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[en] To study the dynamics resonances of the Cl + HD reaction which was proposed to proceed via abstraction mechanism with no clear resonances, we perform dynamics calculations by the multiconfiguration time-dependent Hartree (MCTDH) method based on recently developed neural-networks potential energy surface (Science 347 (2015), 60). The HD molecule in (GS), (EX1), (EX2), and (EX3) states is used for the reactant. For GS, no distinctive resonance peak is found, while for EX1 two distinctive peaks at kinetics energies of and eV are investigated. These resonance peaks are well consistent with the previous results (Science 347 (2015), 60). Moreover, the present MCTDH calculations predict well-marked resonance peaks at , and eV for EX2 and EX3, which indicates that anticipation of the chemical bond softening model (Science 327 (2010), 1501) is confirmed in this work.
[en] The necessity and opportunity of the flywheel usage in the compact hydro-aggregate are considered. An external damping system for a compact hydro-aggregate is developed, and the methods for its realization are given. The opportunity of the flywheel installation as a hydro-aggregate external damping system is presented. The order of calculating the massive rotor parameters of the external damping system is introduced, which can be done based on an equivalent circuit by using the complex magnetic resistance at different operation modes. The mechanical characteristics of the external damping system are calculated and compared with the experimental data where a maximum discrepancy is no more than 6 percent
[en] As star-forming clouds collapse, the gas within them fragments to ever-smaller masses. Naively one might expect this process to continue down to the smallest mass that is able to radiate away its binding energy on a dynamical time-scale, the opacity limit for fragmentation, at ~0.01M⊙. However, the observed peak of the initial mass function (IMF) lies a factor of 20-30 higher in mass, suggesting that some other mechanism halts fragmentation before the opacity limit is reached. Here, we analyse radiation-magnetohydrodynamic simulations of star cluster formation in typical Milky Way environments in order to determine what physical process limits fragmentation in them. We examine the regions in the vicinity of stars that form in the simulations to determine the amounts of mass that are prevented from fragmenting by thermal and magnetic pressure. We show that, on small scales, thermal pressure enhanced by stellar radiation heating is the dominant mechanism limiting the ability of the gas to further fragment. In the brown dwarf mass regime, ~0.01M⊙, the typical object that forms in the simulations is surrounded by gas whose mass is several times its own that is unable to escape or fragment, and instead is likely to accrete. This mechanism explains why ~0.01M⊙ objects are rare: unless an outside agent intervenes (e.g. a shock strips away the gas around them), they will grow by accreting the warmed gas around them. In contrast, by the time stars grow to masses of ~0.2M⊙, the mass of heated gas is only tens of percent of the central star mass, too small to alter its final mass by a large factor. This naturally explains why the IMF peak is at ~0.2M⊙.
[en] Highlights: • CFD method is used to predict natural circulation under swing motions. • CFD method can avoid using land-based correlations to swing system. • Pseudo-steady mass flux amplitude increases linearly with swing angles. • Swing phase difference significantly changes the pseudo-steady parameters. - Abstract: In nuclear power systems, the natural circulation loop will startup to remove the residual heat after losing the power for the forced circulation. The natural circulation will startup if the driving force caused by the density difference is large enough to overcome the resistance of the loop, however, the system will encounter additional forces, including the transport force and the Coriolis force, which may change the driving force and break the stability of natural circulation. In this work, the CFD model for a natural circulation loop was developed to study the dynamic startup performances and the pseudo steady-state operations under swing conditions. Using CFD methodology can avoid employing the correlations for wall friction and heat transfer using in system code, which may be not applicable for swing systems. Based on the CFD analysis, parametric studies were carried out, including swing period, maximum swing angle, heat power, swing center and the swing phase difference. The swing angle, swing period, swing phase difference and heated power can significantly affect the thermohydraulics and stability of the natural circulation systems, while the swing radius has little influence. This work proved that CFD methodology may be qualified for analyzing the natural circulation system under swing conditions.
[en] In this work we investigate the Renner-Teller effect (RTE) in the photoelectron spectra of ClCN and BrCN. The spectra were calculated by a nuclear wave packet propagation on coupled cationic surfaces obtained by the four-component Fock-space coupled cluster method. The scalar relativistic, spin-orbit and electron correlation effects are consistently included in the hypersurfaces for the three internal nuclear degrees of freedom. In contrast to other approaches no coupling matrix elements involving the spin-orbit operator together with an explicit representation of the wave function were necessary. The current study extends earlier work on the RTE for the derivation of the Renner-Teller parameters c and d where only one nuclear degree of freedom was considered (Pernpointner and Salopiata, 2013). The outlined procedure is especially useful for electronic structure methods that yield accurate energies but do not provide an explicit wave function representation.
