Producer income instability and farmers' risk response: The case of major Kenyan export crops

The instability of export earnings in LDCs and its presumably harmful economic effects have been broadly discussed in the economic literature and among policy makers in international meetings. In analyzing these effects, the destabilization of producer incomes and farmers' risk response play a prominent role. Producer incomes may be destabilized by either domestic factors on the supply side (yield instability due to weather, crop diseases, etc.), or by fluctuating producer prices reflecting the instability of international primary commodity markets. If unstable producer incomes induce risk aversion among farmers, the sectoral factor input will be reduced and will be suboptimal from a welfare point of view, thus possibly hampering economic growth. The purpose of this paper is to quantify the effects of producer income instability on farmers' planting and long-run supply decisions in the coffee, tea, and sisal production of the Kenyan large farm sector. Coffee, tea, and sisal are the leading Kenyan export crops, the domestic consumption of which is negligible. About half of the Kenyan coffee and tea, and all the sisal are grown in the large farm sector, and nearly always on plantations. Coffee, tea, and sisal are permanent crops the planting of which requires long-run decisions. It is the long-run we shall focus on in this paper; hence the influence of income instability on short-term production planning will be neglected. The analysis will be based on a time series approach covering the period 1951-1975. In the following section we shall develop the methodological framework of how to measure the risk response of farmers. Next the estimation equations will be specified, and the estimation techniques will be demonstrated. Subsequently, the regression results are presented and interpreted. Some tentative conclusions are drawn in the final section.

Depletion of Specific Cell Populations by Complement Depletion

The purification of immune cell populations is often required in order to study their unique functions. In particular, molecular approaches such as real-time PCR and microarray analysis require the isolation of cell populations with high purity. Commonly used purification strategies include fluorescent activated cell sorting (FACS), magnetic bead separation and complement depletion. Of the three strategies, complement depletion offers the advantages of being fast, inexpensive, gentle on the cells and a high cell yield. The complement system is composed of a large number of plasma proteins that when activated initiate a proteolytic cascade culminating in the formation of a membrane-attack complex that forms a pore on a cell surface resulting in cell death1. The classical pathway is activated by IgM and IgG antibodies and was first described as a mechanism for killing bacteria. With the generation of monoclonal antibodies (mAb), the complement cascade can be used to lyse any cell population in an antigen-specific manner. Depletion of cells by the complement cascade is achieved by the addition of complement fixing antigen-specific antibodies and rabbit complement to the starting cell population. The cells are incubated for one hour at 37°C and the lysed cells are subsequently removed by two rounds of washing. MAb with a high efficiency for complement fixation typically deplete 95-100% of the targeted cell population. Depending on the purification strategy for the targeted cell population, complement depletion can be used for cell purification or for the enrichment of cell populations that then can be further purified by a subsequent method

Hybrid waveguide-bulk multi-path interferometer with switchable amplitude and phase

We design and realise a hybrid interferometer consisting of three paths based on integrated as well as on bulk optical components. This hybrid construction offers a good compromise between stability and footprint on one side and means of intervention on the other. As experimentally verified by the absence of higher-order interferences, amplitude and phase can be manipulated in all paths independently. In conjunction with single photons, the setup can, therefore, be applied for fundamental investigations on quantum mechanics.Comment: accepted in APL Photonic

On Mutualism, Models, and Masting: The Effects of Seed-Dispersing Animals on the plants they Disperse

© 2020 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society Species interactions are context dependent, in that their direction and magnitude can vary across ecological conditions. For seed dispersal interactions—especially interactions between plants and seed-caching animals—the direction of the interactions is often obscured because of seed mortality inherent in seed handling and the delayed effects of fitness benefits received by plants. It is, therefore, an open question in ecology to understand the ecological contexts under which seed dispersal interactions are facilitative, antagonistic or null. We review the fitness benefits of animal-mediated seed dispersal, extend a recently published model to include negative density-dependent effects, and review the feedback between seed production (with a focus on masting) and seed-caching animal populations. Negative density-dependent effects are pervasive and strongly affect the direction of plant-seed-disperser interactions, and including them into models will give a more accurate understanding of the direction of the interaction. Including negative density-dependent effects also makes the interpretation of interaction more mutualistic since seed dispersers decrease seed densities. Additionally, there is substantial interannual variability in seed production in most nut-producing plant species, and the lags between seed production and seed-disperser population sizes complicate and limit inferences made about the direction of interactions in any given short-term study. Synthesis. If we wish to know the direction of species interactions in real ecological communities, we need models that contain a minimum level of biological realism. For complex and long-term phenomena such as context-dependent species interactions we should embrace a multifaceted approach of short-term field research, long-term field research, simple models, and complex models to form a more robust understanding of the ecological problem of context dependency