147,942 research outputs found
Flexible dielectric waveguides with powder cores
Flexible dielectric waveguides have been demonstrated at 10 GHz and 94 GHz using thin-wall polymer tubing filled with low-loss, high-dielectric-constant powders. Absorptive losses of the order of 10 dB/m were measured at 94 GHz. with nickel-aluminium titanate and barium tetratitanate powder in polytetrafluoroethylene (PTFE) lightweight electrical tubing. Bending losses at 94 GHz were negligible for curvature radii greater than 4 cm. M.H. Kuhn's (1974) theory of three-region cylindrical dielectric waveguide was used to calculate dispersion curves for the lower-order modes for several combinations of dimensions and dielectric constants. Good agreement was obtained between experimental and theoretical values of guide wavelength. A scheme is proposed for classifying hybrid modes of three-region guides based on the ratio |Ez/Hz|. For two-region guides, this reduces to E. Snitzer's (1961) familiar scheme
Paintings and their implicit presuppositions : a preliminary report
In a series of earlier papers (Social Science Working Papers 350, 355. 357) we have studied the ways in which differences in "implicit presupposi tions" (i. e •• differences in world views) cause scientists and historians to reach differing conclusions from a consideration of the same evidence. In this paper we show that paintings are characterized by implicit presuppositions similar to those that characterize the written materials -- essays, letters, scientific papers -- we have already studied
Paintings and their implicit presuppositions: High Renaissance and Mannerism
All art historians who are interested in questions of "styles" or "schools" agree in identifying a High Renaissance school of Italian
painting. There is, however, a disagreement, which has seemed nonterminating, regarding Mannerism: Is it another distinct school or
is it merely a late development of the Renaissance school? We believe that this disagreement can be terminated by distinguishing questions of
fact about paintings from questions about the definitions of schools. To this end we have had two representative subsets of paintings--one
earlier, one later--rated on four of the dimensions of implicit presuppositions that we have introduced in other Working Papers. When
the paintings are scaled in this way a very distinct profile emerges for the earlier, or Renaissance, paintings. In contrast, the later, or
Mannerist, paintings are so heterogeneous that we conclude that they are best described as deviations from the Renaissance profile, rather
than a separate school. These results are not unimportant--at least for art historians. But they are more important methodologically
inasmuch as the procedures applied here can be used in classifying and distinguishing from one another all kind of cultural products
Homogenization of the Oscillating Dirichlet Boundary Condition in General Domains
We prove the homogenization of the Dirichlet problem for fully nonlinear
elliptic operators with periodic oscillation in the operator and of the
boundary condition for a general class of smooth bounded domains. This extends
the previous results of Barles and Mironescu in half spaces. We show that
homogenization holds despite a possible lack of continuity in the homogenized
boundary data. The proof is based on a comparison principle with partial
Dirichlet boundary data which is of independent interest.Comment: Version to appear in J. Math. Pures Appl. Added Remarks 1.2 and 1.7.
Removed some extraneous statements of previous results (previously
Corollaries 2.7 and 2.12). Changed the statement and proof of Lemma 3.1 to
fix a small error and R^{-\alpha} is now (N/R)^{\alpha} here and in later
uses of the Lemma. 23 page
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