Statistical analysis and modeling of the local ionospheric critical frequency: a mid-latitude single-station model for use in forecasting

The hourly values of the F-layer critical frequency from the ionospheric sounder in Dourbes (50.1°N, 4.6°E) during the time interval from 1957 to 2010, comprising five solar cycles, were analyzed for the effects of the solar activity. The hourly time series were reduced to hourly monthly medians which in turn were used for fitting a single station foF2 monthly median model. Two functional approaches have been investigated: a statistical approach and a spectral approach. The solar flux F10.7 is used to model the dependence of foF2 on the solar activity and is incorporated into both models by a polynomial expression. The statistical model employs polynomial functions to fit the F-layer critical frequency while the spectral model is based on spectral decomposition of the measured data and offers a better physical interpretation of the fitting parameters. The daytime and nighttime foF2 values calculated by both approaches are compared during high and low solar activity. In general, the statistical model has a slightly lower uncertainty at the expense of the larger number of fitting parameters. However, the spectral approach is superior for modeling the periodic effects and performs better when comparing the results for high and low solar activity. Comparison with the International Reference Ionosphere (IRI 2012) shows that both local models are better at describing the local values of the F-layer critical frequency

Vibrational properties of alpha- and sigma-phase Fe-Cr alloy

Experimental investigation as well as theoretical calculations, of the Fe-partial phonon density-of-states (DOS) for nominally Fe_52.5Cr_47.5 alloy having (a) alpha- and (b) sigma-phase structure were carried out. The former at sector 3-ID of the Advanced Photon Source, using the method of nuclear resonant inelastic X-ray scattering, and the latter with the direct method [K. Parlinski et al., Phys. Rev. Lett. {78, 4063 (1997)]. The characteristic features of phonon DOS, which differentiate one phase from the other, were revealed and successfully reproduced by the theory. Various data pertinent to the dynamics such as Lamb-Mossbauer factor, f, kinetic energy per atom, E_k, and the mean force constant, D, were directly derived from the experiment and the theoretical calculations, while vibrational specific heat at constant volume, C_V, and vibrational entropy, S were calculated using the Fe-partial DOS. Using the values of f and C_V, we determined values for Debye temperatures, T_D. An excellent agreement for some quantities derived from experiment and first-principles theory, like C_V and quite good one for others like D and S was obtained.Comment: 4 pages, 3 figure

Experimental and numerical study of local mean age of air

This paper presents the results from the experimental and numerical study of a room with mixing ventilation, focused on the local mean age of air (LMA). The measurements were performed using the tracer gas concentration decay method. The numerical predictions were obtained from the computational fluid dynamics (CFD) module of the latest version of the ESP-r software

To realisation of chromatic polynomial calculation algorithm

We calculate chromatic polynomial of an undirected graph using the fundamental reduction theorem and reducing to complete graphs. We also find the chromatic number using the chromatic polynomial. The C++ program was created, the result is obtained in the form of falling factorials and afterwards by the powers of x, the applications of chromatic polynomial are given

Ionosphere-plasmasphere response to geomagnetic storms studied with the RMI-Dourbes comprehensive database

Presented is a review of the ionospheric storm research carried out at the Royal Meteorological Institute (RMI)of Belgium.The studies are based on the opportunities offered by the long-term measurements and the accumulated comprehensive database managed by the RMI Geophysics Centre at Dourbes (4.6 °E,50.1 °N).Reported are case studies of major storms,and also results in developing forecasting and density reconstruction methods

Extended reaction kinetics model for non-thermal argon plasmas and its test against experimental data

