On-Line Learning Theory of Soft Committee Machines with Correlated Hidden Units - Steepest Gradient Descent and Natural Gradient Descent -

The permutation symmetry of the hidden units in multilayer perceptrons causes the saddle structure and plateaus of the learning dynamics in gradient learning methods. The correlation of the weight vectors of hidden units in a teacher network is thought to affect this saddle structure, resulting in a prolonged learning time, but this mechanism is still unclear. In this paper, we discuss it with regard to soft committee machines and on-line learning using statistical mechanics. Conventional gradient descent needs more time to break the symmetry as the correlation of the teacher weight vectors rises. On the other hand, no plateaus occur with natural gradient descent regardless of the correlation for the limit of a low learning rate. Analytical results support these dynamics around the saddle point.Comment: 7 pages, 6 figure

Instellar grains within interstellar grains

The discovery of crystals of titanium carbide in an interstellar graphite spherule is reported. The new species is particularly interesting in that it came in a protective wrapping (the graphite spherule) which eliminated the possibility of chemical alteration during its residence in the interstellar medium and in the meteorite in which it was discovered

Tests of Dynamical Flux Emergence as a Mechanism for CME Initiation

Current coronal mass ejection (CME) models set their lower boundary to be in the lower corona. They do not calculate accurately the transfer of free magnetic energy from the convection zone to the magnetically dominated corona because they model the effects of flux emergence using kinematic boundary conditions or simply assume the appearance of flux at these heights. We test the importance of including dynamical flux emergence in CME modeling by simulating, in 2.5D, the emergence of sub-surface flux tubes into different coronal magnetic field configurations. We investigate how much free magnetic energy, in the form of shear magnetic field, is transported from the convection zone to the corona, and whether dynamical flux emergence can drive CMEs. We find that multiple coronal flux ropes can be formed during flux emergence, and although they carry some shear field into the corona, the majority of shear field is confined to the lower atmosphere. Less than 10% of the magnetic energy in the corona is in the shear field, and this, combined with the fact that the coronal flux ropes bring up significant dense material, means that they do not erupt. Our results have significant implications for all CME models which rely on the transfer of free magnetic energy from the lower atmosphere into the corona but which do not explicitly model this transfer. Such studies of flux emergence and CMEs are timely, as we have new capabilities to observe this with Hinode and SDO, and therefore to test the models against observations

Coordinated analysis of two graphite grains from the CO3.0 LAP 031117 meteorite: First identification of a CO Nova graphite and a presolar iron sulfide subgrain

Presolar grains constitute remnants of stars that existed before the formation of the solar system. In addition to providing direct information on the materials from which the solar system formed, these grains provide ground-truth information for models of stellar evolution and nucleosynthesis. Here we report the in-situ identification of two unique presolar graphite grains from the primitive meteorite LaPaz Icefield 031117. Based on these two graphite grains, we estimate a bulk presolar graphite abundance of 5-3+7 ppm in this meteorite. One of the grains (LAP-141) is characterized by an enrichment in 12C and depletions in 33,34S, and contains a small iron sulfide subgrain, representing the first unambiguous identification of presolar iron sulfide. The other grain (LAP-149) is extremely 13C-rich and 15N-poor, with one of the lowest 12C/13C ratios observed among presolar grains. Comparison of its isotopic compositions with new stellar nucleosynthesis and dust condensation models indicates an origin in the ejecta of a low-mass CO nova. Grain LAP-149 is the first putative nova grain that quantitatively best matches nova model predictions, providing the first strong evidence for graphite condensation in nova ejecta. Our discovery confirms that CO nova graphite and presolar iron sulfide contributed to the original building blocks of the solar system.Peer ReviewedPostprint (author's final draft

Response to juglone toxic effect in various genotypes of banana (Musa AA, AAA, AAB, AAAA, AAAB)

