Optimization of a charge-state analyzer for ECRIS beams

A detailed experimental and simulation study of the extraction of a 24 keV He-ion beam from an ECR ion source and the subsequent beam transport through an analyzing magnet is presented. We find that such a slow ion beam is very sensitive to space-charge forces, but also that the neutralization of the beam's space charge by secondary electrons is virtually complete for beam currents up to at least 0.5 mA. The beam emittance directly behind the extraction system is 65 pi mm mrad and is determined by the fact that the ion beam is extracted in the strong magnetic fringe field of the ion source. The relatively large emittance of the beam and its non-paraxiality lead, in combination with a relatively small magnet gap, to significant beam losses and a five-fold increase of the effective beam emittance during its transport through the analyzing magnet. The calculated beam profile and phase-space distributions in the image plane of the analyzing magnet agree well with measurements. The kinematic and magnet aberrations have been studied using the calculated second-order transfer map of the analyzing magnet, with which we can reproduce the phase-space distributions of the ion beam behind the analyzing magnet. Using the transfer map and trajectory calculations we have worked out an aberration compensation scheme based on the addition of compensating hexapole components to the main dipole field by modifying the shape of the poles. The simulations predict that by compensating the kinematic and geometric aberrations in this way and enlarging the pole gap the overall beam transport efficiency can be increased from 16 to 45%

Lifestyle coaches as a central professional in the health care network?:Dynamic changes over time using a network analysis

BackgroundOverweight and obesity are problems that are increasing globally in both children as well as adults, and may be prevented by adopting a healthier lifestyle. Lifestyle coaches counsel overweight and obese children (and their parents) as well as adults in initiating and maintaining healthier lifestyle behaviours. It is currently unclear whether this novel professional in the Dutch health care system functions as a linchpin in networks that evolve around lifestyle-related health problems. The aim of the present study is to investigate the formation and development of networks of lifestyle coaches and their positions within these networks.MethodsIn this longitudinal study, key professionals and professionals within relevant organisations in the Coaching on Lifestyle (CooL) care networks were asked to fill in three online questionnaires. Respondents were asked to indicate whether they collaborated with each of the specified professionals in the context of CooL. The overall network structures and the central role of the lifestyle coaches were examined by using network analysis.ResultsThe results showed that the networks in three out of four regions were relatively centralised, but that none of the networks were dense, and that the professionals seemed to collaborate less with others over time. Half of the lifestyle coaches had a high number of collaborations and a central position within their networks, which also increased over time. In half of the regions, the lifestyle coaches had increased their role as consultants, while their role as gatekeeper and liaison decreased over time. In most regions, the sector of lifestyle coaches had a central position in their networks in just one measurement. Other central sectors were the local sports organisation, public health services, youth health care and the municipal government.ConclusionsOverall, we cannot conclude that more central and denser networks were formed during the study period. In addition, the lifestyle coaches were not often positioned as a central sector within these networks. Entrepreneurial, network and brokering competences are required for lifestyle coaches to build up denser networks.Trial registrationNTR6208; date registered: 13-01-2017; retrospectively registered; Netherlands Trial Register

Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of "meta-atoms". It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.

Associations between Safety from Crime, Cycling, and Obesity in a Dutch Elderly Population: Results from the Longitudinal Aging Study Amsterdam

The objective of this cross-sectional study was to investigate differences in associations between crime rates, cycling, and weight status between people living in low and high socioeconomic status (SES) neighbourhoods. In total, 470 participants in the Longitudinal Aging Study Amsterdam were included (age: 63–70 y). Body height and weight were measured using a stadiometer and calibrated weight scale, respectively. Cycling behaviour was assessed in a face-to-face interview, and neighbourhood crime rates were assessed using data from police reports. Men residing in high SES neighbourhoods cycled more than males residing in low SES neighbourhoods. Cycling was negatively related to crime rates among both men and women living in low SES neighbourhoods. Among men living in low SES neighbourhoods, more cycling was associated with lower BMI. Interventions aiming to prevent obesity in older people may consider aiming at increasing bicycle use in lower SES neighbourhoods, but neighbourhood safety issues should be considered

