642,500 research outputs found
Recommended from our members
Climate Change versus Human Population and Development: Hurricanes, Urbanization, and Tourism Impacts on Land Change in the Tropical Island Ecosystems of RoatĂĄn, 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 regionâs 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 RoatĂĄn, 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 islandâs 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
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
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
Cascade emission in electron beam ion trap plasma of W ion
Spectra of the W 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 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 transitions, while
transitions arise after the cascade emission is
taken into account.Comment: 16 pages including 4 figures and 3 table
Collisional deexcitation of exotic hydrogen atoms in highly excited states. II. Cascade calculations
The atomic cascades in mu-p and pbar-p atoms have been studied in detail
using new results for the cross-sections of the scattering of highly excited
exotic atoms from molecular hydrogen. The cascade calculations have been done
with an updated version of the extended standard cascade model that computes
the evolution in the kinetic energy from the beginning of the cascade. The
resulting X-ray yields, kinetic energy distributions, and cascade times are
compared with the experimental data.Comment: 13 pages, 23 figure
Structural basis for CRISPR RNA-guided DNA recognition by Cascade
The CRISPR (clustered regularly interspaced short palindromic repeats) immune system in prokaryotes uses small guide RNAs to neutralize invading viruses and plasmids. In Escherichia coli, immunity depends on a ribonucleoprotein complex called Cascade. Here we present the composition and low-resolution structure of Cascade and show how it recognizes double-stranded DNA (dsDNA) targets in a sequence-specific manner. Cascade is a 405-kDa complex comprising five functionally essential CRISPR-associated (Cas) proteins (CasA1B2C6D1E1) and a 61-nucleotide CRISPR RNA (crRNA) with 5âČ-hydroxyl and 2âČ,3âČ-cyclic phosphate termini. The crRNA guides Cascade to dsDNA target sequences by forming base pairs with the complementary DNA strand while displacing the noncomplementary strand to form an R-loop. Cascade recognizes target DNA without consuming ATP, which suggests that continuous invader DNA surveillance takes place without energy investment. The structure of Cascade shows an unusual seahorse shape that undergoes conformational changes when it binds target DNA.
Intranuclear cascade models lack dynamic flow
We study the recent claim that the intranuclear cascade model exhibits collective sidewards flow. 4000 intranuclear cascade simulations of the reaction Nb(400 MeV/nucleon)+Nb are performed employing bound and unbound versions of the Cugnon cascade. We show that instability of the target and projectile nuclei in the unbound cascade produces substantial spurious sidewards flow angles, for spectators as well as for participants. Once the nuclear binding is included, the peak of the flow angle distributions for the participants alone is reduced from 35° to 17°. The theoretical ââdataââ are subjected to the experimental multiplicity and efficiency cuts of the plastic ball 4π electronic spectrometer system. The flow angular distributions obtained from the bound cascadeâwith spectators and participants subjected to the plastic ball filterâare forward peaked, in contrast to the plastic ball data. We discuss the uncertainties encountered with the application of the experimental efficiency and multiplicity filter. The influence of the Pauli principle on the flow is also discussed. The lack of flow effects in the cascade model clearly reflects the absence of the nuclear compression energy that can cause substantially larger collective sidewards motionâthere is too little intrinsic pressure built up in the cascade model
- âŠ