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Description:Questo articolo è una versione beta in PDF dell'articolo originale che ho pubblicato su Il Poliedrico all'indirizzo: http://ilpoliedrico.altervista.org/2011/01/quattro-vie-per-dire-addio-ai-combustibili-fossili.html

Descriptions:Di Giorgio Ferrari

Descriptions:Uploaded from Google Docs

Descriptions:Habitable zones around main sequence stars

Descriptions:The Daya Bay Reactor Neutrino Experiment, a multinational collaboration operating in the south of China, today reported the first results of its search for the last, most elusive piece of a long-standing puzzle: how is it that neutrinos can appear to vanish as they travel? The surprising answer opens a gateway to a new understanding of fundamental physics and may eventually solve the riddle of why there is far more ordinary matter than antimatter in the universe today.

Descriptions:Gaetano Di Achille and Brian M. Hynek The climate of early Mars could have supported a complex hydrological system and possibly a northern hemispheric ocean covering up to one-third of the planet’s surface. This notion has been repeatedly proposed and challenged over the past two decades, and remains one of the largest uncertainties in Mars research. Here,we used global databases of known deltaic deposits, valley networks8 and present-day martian topography to test for the occurrence of an ocean on early Mars. The distribution of ancient martian deltas delineates a planet-wide equipotential surface within and along the margins of the northern lowlands. We suggest that the level reconstructed from the analysis of the deltaic deposits may represent the contact of a vast ocean covering the northern hemisphere of Mars around 3.5 billion years ago. This boundary is broadly consistent with palaeoshorelines suggested by previous geomorphologic, thermophysic and topographic analyses, and with the global distribution and age of ancient valley networks. Our findings lend credence to the hypothesis that an ocean formed on early Mars as part of a global and active hydrosphere.

Descriptions:Abstract Purpose: The aim of this study was to apply a Lempel-Ziv complexity measure for quantifying biomedical signals and images. Material and methods: We analyzed angiogenic patterns and the signals (the heart rate, the respiration rate and the blood oxygen concentration). Biomedical signals were obtained by means of Internet. Medical images were from Department of Pathophysiology of Pregnancy Medical University of Białystok. Results: The values of normalized complexity measures for respiratory rate signal are high, what indicates that this time series is close to unstructured randomness. The Lempel-Ziv complexity values for angiogenic patterns were growing with the FIGO stage of disease. Conclusions: Lempel-Ziv complexity may be a very helpful tool in analyzing the signals and images. It can be easily computed from the analysed data.

Descriptions:Surface gravity is one of a star's basic properties, but it is difficult to measure accurately, with typical uncertainties of 25-50 per cent if measured spectroscopically and 90-150 per cent photometrically. Asteroseismology measures gravity with an uncertainty of about two per cent but is restricted to relatively small samples of bright stars, most of which are giants. The availability of high-precision measurements of brightness variations for >150,000 stars provides an opportunity to investigate whether the variations can be used to determine surface gravities. The Fourier power of granulation on a star’s surface correlates physically with surface gravity; if brightness variations on timescales of hours arise from granulation, then such variations should correlate with surface gravity. Here we report an analysis of archival data that reveals an observational correlation between surface gravity and the root-mean-square brightness variations on timescales of less than eight hours for stars with temperatures of 4500-6750 K, log of surface gravities of 2.5-4.5 (cgs units), and having overall brightness variations <25 per cent for inactive Sun-like stars at main-sequence to giant stages of evolution.

Descriptions:Riuscire ad immaginare oggi un buco nero non è difficile, anzi. La fantascienza del XX secolo e il cinema hanno reso i buchi neri talmente familiari quasi da distorcerne il significato. Per la fisica invece sono semplicemente delle regioni di spazio dove materia – o energia – è collassata oltre una certa densità critica, dove la velocità di fuga supera anche la velocità della luce. Tutto quello che è o finisce all’interno di questa regione di spazio si suppone converga verso una singolarità, ovvero un punto geometrico di densità infinita, questo almeno per la meccanica relativistica. Il confine tra questa regione di spazio collassato e il resto dell’universo si chiama orizzonte degli eventi, sede di tutta una serie di bizzarri fenomeni quantistici ancora lungi dall’essere pienamente compresi.

Descriptions:Abstract We discuss a cosmological model where the universe shrinks rather than expands during the radiation and matter dominated periods. Instead, the Planck mass and all particle masses grow exponentially, with the size of atoms shrinking correspondingly. Only dimensionless ratios as the distance between galaxies divided by the atom radius are observable. Then the cosmological increase of this ratio can also be attributed to shrinking atoms. We present a simple model where the masses of particles arise from a scalar “cosmon” field, similar to the Higgs scalar. The potential of the cosmon is responsible for inflation and the present dark energy. Our model is compatible with all present observations. While the value of the cosmon field increases, the curvature scalar is almost constant during all cosmological epochs. Cosmology has no big bang singularity. There exist other, equivalent choices of field variables for which the universe shows the usual expansion or is static during the radiation or matter dominated epochs. For those “field coordinates“ the big bang is singular. Thus the big bang singularity turns out to be related to a singular choice of field coordinates.

