Crack barriers improve the mechanical and thermal properties of non-metallic sinter materials

Means of improving the tensile strength of ceramic composites by introducing ductile intermediate layers capable of absorbing the elastic energy at the rupture front are studied. Tests with an Al203 laminate with niobium inclusions showed that crack propagation could be successfully precluded by dissipation of the energy by deformation and/or delamination at the inclusion/matrix interface

UHF Syledis for Coastal Survey Positioning

UHF positioning systems are intermediate between groundwave HF radio aids, such as Argo and Hi-Fix, and line-of-sight systems, such as Mini-Ranger III and Trisponder. The Canadian Hydrographic Service conducted tests along the coast of Nova Scotia in 1982/83 which showed that UHF propagation velocity is unaffected by the terrain that the signal passes over, that UHF Syledis is effective to about 100 km over water and low-lying land, and that low pressure weather systems reduce Syledis performance. This paper will describe test procedures and results, and the subsequent CHS experience with Syledis in the first year of operational use in 1983

Recruitment of Eph receptors into signaling clusters does not require ephrin contact

Eph receptors and their cell membrane–bound ephrin ligands regulate cell positioning and thereby establish or stabilize patterns of cellular organization. Although it is recognized that ephrin clustering is essential for Eph function, mechanisms that relay information of ephrin density into cell biological responses are poorly understood. We demonstrate by confocal time-lapse and fluorescence resonance energy transfer microscopy that within minutes of binding ephrin-A5–coated beads, EphA3 receptors assemble into large clusters. While remaining positioned around the site of ephrin contact, Eph clusters exceed the size of the interacting ephrin surface severalfold. EphA3 mutants with compromised ephrin-binding capacity, which alone are incapable of cluster formation or phosphorylation, are recruited effectively and become phosphorylated when coexpressed with a functional receptor. Our findings reveal consecutive initiation of ephrin-facilitated Eph clustering and cluster propagation, the latter of which is independent of ephrin contacts and cytosolic Eph signaling functions but involves direct Eph–Eph interactions

A Transiting Planet of a Sun-like Star

A planet transits an 11th magnitude, G1V star in the constellation Corona Borealis. We designate the planet XO-1b, and the star, XO-1, also known as GSC 02041-01657. XO-1 lacks a trigonometric distance; we estimate it to be 200+-20 pc. Of the ten stars currently known to host extrasolar transiting planets, the star XO-1 is the most similar to the Sun in its physical characteristics: its radius is 1.0+-0.08 R_Sun, its mass is 1.0+-0.03 M_Sun, V sini < 3 km/s, and its metallicity [Fe/H] is 0.015+-0.04. The orbital period of the planet XO-1b is 3.941534+-0.000027 days, one of the longer ones known. The planetary mass is 0.90+-0.07 M_Jupiter, which is marginally larger than that of other transiting planets with periods between 3 and 4 days. Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius. If the stellar radius is 1.0+-0.08 R_Sun, then the planetary radius is 1.30+-0.11 R_Jupiter and the inclination of the orbit is 87.7+-1.2 degrees. We have demonstrated a productive international collaboration between professional and amateur astronomers that was important to distinguishing this planet from many other similar candidates.Comment: 31 pages, 9 figures, accepted for part 1 of Ap

Universality classes in nonequilibrium lattice systems

This work is designed to overview our present knowledge about universality classes occurring in nonequilibrium systems defined on regular lattices. In the first section I summarize the most important critical exponents, relations and the field theoretical formalism used in the text. In the second section I briefly address the question of scaling behavior at first order phase transitions. In section three I review dynamical extensions of basic static classes, show the effect of mixing dynamics and the percolation behavior. The main body of this work is given in section four where genuine, dynamical universality classes specific to nonequilibrium systems are introduced. In section five I continue overviewing such nonequilibrium classes but in coupled, multi-component systems. Most of the known nonequilibrium transition classes are explored in low dimensions between active and absorbing states of reaction-diffusion type of systems. However by mapping they can be related to universal behavior of interface growth models, which I overview in section six. Finally in section seven I summarize families of absorbing state system classes, mean-field classes and give an outlook for further directions of research.Comment: Updated comprehensive review, 62 pages (two column), 29 figs included. Scheduled for publication in Reviews of Modern Physics in April 200

Zeroing the Stellar Isochrone Scale: The Red Giant Clump Luminosity at Intermediate Metallicity

The color-magnitude diagrams of the open clusters NGC 2420 and NGC 2506 have been investigated as intermediate links between the solar neighborhood and the Magellanic Clouds. Two sets of theoretical isochrones which include convective overshoot are zeroed to the sun at solar abundance and to the unevolved main sequence dwarfs of the Hipparcos catalog at [Fe/H] = -0.4, requiring a differential of 0.4 mag between the unevolved main sequences at a given color. Adopting E(B-V) = 0.04 and [Fe/H] = -0.39 for NGC 2506 and 0.04 and -0.29 for NGC 2420,the respective apparent moduli are 12.70 and 12.15, while the ages of both clusters are approximately 1.9 +/- 0.2 or 2.2 +/- 0.2 Gyr, depending on the choice of isochrones. From the composite giant branch of the two clusters, the mean clump magnitudes in V and I are found to be 0.47 and -0.48 (-0.17,+0.14). Applying a metallicity correction to the M_I values, the cluster sample of Udalski (1998) leads to (m-M)_0 = 18.42 (+0.17,--0.15) and 18.91 (+0.18,--0.16) for the LMC and SMC, respectively. A caveat to this discussion and to the claim that clusters of the same abundance and age are identical is the observation that the (V-I) colors of the red giants in NGC 2506 are significantly redder at a given (B-V) than the giants in clusters of comparable age and/or metallicity. If the CCD photometry for NGC 2506 is tied to the standard system rather than using a general cluster relation between (B-V) and (V-I), the M_I for the clump will decrease by 0.1 mag.Comment: 1 table, 12 figures. Replaced 20-jan-99 by version with all figures. Accepted for April 1999 Astronomical Journa

Gothic visions of classical architecture in Hablot Knight Browne’s “dark” illustrations for the novels of Charles Dickens

In the early gothic literature of the eighteenth century danger lurked in the darkness beneath the pointed arches of gothic buildings. During the nineteenth century there was a progressive, although never complete, dislocation of gothic literary readings from gothic architecture. This article explores a phase in that development through discussion of a series of ‘dark’ illustrations produced by Hablot Knight Browne to illustrate novels by Charles Dickens. These show the way in which the rounded arches of neo-classical architecture were depicted in the mid-nineteenth century as locales of oppression and obscurity. Such depictions acted, in an age of political and moral reform, to critique the values of the system of power and authority that such architecture represented