Two-neutrino double electron capture on 124^{124}Xe based on an effective theory and the nuclear shell model

We study the two-neutrino double electron capture on $^{124}$Xe based on an effective theory (ET) and large-scale shell model calculations, two modern nuclear structure approaches that have been tested against Gamow-Teller and double-beta decay data. In the ET, the low-energy constants are fit to electron capture and $\beta^{-}$ transitions around xenon. For the nuclear shell model, we use an interaction in a large configuration space that reproduces the spectroscopy of nuclei in this mass region. For the dominant transition to the $^{124}$Te ground state, we find half-lives $T^{2\nu{\rm ECEC}}_{1/2}=(1.3-18)\times 10^{22}$ y for the ET and $T^{2\nu{\rm ECEC}}_{1/2} = (0.43-2.9)\times 10^{22}$ y for the shell model. The ET uncertainty leads to a half-life almost entirely consistent with present experimental limits and largely within the reach of ongoing experiments. The shell model half-life range overlaps with the ET, but extends less beyond current limits. Our findings thus suggest that the two-neutrino double electron capture on $^{124}$Xe has a good chance to be discovered by ongoing or future experiments. In addition, we present results for the two-neutrino double electron capture to excited states of $^{124}$Te.Comment: 5 pages, 2 figure

Three-body forces and proton-rich nuclei

We present the first study of three-nucleon (3N) forces for proton-rich nuclei along the N=8 and N=20 isotones. Our results for the ground-state energies and proton separation energies are in very good agreement with experiment where available, and with the empirical isobaric multiplet mass equation. We predict the spectra for all N=8 and N=20 isotones to the proton dripline, which agree well with experiment for 18Ne, 19Na, 20Mg and 42Ti. In all other cases, we provide first predictions based on nuclear forces. Our results are also very promising for studying isospin symmetry breaking in medium-mass nuclei based on chiral effective field theory.Comment: 5 pages, 4 figures, minor changes, published versio

Uncertainties in constraining low-energy constants from 3^3H β\beta decay

We discuss the uncertainties in constraining low-energy constants of chiral effective field theory from $^3$H $\beta$ decay. The half-life is very precisely known, so that the Gamow-Teller matrix element has been used to fit the coupling $c_D$ of the axial-vector current to a short-range two-nucleon pair. Because the same coupling also describes the leading one-pion-exchange three-nucleon force, this in principle provides a very constraining fit, uncorrelated with the $^3$H binding energy fit used to constrain another low-energy coupling in three-nucleon forces. However, so far such $^3$H half-life fits have only been performed at a fixed cutoff value. We show that the cutoff dependence due to the regulators in the axial-vector two-body current can significantly affect the Gamow-Teller matrix elements and consequently also the extracted values for the $c_D$ coupling constant. The degree of the cutoff dependence is correlated with the softness of the employed NN interaction. As a result, present three-nucleon forces based on a fit to $^3$H $\beta$ decay underestimate the uncertainty in $c_D$. We explore a range of $c_D$ values that is compatible within cutoff variation with the experimental $^3$H half-life and estimate the resulting uncertainties for many-body systems by performing calculations of symmetric nuclear matter.Comment: 9 pages, 11 figures, published version, includes Erratum, which corrects Figs. 2-6 due to the incorrect c_D relation between 3N forces and two-body currents use

Self-compensation in phosphorus-doped CdTe

We investigate the self-compensation mechanism in phosphorus-doped CdTe. The formation energies, charge transition levels, and defects states of several P-related point defects susceptible to cause self-compensation are addressed by first-principles calculations. Moreover, we assess the in uence of the spin-orbit coupling and supercell-size effects on the stability of AX centers donors, which are believed to be responsible for most of the self-compensation. We report an improved result for the lowest-energy configuration of the P interstitial (P$_\text{i}$) and find that the self-compensation mechanism is not due to the formation of AX centers. Under Te-rich growth conditions, (P$_\text{i}$) exhibits a formation energy lower than the substitutional acceptor (P$_\text{Te}$) when the Fermi level is near the valence band, acting as compensating donor. While, for Cd-rich growth conditions, our results suggest that p-type doping is limited by the formation of (P$_\text{Te}$-V$_\text{Te}$) complexes.Comment: 5 page

Coexistence of spherical states with deformed and superdeformed bands in doubly magic 40-Ca; A shell model challenge

Large scale shell model calculations, with dimensions reaching 10**9, are carried out to describe the recently observed deformed (ND) and superdeformed (SD) bands based on the first and second excited 0+ states of 40-Ca at 3.35-MeV and 5.21-MeV respectively. A valence space comprising two major oscillator shells, sd and pf, can accommodate most of the relevant degrees of freedom of this problem. The ND band is dominated by configurations with four particles promoted to the pf-shell (4p-4h in short). The SD band by 8p-8h configurations. The ground state of 40-Ca is strongly correlated, but the closed shell still amounts to 65%. The energies of the bands are very well reproduced by the calculations. The out-band transitions connecting the SD band with other states are very small and depend on the details of the mixing among the different np-nh configurations, in spite of that, the calculation describes them reasonably. For the in-band transition probabilities along the SD band, we predict a fairly constant transition quadrupole moment Q_0(t)~170 e fm**2 up to J=10, that decreases toward the higher spins. We submit also that the J=8 states of the deformed and superdeformed band are maximally mixed.Comment: 12 pages, 9 figure

