Automated Kerogen Classification in Microscope Images of Dispersed Kerogen Preparation

We develop the classification part of a system that analyses transmitted light microscope images of dispersed kerogen preparation. The system automatically extracts kerogen pieces from the image and labels each piece as either inertinite or vitrinite. The image pre-processing analysis consists of background removal, identification of kerogen material, object segmentation, object extraction (individual images of pieces of kerogen) and feature calculation for each object. An expert palynologist was asked to label the objects into categories inertinite and vitrinite, which provided the ground truth for the classification experiment. Ten state-of-the-art classifiers and classifier ensembles were compared: Naïve Bayes, decision tree, nearest neighbour, the logistic classifier, multilayered perceptron (MLP), support vector machines (SVM), AdaBoost, Bagging, LogitBoost and Random Forest. The logistic classifier was singled out as the most accurate classifier, with an accuracy greater than 90. Using a 10 times 10-fold cross-validation provided within the Weka software, we found that the logistic classifier was significantly better than five classifiers (p<0.05) and indistinguishable from the other four classifiers. The initial set of 32 features was subsequently reduced to 6 features without compromising the classification accuracy. A further evaluation of the system alerted us to the possible sensitivity of the classification to the ground truth that might vary from one human expert to another. The analysis also revealed that the logistic classifier made most of the correct classifications with a high certainty.     

Propagation of solar cosmic rays: Diffusion versus focused diffusion

This paper is designed to bring to the attention the fact that the effect of focusing of solar energetic particles is always essential as compared with scattering, no matter how small the value of the mean free path may be. That is why, an ordinary (focusing-free) diffusion approach can not be applied to the solar cosmic ray transport. In the case of high-energy solar particles, the focused diffusion is demonstrated to lead to a power law decay of energetic particle intensity much like an ordinary diffusion. However, the power law index of the decay is renormalized by the focusing.     

Conditional statistics of vertical heat fluxes in local advection conditions

Turbulent fluctuations have been investigated in the internal boundary layer (IBL) which forms after a dry-to-wet surface transition. The IBL is defined as that part of the atmospheric surface layer where the influence of the downstream surface is noticeable. The results of the application of three different quadrant analysis techniques are presented. The three techniques, in increasing order of the amount of information supplied, provide:

1. the diurnal variation of quadrant contribution (C _i), number fraction (T _i) and conditional average (% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiiYdd9qrFfea0dXdf9vqai-hEir8Ve% ea0de9qq-hbrpepeea0db9q8as0-LqLs-Jirpepeea0-as0Fb9pgea% 0lrP0xe9Fve9Fve9qapdbaqaaeGacaGaaiaabeqaamaabaabcaGcba% GaeyykJeUabm4DayaafaGabm4CayaafaGaeyOkJe-aaSbaaSqaaiaa% dMgaaeqaaaaa!4215!\[\langle w's'\rangle _i \], with s = T or q) of vertical sensible and latent heat fluxes,
2. the quadrant contribution and number of samples of different sizes depending on the relative magnitude of each sample, and
3. the distribution of the nondimensional probability density function.

The results show that in the IBL the vertical flux of sensible heat is maintained by (i) a small fraction of large samples with warm air carried upwards, and (ii) a larger fraction of small samples with cool air carried downwards. Both processes are almost equal in importance. In the morning and near the top of the IBL negative temperature fluctuations are limited by the near-uniform temperature conditions upstream and above the IBL. This limitation reduces, at that location, the conditional average of the sinking motions of cool air. Closer to the wet surface the negative temperature fluctuations are less susceptible to the above mentioned limitation. As a consequence contributions from all four quadrants are almost equal leading to a very small vertical heat flux. In the presence of a temperature inversion over both the upstream and the downstream terrain, shear-generated turbulence appears to be the cause of the relative abundance of sinking motions of warm air and rising motions of cool air, leading to a reversal of the sensible heat flux. The latent heat flux is positive (i.e. directed away from the surface) at all times and is maintained in almost equal amount by (i) a small number of large magnitude samples with moist air carried upwards, and (ii) small magnitude samples with sinking motions of dry air. These sinking motions of dry air are far more numerous, especially in the morning, but their conditional average is very small. The abundance of sinking motions of dry air is attributed to the fact that over the downstream terrain evaporation is greatly enhanced, leading to a skewed w′q′ signal. This skewness is clearly visible in the w′q′-probability density distribution of the morning runs. In the evening the asymmetry between these two different contributions disappears. This is because evaporation is greatly reduced and large positive humidity fluctuations no longer occur.     

Singular points of the polarization tensor

The problem to compute the magnetic field above the chromosphere using data of the vector = B _t/Bt that gives the projected field direction can be solved with different approximations. The field of direction vectors is, however, not the only field accessible to observations. The Stokes parameters, which are components of the radiation tensor, can be measured at each point of the image plane. The directions of the eigenvectors of the radiation tensor define two mutually orthogonal systems of integral curves in the image plane. These families of curves have singular points, which are generally of different type than those of the vector field. When the morphology of H chromospheric fibrils are used to infer the topology of the magnetic field, a similar problem is met, suggesting that singular points should also be present there.     

Pb−Sr−Nd−O isotopic constraints on the origin of rhyolites from the Taupo Volcanic Zone of New Zealand: evidence for assimilation followed by fractionation from basalt

A comprehensive Sr–Nd–Pb–O isotopic study is reported for rhyolites from the Maroa Volcanic Centre in the Taupo Volcanic Zone (TVZ) of New Zealand. The Sr–Nd isotopic compositions of the rhyolites (⁸⁷Sr/⁸⁶Sr=0.705236 to 0.705660 and _Nd = 2.0 to 0.2) are intermediate between those of primitive basalts (⁸⁷Sr/⁸⁶Sr=0.70387 and _Nd = 5.3) and the Torlesse basement (⁸⁷Sr/⁸⁶Sr=0.709 and _Nd = -4.5). The relatively low mantle-like oxygen isotopic compositions of ¹⁸ O = 7 ± 0.5 are consistent with the Nd-Sr isotopic constraints in that they can be accounted for by 15% to 25% crustal contamination of a basaltic parent by relatively ¹⁸ O-rich Torlesse metasediment. High precision Pb isotopic analyses of plagioclase separates from the Maroa rhyolites show that they have essentially the same compositions as the Torlesse metasedimentary terrane which is itself distinctive from the Western or Waipapa metasediments. Due to the high concentration of Pb in the Torlesse metasediments (>20 ppm) compared to the basalts (<2 ppm), the Pb isotopic composition of the volcanics may be controlled by relatively small amounts (>10%) of crustal contamination. All these results are shown to be consistent with derivation of the rhyolites by 15% to 25% contamination of relatively primitive basaltic magmas with Torlesse metasedimentary crust, followed by extensive, essentially closed system fractionation of the basalt to a magma of rhyolite composition. It is argued that the processes of assimilation and fractionation are separated in both space and time. The voluminous high silica rhyolites, which make up >97% of the exposed volcanism in the continental margin back-are basin environment of the TVZ, therefore appear to be a product of predominantly new additions to the crust with assimilation-recycling of pre-existing crust being of secondary importance.     

Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers

Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and petroleum. In particular, biomarker lipids produced by a single organism do not necessarily have the same carbon isotopic composition.