. These cell-seeded replacements are designed to match the natural hierarchical structure and function of the native disc and correct spinal kinematics after end-stage disc disease.

In this dissertation, I describe the development of a rat ...