2,628 research outputs found
Emergent quantum matter in graphene nanoribbons
In this book chapter, we introduce different schemes to create quantum states
of matter in engineered graphene nanoribbons. We will focus on the emergence of
controllable magnetic interactions, topological quantum magnets, and the
interplay of magnetism and superconductivity. We comment on the experimental
signatures of those states stemming from their electronic and spin excitations,
that can be observed with atomic resolution using scanning probe techniques.Comment: 14 pages, 9 figures. Submitted book chapter for "Graphene
Nanoribbons", Edited by A. Tejeda, P. Seneor, L. Bre
A mid-term astrometric and photometric study of Trans-Neptunian Object (90482) Orcus
From CCD observations of a fixed and large star field that contained the
binary TNO Orcus, we have been able to derive high-precision relative
astrometry and photometry of the Orcus system with respect to background stars.
The RA residuals of an orbital fit to the astrometric data revealed a
periodicity of 9.7+-0.3 days, which is what one would expect to be induced by
the known Orcus companion. The residuals are also correlated with the
theoretical positions of the satellite with regard to the primary. We therefore
have revealed the presence of Orcus' satellite in our astrometric measurements.
The photocenter motion is much larger than the motion of Orcus around the
barycenter, and we show here that detecting some binaries through a carefully
devised astrometric technique might be feasible with telescopes of moderate
size. We also analyzed the system's mid-term photometry to determine whether
the rotation could be tidally locked to the satellite's orbital period. We
found that a photometric variability of 9.7+-0.3 days is clear in our data, and
is nearly coincident with the orbital period of the satellite. We believe this
variability might be induced by the satellite's rotation. There is also a
slight hint for an additional small variability in the 10 hr range that was
already reported in the literature. This short-term variability would indicate
that the primary is not tidally locked and therefore the system would not have
reached a double synchronous state. Implications for the basic physical
properties of the primary and its satellite are discussed. From angular
momentum considerations we suspect that the Orcus satellite might have formed
from a rotational fission. This requires that the mass of the satellite would
be around 0.09 times that of the primary, close to the value that one derives
by using an albedo of 0.12 for the satellite and assuming equal densities for
both objects.Comment: in Press at A&
Transneptunian objects and Centaurs from light curves
We analyze a vast light curve database by obtaining mean rotational
properties of the entire sample, determining the spin frequency distribution
and comparing those data with a simple model based on hydrostatic equilibrium.
For the rotation periods, the mean value obtained is 6.95 h for the whole
sample, 6.88 h for the Trans-neptunian objects (TNOs) alone and 6.75 h for the
Centaurs. From Maxwellian fits to the rotational frequencies distribution the
mean rotation rates are 7.35 h for the entire sample, 7.71 h for the TNOs alone
and 8.95 h for the Centaurs. These results are obtained by taking into account
the criteria of considering a single-peak light curve for objects with
amplitudes lower than 0.15 mag and a double-peak light curve for objects with
variability >0.15mag. The best Maxwellian fits were obtained with the threshold
between 0.10 and 0.15mag. The mean light-curve amplitude for the entire sample
is 0.26 mag, 0.25mag for TNOs only, and 0.26mag for the Centaurs. The amplitude
versus Hv correlation clearly indicates that the smaller (and collisionally
evolved) objects are more elongated than the bigger ones. From the model
results, it appears that hydrostatic equilibrium can explain the statistical
results of almost the entire sample, which means hydrostatic equilibrium is
probably reached by almost all TNOs in the H range [-1,7]. This implies that
for plausible albedos of 0.04 to 0.20, objects with diameters from 300km to
even 100km would likely be in equilibrium. Thus, the great majority of objects
would qualify as being dwarf planets because they would meet the hydrostatic
equilibrium condition. The best model density corresponds to 1100 kg/m3.Comment: 21 pages, 8 figures. Astronomy & Astrophysics, in pres
Dual activation of pathways regulated by steroid receptors and peptide growth factors in primary prostate cancer revealed by Factor Analysis of microarray data
