Determination of the Gyrotropic Characteristics of Hexaferrite Ceramics From 75 to 600 GHz

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Instrumentation for Millimeter-wave Magnetoelectrodynamic Investigations of Low-Dimensional Conductors and Superconductors

We describe instrumentation for conducting high sensitivity millimeter-wave cavity perturbation measurements over a broad frequency range (40-200 GHz) and in the presence of strong magnetic fields (up to 33 tesla). A Millimeter-wave Vector Network Analyzer (MVNA) acts as a continuously tunable microwave source and phase sensitive detector (8-350 GHz), enabling simultaneous measurements of the complex cavity parameters (resonance frequency and Q-value) at a rapid repetition rate (approx. 10 kHz). We discuss the principal of operation of the MVNA and the construction of a probe for coupling the MVNA to various cylindrical resonator configurations which can easily be inserted into a high field magnet cryostat. We also present several experimental results which demonstrate the potential of the instrument for studies of low-dimensional conducting systems.Comment: 20 pages including fig

A rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets

The cavity perturbation technique is an extremely powerful method for measuring the electrodynamic response of a material in the millimeter- and sub-millimeter spectral range (10 GHz to 1 THz), particularly in the case of high-field/frequency magnetic resonance spectroscopy. However, the application of such techniques within the limited space of a high-field magnet presents significant technical challenges. We describe a 7.62 mm x 7.62 mm (diameter x length) rotating cylindrical cavity which overcomes these problems.Comment: 11 pages including 8 figure

A new look at the cosmic ray positron fraction

The positron fraction in cosmic rays was found to be a steadily increasing in function of energy, above $\sim$ 10 GeV. This behaviour contradicts standard astrophysical mechanisms, in which positrons are secondary particles, produced in the interactions of primary cosmic rays during the propagation in the interstellar medium. The observed anomaly in the positron fraction triggered a lot of excitement, as it could be interpreted as an indirect signature of the presence of dark matter species in the Galaxy. Alternatively, it could be produced by nearby astrophysical sources, such as pulsars. Both hypotheses are probed in this work in light of the latest AMS-02 positron fraction measurements. The transport of the primary and secondary positrons in the Galaxy is described using a semi-analytic two-zone model. MicrOMEGAs is used to model the positron flux generated by dark matter species. The description of the positron fraction from astrophysical sources is based on the pulsar observations included in the ATNF catalogue. We find that the mass of the favoured dark matter candidates is always larger than 500 GeV. The only dark matter species that fulfils the numerous gamma ray and cosmic microwave background bounds is a particle annihilating into four leptons through a light scalar or vector mediator, with a mixture of tau (75%) and electron (25%) channels, and a mass between 0.5 and 1 TeV. The positron anomaly can also be explained by a single astrophysical source and a list of five pulsars from the ATNF catalogue is given. Those results are obtained with the cosmic ray transport parameters that best fit the B/C ratio. Uncertainties in the propagation parameters turn out to be very significant. In the WIMP annihilation cross section to mass plane for instance, they overshadow the error contours derived from the positron data.Comment: 20 pages, 16 figures, accepted for publication in A&A, corresponds to published versio

Rotational Cooling of Polar Molecules by Stark-tuned Cavity Resonance

A general scheme for rotational cooling of diatomic heteronuclear molecules is proposed. It uses a superconducting microwave cavity to enhance the spontaneous decay via Purcell effect. Rotational cooling can be induced by sequentially tuning each rotational transition to cavity resonance, starting from the highest transition level to the lowest using an electric field. Electrostatic multipoles can be used to provide large confinement volume with essentially homogeneous background electric field.Comment: 10 pages, 6 figure

Paleo and historical seismicity in Mallorca (Baleares, Spain): a preliminary approach

The island of Mallorca is subject to low seismic activity. The instrumental record shows that current seismicity is surficial (La isla de Mallorca presenta una actividad sísmica baja. El registro instrumental muestra que la sismicidad actual es superficial

La “Ruta de las huellas fósiles” (Monsagro, Salamanca): un ejemplo de iniciativa geoturística aplicada al desarrollo rural

Se presenta la “Ruta de las huellas fósiles”, realizada en el casco urbano de Monsagro (Sierra de Francia, Salamanca). Mediante seis paneles didácticos e interpretativos, que incluyen el acceso “online” desde las nuevas tecnologías (smartphone, tablets, ipod….) a información complementaria implementada en videos, códigos QR, geoapps y juegos, se han promocionado y divulgado los contenidos geológicos de la zona, basados principalmente en el interés paleontológico de sus icnofósiles, atribuidos a diversos tipos de gusanos y trilobites durante el Ordovícico Inferior, y en el interés geomorfológico de sus cresterías cuarcíticas con relieve apalachiense, del encajamiento fluvial del río Agadón y de sus formaciones superficiales como canchales. Los visitantes señalan como fortalezas de la ruta su fácil y didáctico recorrido, así como la implicación ciudadana en la conservación de las icnitas

Paleo and historical seismicity in Mallorca (Baleares, Spain): a preliminary approach

The island of Mallorca is subject to low seismic activity. The instrumental record shows that current seismicity is surficial (<10 km depth) and low in magnitude (mb<4). Both historical and geological records display the occurrence of strong events, e.g. the 1851 Palma earthquake (VIII, MSK intensity). Data on this destruct ive event indicate that this was a seven month long seismic sequence, with two strong events, causing severe damage and collapse of buildings along Palma bay in addition to moderate ground collapses in the macroseismal zone. The earthquake epicenter was situated between Sa Cabaneta and Sta. Eugènia. This earthquake can be correlated with the trace of the Sencelles fault, the main extensional structure of the island on the surface. The geological and geophysical analyses of recent surface faulting features at the Portol doline (reverse surface faulting) and on the Sta. Eugènia segment of the Sencelles fault (bedrock fault scarp ) suggest recurrent large prehistoric events. Preliminary data show minimum vertical offsets of 2.56 m at the Portol doline and offsets of 3.50m at the Sta. Eugènia bedrock fault scarp. These offsets were accumulated in recent times (Holocene?). Displacements per event can be initially estimated as mean values of 0.88 to 0.40 m in both places, but larger offsets of a maximum of 1.68 m can also be inferred. Specific dendrochronologic, lichenometric, and weathering analyses to assess true single-event slip values, and their time-bracketing will be necessary. The interpretation of these displacement events in terms of earthquake magnitude is not straightforward because of the apparent subordinate nature of the ground rupture at the Po rtol doline and the possible influence of salt tectonics in both places. To address these issues, a fault-trench was planned along the Sencelles fault within the framework of a new research project. The Spanish seismic code (NCS94) assigns an expected maximum ground acceleration of 0.04 g for a 500 year return period to the area. In the light of our data these values are underestimated. The historical and geological records indicate the occurrence of historical VII to VIII MSK, and stronger prehistoric events. Peak ground horizontal accelerations of up to 0.10 g could be expected during modern earthquakes