1,640 research outputs found
Optimising Sparse Matrix Vector multiplication for large scale FEM problems on FPGA
Sparse Matrix Vector multiplication (SpMV) is an important kernel in many scientific applications. In this work we propose an architecture and an automated customisation method to detect and optimise the architecture for block diagonal sparse matrices. We evaluate the proposed approach in the context of the spectral/hp Finite Element Method, using the local matrix assembly approach. This problem leads to a large sparse system of linear equations with block diagonal matrix which is typically solved using an iterative method such as the Preconditioned Conjugate Gradient. The efficiency of the proposed architecture combined with the effectiveness of the proposed customisation method reduces BRAM resource utilisation by as much as 10 times, while achieving identical throughput with existing state of the art designs and requiring minimal development effort from the end user. In the context of the Finite Element Method, our approach enables the solution of larger problems than previously possible, enabling the applicability of FPGAs to more interesting HPC problems
Relaminarisation of Re_Ï=100 channel flow with globally stabilising linear feedback control
The problems of nonlinearity and high dimension have so far prevented a complete solution of the control of turbulent flow. Addressing the problem of nonlinearity, we propose a flow control strategy which ensures that the energy of any perturbation to the target profile decays monotonically. The controllerâs estimate of the flow state is similarly guaranteed to converge to the true value. We present a one-time off-line synthesis procedure, which generalises to accommodate more restrictive actuation and sensing arrangements, with conditions for existence for the controller given in this case. The control is tested in turbulent channel flow (Re_Ïâ=â100) using full-domain sensing and actuation on the wall-normal velocity. Concentrated at the point of maximum inflection in the mean profile, the control directly counters the supply of turbulence energy arising from the interaction of the wall-normal perturbations with the flow shear. It is found that the control is only required for the larger-scale motions, specifically those above the scale of the mean streak spacing. Minimal control effort is required once laminar flow is achieved. The response of the near-wall flow is examined in detail, with particular emphasis on the pressure and wall-normal velocity fields, in the context of Landahlâs theory of sheared turbulence
Relaminarisation of Re_{\tau} = 100 channel flow with globally stabilising linear feedback control
The problems of nonlinearity and high dimension have so far prevented a
complete solution of the control of turbulent flow. Addressing the problem of
nonlinearity, we propose a flow control strategy which ensures that the energy
of any perturbation to the target profile decays monotonically. The
controller's estimate of the flow state is similarly guaranteed to converge to
the true value. We present a one-time off-line synthesis procedure, which
generalises to accommodate more restrictive actuation and sensing arrangements,
with conditions for existence for the controller given in this case. The
control is tested in turbulent channel flow () using full-domain
sensing and actuation on the wall-normal velocity. Concentrated at the point of
maximum inflection in the mean profile, the control directly counters the
supply of turbulence energy arising from the interaction of the wall-normal
perturbations with the flow shear. It is found that the control is only
required for the larger-scale motions, specifically those above the scale of
the mean streak spacing. Minimal control effort is required once laminar flow
is achieved. The response of the near-wall flow is examined in detail, with
particular emphasis on the pressure and wall-normal velocity fields, in the
context of Landahl's theory of sheared turbulence
Entanglement distribution for a practical quantum-dot-based quantum processor architecture
We propose a quantum dot (QD) architecture for enabling universal quantum information processing. Quantum registers, consisting of arrays of vertically stacked self-assembled semiconductor QDs, are connected by chains of in-plane self-assembled dots. We propose an entanglement distributor, a device for producing and distributing maximally entangled qubits on demand, communicated through in-plane dot chains. This enables the transmission of entanglement to spatially separated register stacks, providing a resource for the realization of a sizeable quantum processor built from coupled register stacks of practical size. Our entanglement distributor could be integrated into many of the present proposals for self-assembled QD-based quantum computation (QC). Our device exploits the properties of simple, relatively short, spin-chains and does not require microcavities. Utilizing the properties of self-assembled QDs, after distribution the entanglement can be mapped into relatively long-lived spin qubits and purified, providing a flexible, distributed, off-line resource. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Genetic diversity of a flightless dung beetle appears unaffected by wildfire
