Fermi Surface Study of Quasi-Two-Dimensional Organic Conductors by Magnetooptical Measurements

Magnetooptical measurements of several quasi-two-dimensional (q2D) organic conductors, which have simple Fermi surface structure, have been performed by using a cavity perturbation technique. Despite of the simple Fermi surface structure, magnetooptical resonance results show a dramatic difference for each sample. Cyclotron resonances (CR) were observed for q-(BEDT-TTF)2I3 and (BEDT-TTF)3Br(pBIB), while periodic orbit resonances (POR) were observed for (BEDT-TTF)2Br(DIA) and (BEDT-TTF)3Cl(DFBIB). The selection of the resonance seems to correspond with the skin depth for each sample. The effective mass of POR seems to have a mass enhancement due to the many-body effect, while effective mass of CR is independent of the strength of the electron-electron interaction. The scattering time deduced from each resonance's linewidth will be also presented.Comment: 10 pages, 8 figures, to be published to J. Phys. Soc. Jpn Vol.72 No.1 (accepted

Nyquist method for Wigner-Poisson quantum plasmas

By means of the Nyquist method, we investigate the linear stability of electrostatic waves in homogeneous equilibria of quantum plasmas described by the Wigner-Poisson system. We show that, unlike the classical Vlasov-Poisson system, the Wigner-Poisson case does not necessarily possess a Penrose functional determining its linear stability properties. The Nyquist method is then applied to a two-stream distribution, for which we obtain an exact, necessary and sufficient condition for linear stability, as well as to a bump-in-tail equilibrium.Comment: 6 figure

Cyclotron Resonance in the Layered Perovskite Superconductor Sr2RuO4

We have measured the cyclotron masses in Sr2RuO4 through the observation of periodic-orbit-resonances - a magnetic resonance technique closely related to cyclotron resonance. We obtain values for the alpha, beta and gamma Fermi surfaces of (4.33+/-0.05)me, (5.81+/-0.03)me and (9.71+/-0.11)me respectively. The appreciable differences between these results and those obtained from de Haas- van Alphen measurements are attributable to strong electron-electron interactions in this system. Our findings appear to be consistent with predictions for a strongly interacting Fermi liquid; indeed, semi-quantitative agreement is obtained for the electron pockets beta and gamma.Comment: 4 pages + 3 figure

¿Cómo está afectando el COVID-19 la vida de los/as argentinos/as? -Reporte final

A través de la encuesta COVIDiSTRESS se evaluó el impacto psicológico de la crisis generada por el COVID-19 en más de 100 países de manera longitudinal, especialmente en el estrés. En este informe nos centramos en Argentina y recuperamos los datos de países latinoamericanos con fines comparativos. La recolección de datos se realizó de manera online entre el 30 de marzo y el 30 de mayo de 2020, pero en Argentina se extendió hasta el 7 de junio de 2020. Se definieron fases en consonancia con las fases de administración del aislamiento decretadas por el Gobierno nacional. Concretamente, las fases fueron: 1 = 30 al 31 de marzo; 2 = 1 al 12 de abril; 3 = 13 al 26 de abril; 4 = 27 de abril al 10 de mayo; 5 = 11 al 24 de mayo; y 6 = 25 de mayo al 7 de junio. Participaron 6573 personas, y fueron incluidas en los análisis 6347 dado que se aplicaron algunos criterios de exclusión. Las personas tenían entre 18 y 85 años y eran de distintos géneros (principalmente mujeres) y tenían distintas actividades laborales. Participaron personas de las 23 provincias de Argentina y de CABA, con un predominio de participantes de Córdoba (28.1%). Entre los principales resultados destacamos los siguientes: ● Las personas percibieron un nivel de estrés medio a lo largo de las distintas fases de aislamiento, con un leve incremento desde la fase 2 a la 5 y una posterior disminución en la fase 6. A mayor edad el estrés percibido fue menor. ● Las personas experimentaron niveles intermedios de soledad a lo largo de las fases consideradas, con un leve incremento desde la fase 2 a la 4, y una posterior disminución en las fases 5 y 6. ● Las principales fuentes de malestar identificadas por las personas estuvieron vinculadas a la economía del país, la situación de amigos/as y familiares que viven lejos, el riesgo de contraer el virus, la incertidumbre sobre la duración del aislamiento y las perspectivas laborales futuras. Entre las personas de 18 a 40 años se destacó la preocupación por las perspectivas laborales futuras. ● Las personas expresaron que confiaban más en instituciones como el Sistema sanitario del país y la Organización Mundial de la Salud. Luego, confiaban en el Gobierno, la Policía y la Administración pública. En todos los casos la confianza disminuyó a lo largo de las fases del aislamiento. ● Las personas valoraron como apropiadas las medidas adoptadas por el Gobierno nacional para afrontar la situación generada por el COVID-19 en términos generales, valoración que se sostuvo a lo largo de todas las fases. ● Las personas manifestaron en gran medida haber hecho todo lo posible para reducir el contagio del COVID-19 a lo largo de las fases consideradas, aunque eso disminuyó en las fases 5 y 6. ● El apoyo social percibido por las personas fue alto durante todo el período, con pequeñas variaciones a lo largo de las fases. ● Las estrategias que resultaron más útiles para afrontar la situación fueron el contacto telefónico o virtual con amigos/as y familiares, actividades de entretenimiento, uso de redes sociales y conocimiento de las medidas adoptadas por el Gobierno o los servicios públicos. Las estrategias que resultaron menos útiles fueron jugar a videojuegos online y recurrir a Dios o la religión. Ciencia abierta y acceso abierto COVIDiSTRESS es una investigación global colaborativa que se enmarca en las prácticas de ciencia abierta. Fue creada por investigadores/as de más de 40 países para recolectar rápida y orgánicamente datos sobre las experiencias generadas a partir de la pandemia producida por el COVID-19 en el año 2020. Este informe se focaliza en Argentina y abarca el período del 30 de marzo al 7 de junio. Los análisis que comprenden a otros países comprenden desde el 30 de marzo hasta mayo. Dada la naturaleza del proyecto de ciencia abierta, cualquier persona que tenga interés puede acceder a los datos brutos, como también a versiones curadas de la base de datos lista para realizar análisis, y una lista de todas las variables comprendidas en la encuesta.Fil: Reyna C. Universidad Nacional de Córdoba. Facultad de Psicología; Argentina.Fil: Reyna C. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Psicológicas; Argentina.Fil: Ortiz, M. V. Universidad Nacional de Córdoba. Facultad de Psicología; Argentina.Fil: Ortiz, M. V. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Psicológicas; Argentina.Fil: Mola, D. J. Universidad Nacional de Córdoba. Facultad de Psicología; Argentina.Fil: Mola, D. J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Psicológicas; Argentina.Fil: Correa, P. S. Universidad Nacional de Córdoba. Facultad de Psicología; Argentina.Fil: Correa, P. S. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Psicológicas; Argentina.Fil: Lieberoth A. Aarhus University; Denmark

