Decay of dynamic fracturing based on three-dimensional measurements of clastic-dike geometry

Several fundamental issues of fracture mechanics during the post-dynamic stage are yet not fully understood, including fracture arrest mechanisms, effects of the three-dimensional fracture propagation on fracture aperture and height relations, and the role played by fracture tips on fracture termination. We studied these issues in the seismically active Dead Sea basin, where clastic dikes (>10 m) and numerous smaller dikelets (<1 m) dynamically intruded the late-Pleistocene soft rock of the Lisan Formation. A three-dimensional study of the dikelets shows that they form arrest zones at the tips of the larger clastic dikes. Geometrically, the dikelets are divided into two parts: (1) the main dikelet, in which the aperture profile along the dikelet height is approximately elliptic; and (2) the elongated tip, in which the aperture profile along the tip height is approximately constant. The dikelet aspect ratio is defined as A/H, where A is dikelet aperture and H is dikelet height. A plot of A/H versus H describes power relations with two different zones: (1) Zone A, with a small variation of A/H, between 0.02 and 0.06, for dikelets in height range of 100–700 mm; and (2) Zone B, where the aspect ratio sharply increases to 0.23 in dikelets with heights less than 100 mm. We interpret that during deceleration, when the height of the elongated tip became greater than 1/10 of the dikelet height, inelastic conditions are dominant. Under these conditions, the fracture velocity decreases significantly and the dikelet aspect ratio increases. The present observations and analyses indicate that formation of elongated tips and dike (fracture) segmentation are essential for the decay of the dynamic fracturing.     

Thermal desorption of CH4 retained in CO2 ice

CO₂ ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density, refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that CO₂ traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH₄ in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of several retaining mechanisms related to the structure of CO₂ ice.     

Latent and sensible heat flux predictions from a uniform pine forest using surface renewal and flux variance methods

A surface renewal model that links organized eddy motion to the latent and sensible heat fluxes is tested with eddy correlation measurements carried out in a 13m tall uniform Loblolly pine plantation in Duke Forest, Durham, North Carolina. The surface renewal model is based on the occurance of ramp-like patterns in the scalar concentration measurements. To extract such ramp-like patterns from Eulerian scalar concentration measurements, a newly proposed time-frequency filtering scheme is developed and tested. The time-domain filtering is carried out using compactly-supported orthonormal wavelets in conjunction with the Universal Wavelet Thresholding approach of Donoho and Johnstone, while the frequency filtering is carried out by a band-pass sine filter centered around the ramp-occurrence frequency as proposed by other studies. The method was separately tested for heat and water vapour with good agreement between eddy correlation flux measurements and model predictions. The usefulness of the flux-variance method to predict sensible and latent heat fluxes is also considered. Our measurements suggest that the simple flux-variance method reproduces the measured heat and momentum fluxes despite the fact that the variances were measured within the roughness sublayer and not in the surface layer. Central to the predictions of water vapour fluxes using the flux-variance approach is the similarity between heat and water vapour transport by the turbulent air flow. This assumption is also investigated for this uniform forest terrain.     

Change in North American Atmospheric Conditions Associated with Deep Convection and Severe Weather using CRCM4 Climate Projections

Severe weather has important social and economic impacts. Some studies have indicated that its intensity may increase over this century as a consequence of climate change induced by greenhouse gases. This study aims to investigate the possibility of a future increase in deep convective events over North America resulting from the evolution of favourable atmospheric conditions. Our analysis is based on an ensemble of projections performed using the Canadian Regional Climate Model (CRCM) at 45?km resolution, driven by different Global Climate Models (GCMs) and reanalyses. We concentrate our study on Convective Available Potential Energy (CAPE), vertical wind shear, and convective precipitation. Based on two different approaches to linking atmospheric conditions and severe weather, we find that the number of extreme weather events is expected to increase during the twenty-first century. In agreement with other studies on this subject, we find that CAPE is expected to increase, whereas wind shear is expected to decrease slightly. Through the analysis of the CRCM's convective precipitation outputs, we show that severe convective liquid precipitation events may become both more frequent and slightly more intense. Sensitivity experiments show that results depend on the driving GCM although they confirm the general conclusions. Additional experiments conducted with reduced humidity input at the lateral boundaries show the significant role that the humidity level of the driving GCMs has on simulated extreme regional events. At the regional level results are, in general, consistent with those found at the continental scale, but large inter-regional variations exist.     

Variations in vapor pressure and standardized precipitation evapotranspiration index since AD 1861 over the western Himalaya in India: inference from tree ring-width records

A regional tree ring-width index chronology prepared from various tree core samples of the western Himalaya has been analyzed in relation to climate fluctuations. The correlation analysis of tree ring chronology shows significant positive correlations with regional rainfall and standardized precipitation evapotranspiration index (SPEI) and negative correlations with temperature and vapor pressure (VP) during the spring season. The correlation coefficients (CCs) of tree ring-width index chronology with rainfall, temperature, SPEI, and VP during 1901–1990 are 0.50, −0.49, 0.65, and −0.51, respectively. All CCs are significant at 0.1% level. The highly significant CCs between tree ring-width index chronology and SPEI indicate that tree growth over the western Himalaya is more sensitive to soil moisture availability than rainfall, whereas the rising VP is found to have a significant moisture stress condition to tree growth by accelerating the evapotranspiration, which is not conducive for the development of tree growth in the region. So, based on the strong association between tree ring-width index chronology and SPEI; the reconstructions of SPEI and VP are developed back to AD 1861, that show the long period of dryness during 1936–1963.     

A self-contained GIM-aided Abel retrieval method to improve GNSS-Radio Occultation retrieved electron density profiles

GPS Solutions - A self-contained global ionospheric maps (GIM)-aided Abel retrieval method is adopted that can account for spherical non-uniformity along the radio wave path in the vicinity of the...     

Periodic orbits of the third kind in the restricted three-body problem with oblateness

Recent calculations (analytical and semi-analytical), indicating that thermal effects in the relativistic regime may enhance the stability of spherically-symmetric models, are confirmed in a new example.     

The effects of chemical reactions on the dispersion of air pollutants over area sources

An analytical study has been performed to examine the characteristics of two-dimensional steady-state advective-diffusive transport of air pollutants emitted from ground-based area sources. The solutions for the concentration of air pollutants are obtained by Integral and Variational Imbedding methods taking chemical reaction process into account. A comparative study of concentration is displayed graphically, followed by a quantitative discussion.