Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgr A*), the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4,000,000 times that of the Sun. A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A*, where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering. Here we report observations at a wavelength of 1.3 mm that set a size of 37(+16)(-10) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of Sgr A* emission may not be centred on the black hole, but arises in the surrounding accretion flow.     

Extrusion Freeforming of Millimeter-Wave Electromagnetic Bandgap (EBG) Photonic Crystals

Extrusion freeforming can be used for the rapid prototyping of millimeter-wave electromagnetic bandgap (EBG) structures. In this work, an alumina-polymer paste with a relatively high volatility solvent (propanol) was used and the characteristics of the ceramic paste, particularly the rheological features are described. The advantage of high volatility solvent is that the viscosity and elastic modulus of the paste are increased sharply as the solvent evaporates. Thus, the rigidity of the extruded filament is quickly increased as a small amount of solvent evaporates. Finally, by employing this procedure, different EBG structures such as 2-D, 3-D woodpile and aperiodic structures were fabricated and their bandgaps were measured. The experimental results show that extrusion freeforming is a relatively simple and easy method to fabricate these woodpile structures with a bandgap in the 90–110 GHz region.     

Solid Freeforming and Combinatorial Research

A view of manufacturing processes is presented in which five distinct categories are defined as casting, deformation, machining, joining, and solid freeforming. Solid freeforming is essentially biomimetic and shares problems of morphogenesis with natural processes. Our team in University of London has been exploring three mechanisms of solid freeforming. In dry powder deposition and direct ink-jet printing, the emphasis has turned to the problem of delivering a complex shape in which the three dimensional spatial arrangement of composition is delivered from the design file. In extrusion freeforming, the aim is to control microstructure at hierarchical levels also from the design file. The quest for 3-D functional gradients is satisfied by acoustic and ultrasonic dispensing and mixing of powders so that each layer can be patterned. These methods could be extended to deliver the complex patterns demanded by left-handed microwave metamaterials. Dry powder deposition and direct ink-jet printing are turning towards combinatorial methods in which multiple sample libraries are used to accelerate discovery. In turn, this paves the way for ‘autonomous research machines’ which steer their own search refinements in response to our requests for new materials. In this way, solid freeforming used for sample preparation can give an ‘arm’ to an intelligent machine so that it can conduct its own experimentation and learning; an idea that originated with Alan Turing in the late 1940s.     

The effect of unilateral cerebellar pedunculotomy on the vascular development of the neonatal rat cerebellum

After cerebellar pedunculotomy the density of the blood vessel network in the cerebellar cortex was not different from that in the control animals. But the pattern of the blood vessels was different, being less organized in the operated animals.