First-principles study of lithium-doped carbon clathrates under pressure

We present a theoretical study on the behavior under pressure of the two hypothetical C$_{46}$ and Li$_8$C$_{46}$ type-I carbon clathrates in order to bring new informations concerning their synthesis. Using \textit{ab initio} calculations, we have explored the energetic and structural properties under pressure of these two carbon based cage-like materials. These low-density meta-stable phases show large negative pressure transitions compared to diamond which represent a serious obstacle for their synthesis. However, we evidence that a minimum energy barrier can be reached close to 40 GPa, suggesting that the synthesis of the Li-clathrate under extreme conditions of pressure and temperature may be possible. Electronic band structure with related density of states behavior under pressure as well as the dependence of the active Raman modes with pressure are also examined

Exits from unemployment: recall or new job

This paper studies transitions out of unemployment in Spain distinguishing between recall to the same employer and reemployment in a new job. We use a large sample of newly unemployed workers obtained from Social Security records for Spain. These data contain information about each individual's employer identy before and after the unemployment spell. A discrete-time duration model with competing risks of exits serves us to investigate the factors that influence the probabilities of leaving unemployment to return to the same employer or to find a new job with a different employer. We find that the route to exit unemployment is determinant to understand the influence of individual an job characteristics on the hazard rate, as well as the latter dependence on unemployment duration. The recall hazard rate exhibits positive duration dependence during the first months and negative duration dependence thereafter (it is larger for females), while the new-job hazard presents positive duration dependence (it is larger for males).

Coupling infrared thermography and acoustic emission for damage study in CFRP composites

Improvement of the design and reliability of aeronautical composite structures requires an identification and characterization of their damage evolution. By providing surface thermal fields, infrared thermography has allowed considerable progress in the detection of degradation phenomena. On the other hand, acoustic emission is employed to record the transient waves resulting from released energy during a damage process. This study intends to combine simultaneously these nondestructive methods to investigate the damage behaviour of carbon-fibre composites under tensile load. Experimental results show some correlations between thermal and acoustic events induced by the load according to the damage development

Damage detection in CFRP by coupling acoustic emission and infrared thermography

Acoustic emission (AE) and infrared thermography (IT) are simultaneously combined to identify damage evolution in carbon fibre reinforced composites. Samples are subjected to tensile static loads while acoustic emission sensors and an infrared camera record the acoustic signals and the temperature variations respectively. Unsupervised pattern recognition procedure is applied to identify damage mechanisms from acoustic signals. Thermodynamic arguments are introduced to estimate global heat source fields from thermal measurements and anisotropic heat conduction behavior is taken into account by means of homogenization technique. A spatial and time analysis of acoustic events and heat sources is developed and some correlation range in the AE and IT events amplitude are identified

Wnt/ß-catenin signalling and the dynamics of fate decisions in early mouse embryos and embryonic stem (ES) cells

Wnt/β-catenin signalling is a widespread cell signalling pathway with multiple roles during vertebrate development. In mouse embryonic stem (mES) cells, there is a dual role for β-catenin: it promotes differentiation when activated as part of the Wnt/β-catenin signalling pathway, and promotes stable pluripotency independently of signalling. Although mES cells resemble the preimplantation epiblast progenitors, the first requirement for Wnt/β-catenin signalling during mouse development has been reported at implantation [1,2]. The relationship between β-catenin and pluripotency and that of mES cells with epiblast progenitors suggests that β-catenin might have a functional role during preimplantation development. Here we summarize the expression and function of Wnt/β-catenin signalling elements during the early stages of mouse development and consider the reasons why the requirement in ES cells do not reflect the embryo

