Penn Engineering

The School of Engineering and Applied Science, established in 1852, is composed of six academic departments and numerous interdisciplinary centers, institutes, and laboratories. At Penn Engineering, we are preparing the next generation of innovative engineers, entrepreneurs and leaders. Our unique culture of cooperation and teamwork, emphasis on research, and dedicated faculty advisors who teach as well as mentor, provide the ideal environment for the intellectual growth and development of well-rounded global citizens.

Search results

Now showing 1 - 10 of 1509
  • Publication
    Single-walled carbon nanotubes in superacid: X-ray and calorimetric evidence for partly ordered H2SO4
    (2005-07-01) Zhou, Wei; Fischer, John E; Heiney, P. A; Fan, H.; Davis, Virginia A; Pasquali, M.; Smalley, Richard E
    Liquid anhydrous sulfuric acid forms a partly ordered structure in the presence of single-walled carbon nanotubes (SWNTs). X-ray scattering from aligned fibers immersed in acid shows the formation of molecular shells wrapped around SWNTs. Differential scanning calorimetry of SWNT-acid suspensions exhibits concentration-dependent supercooling/melting behavior, confirming that the partly ordered molecules are a new phase. We propose that charge transfer between nanotube π electrons and highly oxidizing superacid is responsible for the unique partly ordered structure.
  • Publication
    Photoacoustic effect for multiply scattered light
    (2007-09-25) Fisher, Andrew R; Schissler, Andrew J; Schotland, John C
    We consider the photoacoustic effect for multiply scattered light in a random medium. Within the accuracy of the diffusion approximation to the radiative transport equation, we present a general analysis of the sensitivity of a photoacoustic wave to the presence of one or more small absorbing objects. Applications to tumor detection by photoacoustic imaging are suggested.
  • Publication
    Topological conditions for in-network stabilization of dynamical systems
    (2013-04-01) Pajic, Miroslav; Sundaram, Shreyas; Mangharam, Rahul; Pappas, George
    We study the problem of stabilizing a linear system over a wireless network using a simple in-network computation method. Specifically, we study an architecture called the "Wireless Control Network'' (WCN), where each wireless node maintains a state, and periodically updates it as a linear combination of neighboring plant outputs and node states. This architecture has previously been shown to have low computational overhead and beneficial scheduling and compositionality properties. In this paper we characterize fundamental topological conditions to allow stabilization using such a scheme. To achieve this, we exploit the fact that the WCN scheme causes the network to act as a linear dynamical system, and analyze the coupling between the plant's dynamics and the dynamics of the network. We show that stabilizing control inputs can be computed in-network if the vertex connectivity of the network is larger than the geometric multiplicity of any unstable eigenvalue of the plant. This condition is analogous to the typical min-cut condition required in classical information dissemination problems. Furthermore, we specify equivalent topological conditions for stabilization over a wired (or point-to-point) network that employs network coding in a traditional way -- as a communication mechanism between the plant's sensors and decentralized controllers at the actuators.
  • Publication
    Interactive design of complex time-dependent lighting
    (1995-03-01) Dorsey, Julie; Arvo, James; Greenberg, Donald
    Visualizing complicated lighting sequences while designing large theatrical productions proves difficult. The author provides some techniques that achieve fast interaction regardless of scene and lighting complexity, even when used with costly rendering algorithms.
  • Publication
    An Examination of SOFC Anode Functional Layers Based on Ceria in YSZ
    (2007-08-21) Gross, Michael D; Vohs, John M; Gorte, Raymond J
    The properties of solid oxide fuel cell (SOFC) anode functional layers prepared by impregnation of ceria and catalytic metals into porous yttria-stabilized zirconia (YSZ) have been examined for operation at 973 K. By varying the thickness of the functional layer, the conductivity of the ceria-YSZ composite was determined to be only 0.015–0.02 S/cm. The initial performance of anodes made with ceria loadings of 40 or 60 wt % were similar but the anodes with lower loadings lost conductivity above 1073 K due to sintering of the ceria. The addition of dopant levels of catalytic metals was found to be critical. The addition of 1 wt % Pd or Ni decreased the anode impedances in humidified H2 dramatically, while the improvement with 5 wt % Cu was significant but more modest. Pd doping also decreased the anode impedance in dry CH4 much more than did Cu doping; however, addition of either Pd or Cu led to similar improvements for operation in n-butane. Based on these results, suggestions are made for ways to improve SOFC anode functional layers.