In Côte d'Ivoire, Black Sigatoka, caused by Mycosphaerella fijiensis Morelet, is a major constraint in banana plantain production. The use of juglone, a purified toxin of this pathogen, could constitute an alternative in the early selection of new banana genotypes resistant to Black Leaf Streak Disease (BLSD). Local cultivars and hybrids to be vulgarized, were evaluated in order to elucidate the variability of banana varieties and to assess the possibility of using juglone to breed for resistance to BLSD. Necrosis induction bioassays, electrolyte leakage, combined with phenolic compound quantifications were performed on both diploid and triploid reference cultivars, as well as tetraploid hybrids following juglone infiltration. Results show, based on minimal concentrations and intensities of necrosis, that genotypes sensitivity to juglone was generally related to susceptibility to the disease in the field. The tetraploid genotypes exhibited the lowest necrosis intensities when juglone concentration was less than 100 ppm. Forty eight hours after treatment, phenols content of FHIA23 and PITA14 hybrids was at a basal level. These tetraploid banana probably produced antioxidants with high affinity for the active oxygen species (AOS) inducing their tolerance to the disease. This study confirms the use of juglone for simple and rapid screening of banana varieties with resistance to BLSD. Pathological and physiological parameters related to biochemical evaluation, constitute the best strategy for identifying genotype with the greatest resistance to Mycosphaerella fijiensis. However, this great resistance is not systematically related to a higher content in total phenols.Mycosphaerella fijiensis est un parasite nécrotique occasionnant la cercosporiose noire, qui constitue l'une des contraintes majeures à la production de bananes desserts et de plantains en Côte d'Ivoire. L'utilisation de la juglone, un métabolite toxique purifié du pathogène a été envisagée comme une voie de sélection précoce de nouveaux génotypes de bananiers résistants à la maladie des raies noires (MRN). Des cultivars locaux et des hybrides à vulgariser ont été évalués en vue d'élucider la variabilité de réaction entre génotypes et de confirmer la possibilité d'utiliser la juglone pour le criblage de la résistance contre la MRN. Les tests d'induction de nécroses et de perte d'électrolytes associés au dosage quantitatif des composés phénoliques ont été réalisés sur des cultivars diploïdes et triploïdes, ainsi que des hybrides tétraploïdes infiltrés avec la juglone. Les intensités et les concentrations minimales d'induction des nécroses évaluées ont montré que la sensibilité à la juglone des génotypes de bananiers a été globalement identique à leur niveau d'infestation au champ. Pour les génotypes tétraploïdes, les intensités de nécroses ont été plus faibles (< 40 %) lorsque la concentration de juglone a été inférieure à 100 ppm. En outre, 48 h après traitement, les hybrides FHIA23 et PITA14, ont présenté un retour à la teneur initiale en phénols. La forte tolérance de ces hybrides à la maladie serait due à une synthèse d'antioxydants, à forte affinité pour les formes actives d'oxygène (FAO). Ces résultats confirment l'utilisation de la juglone pour le criblage simple et rapide de génotypes de bananiers résistants à la MRN. Une combinaison des paramètres pathologique, physiologique et biochimique constitue une stratégie idéale pour le criblage fiable du génotype le plus résistant à Mycosphaerella fijiensis. Cependant, cette grande résistance n'est pas systématiquement liée à une teneur plus élevée en phénols totaux.Mots Clés: Réaction différentielle, juglone, maladie des raies noires, génotypes de bananiers, composés phénolique

Nonlinear force-free and potential field models of active-region and global coronal fields during the Whole Heliospheric Interval

Between 2008/3/24 and 2008/4/2, the three active regions NOAA active regions 10987, 10988 and 10989 were observed daily by the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) while they traversed the solar disk. We use these measurements and the nonlinear force-free magnetic field code XTRAPOL to reconstruct the coronal magnetic field for each active region and compare model field lines with images from the Solar Terrestrial RElations Observatory (STEREO) and Hinode X-ray Telescope (XRT) telescopes. Synoptic maps made from continuous, round-the-clock Global Oscillations Network Group (GONG) magnetograms provide information on the global photospheric field and potential-field source-surface models based on these maps describe the global coronal field during the Whole Heliospheric Interval (WHI) and its neighboring rotations. Features of the modeled global field, such as the coronal holes and streamer belt locations, are discussed in comparison with extreme ultra-violet and coronagraph observations from STEREO. The global field is found to be far from a minimum, dipolar state. From the nonlinear models we compute physical quantities for the active regions such as the photospheric magnetic and electric current fluxes, the free magnetic energy and the relative helicity for each region each day where observations permit. The interconnectivity of the three regions is addressed in the context of the potential-field source-surface model. Using local and global quantities derived from the models, we briefly discuss the different observed activity levels of the regions.Comment: Accepted for publication in the Solar Physics Whole Heliospheric Interval (WHI) topical issue. We had difficulty squeezing this paper into arXiv's 15 Mb limit. The full paper is available here ftp://gong2.nso.edu/dsds_user/petrie/PetrieCanouAmari.pd

The volume of Gaussian states by information geometry

We formulate the problem of determining the volume of the set of Gaussian physical states in the framework of information geometry. That is, by considering phase space probability distributions parametrized by the covariances and supplying this resulting statistical manifold with the Fisher-Rao metric. We then evaluate the volume of classical, quantum and quantum entangled states for two-mode systems showing chains of strict inclusion

Transient dynamics for sequence processing neural networks

An exact solution of the transient dynamics for a sequential associative memory model is discussed through both the path-integral method and the statistical neurodynamics. Although the path-integral method has the ability to give an exact solution of the transient dynamics, only stationary properties have been discussed for the sequential associative memory. We have succeeded in deriving an exact macroscopic description of the transient dynamics by analyzing the correlation of crosstalk noise. Surprisingly, the order parameter equations of this exact solution are completely equivalent to those of the statistical neurodynamics, which is an approximation theory that assumes crosstalk noise to obey the Gaussian distribution. In order to examine our theoretical findings, we numerically obtain cumulants of the crosstalk noise. We verify that the third- and fourth-order cumulants are equal to zero, and that the crosstalk noise is normally distributed even in the non-retrieval case. We show that the results obtained by our theory agree with those obtained by computer simulations. We have also found that the macroscopic unstable state completely coincides with the separatrix.Comment: 21 pages, 4 figure