A pragmatic approach to multi-class classification

We present a novel hierarchical approach to multi-class classification which is generic in that it can be applied to different classification models (e.g., support vector machines, perceptrons), and makes no explicit assumptions about the probabilistic structure of the problem as it is usually done in multi-class classification. By adding a cascade of additional classifiers, each of which receives the previous classifier's output in addition to regular input data, the approach harnesses unused information that manifests itself in the form of, e.g., correlations between predicted classes. Using multilayer perceptrons as a classification model, we demonstrate the validity of this approach by testing it on a complex ten-class 3D gesture recognition task.Comment: European Symposium on artificial neural networks (ESANN), Apr 2015, Bruges, Belgium. 201

Spatial and temporal distributions of surface mass balance between Concordia and Vostok stations, Antarctica, from combined radar and ice core data: first results and detailed error analysis

Results from ground-penetrating radar (GPR) measurements and shallow ice cores carried out during a scientific traverse between Dome Concordia (DC) and Vostok stations are presented in order to infer both spatial and temporal characteristics of snow accumulation over the East Antarctic Plateau. Spatially continuous accumulation rates along the traverse are computed from the identification of three equally spaced radar reflections spanning about the last 600 years. Accurate dating of these internal reflection horizons (IRHs) is obtained from a depth-age relationship derived from volcanic horizons and bomb testing fallouts on a DC ice core and shows a very good consistency when tested against extra ice cores drilled along the radar profile. Accumulation rates are then inferred by accounting for density profiles down to each IRH. For the latter purpose, a careful error analysis showed that using a single and more accurate density profile along a DC core provided more reliable results than trying to include the potential spatial variability in density from extra (but less accurate) ice cores distributed along the profile. The most striking feature is an accumulation pattern that remains constant through time with persistent gradients such as a marked decrease from 26 mm w.e. yr(-1) at DC to 20 mm w.e. yr(-1) at the south-west end of the profile over the last 234 years on average (with a similar decrease from 25 to 19 mm w.e. yr(-1) over the last 592 years). As for the time dependency, despite an overall consistency with similar measurements carried out along the main East Antarctic divides, interpreting possible trends remains difficult. Indeed, error bars in our measurements are still too large to unambiguously infer an apparent time increase in accumulation rate. For the proposed absolute values, maximum margins of error are in the range 4 mm w.e. yr(-1) (last 234 years) to 2 mm w.e. yr(-1) (last 592 years), a decrease with depth mainly resulting from the time-averaging when computing accumulation rates

North western Alps Holocene paleohydrology recorded by flooding activity in Lake Le Bourget, France and possible relations with Mont-Blanc glaciers fluctuations

International audienceA 14-m long piston core was retrieved from Lake Le Bourget, NWAlps (France), in order to provide a continuous record of flooding events of the Rhone River during the Holocene. The selection of the coring site was based on high resolution seismic profiling, in an area with limited mass wasting deposits and accumulated proximal Rhone River inter-and underflow deposits. The age-depth model of this core is based on (i) 14 AMS radiocarbon dates, (ii)radionuclide dating(137Cs) and (iii) the identification of historical data (flood events, eutrophication of the lake).The sedimentary record dates back to 9400 cal BP, and includes a thin mass wasting event deposited around 4500 cal BP. A multi-proxy approach was used to track the evolution and origin of clastic sedimentation during the Holocene, in order to identify periods of higher hydrologic al activity in the catchment area. Spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals (especially the Illite crystallinity index) allowed locating the main source area of fine grained clastic particles settling at the lake after flood events. This dataset highlights up to 12 periods of more intense flooding events over the last 9400 years in Lake Le Bourget and shows that the main source area of clastic particles during this period is the upper part of the Arve River drainage basin. This part of the catchment area drains several large glaciers from the Mont-Blanc Massif, and fluctuations in Rhone River flood supply in Lake Le Bourget is interpreted as resulting essentially from Mont-Blanc Glacier activity during the Holocene.The comparison of clastic sedimentationin Lake Le Bourget with periods of increasing land use and periods of Alpine glacier and mid-European lake level fluctuations, suggest that the core LDB04 clastic record in Lake Le Bourget is a continuous proxy of the Holocene hydrologic al history of the NW Alps

Treatment of intracranial dural fistulas with Onyx : a prospective cohort, systematic review, and meta-analysis

