RESUMO
Corals are acclimatized to populate dynamic habitats that neighbour coral reefs. Habitats such as seagrass beds exhibit broad diel changes in temperature and pH that routinely expose corals to conditions predicted for reefs over the next 50-100 years. However, whether such acclimatization effectively enhances physiological tolerance to, and hence provides refuge against, future climate scenarios remains unknown. Also, whether corals living in low-variance habitats can tolerate present-day high-variance conditions remains untested. We experimentally examined how pH and temperature predicted for the year 2100 affects the growth and physiology of two dominant Caribbean corals (Acropora palmata and Porites astreoides) native to habitats with intrinsically low (outer-reef terrace, LV) and/or high (neighbouring seagrass, HV) environmental variance. Under present-day temperature and pH, growth and metabolic rates (calcification, respiration and photosynthesis) were unchanged for HV versus LV populations. Superimposing future climate scenarios onto the HV and LV conditions did not result in any enhanced tolerance to colonies native to HV. Calcification rates were always lower for elevated temperature and/or reduced pH. Together, these results suggest that seagrass habitats may not serve as refugia against climate change if the magnitude of future temperature and pH changes is equivalent to neighbouring reef habitats.
Assuntos
Antozoários/fisiologia , Ecossistema , Aclimatação , Animais , Região do Caribe , Concentração de Íons de Hidrogênio , Especificidade da Espécie , Temperatura , Índias OcidentaisRESUMO
Here we report the synthesis of single-walled carbon nanotube bundles by chemical vapor deposition in the presence of electron donor elements (N, P, and Si). In order to introduce each dopant into the graphitic carbon lattice, different precursors containing the doping elements (benzylamine, pyrazine, triphenylphosphine, and methoxytrimethylsilane) were added at various concentrations into ethanol/ferrocene solutions. The synthesized nanotubes and byproduct were characterized by electron microscopy and Raman spectroscopy. Our results reveal intrinsic structural and electronic differences for the N-, P-, and Si- doped nanotubes. These tubes can now be tested for the fabrication of electronic nanodevices, and their performance can be observed.
RESUMO
The US Department of Defense (DOD) is evolving to meet new security challenges in the twenty-first century. Today's challenges result from growing political, environmental, and economic instability in important areas of the globe that threaten national and global security. Immediate outreach to foreign nations in times of violent instability or natural disaster fosters security and stability both for the affected country and for the United States. Foreign humanitarian assistance (FHA) is a rapidly evolving military mission that addresses conflict prevention, conflict, postconflict, and natural disasters. With DOD's extensive global medical resources, it is often uniquely qualified to execute a critical role in relief and/or public health efforts. When and how the American military will act in FHA and disaster relief is a still evolving doctrine with three issues deserving particular attention: aligning operations with host government leadership, preserving humanitarian space, and tailoring the US military's unique resources to the specific political and medical situation at hand. The DOD's response to a large-scale earthquake in Peru suggests useful approaches to these three issues, provides a template for future FHA mission, and points to strategic decisions and operational capabilities that need further development to establish the FHA mission firmly within DOD's repertoire of security engagement activities.
Assuntos
Desastres , Cooperação Internacional , Socorro em Desastres , United States Government Agencies , Altruísmo , Terremotos , Peru , Estados UnidosRESUMO
We found that multiwalled carbon nanotubes (MWNTs) can be opened longitudinally by intercalation of lithium and ammonia followed by exfoliation. Intercalation of open-ended tubes and exfoliation with acid treatment and abrupt heating provided the best results. The resulting material consists of: (i) multilayered flat graphitic structures (nanoribbons), (ii) partially open MWNTs, and (iii) graphene flakes. We called the completely unwrapped nanotubes ex-MWNTs, and their large number of edge atoms makes them attractive for many applications.
RESUMO
We report the use of chemical vapor deposition (CVD) for the bulk production (grams per day) of long, thin, and highly crystalline graphene ribbons (<20-30 microm in length) exhibiting widths of 20-300 nm and small thicknesses (2-40 layers). These layers usually exhibit perfect ABAB... stacking as in graphite crystals. The structure of the ribbons has been carefully characterized by several techniques and the electronic transport and gas adsorption properties have been measured. With this material available to researchers, it should be possible to develop new applications and physicochemical phenomena associated with layered graphene.