BACKGROUND: We use an approach based on Factor Analysis to analyze datasets generated for transcriptional profiling. The method groups samples into biologically relevant categories, and enables the identification of genes and pathways most significantly associated to each phenotypic group, while allowing for the participation of a given gene in more than one cluster. Genes assigned to each cluster are used for the detection of pathways predominantly activated in that cluster by finding statistically significant associated GO terms. We tested the approach with a published dataset of microarray experiments in yeast. Upon validation with the yeast dataset, we applied the technique to a prostate cancer dataset. RESULTS: Two major pathways are shown to be activated in organ-confined, non-metastatic prostate cancer: those regulated by the androgen receptor and by receptor tyrosine kinases. A number of gene markers (HER3, IQGAP2 and POR1) highlighted by the software and related to the later pathway have been validated experimentally a posteriori on independent samples. CONCLUSION: Using a new microarray analysis tool followed by a posteriori experimental validation of the results, we have confirmed several putative markers of malignancy associated with peptide growth factor signalling in prostate cancer and revealed others, most notably ERRB3 (HER3). Our study suggest that, in primary prostate cancer, HER3, together or not with HER4, rather than in receptor complexes involving HER2, could play an important role in the biology of these tumors. These results provide new evidence for the role of receptor tyrosine kinases in the establishment and progression of prostate cancer
Dual activation of pathways regulated by steroid receptors and peptide growth factors in primary prostate cancer revealed by Factor Analysis of microarray data
BACKGROUND: We use an approach based on Factor Analysis to analyze datasets generated for transcriptional profiling. The method groups samples into biologically relevant categories, and enables the identification of genes and pathways most significantly associated to each phenotypic group, while allowing for the participation of a given gene in more than one cluster. Genes assigned to each cluster are used for the detection of pathways predominantly activated in that cluster by finding statistically significant associated GO terms. We tested the approach with a published dataset of microarray experiments in yeast. Upon validation with the yeast dataset, we applied the technique to a prostate cancer dataset. RESULTS: Two major pathways are shown to be activated in organ-confined, non-metastatic prostate cancer: those regulated by the androgen receptor and by receptor tyrosine kinases. A number of gene markers (HER3, IQGAP2 and POR1) highlighted by the software and related to the later pathway have been validated experimentally a posteriori on independent samples. CONCLUSION: Using a new microarray analysis tool followed by a posteriori experimental validation of the results, we have confirmed several putative markers of malignancy associated with peptide growth factor signalling in prostate cancer and revealed others, most notably ERRB3 (HER3). Our study suggest that, in primary prostate cancer, HER3, together or not with HER4, rather than in receptor complexes involving HER2, could play an important role in the biology of these tumors. These results provide new evidence for the role of receptor tyrosine kinases in the establishment and progression of prostate cancer
Distorted Heisenberg Algebra and Coherent States for Isospectral Oscillator Hamiltonians
The dynamical algebra associated to a family of isospectral oscillator
Hamiltonians is studied through the analysis of its representation in the basis
of energy eigenstates. It is shown that this representation becomes similar to
that of the standard Heisenberg algebra, and it is dependent of a parameter
. We name it {\it distorted Heisenberg algebra}, where is the
distortion parameter. The corresponding coherent states for an arbitrary
are derived, and some particular examples are discussed in full detail. A
prescription to produce the squeezing, by adequately selecting the initial
state of the system, is given.Comment: 21 pages, Latex, 3 figures available as hard copies upon request from
the first Autho
Mars Sulfate Formation Sourced in Sulfide-Enriched Subsurface Fluids: The Rio Tinto Model
