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[en] This paper presents an analysis of available options of restructuring of energy sector within the broader context of economic development without undermining the global climate. Such restructuring involves active implementation of emission free energy sources which ensure sustainable generation of electricity of standard quality in a climate-friendly way. Using available statistical data, the authors analyzed the dynamics of global energy consumption in relation to the level of economic development. The hypothesis of saturation of energy demand during the transition to post-industrial economic development has been confirmed. Saturation of energy demand creates opportunities for a wide scale utilization of innovative ecological methods of climate stabilization and environmental restoration. Restructuring of energy sector in environmentally-safe manner can be especially important in the conditions of fast economic growth of the world’s largest developing economies (China and India). Economic growth in these countries is currently characterized by a rapid increase in energy consumption and greenhouse gas emissions. This paper provides quantitative estimates of the investments required for stabilization of global climate under the projections of future energy demands over the next three decades. The proposed scenario of restructuring of energy sector can be economically feasible, and it is quite likely that electricity in the future will be mainly generated from renewable energy sources and nuclear energy. The numeric estimates and the analysis presented in this paper can be used in formulation of climate stabilization policies in a rapidly growing global economy. (author)
[en] The heat transport system of GEN-IV Supercritical Water-Cooled Nuclear Reactors (SCWRs) will operate at pressures close to 25 MPa and outlet temperatures of up to 898 K (625℃). The design and safety analyses of this type of reactors, still necessitate experimental information and validation of pressure drop correlations, the deterioration of forced convection heat transfer and critical (choked) flows models of water above the thermodynamic critical state. Up to now, choked flow data have been collected from experiments carried out at atmospheric discharge pressure conditions, without changing the discharge pressure to verify the occurrence of choking flow and in most of the cases using fluids different than water. This paper presents experimental supercritical water choking flow data collected at Polytechnique Montréal using a convergent-divergent test section by changing the discharge pressure to verify the occurrence of choked flow. The critical mass flux is presented as a function of the temperature difference between a pseudo-critical temperature and the bulk fluid temperature. This representation allows us to assess similar experiments performed by using different test sections. Hence, a comparison of data collected with the actual test section with those previously obtained using 1.0 mm and 1.4 mm diameter sharp-edged orifices, shows peculiar differences. The actual experiments were limited by extremely low values of choking mass flow rates. Furthermore, in some cases, it was observed the presence of an increase in the discharge pressure which seems to indicate the existence of shock-wave structures. As in our previous experiments, we are also able to estimate a pseudo-critical temperature difference below which choking flow systematically occurs. (author)
[en] The results for 2018 presented in this report show that the expansion of renewable energies is making a significant contribution to achieving the climate protection targets in Germany. Overall, fossil energy sources are increasingly being replaced by renewable energies in all consumption sectors, thus permanently avoiding greenhouse gas and air pollutant emissions. Furthermore, the results show that a differentiated consideration of different technologies and sectors is useful and necessary, e.g. when it comes to deriving targeted measures for climate protection and air pollution control, since the specific abatement factors for the greenhouse gases and air pollutants investigated differ considerably in some cases. As a result, the net emissions balance of renewable energy, taking into account upstream chains, shows an avoidance of greenhouse gas emissions of about 187 million tons of CO-equivalents (CO-eq.) in 2018. The electricity sector accounted for 140 million t CO-eq, of which 124 million t are attributable to the amount of electricity eligible for EEG compensation. The heat sector avoided 35 million t and biogenic fuels avoided 8 million t CO-eq. In general, it can be stated that for electricity and heat, the result is significantly influenced by which fossil fuels are replaced by renewable energy sources. In the case of biofuels, the type and origin of the raw materials used are particularly decisive. Unless they are biogenic residues or waste, land-use changes caused by the agricultural cultivation of the energy crops must be taken into account.
[de]Die in diesem Bericht aufgeführten Ergebnisse für das Jahr 2018 zeigen, dass der Ausbau erneuerbarer Energien wesentlich zur Erreichung der Klimaschutzziele in Deutschland beiträgt. Insgesamt werden in allen Verbrauchssektoren fossile Energieträger zunehmend durch erneuerbare Energien ersetzt und damit dauerhaft Treibhausgas- und Luftschadstoffemissionen vermieden. Die Ergebnisse zeigen darüber hinaus, dass eine differenzierte Betrachtung verschiedener Technologien und Sektoren sinnvoll und notwendig ist, wenn es z.B. darum geht, gezielte Maßnahmen zum Klimaschutz und der Luftreinhaltung abzuleiten, da sich die spezifischen Vermeidungsfaktoren für die untersuchten Treibhausgase und Luftschadstoffe teilweise erheblich unterscheiden. Im Ergebnis weist die Netto-Emissionsbilanz der erneuerbaren Energien unter Berücksichtigung der Vorketten eine Vermeidung von Treibhausgasemissionen in Höhe von rund 187 Mio. t CO -Äquivalente (CO-Äq.) im Jahr 2018 aus. Auf den Stromsektor entfielen 140 Mio. t CO-Äq., davon sind 124 Mio. t der Strommenge mit EEG-Vergütungsanspruch zuzuordnen. Im Wärmesektor wurden 35 Mio. t und durch biogene Kraftstoffe 8 Mio. t CO-Äq. vermieden. Generell lässt sich feststellen, dass bei Strom und Wärme das Ergebnis maßgeblich dadurch beeinflusst wird, welche fossilen Brennstoffe durch erneuerbare Energieträger ersetzt werden. Bei den Biokraftstoffen sind insbesondere die Art und Herkunft der verwendeten Rohstoffe ausschlaggebend. Sofern es sich dabei nicht um biogene Reststoffe oder Abfälle handelt, sind Landnutzungsänderungen durch den landwirtschaftlichen Anbau der Energiepflanzen zu beachten.
