arXiv subjects

M. Oxborrow

Publications and source records attributed to M. Oxborrow.

5 recordsLinked to original sources

arXiv2011

Ab-initio tiling and atomic structure for decagonal ZnMgDy quasicrystal

We discover the detailed atomic structure of $d$-MgZnY, a stable decagonal quasicrystal alloy of the layered Frank-Kasper type, and related phases, using the "tiling and decoration" approach. The atoms have invariable sites in the rectangle and triangle tiles of a 10-fold-symmetric planar tiling. To discover the lowest-energy structures, we combine the methods of density functional theory (DFT) total energy calculations, empirical oscillating pair potentials (fitted to DFT), fitting effective Hamiltonians for tilings, and discovering optimum tiling structures using a nonlocal tile-reshuffling algorithm. We find a family of practically stable compounds with varying composition, including the decagonal quasicrystal and the known Mg$_4$Zn$_7$ phase these are more stable than competing icosahedral structures by a small margi

cond-mat.mtrl-sci↗

arXiv2010

Observation of Periodic Orbits on Curved Two - dimensional Geometries

We measure elastomechanical spectra for a family of thin shells. We show that these spectra can be described by a "semiclassical" trace formula comprising periodic orbits on geodesics, with the periods of these orbits consistent with those extracted from experiment. The influence of periodic orbits on spectra in the case of two-dimensional curved geometries is thereby demonstrated, where the parameter corresponding to Planck's constant in quantum systems involves the wave number and the curvature radius. We use these findings to explain the marked clustering of levels when the shell is hemispherical.

nlin.CD↗

arXiv2009

ELISA: a cryocooled 10 GHz oscillator with 10-15 frequency stability

This article reports the design, the breadboarding and the validation of an ultra-stable Cryogenic Sapphire Oscillator operated in an autonomous cryocooler. The objective of this project was to demonstrate the feasibility of a frequency stability of 3x10-15 between 1 s and 1,000 s for the European Space Agency deep space stations. This represents the lowest fractional frequency instability ever achieved with cryocoolers. The preliminary results presented in this paper validate the design we adopted for the sapphire resonator, the cold source and the oscillator loop.

physics.ins-det↗

arXiv2005

Maser Oscillation in a Whispering-Gallery-Mode Microwave Resonator

We report the first observation of above-threshold maser oscillation in a whispering-gallery(WG)-mode resonator, whose quasi-transverse-magnetic, 17th azimuthal-order WG mode, at a frequency of approx. 12.038 GHz, with a loaded Q of several hundred million, is supported on a cylinder of mono-crystalline sapphire. An electron spin resonance (ESR) associated with Fe3+ ions, that are substitutively included within the sapphire at a concentration of a few parts per billion, coincides in frequency with that of the (considerably narrower) WG mode. By applying a c.w. `pump' to the resonator at a frequency of approx. 31.34 GHz, with no applied d.c. magnetic field, the WG (`signal') mode is energized through a three-level maser scheme. Preliminary measurements demonstrate a frequency stability (Allan deviation) of a few times 1e-14 for sampling intervals up to 100 s.

quant-ph↗

arXiv2005

Counting function for a sphere of anisotropic quartz

We calculate the leading Weyl term of the counting function for a mono-crystalline quartz sphere. In contrast to other studies of counting functions, the anisotropy of quartz is a crucial element in our investigation. Hence, we do not obtain a simple analytical form, but we carry out a numerical evaluation. To this end we employ the Radon transform representation of the Green's function. We compare our result to a previously measured unique data set of several tens of thousands of resonances.

nlin.CD↗