Influence Of Sublimation Research Articles

Variability in Snowpack Isotopic Composition between Open and Forested Areas in the West Siberian Forest Steppe

The stable water isotopes in snow (primarily 18O and 2H) are widely used for tracing hydrological and ecological processes. However, isotopic signatures of snow can be significantly modified by topography and land cover. This study assesses spatial and temporal variability of the bulk snowpack isotopic composition (δ18O, δ2H, d-excess) between forested (pine and birch) and open areas in the West Siberian forest steppes. Isotopic samples were collected over the peak snow accumulation in 2017–2019. The snow isotopic composition within forested areas differed from open steppes, mainly in reducing d-excess (1.6‰ on average). We did not find a significant effect of canopy interception on snow enrichment in heavier isotopes. Snowpack in the pine forests was even lighter by 3.6‰ for δ2H compared to open areas, probably, due to low energy inputs and interception capacity. Additionally, snow depth significantly influenced the isotopic composition spatial variability. As snow depth increased, δ18O and δ2H values decreased due to conservation within the snowpack and less influence of sublimation and moisture exchange with the soil. However, this pattern was only evident in winters with below-average snow depth. Therefore, taking into account snow depth spatial and seasonal variability is advisable when applying the isotopic methods.

Influence of sublimation of destruction products on the pattern of DSC thermograms of polymeric materials

Differential-scanning-calorimetry thermograms measured for various polymers (atactic poly(methyl methacrylate), low-density polyethylene, and polytetrafluoroethylene) are analyzed with allowance for simultaneously obtained thermogravimetric-analysis data. Special attention is paid to the interpretation of “false” peaks arising owing to the synchronism of strong endothermic processes of sublimation of destruction products and other thermal processes.

Influence of sublimation and pyrolysis on quasi-steady deflagrations in confined porous energetic materials

Deflagrations in porous energetic materials under confinement are generally characterized by a relatively rapid increase in the burning rate as the pressure difference, or overpressure, in the burned-gas region relative to that deep within the pores of the unburned solid increases. Specifically, there appears to be a range of overpressures in which the sensitivity, or slope, of the propagation speed as a function of overpressure transitions from relatively small to large values. This effect has been qualitatively attributed to the fact that a sufficient overpressure reverses the gas flow and thus allows the burned gas to permeate, and therefore preheat, the porous material. However, quantitative descriptions of both the process itself and the corresponding burning-rate dependencies have only recently been achieved. The present work reflects a further refinement in this analytical description in that the melt layer, which underlies several previous studies and is likely to exist only at modest overpressures, is replaced by sublimation and pyrolysis at the material surface, followed by an attached gas flame that converts the unburned gaseous reactants to final products. As a result, gaseous reactants as well as products now permeate the porous solid, thereby affecting the propagation speed significantly and modifying both the combustion-wave structure and the transition to convection-enhanced burning.

Influence of sublimation on stable isotope records recovered from high‐altitude glaciers in the tropical Andes

Sublimation dominates the ablation process on cold, high‐altitude glaciers in the tropical Andes. Transport of water vapor through the firn and exchange with ambient moisture alter the stable isotope composition of the surface layers. A sublimation experiment carried out during an ice core drilling campaign on Cerro Tapado (5536 m above sea level, 30°08′S, 69°55′W) revealed a strong enrichment in the 2H and 18O content in the surface layer. Concerning the deuterium excess, a decrease occurred at daytime, while during the night, the values remained comparatively constant. At daytime the sublimation is enhanced due to the higher moisture deficit of the ambient air accompanied by relatively high firn surface temperatures. Low surface temperatures at night cause condensation of water vapor in the firn pores near the surface and thus inhibit penetration of the isotopically enriched surface front into deeper firn layers. Measuring an isotope profile obtained through detailed sampling between the surface and 38 cm depth proved this mechanism. The observed modification of the isotopic composition at the surface was quantitatively described by a model, which also reproduced the mass loss measured with sublimation pans and calculated from relevant meteorological data. The results of this study suggest that the influence of sublimation on the preserved isotope record of ice cores under comparable environmental conditions is rather limited. In any case, simultaneous measurements of δ2H and δ18O help to identify layers in an ice core which might be effected by sublimation. However, since the mass loss due to sublimation was of the order of 2–4 mm per day during the experiment, important palaeoinformation from an isotope record could be eliminated during extended dry periods.

Mass loss rate of the zodiacal dust cloud

The mass loss rate of the zodiacal dust cloud near the Sun has been estimated on the basis of the orbital behaviour of circumsolar dust grains suffering sublimation. It is found that the solar dust ring located at 4 solar radii from the Sun, which consists of grains whose inward spiraling due to the Poynting-Robertson effect is stopped by the influence of sublimation, loses its mass at a rate of 3.5∼0.35 tons per second.

Thermal Emission of Interplanetary Dust Cloud Models.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Thermal Emission of Interplanetary Dust Cloud Models. Kaiser, C. Abstract A method is described for computing the thermal emission of the interplanetary dust material. Processes specifically included in these models are the optics and thermodynamics of the dust particles, the Poynting-Robertson effect and the physics of sublimation, while the effects of the coronal gas and the solar wind are neglected. Special attention is given to the variation of the temperature with particle size and the influence of sublimation on the space and size distribution of particles near the sun. Models are constructed for a well-known substance to show the qualitative features of the thermal emission, and the procedure is then reversed to deduce some properties of the interplanetary dust material from recent observations. Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110446 Bibcode: 1967AJ.....72Q.807K full text sources ADS |