Summary Surface morphology and molecular arrangement have been recorded by atomic force microscopy (AFM) on polytetrafluoroethylene (PTFE) and on polycarbonate (PC) films. In a thin layer of PTFE deposited by rubbing polymer on hot glass substrate unidirectional orientation of polymer has been revealed. Individual polymer chains have been visualized. An interchain distance of .53 nm and several periodicities along the chain contours have been found-.44 nm, .62 nm and .82 nm-in accordance with a 13/6 helix.The monitoring of surface changes during thermal treatment of amorphous-bis-phenol A-PC film has been realized by AFM. Different types of surface morphology were revealed. Spherulites are formed during polymer crystallization. In most cases, however, numerous nanocrystallites appeared after thermal treatment. On their surfaces well-ordered atomic scale AFM images have been received. The arrangement of AFM patterns can be characterized by periodicities of .50 nm and .52 nm in the orthogonal directions. Polycarbonate oligomers-as the product of surface degradation-effectively might form the observed nanocrystallites.Prof. Dr. G. Zachmann zum 60. Geburtstag herzlichst gewidmetThese results were given by us first in a lecture in Baltimore, at the 5th ISPAC Symposium on May 31, 1991, and in a lecture in Santa Barbara, at the Nanoscope Users Meeting on June 25, 1991 相似文献
The estimation of the Direction-Of-Arrival (DOA) and the variance of the angular spread, using an array of sensors in the
case of a Ricean channel is considered, using the Maximum-Likelihood, Least-Squares and Weighted Least Squares criteria. The
Cramér-Rao bound is also obtained for the problem of interest. Simplification of the cost functions to reduce the dimension
of the problem has been carried out and the performance of the methods has been studied based on numerical experiments.
A major part of the work was carried out when K V S Hari was visiting the Department of Signals, Sensors and Systems during
Jul–Sep 1995, on leave from the Indian Institute of Science 相似文献
An experimental investigation of heat transfer and pressure drop from a new type of corrugated channels is presented. The investigation has been carried out for Reynolds numbers in the range of for one corrugated and one smooth channel. It is found that the heat transfer from the corrugated channel is up to 3.5 times higher than for the smooth one. The pressure drop is however large (5 – 6 times the value of a smooth channel) and it is suggested that the corrugation height and length should be altered in order to balance the increases in heat transfer and pressure drop. 相似文献
In his unpublished MA thesis of 1921, the young Hotelling invented an ingenious model of population growth and diffusion. The contribution remained widely unknown until Waldo Tobler and Alan Wilson edited it as an article in 1978. Not even then did it trigger off any outburst of contributions. Meanwhile, in 1951, Skellam invented exactly the same model for non-human populations. Unlike in economics, it was a great success in ecology. In a recent contribution Skellam is named Father of Ecological Diffusion and more than a thousand articles on the subject are listed. There were many attempts at solving the equation, but none were quite successful. The Hotelling and Skellam models both assumed a given saturation population that nature could support. In 1985 the present author suggested that an explicit production function be introduced in the Hotelling model, as man produces his own means of subsistence. Moreover it was proposed that diffusion be related to spatial differences in per capita productivity, rather than to those in population density. The present contribution is a rejoinder. It is shown that the stationary solutions to the original Hotelling model are periodic and dip into negative populations, whereas this is avoided by the modified model suggested. It can thus be used to show how agglomerative structures may evolve. 相似文献
Various sialon materials have been prepared by pressureless sintering at 1775 and 1825 °C using Y2O3 and/or Ce02 as sintering aids. Constant molar amounts of the oxide mixtures were added in the ratios Y2O3/CeO2: 100/0, 75/25, 50/50, 25/75, 0/100 corresponding to 6.0 and 9.25 wt% for the pure Y2O3 and pure CeO2, respectively. Only one of the compositional series reached full density at 1775 °C with cerium replacing yttrium, whereas at 1825 °C all compositional series except one became dense. The samples sintered showed that yttrium but not cerium stabilizes the sialon phase in these ceramics. The dense cerium-sialon ceramics sintered at 1825 °C have as good hardness and indentation fracture toughness as the corresponding yttrium-sialon ceramics, or even higher for the sialon type of materials. For the mixed - sialon materials the hardness decreased as the amount of a sialon phase decreased by increasing cerium-doping. 相似文献
We present a number of alternative ways of handling transitive binary relations that commonly occur in first-order problems, in particular equivalence relations, total orders, and transitive relations in general. We show how such relations can be discovered syntactically in an input theory, and how they can be expressed in alternative ways. We experimentally evaluate different such ways on problems from the TPTP, using resolution-based reasoning tools as well as instance-based tools. Our conclusions are that (1) it is beneficial to consider different treatments of binary relations as a user, and that (2) reasoning tools could benefit from using a preprocessor or even built-in support for certain types of binary relations.