Geometry of Keplerian disk systems and bounds on masses of their components

We investigate accreting disk systems with polytropic gas in Keplerian motion. Numerical data and partial analytic results show that the self-gravitation of the disk speeds up its rotation -- its rotational frequency is larger than that given by the well known strictly Keplerian formula that takes into account the central mass only. Thus determination of central mass in systems with massive disks requires great care -- the strictly Keplerian formula yields only an upper bound. The effect of self-gravity depends on geometric aspects of disk configurations. Disk systems with a small (circa $10^{-4}$) ratio of the innermost radius to the outermost disk radius have the central mass close to the upper limit, but if this ratio is of the order of unity then the central mass can be smaller by many orders of magnitude from this bound.Comment: 20 pages, 10 figure

Efficient Exploitation of Radio Frequency and Visible Light Communication Bands for D2D in Mobile Networks

The concept of device-to-device (D2D) communication, combining common radio frequency (RF) and visible light communication (VLC), is seen as a feasible way how to cope with spectrum crunch in the RF domain and how to maximize spectral efficiency in general. In this paper, our objective is to decide when RF should be utilized or if VLC proves to be the more profitable option. The selection between RF and VLC is defined as a multi-objective optimization problem targeting primarily to minimize the outage ratio while the secondary objective is to maximize the sum capacity of D2D pairs, composed by D2D transmitters and D2D receivers. To solve this problem, we design a centralized low-complexity heuristic algorithm selecting either RF or VLC band for each D2D pair relying on the mutual interference among the pairs. For interpretation of the mutual interference among the D2D pairs, we exploit directed weighted graphs adopted from the graph theory. The simulation results show that the proposed algorithm outperforms state-of-the-art algorithms in terms of the outage ratio, sum capacity and average energy efficiency. What is more, despite a very low complexity, the proposed algorithm reaches a close-to-optimum performance provided by the exhaustive search algorithm

Enhanced time response of 1-in. LaBr3(Ce) crystals by leading edge and constant fraction techniques

We have characterized in depth the time response of three detectors equipped with cylindrical LaBr$_{3}$ (Ce) crystals with dimensions of 1-in. in height and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and 10%. Measurements were performed at $^{60}$Co and $^{22}$Na {\gamma}-ray energies against a fast BaF$_{2}$ reference detector. The time resolution was optimized by the choice of the photomultiplier bias voltage and the fine tuning of the parameters of the constant fraction discriminator, namely the zero-crossing and the external delay. We report here on the optimal time resolution of the three crystals. It is observed that timing properties are influenced by the amount of Ce doping and the crystal homogeneity. For the crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays in addition to the Hamamatsu R9779 PMT has made it possible to improve the LaBr$_{3}$(Ce) time resolution from the best literature value at 60Co photon energies to below 100 ps.Comment: Article submitted to Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipmen

A new characterization of endogeny

Aldous and Bandyopadhyay have shown that each solution to a recursive distributional equation (RDE) gives rise to recursive tree process (RTP), which is a sort of Markov chain in which time has a tree-like structure and in which the state of each vertex is a random function of its descendants. If the state at the root is measurable with respect to the sigma field generated by the random functions attached to all vertices, then the RTP is said to be endogenous. For RTPs defined by continuous maps, Aldous and Bandyopadhyay showed that endogeny is equivalent to bivariate uniqueness, and they asked if the continuity hypothesis can be removed. We introduce a higher-level RDE that through its $n$-th moment measures contains all $n$-variate RDEs. We show that this higher-level RDE has minimal and maximal fixed points with respect to the convex order, and that these coincide if and only if the corresponding RTP is endogenous. As a side result, this allows us to answer the question of Aldous and Bandyopadhyay positively.Comment: 17 pages. Corrected formula (6.12), part of which was accidentally deleted in the previous versio

Search for octupole correlations in 147^{147}Nd

Properties of excited states in $^{147}$Nd have been studied with multispectra and $\gamma \gamma$ coincidence measurements. Twenty-four new $\gamma$-lines and three new levels have been introduced into the level scheme of $^{147}$Nd. Lifetimes of eight excited levels in $^{147}$Nd, populated in the $\beta$ decay of $^{147}$Pr, have been measured using the advanced time-delayed $\beta\gamma\gamma$(t) method. Reduced transition probabilities have been determined for 30 $\gamma$-transitions in $^{147}$Nd. Potential energy surfaces on the ($\beta_{2}$,$\beta_{3}$) plane calculated for $^{147}$Nd using the Strutinsky method predict two single quasiparticle configurations with nonzero octupole deformation, with K=1/2 and K=5/2. We do not observe parity doublet bands with K=5/2. For pair of opposite parity bands that could form the K=1/2 parity doublet we were able only to determine lower limit of the dipole moment, $|D_0|\geq$0.02 e$\cdot fm$.Comment: Submitted to PR