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.

 

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  • Publication
    A Hierarchical Database Model for a Logic Programming Language
    (1988-03-01) Finin, Timothy; McGuire, James
    This paper presents an extended Clausal Database Model for a logic programming language. Instead of being restricted to one global database, as is the case with Prolog, we allow segmentation of the database into database units which are linked together into a semi-lattice. Each database unit defines a database view which includes clauses which have been asserted into that unit as well as clauses inherited from its ancestors higher in the lattice structure. This model supports arbitrary retraction. Retracting a clause in a database unit effectively blocks its inheritance for that unit and all of its descendants. Motivations for using this model are given. We also discuss the implementation of a Prolog meta-interpreter that uses this model. (hereafter referred to as (Phd) or Prolog Hierarchical Database) This meta-interpreter is in the spirit of Prolog and therefore has a version of assert, retract and cut.
  • 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
    Motion Planning for Redundant Branching Articulated Figures with Many Degrees of Freedom
    (1992-07-08) Ching, Wallace S.; Badler, Norman I
    A fast algorithm is presented that can handle the motion planning problem for articulated figures with branches and many degrees of freedom. The algorithm breaks down the degrees of freedom of the figure into Cspace groups and compute the free motion for each of these groups in a sequential fashion. It traverses the tree in a depth first order to compute the motion for all the branches. A special playback routine is then used to traverse the tree again in a reverse order to playback the final motion. The planner runs in linear time with respect to the total number of Cspace groups without backtracking. We believe that the planner would find a path in most cases and is fast enough for practical use in a wide range of applications.
  • Publication
    Virtual Human Animation Based on Movement Observation and Cognitive Behavior Models
    (1999-05-01) Badler, Norman I; Chi, Diane M.; Chopra-Khullar, Sonu
    Automatically animating virtual humans with actions that reflect real human motions is still a challenge. We present a framework for animation that is based on utilizing empirical and validated data from movement observation and cognitive psychology. To illustrate these, we demonstrate a mapping from Effort motion factors onto expressive arm movements, and from cognitive data to autonomous attention behaviors. We conclude with a discussion on the implications of this approach for the future of real-time virtual human animation.
  • Publication
    Dynamic Network Construction and Updating Techniques for the Diagnoses of Acute Abdominal Pain
    (1992-08-01) Provan, Gregory; Clarke, John R
    Computing diagnoses in domains with continuously changing data is a difficult, but essential aspect of solving many problems. To address this task, this paper describes a dynamic influence diagram (ID) construction and updating system, DYNASTY, and its application to constructing a decision-theoretic model to diagnose acute abdominal pain, a domain in which the findings evolve during the diagnostic process. For a system which evolves over time, DYNASTY constructs a parsimonious ID, and then dynamically updates the ID, rather than constructing a new network from scratch for every time interval. In addition, DYNASTY contains algorithms for testing the sensitivity of the constructed network's system parameters. The main contributions of this paper are: (1) presenting an efficient temporal influence diagram technique based on parsimonious model construction; and (2) formalizing the principles underlying a diagnostic tool for acute abdominal pain which explicitly models time-varying findings.
  • Publication
    Fast Image Segmentation
    (1989-07-01) Corke, Peter I; Anderson, Helen I
    Image segmentation remains one of the greatest problems in machine vision. The technique described here takes an image and a geometric description of the object required, determines multiple binary thresholds to segment the image, and combines the information from the appropriate thresholds. By utilizing region-growing hardware it is possible to achieve segmentation in less than 2 seconds.
  • Publication
    On Broadcast Disk Paging
    (1999-03-13) Khanna, Sanjeev; Liberatore, Vincenzo
    Broadcast disks are an emerging paradigm for massive data dissemination. In a broadcast disk, data is divided into n equal-sized pages, and pages are broadcast in a round-robin fashion by a server. Broadcast disks are effective because many clients can simultaneously retrieve any transmitted data. Paging is used by the clients to improve performance, much as in virtual memory systems. However, paging on broadcast disks differs from virtual memory paging in at least two fundamental aspects: - A page fault in the broadcast disk model has a variable cost that depends on the requested page as well as the current state of the broadcast. - Prefetching is both natural and a provably essential mechanism for achieving significantly better competitive ratios in broadcast disk paging. In this paper, we design a deterministic algorithm that uses prefetching to achieve an O(n log k) competitive ratio for the broadcast disk paging problem, where k denotes the size of the client's cache. We also show a matching lower bound of Ω(n log k) that applies even when the adversary is not allowed to use prefetching. In contrast, we show that when prefetching is not allowed, no deterministic online algorithm can achieve a competitive ratio better than Ω(nk). Moreover, we show a lower bound of Ω(n log k) on the competitive ratio achievable by any nonprefetching randomized algorithm against an oblivious adversary. These lower bounds are trivially matched from above by known results about deterministic and randomized marking algorithms for paging. An interpretation of our results is that in the broadcast disk paging, prefetching is a perfect substitute for randomization.
  • Publication
    Role and Organization of Transfers in Transit Networks
    (1992) Vuchic, Vukan R; Musso, Antonio
    Passenger transfers among transit lines involve certain "resistance", because they cause some delay and require passenger orientation and walking between vehicles on different lines. Therefore it is sometimes believed that transfers are undesirable and that they should be avoided whenever possible. The fact is, however, that transit networks with many transfer opportunities offer passengers much greater selection of travel paths than networks with disconnected lines which involve no transferring. In addition, the more transferring is performed, the greater is network efficiency, because each line can be designed optimally for its physical conditions, volume and character of demand. Consequently, when transfers are planned correctly, the resistance for passengers can be easily outweighed by the benefits transfers bring with respect to line alignments, schedules and, eventually, in better services offered. Passenger transfers among lines thus represent an important element of transit travel.
  • Publication
    Kelvin-Helmhotz Instability for Parallel Flow in Porous Media: A Linear Theory
    (1982) Bau, Haim H.
    Two fluid layers in fully-saturated porous media are considered. The lighter fluid is above the heavier one so that in the absence of motion the arrangement is stable and the interface is flat. It is shown that when the fluids are moving parallel to each other at different velocities, the interface may become unstable (the Kelvin-Helmholtz instability). The corresponding conditions for marginal stability are derived for Darcian and non-Darcian flows. In both cases, the velocities should exceed some critical values in order for the instability to manifest itself. In the case of Darcy's flow, however, an additional condition, involving the fluids' viscosity and density ratios, is required.
  • Publication
    CCSR: A Calculus for Communicating Shared Resources
    (1990-03-12) Gerber, Richard; Lee, Insup
    The timing behavior of a real-time system depends not only on delays due to process synchronization, but also on the availability of shared resources. Most current real-time models capture delays due to process synchronization; however, they abstract out resource-specific details by assuming idealistic operating environments. On the other hand, scheduling and resource allocation algorithms used for real-time systems ignore the effect of process synchronization except for simple precedence relations between processes. To bridge the gap between these two disciplines, we have developed a formalism called Communicating Shared Resources, or CSR. This paper presents the priority-based process algebra called the Calculus for Communicating Shared Resources (CCSR), which provides an equational characterization of the CSR language. The computation model of CCSR is resource-based in that multiple resources execute synchronously, while processes assigned to the same resource are interleaved according to their priorities. CCSR possesses a prioritized strong equivalence for terms based on strong bisimulation. The paper also describes a producer and consumer problem whose correct timing behavior depends on priority.