The extensive evidence for sulfate deposits on Mars provided by analyses of MER and Mars Express data shows that the sulfur played an essential role in the geochemical cycles of the planet, including reservoirs in the atmosphere, hydro-sphere and geosphere. Overall the data are consistent with a fluvial/lacustrine-evaporative origin of at least some of the sulfate deposits, with mineral precipitation through oversaturation of salty acidic fluids enriched in sulfates. This scenario requires reservoirs of sulfur and associated cations, as well as an acidic and oxidizing hydrochemistry which could be provided by surface and subsurface catching of meteoric waters resulting in the presence of sulfur-bearing gases and steam photochemistry. In this work we suggest a new scenario for the extensive generation of sulfates in Mars based on the observation of seasonal changes in the redox and pH of subsurface waters enriched in sulfur that supply the acidic Mars process analog of Rio Tinto. This model considers the long-term subsurface storage of sulfur during most of Noachian and its release from the late Noachian to Hesperian time through weathering by meteoric fluids that would acidify and oxidize the sulfur bearing compounds stored in the subsurface
Magma displacements under insular volcanic fields, applications to eruption forecasting: El Hierro, Canary Islands, 2011-2013
Significant deformations, followed by increased seismicity detected since 2011 July at El Hierro, Canary Islands, Spain, prompted the deployment of additional monitoring equipment. The climax of this unrest was a submarine eruption first detected on 2011 October 10, and located at about 2 km SW of La Restinga, southernmost village of El Hierro Island. The eruption ceased on 2012 March 5, after the volcanic tremor signals persistently weakened through 2012 February. However, the seismic activity did not end with the eruption, as several other seismic crises followed. The seismic episodes presented a characteristic pattern: over a few days the number and magnitude of seismic event increased persistently, culminating in seismic events severe enough to be felt all over the island. Those crises occurred in 2011 November, 2012 June and September, 2012 December to 2013 January and in 2013 March-April. In all cases the seismic unrest was preceded by significant deformations measured on the island's surface that continued during the whole episode. Analysis of the available GPS and seismic data suggests that several magma displacement processes occurred at depth from the beginning of the unrest. The first main magma movement or 'injection' culminated with the 2011 October submarine eruption. A model combining the geometry of the magma injection process and the variations in seismic energy release has allowed successful forecasting of the new-vent opening.CSIC [2011-30E070]; MINECO [CGL2011-28682-C02-01]; bilateral UNAM (Mexico) - CSIC (Spain) program; Mayor's Office of El Pinar de El Hierroinfo:eu-repo/semantics/publishedVersio
Engineering spin exchange in nonbipartite graphene zigzag edges
The rules that govern spin exchange interaction in pristine graphene nanostructures are constrained by the bipartite character of the lattice, so that the sign of the exchange is determined by whether magnetic moments are on the same sublattice or not. The synthesis of graphene ribbons with perfect zigzag edges and a fluoranthene group with a pentagon ring, a defect that breaks the bipartite nature of the honeycomb lattice, has been recently demonstrated. Here we address how the electronic and spin properties of these structures are modified by such defects, both for indirect exchange interactions as well as the emergent edge magnetism, studied both with density functional theory and mean-field Hubbard model calculations. In all instances we find that the local breakdown of the bipartite nature at the defect reverts the sign of the otherwise ferromagnetic correlations along the edge, introducing a locally antiferromagnetic intraedge coupling and, for narrow ribbons, also revert the antiferromagnetic interedge interactions that are normally found in pristine ribbons. Our findings show that these pentagon defects are a resource that permits us to engineer the spin exchange interactions in graphene-based nanostructures
Calculation of Band Edge Eigenfunctions and Eigenvalues of Periodic Potentials through the Quantum Hamilton - Jacobi Formalism
We obtain the band edge eigenfunctions and the eigenvalues of solvable
periodic potentials using the quantum Hamilton - Jacobi formalism. The
potentials studied here are the Lam{\'e} and the associated Lam{\'e} which
belong to the class of elliptic potentials. The formalism requires an
assumption about the singularity structure of the quantum momentum function
, which satisfies the Riccati type quantum Hamilton - Jacobi equation, in the complex plane. Essential
use is made of suitable conformal transformations, which leads to the
eigenvalues and the eigenfunctions corresponding to the band edges in a simple
and straightforward manner. Our study reveals interesting features about the
singularity structure of , responsible in yielding the band edge
eigenfunctions and eigenvalues.Comment: 21 pages, 5 table
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