Food neophobia and mealtime food consumption in 4-5 year old children.

Background: Previous research has documented a negative association between maternal report of child food neophobia and reported frequency of consumption of fruit, vegetables, and meat. This study aimed to establish whether neophobia is associated with lower intake of these food types in naturalistic mealtime situations. Methods: One hundred and nine parents of 4–5 year olds completed questionnaires which included a six-item version of the Child Food Neophobia Scale (CFNS). The children took part in a series of 3 test lunch meals at weekly intervals at school at which they were presented with: chicken, cheese, bread, cheese crackers, chocolate biscuits, grapes and tomatoes or carrot sticks. Food items served to each child were weighed before and after the meal to assess total intake of items in four categories: Fruit and vegetables, Protein foods, Starchy foods and Snack foods. Pearson Product Moment Correlations and independent t tests were performed to examine associations between scores on the CFNS and consumption during lunches. Results: Neophobia was associated with lower consumption of fruit and vegetables, protein foods and total calories, but there was no association with intake of starch or snack foods. Conclusion: These results support previous research that has suggested that neophobia impacts differentially on consumption of different food types. Specifically it appears that children who score highly on the CFNS eat less fruit, vegetables and protein foods than their less neophobic peers. Attempts to increase intake of fruit, vegetables and protein might usefully incorporate strategies known to reduce the neophobic response

Quasiparticle dynamics in aluminium superconducting microwave resonators

This thesis describes the intrinsic limits of superconducting microresonator detectors. In a superconductor at low temperature, most of the electrons are paired into so called Cooper pairs, which cause the well-known electrical conduction without resistance. Superconducting microwave resonators have therefore very high quality factors and are sensitive to the smallest signals. A small change in the number of Cooper pairs can therefore be detected with these resonators. The binding energy in a superconductor, such as aluminium, is low, which makes such a detector suitable for detection of submillimetre radiation, a wavelength range that is particularly interesting for astronomy. Each resonator can have a slightly different length, and thus a different resonant frequency, which enables the readout of thousands of resonators (pixels) with a single readout line. Because the detector principle relies on counting the number of broken Cooper pairs (so called quasiparticles), the most fundamental source of noise of these resonator detectors is due to fluctuations in the number of quasiparticles. We demonstrate that superconducting aluminium resonators are indeed limited by these fluctuations. We show that a measurement of these fluctuations also provides access to the number of quasiparticles and their lifetime, which are intrinsic properties of the superconductor itself. At decreasing temperatures the number of quasiparticles is expected to decrease exponentially. However, we observe that the number of quasiparticles and their lifetime saturate at low temperature. Measurements of these quasiparticle fluctuations as a function of the microwave readout power revealed that the excess quasiparticles at low temperature are due to microwave power dissipation. The second main topic of this thesis is therefore how the microwave readout signal affects the superconductor and the resonator response. We show that the resonator response becomes strongly nonlinear due to readout power absorption. Since the microwave photon energy is lower than the pair-breaking energy, the microwave signal should not be able to break Cooper pairs. We show that the creation of excess quasiparticles is due to an intricate effect, the redistribution of quasiparticles over energy due to readout power absorption. Finally, we report an experiment in which we apply terahertz radiation to a microwave resonator detector. To demonstrate that the detector is sensitive enough to be used in a camera aboard a cooled space telescope, the conditions for such an instrument have to be mimicked in the test-setup. We observe that the noise of the detector is limited by photon-noise, fundamental fluctuations due to the source of radiation, and that the sensitivity fulfils the requirements for a space telescope.Kavli Institute of Nanoscience DelftApplied Science

The discovery, disappearance and re-emergence of radiation-stimulated superconductivity

We trace the historical fate of experiment and theory of microwave-stimulated superconductivity as originally reported for constriction-type superconducting weak links. It is shown that the observed effect disappeared by improving weak links to obtain the desired Josephson properties. Separate experiments were carried out to evaluate the validity of the proposed theory of Eliash'berg for energy-gap-enhancement in superconducting films in a microwave field, without reaching a full quantitatively reliable measurement of the stimulated energy gap in a microwave field, but convincing enough to understand the earlier deviations from the Josephson-effect. Over the same time period microwave-stimulated superconductivity continued to be present in superconductor-normal metal-superconductor Josephson weak links. This experimental body of work was left unexplained for several decades and could only be understood properly after the microscopic theory of the proximity-effect had matured enough, including its non-equilibrium aspects. It implies that the increase in critical current in weak-link Josephson-junctions is due to an enhancement of the phase-coherence rather than to an enhancement of the energy-gap as proposed by Eliash'berg. The complex interplay between proximity-effect and the occupation of states continues to be, in a variety of ways, at the core of the ongoing research on hybrid Josephson-junctions. The subject of radiation-enhanced superconductivity has re-emerged in the study of the power-dependence of superconducting microwave resonators, but also in the light-induced emergence of superconductivity in complex materials.QN/Klapwijk La

