The phase-switched screen

Conventional (passive) radar-absorbent materials operate either by phase cancellation or by absorbing incident electromagnetic energy and converting it into heat. This paper examines a new type of active "absorber," called the phase-switched screen (PSS). The PSS operates quite differently from passive absorbers in that it exhibits an apparently low value of reflectivity by redistributing the electromagnetic energy incident upon it over a bandwidth that is wide enough to ensure that little reflected energy falls within the pass-band of the receiver. The discussion considers the basic temporal and spectral properties of several PSS topologies, and includes measured data on both planar and cylindrical PSS structures

Early research on the biological effects of microwave radiation: 1940?1960

Two overriding considerations shaped the development of early research on the biological effects of microwave radiation?possible medical application (diathermy) and uncertainty about the hazards of exposure to radar. Reports in the late 1940s and early 1950s of hazards resulting from microwave exposure led to the near abandonment of medical research related to microwave diathermy at the same time that military and industrial concern over hazards grew, culminating in the massive research effort known as ?the Tri-Service program? (1957?1960). Both the early focus on medical application and the later search for hazards played important roles in dictating how this field of research developed as a science

Interferometry meets the third and fourth dimensions in galaxies

Radio astronomy began with one array (Jansky's) and one paraboloid of revolution (Reber's) as collecting areas and has now reached the point where a large number of facilities are arrays of paraboloids, each of which would have looked enormous to Reber in 1932. In the process, interferometry has contributed to the counting of radio sources, establishing superluminal velocities in AGN jets, mapping of sources from the bipolar cow shape on up to full grey-scale and colored images, determining spectral energy distributions requiring non-thermal emission processes, and much else. The process has not been free of competition and controversy, at least partly because it is just a little difficult to understand how earth-rotation, aperture-synthesis interferometry works. Some very important results, for instance the mapping of HI in the Milky Way to reveal spiral arms, warping, and flaring, actually came from single moderate-sized paraboloids. The entry of China into the radio astronomy community has given large (40-110 meter) paraboloids a new lease on life.Comment: Virginia Trimble 2014, in IAU Symp. 309 "Galaxy in 3D across the Universe", B.L. Ziegler, F. Combes, H. Dannerbauer, M. Verdugo, Eds. (Cambridge: Cambridge Uni. Press) in press NOTE - Should be "Galaxies" not "Galaxy

Shifting perspectives: holography and the emergence of technical communities

Holography, the technology of three-dimensional imaging, has repeatedly been reconceptualised by new communities. Conceived in 1947 as a means of improving electron microscopy, holography was revitalized in the early 1960s by engineer-scientists at classified laboratories. The invention promoted the transformation of a would-be discipline (optical engineering) and spawned limited artist-scientist collaborations. However, a separate artisanal community promoted a distinct countercultural form of holography via a revolutionary technology: the sandbox optical table. Their tools, sponsorship, products, literature and engagement with wider culture differentiated the communities, which instituted a limited ‘technological trade’. The subject strikingly illustrates the co-evolution of new technology along with highly dissimilar user groups, neither of which fostered the secure establishment of a profession or discipline. The case generalises the concept of 'research-technologists' and 'peripheral science', and extends the ideas of Langdon Winner by demonstrating how the political dimensions of a technology can be important but evanescent in the growth of technical communities

Planetary astronomy

The authors profile the field of astronomy, identify some of the key scientific questions that can be addressed during the decade of the 1990's, and recommend several facilities that are critically important for answering these questions. Scientific opportunities for the 1990' are discussed. Areas discussed include protoplanetary disks, an inventory of the solar system, primitive material in the solar system, the dynamics of planetary atmospheres, planetary rings and ring dynamics, the composition and structure of the atmospheres of giant planets, the volcanoes of IO, and the mineralogy of the Martian surface. Critical technology developments, proposed projects and facilities, and recommendations for research and facilities are discussed

Ethnographies of critique: critical judgment as cultural practice

INTRODUCTION This paper sketches out some preliminary thoughts about what it might mean to conceptualise critique as a textured and variegated cultural practice, and whether it is possible and desirable to study it as we do other cultural practices, ethnographically. I would like to begin by posing three questions, taking as a point of departure Nikolas Kompridis’ statement that in modern capitalist societies there is nothing ‘more urgent today than to resist the sense that our possibilities are contracting or that they are exhausted’ (2006: 280). First, then, is this statement true, in the broadest sense of the term? Second, if this were the case, what kind of cultural practices, what kinds of knowledge, and what ways of being with others have the effect of opening futures up rather than closing them down—and should we necessarily accept the ones that critical theorists recommend as positive goods? Finally, if we can recognise these practices in theoretical or philosophical terms, should we also try to study them in more ‘empirical’ or interpretive ways

Factors leading to the formation of arc cloud complexes

A total of 12 mesoscale convective systems (MCSs) were investigated. The duration of the gust front, produced by each MCS, was used to classify the MCSs. Category 1 MCSs were defined as ones that produced a gust front and the gust front lasted for more than 6 h. There were 7 category 1 MCSs in the sample. Category 2 MCSs were defined as ones that produced a gust front and the gust front lasted for 6 h or less. There were 4 category 2 MCSs. The MCS of Case 12 was not categorized because the precipitation characteristics were similar to a squall line, rather than an MCS. All of the category 1 MCSs produced arc cloud complexes (ACCs), while only one of the category 2 MCSs produced an ACC. To determine if there were any differences in the characteristics between the MCSs of the two categories, composite analyses were accomplished. The analyses showed that there were significant differences in the characteristics of category 1 and 2 MCSs. Category 1 MCSs, on average, had higher thunderstorm heights, greater precipitation intensities, colder cloud top temperatures and produced larger magnitudes of surface divergence than category 2 MCSs