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University of Notre Dame

1. Baoyang Deng. Bifurcations and Symmetries of Optimal Solutions for Distributed Robotic Systems</h1>.

Degree: Aerospace and Mechanical Engineering, 2011, University of Notre Dame

URL: https://curate.nd.edu/show/sf268338x32

In this thesis, we consider the motion
planning problem for a symmetric distributed system which consists
of a group of autonomous mobile robots operating in a
two-dimensional obstacle-free environment. Each robot has a
predefined initial state and final state and the problem is to find
the optimal path between two states for every robot. The path is
optimized with respect to the control effort and the deviation from
a desired formation. Due to scaling issues, it becomes more and
more difficult and sometimes infeasible to numerically find
solutions to the problem as the number of robots increases. One
goal of this thesis is to exploit symmetries in distributed control
systems to reduce the computational effort to determine solutions
for optimal control of such systems. One way to characterize a
distributed system is that it is a control system in which the
state space is naturally decomposed into multiple subsystems, each
of which typically only interacts with a limited subset of the
other subsystems. A symmetric distributed system can be defined
when the subsystems are diffeomorphically related. The optimal
control problem for distributed systems may not scale well with the
size of the overall system; hence, our efforts are directed toward
exactly solving the optimization problem for large scale systems by
working with a reduced order model that is determined by
considering invariance properties with respect to certain group
actions of the governing equations of the overall system.
This thesis also studies bifurcations and multiple
solutions of the optimal control problem for mobile robotic
systems. While the existence of multiple local solutions to a
nonlinear optimization problem is not unexpected, the nature of the
solutions are such that a relatively rich and interesting structure
is present, which potentially could be exploited for controls
purposes. The bifurcation parameter is the relative weight given to
penalizing the deviation from the desired formation versus control
effort. Numerically it is shown that as this number varies,
bifurcations of solutions are obtained. Theoretic results of this
paper relate to the symmetric properties of these bifurcations and
the number and existence of multiple solutions for large and small
values of the bifurcation parameter. Understanding the existence
and nature of multiple solutions for optimization problems of this
type is also of practical importance due to the ubiquity of
gradient-based optimization methods where the search method will
typically converge to the nearest local
optimum.
*Advisors/Committee Members: Bill Goodwine, Committee Chair, Alan C Seabaugh , Committee Chair, John E Renaud, Committee Member, Mihir Sen, Committee Member, Panos Antsaklis , Committee Member.*

Subjects/Keywords: symmetry; distributed system; Bifurcation

Record Details Similar Records

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Deng, B. (2011). Bifurcations and Symmetries of Optimal Solutions for Distributed Robotic Systems</h1>. (Thesis). University of Notre Dame. Retrieved from https://curate.nd.edu/show/sf268338x32

Note: this citation may be lacking information needed for this citation format:

Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^{th} Edition):

Deng, Baoyang. “Bifurcations and Symmetries of Optimal Solutions for Distributed Robotic Systems</h1>.” 2011. Thesis, University of Notre Dame. Accessed September 24, 2020. https://curate.nd.edu/show/sf268338x32.

Note: this citation may be lacking information needed for this citation format:

Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^{th} Edition):

Deng, Baoyang. “Bifurcations and Symmetries of Optimal Solutions for Distributed Robotic Systems</h1>.” 2011. Web. 24 Sep 2020.

Vancouver:

Deng B. Bifurcations and Symmetries of Optimal Solutions for Distributed Robotic Systems</h1>. [Internet] [Thesis]. University of Notre Dame; 2011. [cited 2020 Sep 24]. Available from: https://curate.nd.edu/show/sf268338x32.