Dimension reduction in heterogeneous parametric spaces with application to naval engineering shape design problems

We present the results of the first application in the naval architecture field of a methodology based on active subspaces properties for parameter space reduction. The physical problem considered is the one of the simulation of the hydrodynamic flow past the hull of a ship advancing in calm water. Such problem is extremely relevant at the preliminary stages of the ship design, when several flow simulations are typically carried out by the engineers to assess the dependence of the hull total resistance on the geometrical parameters of the hull, and others related with flows and hull properties. Given the high number of geometric and physical parameters which might affect the total ship drag, the main idea of this work is to employ the active subspaces properties to identify possible lower dimensional structures in the parameter space. Thus, a fully automated procedure has been implemented to produce several small shape perturbations of an original hull CAD geometry, in order to exploit the resulting shapes and to run high fidelity flow simulations with different structural and physical parameters as well, and then collect data for the active subspaces analysis. The free form deformation procedure used to morph the hull shapes, the high fidelity solver based on potential flow theory with fully nonlinear free surface treatment, and the active subspaces analysis tool employed in this work have all been developed and integrated within SISSA mathLab as open source tools. The contribution will also discuss several details of the implementation of such tools, as well as the results of their application to the selected target engineering problem

Characterization of the S = 9 excited state in Fe8Br8 by Electron Paramagnetic Resonance

High Frequency electron paramagnetic resonance has been used to observe the magnetic dipole, $\Delta$ M$_s$ = $\pm$ 1, transitions in the $S = 9$ excited state of the single molecule magnet Fe$_8$Br$_8$. A Boltzmann analysis of the measured intensities locates it at 24 $\pm$ 2 K above the $S = 10$ ground state, while the line positions yield its magnetic parameters D = -0.27 K, E = $\pm$0.05 K, and B$_4^0$ = -1.3$\times$ 10$^{-6}$ K. D is thus smaller by 8% and E larger by 7% than for $S = 10$. The anisotropy barrier for $S = 9$ is estimated as 22 K,which is 25% smaller than that for $S = 10$ (29 K). These data also help assign the spin exchange constants(J's) and thus provide a basis for improved electronic structure calculations of Fe$_8$Br$_8$.Comment: 7 pages, Figs included in text, submitted to PR

Ovarian Hyperstimulation Syndrome with pleural effusion: a case report

In corporate governance systems boards perform three functions: the interlocking function (from a resource-dependency and network perspective), a monitoring function (from an agency perspective), and a strategic function (from a strategic choice perspective). In a one-tier board the board of directors incorporates non-executive directors (outsiders, they sometimes represent the interests of key-stakeholders) and executive directors (top management) of the firm. In a two-tier board there is a clear distinction between the directors as members of a supervisory board and the top management team. The board serves in this respect as a supervisory board vis à vis the management board. In the Netherlands a two-tier board is prevalent. Firms who act under the structural regime have boards that are characterized by the co-option principle. This means that board members have to act in the best interest of the firm and ultimately choose each other (and are not chosen by the shareholders or other stakeholders). Co-option has some advantages, but also some clear drawbacks, such as the potentiality of groupthink. The structural regime and other governance regimes, in which the relationship between supervisory board and management board is established, have moderating effects on the hypothesized relationships between the three functions and performance of firms.

Detailed single crystal EPR lineshape measurements for the single molecule magnets Fe8Br and Mn12-ac

It is shown that our multi-high-frequency (40-200 GHz) resonant cavity technique yields distortion-free high field EPR spectra for single crystal samples of the uniaxial and biaxial spin S = 10 single molecule magnets (SMMs) [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O and [Fe8O2(OH)12(tacn)6]Br8.9H2O. The observed lineshapes exhibit a pronounced dependence on temperature, magnetic field, and the spin quantum numbers (Ms values) associated with the levels involved in the transitions. Measurements at many frequencies allow us to separate various contributions to the EPR linewidths, including significant D-strain, g-strain and broadening due to the random dipolar fields of neighboring molecules. We also identify asymmetry in some of the EPR lineshapes for Fe8, and a previously unobserved fine structure to some of the EPR lines for both the Fe8 and Mn12 systems. These findings prove relevant to the mechanism of quantum tunneling of magnetization in these SMMs.Comment: Phys. Rev. B, accepted with minor revision