Model approximation for batch flow shop scheduling with fixed batch sizes

Batch flow shops model systems that process a variety of job types using a fixed infrastructure. This model has applications in several areas including chemical manufacturing, building construction, and assembly lines. Since the throughput of such systems depends, often strongly, on the sequence in which they produce various products, scheduling these systems becomes a problem with very practical consequences. Nevertheless, optimally scheduling these systems is NP-complete. This paper demonstrates that batch flow shops can be represented as a particular kind of heap model in the max-plus algebra. These models are shown to belong to a special class of linear systems that are globally stable over finite input sequences, indicating that information about past states is forgotten in finite time. This fact motivates a new solution method to the scheduling problem by optimally solving scheduling problems on finite-memory approximations of the original system. Error in solutions for these “t-step” approximations is bounded and monotonically improving with increasing model complexity, eventually becoming zero when the complexity of the approximation reaches the complexity of the original system.United States. Department of Homeland Security. Science and Technology Directorate (Contract HSHQDC-13-C-B0052)United States. Air Force Research Laboratory (Contract FA8750-09-2-0219)ATK Thiokol Inc

Epitaxial Growth and Processing of Compound Semiconductors

Contains an introduction and reports on six research projects.Defense Advanced Research Projects Agency/U.S. Navy - Office of Naval Research University Research Initiative Subcontract N00014-92-J-1893Joint Services Electronics Program Grant DAAH04-95-1-0038National Center for Integrated Photonics Technology Contract 542-381National Science Foundation Grant DMR 92-02957MIT Lincoln Laboratory Contract BX-6085National Center for Integrated Photonics Technology Subcontract 542-383U.S. Air Force - Office of Scientific Research Grant F49620-96-1-0126U.S. Navy - Office of Naval Research Grant N00014-91-J-1956National Science Foundation Grant DMR 94-0033

Piloting epitaxy with ellipsometry as an in-situ sensor technology

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 107-113).Epitaxial processes are deposition processes that produce crystalline films with nano-scale precision. Many compound semiconductor devices rely on epitaxy to produce high-quality crystalline films with a specified compositional profile as a function of film thickness. Although various epitaxial processes, such as molecular beam epitaxy or metal-organic chemical vapor deposition, have long been known to be capable of producing such films with mono-layer precision, doing so often requires significant calibration and many trial-and-error attempts before success is realized. Ellipsometry is an established optical characterization method that uses the polarization state of reflected light to determine the alloy composition of a grown film. As a non-invasive sensor technology, ellipsometry has more recently been deployed as an in-situ sensor to characterize films as they grow. This thesis takes a comprehensive view of the issues and impact associated with the use of ellipsometry as an in-situ sensor to control epitaxy in real time. A dynamic model of the physics associated with ellipsometry and growing films is developed from first principles, and this model is used to highlight some of the capabilities and limitations of ellipsometry as a measurement device for feedback control. A control problem is then formulated that substitutes the actual design objective with one more amenable to feedback design, and standard linear tools are used for feedback design. Simulations show that these designs look promising, even for the reliable growth of quaternary graded structures.by Sean C. Warnick.Ph.D

Feedback control of organometallic vapor-phase epitaxial growth of aluminum gallium arsenide devices

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Includes bibliographical references (leaves 67-69).by Sean C. Warnick.M.S