Theory of Cherenkov radiation in periodic dielectric media: Emission spectrum

The Cherenkov radiation is substantially modified in the presence of a medium with a nontrivial dispersion relation. We consider Cherenkov emission spectra of a point charge moving in general three- (3D) and two-dimensional (2D) photonic crystals. Exact analytical expressions for the spectral distribution of the radiated power are obtained in terms of the Bloch mode expansion. The resulting expression reduces to a simple contour integral (3D case) or a one-dimensional sum (2D case) over a small fraction of the reciprocal space, which is defined by the generalized Cherenkov condition. We apply our method to a specific case of an electron moving with different velocities in a 2D square-lattice photonic crystal. Our method demonstrates an excellent agreement with numerically rigorous finite-difference time-domain calculations while being less demanding on computational resources.Comment: to appear in Phys. Rev.

Surfaces roughness effects on the transmission of Gaussian beams by anisotropic parallel plates

Influence of the plate surfaces roughness in precise ellipsometry experiments is studied. The realistic case of a Gaussian laser beam crossing a uniaxial platelet is considered. Expression for the transmittance is determined using the first order perturbation theory. In this frame, it is shown that interference takes place between the specular transmitted beam and the scattered field. This effect is due to the angular distribution of the Gaussian beam and is of first order in the roughness over wavelength ratio. As an application, a numerical simulation of the effects of quartz roughness surfaces at normal incidence is provided. The interference term is found to be strongly connected to the random nature of the surface roughness.Comment: 18 pages, Journal of Physics D: Applied Physics, volume 36, issue 21, pages 2697 - 270

Process evaluation of the healthy primary School of the Future: the key learning points

Background While schools have potential to contribute to children’s health and healthy behaviour, embedding health promotion within complex school systems is challenging. The ‘Healthy Primary School of the Future’ (HPSF) is an initiative that aims to integrate health and well-being into school systems. Central to HPSF are two top-down changes that are hypothesized as being positively disruptive to the Dutch school system: daily free healthy lunches and structured physical activity sessions. These changes are expected to create momentum for bottom-up processes leading to additional health-promoting changes. Using a programme theory, this paper explores the processes through which HPSF and the school context adapt to one another. The aim is to generate and share knowledge and experiences on how to implement changes in the complex school system to integrate school health promotion. Methods The current study involved a mixed methods process evaluation with a contextual action-oriented research approach. The processes of change were investigated in four Dutch primary schools during the development year (2014–2015) and the first two years of implementation (2015–2017) of HPSF. The schools (each with 15–26 teachers and 233–389 children) were in low socio-economic status areas. Measurements included interviews, questionnaires, observations, and analysis of minutes of meetings. Results Top-down advice, combined with bottom-up involvement and external practical support were key facilitators in embedding HPSF within the schools’ contexts. Sufficient coordination and communication at the school level, team cohesion, and feedback loops enhanced implementation of the changes. Implementation of the healthy lunch appeared to be disruptive and create momentum for additional health-promoting changes. Conclusions Initiating highly visible positive disruptions to improve school health can act as a catalyst for wider school health promotion efforts. Conditions to create a positive disruption are enough time, and sufficient bottom-up involvement, external support, team cohesion and coordination. The focus should be on each specific school, as each school has their own starting point and process of change

Isotope effects in switchable metal-hydride mirrors

Measurements of optical reflectance, transmittance, and electrical resistivity on the switchable mirror systems YHx and YDx show that the absorption of hydrogen induces the same variations as that of deuterium. In both cases there is a weak transparency window for the metallic dihydride (dideuteride) phase and a yellowish transparency in the insulating trihydride (trideuteride) phase. The slightly higher electrical resistivity of the deuterides is related to the lower energy of their optical phonons. The absence of significant isotope effects in the optical properties of YHx(YDx) is at variance with Peierls-like theoretical models. It is, however, compatible with strong electron correlation model