241 research outputs found
FISCAL POLICY IN ENDOGENOUS ECONOMIC GROWTH MODELS WITH TWO R&D SECTORS
No full textThis paper is intended to investigate the possibilities for governmentinterventions based on fiscal policy measures in economies like those described inendogenous growth models with two R/D sectors.fiscal policy, endogenous economic growth
Characterization of Thin Film Photoanodes for Solar Water Splitting
No full textFor centuries, mankind has mostly used fossil fuels, i.e., natural gas, coal, and oil for its energy needs. With the fast rise of the world population and the rising standards of living in the developing countries, the amount of energy the world is going to need in the coming decades will grow enormously. Due to environmental concerns and the need to secure the energy supply, more actions have to be taken in the development and implementation of cleaner technologies, based on solar, wind, geothermal power, and biomass, combined with storage technologies such as batteries and hydrogen. Moreover, to fulfill the future global energy demand, all of the available energy sources will be needed. Despite the fact that solar energy is abundant, clean, and widely available, only a small percentage of this energy is utilized through conversion to electricity by photovoltaic systems. This is partly due to the need for smart technological inventions to make the alternative energy cost-effective and competitive with the conventional energy production. The Netherlands intends to increase the percentage of energy produced by sustainable sources from 4% nowadays to 20% in 2020. When considering sustainable energy production, also energy storage has to be investigated, since especially solar and wind energy are not continuous. In the chain of solar energy production and the need for energy storage, hydrogen is a promising storage candidate due to its high gravimetric energy density and its nonpollutive combustion product, water. Nowadays, hydrogen can be produced by a number of processes, such as electrolysis of water, steam reforming of natural gas, and biomass conversion, which directly or indirectly release large amounts of carbon dioxide into the atmosphere. An elegant alternative will be the use of solar energy for the electrolysis of water in a photoelectrochemical cell. Direct photoelectrolysis has the potential to be economically more attractive than coupled systems of photovoltaic cells and electrolysers. Additional information regarding this subject can be found in Chapter 1, as well as the necessary requirements for the photoelectrodes. In this thesis three different metal oxides, TiO2, InVO4, and Fe2O3 are investigated as photoanodes for water splitting applications. The aim of the research presented in this thesis is two-fold. First, the use of low-cost deposition techniques for the preparation of efficient thin-film photoanodes is explored. Special attention is given to the possibility to introduce dopants in a controlled manner. Second, the influence of the presence of ionic point defects on the photoelectrochemical performance of the materials is investigated. Titanium dioxide has long been considered as one of the most promising semiconductors for photoelectrolysis applications due to its low cost, non-toxicity, and excellent stability against corrosion. However, because of its wide bandgap (3.2 eV for anatase) the utilization of TiO2 typically remains confined to the UV light region, which constitutes only a small fraction (2-3%) of the solar radiation reaching the earth surface. Therefore, shifting its photoresponse into the visible range of the solar spectrum would enhance its potential for chemical solar energy conversion. Attempts to achieve this performance are typically focused on adding dopants. In Chapter 2 Fe- and C-doped TiO2 thin films have been investigated. Pulsed spray pyrolysis is employed to deposit high quality dense films. The prepared films are crystalline with an anatase structure and a post-deposition anneal does not change the morphology. For the Fe-doped TiO2 a small sub-bandgap photoresponse is observed, which is attributed to the presence of additional states located just above the valence band. Little or no visible-light photoresponse is observed for the C-doped anatase TiO2, which is attributed to a (too) low carbon content. However, the photocurrent at h?>Eg is significantly larger for C-doped TiO2 than for undoped TiO2. The strong enhancement of UV photoresponse is most likely caused by a change in the electronic structure of the material due to the presence of carbon and/or related defects. Photoluminescence measurements suggest that the defects present in oxidized carbon-doped anatase resemble those present in undoped, partially reduced TiO2. Although the exact nature of these defects is unknown, impedance measurements reveal a donor density of 1019-1020 cm-3 in C-doped TiO2. The high UV photoresponse is rather surprising for such a high donor density, and illustrates the intriguing, but still poorly understood properties of anion dopants. From the synthesis point of view, the preparation of carbon-doped TiO2 photoanodes was found to be challenging. A more simple approach is to prepare C-doped powders by solid-state reactions at high temperatures. Such a system can serve as a convenient screening method for selecting suitable anion dopants by analyzing the evolved gases, even if the efficiencies are very low. In Chapter 3 the focus is on the addition of carbon as dopant to anatase TiO2 by a post-deposition thermal treatment in a hexane-rich environment. Both thin films prepared by spray pyrolysis and mesoporous TiO2 photoelectrodes prepared by doctor-blading a paste of TiO2 nanoparticles are investigated. It is found that the carbon is mainly located at the surface of the TiO2. While it causes a black coloring