Bose-Einstein condensation in a circular waveguide

We have produced Bose-Einstein condensates in a ring-shaped magnetic waveguide. The few-millimeter diameter, nonzero-bias ring is formed from a time-averaged quadrupole ring. Condensates that propagate around the ring make several revolutions within the time it takes for them to expand to fill the ring. The ring shape is ideally suited for studies of vorticity in a multiply connected geometry and is promising as a rotation sensor.     

Summing over a network without revealing summands

Consider a network in which each node possesses a secret member of a finite abelian group. In this paper we present a protocol by which the nodes can compute the sums of their secret elements without revealing them to each other. The security against discovery of the secret values as a result of conspiracies among nodes or compromise of channels between nodes is shown to depend on the connectivity of the graph defined by the network. Moreover, we are able to quantify exactly the amount of information revealed as a result of a conspiracy of a given set of nodes or compromise of a given set of channels.     

Preparation of Phase Pure Cubic Gallium Nitride, c-GaN, by Ammonothermal Conversion of Gallium Imide, {Ga(NH)3/2} n

Gallium imide, {Ga(NH)_3/2} _n , was sealed in quartz tubes with anhydrous NH₃ and NH₄X (X=Cl, Br, I) and heated vertically in an autoclave with the hot-zone (bottom) temperature ranging from 300–530°C. With NH₄I mineralizer, the imide was converted to primarily the zinc-blende phase of GaN (c-GaN), usually in the form of micron sized or smaller tetrahedra. With NH₄Cl mineralizer, hexagonal GaN nanoparticles formed instead, and NH₄Br facilitated the conversion of imide to irregular h-GaN nanoparticles at lower temperatures, and larger particles above 500°C. At the higher temperatures, chemical transport took place and GaN crystals grew on the walls at the middle to the top of the tube. Most of the deposited GaN was cubic, usually in a heavily etched triangular prismatic morphology. Several experiments were performed in a Pt lined pressure vessel in order to demonstrate that the synthesis method can be scaled up.