Towards exascale real-time RFI mitigation

We describe the design and implementation of an extremely scalable real-time RFI mitigation method, based on the offline AOFlagger. All algorithms scale linearly in the number of samples. We describe how we implemented the flagger in the LOFAR real-time pipeline, on both CPUs and GPUs. Additionally, we introduce a novel simple history-based flagger that helps reduce the impact of our small window on the data. By examining an observation of a known pulsar, we demonstrate that our flagger can achieve much higher quality than a simple thresholder, even when running in real time, on a distributed system. The flagger works on visibility data, but also on raw voltages, and beam formed data. The algorithms are scale-invariant, and work on microsecond to second time scales. We are currently implementing a prototype for the time domain pipeline of the SKA central signal processor.Comment: 2016 Radio Frequency Interference (RFI2016) Coexisting with Radio Frequency Interference, Socorro, New Mexico, USA, October 201

Electron Spin Resonance of Photochromic β-Tetrachloro-α-ketonaphthalene

A triplet ESR spectrum has been observed in a powdered sample of β 2,3,4,4-tetra-chloro-α-ketonaphthalene after UV irradiation. The spectrum could be reproduced by computer simulation using an anisotropic g-tensor (gxx = 2.00950, gyy = 2.00280, gzz = 2.00232) and zero-field splitting parameters D’ and E’ of 99 and 2.3 gauss respectively. The results are discussed in terms of the earlier proposed photodissociation into a naphthoxyl radical and a chlorine atom

Electron Spin Resonance of Photochromic β-Tetrachloro-α-ketonaphthalene

A triplet ESR spectrum has been observed in a powdered sample of β 2,3,4,4-tetra-chloro-α-ketonaphthalene after UV irradiation. The spectrum could be reproduced by computer simulation using an anisotropic g-tensor (gxx = 2.00950, gyy = 2.00280, gzz = 2.00232) and zero-field splitting parameters D’ and E’ of 99 and 2.3 gauss respectively. The results are discussed in terms of the earlier proposed photodissociation into a naphthoxyl radical and a chlorine atom

Real-Time Dedispersion for Fast Radio Transient Surveys, using Auto Tuning on Many-Core Accelerators

Dedispersion, the removal of deleterious smearing of impulsive signals by the interstellar matter, is one of the most intensive processing steps in any radio survey for pulsars and fast transients. We here present a study of the parallelization of this algorithm on many-core accelerators, including GPUs from AMD and NVIDIA, and the Intel Xeon Phi. We find that dedispersion is inherently memory-bound. Even in a perfect scenario, hardware limitations keep the arithmetic intensity low, thus limiting performance. We next exploit auto-tuning to adapt dedispersion to different accelerators, observations, and even telescopes. We demonstrate that the optimal settings differ between observational setups, and that auto-tuning significantly improves performance. This impacts time-domain surveys from Apertif to SKA.Comment: 8 pages, accepted for publication in Astronomy and Computin

Relativistic and correlation effects on molecular properties - the interhalogens CIF, BrF, BrCI, IF, ICI and IBr

The effect of relativity on the properties of the interhalogens ClF, BrF, BrCl, IF, IBr, and IBr is studied by comparing relativistic and nonrelativistic calculations. Bond lengths, harmonic frequencies, and dissociation energies show that the bond is weakened in the relativistic formalism. Relativity increases the electric dipole moment whereas the electric quadrupole moment and dipole polarizability display an irregular behavior. The relativistic contributions to the electric dipole and quadrupole moment of the iodine containing molecules are 10%–20% of the total value, whereas the contributions in the other molecules cannot be neglected. The value of the electric quadrupole moment is dominated by the relativistic contributions