Descriptions:In an as-yet-unpublished report, an international panel of geoscientists has concluded that a pair of deadly earthquakes that struck the Italian region of Emilia-Romagna in 2012 could have been triggered by the extraction of petroleum at a local oil field. Fear of humanmade seismicity has already sparked fierce opposition against new oil and gas drilling efforts in Italy, and some say the report could lead the country's regional presidents to turn down new requests for fossil-fuel exploration.

Descriptions:I. Sagert Michigan State University, East Lansing, Michigan, USA International Symposium on Nuclear Symmetry Energy (NuSYM11) Smith College, Northampton, Massachusetts. 17-20 June, 2011

Descriptions:The concept of neutron star maximum mass is revisited. In particular we show that when the dynamical processes occuring in the first few seconds after the neutron star birth are considered, the concept of neutron star maximum mass, as introduced by Oppenheimer and Volkoff, is partially inadequate. We show that both the maximum mass concept and the final stages of the evolution of massive stars depend on the composition of the neutron star material. In particular, we find two different scenarios depending on the absence or presence of negatively charged hadrons among the constituents. In the first scenario, we show that the Oppenheimer Volkoff mass M_OV_ does not represent the boundary between the value of the masses of neutron stars and black holes. In fact, we find a mass range in which both a neutron star and a black hole may exist. In the second scenario we show that, contrary to the standard view, it is possible to have a supernova explosion (accompained by nucleosynthesis and neutrino emission) followed by the delayed formation of a black hole. The latter mechamism could explain the lack of any observational evidence for a neutron star in the remnant of the supernova 1987A.

Descriptions:Abstract. We review several theories of origin and evolution of the recently discovered extrasolar planetary systems. The properties of these systems were unexpected. This motivated theorists to extend and revise many preexisting theories. Important extensions include migration of bodies and planetary eccentricity pumping by planet-planet interaction, and primordial disk-planet interaction. Progress in observational techniques might allow us to find which of these two types of interaction is mainly responsible for the observed variety of orbits and exoplanet masses. New insights into the formation of our own system can be gained by asking why Jupiter and Saturn are not larger, closer to the sun and/or do not follow noticeably elliptic orbits. Scenarios of planet migration in disks may change markedly on accounta new mode of migration, which does not have a predetermined direction ingiven protoplanetary disk, provided it has zones of low and high density. We present the first simulations of planets undergoing a rapid (runaway) migration. Migration can be inward or outward, depending on the initial disk density distribution. The process is driven by corotational gas flows and orbital libration of underdense disk gas, rather than the previously considered Lindblad resonances or disk viscosity. With characteristic time scale <100 orbital periodsrealistically dense disks, runaway migration can be stopped by density gradients, e.g., at the inner boundary of the magnetically inactive ‘dead zone’ ofprotoplanetary disk, located from 0.1 to a few AU from the star.

Descriptions:The concentration of methane (CH4), the most abundant organic trace gas in the atmosphere, has increased dramatically over the last few centuries, more than doubling its concentration. The increasing concentrations of methane are of special concern because of its effects on climate and atmospheric chemistry. On a per molecule basis, additional methane is much more effective as a greenhouse gas than additional CO2. Methane is also important to both tropospheric and stratospheric chemistry. Here, we examine past trends in the concentration of methane, the sources and sinks affecting its growth rate, and the factors that could affect its growth rate in the future. This study also examines the current understanding of the effects of methane on atmospheric chemistry and climate.

Descriptions:DIRETTIVA 2009/136/CE DEL PARLAMENTO EUROPEO E DEL CONSIGLIO del 25  novembre 2009 recante modifica della direttiva 2002/22/CE relativa al servizio universale e ai diritti degli utenti in materia di reti e di servizi di comunicazione elettronica, della direttiva 2002/58/CE relativa al trattamento dei dati personali e alla tutela della vita privata nel settore delle comunicazioni elettroniche e del regolamento (CE) n.  2006/2004 sulla cooperazione tra le autorità nazionali responsabili dell’esecuzione della normativa a tutela dei consumatori

Descriptions:Se il dialogo da cui scaturì il celebre Paradosso di Fermi "Allora dove sono gli altri?"abbia mai avuto luogo o meno non sta a me accertarlo, ma ormai esso è talmente entrato nell'immaginario collettivo che è diventato come la celebre Mela di Newton. Apocrifa o meno, comunque è una leggenda che merita una risposta. Una risposta che per certi versi è come tentare di risolvere l'Equazione di Drake o almeno l'ultima e più grande incognita dell'Equazione: il fattore L . A differenza di altri studi passati, qui si è cercato di basare questo studio sull'ipotesi (altrettanto opinabile quanto supporre l'esistenza certa di altre forme di vita intelligenti nell'universo basandosi sul fatto che Noi esistiamo) che l'esperienza umana sia tipica anche per il resto dell'universo. Partendo da questa ipotesi si è infine tentato di applicare le stesse spinte sociali umane per tentare una risposta a questa domanda.