Lattice dynamics study of cubic Tb2O3

"This is the peer reviewed version of the following article: Ibáñez, Jordi, Oriol Blázquez, Sergi Hernández, Blas Garrido, Plácida Rodríguez-Hernández, Alfonso Muñoz, Matias Velázquez, Philippe Veber, and Francisco Javier Manjón. 2018. Lattice Dynamics Study of Cubic Tb 2 O 3. Journal of Raman Spectroscopy 49 (12). Wiley: 2021 27. doi:10.1002/jrs.5488, which has been published in final form at https://doi.org/10.1002/jrs.5488. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] We report a joint experimental and theoretical study of the lattice dynamics of cubic Tb2O3. Up to 16 optical Raman-active modes have been observed with polarized and unpolarized Raman scattering measurements on a high-quality Tb2O3 single crystal. The measured wavenumbers have been compared with those of other rare-earth (RE) and related sesquioxides with cubic (C-type or bixbyite) structure. First-principles calculations have allowed us to assign the symmetry of the experimentally observed Raman-active modes. Additional lattice-dynamical calculations on the related cubic RE sesquioxides Dy2O3, Gd2O3, Eu2O3, and Sm2O3 indicate that the phonon wavenumbers of the Raman-active modes in these compounds are monotonically reduced with increasing the lattice parameter along the Dy2O3-Tb2O3-Gd2O3-Eu2O3-Sm2O3 series, thus prompting for a revision of the experimental Raman spectra of some of these compounds (mainly Eu2O3 but also Gd2O3).This study was supported by the Spanish Ministerio de Economía y Competitividad under Projects MAT2015-71070-REDC, MAT2015-71035-R, MAT2016-75586-C4-2-P/3-P, and FIS2017-2017-83295-P.Ibanez, J.; Blazquez, O.; Hernandez, S.; Garrido, B.; Rodríguez-Hernández, P.; Munoz, A.; Velazquez, M.... (2018). Lattice dynamics study of cubic Tb2O3. Journal of Raman Spectroscopy. 49(12):2021-2027. https://doi.org/10.1002/jrs.5488S202120274912Pan, T.-M., Chen, F.-H., & Jung, J.-S. (2010). Structural and electrical characteristics of high-k Tb2O3 and Tb2TiO5 charge trapping layers for nonvolatile memory applications. Journal of Applied Physics, 108(7), 074501. doi:10.1063/1.3490179Kao, C. H., Liu, K. C., Lee, M. H., Cheng, S. N., Huang, C. H., & Lin, W. K. (2012). High dielectric constant terbium oxide (Tb2O3) dielectric deposited on strained-Si:C. Thin Solid Films, 520(8), 3402-3405. doi:10.1016/j.tsf.2011.10.173Gray, N. W., Prestgard, M. C., & Tiwari, A. (2014). Tb2O3 thin films: An alternative candidate for high-k dielectric applications. Applied Physics Letters, 105(22), 222903. doi:10.1063/1.4903072Geppert, I., Eizenberg, M., Bojarczuk, N. A., Edge, L. F., Copel, M., & Guha, S. (2010). Determination of band offsets, chemical bonding, and microstructure of the (TbxSc1−x)2O3/Si system. Journal of Applied Physics, 108(2), 024105. doi:10.1063/1.3427554Belaya, S. V., Bakovets, V. V., Boronin, A. I., Koshcheev, S. V., Lobzareva, M. N., Korolkov, I. V., & Stabnikov, P. A. (2014). Terbium oxide films grown by chemical vapor deposition from terbium(III) dipivaloylmethanate. Inorganic Materials, 50(4), 379-386. doi:10.1134/s0020168514040037Bakovets, V. V., Belaya, S. V., Lobzareva, M. N., & Maksimovskii, E. A. (2014). Kinetics of terbium oxide film growth from Tb(dpm)3 vapor. Inorganic Materials, 50(6), 576-581. doi:10.1134/s0020168514060016Veber, P., Velázquez, M., Gadret, G., Rytz, D., Peltz, M., & Decourt, R. (2015). Flux growth at 1230 °C of cubic Tb2O3single crystals and characterization of their optical and magnetic properties. CrystEngComm, 17(3), 492-497. doi:10.1039/c4ce02006eAbrashev, M. V., Todorov, N. D., & Geshev, J. (2014). Raman spectra of R2O3 (R—rare earth) sesquioxides with C-type bixbyite crystal structure: A comparative study. Journal of Applied Physics, 116(10), 103508. doi:10.1063/1.4894775Urban, M. W., & Cornilsen, B. C. (1987). Bonding anomalies in the rare earth sesquioxides. Journal of Physics and Chemistry of Solids, 48(5), 475-479. doi:10.1016/0022-3697(87)90108-9Hohenberg, P., & Kohn, W. (1964). Inhomogeneous Electron Gas. Physical Review, 136(3B), B864-B871. doi:10.1103/physrev.136.b864Kresse, G., & Furthmüller, J. (1996). Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Computational Materials Science, 6(1), 15-50. doi:10.1016/0927-0256(96)00008-0Blöchl, P. E. (1994). Projector augmented-wave method. Physical Review B, 50(24), 17953-17979. doi:10.1103/physrevb.50.17953Kresse, G., & Joubert, D. (1999). From ultrasoft pseudopotentials to the projector augmented-wave method. Physical Review B, 59(3), 1758-1775. doi:10.1103/physrevb.59.1758Perdew, J. P., Burke, K., & Ernzerhof, M. (1996). Generalized Gradient Approximation Made Simple. Physical Review Letters, 77(18), 3865-3868. doi:10.1103/physrevlett.77.3865Perdew, J. P., Ruzsinszky, A., Csonka, G. I., Vydrov, O. A., Scuseria, G. E., Constantin, L. A., … Burke, K. (2008). Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces. Physical Review Letters, 100(13). doi:10.1103/physrevlett.100.136406Monkhorst, H. J., & Pack, J. D. (1976). Special points for Brillouin-zone integrations. Physical Review B, 13(12), 5188-5192. doi:10.1103/physrevb.13.5188Garcia-Domene, B., Ortiz, H. M., Gomis, O., Sans, J. A., Manjón, F. J., Muñoz, A., … Tyagi, A. K. (2012). High-pressure lattice dynamical study of bulk and nanocrystalline In2O3. Journal of Applied Physics, 112(12), 123511. doi:10.1063/1.4769747Gomis, O., Santamaría-Pérez, D., Ruiz-Fuertes, J., Sans, J. A., Vilaplana, R., Ortiz, H. M., … Mollar, M. (2014). High-pressure structural and elastic properties of Tl2O3. Journal of Applied Physics, 116(13), 133521. doi:10.1063/1.4897241K.Parlinski Phonon code seehttp://www.computingformaterials.com/.Todorov, N. D., Abrashev, M. V., Marinova, V., Kadiyski, M., Dimowa, L., & Faulques, E. (2013). Raman spectroscopy and lattice dynamical calculations of Sc2O3single crystals. Physical Review B, 87(10). doi:10.1103/physrevb.87.104301White, W. B., & Keramidas, V. G. (1972). Vibrational spectra of oxides with the C-type rare earth oxide structure. Spectrochimica Acta Part A: Molecular Spectroscopy, 28(3), 501-509. doi:10.1016/0584-8539(72)80237-xKranert, C., Schmidt-Grund, R., & Grundmann, M. (2014). Raman active phonon modes of cubic In2O3. physica status solidi (RRL) - Rapid Research Letters, 8(6), 554-559. doi:10.1002/pssr.201409004Ubaldini, A., & Carnasciali, M. M. (2008). Raman characterisation of powder of cubic RE2O3 (RE=Nd, Gd, Dy, Tm, and Lu), Sc2O3 and Y2O3. Journal of Alloys and Compounds, 454(1-2), 374-378. doi:10.1016/j.jallcom.2006.12.067Mochizuki, S., Fujishiro, F., & Ishiwata, K. (2005). Photo-induced valence-number changes and defects in Eu2O3fine particle films. Journal of Physics: Conference Series, 21, 189-194. doi:10.1088/1742-6596/21/1/03