Readout-power heating and hysteretic switching between thermal quasiparticle states in kinetic inductance detectors

A model is presented for readout-power heating in kinetic inductance detectors. It is shown that the power dissipated by the readout signal can cause the temperature of the quasiparticle system in the superconducting resonator to switch between well-defined states. At low readout powers, only a single solution to the heat balance equation exists, and the resonance curve merely distorts as the readout power is increased. At high readout powers, three states exist, two of which are stable, and the resonance curve shows hysteretic switching. The power threshold for switching depends on the geometry and material used but is typically around ?70 dBm for Aluminum resonators. A comprehensive set of simulations is reported, and a detailed account of the switching process is given. Experimental results are also shown, which are in strong qualitative agreement with the simulations. The general features of the model are independent of the precise cooling function, and are even applicable for resonators on suspended, thermally isolated, dielectric membranes, where an increase in quasiparticle lifetime is expected. We discuss various extensions to the technique, including the possibility of recovering the cooling function from large-signal measurements of the resonance curve.QN/Quantum NanoscienceApplied Science

Image beam from a wire laser

We demonstrate the formation of a narrow beam from a long (L??) laser with subwavelength transverse dimensions (wire laser) as an image of the subwavelength laser waveguide formed by a spherical lens. The beam is linearly diverging with the angle determined by the ratio of the wavelength to the lens radius, while the minimum beam spot size is the same as that of the image of a point source. We realize such a beam experimentally using a terahertz quantum cascade wire laser.QN/Quantum NanoscienceApplied Science

Rivierwaterbouwkunde

Civil Engineering and GeosciencesHydraulic Engineerin

Phonon-Trapping-Enhanced Energy Resolution in Superconducting Single-Photon Detectors

A noiseless, photon-counting detector, which resolves the energy of each photon, could radically change astronomy, biophysics, and quantum optics. Superconducting detectors promise an intrinsic resolving power at visible wavelengths of R=E/δE≈100 due to their low excitation energy. We study superconducting energy-resolving microwave kinetic inductance detectors (MKIDs), which hold particular promise for larger cameras. A visible and near-infrared photon absorbed in the superconductor creates a few thousand quasiparticles through several stages of electron-phonon interaction. Here we demonstrate experimentally that the resolving power of MKIDs at visible to near-infrared wavelengths is limited by the loss of hot phonons during this process. We measure the resolving power of our aluminum-based detector as a function of photon energy using four lasers with wavelengths between 1545-402nm. For detectors on thick SiN/Si and sapphire substrates the resolving power is limited to 10-21 for the respective wavelengths, consistent with the loss of hot phonons. When we suspend the sensitive part of the detector on a 110-nm-thick SiN membrane, the measured resolving power improves to 19-52, respectively. The improvement is equivalent to a factor 8±2 stronger phonon trapping on the membrane, which is consistent with a geometrical phonon propagation model for these hot phonons. We discuss a route towards the Fano limit by phonon engineering.Tera-Hertz SensingQN/van der Zant La

Strong reduction of quasiparticle fluctuations in a superconductor due to decoupling of the quasiparticle number and lifetime

We measure temperature-dependent quasiparticle fluctuations in a small Al volume, embedded in a NbTiN superconducting microwave resonator. The resonator design allows for readout close to equilibrium. By placing the Al film on a membrane, we enhance the fluctuation level and separate quasiparticle effects from phonon effects. When lowering the temperature, the recombination time saturates and the fluctuation level reduces by a factor ∼100. From this we deduce that the number of free quasiparticles is still thermal. Therefore, the theoretical, inverse relation between the quasiparticle number and recombination time is invalid in this experiment. This is consistent with quasiparticle trapping, where on-trap recombination limits the observed quasiparticle lifetime.Tera-Hertz Sensin

Rivierwaterbouwkunde

Deze syllabus beoogt een overzicht te geven van de basiskennis die nodig is om ingrepen in de rivier voor te bereiden en de gevolgen ervan te kunnen inschatten. Er wordt ingegaan op het gebruik dat de mens maakt van de rivier en op de kennis van de hydraulica, het sedimenttransport en de morfologie. Aan het einde van het dictaat worden praktijkvoorbeelden behandeld, waarvan een aantal is geënt op het Nederlandse deel van de Rijn.Civil Engineering and GeosciencesHydraulic Engineerin

River Engineering

In this syllabus an overview is given of the basic knowledge, which is required to prepare interventions in rivers and to estimate the consequences of these interventions. The utilization of the river for human purposes and the knowledge of hydraulics, sediment transport and morphology will be treated. At the end of this syllabus some practice examples are discussed, of which a few are focused on the Dutch section of the Rhine River.Civil Engineering and GeosciencesHydraulic Engineerin