Resistance of polymeric structures to nitrogen tetroxide Progress report

Resistance of polyethylene structures to nitrogen tetroxide degradatio

Optimal Competition and Allocation of Space in Shopping Centers

This article explains why a profit-maximizing developer may include multiple, competing outlets in a shopping center. While competing outlets presumably dissipate potential profits, thereby lowering aggregate rents that the developer can extract, the presence of shopping externalities causes the developer to be interested not just in individual store profits, but also in the traffic they generate throughout the center. And since competition among identical stores increases traffic, it can create an offsetting advantage that favors multiple outlets. The article provides a theoretical analysis of this problem and illustrates its implications for tenant mix by applying the theory to the problem of filling a vacant store. The paper concludes by explicitly relating the analysis to Brueckner's (1993) model of the optimal allocation of space in shopping centers.

Planar Heterostructure Barrier Varactor Diodes for Millimetre Wave Applications

This thesis deals with fabrication, characterisation and modelling of the Heterostructure Barrier Varactor (HBV) diode and its use in frequency multiplier applications. Different aspects of material structures and frequency multipliers are described. The aim of the work presented is to develop design methods and processes to fabricate state-of-the-art planar HBVs and multipliers in the millimetre and submillimetre wave length region.<p /> Results from AlGaAs HBV frequency tripler measurements are presented. Simulations and cooled measurements show that excessive conduction current due to self-heating degrades the multiplier efficiency. A new design of planar GaAs-based HBVs with reduced thermal resistance and series resistance have been fabricated. A state-of-the-art performance of 4,8% efficiency and an output power of 4 mW at 246 GHz was achieved.<p /> A novel fabrication process where HBV diodes are fabricated on a copper substrate is proposed. This reduces thermal resistance and parasitic resistance without degrading the electrical characteristics.<p /> A 141 GHz quasi-optical HBV tripler is presented. A peak flange-to-flange efficiency of 8% and an output power of 11,5 mW was achieved.<p /> Different III-V material systems for HBVs have been tested. The results of lattice matched and pseudomorphic GaAs/AlGaAs, InGaAs/InAlAs, InAs/AlSb and phosphide containing materials for HBVs are presented. The state-of-the-art material for millimetre and submillimetre wave HBVs is the In_0,53GaAs/In_0,52AlAs system with a thin AlAs layer (30 Å) in the middle of the barrier.<p /> Both simple analytical models and a self-consistent Poisson/Schroedinger approach are used to predict and optimise HBV diodes. Finally, a simple quick-design method for calculation of optimum embedding impedances, optimum conversion efficiency and pump power for HBV triplers are presented

Hybrid Position and Impedance Control of a Forging Process

Pick and place robotic material handling has been a key to increase piece rates and reduced variability in forging processes. One of the drawbacks to current pick and place robotic material handling methods is the inability to locate the part after a forging operation and move it to the next position in a timely manner. If the billet changes position during the forging process, the manipulator will take longer to find the part and transfer it to the next station or the manipulator will be unable to move the part to the next position correctly which may cause scrap. Another drawback is due to the fact that the robot must let go of the billet and move out of the way of the equipment so to not get damaged. This adds extra time to the cycle and reduces productivity. By using sliding mode controls the robotic manipulator will be able to maintain hold of the billet during forging process and rapidly move the part to the next operation. This reduces handling time and possible scrap. The sliding mode controller will be designed to regulate the center position of the billet and the impedance of the gripper. Impedance is the way that a controller can control the force developed in a system. By controlling the impedance of the gripper, the forces on the outside of the billet will be maintained at a level that prevents the billet and the gripper from being destroyed. A mock forging operation was setup and tested to show how the system would work with a simplified grippe

Hybrid Position and Impedance Control of a Forging Process

Pick and place robotic material handling has been a key to increase piece rates and reduced variability in forging processes. One of the drawbacks to current pick and place robotic material handling methods is the inability to locate the part after a forging operation and move it to the next position in a timely manner. If the billet changes position during the forging process, the manipulator will take longer to find the part and transfer it to the next station or the manipulator will be unable to move the part to the next position correctly which may cause scrap. Another drawback is due to the fact that the robot must let go of the billet and move out of the way of the equipment so to not get damaged. This adds extra time to the cycle and reduces productivity. By using sliding mode controls the robotic manipulator will be able to maintain hold of the billet during forging process and rapidly move the part to the next operation. This reduces handling time and possible scrap. The sliding mode controller will be designed to regulate the center position of the billet and the impedance of the gripper. Impedance is the way that a controller can control the force developed in a system. By controlling the impedance of the gripper, the forces on the outside of the billet will be maintained at a level that prevents the billet and the gripper from being destroyed. A mock forging operation was setup and tested to show how the system would work with a simplified grippe

The Unbearable Lightness of Education

The title of this keynote address is a play upon the title of Milan Kundera’s anti-totalitarian novel, The Unbearable Lightness of Being. Kundera found the life of each of us greatly shaped by chance, largely indeterminate, noting our resistance to rules and customs, yet constrained by comfort, fear, and habit. He spoke of lives as events occurring but once, each moment unique in vital ways and too weak a guide to events still to come. “Everything occurs but once,” he said

Hybrid Position and Impedance Control of a Forging Process

Pick and place robotic material handling has been a key to increase piece rates and reduced variability in forging processes. One of the drawbacks to current pick and place robotic material handling methods is the inability to locate the part after a forging operation and move it to the next position in a timely manner. If the billet changes position during the forging process, the manipulator will take longer to find the part and transfer it to the next station or the manipulator will be unable to move the part to the next position correctly which may cause scrap. Another drawback is due to the fact that the robot must let go of the billet and move out of the way of the equipment so to not get damaged. This adds extra time to the cycle and reduces productivity. By using sliding mode controls the robotic manipulator will be able to maintain hold of the billet during forging process and rapidly move the part to the next operation. This reduces handling time and possible scrap. The sliding mode controller will be designed to regulate the center position of the billet and the impedance of the gripper. Impedance is the way that a controller can control the force developed in a system. By controlling the impedance of the gripper, the forces on the outside of the billet will be maintained at a level that prevents the billet and the gripper from being destroyed. A mock forging operation was setup and tested to show how the system would work with a simplified grippe

Response to Haskell: Academic Freedom, Tenure, and Student Evaluation of Faculty

Haskell (1997) argued that the administrative practice of student evaluation of faculty is a threat to academic freedom. However, before that claim can be substantiated, several prior questions must be addressed: To whom does academic freedom belong? Individual faculty? The academy? Whose actions can violate the right? Can any lines be drawn based on whether the substance or form of classroom behavior is influenced? And still another crucial point is whether a body can violate academic freedom without any intent to interfere with or control the substance of what is said to students

Are We Buyers or Hosts? A Memetic Approach to the First Amendment

The First Amendment is often analyzed using the metaphor of the marketplace of ideas. Making use of memetic analysis, this article suggests that ideas should not be treated as inert products that we choose but as living things that sometimes exert some influence over their environment. Some of the ideas are more adept at surviving than others, and the ones that survive will not necessarily be good for humans. To account for the ability of some memes to replicate dangerously, the First Amendment should be read to allow governments to punish a speaker who advocates or threatens physical injury (other than punishment by the state) to the person or possessions of those who promote, oppose, or fail to espouse a certain idea. In other words, the constitution should allow us to be somewhat more intolerant of intolerance