BACKGROUND Onyx is important embolic material in the endovascular treatment of intracranial dural arteriovenous fistula (DAVF). However, its impact on DAVF occlusion rates, morbidity, mortality, and complication rates is not fully examined. OBJECTIVE To improve understanding of safety and effectiveness profiles associated with transarterial endovascular treatment using Onyx for intracranial DAVF METHODS We analyzed data from our prospective clinical registry and conducted a systematic review of all previous transarterial embolization studies using Onyx published between January 2005 and December 2015 in MEDLINE and EMBASE. RESULTS In the prospective study, 41 transarterial procedures were performed in 33 consecutive patients harboring 36 DAVFs. Complete initial exclusion was obtained in 32 of 36 (88.9%) fistulas; 31 fistulas were followed up showing 4 (12.9%) recurrences. Procedure-related morbidity and mortality were 3% and 0%, respectively. The literature review identified 19 studies involving a total of 425 patients with 463 DAVFs. Meta-analysis, including our registry data, showed an initial complete occlusion rate of 82% (95% confidence interval [CI]: 74%, 88%; I2, 70.6%), and recurrence rate at midterm of 2% (95% CI: 0%, 5%; I2, 21.5%). Pooled postoperative neurological deficit, procedure-related morbidity, and mortality rates were 4% (95% CI: 2%, 6%; I2, 0%), 3% (95% CI: 1%, 5%; I2, 0%), and 0%, respectively. CONCLUSION This meta-analysis suggests that transarterial embolization with Onyx is a safe treatment modality for DAVFs. Although Onyx showed a low recurrence rate at midterm, the long-term risk is poorly addressed in our study and should warrant a longer follow-up

Chemical cycling and deposition of atmospheric mercury in Polar Regions: review of recent measurements and comparison with models

Mercury (Hg) is a worldwide contaminant that can cause adverse health effects to wildlife and humans. While atmospheric modeling traces the link from emissions to deposition of Hg onto environmental surfaces, large uncertainties arise from our incomplete understanding of atmospheric processes (oxidation pathways, deposition, and re-emission). Atmospheric Hg reactivity is exacerbated in high latitudes and there is still much to be learned from polar regions in terms of atmospheric processes. This paper provides a synthesis of the atmospheric Hg monitoring data available in recent years (2011–2015) in the Arctic and in Antarctica along with a comparison of these observations with numerical simulations using four cutting-edge global models. The cycle of atmospheric Hg in the Arctic and in Antarctica presents both similarities and differences. Coastal sites in the two regions are both influenced by springtime atmospheric Hg depletion events and by summertime snowpack re-emission and oceanic evasion of Hg. The cycle of atmospheric Hg differs between the two regions primarily because of their different geography. While Arctic sites are significantly influenced by northern hemispheric Hg emissions especially in winter, coastal Antarctic sites are significantly influenced by the reactivity observed on the East Antarctic ice sheet due to katabatic winds. Based on the comparison of multi-model simulations with observations, this paper discusses whether the processes that affect atmospheric Hg seasonality and interannual variability are appropriately represented in the models and identifies research gaps in our understanding of the atmospheric Hg cycling in high latitudes

Joint stereo-PIV and NO-LIF in turbulent premixed hydrogen-air flames

A new technique to simultaneously and instantaneously resolve 3D velocity/2D strain rate fields and scalar/scalar gradient fields was developed and evaluated in this study. This technique combines Planar Laser Induced Fluorescence of the NO radical (NO-PLIF) and Stereoscopic Particle Image Velocimetry (SPIV). It was found that the NO-PLIF technique allowed the determination of various iso-c contours and as such would, in principle, allow the study of the influence of the heat release on various properties, provided a calibration of the NO-PLIF signal as a function of temperature is achieved. It was also shown that the NO-PLIF technique may not be unambiguous at detecting flame extinction. The SPIV technique allowed the determination of the velocities in 3D and of the strain rates in 2D from which the most extensive and the most compressive strain rates but not the intermediate strain rate could be extracted. Information on strain rates and progress variable gradients were of particular interest in this study as they were needed to study the turbulence-scalar interaction which appears explicitly in the transport equation for the scalar dissipation rate which was derived recently. Using the technique above mentioned, this work also aimed at gathering and analysing data such as flame normal orientation, progress variable gradients, velocity change across the flame front and strain rates along the flame contours in turbulent premixed hydrogen/air flames with added nitrogen. The flame normal orientation was found to be consistent with the regime of the flames studied. A new method was designed and presented to infer from the progress variable gradients the component of the flame normal in the third dimension. The velocity change across the flame front, inferred from the SPIV data, was found to be extremely small. It is thought that the (low) heat release of the flames studied contributed more to corrugation of the flame front than acceleration of the gases across the flame front. The strain rates were studied along apparently non-wrinkled and clearly wrinkled flame contours. Their variation could not successfully be linked to curvature solely. Their values were mostly below the value expected for extinction strain rates. Last, this study aimed at investigating the turbulence-scalar interactions in turbulent premixed hydrogen/air flames with added nitrogen via the characteristics of the alignment of the flame normal vectors with the principal strain rates. The results of this study are quite different from earlier experimental results obtained for turbulent premixed ethylene/air flames. The strong preferential alignment of the flame front normal with the most extensive strain rate observed for ethylene/air flames could not be observed for the hydrogen/air flames with added nitrogen studied in the present work. The key outcome of this study was that no preferential alignment could be observed for most of the flames. A slight preferential alignment of the flame front normal with the most compressive strain rate was observed for the flames with very low adiabatic flame temperature. The differences observed were attributed partly to Lewis number effects and partly to the low heat release superimposed on the hydrodynamic fields in the flames studied

Understanding mercury oxidation and air–snow exchange on the East Antarctic Plateau: a modeling study

