Organic open field cultivation in the Netherlands

The arable farming and field vegetable cultivation sector is a significant part of the organic agricultural sector in the Netherlands. The sector produces not only vegetables for human consumption, but also organic animal feed such as maize an cereals. To facilitate organic farmers, Wageningen UR and Louis Bolk Institute carry out a variety or research aimed specifically at organic arable farming and field vegetable production. The report contains sector facts, sector aspirations, current affairs and research projects

Dutch soil management and soil fertility

The organic sector depends heavily on its soils. In the Netherlands, relatively little acreage is available per farm compared to other countries. This means that the soil has to be kept in optimal shape for production, be it vegetables, cereals, potatoes or animal feed and grassland. To facilitate organic farmers, Wageningen UR and Louis Bolk Institute carry out a variety of research aimed specifically at soil management and soil fertility. The report contains sector facts, sector aspirations, current affairs and research projects

Climate impact of organic production in the Netherlands

All agricultural activities have an impact in terms of greenhouse gases and energy use, and organic agriculture is no exception. The Dutch organic sector strives to use sustainable energy and keep its climate impact as low as possible. To facilitate organic farmers, Wageningen UR and Louis Bolk Institute carry out a variety of research aimed specifically at energy use and greenhouse gas emissions. The report contains sector facts, sector aspirations, current affairs and research projects

Floquet Topological Polaritons in Semiconductor Microcavities

We propose and model Floquet topological polaritons in semiconductor microcavities, using the interference of frequency detuned coherent fields to provide a time periodic potential. For arbitrarily weak field strength, where the Floquet frequency is larger than the relevant bandwidth of the system, a Chern insulator is obtained. As the field strength is increased, a topological phase transition is observed with an unpaired Dirac cone proclaiming the anomalous Floquet topological insulator. As the relevant bandwidth increases even further, an exotic Chern insulator with flat band is observed with unpaired Dirac cone at the second critical point. Considering the polariton spin degree of freedom, we find that the choice of field polarization allows oppositely polarized polaritons to either co-propagate or counter-propagate in chiral edge states.Comment: Accepted by PR

Application of Molybdenum Carbide Catalysts for the CO2-assisted Oxidative Dehydrogenation of Ethane

The rising demand for light olefins is at present mainly met via catalytic/thermal dehydrogenation of alkanes at temperatures of up to 900 °C. Under these severe process conditions, competing side reactions and catalyst deactivation via coking are the major challenges. Co-feeding an oxidant significantly decreases the reaction temperature. The oxidative dehydrogenation of ethane to ethylene, using CO2 as the oxidant (CO2-ODH), has earned a lot of interest in the past decade. The use of CO2, a soft oxidant in comparison to O2, prevents the overoxidation reaction of the paraffin to CO2 and allows for improved heat control. Besides that, the coking effect, which is believed to be the main catalyst deactivation pathway during these high temperature processes, could be significantly lowered due to the reverse Boudouard reaction. The most common catalytic materials reported are reducible metal oxides (MOx) due to their redox properties; a key concept to activate the C-H bond of the alkane and subsequently activate CO2. Besides metal oxides, transition metal carbides have also shown to be active for the CO2-ODH, reaching high yields of ethylene. Specifically, molybdenum carbide (MoxCy) has shown to be a highly efficient catalyst for CO2 activation and alkane dehydrogenation, demonstrating its ability to cleave C-H bonds. These characteristics are important in making a MoxCy-based catalyst a serious candidate for the CO2- ODH of light alkanes. This work entails the design of novel MoxCy-based catalysts for application in the CO2-ODH of C2H6. Previous work on MoxCy-based catalysts found that the bulk material has limited activity and selectivity towards producing C2H4 but is significantly improved once dispersed on a support material. The type of support material dictates whether the CO2-ODH reaction takes place, or if one of the major side reactions, the dry-reforming of C2H6 to synthesis gas, is preferred. In this study, MoxCy nanoparticles were prepared via various (novel) synthesis techniques, dispersed on a variety of MOx support materials as well as modified with various promoters. Besides the exploratory nature of this study, gaining knowledge on the activity of the various formulations of MoxCy-based catalysts, the preparation conditions of the carbide materials were investigated. To prepare MoxCy, the precursor samples (in the molybdate or oxide phase) are exposed to a temperature programmed treatment (carburization) in the presence of a carbonaceous and reductive gas mixture. The carbide formation, in terms of crystallite structure, surface composition as well as potential fouling mechanisms is highly dependent on the heating rate, gas mixture, final temperature and precursor composition. Various experiments utilizing in situ characterization techniques, such as in situ X-ray diffraction, X-ray adsorption and Raman spectroscopy as well as online product analysis techniques were employed to gain knowledge on the carburization process, the structural and chemical properties and their effect on the activity of the various prepared catalysts in the CO2-ODH as well as the reverse water-gas-shift reaction. The use of MoxCy-based catalysts in the CO2-ODH reaction has not been thoroughly investigated in literature before and is still a very new topic to the scientific community. The presented research can contribute on various aspects of the use and viability of MoxCy-based catalysts in CO2 utilizing reactions and can be extended to dry-reforming or CO2 hydrogenation to fuels. In terms of catalyst synthesis, the extensive characterization exposing the various possible crystal structures of MoxCy nanoparticles and application of surface sensitive techniques, allowed for a better understanding of the possible active phases responsible for CO2 and alkane activation. Besides the identification of the active phase, the deactivation mechanism for MoxCy-based catalysts in the CO2-ODH reaction is studied in more detail by focusing on the crystal structure and the presence of carbon on the catalyst surface. By varying catalyst compositions as well as reaction conditions, including the use of various co-feeding experiments, an increase in catalytic stability, while maintaining high yields of the desired product from CO2-ODH (ethylene), was achieved

Killing Tensors in Koutras-McIntosh Spacetimes

This thesis is concerned with the (non)existence of Killing Tensors in Koutras-McIntosh spacetimes. Killing tensors are of particular interest in general relativity, because these correspond to conserved quantities for the geodesic motion. For instance, Carter found such a conserved quantity in the Kerr metric which he used to explicitly integrate the geodesic equations. The equation defining a Killing tensor is actually an overdetermined linear first order partial differential equation. We shall study the Killing equation using methods from the geometric theory of PDEs. More precisely, we use Cartan's prolongation method to prove the (non)existence of Killing tensors in several Koutras-McIntosh spacetimes. A subclass of the Koutras--McIntosh spacetimes are the conformally flat pp-waves. We show that a generic conf. flat pp-wave has an irreducible Killing 2-tensor, which reproves a result obtained by Keane and Tupper using a different method. Moreover, we prove in particular examples of pp-waves that all Killing tensors of degree 3 and 4 are reducible. We then study the Wils metric, another subclass of the Koutras-McIntosh spacetimes. This metric has a univariate function as its parameter. By using Cartan's prolongation method we deduce the explicit form of the function for which the Wils metric admits a Killing vector, and for which a Killing 2-tensor. This existence result for a Killing vector makes a statement by Koutras and McIntosh more precise. Finally, we show in particular examples of a Wils metric that all Killing 3- and 4-tensors are reducible