Are small diamonds thermodynamically stable in the interstellar medium?

Very small diamond particles (50 Å diameter) are shown to be thermodynamically stable with respect to similar sized graphite particles for reasonable values of the surface free energies of diamond and graphite. Small diamonds are likely to be stable against both thermal evaporation and chemical attack in the general interstellar medium. A few of the consequences of these conclusions are examined.     

Climate change and its implications for water resources management in south Florida

Recent climate change projections suggest that negative impacts on flood control and water supply functions and on existing and future ecosystem restoration projects in south Florida are possible. An analysis of historical rainfall and temperature data of the Florida peninsula indicates that there were no discernible trends in both the long-term record and during the more recent period (1950–2007). A comparison of General Circulation Model (GCM) results for the 20th century with the historical data shows that many of the GCMs do not capture the statistical characteristics of regional rainfall and temperature regimes in south Florida. Investigation of historical sea level data at Key West finds evidence for an increase in the occurrence and variance of maximum sea level events for the period 1961–2008 in relation to 1913–1960, along with a shift of energy from shorter to longer timescales. In order to understand the vulnerability of the water management system in south Florida in response to changing precipitation and evapotranspiration forcing, a sensitivity analysis using a regional-scale hydrologic and water management model is conducted. Model results suggest that projected climate change has potential to reduce the effectiveness of water supply and flood control operations for all water sectors. These findings emphasize that questions on the potential impacts of climate change need to be investigated with particular attention paid to the uncertainties of such projections.     

Sea level history of the northern Gulf of Mexico coast and sea level rise scenarios for the near future

The sea level history of the northern Gulf of Mexico during recent geologic time has closely followed global eustatic sea level change. Regional effects due to tectonics and glacio-isostasy have been minimal. Over the past several million years the northern Gulf coast, like most stable coastal regions of the globe, has experienced major swings of sea level below and above present level, accompanied by major shifts in shoreline position. During advances of the northern hemisphere ice sheets, sea level dropped by more than 100 m, extending the shoreline in places more than 100 km onto the shelf. For much of the period since the last glacial maximum (LGM), 20,000 years ago, the region has seen rates of sea level rise far in excess of those experienced during the period represented by long-term tide gauges. The regional tide gauge record reveals that sea level has been rising at about 2 mm/year for the past century, while the average rate of rise since the LGM has been 6 mm/year, with some periods of abrupt rise exceeding 40 mm/year. During times of abrupt rise, Gulf of Mexico shorelines were drowned in place and overstepped. The relative stability of modern coastal systems is due primarily to stabilization of sea level approximately 6,000 years ago, resulting in the slow rates of rise experienced during historic time. Recent model projections of sea level rise over the next century and beyond may move northern Gulf coastal environments into a new equilibrium regime, more similar to that experienced during the deglaciation than that which has existed during historic time.     

Is Sustainable Adaptation Possible? Determinants of Adaptation on Mount Kilimanjaro

Adaptation is increasingly planned and funded to reduce negative impacts of climate change for vulnerable social groups; however, vulnerable groups have the least capacity to adapt. Adaptation is therefore unlikely to produce socially sustainable or equitable outcomes. Six adaptation processes on Mount Kilimanjaro, Tanzania, are modeled with logistic regression to identify their determinant factors. Most adaptations simply reproduce unsustainable patterns of social vulnerability rooted in unequal access to land and other resource entitlements. A few exceptions are observed, where low costs, widely accessible knowledge, and community groups with cross-scale social networks enabled vulnerable social groups to implement adaptations.     

The signature of a black hole transit

A black hole transiting a companion star in a binary system will produce a time-varying intensity profile as observed at the Earth because of the Einstein photometric effect (gravitational lens phenomenon). If the transited star is an early-type supergiant with electron scattering as its dominant atmospheric opacity source, then variable linear polarization will also result from the destruction of the circular symmetry of the observed stellar disk. The simultaneous variation of the three Stokes parametersI, Q, andU may be thought of as the signature of a black hole transit. Monte-Carlo calculations show that the effect has the properties expected from qualitative considerations. The amplitude of the photometric and polarimetric light curves in a typical X-ray binary is too small to be observed with present instrumentation. A black hole transit might be detectable in a binary having a large separation of the components. The signature is also masked in close binaries by the much larger variability caused by the changing aspect of the tidally distorted OB star. The polarization induced by tidal distortion always produces a derived inclination of 90° when the standard method of analyzing the data is used. This effect may contribute to the unrealistically large values of inclination derived from polarimetric observations for the Cyg XR-1/HDE226868 system.