The fate of spiral galaxies in clusters: The star formation history of the anemic Virgo cluster galaxy NGC 4569

We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (Hα) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the Hα rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in cluster

Supernova Neutrino Oscillations

Observing a high-statistics neutrino signal from a galactic supernova (SN) would allow one to test the standard delayed explosion scenario and may allow one to distinguish between the normal and inverted neutrino mass ordering due to the effects of flavor oscillations in the SN envelope. One may even observe a signature of SN shock-wave propagation in the detailed time-evolution of the neutrino spectra. A clear identification of flavor oscillation effects in a water Cherenkov detector probably requires a megatonne-class experiment.Comment: Proc. 129 Nobel Symposium "Neutrino Physics", 19-24 Aug 2004, Swede

GCRT J1745-3009 as a Transient White Dwarf Pulsar

A transient radio source in the direction of the Galactic Center, GCRT J1745-3009, exhibited 5 peculiar consecutive outbursts at 0.33 GHz with a period of 77.13 minutes and a duration of ~10 minutes for each outburst. It has been claimed to be the prototype of a hitherto unknown class of transient radio sources. We interpret it as a transient white dwarf pulsar with a period of 77.13 minutes. The ~10-minute flaring duration corresponds to the epoch when the radio beam sweeps our line of sight. The bursting epoch corresponds to the episodes when stronger sunspot-like magnetic fields emerge into the white dwarf polar cap region during which the pair production condition is satisfied and the white dwarf behaves like a radio pulsar. It switches off as the pair production condition breaks down.Comment: minor changes, ApJL, in pres

Image effects in transport at metal-molecule interfaces

We present a method for incorporating image-charge effects into the description of charge transport through molecular devices. A simple model allows us to calculate the adjustment of the transport levels, due to the polarization of the electrodes as charge is added to and removed from the molecule. For this, we use the charge distributions of the molecule between two metal electrodes in several charge states, rather than in gas phase, as obtained from a density-functional theory-based transport code. This enables us to efficiently model level shifts and gap renormalization caused by image-charge effects, which are essential for understanding molecular transport experiments. We apply the method to benzene di-amine molecules and compare our results with the standard approach based on gas phase charges. Finally, we give a detailed account of the application of our approach to porphyrin-derivative devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8, 282 (2013)], which demonstrates the importance of accounting for image-charge effects when modeling transport through molecular junctions

Trans-Planckian Dark Energy?

It has recently been proposed by Mersini et al. 01, Bastero-Gil and Mersini 02 that the dark energy could be attributed to the cosmological properties of a scalar field with a non-standard dispersion relation that decreases exponentially at wave-numbers larger than Planck scale (k_phys > M_Planck). In this scenario, the energy density stored in the modes of trans-Planckian wave-numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present article examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave-numbers considered, hence the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order M_Planck^4) for modes with momenta of order M_Planck, far in excess of the background energy density. We evaluate the amount of fine-tuning in the initial data necessary to avoid this back-reaction problem and find it is of order H/M_Planck. We also argue that the equation of state of the trans-Planckian modes is not vacuum-like. Therefore this model does not provide a suitable explanation for the dark energy.Comment: RevTeX - 15 pages, 7 figures: final version to appear in PRD, minor changes, 1 figure adde

A Melissopalynological map of the south and southwest of the Buenos Aires province, Argentina

El objetivo de este trabajo fue elaborar un mapa melitopalinológico del sur y sudoeste de la provincia de Buenos Aires, Argentina, con datos de análisis polínicos de 127 muestras de miel provenientes de las eco-regiones Pampa, Distrito del Caldén en el Espinal, y Monte de Llanuras y Mesetas, recolectadas en el período 1992-2002. Utilizando análisis de componentes principales y de cluster, los partidos se agruparon en cinco regiones: I (Tres Arroyos, San Cayetano, Coronel Pringles y Coronel Dorrego), II (Guaminí, Saavedra, Coronel Suárez y Adolfo Alsina), III (Coronel Rosales, Monte Hermoso, Bahía Blanca y Villarino), IV (Patagones y Tornquist) y V (Puán). En las Regiones I, III y IV el 80% de las muestras fueron monoflorales. La Región I se caracterizó por la presencia de un 50% de mieles de Helianthus annuus y de un 10% de mieles de trébol; la Región III por 60% de mieles de Eucalyptus sp.; y la Región IV por 30% de mieles de Diplotaxis tenuifolia. En las Regiones II y V el 50% de las mieles fueron monoflorales: la Región II se distinguió por la presencia de 50% de mieles de H. annuus y la Región V por 15% de mieles de Larrea divaricata y 15% de mieles de Vicia sp. Las mieles multiflorales de la Región V se destacaron por la presencia de pólen de Condalia microphylla. La mayor diversidad de tipos polínicos correspondió a las familias Fabaceae y Asteraceae. La asociación de Eucalyptus sp., Centaurea sp. y Diplotaxis tenuifolia caracterizó a las mieles de las cinco regiones. La variabilidad natural de las muestras de miel hace muy difícil definir límites precisos entre las diferentes regiones.The aim of this work was to produce a melissopalynological map of the south and southwest of the Buenos Aires Province, Argentina, using pollen analysis data pertaining to 127 honey samples from the Pampa, Espinal (the Calden District), and Monte de Llanuras y Mesetas ecoregions, collected over the period 1992-2002. Using principal components and hierarchical cluster analysis, the different districts were grouped into five regions: I (Tres Arroyos, San Cayetano, Coronel Pringles and Coronel Dorrego), II (Guaminí, Saavedra, Coronel Suárez and Adolfo Alsina), III (Coronel Rosales, Monte Hermoso, Bahía Blanca and Villarino), IV (Patagones and Tornquist), and V (Puán). In Regions I, III and IV, 80% of honey samples were monofloral: Region I was characterized by the presence of 50% Helianthus annuus honeys and 10% clover honeys, Region III by 65% Eucalyptus sp. honeys, and Region IV by 30% Diplotaxis tenuifolia honeys. In Regions II and V, 50% of honeys were monofloral. Region II was distinguished by the presence of 50% H. annuus honeys, and Region V by 15% Larrea divaricata and 15% Vicia sp. honeys. The multifloral honeys of Region V included samples containing Condalia microphylla pollen. The families Fabaceae and Asteraceae provided the greatest diversity of pollen types. The association of Eucalyptus sp., Centaurea sp., and Diplotaxis tenuifolia characterised the honeys from all five regions. The natural variability of honey samples renders it very difficult to define the boundaries between the different regions

Characterization of honeys from west and south Buenos Aires province, Argentina

Pollen analyses were carried out on 33 honey samples from Espinal, Monte de Llanuras y Mesetas and Pampeana phytogeographical Provinces, collected during the 2000-2001 period. Sample processing as well as qualitative and quantitative analyses were performed according to standard techniques. Sixty-seven morphological pollen types were identified. The association of Eucalyptus sp. (E. camaldulensis Dehnh., E. viminalis Labill.), Centaurea sp. (C. solstitialis L., C. calcitrapa L.) and Diplotaxis tenuifolia DC. characterized these honeys. Twelve samples were unifloral: six from Eucalyptus sp., five from Helianthus annuus L., and one from Brassicaceae. Asteraceae and Fabaceae were the most representative botanical families