Fascículo II. Plantas fósiles

Los fósiles vegetales hallados en la Provincia de Buenos Aires, están principalmente representados por aquellos de la flora pérmica de la Sierra de Pillahuincó, ya que no se conocen otros restos vegetales en el Paleozoico, aparte de ciertos restos de naturaleza problemática, y no se han hallado sedimentos mesozoicos. Con respecto a formaciones sedimentarias más jóvenes, sólo hay citas aisladas de restos vegetales sin descripción. En 1916 Wichmann cita fructificaciones de Charáceas para el Pospampeano de Bahía Blanca en comparación con material de Río Negro, de las cuales ilustra un ejemplar que considera genéricamente indeterminable por carecer de la corona apical de células que permitiría saber si se trata de Chara o Nitella. En 1933 Rusconi cita, en una nota preliminar, la presencia de leños fósiles en las arenas puelchenses de Villa Ballester, cita que reitera en 1934, también sin determinación del material. Posteriormente dicho autor entrega ese material al profesor A. C. Scala para su determinación, quien fallece antes de describirlo, pero dejando la determinación respectiva, (in schedis) que Rusconi transcribe en 1934, con el número de su colección particular. Tales determinaciones son: “ N° 570 a 573, Quebrado Colorado (Schinopsis Lorentzii) N° 574, Quebrado colorado? N° 575, muy descompuesto (Quebracho colorado?) N° 576, Cedro colorado (Cedrela fissilis) N° 577, cortezas y leños de algarrobo (negro?) N° 578, Algarrobo (negro?, Prosopis nigra) N° 579, corteza de (quebracho colorado?) Nº 580, Mora (?), Chlorophora tinctoriá) N° 581, Urunday (?) (Astronium balansae) N° 582, Ceibo (Erythrina cristagalli) ” En 1936 y 1937 Rusconi vuelve a citar estos ejemplares en una lista sobre organismos fósiles del Puelcbense de Buenos Aires. Otras citas se refieren a microfósiles de Buenos Aires que 6on considerados en otra parte de esta obra. La flora de las sierras australes de Buenos Aires fue estudiada por Harrington en 1934, cuya enumeración cita posteriormente en 1947 con el agregado de Walkomia sp. Desde entonces, salvo dos notas del autor (1962 a y b) no hubo otro aporte al conocimiento de dicha flora, por tal motivo, en base a nuevas colecciones hechas por los doctores, A. Amos, H. Castellaro, T. Suero y el autor y el material original de Harrington, se ha hecho en este trabajo, una revisión de la flora de la Sierra de Pillahuincó.Digitalizado en SEDICI-CIC Digita

MOCDroid: multi-objective evolutionary classifier for Android malware detection

Malware threats are growing, while at the same time, concealment strategies are being used to make them undetectable for current commercial Anti-Virus. Android is one of the target architectures where these problems are specially alarming, due to the wide extension of the platform in different everyday devices.The detection is specially relevant for Android markets in order to ensure that all the software they offer is clean, however, obfuscation has proven to be effective at evading the detection process. In this paper we leverage third-party calls to bypass the effects of these concealment strategies, since they cannot be obfuscated. We combine clustering and multi-objective optimisation to generate a classifier based on specific behaviours defined by 3rd party calls groups. The optimiser ensures that these groups are related to malicious or benign behaviours cleaning any non-discriminative pattern. This tool, named MOCDroid, achieves an ac-curacy of 94.6% in test with 2.12% of false positives with real apps extracted from the wild, overcoming all commercial Anti-Virus engines from VirusTotal

El ICMA instala un nuevo detector de neutrones en el Institut Laue-Langevin

Página web divulgativa.El Instituto de Ciencia Materiales de Aragón (ICMA) ha desarrollado un detector de neutrones, y ya lo está instalando en el Institut Laue-Langevin (ILL) de Grenoble (Francia), centro de referencia mundial en técnicas neutrónicas. Además, el Instituto gestionará para toda España los instrumentos españoles del ILL.Peer Reviewe

Electric field and exciton structure in CdSe nanocrystals

Quantum Stark effect in semiconductor nanocrystals is theoretically investigated, using the effective mass formalism within a $4\times 4$ Baldereschi-Lipari Hamiltonian model for the hole states. General expressions are reported for the hole eigenfunctions at zero electric field. Electron and hole single particle energies as functions of the electric field ($\mathbf{E}_{QD}$) are reported. Stark shift and binding energy of the excitonic levels are obtained by full diagonalization of the correlated electron-hole Hamiltonian in presence of the external field. Particularly, the structure of the lower excitonic states and their symmetry properties in CdSe nanocrystals are studied. It is found that the dependence of the exciton binding energy upon the applied field is strongly reduced for small quantum dot radius. Optical selection rules for absorption and luminescence are obtained. The electric-field induced quenching of the optical spectra as a function of $\mathbf{E}_{QD}$ is studied in terms of the exciton dipole matrix element. It is predicted that photoluminescence spectra present anomalous field dependence of the emission lines. These results agree in magnitude with experimental observation and with the main features of photoluminescence experiments in nanostructures.Comment: 9 pages, 7 figures, 1 tabl