Reduction of secondary electron yield for E-cloud mitigation laser ablation surface engineering

Developing a surface with low Secondary Electron Yield (SEY) is one of the main ways of mitigating electron cloud and beam-induced electron multipacting in high-energy charged particle accelerators. In our previous publications, a low SEY < 0.9 for as-received metal surfaces modified by a nanosecond pulsed laser was reported. In this paper, the SEY of laser-treated blackened copper has been investigated as a function of different laser irradiation parameters. We explore and study the influence of micro- and nano-structures induced by laser surface treatment in air of copper samples as a function of various laser irradiation parameters such as peak power, laser wavelength (λ = 355 nm and 1064 nm), number of pulses per point (scan speed and repetition rate) and fluence, on the SEY. The surface chemical composition was determined by x-ray photoelectron spectroscopy (XPS) which revealed that heating resulted in diffusion of oxygen into the bulk and induced the transformation of CuO to sub-stoichiometric oxide. The surface topography was examined with high resolution scanning electron microscopy (HRSEM) which showed that the laser-treated surfaces are dominated by microstructure grooves and nanostructure features

Low secondary electron yield of laser treated surfaces of copper, aluminium and stainless steel

Reduction of SEY was achieved by surface engineering through laser ablation with a laser operating at • = 355 nm. It was shown that the SEY can be reduced to near or below 1 on copper, aluminium and 316LN stainless steel. The laser treated surfaces show an increased surface resistance, with a wide variation in resistance found de-pending on the exact treatment details. However, a treated copper surface with similar surface resistance to aluminium was produced

Dealing with Multiple Classes in Online Class Imbalance Learning

Online class imbalance learning deals with data streams having very skewed class distributions in a timely fashion. Although a few methods have been proposed to handle such problems, most of them focus on two-class cases. Multi-class imbalance imposes additional challenges in learning. This paper studies the combined challenges posed by multi-class imbalance and online learning, and aims at a more effective and adaptive solution. First, we introduce two resampling-based ensemble methods, called MOOB and MUOB, which can process multi-class data directly and strictly online with an adaptive sampling rate. Then, we look into the impact of multi-minority and multi-majority cases on MOOB and MUOB in comparison to other methods under stationary and dynamic scenarios. Both multi-minority and multi-majority make a negative impact. MOOB shows the best and most stable G-mean in most stationary and dynamic cases

Supplementary Information from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’

Fig. S8b from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’

Fig. S8a from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’

Fig. S5b from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’

Fig. S4a from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’

Supp. Info. MATLAB figure Names and Captions from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’

Fig. S7b from Tensile fracture of a single crack in first-year sea ice

The breakup of sea ice in the Arctic and Antarctic has been studied during three field trips in the spring of 1993 at Resolute, N.W.T. and the fall of 2001 and 2004 on McMurdo Sound via <i>in situ</i> cyclic loading and fracture experiments. In this paper, the back-calculated fracture information necessary to the specification of an accurate viscoelastic fictitious (cohesive) crack model is presented. In particular, the changing shape of the stress separation curve with varying conditions and loading scenarios is revealed.This article is part of the theme issue ‘Modelling of sea-ice phenomena’