Improved real-space genetic algorithm for crystal structure and polymorph prediction

Existing genetic algorithms for crystal structure and polymorph prediction can suffer from stagnation during evolution, with a consequent loss of efficiency and accuracy. An improved genetic algorithm is introduced herein which penalizes similar structures and so enhances structural diversity in the population at each generation. This is shown to improve the quality of results found for the theoretical prediction of simple model crystal structures. In particular, this method is demonstrated to find three new zero-temperature phases of the Dzugutov potential that have not been previously reported

Development of a magneforming process for the fabrication of thin-wall tungsten cylinders final report

Magneforming process - high energy rate metal forming technique for fabrication of thin wall tungsten cylinder

The impact of lightning on tropospheric ozone chemistry using a new global lightning parametrisation

A lightning parametrisation based on upward cloud ice flux is implemented in a chemistry–climate model (CCM) for the first time. The UK Chemistry and Aerosols model is used to study the impact of these lightning nitric oxide (NO) emissions on ozone. Comparisons are then made between the new ice flux parametrisation and the commonly used, cloud-top height parametrisation. The ice flux approach improves the simulation of lightning and the temporal correlations with ozone sonde measurements in the middle and upper troposphere. Peak values of ozone in these regions are attributed to high lightning NO emissions. The ice flux approach reduces the overestimation of tropical lightning apparent in this CCM when using the cloud-top approach. This results in less NO emission in the tropical upper troposphere and more in the extratropics when using the ice flux scheme. In the tropical upper troposphere the reduction in ozone concentration is around 5–10 %. Surprisingly, there is only a small reduction in tropospheric ozone burden when using the ice flux approach. The greatest absolute change in ozone burden is found in the lower stratosphere, suggesting that much of the ozone produced in the upper troposphere is transported to higher altitudes. Major differences in the frequency distribution of flash rates for the two approaches are found. The cloud-top height scheme has lower maximum flash rates and more mid-range flash rates than the ice flux scheme. The initial Ox (odd oxygen species) production associated with the frequency distribution of continental lightning is analysed to show that higher flash rates are less efficient at producing Ox; low flash rates initially produce around 10 times more Ox per flash than high-end flash rates. We find that the newly implemented lightning scheme performs favourably compared to the cloud-top scheme with respect to simulation of lightning and tropospheric ozone. This alternative lightning scheme shows spatial and temporal differences in ozone chemistry which may have implications for comparison between models and observations, as well as for simulation of future changes in tropospheric ozone

The Moduli Space of BPS Domain Walls

N=2 SQED with several flavors admits multiple, static BPS domain wall solutions. We determine the explicit two-kink metric and examine the dynamics of colliding domain walls. The multi-kink metric has a toric Kahler structure and we reduce the Kahler potential to quadrature. In the second part of this paper, we consider semi-local vortices compactified on circle. We argue that, in the presence of a suitable Wilson line, the vortices separate into domain wall constituents. These play the role of fractional instantons in two-dimensional gauge theories and sigma-models.Comment: 16 pages, LaTex, 2 figures; factors of zeta corrected, meaning of cross-terms elucidated, further clarifying comments; (more) references adde

Quantum Breathing Mode of Interacting Particles in a One-dimensional Harmonic Trap

Extending our previous work, we explore the breathing mode---the [uniform] radial expansion and contraction of a spatially confined system. We study the breathing mode across the transition from the ideal quantum to the classical regime and confirm that it is not independent of the pair interaction strength (coupling parameter). We present the results of time-dependent Hartree-Fock simulations for 2 to 20 fermions with Coulomb interaction and show how the quantum breathing mode depends on the particle number. We validate the accuracy of our results, comparing them to exact Configuration Interaction results for up to 8 particles

Noncentral extensions as anomalies in classical dynamical systems

A two cocycle is associated to any action of a Lie group on a symplectic manifold. This allows to enlarge the concept of anomaly in classical dynamical systems considered by F. Toppan [in J. Nonlinear Math. Phys. 8, no.3 (2001) 518-533] so as to encompass some extensions of Lie algebras related to noncanonical actions.Comment: arxiv version is already officia

Erratum: Improved real-space genetic algorithm for crystal structure and polymorph prediction [Phys. Rev. B 77, 134117 (2008)]

In our earlier work, there was an error in the derivation of the spherically averaged scattering intensity, presented as Eq. (5) in the original paper. This equation should have readΛ(kr)=∑n=1Nρ′(n)2+2∑n=1N∑m>nNρ′(n)ρ′(m)j0(kr∣∣∣∣rn−rm|), (5)where j0(r) is the spherical Bessel function of the first kind

The barriers to and enablers of providing reasonably adjusted health services to people with intellectual disabilities in acute hospitals: evidence from a mixed-methods study.

