The Effect of Diffuse Light on Crops

Light is not evenly distributed in Dutch glass greenhouses, but this can be improved with diffuse light. Modern greenhouse coverings are able to transform most of the light entering the greenhouse into diffuse light. Wageningen UR Greenhouse Horticulture has studied the effect of diffuse light on crops for several years. Modelling and experimental studies showed that crops such as fruit vegetables with a high plant canopy as well as ornamentals with a small plant canopy can utilize diffuse light better than direct light. Diffuse light penetrates the middle layers of a high-grown crop and results in a better horizontal light distribution in the greenhouse. Diffuse light is absorbed to a better degree by the middle leaf layers of cucumber, resulting in a higher photosynthesis. The actual photosynthesis of four pot plant species was found to be increased and crop temperatures were lower during high irradiation. The yield of cucumbers was increased, and the growth rate of several potted plants was increased. These investigations have resulted in a quantitative foundation for the potentials of diffuse light in Dutch horticultural greenhouses and the selection and verification of technological methods to convert direct sunlight into diffuse light

Vertical flows and mass flux balance of sunspot umbral dots

A new Stokes inversion technique that greatly reduces the effect of the spatial point spread function of the telescope is used to constrain the physical properties of umbral dots (UDs). The depth-dependent inversion of the Stokes parameters from a sunspot umbra recorded with Hinode SOT/SP revealed significant temperature enhancements and magnetic field weakenings in the core of the UDs in deep photospheric layers. Additionally, we found upflows of around 960 m/s in peripheral UDs (i.e., UDs close to the penumbra) and $\approx$ 600 m/s in central UDs. For the first time, we also detected systematic downflows for distances larger than 200 km from the UD center that balance the upflowing mass flux. In the upper photosphere, we found almost no difference between the UDs and their diffuse umbral background.Comment: Accepted for publication in Astronomy and Astrophysic

Measuring the Wilson depression of sunspots using the divergence-free condition of the magnetic field vector

Context: The Wilson depression is the difference in geometric height of unit continuum optical depth between the sunspot umbra and the quiet Sun. Measuring the Wilson depression is important for understanding the geometry of sunspots. Current methods suffer from systematic effects or need to make assumptions on the geometry of the magnetic field. This leads to large systematic uncertainties of the derived Wilson depressions. Aims: We aim at developing a robust method for deriving the Wilson depression that only requires the information about the magnetic field that is accessible from spectropolarimetry, and that does not rely on assumptions on the geometry of sunspots or on their magnetic field. Methods: Our method is based on minimizing the divergence of the magnetic field vector derived from spectropolarimetric observations. We focus on large spatial scales only in order to reduce the number of free parameters. Results: We test the performance of our method using synthetic Hinode data derived from two sunspot simulations. We find that the maximum and the umbral averaged Wilson depression for both spots determined with our method typically lies within 100 km of the true value obtained from the simulations. In addition, we apply the method to Hinode observations of a sunspot. The derived Wilson depression (about 600 km) is consistent with results typically obtained from the Wilson effect. We also find that the Wilson depression obtained from using horizontal force balance gives 110 - 180 km smaller Wilson depressions than both, what we find and what we deduce directly from the simulations. This suggests that the magnetic pressure and the magnetic curvature force contribute to the Wilson depression by a similar amount.Comment: 12 pages, 8 figures. Accepted for publication in Astronomy & Astrophysic

Inclinations of small quiet-Sun magnetic features based on a new geometric approach

High levels of horizontal magnetic flux have been reported in the quiet-Sun internetwork, often based on Stokes profile inversions. Here we introduce a new method for deducing the inclination of magnetic elements and use it to test magnetic field inclinations from inversions. We determine accurate positions of a set of small, bright magnetic elements in high spatial resolution images sampling different photospheric heights obtained by the Sunrise balloon-borne solar observatory. Together with estimates of the formation heights of the employed spectral bands, these provide us with the inclinations of the magnetic features. We also compute the magnetic inclination angle of the same magnetic features from the inversion of simultaneously recorded Stokes parameters. Our new, geometric method returns nearly vertical fields (average inclination of around 14 deg with a relatively narrow distribution having a standard deviation of 6 deg). In strong contrast to this, the traditionally used inversions give almost horizontal fields (average inclination of 75+-8 deg) for the same small magnetic features, whose linearly polarised Stokes profiles are adversely affected by noise. The almost vertical field of bright magnetic features from our geometric method is clearly incompatible with the nearly horizontal magnetic fields obtained from the inversions. This indicates that the amount of magnetic flux in horizontal fields deduced from inversions is overestimated in the presence of weak Stokes signals, in particular if Stokes Q and U are close to or under the noise level. By combining the proposed method with inversions we are not just improving the inclination, but also the field strength. This technique allows us to analyse features that are not reliably treated by inversions, thus greatly extending our capability to study the complete magnetic field of the quiet Sun.Comment: 12 pages, 9 figures, 1 table; Accepted for publication in Astronomy & Astrophysic

