Properties of the Intergalactic Magnetic Field Constrained by Gamma-ray Observations of Gamma-Ray Bursts

The magnetic field in intergalactic space gives important information about magnetogenesis in the early universe. The properties of this field can be probed by searching for radiation of secondary e$^+$e$^-$ pairs created by TeV photons, that produce GeV range radiation by Compton-scattering cosmic microwave background (CMB) photons. The arrival times of the GeV "echo" photons depend strongly on the magnetic field strength and coherence length. A Monte Carlo code that accurately treats pair creation is developed to simulate the spectrum and time-dependence of the echo radiation. The extrapolation of the spectrum of powerful gamma-ray bursts (GRBs) like GRB 130427A to TeV energies is used to demonstrate how the IGMF can be constrained if it falls in the $10^{-21}$ - $10^{-17}$ G range for 1 Mpc coherence length.Comment: 8 pages, 6 figure

Low power laser generated ultrasound : signal processing for time domain data acquisition

The use of low power modulated laser diode systems has previously been established as a suitable method for non-destructive laser generation of ultrasound. Using a quasi-continuous optical excitation amplified by an erbium-doped fibre amplifier (EDFA) allows flexible generation of ultrasonic waves, offering control of further parameters such as the frequency content or signal shape. In addition, pseudo-random binary sequences (PRBS) can be used to improve the detected impulse response. Here we compare two sequences, the m-sequence and the Golay code, and discuss the advantages and practical limits of their application with laser diode based optical excitation of ultrasound

AMO-Forced Regional Processes Affecting Summertime Precipitation Variations in the Central United States

Numerous previous studies have provided insight into the influence of the Atlantic multidecadal oscillation (AMO) on North American precipitation. However, these studies focused on large-scale processes, and additional studies are needed to gain understanding of local and regional processes that develop in different phases of the AMO and substantiate its influences on precipitation. In this study, the Weather Research and Forecasting (WRF) regional model is used to examine AMO-forced local and regional processes and how they have affected summertime precipitation variation in the central United States. While moisture transport and convergence by the Great Plains low-level jet have been recognized as necessary conditions for summer precipitation, model simulations show similar low-level moisture flux convergence in the central United States between the cold and warm phases of the AMO. However, there was a strong moistening in the lower troposphere during the AMO cold phase, making the atmosphere more unstable for convection and precipitation. The source of the moisture was found to be a strong positive surface evaporation–precipitation feedback initiated and sustained by increased relative vorticity along a frontal zone. Along the frontal zone, isentropic stretching of the upper-level atmosphere and cyclonic circulation anomalies increased the relative vorticity during theAMOcold phase, providing the dynamic support needed to release the low-level moist instability and produce the increased precipitation. These results indicate that the dynamics of the circulation in the AMO cold phase played key roles to organize regional vorticity processes that further sustained a coupling of precipitation and the surface evaporation and perpetuated the precipitation

AMO-Forced Regional Processes Affecting Summertime Precipitation Variations in the Central United States

Numerous previous studies have provided insight into the influence of the Atlantic multidecadal oscillation (AMO) on North American precipitation. However, these studies focused on large-scale processes, and additional studies are needed to gain understanding of local and regional processes that develop in different phases of the AMO and substantiate its influences on precipitation. In this study, the Weather Research and Forecasting (WRF) regional model is used to examine AMO-forced local and regional processes and how they have affected summertime precipitation variation in the central United States. While moisture transport and convergence by the Great Plains low-level jet have been recognized as necessary conditions for summer precipitation, model simulations show similar low-level moisture flux convergence in the central United States between the cold and warm phases of the AMO. However, there was a strong moistening in the lower troposphere during the AMO cold phase, making the atmosphere more unstable for convection and precipitation. The source of the moisture was found to be a strong positive surface evaporation–precipitation feedback initiated and sustained by increased relative vorticity along a frontal zone. Along the frontal zone, isentropic stretching of the upper-level atmosphere and cyclonic circulation anomalies increased the relative vorticity during theAMOcold phase, providing the dynamic support needed to release the low-level moist instability and produce the increased precipitation. These results indicate that the dynamics of the circulation in the AMO cold phase played key roles to organize regional vorticity processes that further sustained a coupling of precipitation and the surface evaporation and perpetuated the precipitation

Low power laser generated ultrasound : signal processing for time domain data acquisition

The use of low power modulated laser diode systems has previously been established as a suitable method for non-destructive laser generation of ultrasound. Using a quasi-continuous optical excitation amplified by an erbium-doped fibre amplifier (EDFA) allows flexible generation of ultrasonic waves, offering control of further parameters such as the frequency content or signal shape. In addition, pseudo-random binary sequences (PRBS) can be used to improve the detected impulse response. Here we compare two sequences, the m-sequence and the Golay code, and discuss the advantages and practical limits of their application with laser diode based optical excitation of ultrasound

Characterization of biomass burning emissions from cooking fires, peat, crop residue, and other fuels with high-resolution proton-transfer-reaction time-of-flight mass spectrometry

We deployed a high-resolution proton-transferreaction time-of-flight mass spectrometer (PTR-TOF-MS) to measure biomass-burning emissions from peat, crop residue, cooking fires, and many other fire types during the fourth Fire Lab at Missoula Experiment (FLAME-4) laboratory campaign. A combination of gas standard calibrations and composition sensitive, mass-dependent calibration curves was applied to quantify gas-phase non-methane organic compounds (NMOCs) observed in the complex mixture of fire emissions. We used several approaches to assign the best identities to most major “exact masses”, including many high molecular mass species. Using these methods, approximately 80–96% of the total NMOC mass detected by the PTR-TOFMS and Fourier transform infrared (FTIR) spectroscopy was positively or tentatively identified for major fuel types. We report data for many rarely measured or previously unmeasured emissions in several compound classes including aromatic hydrocarbons, phenolic compounds, and furans; many of these are suspected secondary organic aerosol precursors. A large set of new emission factors (EFs) for a range of globally significant biomass fuels is presented. Measurements show that oxygenated NMOCs accounted for the largest fraction of emissions of all compound classes. In a brief study of various traditional and advanced cooking methods, the EFs for these emissions groups were greatest for open threestone cooking in comparison to their more advanced counterparts. Several little-studied nitrogen-containing organic compounds were deteched from many fuel types, that together accounted for 0.1-8.7% of the fuel nitrogen, and some may play a role in new particle formation