Dimensional changes in dental plaster during the setting process.
The authors, using an NIN apparatus, examined the dimensional changes occurring in dental plaster during the setting process from its slurry state immediately after being mixed to its solid state, and the following results were obtained : 1) Linear shrinkage that can be seen in the initial stage of the setting process shows a tendency to become larger when the water/powder ratio is increased, and the length of the specimen is shorter. 2) Expansion initiation time shows a tendency to be quickened when the water/powder ratio is reduced, but little difference due to the length of the specimen is recognizable. 3) The apparent linear expansion shows a tendency to become larger when the water/powder ratio is smaller, and when the length of the specimen is shorter. 4) Velocity (time constant) from the beginning of expansion to the maximum expansion is almost constant, being little influenced by the water/powder ratio and the length of the specimen.
Development of measurement apparatus for expansion and shrinkage during setting, using a non-contact micro displacement meter.
Dental plaster and investment are used after being mixed with water or another liquid. Therefore, when they start setting, their condition changes from fluid to non-fluid. In other words, for some time after they are mixed with water or liquid, they look slurry, but as soon as setting begins they cease to be slurry and become solid, while at the same time they start expanding. In order to measure the dimensional change of this kind of material at the time of setting, it is preferable to measure it automatically under a loadless, non-contact condition immediately after it is mixed with water until the time when it has become solid. The conventional apparatus used for this purpose includes the following: comparator [1-4], micrometer microscope [5-8], dialgauge micrometer [1,2,7-20], straingauge extensometer [21,22], cathetometer & photographing [23], electromicrometer [24-28], micro-displacement meter [29-31], optomicrometer [32], etc. However, none of these seem to satisfy, in the strictest sense, the exact measuring condition stated above. Therefore we, the authors of this report, thought of pursuing and examining the actual dimensional change occurring in the mixture of plaster and investment from its slurry to solid condition at the time of setting. First of all, we tried to develop a kind of measuring apparatus which would fit the purpose of our research. We test-developed and examined the automatic measuring apparatus with a built-in, non-contact micro-displacement meter, which we named "NIN Setting Expansion and Shrinkage Apparatus" (which hereinafter we shall call "NIN Apparatus" for short). We actually used this test-developed NIN Apparatus by using for material the
Working Knowledge: Employee Innovation and the Rise of Corporate Intellectual Property, 1800-1930
This book presents the legal and business history of corporate ownership of employee knowledge. Skilled workers of the early nineteenth century enjoyed a degree of professional independence because workplace knowledge and technical skill were their 'property,' or at least their attribute. In most sectors of today's economy, however, it is a foundational and widely accepted truth that businesses retain legal ownership of employee-generated intellectual property. In "Working Knowledge", Catherine Fisk chronicles the legal and social transformations that led to the transfer of ownership of employee innovation from labor to management. This deeply contested development was won at the expense of workers' entrepreneurial independence and ultimately, Fisk argues, economic democracy. By reviewing judicial decisions and legal scholarship on all aspects of employee-generated intellectual property and combing the archives of major nineteenth-century intellectual property - producing companies - including DuPont, Rand McNally, and the American Tobacco Company - Fisk makes a highly technical area of law accessible to general readers while also addressing scholarly deficiencies in the histories of labor, intellectual property, and the business of technology.