Constraints on cosmic ray loading and PeV neutrino production in blazars

IceCube has detected a cumulative flux of PeV neutrinos, which origin is unknown. Blazars, active galactic nuclei with relativistic jets pointing to us, are long and widely expected to be one of the strong candidates of high energy neutrino sources. The neutrino production depends strongly on the cosmic ray power of blazar jets, which is largely unknown. The recent null results in stacking searches of neutrinos for several blazar samples by IceCube put upper limits on the neutrino fluxes from these blazars. Here we compute the cosmic ray power and PeV neutrino flux of Fermi-LAT blazars, and find that the upper limits for known blazar sources give stringent constraint on the cosmic ray loading factor of blazar jets (i.e., the ratio of the cosmic ray to bolometric radiation luminosity of blazar jets), \xi_{\rm cr}\la(2-10)\zeta^{-1} (with \zeta\la1 the remained fraction of cosmic ray energy when propagate into the blazar broad line region) for flat cosmic ray spectrum, and that the cumulative PeV neutrino flux contributed by all-sky blazars is a fraction \la(10-50)\% of the IceCube detected flux.Comment: 9 pages, accepted by JCAP. Much more expanded and detailed description/explanation; conclussion unchange

High-energy cosmic ray nuclei from tidal disruption events: Origin, survival, and implications

Tidal disruption events (TDEs) by supermassive or intermediate mass black holes have been suggested as candidate sources of ultrahigh-energy cosmic rays (UHECRs) and high-energy neutrinos. Motivated by the recent measurements from the Pierre Auger Observatory, which indicates a metal-rich cosmic-ray composition at ultrahigh energies, we investigate the fate of UHECR nuclei loaded in TDE jets. First, we consider the production and survival of UHECR nuclei at internal shocks, external forward and reverse shocks, and nonrelativistic winds. Based on the observations of Swift J1644+57, we show that the UHECRs can survive for external reverse and forward shocks, and disk winds. On the other hand, UHECR nuclei are significantly disintegrated in internal shocks, although they could survive for low-luminosity TDE jets. Assuming that UHECR nuclei can survive, we consider implications of different composition models of TDEs. We find that the tidal disruption of main sequence stars or carbon-oxygen white dwarfs does not successfully reproduce UHECR observations, namely the observed composition or spectrum. The observed mean depth of the shower maximum and its deviation could be explained by oxygen-neon-magnesium white dwarfs, but they may be too rare to be the sources of UHECRs.Comment: 16 pages, 15 figures, published in PR

Effective Hamiltonian for surface states of \ce{Bi2Te3} nanocylinders with hexagonal warping

The three-dimensional topological insulator \ce{Bi2Te3} differs from other topological insulators in the \ce{Bi2Se3} family in that the effective Hamiltonian of its surface states on a flat semi-infinite slab requires the addition of a cubic momentum hexagonal warping term in order to reproduce the experimentally measured constant energy contours. In this work, we derive the appropriate effective Hamiltonian for the surface states of a \ce{Bi2Te3} \textit{cylinder} incorporating the corresponding hexagonal warping terms in a cylindrical geometry. We show that at the energy range where the surface states dominate, the effective Hamiltonian adequately reproduces the dispersion relation obtained from a full four-band Hamiltonian, which describe both the bulk and surface states. As an example application of our effective Hamiltonian, we study the transmission between two collinear \ce{Bi2Te3} cylinders magnetized in different directions perpendicular to their axes. We show that the hexagonal warping term results in a transmission profile between the cylinders which may be of utility in a multiple state magnetic memory bit

Childhood Malnutrition In China: Change Of Inequality In A Decade

A concentration index methodology to analyze the inequality in childhood malnutrition in China is outlined. Height-for-age z score is used as a measure of childhood malnutrition. Using household survey data from nine Chinese provinces, it is found that per-capita household income, household head's education, urban residence and access to a bus stop reduced malnutrition. Child's age had a nonlinear effect on the malnutrition status. Income growth and access to public transportation reduced the inequality, while rural-urban gap, provincial differentiation, and unequal distribution of household head's education increased inequality in childhood malnutrition. Gender is not a factor in either malnutrition status or inequality. Investments in infrastructure and welfare programs are recommended to reduce the inequality.Food Consumption/Nutrition/Food Safety,

Positive Analysis of Invasive Species Control as a Dynamic Spatial Process

This paper models control of invasive buffelgrass (Pennisetum ciliare), a fire-prone African bunchgrass spreading rapidly across the southern Arizona desert as a spatial dynamic process. Buffelgrass spreads over a gridded landscape. Weed carrying capacity, treatment costs, and damages vary over grid cells. Damage from buffelgrass depends on its spatial distribution in relation to valued resources. We conduct positive analysis of recommended heuristic strategies for buffelgrass control, evaluating their ability to prevent weed establishment and to reduce damage indices over time. The high dimensionality of the problem makes full dynamic optimization intractable. However, two heuristic strategies – potential damage weighting and consecutive year treatment – perform well in terms of percent damage reduction relative to no treatment and to static optimization. Results also suggest specific recommendations for deployment of rapid rapid-response teams to prevent invasions in new areas. The long-run population size and spatial distribution of buffelgrass is sensitive to priority weights for protection of different resources. Land managers with different priorities may pursue quite different control strategies, which may pose a challenge for coordinating control across jurisdictions.invasive species, integer programming, Crop Production/Industries, Environmental Economics and Policy, Q57, Q58,

A tunable radiation source by coupling laser-plasma-generated electrons to a periodic structure

Near-infrared radiation around 1000 nm generated from the interaction of a high-density MeV electron beam, obtained by impinging an intense ultrashort laser pulse on a solid target, with a metal grating is observed experimentally. Theoretical modeling and particle-in-cell simulation suggest that the radiation is caused by the Smith-Purcell mechanism. The results here indicate that tunable terahertz radiation with tens GV=m field strength can be achieved by using appropriate grating parameter