Communications for Next Generation single chip computers

It is the thesis of this report that much of what is presently thought to require specialized VLSI functions might instead be achieved by combinations of fast general purpose single chip computers with upgraded communication facilities. To this end, the characteristics of applications of this nature are first surveyed briefly and some working principles established. In the light of these, three different chip philosophies are explored in some detail. This study shows that some upgrading of typical single chip I/O will definitely be necessary, but that this upgrading does not have to be complex and that true multiprocessor-multibus operation could be achieved without excessive cost

Reaction paths of alane dissociation on the Si(001) surface

Building on our earlier study, we examine the kinetic barriers to decomposition of alane, AlH$_3$, on the Si(001) surface, using the nudged elastic band (NEB) approach within DFT. We find that the initial decomposition to AlH with two H atoms on the surface proceeds without a significant barrier. There are several pathways available to lose the final hydrogen, though these present barriers of up to 1 eV. Incorporation is more challenging, with the initial structures less stable in several cases than the starting structures, just as was found for phosphorus. We identify a stable route for Al incorporation following selective surface hydrogen desorption (e.g. by STM tip). The overall process parallels PH$_3$, and indicates that atomically precise acceptor doping should be possible.Comment: 19 pages, 8 figures, submitted to J. Physics.: Condens. Matte

Low-loss directional cloaks without superluminal velocity or magnetic response

The possibility of making an optically large (many wavelengths in diameter) object appear invisible has been a subject of many recent studies. Exact invisibility scenarios for large (relative to the wavelength) objects involve (meta)materials with superluminal phase velocity (refractive index less than unity) and/or magnetic response. We introduce a new approximation applicable to certain device geometries in the eikonal limit: piecewise-uniform scaling of the refractive index. This transformation preserves the ray trajectories, but leads to a uniform phase delay. We show how to take advantage of phase delays to achieve a limited (directional and wavelength-dependent) form of invisibility that does not require loss-ridden (meta)materials with superluminal phase velocities.Comment: 3 pages, 2 figure

Alane adsorption and dissociation on the Si(001) surface

We used DFT to study the energetics of the decomposition of alane, AlH3, on the Si(001) surface, as the acceptor complement to PH3. Alane forms a dative bond with the raised atoms of silicon surface dimers, via the Si atom lone pair. We calculated the energies of various structures along the pathway of successive dehydrogenation events following adsorption: AlH2, AlH and Al, finding a gradual, significant decrease in energy. For each stage, we analyse the structure and bonding, and present simulated STM images of the lowest energy structures. Finally, we find that the energy of Al atoms incorporated into the surface, ejecting a Si atom, is comparable to Al adatoms. These findings show that Al incorporation is likely to be as precisely controlled as P incorporation, if slightly less easy to achieve.Comment: Submitted to J. Phys.: Condens. Matte

Flow stabilization with active hydrodynamic cloaks

We demonstrate that fluid flow cloaking solutions based on active hydrodynamic metamaterials exist for two-dimensional flows past a cylinder in a wide range of Reynolds numbers, up to approximately 200. Within the framework of the classical Brinkman equation for homogenized porous flow, we demonstrate using two different methods that such cloaked flows can be dynamically stable for $Re$ in the range 5-119. The first, highly efficient, method is based on a linearization of the Brinkman-Navier-Stokes equation and finding the eigenfrequencies of the least stable eigen-perturbations; the second method is a direct, numerical integration in the time domain. We show that, by suppressing the Karman vortex street in the weekly turbulent wake, porous flow cloaks can raise the critical Reynolds number up to about 120, or five times greater than for a bare, uncloaked cylinder.Comment: 5 pages, 3 figure

Fluid flow control with transformation media

We introduce a new concept for the manipulation of fluid flow around three-dimensional bodies. Inspired by transformation optics, the concept is based on a mathematical idea of coordinate transformations and physically implemented with anisotropic porous media permeable to the flow of fluids. In two situations - for an impermeable object placed either in a free-flowing fluid or in a fluid-filled porous medium - we show that the object can be coated with an inhomogeneous, anisotropic permeable medium, such as to preserve the flow that would have existed in the absence of the object. The proposed fluid flow cloak eliminates downstream wake and compensates viscous drag, hinting us at the possibility of novel propulsion techniques.Comment: 4 pages, 7 figure

CONSUMER ACCEPTANCE OF FORAGE FINISHED BEEF

Consumer/Household Economics,