OBJECTIVE: To identify the factors that promote and compromise the implementation of reasonably adjusted healthcare services for patients with intellectual disabilities in acute National Health Service (NHS) hospitals. DESIGN: A mixed-methods study involving interviews, questionnaires and participant observation (July 2011-March 2013). SETTING: Six acute NHS hospital trusts in England. METHODS: Reasonable adjustments for people with intellectual disabilities were identified through the literature. Data were collected on implementation and staff understanding of these adjustments. RESULTS: Data collected included staff questionnaires (n=990), staff interviews (n=68), interviews with adults with intellectual disabilities (n=33), questionnaires (n=88) and interviews (n=37) with carers of patients with intellectual disabilities, and expert panel discussions (n=42). Hospital strategies that supported implementation of reasonable adjustments did not reliably translate into consistent provision of such adjustments. Good practice often depended on the knowledge, understanding and flexibility of individual staff and teams, leading to the delivery of reasonable adjustments being haphazard throughout the organisation. Major barriers included: lack of effective systems for identifying and flagging patients with intellectual disabilities, lack of staff understanding of the reasonable adjustments that may be needed, lack of clear lines of responsibility and accountability for implementing reasonable adjustments, and lack of allocation of additional funding and resources. Key enablers were the Intellectual Disability Liaison Nurse and the ward manager. CONCLUSIONS: The evidence suggests that ward culture, staff attitudes and staff knowledge are crucial in ensuring that hospital services are accessible to vulnerable patients. The authors suggest that flagging the need for specific reasonable adjustments, rather than the vulnerable condition itself, may address some of the barriers. Further research is recommended that describes and quantifies the most frequently needed reasonable adjustments within the hospital pathways of vulnerable patient groups, and the most effective organisational infrastructure required to guarantee their use, together with resource implications

Detecting the Earliest Galaxies Through Two New Sources of 21cm Fluctuations

The first galaxies that formed at a redshift ~20-30 emitted continuum photons with energies between the Lyman-alpha and Lyman limit wavelengths of hydrogen, to which the neutral universe was transparent except at the Lyman-series resonances. As these photons redshifted or scattered into the Lyman-alpha resonance they coupled the spin temperature of the 21cm transition of hydrogen to the gas temperature, allowing it to deviate from the microwave background temperature. We show that the fluctuations in the radiation emitted by the first galaxies produced strong fluctuations in the 21cm flux before the Lyman-alpha coupling became saturated. The fluctuations were caused by biased inhomogeneities in the density of galaxies, along with Poisson fluctuations in the number of galaxies. Observing the power-spectra of these two sources would probe the number density of the earliest galaxies and the typical mass of their host dark matter halos. The enhanced amplitude of the 21cm fluctuations from the era of Lyman-alpha coupling improves considerably the practical prospects for their detection.Comment: 11 pages, 7 figures, ApJ, published. Normalization fixed in top panels of Figures 4-

Trigonometric Sutherland systems and their Ruijsenaars duals from symplectic reduction

Besides its usual interpretation as a system of $n$ indistinguishable particles moving on the circle, the trigonometric Sutherland system can be viewed alternatively as a system of distinguishable particles on the circle or on the line, and these 3 physically distinct systems are in duality with corresponding variants of the rational Ruijsenaars-Schneider system. We explain that the 3 duality relations, first obtained by Ruijsenaars in 1995, arise naturally from the Kazhdan-Kostant-Sternberg symplectic reductions of the cotangent bundles of the group U(n) and its covering groups $U(1) \times SU(n)$ and ${\mathbb R}\times SU(n)$, respectively. This geometric interpretation enhances our understanding of the duality relations and simplifies Ruijsenaars' original direct arguments that led to their discovery.Comment: 34 pages, minor additions and corrections of typos in v