arXiv subjects

M. Soriano

Publications and source records attributed to M. Soriano.

9 recordsLinked to original sources

arXiv2018

Lost Waterways: Clues from Digitized Historical Maps of Manila and Other Philippine Cities

We search for lost bodies of water in the cities of Manila, Tacloban, Iloilo, Cebu, Davao, and Naga by aligning their digitized Spanish-era and American-era maps to Google maps. These vanished ancient waterways can either become flooding hazards in case of extreme weather events, or liquefaction hazards, in case of earthquakes. Digitized historical maps of the cities were georectified, overlaid on current Google maps, and checked for potential missing bodies of water. Inspection through field visits and interviews with locals were conducted to verify the actual status of suspected sites. The validation identified lost, found, and even new bodies of water. There was also evidence of affected buildings, rainless flooding, and a new normal for the meaning of flooding among frequently inundated residents.

cs.CY↗

arXiv2017

DSN Transient Observatory

The DSN Transient Observatory (DTO) is a signal processing facility that can monitor up to four DSN downlink bands for astronomically interesting signals. The monitoring is done commensally with reception of deep space mission telemetry. The initial signal processing is done with two CASPER ROACH1 boards, each handling one or two baseband signals. Each ROACH1 has a 10~GBe interface with a GPU-equipped Debian Linux workstation for additional processing. The initial science programs include monitoring Mars for electrostatic discharges, radio spectral lines, searches for fast radio bursts and pulsars and SETI. The facility will be available to the scientific community through a peer review process.

astro-ph.IM↗

arXiv2014

Theory of projections with non-orthogonal basis sets: Partitioning techniques and effective Hamiltonians

Here we present a detailed account of the fundamental problems one encounters in projection theory when non-orthogonal basis sets are used for representation of the operators. In particular, we re-examine the use of projection operators in connection with the calculation of projected (or reduced) Green's functions and associated physical quantities such as the local density of states (LDOS), local charge, and conductance. The unavoidable ambiguity in the evaluation of the LDOS and charge is made explicit with the help of simple examples of metallic nanocontacts while the conductance, within certain obvious limits, remains invariant against the type of projection. We also examine the procedure to obtain effective Hamiltonians from reduced Green's functions. For completeness we include a comparison with results obtained with block-orthogonal basis sets where both direct and dual spaces are used.

cond-mat.mes-hall↗

arXiv2013

Kondo effect and spin quenching in high-spin molecules on metal substrates

Using a state-of-the art combination of density functional theory and impurity solver techniques we present a complete and parameter-free picture of the Kondo effect in the high-spin ($S=3/2$) coordination complex known as Manganese Phthalocyanine adsorbed on the Pb(111) surface. We calculate the correlated electronic structure and corresponding tunnel spectrum and find an asymmetric Kondo resonance, as recently observed in experiments. Contrary to previous claims, the Kondo resonance stems from only one of three possible Kondo channels with origin in the Mn 3d-orbitals, its peculiar asymmetric shape arising from the modulation of the hybridization due to strong coupling to the organic ligand. The spectral signature of the second Kondo channel is strongly suppressed as the screening occurs via the formation of a many-body singlet with the organic part of the molecule. Finally, a spin-1/2 in the 3d-shell remains completely unscreened due to the lack of hybridization of the corresponding orbital with the substrate, hence leading to a spin-3/2 underscreened Kondo effect.

cond-mat.mes-hall↗

arXiv2012

Manipulation of the magnetic ground state of individual manganese phtalocyanines by coordination to CO molecules

We show that the magnetic state of individual manganese phthalocyanine (MnPc) molecules on a Bi(110) surface is modified when the Mn2+ center coordinates to CO molecules adsorbed on top. Using scanning tunneling spectroscopy we identified this change in magnetic properties from the broadening of a Kondo-related zero-bias anomaly when the CO-MnPc complex is formed. The original magnetic state can be recovered by selective desorption of individual CO molecules. First principle calculations show that the CO molecule reduces the spin of the adsorbed MnPc from S = 1 to S = 1=2 and strongly modifies the respective screening channels, driving a transition from an underscreened Kondo state to a state of mix-valence.

