Search

The space segment of the Global Navigation Satellite System (GNSS) is equipped with highly stable atomic clocks. In order to use these clocks as references, their time offsets must be estimated from ground measurements as accurately as possible. This work presents a multi‐frequency and multi‐constellation method for estimating satellite and receiver clock corrections, starting from unambiguous, uncombined, and undifferenced carrier‐phase measurements. A byproduct of the estimation process is phase biases (i.e., the hardware delays of the carrier‐phase measurements occurring at receivers and satellites). The stability and predictability of our clock estimates for receivers and satellites (GPS and Galileo) are compared with those obtained by the International GNSS Service (IGS), whereas the phase biases are assessed against two independent determinations involving combinations of carrier‐phase measurements. We conclude that the method reduces day boundary discontinuities in the clock corrections, and that the estimated phase biases reproduce variabilities already observed by other authors. [ABSTRACT FROM AUTHOR]

We present a FORTRAN code based on a new powerful and efficient computational approach to solve the double exchange problem for high-nuclearity MV clusters containing arbitrary number of localized spins and itinerant electrons. We also report some examples in order to show the possibilities of the program. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [ABSTRACT FROM AUTHOR]

The Abel inversion method is the classic approach to retrieve electron density profiles from radio occultation measurements, assuming that the electron density is only dependent upon height. In the early 2000s, the total electron content (TEC)‐aided inversion method was introduced, where horizontal gradients in the electron density distribution are taken into account by using information from an external model of total electron content (TEC). We show how the quality of the chosen external ionospheric model influences the radio occultation retrievals. Using a two‐layer TEC model, the 68% percentiles of the global error distributions of retrieved critical frequency and bottomside ionospheric electron content for 2014 improve more than 30%, with regard to the classic Abel inversion results. In a well‐sounded region like Europe, this improvement raises to about 40–45%, while 10% improvement is achieved using two‐layer maps with regard to the retrievals using single‐layer TEC maps. We point out that using the TEC to describe the horizontal gradient incurs an implicit mismodeling that, until now, has not been taken into account. A new technique is presented that, thanks to TEC modeling by means of two layers, can assess the impacts of such mismodeling. From this technique, a method to select the most accurate radio occultation retrievals is applied to demonstrate that the resulting errors in the retrieved critical frequencies for the European region are smaller than 7% in nearly 82% of the cases, very similar to the relative difference between measurements of two nearby ionosondes. Key Points: TEC‐aided radio occultation (RO) retrieval of electron density is demonstrated to be more accurate than the classic method assuming spherical symmetryThis accuracy increases with the accuracy of the TEC model used. A method based in two‐layer TEC maps is introduced for selecting the most accurate RO retrievalsCritical frequency RO retrievals aided by two‐layer TEC maps provide similar accuracy as ionosonde measurements in the European region [ABSTRACT FROM AUTHOR]

The compounds K12LnP5W30O110 ·nH2O (Ln3+: Tb, Dy, Ho, Er, Tm, and Yb) are prepared from aqueous solutions of K12.5Na1.5 [NaP5W30O110] and LnCl3 (autoclave, 160 °C, 24 h) and characterized by static and dynamic magnetic measurements. [ABSTRACT FROM AUTHOR]