The distribution of potential West Nile virus vectors, Culex pipiens pipiens and Culex pipiens quinquefasciatus (Diptera: Culicidae), in Mexico City

<p>Abstract</p> <p>Background</p> <p><it>Culex </it>spp. mosquitoes are considered to be the most important vectors of West Nile virus (WNV) detected in at least 34 species of mosquitoes in the United States. In North America, <it>Culex pipiens pipiens, Culex pipiens quinquefasciatus</it>, and <it>Culex tarsalis </it>are all competent vectors of WNV, which is considered to be enzootic in the United States and has also been detected in equines and birds in many states of Mexico and in humans in Nuevo Leon. There is potential for WNV to be introduced into Mexico City by various means including infected mosquitoes on airplanes, migrating birds, ground transportation and infected humans. Little is known of the geographic distribution of <it>Culex pipiens </it>complex mosquitoes and hybrids in Mexico City. <it>Culex pipiens pipiens </it>preferentially feed on avian hosts; <it>Culex pipiens quinquefasciatus </it>have historically been considered to prefer mammalian hosts; and hybrids of these two species could theoretically serve as bridge vectors to transmit WNV from avian hosts to humans and other mammalian hosts. In order to address the potential of WNV being introduced into Mexico City, we have determined the identity and spatial distribution of <it>Culex pipiens </it>complex mosquitoes and their hybrids.</p> <p>Results</p> <p>Mosquito larvae collected from 103 sites throughout Mexico City during 2004-2005 were identified as <it>Culex, Culiseta </it>or <it>Ochlerotatus </it>by morphological analysis. Within the genus <it>Culex</it>, specimens were further identified as <it>Culex tarsalis </it>or as belonging to the <it>Culex pipiens </it>complex. Members of the <it>Culex pipiens </it>complex were separated by measuring the ratio of the dorsal and ventral arms (DV/D ratio) of the male genitalia and also by using diagnostic primers designed for the <it>Ace.2 </it>gene. <it>Culex pipiens quinquefasciatus </it>was the most abundant form collected.</p> <p>Conclusions</p> <p>Important WNV vectors species, <it>Cx. p. pipiens</it>, <it>Cx. p. quinquefasciatus </it>and <it>Cx. tarsalis</it>, are all present in Mexico City. Hybrids of <it>Cx. p. pipiens </it>and <it>Cx. p. quinquefasciatus </it>were also collected and identified. The presence and abundance of these WNV competent vectors is a cause for concern. Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.</p