The Effect of Website Interactivity on Political Involvement:The Moderating Role of Political Cynicism

This study examines the extent to which interactive communication on political websites affects various forms of citizens’ involvement in politics, and the moderating role of political cynicism in this relationship. Based on the outcomes of a laboratory experiment with a single-factor (interactivity: low vs. medium vs. high interactivity) between-subjects design, we found that interactive political websites have a positive effect on citizen involvement, and this effect is particularly present for websites with high levels of interactivity. We also demonstrate that interactivity effects are, to some extent, contingent on citizens’ political cynicism. For higher levels of political cynicism, deviations in the level of interactivity make less of a difference in their impact on political involvement

Screening Mothers: Representations of motherhood in Australian films from 1900 to 1988.

Although the position of mothers has changed considerably since the beginning of the twentieth century, an idealised notion of motherhood persists. The cinema provides a source of information about attitudes towards mothering in Australian society which is not diminished by the fact that mothers are often marginal to the narrative. While the study recognises that cinematic images are not unconditionally authoritative, it rests on the belief that films have some capacity to reflect and influence society. The films are placed in an historical context with regard to social change in Australian society, so that the images can be understood within the context of the time of the making and viewing of the films. The depictions of the mother are scrutinised with regard to her appearance, her attitude, her relationship with others and the expectations, whether explicit or implicit, of her role. Of particular significance is what happens to her during the film and whether she is punished or rewarded for her behaviour. The conclusions reached after analysis are used to challenge those ideas which assume that portrayals of motherhood are unchangeable and timeless. The study examines Australian feature films from 1900 to 1988. To augment its historical focus, it uses sociological, psychoanalytical and feminist theoretical writing with special relevance for motherhood and mothering practice. Looking at areas of importance to mothers, it comprises an exploration of what makes a mother good or bad; the significance of the birth of female and male children; the relationship of mothers to daughters; the mother's sexuality and the metaphor of the missing mother. It shows that images of motherhood on screen are organised according to political, social and economic requirements in the community. Further, films frequently show mothers in traditional roles which are useful for maintaining notions of patriarchal privilege in society. The analysis exposes stereotypical depictions of motherhood which are often inaccurate, unfair and oppressive to women

The Importance of E ective States: State Capacity and Economic Development

Political scientists have long suspected that differences in the degree to which governments are able to effectively implement and enforce public policy (i.e. state capacity) are at the root of economic (under)development. Measurement error and endogeneity have, however, prevented researchers from obtaining a credible estimate of the effect of state capacity on economic performance. Using an improved measure of state capacity and exposure to 1700-1788 inter-state warfare as an instrument, I find that state capacity alone is able to explain 57% of all cross-country differences in GDP per capita and that its effect is larger than other prominent explanations for cross-country differences in economic development, such as: constraints on the executive, democracy, latitude, landlockedness, social capital, natural resources, legal origins, ethnic fractionalization, and others. Using mediation analysis I find that state capacity affects economic development through factors that enable markets to allocate resources more efficiently (law and order), and through better performance in sectors where market failures are prone to arise (education, infrastructure, and technology). I find that these results are robust to more than 100 controls and show empirically that the IV estimates are robust to relatively large violations of the exclusion restriction. I also find that state capacity explains a significant fraction of cross-country growth rates over the 1950 to 2010 period

Emission Lines in the Spectrum of the 3He Star 3 Cen A

Emission in the 4d - 4f transitions of MnII (multiplet 13, 6122-6132 Ang), in the 4f - 6g transitions of PII, and in 6149.5 Ang of HgII has been detected in the spectrum of the helium weak star 3 Centauri A (B5 III-IVp). Weaker emission from the same MnII multiplet is also seen in the hot, mild HgMn star 46 Aquila (B9 III).It is suggested that the emission is of photospheric origin and may be evidence for the stratification of manganese, phosphorus and mercury in the photosphere of 3 CenA, and of manganese in 46Aql.Comment: 16 pages, 3 figure