Gradient boosting decision trees classification of blazars of uncertain type in the fourth Fermi-LAT catalog

The deepest all-sky survey available in the $\gamma$-ray band - the last release of the Fermi-LAT catalogue (4FGL-DR3) based on the data accumulated in 12 years, contains more than 6600 sources. The largest population among the sources is blazar subclass - 3743, $60.1\%$ of which are classified as BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the rest are listed as blazar candidates of uncertain type (BCU) as their firm optical classification is lacking. The goal of this study is to classify BCUs using different machine learning algorithms which are trained on the spectral and temporal properties of already classified BL Lacs and FSRQs. Artificial Neural Networks, \textit{XGBoost} and LightGBM algorithms are employed to construct predictive models for BCU classification. Using 18 input parameters of 2219 BL Lacs and FSRQs, we train (80\% of the sample) and test (20\%) these algorithms and find that LightGBM model, state-of-the-art classification algorithm based on gradient boosting decision trees, provides the highest performance. Based on our best model, we classify 825 BCUs as BL Lac candidates and 405 as FSRQ candidates, however, 190 remain without a clear prediction but the percentage of BCUs in 4FGL is reduced to 5.1\%. The $\gamma$-ray photon index, synchrotron peak frequency, and high energy peak frequency of a large sample are used to investigate the relationship between FSRQs and BL Lacs (LBLs, IBLs, and HBLs).Comment: Accepted for publication in MNRA

Modeling of Nanoindentation in Ni-Graphene Nanocomposites: A Molecular Dynamics Sensitivity Study

Using molecular dynamics simulation, we perform nanoindentation simulations on a Ni-graphene model system, in which a graphene flake coats the grain boundary of a Ni bi-crystal. Material strengthening or weakening by inclusion of graphene is discussed with the help of the force needed to indent to a specified depth. By varying the depth of the graphene flake with respect to the indentation depth we identify the distance up to which graphene influences the indentation behavior. In addition, we vary the details of the modeling of the graphene flake in the matrix metal and determine their influence on the performance of the nanocomposite. Our results indicate that the modeling results are robust against variations in the modeling of the graphene flake

Nonequilibrium electrons in tunnel structures under high-voltage injection

We investigate electronic distributions in nonequilibrium tunnel junctions subject to a high voltage bias $V$ under competing electron-electron and electron-phonon relaxation processes. We derive conditions for reaching quasi-equilibrium and show that, though the distribution can still be thermal for low energies where the rate of the electron-electron relaxation exceeds significantly the electron-phonon relaxation rate, it develops a power-law tail at energies of order of $eV$. In a general case of comparable electron-electron and electron-phonon relaxation rates, this tail leads to emission of high-energy phonons which carry away most of the energy pumped in by the injected current.Comment: Revised versio

Effect of autoclave processing and gamma irradiation on apparent ileal amino acids digestibility of cottonseed meal in male broiler breeders

The objective of this study was to investigate the effect of autoclaving and different doses of gamma irradiation on the apparent ileal digestibility of amino acids of cottonseed meal in male broiler breeders. Samples were irradiated in a gamma cell at total doses of 15, 30 and 45 kGy. One package (control) was left at room temperature: Similar to the other treatments, evaporation decreased the moisture content of the samples. Autoclaving of cottonseed meal for 15 min at 121°C was studied. The treatments were: (1) control, untreated cottonseed meal diet; (2) autoclaved cottonseed meal diet; (3) cottonseed meal diet gamma irradiated at a dose of 15 kGy; (4) cottonseed meal diet gamma irradiated at a dose of 30 kGy; (5) cottonseed meal diet gamma irradiated at a dose of 45 kGy. The results show that autoclaving for 15 min at 121°C did not have a statistically significant effect on the apparent ileal digestibility of the amino acids in cottonseed meal when compared with the control treatment. The results also show that gamma irradiation of cottonseed meal were not effective in increasing the apparent digestibility of amino acids. In addition, irradiation of cottonseed meal did not improve the apparent digestibility of amino acids in comparison with the other processing methods only, but also significantly decreased it (p<0.05).Key words: Gamma irradiation, digestibility, amino acid, cottonseed meal, broiler

Experimental Investigation of the Nature of the Knee in the Primary Cosmic Ray Energy Spectrum with the GAMMA experiment