[en] Biomass has attracted considerable attention as energy, economic, and environmental asset, as result of its abundance and range of properties. The use of mesoporous catalysts during fast pyrolysis has been a highly important route to improve efficiency as well adding value to biomass. The addition of titanium to molecular sieves increases the efficiency of the pyrolysis reaction by improving production and selectivity of products of interest. This study aims at analyzing the catalytic pyrolysis products of elephant grass using titanium catalysts prepared at different Si/Ti molar ratios, i.e., 25 and 50. The material was supported on MCM-41 for the catalytic pyrolysis of biomass. The biomass pyrolysis reactions were performed in a micropyrolyzer coupled to a GC/MS analyzer. The Ti-MCM-41 samples were characterized by XRD, BET-specific area, and UV-visible. The distribution of pyrolysis products depended on process parameters such as temperature and catalyst type. The highest yield for hydrocarbon production, such as styrene, benzene, methylbenzene, and naphthalene, was observed at 600 °C using Si/Ti equal to 50.
[en] Many-body dipolar effects in Fermi gases are quite subtle as they energetically compete with the large kinetic energy at and below the Fermi surface (FS). Recently it was experimentally observed in a sample of erbium atoms that its FS is deformed from a sphere to an ellipsoid due to the presence of the anisotropic and long-range dipole–dipole interaction Aikawa et al (2014 Science 345 1484). Moreover, it was suggested that, when the dipoles are rotated by means of an external field, the FS follows their rotation, thereby keeping the major axis of the momentum-space ellipsoid parallel to the dipoles. Here we generalise a previous Hartree–Fock mean-field theory to systems confined in an elongated triaxial trap with an arbitrary orientation of the dipoles relative to the trap. With this we study for the first time the effects of the dipoles’ arbitrary orientation on the ground-state properties of the system. Furthermore, taking into account the geometry of the system, we show how the ellipsoidal FS deformation can be reconstructed, assuming ballistic expansion, from the experimentally measurable real-space aspect ratio after a free expansion. We compare our theoretical results with new experimental data measured with erbium Fermi gas for various trap parameters and dipole orientations. The observed remarkable agreement demonstrates the ability of our model to capture the full angular dependence of the FS deformation. Moreover, for systems with even higher dipole moment, our theory predicts an additional unexpected effect: the FS does not simply follow rigidly the orientation of the dipoles, but softens showing a change in the aspect ratio depending on the dipoles’ orientation relative to the trap geometry, as well as on the trap anisotropy itself. Our theory provides the basis for understanding and interpreting phenomena in which the investigated physics depends on the underlying structure of the FS, such as fermionic pairing and superfluidity. (paper)
[en] Transitions between magnetic states of one and two ring kagome spin ice elements consisting of 6 and 11 prolate magnetic islands are calculated and the lifetime of the ground states evaluated using harmonic transition state theory and the stationary state approximation. The calculated values are in close agreement with experimental lifetime measurements made by Farhan and co-workers (Farhan et al 2013 Nat. Phys. 9 375) when values of the parameters in the Hamiltonian are chosen to be best estimates for a single island, obtained from measurements and micromagnetic modeling. The effective pre-exponential factor in the Arrhenius rate law for the elementary steps turns out to be quite small, on the order of 109 s−1, three orders of magnitude smaller than has been assumed in previous analysis of the experimental data, while the effective activation energy is correspondingly lower than the previous estimate. The application of an external magnetic field is found to strongly affect the energy landscape of the system. Even a field of can eliminate states that correspond to ground states in the absence of a field. The theoretical approach presented here and the close agreement found with experimental data demonstrates that the properties of spin ice systems can be calculated using the tools of rate theory and a Hamiltonian parametrized only from the properties of a single island. (paper)
[en] The fission pathway of even–even actinide nuclei have been systematically calculated using the deformation-constrained nuclear density functional theory beyond the second fission barriers within the UNEDF1 energy-density functionals (EDFs). Our calculated results show that, allowing for triaxial deformation, the second fission barriers are lowered by a few hundreds of keV to 2 MeV. For the heaviest actinides, it is found that inclusion of triaxial deformation reduces the outer barrier significantly.
[en] Highly microporous carbons were prepared from argan nut shell (ANS) using steam activation method. The carbons prepared (ANS@H2O-30, ANS@H2O-90, and ANS@H2O-120) were characterized using X-ray diffraction, scanning electron microscopy, Fourier-transform infrared, nitrogen adsorption, total X-ray fluorescence, and temperature-programmed desorption (TPD). The ANS@H2O-120 was found to have a high surface area of 2853 m2/g. The adsorption of bisphenol A and diuron on ANS@H2O-120 was investigated. The isotherm data were fitted using Langmuir and Freundlich models. Langmuir isotherm model presented the best fit to the experimental data suggesting micropore filling of ANS@H2O-120. The ANS@H2O-120 adsorbent demonstrated high monolayer adsorption capacity of 1408 and 1087 mg/g for bisphenol A and diuron, respectively. The efficiency of the adsorption was linked to the porous structure and to the availability of the surface adsorption sites on ANS@H2O-120. Response surface method was used to optimize the removal efficiency of bisphenol A and diuron on ANS@H2O-120 from aqueous solution. .