Spatial dependence of the local diffusion coefficient measured upstream of the November 12, 1978 interplanetary traveling shock

Characteristics of wuprathermal particles accelerated by quasi-parallel interplanetary traveling shocks have been generally explained in terms of a first order Fermi mechanism. Such models require diffusive scattering of particles upstream of the shock. This scattering is characterized by a local diffusion coefficient, kappa, which is determined by the local power density of waves in the upstream region. The dependence of the diffusion coefficient of suprathermal upstream protons on distance from the November 12, 1978 interplanetary traveling shock using a different approach is studied. Unlike previous studies this method, which is based on measurements of particle streaming and intensity gradients, does not rely on predictions. The local spatial variations of Kappa upstream of the November 12, 1978 shock have been chosen for study because the characteristics of this quasi-parallel shock have been extensively studied, and also because of its favorable geometry (i.e. B field nearly radial)

Iron charge states observed in the solar wind

Solar wind measurements from the ULECA sensor of the Max-Planck-Institut/University of Maryland experiment on ISEE-3 are reported. The low energy section of approx the ULECA sensor selects particles by their energy per charge (over the range 3.6 keV/Q to 30 keV/Q) and simultaneously measures their total energy with two low-noise solid state detectors. Solar wind Fe charge state measurements from three time periods of high speed solar wind occurring during a post-shock flow and a coronal hole-associated high speed stream are presented. Analysis of the post-shock flow solar wind indicates the charge state distributions for Fe were peaked at approx +16, indicative of an unusually high coronal temperature (3,000,000 K). In contrast, the Fe charge state distribution observed in a coronal hole-associated high speed stream peaks at approx -9, indicating a much lower coronal temperature (1,400,000 K). This constitutes the first reported measurements of iron charge states in a coronal hole-associated high speed stream

Observation of pick-up ions in the solar wind: Evidence for the source of the anomalous cosmic ray component?

Singly ionized energetic helium has been observed in the solar wind by using the time of flight spectrometer SULEICA on the AMPTE/IRM satellite between September and December, 1984. The energy density spectrum shows a sharp cut off which is strongly correlated with the four fold solar wind bulk energy. The absolute flux of the He(+)ions of about 10000 ion/sq cm.s is present independent of the IPL magnetic field orientation. The most likely source is the neutral helium of the interstellar wind which is ionized by solar UV radiation. It is suggested that these particles represent the source of the anomalous cosmic ray component

Language influences on tweeter geolocation

We investigate the influence of language on the accuracy of geolocating Twitter users. Our analysis, using a large corpus of tweets written in thirteen languages, provides a new understanding of the reasons behind reported performance disparities between languages. The results show that data imbalance has a greater impact on accuracy than geographical coverage. A comparison between micro and macro averaging demonstrates that existing evaluation approaches are less appropriate than previously thought. Our results suggest both averaging approaches should be used to effectively evaluate geolocation

Unraveling the 0νββ decay mechanisms

We discuss the possibilities of distinguishing among different mechanisms of neutrinoless double beta decay arising in the effective field theory framework. Following the review and detailed investigation of the particular ways of discrimination, we conclude that the 32 different low-energy effective operators can be split into multiple groups that are in principle distinguishable from each other by measurements of the phase-space observables and by comparison of the decay rates obtained using different isotopes. This would require not only a substantial experimental precision but necessarily also a considerable improvement of the current theoretical knowledge of the underlying nuclear physics. Specifically, the limiting aspect in our approach turns out to be the currently unknown or uncertain values of low-energy constants. Besides the study adopting the effective field theory language we also look into several typical UV models

Comparaison de différents protocoles de spéciation séquentielle du phosphore dans des sédiments de rivière