cond-mat.mes-hall↗

arXiv2012

First Light for the First Station of the Long Wavelength Array

The first station of the Long Wavelength Array (LWA1) was completed in April 2011 and is currently performing observations resulting from its first call for proposals in addition to a continuing program of commissioning and characterization observations. The instrument consists of 258 dual-polarization dipoles, which are digitized and combined into beams. Four independently-steerable dual-polarization beams are available, each with two "tunings" of 16 MHz bandwidth that can be independently tuned to any frequency between 10 MHz and 88 MHz. The system equivalent flux density for zenith pointing is ~3 kJy and is approximately independent of frequency; this corresponds to a sensitivity of ~5 Jy/beam (5sigma, 1 s); making it one of the most sensitive meter-wavelength radio telescopes. LWA1 also has two "transient buffer" modes which allow coherent recording from all dipoles simultaneously, providing instantaneous all-sky field of view. LWA1 provides versatile and unique new capabilities for Galactic science, pulsar science, solar and planetary science, space weather, cosmology, and searches for astrophysical transients. Results from LWA1 will detect or tightly constrain the presence of hot Jupiters within 50 parsecs of Earth. LWA1 will provide excellent resolution in frequency and in time to examine phenomena such as solar bursts, and pulsars over a 4:1 frequency range that includes the poorly understood turnover and steep-spectrum regimes. Observations to date have proven LWA1's potential for pulsar observing, and just a few seconds with the completed 256-dipole LWA1 provide the most sensitive images of the sky at 23 MHz obtained yet. We are operating LWA1 as an open skies radio observatory, offering ~2000 beam-hours per year to the general community.

astro-ph.IM↗

arXiv2010

New seismic analysis of the exoplanet-host star Mu Arae

We present detailed modelling of the exoplanet-host star Mu Arae, using a new method for the asteroseismic analysis, and taking into account the new value recently derived for the Hipparcos parallax. The aim is to obtain precise parameters for this star and its internal structure, including constraints on the core overshooting. We computed new stellar models in a wider range than Bazot et al. (2005), with various chemical compositions ([Fe/H] and Y), with or without overshooting at the edge of the core. We computed their adiabatic oscillation frequencies and compared them to the seismic observations. For each set of chemical parameters, we kept the model which represented the best fit to the echelle diagram. Then, by comparing the effective temperatures, gravities and luminosities of these models with the spectroscopic error boxes, we were able to derive precise parameters for this star. First we find that all the models which correctly fit the echelle diagram have the same mass and radius, with an uncertainty of the order of one percent. Second, the final comparison with spectroscopic observations leads to the conclusion that besides its high metallicity, Mu Arae has a high helium abundance of the order of Y=0.3. Knowing this allows finding precise values for all the other parameters, mass, radius and age.

astro-ph.SR↗

arXiv2008

Asteroseismology of solar-type stars: signatures of convective and/or helium cores

Asteroseismology of solar-type stars is an important tool for constraining stellar parameters and internal structure. Several frequency combinations are largely used for comparisons between models and observations. In particular, the ``small separations'' are very sensitive to stellar cores. We showed in a previous paper that they can change sign, in contradiction with the ``asymptotic theory'', and that this behaviour could correspond to signatures of convective and/or helium cores. Here we analyse this behaviour in detail by systematic modelling during stellar evolution. We computed evolutionary tracks for models with various masses (from 1.05 to 1.25 Msun) and various chemical composition, with and without overshooting. We computed the adiabatic oscillation frequencies of the models and analysed the evolution of their small separations along an evolutionary track. We found that, for all cases, the stars go through a stage, during their evolution time, where the small separations computed between degrees l=0 and l=2 become negative in the observed range of frequencies. This behaviour is clearly related to the signature of a helium-rich core. We discuss the consequences for the interpretation of the acoustic frequencies observed in solar-type stars.

astro-ph↗

arXiv2007

The CoRoT primary target HD 52265: models and seismic tests

HD 52265 is the only known exoplanet-host star selected as a main target for the seismology programme of the CoRoT satellite. As such, it will be observed continuously during five months, which is of particular interest in the framework of planetary systems studies. This star was misclassified as a giant in the Bright Star Catalog, while it is more probably on the main-sequence or at the beginning of the subgiant branch. We performed an extensive analysis of this star, showing how asteroseismology may lead to a precise determination of its external parameters and internal structure. We first reviewed the observational constraints on the metallicity, the gravity and the effective temperature derived from the spectroscopic observations of HD 52265. We also derived its luminosity using the Hipparcos parallax. We computed the evolutionary tracks for models of various metallicities which cross the relevant observational error boxes in the gravity-effective temperature plane. We selected eight different stellar models which satisfy the observational constraints, computed their p-modes frequencies and analysed specific seismic tests. The possible models for HD 52265, which satisfy the constraints derived from the spectroscopic observations, are different in both their external and internal parameters. They lie either on the main sequence or at the beginning of the subgiant branch. The differences in the models lead to quite different properties of their oscillation frequencies. We give evidences of an interesting specific behaviour of these frequencies in case of helium-rich cores: the ``small separations'' may become negative and give constraints on the size of the core. We expect that the observations of this star by the CoRoT satellite wi ll allow choosing between these possible models.

astro-ph↗