Distinct diurnal and seasonal variations of mercury (Hg) have been observed in near-surface air at Concordia Station on the East Antarctic Plateau, but the processes controlling these characteristics are not well understood. Here, we use a box model to interpret the Hg0 (gaseous elemental mercury) measurements in thes year 2013. The model includes atmospheric Hg0 oxidation (by OH, O3, or bromine), surface snow HgII (oxidized mercury) reduction, and air-snow exchange, and is driven by meteorological fields from a regional climate model. The simulations suggest that a photochemically driven mercury diurnal cycle occurs at the air-snow interface in austral summer. The fast oxidation of Hg0 in summer may be provided by a two-step bromine-initiated scheme, which is favored by low temperature and high nitrogen oxides at Concordia. The summertime diurnal variations of Hg0 (peaking during daytime) may be confined within several tens of meters above the snow surface and affected by changing mixed layer depths. Snow re-emission of Hg0 is mainly driven by photoreduction of snow HgII in summer. Intermittent warming events and a hypothesized reduction of HgII occurring in snow in the dark may be important processes controlling the mercury variations in the non-summer period, although their relative importance is uncertain. The Br-initiated oxidation of Hg0 is expected to be slower at Summit Station in Greenland than at Concordia (due to their difference in temperature and levels of nitrogen oxides and ozone), which may contribute to the observed differences in the summertime diurnal variations of Hg0 between these two polar inland stations.National Science Foundation (U.S.) (Grant ACP-1053648

A Comparison Of New Calculations Of The Yearly 10Be Production In The Earths Polar Atmosphere By Cosmic Rays With Yearly 10Be Measurements In Multiple Greenland Ice Cores Between 1939 And 1994 - A Troubling Lack Of Concordance Paper #2

We have compared the yearly production rates of 10Be by cosmic rays in the Earths polar atmosphere over the last 50-70 years with 10Be measurements from two separate ice cores in Greenland. These ice cores provide measurements of the annual 10Be concentration and 10Be flux levels during this time. The scatter in the ice core yearly data vs. the production data is larger than the average solar 11 year production variations that are being measured. The cross correlation coefficients between the yearly 10Be production and the ice core 10Be measurements for this time period are <0.4 in all comparisons between ice core data and 10Be production, including 10Be concentrations, 10Be fluxes and in comparing the two separate ice core measurements. In fact, the cross correlation between the two ice core measurements, which should be measuring the same source, is the lowest of all, only ~0.2. These values for the correlation coefficient are all indicative of a "poor" correlation. The regression line slopes for the best fit lines between the 10Be production and the 10Be measurements used in the cross correlation analysis are all in the range 0.4-0.6. This is a particular problem for historical projections of solar activity based on ice core measurements which assume a 1:1 correspondence. We have made other tests of the correspondence between the 10Be predictions and the ice core measurements which lead to the same conclusion, namely that other influences on the ice core measurements, as large as or larger than the production changes themselves, are occurring. These influences could be climatic or instrumentally based. We suggest new ice core measurements that might help in defining more clearly what these influences are and-if possible-to correct for them.Comment: 24 pages, 6 figure

Multi-model study of mercury dispersion in the atmosphere : Atmospheric processes and model evaluation

Current understanding of mercury (Hg) behavior in the atmosphere contains significant gaps. Some key characteristics of Hg processes, including anthropogenic and geogenic emissions, atmospheric chemistry, and air-surface exchange, are still poorly known. This study provides a complex analysis of processes governing Hg fate in the atmosphere involving both measured data from ground-based sites and simulation results from chemical transport models. A variety of long-term measurements of gaseous elemental Hg (GEM) and reactive Hg (RM) concentration as well as Hg wet deposition flux have been compiled from different global and regional monitoring networks. Four contemporary global-scale transport models for Hg were used, both in their state-of-the-art configurations and for a number of numerical experiments to evaluate particular processes. Results of the model simulations were evaluated against measurements. As follows from the analysis, the interhemispheric GEM gradient is largely formed by the prevailing spatial distribution of anthropogenic emissions in the Northern Hemisphere. The contributions of natural and secondary emissions enhance the south-to-north gradient, but their effect is less significant. Atmospheric chemistry has a limited effect on the spatial distribution and temporal variation of GEM concentration in surface air. In contrast, RM air concentration and wet deposition are largely defined by oxidation chemistry. The Br oxidation mechanism can reproduce successfully the observed seasonal variation of the RM=GEM ratio in the near-surface layer, but it predicts a wet deposition maximum in spring instead of in summer as observed at monitoring sites in North America and Europe. Model runs with OH chemistry correctly simulate both the periods of maximum and minimum values and the amplitude of observed seasonal variation but shift the maximum RM=GEM ratios from spring to summer. O3 chemistry does not predict significant seasonal variation of Hg oxidation. Hence, the performance of the Hg oxidation mechanisms under study differs in the extent to which they can reproduce the various observed parameters. This variation implies possibility of more complex chemistry and multiple Hg oxidation pathways occurring concurrently in various parts of the atmosphere