Direct printing of polymer microstructures on flat and spherical surfaces using a letterpress technique

We have developed a letterpress technique capable of printing polymer films with micrometer scale feature sizes onto flat or spherically shaped nonporous substrates. This printing technique deposits polymer only in desired regions thereby eliminating subsequent developing and subtraction steps. Flat or curved printing plates, which are fabricated from either rigid or deformable materials, are used to transfer thin molten polymer films onto flat target substrates. By deforming the printing plates into a spherical shape, it is also possible to print patterned films onto the concave side of a spherically deformed target substrate. These printed films serve as good resists for both wet chemical etching and reactive ion etching. Interferometric measurements of the polymer film thickness are used to probe physical mechanisms affecting printing instabilities, pattern fidelity, and edge resolution. Our experimental study indicates that this letterpress technique may prove suitable for high-throughput device fabrication involving large-area microelectronics

Photoresist-free printing of amorphous silicon thin-film transistors

Conventional fabrication of amorphous silicon thin-film transistors (a-Si TFTs) requires patterning numerous photoresist layers, a subtractive process that is time consuming and expensive. This letter describes transistor fabrication by a photoresist-free approach in which polymer etch masks are letterpress printed from flexible polyimide stamps. Pattern registration is achieved through optical alignment since the printed masks are thin and optically transparent. This modified fabrication scheme produces transistor performance equivalent to conventionally fabricated a-Si TFTs. The ability to directly print etch masks onto nonhomogeneous substrates brings one step closer the realization of flexible, large-area, macroelectronic fabrication

Morphology of liquid microstructures on chemically patterned surfaces

We study the equilibrium conformations of liquid microstructures on flat but chemically heterogeneous substrates using energy minimization computations. The surface patterns, which establish regions of different surface energy, induce deformations of the liquid–solid contact line. Depending on the geometry, these deformations either promote or impede capillary breakup and bulge formation. The contact angles of the liquid on the hydrophilic and hydrophobic regions, as well as the pattern geometry and volume of liquid deposited, strongly affect the equilibrium shapes. Moreover, due to the small scale of the liquid features, the presence of chemical or topological surface defects significantly influence the final liquid shapes. Preliminary experiments with arrays of parallel hydrophilic strips produce shapes resembling the simulated forms. These encouraging results provide a basis for the development of high resolution lithography by direct wet printing

A Computer Simulation Of Auroral Arc Formation

Thesis (Ph.D.) University of Alaska Fairbanks, 1981Recent satellite measurements have revealed two intriguing features associated with the formation of auroral arcs. The first is that an auroral arc is produced by a sheet of electrons accelerated along a geomagnetic field-aligned potential drop, and the second is that these electrons carry a field-aligned, upward directed electric current. In order to explain these measurements, a self-consistent, time dependent, computer simulation of auroral arc formation has been developed. The simulation demonstrates for the first time that a stable V-shaped potential structure, called an auroral double layer, develops spontaneously as a result of an ion shielded electron current sheet interacting with a conducting ionosphere. The double layer accelerates current-carrying electrons into the upper atmosphere at auroral energies. The double layer potential depends critically on the drift speed of the current-carrying electrons and on the temperature of the ambient shielding ions. Localized double layers occur near the ionosphere when the geomagnetic field is assumed to be uniform, but when a converging magnetic field is introduced, the double layer becomes extended due to the presence of an additional population of electrons trapped between the magnetic mirror and the double layer potential. The simulated auroral current sheet is subject to auroral curl and fold type deformations due to unstable Kelvin-Helmholtz waves. The previous incompletely understood auroral fold producing mechanism is described

For Country, Liberty, and Money: Privateering and the Ideologies of the American Revolution

Along with service in the Continental Army and Navy and the various state militias, American patriots during the Revolutionary War had the option of sailing aboard privateers, private ships authorized to attack British commerce during the war. Where studies analyzing other military forces during the Revolution have been more nuanced, scholars that have looked at privateering have either focused on its strategic effectiveness during the conflict or merely written it off as a profit-driven phenomenon of maritime plunder. Privateering played a role in the course of the Revolution to a degree, but more importantly the practice was influenced by the ideological considerations that framed the Revolution itself—considerations that are ignored when privateering is seen through the eyes of the profit-narrative. While in part motivated by profit, privateering during the American War for Independence can only be fully understood when placed in the context of contemporary debates over liberty, republicanism, and identity. These debates stretched across the range of actors involved in privateering, from the sailors crewing privateer vessels to the merchants investing in privateer expeditions. This thesis will draw upon existing literature on privateering, Revolutionary ideology, and original analysis of primary source information including correspondence, government documents, and individual narratives to place privateering within the broader framework of the Revolutionary period. In doing so, it will add a more complex and multilayered approach to privateering to place that scholarship alongside other studies of military phenomena during the American Revolution

For Country, Liberty, and Money: Privateering and the Ideologies of the American Revolution

Along with service in the Continental Army and Navy and the various state militias, American patriots during the Revolutionary War had the option of sailing aboard privateers, private ships authorized to attack British commerce during the war. Where studies analyzing other military forces during the Revolution have been more nuanced, scholars that have looked at privateering have either focused on its strategic effectiveness during the conflict or merely written it off as a profit-driven phenomenon of maritime plunder. Privateering played a role in the course of the Revolution to a degree, but more importantly the practice was influenced by the ideological considerations that framed the Revolution itself—considerations that are ignored when privateering is seen through the eyes of the profit-narrative. While in part motivated by profit, privateering during the American War for Independence can only be fully understood when placed in the context of contemporary debates over liberty, republicanism, and identity. These debates stretched across the range of actors involved in privateering, from the sailors crewing privateer vessels to the merchants investing in privateer expeditions. This thesis will draw upon existing literature on privateering, Revolutionary ideology, and original analysis of primary source information including correspondence, government documents, and individual narratives to place privateering within the broader framework of the Revolutionary period. In doing so, it will add a more complex and multilayered approach to privateering to place that scholarship alongside other studies of military phenomena during the American Revolution

RISK AND MARKET PARTICIPANT BEHAVIOR IN THE U.S. SLAUGHTER-CATTLE MARKET

Incomplete information generates uncertainty for market participants in the slaughter-cattle market. Buyer and seller behavior in the presence of that uncertainty is examined. Statistically significant risk premiums are charged by packers when buying slaughter cattle on either a live- or dressed-weight basis compared to buying on a grade-and-yield basis. Pratt-Arrow risk-aversion coefficients are calculated for buyers and these remain constant over all marketing methods. Sellers market cattle under all three marketing methods, suggesting producersÂ’' attitudes toward risk (risk-aversion coefficients) vary.Risk and Uncertainty,

A Comprehensive Approach to Algorithmic Machine Sorting of Library of Congress Call Numbers

This paper details an approach for accurately machine sorting Library of Congress (LC) call numbers which improves considerably upon other methods reviewed. The authors have employed this sorting method in creating an open-source software tool for library stacks maintenance, possibly the first such application capable of sorting the full range of LC call numbers. The method has potential application to any software environment that stores and retrieves LC call number information