Intermediate valence of CeNi2Al3 compound and its evidences: Theoretical and experimental approach

We present measurements of magnetic, transport and electronic properties obtained for polycrystalline CeNi2Al3 intermetallic compound. Magnetic susceptibility χ(T) was investigated in the range from 2 to 700 K, and its behavior is characteristic of a compound with unstable valence, varying between Ce3þ and Ce4þ. In the temperature range down to 2 K there was no trace of magnetic order, no anomalies in the temperature dependence of the specific heat were found. The Sommerfeld coefficient extracted from the linear term of the heat capacity takes a value of γ ¼ 21 mJ/(mol K2). The dependence of S(T) is linear up to about 25 K, which is symptomatic of a thermopower in the Fermi’s liquid regime. The structure of satellites in the Ce(3d) electron spectrum obtained by the X-ray photoelectron spectroscopy (XPS) method indicates that the states of Ce(4f) are of mixed valence character. Analysis of Ce(3d) states based on Gunnarsson-Sch€onhammer theory shows that the energy of hybridization of Ce(4f) states with a conduction band is about 78 meV. For more detailed information about electronic states the fully relativistic band structure was calculated within the density functional theory (DFT) for the first time. Below Fermi’s energy, the density of states is mainly formed by Ni(3d) states hybridized with Ce(4f) ones

A gravitationally lensed quasar discovered in OGLE

Indexación: Scopus; Web of Science.We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the ~670deg2 area encompassing the Magellanic Clouds. The source was selected as one of ~60 'red W1-W2' mid-infrared objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made 'the other way around', meaning we first measured the time delay between the two lensed quasar images of -132 < tAB < -76 d (90 per cent CL), with the median tAB ~-102 d (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5 arcsec on the sky, with I ~20.0mag and I ~19.6mag, respectively, and a lensing galaxy that becomes detectable as I ~21.5 mag source, 1.0 arcsec from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at z=2.16 in the New Technology Telescope spectra. The spectral energy distribution (SED) fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of z ~0.9 ± 0.2 (90 per cent CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model). © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.https://academic.oup.com/mnras/article/476/1/663/483368

The Araucaria Project. The Distance to the Local Group Galaxy NGC 6822 from Cepheid Variables discovered in a Wide-Field Imaging Survey

We have obtained mosaic images of NGC 6822 in V and I bands on 77 nights. From these data, we have conducted an extensive search for Cepheid variables over the entire field of the galaxy, and we have found 116 such variables with periods ranging from 1.7 to 124 days. We used the long-period ($>$ 5.6 days) Cepheids to establish the period-luminosity relations in V, I and in the reddening-independent Wesenheit index, which are all very tightly defined. Fitting the OGLE LMC slopes in the various bands to our data, we have derived distance values for NGC 6822 in V, I and ${\rm W}_{\rm I}$ which agree very well among themselves. Our adopted best distance value from the reddening-free Wesenheit index is 23.34 $\pm$ 0.04 (statistical) $\pm$ 0.05 (systematic) mag. This value agrees within the combined 1 sigma uncertainties with a previous distance value derived for NGC 6822 by McAlary et al. from near-IR photometry of 9 Cepheids, but our new value is significantly more accurate. We compare the slopes of the Cepheid PL relation in V and I as determined in the five best-observed nearby galaxies, which span a metallicity range from -1.0 to -0.3 dex, and find the data consistent with no metallicity dependence of the PL relation slope in this range. Comparing the magnitudes of 10-day Cepheids with the I-band magnitudes of the TRGB in the same set of galaxies, there is no evidence either for a significant variation of the period-luminosity zero points in V and I. The available data limit such a zero point variation to less than 0.03 mag, in the considered low-metallicity regime.Comment: Latex, Astronomical Journal accepte

Long and short paths in uniform random recursive dags

In a uniform random recursive k-dag, there is a root, 0, and each node in turn, from 1 to n, chooses k uniform random parents from among the nodes of smaller index. If S_n is the shortest path distance from node n to the root, then we determine the constant \sigma such that S_n/log(n) tends to \sigma in probability as n tends to infinity. We also show that max_{1 \le i \le n} S_i/log(n) tends to \sigma in probability.Comment: 16 page

Interface Mixing in Fe/Si Multilayers Observed by the In Situ Conductance Measurements

In this contribution the in situ conductance vs. deposition time dependences of Fe/Si multilayers are analysed. The plot of resistance multiplied by the square of the thickness as a function of iron thickness shows that during the iron deposition initially amorphous-like Fe-Si mixture is formed, next the mixture crystallises, and finally bcc-Fe phase appears. The interface mixing is also manifested by the reduction of the total multilayer thickness measured by small angle X-ray diffraction

Microlensing optical depth toward the Galactic Bulge using bright sources from OGLE-II

We present a measurement of the microlensing optical depth toward the Galactic Bulge based on 4 years of the OGLE-II survey using Red Clump Giant (RCG). Using 32 events we find tau=2.55_{-0.46}^{+0.57}* 10^{-6} at (l,b)=(1.16, -2.75). Taking into account the measured gradient along the Galactic latitude b, tau = [ (4.48+/- 2.37) + (0.78+/- 0.84)* b]* 10^{-6}, this value is consistent with previous measurements using RCG sources and recent theoretical predictions. We determine the microlensing parameters and select events using a model light curve with the flux blending. We find that ~38% of the OGLE-II events which appear to have RCG sources are actually due to much fainter stars blended with a bright companion. We show explicitly that model fits without blending result in similar tau estimates through partial cancellation of contributions from higher detection efficiency, underestimated time-scales and larger number of selected events. This approach, however, leads to biased time-scale distributions and event rates. Consequently, microlensing studies should carefully consider source confusion effects even for bright stars.Comment: 49 pages and 18 figures, ApJ in press, the value changed due to the systematic correctio

Determination of the map of efficiency of the J-PET detector with the GATE package

A novel PET detector consisting of strips of polymer scintillators is being developed by the J-PET Collaboration. The map of efficiency and the map of geometrical acceptance of the 2-strip J-PET scanner are presented. Map of efficiency was determined using the Monte Carlo simulation software GATE based on GEANT4. Both maps were compared using method based on the chi2 test.Comment: 14 pages, 9 figures, proceeding from conference Symposium on Positron Emission Tomography: http://koza.if.uj.edu.pl/pet-symposium-2013