Effects of Defects on Friction for a Xe Film Sliding on Ag(111)

The effects of a step defect and a random array of point defects (such as vacancies or substitutional impurities) on the force of friction acting on a xenon monolayer film as it slides on a silver (111) substrate are studied by molecular dynamic simulations and compared with the results of lowest order perturbation theory in the substrate corrugation potential. For the case of a step, the magnitude and velocity dependence of the friction force are strongly dependent on the direction of sliding respect to the step and the corrugation strength. When the applied force F is perpendicular to the step, the film is pinned forF less than a critical force Fc. Motion of the film along the step, however, is not pinned. Fluctuations in the sliding velocity in time provide evidence of both stick-slip motion and thermally activated creep. Simulations done with a substrate containing a 5 percent concentration of random point defects for various directions of the applied force show that the film is pinned for the force below a critical value. The critical force, however, is still much lower than the effective inertial force exerted on the film by the oscillations of the substrate in experiments done with a quartz crystal microbalance (QCM). Lowest order perturbation theory in the substrate potential is shown to give results consistent with the simulations, and it is used to give a physical picture of what could be expected for real surfaces which contain many defects.Comment: 13 pages, 17 figures, latex plus postscript files for figure

Theory of a Possible Mechanism for Lubrication and Surface Protection by an Electrically Neutral Hydrogels

It is demonstrated that polymers sticking out of the surface of a neutral hydrogel are capable of preventing adhesive forces from pulling a hydrogel into close contact with a surface against which it is pressed. The proposed mechanism for lubrication or surface protection suggests a possible mechanism for protecting the cornea from a contact lens, which is held against the eye by Laplace pressure. This mechanism, however, is only able to keep a gel coated surface from sticking to a surface against which it is pressed, if the gel and surface are bathed in fluid. Expected optical properties of the gel-surface interface are discussed, in order to suggest possible ways to study the gel-solid interface experimentally

Institutions and Technological Innovation During the Early Economic Growth: Evidence from the Great Inventors of the United States, 1790-1930

Employing a sample of renowned U.S. inventors that combines biographical detail with information on the patents they received over their careers, we highlight the impact of early U.S. patent institutions in providing broad access to economic opportunity and in encouraging trade in new technological knowledge. Through setting low fees and establishing administrative procedures for application, the United States deliberately created a patent system that allowed a much wider range, in socioeconomic class terms, of technologically creative individuals to obtain property rights to their inventions than did European patent institutions. Moreover, by requiring that applications be examined for novelty by technical experts, and by enforcing patent rights strictly, the U.S. system reduced uncertainty about the validity of patent rights, and in that way lowered the cost of transacting in them. Creating secure assets in new technological knowledge and facilitating access to markets in technology in this way both stimulated specialization at invention and further enhanced the opportunities available to technologically creative individuals who would otherwise have lacked the capital to directly extract returns from their efforts. Indeed, we show that until the late 19th century, the 'great inventors' of the U.S. generally had backgrounds that permitted them only limited formal schooling, and made extensive use of their abilities under the patent system to extract returns from trading their patent rights. The usefulness of the 19th century U.S. patent system to inventors with humble origins may have implications for the design of intellectual property institutions in contemporary developing countries.

Institutions and Technological Innovation During Early Economic Growth: Evidence from the Great Inventors of the United States, 1790 – 1930

Biographical information on a sample of renowned U.S. inventors is combined with information on the patents they received over their careers, and employed to highlight the implications of patent institutions for markets in inventions and for democratization. The United States deliberately created a patent system that differed from existing European systems in ways that significantly affected the course of technological change. Patent rights in the U.S. helped to define and enforce tradable assets in new technological knowledge. By facilitating access to such markets in technology, patents enhanced the benefits to relatively disadvantaged individuals who might otherwise have been unable to directly extract returns from their technological creativity, and their response to such incentives increased overall technological progress. For this reason, despite the defects of patent monopolies, developing economies today may still advance technological progress and improve social welfare by providing broad access to property rights in inventions.