The wildfires of Australiaâs Black Summer in 2019/2020 caused a massive loss of wildlife and habitats, but the effects of the fire on invertebrate species post-burn are unknown. We hypothesised that the fires would negatively affect the genetic diversity of invertebrate species by impeding movement between populations due to habitat loss. We studied the genetic diversity of a flightless dung beetle, Amphistomus primonactus Matthews 1974, to determine the impact of the wildfires on this species. We examined 90 SNPs from 193 individuals across seven localities impacted by the wildfires in north-eastern New South Wales. We used STRUCTURE to determine the overall population structure of the seven localities. We calculated four within-locality genetic diversity measures (observed heterozygosity (Ho), unbiased expected heterozygosity (uHe), Shannonâs Information (1 H), and the inbreeding coefficient (FIS). We calculated three between-locality genetic diversity measures (Fixation Index (FST), Hedrickâs GâST, and Shannonâs Mutual Information (I). We used partial Mantel tests to compare the between-locality genetic diversity measures with the mean fire intensity along each pairwise linear transect, while accounting for genetic variation due to geographic distance. We compared the within-locality genetic diversity measures to the mean fire intensity at each site. STRUCTURE showed a large degree of intermixing between localities. We found no significant effect of fire on any within-locality genetic diversity measure, or on any between-locality genetic diversity measure. We suggest that the genetic diversity of A. primonactus was not significantly affected by the Black Summer wildfires. Implications for insect conservation: Our results show that the 2019/2020 wildfires had a negligible impact on the genetic structure of A. primonactus. This offers a promising outlook for the species in its recovery from the fires
Time-Lapse Acoustic Imaging of Mesoscale and Fine-Scale Variability within the Faroe-Shetland Channel
We describe and analyze the results of a threeâdimensional seismic (i.e. acoustic) reflection survey from the FaroeâShetland Channel that is calibrated with nearâcoincident hydrographic and satellite observations. 54 vertical seismic transects were acquired over a period of 25 days. On each transect, a 250ââ400 m band of reflections is observed within the water column. Hydrographic measurements demonstrate that this reflective band is caused by temperature variations within the pycnocline that separates warm, nearâsurface waters of Atlantic origin from cold, deep waters which flow southward from the Nordic Seas. Tilting of reflective surfaces records geostrophic shear between these nearâsurface and deep waters. Measurements of temporal changes of pycnoclinic depth and of reflection tilt are used to infer the existence of an anticyclonic vortex that advects northeastward. Comparison with satellite measurements of seaâsurface temperature and height suggests that this vortex is caused by meandering of the Continental Slope Current. A model of a Gaussian vortex is used to match seismic and satellite observations. This putative vortex has a core radius of 20â30 km and a maximum azimuthal velocity of 0.3ââ0.4 m sâ1. It translates at 0.01ââ0.1 m sâ1. Within the pycnocline, diapycnal diffusivity, K , is estimaed by analyzing the turbulent spectral subrange of tracked reflections. K varies between 10â5.7 and 10â5.0 m 2 sâ1 in a pattern that is broadly consistent with translation of the vortex. Our integrated study demonstrates the ability of timeâlapse seismic reflection surveying to dynamically resolve the effects that mesoscale activity has upon deep thermohaline structure on scales from meters to hundreds of kilometers.Natural Environment Research Council (NERC)
Engineering and Physical Science Research Council
794 Program Grant EP/K034529/
Hypervelocity Stars from the Andromeda Galaxy
Hypervelocity stars (HVSs) discovered in the Milky Way (MW) halo are thought
to be ejected from near the massive black hole (MBH) at the galactic centre. In
this paper we investigate the spatial and velocity distributions of the HVSs
which are expected to be similarly produced in the Andromeda galaxy (M31). We
consider three different HVS production mechanisms: (i) the disruption of
stellar binaries by the galactocentric MBH; (ii) the ejection of stars by an
in-spiraling intermediate mass black hole; and (iii) the scattering of stars
off a cluster of stellar-mass black holes orbiting around the MBH. While the
first two mechanisms would produce large numbers of HVSs in M31, we show that
the third mechanism would not be effective in M31. We numerically calculate
1.2*10^6 trajectories of HVSs from M31 within a simple model of the Local Group
and hence infer the current distribution of these stars. Gravitational focusing
of the HVSs by the MW and the diffuse Local Group medium leads to high
densities of low mass (~ solar mass) M31 HVSs near the MW. Within the
virialized MW halo, we expect there to be of order 1000 HVSs for the first
mechanism and a few hundred HVSs for the second mechanism; many of these stars
should have distinctively large approach velocities (< -500 km/s). In addition,
we predict ~5 hypervelocity RGB stars within the M31 halo which could be
identified observationally. Future MW astrometric surveys or searches for
distant giants could thus find HVSs from M31.Comment: 14 pages, 6 figures, changed to match version accepted by MNRA
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