An extended reaction kinetics model (RKM) suitable for the analysis of weakly ionised, non-thermal argon plasmas with gas temperatures around 300 K at sub-atmospheric and atmospheric pressures is presented. It considers 23 different species including electrons as well as the ground state atom, an atomic and molecular ion, four excited molecular states, and 15 excited atomic states of argon, where all individual 1s and 2p states (in Paschen notation) are included as a separate species. This 23-species RKM involves 409 collision processes and radiative transitions and recent electron collision cross section data. It is evaluated by means of results of time- and space-dependent fluid modelling of argon discharges and their comparison with measured data for two different dielectric barrier discharge configurations as well as a micro-scaled atmospheric-pressure plasma jet setup. The results are also compared with those obtained by use of a previously established 15-species RKM involving only the two lumped 2p states 2p10…5 and 2´p4 … 1. It is found that the 23-species RKM shows generally better agreement with experimental data and provides more options for direct comparison with measurements than the frequently used 15-species RKM

The effect of oxygen admixture on the properties of microwave generated plasma in Ar-O2: A modelling study

This work presents results of a self-consistent modelling analysis on microwave plasma generated in Ar-O2 mixtures at a frequency of 2.45 GHz at atmospheric pressure. The study focuses on how the plasma properties are influenced by the increase of the oxygen fraction in the gas mixture. The oxygen admixture is increased from 1% up to 95% in mass for values of the input microwave power of 1 and 1.5 kW. The results show that for a power of 1 kW and gradually increasing the oxygen admixture from 1% to 25% the electron density drops by a factor of more than four due to the energy lost by the electrons due to dissociation of oxygen molecules and the gas heating. An analysis of the number densities of species produced in the Ar-O2 plasma is presented. Oxygen admixtures of above 50% are considered along with an increase of the input microwave power in order to supply the discharge with electron number density values of the order of 1019 m-3. Gas temperatures above 3700 K are obtained in the plasma core along with a strong production of oxygen atoms with a number density of the order of 1023 m-3

Cryogenic heat exchangers for process cooling and renewable energy storage: A review

© 2019 The cryogenic industry has experienced remarkable expansion in recent years. Cryogenic technologies are commonly used for industrial processes, such as air separation and natural gas liquefaction. Another recently proposed and tested cryogenic application is Liquid Air Energy Storage (LAES). This technology allows for large-scale long-duration storage of renewable energy in the power grid. One major advantage over alternative storage techniques is the possibility of efficient integration with important industrial processes, e.g., refrigerated warehousing of food and pharmaceuticals. Heat exchangers are among the most important components determining the energy efficiency of cryogenic systems. They also constitute the necessary interface between a LAES system and the industrial process utilizing the available cooling effect. The present review aims to familiarise energy professionals and stakeholders with the latest achievements, innovations, and trends in the field of cryogenic heat exchangers, with particular emphasis on their applications to LAES systems employing renewable energy resources. Important innovations in coil-wound and plate-fin heat exchanger design and simulation methods are reviewed among others, while special attention is given to regenerators as a prospective component of cryogenic energy storage systems. This review also reveals that the geographical spread of research and development activities has recently expanded from well-established centers of excellence to rather active emerging establishments around the globe

Ab initio and nuclear inelastic scattering studies of Fe3_3Si/GaAs heterostructures

The structure and dynamical properties of the Fe$_3$Si/GaAs(001) interface are investigated by density functional theory and nuclear inelastic scattering measurements. The stability of four different atomic configurations of the Fe$_3$Si/GaAs multilayers is analyzed by calculating the formation energies and phonon dispersion curves. The differences in charge density, magnetization, and electronic density of states between the configurations are examined. Our calculations unveil that magnetic moments of the Fe atoms tend to align in a plane parallel to the interface, along the [110] direction of the Fe$_3$Si crystallographic unit cell. In some configurations, the spin polarization of interface layers is larger than that of bulk Fe$_3$Si. The effect of the interface on element-specific and layer-resolved phonon density of states is discussed. The Fe-partial phonon density of states measured for the Fe$_3$Si layer thickness of three monolayers is compared with theoretical results obtained for each interface atomic configuration. The best agreement is found for one of the configurations with a mixed Fe-Si interface layer, which reproduces the anomalous enhancement of the phonon density of states below 10 meVComment: 14 pages, 9 figures, 4 table