  • Publication
    Token Coherence: A New Framework for Shared-Memory Multiprocessors
    (2003-11-01) Martin, Milo; Hill, Mark D; Wood, David A
    Commercial workload and technology trends are pushing existing shared-memory multiprocessor coherence protocols in divergent directions. Token Coherence provides a framework for new coherence protocols that can reconcile these opposing trends.
  • Publication
    Interaction of the Gelsolin-Derived Antibacterial PBP 10 Peptide with Lipid Bilayers and Cell Membranes
    (2006-09-01) Bucki, Robert; Janmey, Paul
    PBP 10, an antibacterial, cell membrane-permeant rhodamine B-conjugated peptide derived from the polyphosphoinositide binding site of gelsolin, interacts selectively with both lipopolysaccharides (LPS) and lipoteichoic acid (LTA), the distinct components of gram-negative and gram-positive bacteria, respectively. Isolated LPS and LTA decrease the antimicrobial activities of PBP 10, as well as other antimicrobial peptides, such as cathelicidin-LL37 (LL37) and mellitin. In an effort to elucidate the mechanism of bacterial killing by PBP 10, we compared its effects on artificial lipid bilayers and eukaryotic cell membranes with the actions of the mellitin, magainin II, and LL37 peptides. This study reveals that pore formation is unlikely to be involved in PBP 10-mediated membrane destabilization. We also investigated the effects of these peptides on platelets and red blood cells (RBCs). Comparison of these antimicrobial peptides shows that only mellitin has a toxic effect on platelets and RBCs in a concentration range concomitant with its bactericidal activity. The hemolytic activities of the PBP 10 and LL37 peptides significantly increase when RBCs are osmotically swollen in hypotonic solution, indicating that these antibacterial peptides may take advantage of the more extended form of bacterial membranes in exerting their killing activities. Additionally, we found that LL37 hemolytic activity was much higher when RBCs were induced to expose phosphatidylserine to the external leaflet of their plasma membranes. This finding suggests that asymmetrical distribution of phospholipids in the external membranes of eukaryotic cells may represent an important factor in determining the specificity of antibacterial peptides for targeting bacteria rather than eukaryotic cells.
  • Publication
    Robo4x - Video 9.3a
    (2017-10-02) Koditschek, Daniel
    So let's just remember what the big picture looks like and what we're trying to do. You'll recall from our approach to vertical hoppers, that what we're trying to develop a model of the continuous time vector field and then the continuous time of flow for each of the different contact modes.
  • Publication
    A Discrete-Time Stochastic Model of Job Matching
    (2003-01-01) Smith, Tony E; Zenou, Yves
    In this paper, an explicit micro scenario is developed which yields a well-defined aggregate job matching function. In particular, a stochastic model of job-matching behavior is constructed in which the system steady state is shown to be approximated by an exponential-type matching function, as the population becomes large. This steady-state approximation is first derived for fixed levels of both wages and search intensities, where it is shown (without using a free-entry condition) that there exists a unique equilibrium. It is then shown that if job searchers are allowed to choose their search intensities optimally, this model is again consistent with a unique steady state. Finally, the assumption of a fixed wage is relaxed, and an optimal 'offer wage' is derived for employers.
  • Publication
    Omnidirectional video
    (2003-01-01) Geyer, Christopher M; Daniilidis, Kostas
    Omnidirectional video enables direct surround immersive viewing of a scene by warping the original image into the correct perspective given a viewing direction. However, novel views from viewpoints off the camera path can only be obtained if we solve the 3D motion and calibration problem. In this paper we address the case of a parabolic catadioptric camera – a paraboloidal mirror in front of an orthographic lens – and we introduce a new representation, called the circle space, for points and lines in such images. In this circle space, we formulate an epipolar constraint involving a 4x4 fundamental matrix. We prove that the intrinsic parameters can be inferred in closed form from the 2D subspace of the new fundamental matrix from two views if they are constant or from three views if they vary. Three dimensional motion and structure can then be estimated from the decomposition of the fundamental matrix.