We report on strong backward stimulated emission at 337 nm in nitrogen gas pumped by circularly polarized femtosecond laser pulses at 800 nm. A distinct dependence of the backward UV spectrum on pump laser polarization and intensity is observed, pointing to the occurrence of backward amplified spontaneous emission inside filaments. We attribute the population inversion to inelastic collision be...

The future of ground based gamma ray astronomy lies in large arrays of Imaging Atmospheric Cherenkov Telescopes (IACT) with better capabilities: lower energy threshold, higher sensitivity, better resolution and background rejection. Currently, designs for the next generation of IACT arrays are being explored by various groups. We have studied possible configurations with a large number of teles...

The IceCube Neutrino Observatory is the world’s largest high energy neutrino telescope, using the Antarctic ice cap as a Cherenkov detector medium. DeepCore, the low energy extension to IceCube, is an infill array with a fiducial volume of around 30 MTon in the deepest, clearest ice, aiming for an energy threshold as low as 10 GeV and extending IceCube’s sensitivity to indirect dark matter sear...

Velocity measurements of wind blowing near the North Sea border of Northern Germany and velocity measurements under local isotropic conditions of a turbulent wake behind a cylinder are compared. It is shown that wind gusts – measured by means of velocity increments – do show similar statistics to the laboratory data, if they are conditioned on an averaged wind speed value. Clear differences bet...

RF ionization rates for mixtures of air with bariurn are computed using a Fokker-Planck code. It is shown that there is an optimum mixing ratio of barium to air, significantly ower than unity, which maximizes the ionization rate for a given value of incident RF power density and frequency. Rocket injection of barium at a selected height reduces ignificant/y the RF breakdown threshold for the mi...

MAGIC is presently the imaging atmospheric Cherenkov telescope with the largest reflecting surface and the lowest energy threshold. MAGIC concluded its first year of regular observation in April 2006. During this period and the preceding commissioning phase, 25 Active Galactic Nuclei have been observed and VHE γ-ray emission has been confirmed by 4 of them. Two more AGNs have been detected as γ...

The rate of movement for 3and 10-cm-high granule ripples was documented in September of 2006 at Great Sand Dunes National Park and Preserve during a particularly strong wind event. Impact creep induced by saltating sand caused 24 granules min 1 to cross each cm of crest length during wind that averaged 9 m s 1 (at a height well above 1 m), which is substantially larger than the threshold for sa...

The decline of atmospheric CO2 over the last 65 million years (Ma) resulted in the 'CO2-starvation' of terrestrial ecosystems and led to the widespread distribution of C4 plants, which are less sensitive to CO2 levels than are C3 plants. Global expansion of C4 biomass is recorded in the diets of mammals from Asia, Africa, North America, and South America during the interval from about 8 to 5 Ma...

We consider the problem of monitoring the concentration and dispersion of pollutants in the atmosphere using a collection of randomly scattered sensors. The sensors are capable of only indicating that the concentration has exceeded a randomly selected threshold and providing this information through a transponder-like mechanism to an airborne imaging radar. We use this information together with...

Velocity measurements of wind blowing near the North Sea border of Northern Germany and velocity measurements under local isotropic conditions of a turbulent wake behind a cylinder are compared. It is shown that wind gusts – measured by means of velocity increments – do show similar statistics to the laboratory data, if they are conditioned on an averaged wind speed value. Clear differences bet...