We present preliminary results obtained by a novel difference method for the study of the nature of the knee in the energy spectrum of the primary cosmic radiation. We have applied this method to data from the GAMMA experiment in Armenia. The analysis provides evidence for the possible existence of a nearby source of primary cosmic rays in the Southern hemisphere.Comment: 17 pages, 5 figure

Childhood Remembered: Reflections on the Role of Play for Holistic Education in Armenia, Kuwait, Saudi Arabia, the USA, and Wales

Play remains a topic for discussion, debate, and research within the education community. Zigler and Bishop-Josef (2004) provide an historical overview of early childhood; one of their main findings is play is under siege in many educational circles. The authors indicate, through time, there is a move away from play-oriented learning activities to a narrow focus on academics. Outside of the United States, and in many other countries, shifts occurred toward education focusing on academic skills that “deepen the damage and [make] more permanent the ‘achievement’ gap” between many children (Meier, 2009, p. 12). In opposition to this trend, advocates continue to call for more play-oriented and holistic approaches to learning, arguing the play vs. academics debate with academic support for and against the role of play in early childhood (Miller, 2008). Although this work provides important contributions to the field, prior research often gives little voice to teachers’ perceptions about play, especially from varied and diverse cultural backgrounds. In this article, we argue for a broader view of education in line with Plato’s observation (gender not withstanding) that “The direction in which education starts a man will determine his future life” (Jowett, 1874, p. 249). The current approach draws on the recommendation that we move beyond the typical developmental research view to use an interpretivist analysis that considers history, culture, and context (Swadener & Kessler, 1991). We begin with a short overview of the potential and traditional developmental and academic benefits of play. Our argument then focuses on a less common consideration of the holistic benefit of play: We explore teachers’ cultural reflections about the nature and worth of play through the authors’ personal accounts of playful childhood in Armenia, Great Britain, Kuwait, Saudi Arabia, and the United States of America. Finally, we provide recommendations for the value of play as part of a whole child education

Tkachenko modes as sources of quasiperiodic pulsar spin variations

We study the long wavelength shear modes (Tkachenko waves) of triangular lattices of singly quantized vortices in neutron star interiors taking into account the mutual friction between the superfluid and the normal fluid and the shear viscosity of the normal fluid. The set of Tkachenko modes that propagate in the plane orthogonal to the spin vector are weakly damped if the coupling between the superfluid and normal fluid is small. In strong coupling, their oscillation frequencies are lower and are undamped for small and moderate shear viscosities. The periods of these modes are consistent with the observed ~100-1000 day variations in spin of PSR 1828-11.Comment: 7 pages, 3 figures, uses RevTex, v2: added discussion/references, matches published versio

Should we doubt the cosmological constant?

While Bayesian model selection is a useful tool to discriminate between competing cosmological models, it only gives a relative rather than an absolute measure of how good a model is. Bayesian doubt introduces an unknown benchmark model against which the known models are compared, thereby obtaining an absolute measure of model performance in a Bayesian framework. We apply this new methodology to the problem of the dark energy equation of state, comparing an absolute upper bound on the Bayesian evidence for a presently unknown dark energy model against a collection of known models including a flat LambdaCDM scenario. We find a strong absolute upper bound to the Bayes factor B between the unknown model and LambdaCDM, giving B < 3. The posterior probability for doubt is found to be less than 6% (with a 1% prior doubt) while the probability for LambdaCDM rises from an initial 25% to just over 50% in light of the data. We conclude that LambdaCDM remains a sufficient phenomenological description of currently available observations and that there is little statistical room for model improvement.Comment: 10 pages, 2 figure

Observation of Resonant Diffusive Radiation in Random Multilayered Systems

Diffusive Radiation is a new type of radiation predicted to occur in randomly inhomogeneous media due to the multiple scattering of pseudophotons. This theoretical effect is now observed experimentally. The radiation is generated by the passage of electrons of energy 200KeV-2.2MeV through a random stack of films in the visible light region. The radiation intensity increases resonantly provided the Cherenkov condition is satisfied for the average dielectric constant of the medium. The observed angular dependence and electron resonance energy are in agreement with the theoretical predictions. These observations open a road to application of diffusive radiation in particle detection, astrophysics, soft X-ray generation and etc.. `Comment: 4pages, 4figure