of the mesoporous TiO2 film, it does not enhance the photocatalytic activity in the visible part of the spectrum. Only a small amount of carbon (3 and it has a near-optimal bandgap of 2.1 eV that enables up to 32% sunlight absorption. It is also an abundant and inexpensive semiconductor. However, certain intrinsic properties of Fe2O3 limit its performance as a photoelectrode. It shows a poor conductivity, which often leads to a high recombination rate, the energy level of the conduction band is too low for hydrogen evolution, it has slow kinetics for water oxidation, and a modest optical absorption coefficient. The main goal of the research in this chapter is on the preparation of Fe2O3 nanorods perpendicular to the substrate. Such a morphology could improve the efficiency of Fe2O3 photoanodes by decreasing the diffusion path length of the photo-generated holes. To achieve this, electrodeposition of Fe followed by thermal oxidation (EDOX) is explored as a new method to obtain these photoelectrodes efficiently in a short time and with the possibility to control the morphology. It is observed that after reaching a certain thickness or at a sufficiently high deposition current (2 mA/cm2) nano-sized needle- like features start to form. A further increase of the deposition current to 3 mA/cm2 results in a columnar growth consisting of small irregular crystallites stacked on top of each other. In contrast, it has been observed that when a Si precursor is present in the electrolyte solution during the electrodeposition, compact dense Fe2O3 films consisting of spherical particles are formed after the post-deposition oxidation. XRD analysis and Raman spectroscopy show that the Fe2O3 films mainly consist of the ?- Fe2O3 hematite phase. An important advantage of the EDOX method is that low-cost equipment can be used. Moreover, the direct thermal oxidation of electrodeposited Fe avoids the formation of undesired intermediate phases, such as FeOOH. Finally, the electrodeposition process takes place in a non-aqueous solvent, which allows the use of certain dopant precursors (e.g. TiCl4) that cannot be used in aqueous systems. This is an important advantage of this approach compared to other efforts in the literature. Although the EDOX method has been successfully demonstrated, an important remaining challenge is to improve control over the morphology and the doping density. Further improvements of the morphology may be possible by adding additives to the electrolyte solution, or by controlling the process parameters during oxidation of the electrodeposited iron. In conclusion, it has been demonstrated in this thesis that high-quality metal oxides can be prepared by low-cost techniques. Concomitantly, the impact of the ionic point defects on the performance of those photoanode materials is addressed and important material properties are determined. The attempts to enhance the visible-light response does not always result in higher efficiencies, due to low dopant concentrations in TiO2 films, poor electronic properties of InVO4 thin films, and morphology challenges for Fe2O3 to overcome its limitation as photoanode material. Nevertheless, important properties of the thin film photoanodes have been investigated and determined. No binary oxide solely can split water with a reasonable efficiency unless a tandem cell approach with suitable oxides is used. In principle, a lot can be gained by directing future research efforts towards ternary and even more complex metal oxides. In this case, however, the control over the stoichiometry of the metal ions remains challenging compared to simple binary oxides as has been demonstrated by the results on InVO4. While for some of the alternative energy sources technological breakthroughs have been achieved and new technologies are developed, for the hydrogen economy and in particular for the photoelectrochemical water splitting with metal oxides, more research is needed in developing low-cost techniques to make highly structured electrodes with large aspect ratios, to develop synthesis and/or doping strategies to suppress undesired defects present in the ternary oxides with non-stoichiometric metal:metal ratios, and not the least, in finding new and improving existing materials. When these challenges are met, photoelectrochemical water splitting may emerge as an economically viable and truly renewable pathway towards clean hydrogen.Materials for Energy Conversion and StorageApplied Science
Assessment of left ventricular untwisting by speckle-tracking echocardiography in patients with aortic regurgitation
No full textBackground: Left ventricular (LV) twist, as a result of counter-rotation of the apex and base during systole, and its subsequent untwisting during diastole represent important components of LV contractility and diastolic suction. Data regarding LV untwisting in AR patients are lacking.
Purpose: To assess LV untwisting and its determinants in patients with significant chronic AR.
Methods: We prospectively studied 35 patients withmoderate and severe chronic AR and 20 normal subjects. Exclusion criteria for AR patients were LV ejection fraction (LVEF) ≤50%, significant coronary artery disease, any LV wall motion abnormality, more than mild associated valvular heart disease, non-sinus rhythm. Basal and apical LV rotation and LV torsion were quantified from two-dimensional greyscale LV parasternal short-axis images by speckle tracking echocardiography (STE). LV untwisting was assessed by measuring peak untwisting velocity as the net difference in peak diastolic apical and basal rotation rates on the torsional velocity curve. Time to peak untwisting velocity (TTPUV) was normalized to diastolic duration. Analysis of left atrium (LA) strain and strain-rate parameters was performed on the same 4-chamber view in which LA volume was measured.
