Time-resolved measurements of nanoscale surface pattern formation kinetics in two dimensions on ion-irradiated Si

The nanoscale kinetics of surface topography evolution on silicon surfaces irradiated with 1 keV Ar+ ions is examined in both directions perpendicular and parallel to the projection of the ion beam on the surface. We use grazing incidence small angle x-ray scattering to measure in situ the evolution of surface morphology via the linear dispersion relation. We study the transition from surface ultra-smoothening at low angles of deviation from normal ion incidence to a pattern-forming instability at high incidence angles. A model based on the effects of impact-induced redistribution of those atoms that are not sputtered away explains both the observed ultra-smoothening at low angles from normal ion incidence and the instability at higher angles and accounts quantitatively for the measured two-dimensional dispersion relation and its dependence on incidence angle.Physic

Weather and our food supply

The steep rate of increase in yield of grain crops in the United States since the mid-1950\u27s has resulted in the use of the term explosion in technology. Surplus grains piled up to such proportions after the 1960 · harvest that acreage control appeared. to be in order. But despite substantial reductions in acreages after 1960 the increased output per acre has just about compensated for acreage reductions. During this period of rapid increase in output per acre there has been a growing tendency to believe that technology has reduced the influence of weather on grain production so that we no longer need to fear shortages due to unfavorable weather. There is also a popular belief that acreage control$ fail to achieve the objective of production control, and that public funds are being wasted in storing surplus grains which we don\u27t need. There is increasing evidence, however, that a period of favorable weather interacted with technology to produce our recent high yields, and that perhaps half of the increase in yield per acre since 1950 has been due to a change to more favorable weather for grain crops. These findings have important implications in continued support for research in production technology and in the way in which we look at our surplus stocks of feed and food grains. If a period of favorable weather has been responsible for half of the increase in yields since 19501 then what can we expect if the weather trend reverses itself for a few years? Do we have periodicity in weather, and have we just passed through a run of favorable years that might be followed by a run of unfavorable years? Should we treat our surplus grains as reserves? How does our rate of growth in grain output compare with the needs of a growing world population? And of course I in the background of these questions is one big question -- how much of our recent high yields is really due to weather? To answer these important questions the Center for Agriculture and Economic Development invited outstanding authorities to present their ideas under three main headings: (1) Techniques for Evaluation of Weather Variables in Agricultural Production I (2) Periodicity in Weather Patterns: Implications in Agriculture I and (3) Weather Considerations in Agricultural Policy. The papers have been assembled in the order of their presentation under the general outline above.https://lib.dr.iastate.edu/card_reports/1021/thumbnail.jp

LeptonInjector and LeptonWeighter: A neutrino event generator and weighter for neutrino observatories

We present a high-energy neutrino event generator, called LeptonInjector, alongside an event weighter, called LeptonWeighter. Both are designed for large-volume Cherenkov neutrino telescopes such as IceCube. The neutrino event generator allows for quick and flexible simulation of neutrino events within and around the detector volume, and implements the leading Standard Model neutrino interaction processes relevant for neutrino observatories: neutrino-nucleon deep-inelastic scattering and neutrino-electron annihilation. In this paper, we discuss the event generation algorithm, the weighting algorithm, and the main functions of the publicly available code, with examples.Comment: 28 pages, 10 figures, 3 table

All-flavor constraints on nonstandard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data

We report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained

New Flux Limits in the Low Relativistic Regime for Magnetic Monopoles at IceCube

Magnetic monopoles are hypothetical particles that carry magnetic charge. Depending on their velocity, different light production mechanisms exist to facilitate detection. In this work, a previously unused light production mechanism, luminescence of ice, is introduced. This light production mechanism is nearly independent of the velocity of the incident magnetic monopole and becomes the only viable light production mechanism in the low relativistic regime (0.1-0.55c). An analysis in the low relativistic regime searching for magnetic monopoles in seven years of IceCube data is presented. While no magnetic monopole detection can be claimed, a new flux limit in the low relativistic regime is presented, superseding the previous best flux limit by 2 orders of magnitude