[en] Following the example of other environmental footprints (such as the carbon footprint), the 'material footprint' is an indicator that allows us to take into account the full amount of raw materials used to satisfy a given country's level of domestic consumption. The results provide a better representation of the true impact of resource use, including both materials extracted within the country and those mobilized indirectly outside our borders in order to produce and transport imported products. The inclusion of indirect material flows raises significantly the level of the quantified apparent flows. These indirect flows involve, notably, imports of fossil fuels and metallic minerals, both of which contribute to increasing France's material footprint. Our national footprint stood at 13.2 tonnes per capita in 2014, yet remains lower than the European average, and has fallen slightly since 2008
[en] Highlights: • Historical overview of the development of advanced reactors. • Focus on the Generation IV International Forum and role of international collaboration. • Identification of challenges to be addressed to enable deployment of advanced reactors. - Abstract: This paper provides a historical overview of the development of advanced reactors, with a focus on Generation IV reactors and the unique international cooperative R&D framework that was put in place within the Generation IV International Forum. Drawing on the expertise developed at the Nuclear Energy Agency, the paper analyses the challenges for deploying advanced reactors in future energy markets, including evolving market requirements and economic considerations, regulatory challenges, research infrastructure needs and human resource issues. The paper concludes on the role of nuclear research and innovation to ensure the conditions for successful deployment of advanced reactors and competition with alternative technologies.
[en] Highlights: • Biodiversity and ecosystem services of biomass crops were studied at plot to landscape levels. • Metrics of biodiversity included taxonomic richness of plants, insects, soil microbes and birds. • Biodiversity and ecosystem processes generally increased with increasing perenniality and within-crop diversity. • Evaluating tradeoffs among ecosystem services can inform biomass crop selection and placement in agricultural landscapes. - Abstract: Biomass cropping systems have the potential to alter the ecosystem services provided by agricultural landscapes. Depending on crop type and management, strategic incorporation of biomass cropping systems into existing agricultural landscapes could enhance a range of ecosystem services while mitigating some disservices. Here, we review the approaches and findings of eight years of research into the potential effects of a range of biomass cropping systems on ecosystem services in the North Central US. Our research was framed by an initial assessment of the abundance and distribution of multiple taxa (i.e., biodiversity) within candidate biomass cropping systems. The processes underpinning important ecosystem services in each system were then measured or modeled, related to biodiversity metrics, and used to explore the influence of management scenarios on biodiversity and ecosystem processes. We also used these data and models to develop a decision support system that allows stakeholders to consider tradeoffs and synergies under alternative landscape composition, configuration, and agronomic management. Perennial grass cropping systems provided the greatest potential to promote multiple ecosystem services. More diverse perennial grasslands that include forbs have the potential to increase pest suppression and pollination, decrease greenhouse gas emissions, and enhance grassland bird communities, but likely at the expense of biomass yield. Providing stakeholders and policymakers with information about the expected mix of ecosystem services supported by different biomass feedstock cropping systems in advance of their adoption offers the potential for informed choices to guide the implementation and management of future biomass-producing landscapes.
[en] Atriplex canescens canopy cover, biomass production, and nutrient content were evaluated after four years of livestock grazing exclusion and mechanical shrub removal, except A. canescensin an arid rangeland with a slightly saline soil and with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico (24° N). Twenty 3 × 3 m paddocks were established in terrains with three levels of electric conductivity (EC): <1.4 dS/m (n=7), 1.4–1.6 dS/m (n=7) and >1.6 dS/m. Atriplex canescens canopy cover was higher (49.5%; p<0.01) on paddocks with soil EC >1.6 dS/m than paddocks with soil EC <1.4 and 1.4–1.6 dS/m (32.1 and 22.9%, respectively). Above-ground biomass did not differ between paddocks with soils with EC of <1.4 and 1.4–1.6 dS/m (1309 ± 535 and 1372 ± 180 kg DM/ha), but biomass increased 2.7 times (p<0.01) when soil EC was greater than 1.6 dS/m. The soil EC had no effect on the levels of crude protein (range 13.6 to 14.3%), neutral detergent fiber (range 56.5 to 57.7%) and ash (range 14.5 to 16.4%). In vitro dry matter digestibility (IVDMD) of the foliage of A. canescens was not affected by of soil EC level (range 60.4 to 62.2%). It was concluded that in an arid rangeland with slight saline soil, the increase in salinity favors canopy cover and biomass production of A. canescens without altering nutrient content and IVDMD of this fodder shrub.
[en] Highlights: • The LBE-helium experimental loop of ADS (LELA) is introduced. • The ε-NTU correlation of LBE-helium heat exchanger is verified experimentally. • The effectiveness of LBE-helium heat exchanger is 0.8–0.88 at Rc = 0.45–0.77. • Pressure drops and heat transfer characteristics are investigated experimentally. - Abstract: Accelerator driven sub-critical system (ADS) has been universally regarded as the most promising approach to dispose the long-lived nuclear wastes. Lead bismuth eutectic (LBE) is the suitable coolant and spallation target material for ADS. But some theoretical models and empirical correlations of LBE are different from that of the existing conventional fluid. The performances of intermediate heat exchanger and heat transfer characteristics of LBE-helium two-loop cooling system are still not fully understood. The experimental investigation of the LBE-helium heat exchanger is performed in the present research. The effectiveness-NTU correlation of LBE-helium heat exchanger is verified experimentally in the LBE-helium experimental loop of ADS. The experimental results indicate that the effectiveness of LBE-helium heat exchanger is 0.8–0.88 at Rc = 0.45–0.77. The Moody correlation of friction factor is in reasonable agreement with the experimental data. The overall heat transfer coefficient and actual heat transfer rate increase with increasing LBE inlet temperature, and decrease with increasing helium inlet temperature. As helium inlet flowrate increases, overall heat transfer coefficient and actual heat transfer rate increase remarkably.