Results: Age and gender of patients were similar in both groups. There was no difference in mean LVEF between groups (60±4% in AR group vs 62±3% in control group, p=0.15). Peak LV untwisting velocity was significantly reduced in the AR group compared with the control group (-117.7±35.0°/s vs -143.1±47.6°, p=0.028). Also, peak apical diastolic rotation rate was lower in the AR group (- 80.8±41.0°/s vs -105.0±32.7°/s p=0.028). TTPUV was similar in both groups (p=0.189). In AR patients, peak LV untwisting velocity correlated with peak apical diastolic rotation rate (r=0.75, p<0.001) but not with peak basal diastolic rotation rate (r=0.02, p=0.934). At univariate analysis, peak LV untwisting velocity correlated
significantly with age (r=0.41, p=0.014), end-systolic LV volume (r=0.35, p=0.041), LV mass index (r=0.42, p=0.013), LA volume index (r=0.45, p=0.008), and peak early-diastolic LA strain rate (ESr) (r=0.51, p=0.004). At multivariable analysis LV mass index emerged as an independent determinant of peak LV untwisting velocity (p=0.044).
Conclusions: LV untwisting is reduced in patients with significant AR and normal LVEF, and this is due to significantly decreased apical diastolic rotation rate. LV mass emerged as an independent determinant of LV untwisting velocity in these patients, suggesting that LV hypertrophy impacts on LV torsional dynamics in this setting
Classification-relevant Importance Measures for the West German Business Cycle
No full textWhen analyzing business cycle data, one observes that the relevant predictor variables are often highly correlated. This paper presents a method to obtain measures of importance for the classification of data in which such multicollinearity is present. In systems with highly correlated variables it is interesting to know what changes are inflicted when a certain predictor is changed by one unit and all other predictors according to their correlation to the first instead of a ceteris paribus analysis. The approach described in this paper uses directional derivatives to obtain such importance measures. It is shown how the interesting directions can be estimated and different evaluation strategies for characteristics of classification models are presented. The method is then applied to linear discriminant analysis and multinomial logit for the classification of west German business cycle phases. --
Quantitative Solutions for the Substantiation of Decisions on the Food Market
No full textThe present paper intends, by using the spectral analysis, to measure and analyze the intensity of systematic variations of the time series referring to one of the most sensitive and important statistical macro-economic indicators, which has a significant impact upon all the economic and social policy decisions – the average monthly rate of consumer prices for food commodities.Fourier series; seasonality; consumer prices; food commodities.
Impact of physical exercise on parameters of arterial stiffness and wave intensity measured at carotid artery level
No full textFinal Report - Nutrient and ecological histories in Barnegat Bay, New Jersey
No full textThe report described a project to collect sediment cores from the tidal region of Barnegat Bay to determine the chronology of nutrient changes and associated ecosystem level responses
Photoelectrochemical Characterization of Sprayed alpha-Fe2O3 Thin Films: Influence of Si Doping and SnO2 Interfacial Layer
No full texta-Fe2O3 thin film photoanodes for solar water splitting were prepared by spray pyrolysis of Fe(AcAc)3. The donor density in the Fe2O3 films could be tuned between 10171020cm-3 by doping with silicon. By depositing a 5 nm SnO2 interfacial layer between the Fe2O3 films and the transparent conducting substrates, both the reproducibility and the photocurrent can be enhanced. The effects of Si doping and the presence of the SnO2 interfacial layer were systematically studied. The highest photoresponse is obtained for Fe2O3 doped with 0.2% Si, resulting in a photocurrent of 0.37mA/cm2 at 1.23VRHE in a 1.0M KOH solution under 80mW/cm2 AM1.5 illumination.Applied Science
Correction to: Gastrointestinal ultrasonographic findings in cats with Feline panleukopenia: a case series (BMC Veterinary Research, (2021), 17, 1, (20), 10.1186/s12917-020-02720-w)
No full textAn amendment to this paper has been published and can be accessed via the original article
The typology of human constitutions in Hippocrates’ De victu 1, 32. Wiener Studien|Wiener Studien 124 124|
No full textThe paper offers an interpretation of a rather intriguing chapter of the Hippocratic treatise De victu. The author argues that the human constitutions described in De victu 1, 32 are to be regarded in the metaphysical and anthropological context of Book I of the treatise, according to which everything can be reduced to two elements (fire and water) and four properties (warm, dry, cold, wet)
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