Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>Interpreting high-energy, astrophysical phenomena, such as supernova explosions or neutron-star collisions, requires a robust understanding of matter at supranuclear densities. However, our knowledge about dense matter explored in the cores of neutron stars remains limited. Fortunately, dense matter is not probed only in astrophysical observations, but also in terrestrial heavy-ion collision experiments. Here we use Bayesian inference to combine data from astrophysical multi-messenger observations of neutron stars<jats:sup>1–9</jats:sup> and from heavy-ion collisions of gold nuclei at relativistic energies<jats:sup>10,11</jats:sup> with microscopic nuclear theory calculations<jats:sup>12–17</jats:sup> to improve our understanding of dense matter. We find that the inclusion of heavy-ion collision data indicates an increase in the pressure in dense matter relative to previous analyses, shifting neutron-star radii towards larger values, consistent with recent observations by the Neutron Star Interior Composition Explorer mission<jats:sup>5–8</jats:sup>,<jats:sup>18</jats:sup>. Our findings show that constraints from heavy-ion collision experiments show a remarkable consistency with multi-messenger observations and provide complementary information on nuclear matter at intermediate densities. This work combines nuclear theory, nuclear experiment and astrophysical observations, and shows how joint analyses can shed light on the properties of neutron-rich supranuclear matter over the density range probed in neutron stars.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Spatially resolved vibrational mapping of nanostructures is indispensable to the development and understanding of thermal nanodevices<jats:sup>1</jats:sup>, modulation of thermal transport<jats:sup>2</jats:sup> and novel nanostructured thermoelectric materials<jats:sup>3–5</jats:sup>. Through the engineering of complex structures, such as alloys, nanostructures and superlattice interfaces, one can significantly alter the propagation of phonons and suppress material thermal conductivity while maintaining electrical conductivity<jats:sup>2</jats:sup>. There have been no correlative experiments that spatially track the modulation of phonon properties in and around nanostructures due to spatial resolution limitations of conventional optical phonon detection techniques. Here we demonstrate two-dimensional spatial mapping of phonons in a single silicon–germanium (SiGe) quantum dot (QD) using monochromated electron energy loss spectroscopy in the transmission electron microscope. Tracking the variation of the Si optical mode in and around the QD, we observe the nanoscale modification of the composition-induced red shift. We observe non-equilibrium phonons that only exist near the interface and, furthermore, develop a novel technique to differentially map phonon momenta, providing direct evidence that the interplay between diffuse and specular reflection largely depends on the detailed atomistic structure: a major advancement in the field. Our work unveils the non-equilibrium phonon dynamics at nanoscale interfaces and can be used to study actual nanodevices and aid in the understanding of heat dissipation near nanoscale hotspots, which is crucial for future high-performance nanoelectronics.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Rapid and reliable estimation of large earthquake magnitude (above 8) is key to mitigating the risks associated with strong shaking and tsunamis<jats:sup>1</jats:sup>. Standard early warning systems based on seismic waves fail to rapidly estimate the size of such large earthquakes<jats:sup>2–5</jats:sup>. Geodesy-based approaches provide better estimations, but are also subject to large uncertainties and latency associated with the slowness of seismic waves. Recently discovered speed-of-light prompt elastogravity signals (PEGS) have raised hopes that these limitations may be overcome<jats:sup>6,7</jats:sup>, but have not been tested for operational early warning. Here we show that PEGS can be used in real time to track earthquake growth instantaneously after the event reaches a certain magnitude. We develop a deep learning model that leverages the information carried by PEGS recorded by regional broadband seismometers in Japan before the arrival of seismic waves. After training on a database of synthetic waveforms augmented with empirical noise, we show that the algorithm can instantaneously track an earthquake source time function on real data. Our model unlocks ‘true real-time’ access to the rupture evolution of large earthquakes using a portion of seismograms that is routinely treated as noise, and can be immediately transformative for tsunami early warning.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Archaeological remains of agrarian-based, low-density urbananism<jats:sup>1–3</jats:sup> have been reported to exist beneath the tropical forests of Southeast Asia, Sri Lanka and Central America<jats:sup>4–6</jats:sup>. However, beyond some large interconnected settlements in southern Amazonia<jats:sup>7–9</jats:sup>, there has been no such evidence for pre-Hispanic Amazonia. Here we present lidar data of sites belonging to the Casarabe culture (around <jats:sc>ad</jats:sc> 500 to <jats:sc>ad</jats:sc> 1400)<jats:sup>10–13</jats:sup> in the Llanos de Mojos savannah–forest mosaic, southwest Amazonia, revealing the presence of two remarkably large sites (147 ha and 315 ha) in a dense four-tiered settlement system. The Casarabe culture area, as far as known today, spans approximately 4,500 km<jats:sup>2</jats:sup>, with one of the large settlement sites controlling an area of approximately 500 km<jats:sup>2</jats:sup>. The civic-ceremonial architecture of these large settlement sites includes stepped platforms, on top of which lie U-shaped structures, rectangular platform mounds and conical pyramids (which are up to 22 m tall). The large settlement sites are surrounded by ranked concentric polygonal banks and represent central nodes that are connected to lower-ranked sites by straight, raised causeways that stretch over several kilometres. Massive water-management infrastructure, composed of canals and reservoirs, complete the settlement system in an anthropogenically modified landscape. Our results indicate that the Casarabe-culture settlement pattern represents a type of tropical low-density urbanism that has not previously been described in Amazonia.</jats:p>