1,565 research outputs found
The fossil record of the genus Canis (Canidae, Carnivora, Mammalia) from the Upper Valdarno: A critical revision in the frame of the early and Middle Pleistocene canids of Eurasia
The Montopoli site, a reference Local Fauna in the Pliocene and Pleistocene European Large Mammals Biochronology, first discovered by Giovanni Capellini (1833-1922)
Forward and hybrid path-integral methods in photoelectron holography: sub-barrier corrections, initial sampling and momentum mapping
We construct two strong-field path integral methods with full Coulomb
distortion, in which the quantum pathways are mimicked by interfering electron
orbits: the rate-based CQSFA (R-CQSFA) and the hybrid forward-boundary CQSFA
(H-CQSFA). The methods have the same starting point as the standard Coulomb
quantum-orbit strong-field approximation (CQSFA), but their implementation does
not require pre-knowledge of the orbits' dynamics. These methods are applied to
ultrafast photoelectron holography. In the rate-based method, electron orbits
are forward propagated and we derive a non-adiabatic ionization rate from the
CQSFA, which includes sub-barrier Coulomb corrections and is used to weight the
initial orbit ensemble. In the H-CQSFA, the initial ensemble provides initial
guesses for a subsequent boundary problem and serves to include or exclude
specific momentum regions, but the ionization probabilities associated with
individual trajectories are computed from sub-barrier complex integrals. We
perform comparisons with the standard CQSFA and \textit{ab-initio} methods,
which show that the standard, purely boundary-type implementation of the CQSFA
leaves out whole sets of trajectories. We show that the sub-barrier Coulomb
corrections broaden the resulting photoelectron momentum distributions (PMDs)
and improve the agreement of the R-CQSFA with the H-CQSFA and other approaches.
We probe different initial sampling distributions, uniform and otherwise, and
their influence on the PMDs. We find that initial biased sampling emphasizes
rescattering ridges and interference patterns in high-energy ranges, while an
initial uniform sampling guarantees accurate modeling of the holographic
patterns near the ionization threshold or polarization axis. Our results are
explained using the initial to final momentum mapping for different types of
interfering trajectories.Comment: 25 pages revtex, 14 figures; in the revised version, some
explanations have been extended and some figures have been modifie
La fauna di Cava Monticino (Brisighella, RA) nel contesto dei popolamenti continentali dell’area circum-mediterranea durante il Miocene terminale
A 450 million years long latitudinal gradient in age-dependent extinction.
Leigh Van Valen famously stated that under constant conditions extinction probability is independent of species age. To test this 'law of constant extinction', we developed a new method using deep learning to infer age-dependent extinction and analysed 450Â myr of marine life across 21 invertebrate clades. We show that extinction rate significantly decreases with age in >Â 90% of the cases, indicating that most species died out soon after their appearance while those which survived experienced ever decreasing extinction risk. This age-dependent extinction pattern is stronger towards the Equator and holds true when the potential effects of mass extinctions and taxonomic inflation are accounted for. These results suggest that the effect of biological interactions on age-dependent extinction rate is more intense towards the tropics. We propose that the latitudinal diversity gradient and selection at the species level account for this exceptional, yet little recognised, macroevolutionary and macroecological pattern
A 450 million years long latitudinal gradient in age-dependent extinction
Leigh Van Valen famously stated that under constant conditions extinction probability is independent of species age. To test this 'law of constant extinction', we developed a new method using deep learning to infer age-dependent extinction and analysed 450 myr of marine life across 21 invertebrate clades. We show that extinction rate significantly decreases with age in > 90% of the cases, indicating that most species died out soon after their appearance while those which survived experienced ever decreasing extinction risk. This age-dependent extinction pattern is stronger towards the Equator and holds true when the potential effects of mass extinctions and taxonomic inflation are accounted for. These results suggest that the effect of biological interactions on age-dependent extinction rate is more intense towards the tropics. We propose that the latitudinal diversity gradient and selection at the species level account for this exceptional, yet little recognised, macroevolutionary and macroecological pattern
Applicazioni di paleontologia virtuale su resti fossili e blocchi ossiferi di Cava Monticino (Brisighella, RA)
A millisecond pulsar in a stellar triple system
Gravitationally bound three-body systems have been studied for hundreds of
years and are common in our Galaxy. They show complex orbital interactions,
which can constrain the compositions, masses, and interior structures of the
bodies and test theories of gravity, if sufficiently precise measurements are
available. A triple system containing a radio pulsar could provide such
measurements, but the only previously known such system, B1620-26 (with a
millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of
several decades), shows only weak interactions. Here we report precision timing
and multi-wavelength observations of PSR J0337+1715, a millisecond pulsar in a
hierarchical triple system with two other stars. Strong gravitational
interactions are apparent and provide the masses of the pulsar (1.4378(13)
Msun, where Msun is the solar mass and the parentheses contain the uncertainty
in the final decimal places) and the two white dwarf companions (0.19751(15)
Msun and 0.4101(3) Msun), as well as the inclinations of the orbits (both
approximately 39.2 degrees). The unexpectedly coplanar and nearly circular
orbits indicate a complex and exotic evolutionary past that differs from those
of known stellar systems. The gravitational field of the outer white dwarf
strongly accelerates the inner binary containing the neutron star, and the
system will thus provide an ideal laboratory in which to test the strong
equivalence principle of general relativity.Comment: 17 pages, 3 figures, 1 table. Published online by Nature on 5 Jan
2014. Extremely minor differences with published version may exis
Advanced Parental Age and the Risk of Autism Spectrum Disorder
This study evaluated independent effects of maternal and paternal age on risk of autism spectrum disorder. A case-cohort design was implemented using data from 10 US study sites participating in the Centers for Disease Control and Prevention's Autism and Developmental Disabilities Monitoring Network. The 1994 birth cohort included 253,347 study-site births with complete parental age information. Cases included 1,251 children aged 8 years with complete parental age information from the same birth cohort and identified as having an autism spectrum disorder based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria. After adjustment for the other parent's age, birth order, maternal education, and other covariates, both maternal and paternal age were independently associated with autism (adjusted odds ratio for maternal age â„35 vs. 25â29 yearsâ=â1.3, 95% confidence interval: 1.1, 1.6; adjusted odds ratio for paternal age â„40 years vs. 25â29 yearsâ=â1.4, 95% confidence interval: 1.1, 1.8). Firstborn offspring of 2 older parents were 3 times more likely to develop autism than were third- or later-born offspring of mothers aged 20â34 years and fathers aged <40 years (odds ratio = 3.1, 95% confidence interval: 2.0, 4.7). The increase in autism risk with both maternal and paternal age has potential implications for public health planning and investigations of autism etiology
Study of the reaction pbar p -> phi phi from 1.1 to 2.0 GeV/c
A study has been performed of the reaction pbar p -> 4K using in-flight
antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen
jet target. The reaction is dominated by the production of a pair of phi
mesons. The pbar p -> phi phi cross section rises sharply above threshold and
then falls continuously as a function of increasing antiproton momentum. The
overall magnitude of the cross section exceeds expectations from a simple
application of the OZI rule by two orders of magnitude. In a fine scan around
the xi/f_J(2230) resonance, no structure is observed. A limit is set for the
double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2
resonance of M = 2.235 GeV and Width = 15 MeV.Comment: 13 pages, 13 figures, 2 tables, Latex. To be published in Phys. Rev.
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