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[en] The ionospheric medium characterized by its density profile presents an important spatial and temporal variation. At present the access to the profile is obtained either by a modeling of a great number of previously acquired values or by measurements of propagation delays obtained with vertical or oblique soundings working at 2 to 25 MHz. The operation consisting in changing measurements to the density profile is called inversion. For most applications the temporal variation of the ionosphere necessitates obtaining the density profile at least every 15 min. The passage from one to another profile corresponds to what we call reactualizing. The aim of this paper is to propose a method for reactualizing the density profile which rests on both estimated models of propagation (and hence on profile) which initialize the inversion (and which could be assimilated to a previous measurement) and on the measurements of group delay times and/or goniometry for known connections with a limited number of frequencies. The first inversion trials show the originality of the method and also display the following difficulties: important number of parameters, instability, sensitivity to initial conditions (which requires reliable ionospheric forecasts). Numerous HF applications (radiolocation, HF radar, oblique sounding) justify however the interest of this study. The complexity of the problem necessitates a learning phase described briefly in this paper
[en] The ATS-6 data for a period of 1975-76 is used for the study of slab thickness during two moderate storms (Ksub(p)<=4-) around the crest of the anomaly, Ahmedabad and a very great (Ksub(p)<=7), a great (Ksub(p)<=4) and a moderate storm (Ksub(p)<=6+) outside the equatorial anomaly region, Delhi. While at Ahmedabad, on the average, the slab thickness is found to be above the frequency. Comparison of slab thickness with foF2 and the equatorial magnetic record (for Ahmedabad only) shows that the foF2 changes alone cannot be held responsible for the slab thickness variation and thus entry of the plasma flux from the plasmasphere cannot be ruled out. The pressure variation effect of storm-time heating on the slab thickness at Ahmedabad is that even for Ksub(p)=8, the thermal expansion and the contraction effects are unable to explain complete quantitative and qualitative features of the observations
[en] The ionosphere has been subjected to investigation by both the geophysic and geodesy communities. Each with their own concern on the different effects of the ionosphere. In this paper, discussion on a method developed in estimating the vertical electron content using the measured Doppler count observed by a dual frequency transit Doppler receiver is presented. An algorithm developed for the estimation procedure is also discussed. (author)
[en] The performance of correlated optimized effective potential (OEP) functionals based on the spin-resolved second-order correlation energy is analysed. The relative importance of singly- and doubly- excited contributions as well as the effect of scaling the same- and opposite- spin components is investigated in detail comparing OEP results with Kohn–Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaled-opposite–spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view. We find that for high accuracy, a careful, system dependent, selection of the scaling coefficient is required. We analyse several size-extensive approaches for this selection. Finally, we find that a composite approach, named OEP2-SOSh, based on a post-SCF rescaling of the correlation energy can yield high accuracy for many properties, being comparable with the most accurate OEP procedures previously reported in the literature but at substantially reduced computational effort
[en] Synchrotron X-ray reflectivity is used to study the electron density as a function of depth through the bulk water/2-heptanone interface. The measured interfacial width of 7.0 ± 0.2 (angstrom) is comparable to the value calculated from capillary wave theory (7.3 (angstrom)) using the measured interfacial tension of 12.6 mN/m. This result is consistent with capillary wave theory and molecular dynamics simulations that describe a molecularly sharp interface roughened by thermal fluctuations.
[en] One of the proposals under consideration for future upgrades of the LHC injector complex entails the replacement of the PS with the PS2, a longer circumference and higher energy synchrotron, with electron cloud effects representing a potentially serious limitation to the achievement of the upgrade goals. We report on ongoing numerical studies aiming at estimating the e-cloud density threshold for the occurrence of single bunch instabilities.
[en] We propose using beam scrubbing to mitigate the electron cloud effect in the eRHIC. The bunch number is adjusted below the heat load limit, then it increases with the reduced secondary electron yield resulted from the beam scrubbing, up to the design bunch number. Since the electron density threshold of beam instability is lower at the injection, a preliminary injection scrubbing should go first, where large chromaticity can be used to keep the beam in the ring for scrubbing. After that, the beam can be ramped to full energy, allowing physics scrubbing. Simulations demonstrated that with beam scrubbing in a reasonable period of time, the eRHIC baseline design is feasible.