Beyond basis invariants

Physical observables cannot depend on the basis one chooses to describe fields. Therefore, all physically relevant properties of a model are, in principle, expressible in terms of basis-invariant combinations of the parameters. However, in many cases it becomes prohibitively difficult to establish key physical features exclusively in terms of basis invariants. Here, we advocate an alternative route in such cases: the formulation of basis-invariant statements in terms of basis-covariant objects. We give several examples where the basis-covariant path is superior to the traditional approach in terms of basis invariants. In particular, this includes the formulation of necessary and sufficient basis-invariant conditions for various physically distinct forms of CP conservation in two- and three-Higgs-doublet models.Comment: 20 pages, no figure

Production And Studies Of Photocathodes For High Intensity Electron Beams

For short, high-intensity electron bunches, alkali-tellurides have proved to be a reliable photo-cathode material. Measurements of lifetimes in an RF gun of the CLIC Test Facility II at field strengths greater than 100 MV/m are presented. Before and after using them in this gun, the spectral response of the Cs-Te and Rb-Te cathodes were determined with the help of an optical parametric oscillator. The behaviour of both materials can be described by Spicer's 3-step model. Whereas during the use the threshold for photo-emission in Cs-Te was shifted to higher photon energies, that of Rb-Te did not change. Our latest investigations on the stoichiometric ratio of the components are shown. The preparation of the photo-cathodes was monitored with 320 nm wavelength light, with the aim of improving the measurement sensitivity. The latest results on the protection of Cs-Te cathode surfaces with CsBr against pollution are summarized. New investigations on high mean current production are presented.Comment: Submission to LINAC2000 conference, Paper number MOB08, 3 pages, 6 figure

Den danske dyrkningsjords tilstand og kvalitet - konsekvenser af trafik og jordbearbejdning

Et alsidigt sædskifte og/eller tilførsel af organisk stof til jorden giver en god jordkvalitet (her defineret som en gunstig jordstruktur). Ensidige driftsformer kan i sig selv give anledning til en dårlig jordkvalitet. Jordpakning via trafik på jorden kan eliminere de gode effekter af et godt sædskifte og tilførsel af organisk stof. Trafik på jorden og i endnu højere grad intensiv jordbearbejdning øger risikoen for, at jordens lermineraler dispergeres til vandfasen. Dette kan give tilslemning og skorpedannelse på jorden og indebærer endvidere en risiko for nedvaskning af de vigtige lermineraler fra dyrkningslaget. Der bør foretages undersøgelser af omfanget af denne proces med de i dag anvendte bearbejdningsteknikker. Komprimering af jorden under normal bearbejdningsdybde via pløjning med hjulet i furebunden og via kørsel med meget tunge maskiner er i dag en realitet for stort set hele den danske landbrugsjord. Det anbefales stærkt, at landbruget overgår til pløjesystemer med alle fire hjul ’på land’ (’on-land’ pløjning). Det anbefales ligeledes, at belastningen (vægten) ved kørsel på forårs- og efterårsvåd jord ikke overstiger 6 tons på enkelt-aksel og 8-10 tons på boogi-aksel. Anvendelse af bæltekøretøjer er muligvis en løsning på pakningsproblemet. Det forudsætter dog, at de anvendte maskiner giver anledning til reelt meget lave marktryk (<50 kPa) over hele trædefladen. Der bør gennemføres flere undersøgelser af, hvorvidt de i dag tilgængelige bæltekøretøjer opfylder disse kriterier ved alle arbejdsoperationer

Unobserved heterogeneity between individuals in Group-Focused Enmity

Group-focused enmity (GFE) and related research have mostly focused on variable-centred analyses such as structural equation modelling and factor analysis, implicitly assuming that the results apply uniformly to all participants in the sample. Person-centred research questions and analysis methods, which investigate unobserved heterogeneity in the sample, have been lacking in GFE research. Nonetheless, initial evidence exists from research on Islamophobia and GFE that various unobserved latent classes (i.e., subgroups) differing in their average prejudice can be identified within one dataset. In this manuscript, we applied factor mixture modelling to investigate unobserved heterogeneity using the data of the German GFE survey 2011. We found two latent classes of equivalent factor-analytical composition with consistently high versus low expressions of target-specific prejudice. No comparison of latent GFE means was possible. Membership in the high prejudice latent class was associated with higher age, right-wing political orientation, high right-wing authoritarianism and high social dominance orientation. Our findings demonstrate the importance of exploring unobserved heterogeneity in attitudes research and outline how person-centred research can complement variable-centred research in order to understand social-psychological phenomena

Towards LES of bubble-laden channel flows:Sub-grid scale closures for momentum advection

This paper presents an a-posteriori assessment of different LES sub-grid scale closures for momentum advection in the context of bubble-laden channel flows. The numerical approach is based on the Volume-of-Fluid method in combination with the onefluid formulation of the incompressible Navier-Stokes equations. To study the behavior of different subgrid scale models, a turbulent bubble-laden downflow channel is simulated at a friction Reynolds number of ReΤ = 590. The setup is chosen such that the bubbles are nearly spherical, but mildly wobbling. Both functional models of eddy viscosity type and scale similarity type models are used to close the sub-grid scale stresses. The results are compared to a direct numerical simulation of the same setup. It is found that the stream-wise volumetric flow rate depends strongly on the closure model as well as the grid resolution. While some models lead to an improvement compared to the LES without an explicit model, the comparably dissipative nature of the QUICK scheme prevents a clear assessment of some more advanced modeling strategies

Ion Trap Mass Spectrometers for Identity, Abundance and Behavior of Volatiles on the Moon

NASA GSFC and The Open University (UK) are collaborating to deploy an Ion Trap Mass Spectrometer on the Moon to investigate the lunar water cycle. The ITMS is flight-proven throughthe Rosetta Philae comet lander mission. It is also being developed under ESA funding to analyse samples drilled from beneath the lunar surface on the Roscosmos Luna-27 lander (2025).Now, GSFC and OU will now develop a compact ITMS instrument to study the near-surface lunar exosphere on board a CLPS Astrobotic lander at Lacus Mortis in 2021