Note: this citation may be lacking information needed for this citation format:

Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Deng B. Bifurcations and Symmetries of Optimal Solutions for Distributed Robotic Systems</h1>. [Thesis]. University of Notre Dame; 2011. Available from: https://curate.nd.edu/show/sf268338x32

Not specified: Masters Thesis or Doctoral Dissertation

University of Notre Dame

2. Qin Zhang. Interband Tunnel Transistors</h1>.

Degree: Electrical Engineering, 2009, University of Notre Dame

URL: https://curate.nd.edu/show/5h73pv65c7m

Interband tunnel transistors have been
attracting increasing attention because of their potential to
achieve subthreshold swings below the 60 mV/decade thermionic
limit, and realize high performance and low power dissipation
simultaneously. This work explores the design and modeling of
semiconducting and graphene nanoribbon-based tunnel transistors, to
understand the performance measures and guide the experimental
development. Experiments in the formation of Ge interband junctions
are also described. Analytic
expressions for Zener tunneling in one-, two-, and
three-dimensional semiconductors are derived to establish the
guidelines for tunnel transistor design. An analytic expression is
derived, showing that the subthreshold swing of interband tunnel
transistors is a function of the gate-to-source voltage and can be
less than the thermionic limit of 60 mV/decade in MOSFET. Based on
this expression, a new fully-depleted interband tunnel transistor
structure is proposed and designed. The low subthreshold swing is
verified by Synopsys TCAD simulation. Germanium interband tunnel
transistors are shown by simulation to exhibit improved on-state
performance vs. Si, because of the smaller bandgap and effective
mass. To realize the proposed Ge interband tunnel transistor, a
rapid melt growth process was developed to form submicron p+n+ Ge
tunnel junctions. Transmission electron microscopy (TEM) reveals
the regrown film and a contact microstructure consistent with the
Al-Ge phase diagram. Negative differential resistances are observed
which indicate the junction was abrupt heavily-doped.
A graphene nanoribbon (GNR) tunnel transistor is
first proposed and modeled analytically by quasi-1D Poisson
equation. An improved numerical model is developed that treates
energy-dependent transmission coefficients, direct source-to-drain
tunneling, and self-consistent channel electrostatics. Graphene
nanoribbons have a width-tunable bandgap and ultra-thin body layer,
which is especially favorable for tunnel transistor applications.
It is shown by simulation that the GNR tunnel transistors at the
long channel limit can operate at 0.1 V with an ultra-low
subthreshold swing of 2.8 mV/decade, but the subthreshold swing and
off-state current are degraded at short channel length due to
direct source-to-drain tunneling. Smaller ribbon widths (down to a
certain limit) can significantly improve the off-state behavior
without considerably affecting the on-state current density and
speed. For 20 nm channel length, GNR tunnel transistors with ribbon
width of 2 and 3 nm can achieve high performance and low operating
power simultaneously, meeting 2012 ITRS
targets.
*Advisors/Committee Members: Thomas Kosel, Committee Member, Debdeep Jena , Committee Member, Gary Bernstein , Committee Member, Alan C. Seabaugh, Committee Chair.*

Subjects/Keywords: Zener tunneling; graphene; tunnel transistor

Record Details Similar Records

❌

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^{th} Edition):

Zhang, Q. (2009). Interband Tunnel Transistors</h1>. (Thesis). University of Notre Dame. Retrieved from https://curate.nd.edu/show/5h73pv65c7m

Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^{th} Edition):

Zhang, Qin. “Interband Tunnel Transistors</h1>.” 2009. Thesis, University of Notre Dame. Accessed September 24, 2020. https://curate.nd.edu/show/5h73pv65c7m.

Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^{th} Edition):

Zhang, Qin. “Interband Tunnel Transistors</h1>.” 2009. Web. 24 Sep 2020.

Vancouver:

Zhang Q. Interband Tunnel Transistors</h1>. [Internet] [Thesis]. University of Notre Dame; 2009. [cited 2020 Sep 24]. Available from: https://curate.nd.edu/show/5h73pv65c7m.

Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Zhang Q. Interband Tunnel Transistors</h1>. [Thesis]. University of Notre Dame; 2009. Available from: https://curate.nd.edu/show/5h73pv65c7m

Not specified: Masters Thesis or Doctoral Dissertation