685 research outputs found
Magnetic, electrical, and GPR waterborne surveys of moraine deposits beneath a lake: A case history from Turin, Italy
Bathymetry and bottom sediment types of inland water basins provide meaningful information to estimate water reserves and possible connections between surface and groundwater. Waterborne geophysical surveys can be used to obtain several independent physical parameters to study the sediments. We explored the possibilities of retrieving information on both shallow and deep geological structures beneath a morainic lake by means of waterborne nonseismic methods. In this respect, we discuss simultaneous magnetic, electrical, and groundpenetrating radar (GPR) waterborne surveys on the Candia morainic lake in northerly Turin (Italy).We used waterborne GPR to obtain information on the bottom sediment and the bathymetry needed to constrain the magnetic and electrical inversions. We obtained a map of the total magnetic field (TMF) over the lake from which we computed a 2D constrained compact magnetic inversion for selected profiles, along with a laterally constrained inversion for one electrical profile. The magnetic survey detected some deep anomalous bodies within the subbottom moraine. The electrical profiles gave information on the more superficial layer of bottom sediments. We identify where the coarse morainic material outcrops from the bottom finer sediments from a correspondence between high GPR reflectivity, resistivity, and magnetic anomalie
Proximity Eliashberg theory of electrostatic field-effect-doping in superconducting films
We calculate the effect of a static electric field on the critical
temperature of a s-wave one band superconductor in the framework of proximity
effect Eliashberg theory. In the weak electrostatic field limit the theory has
no free parameters while, in general, the only free parameter is the thickness
of the surface layer where the electric field acts. We conclude that the best
situation for increasing the critical temperature is to have a very thin film
of a superconducting material with a strong increase of electron-phonon (boson)
constant upon charging.Comment: 9 pages, 5 figure
Carrier mobility and scattering lifetime in electric double-layer gated few-layer graphene
We fabricate electric double-layer field-effect transistor (EDL-FET) devices
on mechanically exfoliated few-layer graphene. We exploit the large capacitance
of a polymeric electrolyte to study the transport properties of three, four and
five-layer samples under a large induced surface charge density both above and
below the glass transition temperature of the polymer. We find that the carrier
mobility shows a strong asymmetry between the hole and electron doping regime.
We then employ ab-initio density functional theory (DFT) calculations to
determine the average scattering lifetime from the experimental data. We
explain its peculiar dependence on the carrier density in terms of the specific
properties of the electrolyte we used in our experiments.Comment: 6 pages, 3 figure
Control of bulk superconductivity in a BCS superconductor by surface charge doping via electrochemical gating
The electrochemical gating technique is a powerful tool to tune the surface conduction properties
of various materials by means of pure charge doping, but its efficiency is thought to be hampered in
materials with a good electronic screening. We show that, if applied to a metallic superconductor
(NbN thin films), this approach allows observing reversible enhancements or suppressions of the bulk
superconducting transition temperature, which vary with the thickness of the films. These results
are interpreted in terms of proximity effect, and indicate that the effective screening length depends
on the induced charge density, becoming much larger than that predicted by standard screening
theory at very high electric fields
Multi-Valley Superconductivity In Ion-Gated MoS2 Layers
Layers of transition metal dichalcogenides (TMDs) combine the enhanced
effects of correlations associated with the two-dimensional limit with
electrostatic control over their phase transitions by means of an electric
field. Several semiconducting TMDs, such as MoS, develop superconductivity
(SC) at their surface when doped with an electrostatic field, but the mechanism
is still debated. It is often assumed that Cooper pairs reside only in the two
electron pockets at the K/K' points of the Brillouin Zone. However,
experimental and theoretical results suggest that a multi-valley Fermi surface
(FS) is associated with the SC state, involving 6 electron pockets at the Q/Q'
points. Here, we perform low-temperature transport measurements in ion-gated
MoS flakes. We show that a fully multi-valley FS is associated with the SC
onset. The Q/Q' valleys fill for dopingcm, and the
SC transition does not appear until the Fermi level crosses both spin-orbit
split sub-bands Q and Q. The SC state is associated with the FS
connectivity and promoted by a Lifshitz transition due to the simultaneous
population of multiple electron pockets. This FS topology will serve as a
guideline in the quest for new superconductors.Comment: 12 pages, 7 figure
Notes on the diet of seven terrestrial frogs in three agroecosystems and forest remnants in Northwestern São Paulo State, Brazil.
