Periodic orbit spectrum in terms of Ruelle--Pollicott resonances

Fully chaotic Hamiltonian systems possess an infinite number of classical solutions which are periodic, e.g. a trajectory ``p'' returns to its initial conditions after some fixed time tau_p. Our aim is to investigate the spectrum tau_1, tau_2, ... of periods of the periodic orbits. An explicit formula for the density rho(tau) = sum_p delta (tau - tau_p) is derived in terms of the eigenvalues of the classical evolution operator. The density is naturally decomposed into a smooth part plus an interferent sum over oscillatory terms. The frequencies of the oscillatory terms are given by the imaginary part of the complex eigenvalues (Ruelle--Pollicott resonances). For large periods, corrections to the well--known exponential growth of the smooth part of the density are obtained. An alternative formula for rho(tau) in terms of the zeros and poles of the Ruelle zeta function is also discussed. The results are illustrated with the geodesic motion in billiards of constant negative curvature. Connections with the statistical properties of the corresponding quantum eigenvalues, random matrix theory and discrete maps are also considered. In particular, a random matrix conjecture is proposed for the eigenvalues of the classical evolution operator of chaotic billiards

A Global View on Star Formation: The GLOSTAR Galactic Plane Survey: II Supernova Remnants in the first quadrant of the Milky Way

Context. The properties of the population of the Galactic Supernova Remnants (SNRs) are essential to our understanding of the dynamics of the Milky Way’s interstellar medium (ISM). However, the completeness of the catalog of Galactic SNRs is expected to be only ∼30%, with on order 700 SNRs yet to be detected. Deep interferometric radio continuum surveys of the Galactic plane help in rectifying this apparent deficiency by identifying low surface brightness SNRs and compact SNRs that have not been detected in previous surveys. However, SNRs are routinely confused with H ii regions, which can have similar radio morphologies. Radio spectral index, polarization, and emission at mid-infrared (MIR) wavelengths can help distinguish between SNRs and H ii regions. Aims. We aim to identify SNR candidates using continuum emission from the Karl G. Jansky Very Large Array Global view of the Star formation in the Milky Way (GLOSTAR) survey. Methods. GLOSTAR is a C-band (4–8 GHz) radio wavelength survey of the Galactic plane covering 358◦ ≤ l ≤ 60◦, |b| ≤ 1◦. The continuum images from this survey that resulted from observations in the array’s most compact configuration have an angular resolution of 18″. We searched for SNRs in these images to identify known SNRs, previously-identified SNR candidates and new SNR candidates. We study these objects in MIR surveys and the GLOSTAR polarization data to classify their emission as thermal or nonthermal. Results. We identify 157 SNR candidates, out of which 80 are new. Polarization measurements provide evidence of nonthermal emission from 9 of these candidates. We find that two previously identified candidates are filaments. We also detect emission from 91 out of 94 known SNRs in the survey region. Four of these are reclassified as H ii regions following detection in MIR surveys. Conclusions. The better sensitivity and resolution of the GLOSTAR data have led to the identification of 157 SNR candidates, along with the reclassification of several misidentified objects. We show that the polarization measurements can identify nonthermal emission, despite the diffuse Galactic synchrotron emission. These results underscore the importance of higher resolution and higher sensitivity radio continuum data in identifying and confirming SNRs

Theoretical investigation on site preference of foreign atoms in rare-earth intermetallics

This paper adopts the lattice inversion method in acquiring the interatomic potentials related to rare-earth and transition metals and characterizes the site occupancies of Fe and Co in Y(Co,Fe)5, Y2(Co,Fe)17, Y3(Fe,Co,M)29, and YTi(Fe,Co)11 by combining these potentials with computer simulation. The results of this research are in good agreement with experimental data. The substitution behaviors and the energy variation introduced by alloying elements M (M=V, Mo, Cu, Ni) in YTi(Fe,M)11 are also calculated. A special importance is laid on the statistical analysis of the structure of YTi(Fe,Co)11. This research is the first to present the phonon density of states of 1:12 structures, and it also carries out a qualitative analysis featuring the coordination and the relevant potentials

SiO2 modified Co-ferrite with high coercivity

Journal of Magnetism and Magnetic Materials226-230PART II1382-1384JMMM

Improved hydrogen storage of LiBH4 catalyzed magnesium

The effect of LiBH4 on the hydrogen sorption performance of magnesium was investigated. It was found that the hydrogen storage properties of LiBH4/Mg mixtures exhibit a dramatic improvement as compared to plain magnesium powder. For example, at 250°C, a LiBH4/Mg (mass ratio 1:4) composite can absorb 6.7 wt % hydrogen in 60 min, while only less than 1 wt % hydrogen was absorbed by pure magnesium in the same period under similar conditions. The hydrogen desorption properties of the composite at 350°C were also improved significantly as compared to the plain magnesium powder. Furthermore, highly activated magnesium hydride was synthesized directly by ball milling LiBH4/Mg mixtures under high hydrogen pressure. The synthesized magnesium hydride exhibits superior kinetics, absorbing 5.78 wt % hydrogen at the relatively low temperature of 200°C within 100 min