Trois méthodes classiques de spéciation séquentielle du phosphore ont été appliquées aux sédiments de la rivière Sûre, à une sélection de ses affluents de taille variable, ainsi qu'aux sédiments du prébarrage Misère, un petit réservoir eutrophe situé sur la Sûre. Les protocoles comparés sont ceux de HIELTJES et LIJKLEMA (H et L), de PALUDAN et JENSEN (P et J) et de GOLTERMAN et BOOMAN (G et B).Le phosphore total des sédiments étudiés s'élève à 0,6 mg·P·g-1 séd. sec pour les petits sous-bassins expérimentaux (de l'ordre de 1 km2), à 0,8-1,0 mg·P·g-1 séd. sec pour les bassins de taille moyenne (20 à 320 km2) et à 1,8 mg·P·g-1 séd. sec pour le prébarrage Misère. Les schémas de (H et L) et de (P et J) reproduisent de façon similaire les différences qualitatives existant entre les sédiments. Toutefois les parts relatives des différentes fractions varient selon le protocole utilisé. Les rendements d'extraction obtenus avec le schéma de (G et B) sont sensiblement supérieurs aux deux autres méthodes et sont très liés aux teneurs en phosphore total des mêmes échantillons.Pour le P-labile, une bonne corrélation est obtenue entre les concentrations extraites selon les protocoles de (H et L) et (P et J) (R2 =0,84, P < 0,001) ; cependant les valeurs absolues sont 40 % supérieures pour le premier (H et L) qui utilise NH4Cl comme extractant au lieu de H2O. La fraction P- (Fe+Al) de (H et L) et la somme des fractions P-Fe et P-Al de (P et J) sont également bien corrélées (R2 =0,90, P < 0,001), mais avec des valeurs 30 % supérieures pour le second protocole (P et J) qui réalise l'extraction en deux étapes. La fraction P-Fe de (G et B) est moins bien corrélée à la fraction P-Fe de (P et J) (R2 =0,74, P < 0,01), et les résultats obtenus selon ces deux protocoles sont très éloignés en valeur absolue. Quant à la fraction P-Ca, les résultats du protocole de (G et B) ne sont ni corrélés ni similaires à ceux des deux autres schémas, en raison de la nature complètement différente des extractants appliqués.The Haute-Sûre river, with a rural watershed of 428 km2 is the principal entry of the Esch-sur-Sûre reservoir, which is mainly used for drinking-water supply. The role of particulate phosphorus (suspended matter and sediments) is important to maintain the trophic level of lakes, and in particular of reservoirs, often receiving higher external nutrient loads than natural lakes. Indeed, phosphorus flux in the Haute-Sûre basin occurs mainly in particulate form, closely linked to the hydrological and morphological conditions of its drainage basin. Several authors have shown that the fractionation of sedimentary phosphorus is strongly correlated with its bioavailability.This study was carried out in the framework of a larger project concerning the characterisation of the phosphorus from the sediments of the Sûre river watershed. The choice among the fractionation procedures described in literature and the comparison of the different results remains often difficult because of the different nature of the proposed extracting solutions, but also because of variable solid: liquid ratios, or the different exposure times proposed. Three traditional fractionation methods, HIELTJES and LIJKLEMA (H and L) (1980), PALUDAN and JENSEN (P and J) (1995) and GOLTERMAN and BOOMAN (G and B) (1988), were thus tested in the present study and applied to sediments from the Sûre river bed and a selection of its tributaries of variable size as well as to the Misère predam sediments, a small reservoir located upstream from the main reservoir.The first protocol (H and L) classes the sedimentary phosphorus in four fractions: labile-P obtained with a NO4C1 1M solution, (Fe+Al)-P with NaOH 0.1M as reagent, Ca-P with a HCl 0.5 M solution and residual-P obtained by difference of the three precedent fractions with total P. The second (P and J) separates sedimentary phosphorus in 6 fractions: labile-P extracted with H2O, Fe-P with a dithionite-bicarbonate solution (NaHCO3 0.11 M and Na2 S2 O4 0.11 M), Al-P with a NaOH 0.1 M solution after acidification of the supernatant to pH=1 and separation of the resultant precipitate, AH-P (humic acids - P) obtained after mineralisation (H2 SO4 /K2 SO4 sat. at 400°C) of the previous precipitate, Ca-P with a HCl 0.5 M solution, and finally residual-P after drying and mineralisation of the sediment having undergone all the previous steps (H2 SO4 /K2 SO4 sat. at 400°C). The third tested protocol (G and B) proposes chelates as extracting solutions: the fraction Fe-P with Ca-NTA/dithionite (CaCO3 0.04 M + NTA 0.02 M - Na2 S2 O4 0.045 M), and the Ca-P fraction with Na-EDTA 0.05 M at pH=8.The obtained results demonstrate a substantial difference between the sampled sediments. The total phosphorus content of the sampled sediments varied between 0.6 mg·P·g-1 dw for the small experimental basins (around 1 km2), 0.8 to 1.0 mg·P·g-1 dw for the medium-sized basins (20 to 320 km2) and 1.8 mg·P·g-1 dw for the Misère predam (lentic system). As regards the phosphorus fractionation, the (H and L) and the (P and J) procedures are concordant from the qualitative point of view, the relative importance of the different fractions varying nevertheless according to the used scheme. With the (G and B) method the extracted P fractions were highest. In relative terms (% P-fraction in relation to total-P), the sampled sediments have a very similar behaviour according to (G and B), the quantitative differences between samples being strongly correlated to their total phosphorus content.A good correlation was found between the labile-P fractions determined according to (H and L) and according to (P and J) (R2=0.84, P < 0.001) with however 40% higher values for (H and L). The P-(Fe+Al) fraction of (H and L) and the sum of the fractions P-Fe + P-Al of (P and J) are correlated as well (R2=0.90, P < 0.001) with 30% higher values for (P and J). Regarding the P-Fe fraction, the results obtained with the (G and B) and (P and J) protocols are correlated (R2=0.74, P < 0.01), but results are quantitatively quite different. The P-Ca fraction of the (G and B) protocol is badly correlated and very different from the two other procedures, because of the completely different nature of the extracting solutions

Self-Regulation of Solar Coronal Heating Process via Collisionless Reconnection Condition

I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly-reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nano-flares), evaporation episodes, and long periods of slow magnetic stress build-up and radiative cooling of the coronal plasma.Comment: 4 pages; Phys. Rev. Lett., in pres

Using score differences for search result diversification

We investigate the application of a light-weight approach to result list clustering for the purposes of diversifying search results. We introduce a novel post-retrieval approach, which is independent of external information or even the full-text content of retrieved documents; only the retrieval score of a document is used. Our experiments show that this novel approach is bene cial to e ectiveness, albeit only on certain baseline systems. The fact that the method works indicates that the retrieval score is potentially exploitable in diversity