Split energy cascade in turbulent thin fluid layers

We discuss the phenomenology of the split energy cascade in a three-dimensional thin fluid layer by mean of high resolution numerical simulations of the Navier-Stokes equations. We observe the presence of both an inverse energy cascade at large scales, as predicted for two-dimensional turbu- lence, and of a direct energy cascade at small scales, as in three-dimensional turbulence. The inverse energy cascade is associated with a direct cascade of enstrophy in the intermediate range of scales. Notably, we find that the inverse cascade of energy in this system is not a pure 2D phenomenon, as the coupling with the 3D velocity field is necessary to guarantee the constancy of fluxes

Climate Change versus Human Population and Development: Hurricanes, Urbanization, and Tourism Impacts on Land Change in the Tropical Island Ecosystems of Roatán, Honduras

Relatively little scholarship has compared the ecological impact of acute climate-related events versus chronic human pressures. Despite mounting pressures from climate change and rapid tourism development across the Caribbean, even less research has assessed the relative impacts of biophysical versus anthropogenic pressures on the region’s island landscapes. We compare the effects of an extreme climate event in the years immediately following Hurricane Mitch in 1998 relative to thirty years of rapid urbanization and tourism development on Roatán, Honduras. Results from a random forest classifier applied to thirteen Landsat Thematic Mapper (TM) and Operational Land Imager (OLI) scenes, indicate that between 1985 and 2015 urban area increased by 982.8 ha (227.7%), with 224.1 ha (-19.1%) of mangroves converted to urban areas. This compares to a 37% (384.9 ha) decrease in mangroves immediately following Hurricane Mitch. Mangroves in protected areas have fully recovered since Mitch, demonstrating their resiliency. Despite being illegal, mangrove deforestation across all unprotected areas accelerated to accommodate increasing urban area. Given that mangroves provide vital protection to an island’s coastline and represent a major carbon-sink, and that extreme hurricanes in the Caribbean are projected to double in the coming decades due to climate change, this research suggests that rapid urbanization and tourism development in the Caribbean may decrease island ecosystem resiliency to environmental stressors

Optically induced transparency in bosonic cascade lasers

Bosonic cascade lasers are terahertz (THz) lasers based on stimulated radiative transitions between bosonic condensates of excitons or exciton-polaritons confined in a trap. We study the interaction of an incoming THz pulse resonant in frequency with the transitions between neighboring energy levels of the cascade. We show that at certain optical pump conditions the cascade becomes transparent to the incident pulse: it neither absorbs nor amplifies it, in the mean field approximation. The populations of intermediate levels of the bosonic cascade change as the THz pulse passes, nevertheless. In comparison, a fermionic cascade laser does not reveal any of these properties.Comment: 4 pages, 5 figure

Direct numerical experiment on measuring of dispersion relation for gravity waves in the presence of condensate

During previous numerical experiments on isotropic turbulence of surface gravity waves we observed formation of the long wave background (condensate). It was shown (Korotkevich, Phys. Rev. Lett. vol. 101 (7), 074504 (2008)), that presence of the condensate changes a spectrum of direct cascade, corresponding to the flux of energy to the small scales from pumping region (large scales). Recent experiments show that the inverse cascade spectrum is also affected by the condensate. In this case mechanism proposed as a cause for the change of direct cascade spectrum cannot work. But inverse cascade is directly influenced by the linear dispersion relation for waves, as a result direct measurement of the dispersion relation in the presence of condensate is necessary. We performed the measurement of this dispersion relation from the direct numerical experiment. The results demonstrate that in the region of inverse cascade influence of the condensate cannot be neglected.Comment: 5 pages, 3 figure

Cascade emission in electron beam ion trap plasma of W25+^{25+} ion

Spectra of the W$^{25+}$ ion are studied using the collisional-radiative model (CRM) with an ensuing cascade emission. It is determined that the cascade emission boosts intensities only of a few lines in the $10 - 3$ nm range. The cascade emission is responsible for the disappearance of structure of lines at about 6 nm in the electron beam ion trap plasma. Emission band at 4.5 to 5.3 nm is also affected by the cascade emission. The strongest lines in the CRM spectrum correspond to $4d^{9} 4f^{4} \rightarrow 4f^{3}$ transitions, while $4f^{2} 5d \rightarrow 4f^{3}$ transitions arise after the cascade emission is taken into account.Comment: 16 pages including 4 figures and 3 table

Cascade and anti-Cascade Polarization Measurements at 800 GeV/c

The polarization of neutral Cascade and anti-Cascade hyperons produced by 800 GeV/c protons on a BeO target at a fixed targeting angle of 4.8 mrad is measured by the KTeV experiment at Fermilab. Our result of 9.7% for the neutral Cascade polarization shows no significant energy dependence when compared to a result obtained at 400 GeV/c production energy and at twice our targeting angle. The polarization of the neutral anti-Cascade is measured for the first time and found to be consistent with zero. We also examine the dependence of polarization on transverse production momentum.Comment: 4 page PR