Anurans are predators of a great diversity of invertebrates, but studies on agroecosystems are very scarce. Herein we described the diet composition of seven species of terrestrial anurans captured in three different agroecosystems (corn, soybean and rubber tree) and in forest remnants of the Northwestern region of São Paulo state, Brazil. Ten prey categories were identified in the stomachs of 80 specimens belonging to the families Bufonidae, Leptodactylidae and Microhylidae. Hymenoptera (Formicidae) was consumed by all species. Coleoptera was the most frequent item, consumed by six of the even species followed by Araneae and Isoptera. Isoptera was the most abundant item followed by Formicidae, Coleoptera and Araneae. Adults and juveniles of Physalaemus nattereri, the most abundant species in our study, consumed Formicidae and Isoptera more than other food items and there is not a significant difference in the abundance of consumed prey items between the age categories. In summary, the majority of the studied species can be considered generalists predators and, probably, consumed the prey items available in the environment. The most abundant species found in our study can be considered here as having a specialized diet, by consuming social insects in great frequency.Published online on 12 August 2015
Generating a magellanic star cluster catalog with ASteCA
An increasing number of software tools have been employed in the recent years for the automated or semi-automated processing of astronomical data. The main advantages of using these tools over a standard by-eye analysis include: speed (particularly for large databases), homogeneity, reproducibility, and precision. At the same time, they enable a statistically correct study of the uncertainties associated with the analysis, in contrast with manually set errors, or the still wide spread practice of simply not assigning errors. We present a catalog comprising 210 star clusters located in the Large and Small Magellanic Clouds, observed with Washington CT 1 photometry. Their fundamental parameters were estimated through an homogeneous,automatized and completely unassisted process, via the Automated Stellar Cluster Analysis package (ASteCA).Our results are compared with two types of studies on these clusters: one where the photometry is the same, andanother where the photometric system is different than that employed by ASteCA.Fil: Perren, Gabriel Ignacio. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de AstrofÃsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas. Instituto de AstrofÃsica La Plata; ArgentinaFil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Vázquez, R. A.. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentin
Withholding irrigation during the establishment phase affected growth and physiology of Norway maple (Acer platanoides) and linden (Tilia spp.).
Age Determination of Fifteen Old to Intermediate-Age Small Magellanic Cloud Star Clusters
We present CMDs in the V and I bands for fifteen star clusters in the Small
Magellanic Cloud (SMC) based on data taken with the Very Large Telescope (VLT,
Chile). We selected these clusters from our previous work, wherein we derived
cluster radial velocities and metallicities from Calcium II infrared triplet
(CaT) spectra also taken with the VLT. We discovered that the ages of six of
our clusters have been appreciably underestimated by previous studies, which
used comparatively small telescopes, graphically illustrating the need for
large apertures to obtain reliable ages of old and intermediate-age SMC star
clusters. In particular, three of these clusters, L4, L6 and L110, turn out to
be amongst the oldest SMC clusters known, with ages of 7.9 +- 1.1, 8.7 +- 1.2
and 7.6 +- 1.0 Gyr, respectively, helping to fill a possible "SMC cluster age
gap" (Glatt et al. 2008). Using the present ages and metallicities from Parisi
et al. (2009), we analyze the age distribution, age gradient and age
metallicity relation (AMR) of a sample of SMC clusters measured homogeneously.
There is a suggestion of bimodality in the age distribution but it does not
show a constant slope for the first 4 Gyr (Piatti 2011), and we find no
evidence for an age gradient. Due to the improved ages of our cluster sample,
we find that our AMR is now better represented in the intermediate/old period
than that we derived in Parisi et al. (2009), where we simply took ages
available in the literature. Additionally, clusters younger than aprox. 4 Gyr
now show better agreement with the bursting model, but we confirm that this
model is not a good representation of the AMR during the intermediate-age/old
period. A more complicated model is needed to explain the SMC chemical
evolution in that period.Comment: 76 pages, 32 figures. Accepted for publication in A
The VMC Survey - XIII : Type II Cepheids in the Large Magellanic Cloud
Date of Acceptance: 27/10/2014The VISTA (Visible and Infrared Survey Telescope for Astronomy) survey of the Magellanic Clouds System (VMC) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near-complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III (Optical Gravitational Lensing Experiment) survey. We present J and Ks light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW Vir) and 27 RV Tau variables. We complement our near-infrared photometry with the V magnitudes from the OGLE III survey, allowing us to build a variety of period-luminosity (PL), period-luminosity-colour (PLC) and period-Wesenheit (PW) relationships, including any combination of the V, J, Ks filters and valid for BL Her and W Vir classes. These relationships were calibrated in terms of the LMC distance modulus, while an independent absolute calibration of the PL(Ks) and the PW(Ks, V) was derived on the basis of distances obtained from Hubble Space Telescope parallaxes and Baade-Wesselink technique. When applied to the LMC and to the Galactic globular clusters hosting T2CEPs, these relations seem to show that (1) the two Population II standard candles RR Lyrae and T2CEPs give results in excellent agreement with each other; (2) there is a discrepancy of ~0.1 mag between Population II standard candles and classical Cepheids when the distances are gauged in a similar way for all the quoted pulsators. However, given the uncertainties, this discrepancy is within the formal 1σ uncertainties.Peer reviewedFinal Accepted Versio
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