Potential mechanical loss mechanisms in bulk materials for future gravitational wave detectors

Low mechanical loss materials are needed to further decrease thermal noise in upcoming gravitational wave detectors. We present an analysis of the contribution of Akhieser and thermoelastic damping on the experimental results of resonant mechanical loss measurements. The combination of both processes allows the fit of the experimental data of quartz in the low temperature region (10 K to 25 K). A fully anisotropic numerical calculation over a wide temperature range (10 K to 300 K) reveals, that thermoelastic damping is not a dominant noise source in bulk silicon samples. The anisotropic numerical calculation is sucessfully applied to the estimate of thermoelastic noise of an advanced LIGO sized silicon test mass.Comment: 7 pages, 3 figures, submitted to Journal of Physics: Conference Series (AMALDI8

Noninvasive stimulation of the ventromedial prefrontal cortex modulates rationality of human decision-making

The framing-effect is a bias that affects decision-making depending on whether the available options are presented with positive or negative connotations. Even when the outcome of two choices is equivalent, people have a strong tendency to avoid the negatively framed option. The ventromedial prefrontal cortex (vmPFC) is crucial for rational decision-making, and dysfunctions in this region have been linked to cognitive biases, impulsive behavior and gambling addiction. Using a financial decision-making task in combination with magnetoencephalographic neuroimaging, we show that excitatory compared to inhibitory non-invasive transcranial direct current stimulation (tDCS) of the vmPFC reduces framing-effects while improving the assessment of loss-probabilities, ultimately leading to increased overall gains. Behavioral and neural data consistently suggest that this improvement in rational decision-making is predominately due to an attenuation of biases towards negative affect (loss-aversion and risk-aversion). These findings recommend further research towards clinical applications of vmPFC-tDCS as in addictive disorders

Waveguide grating mirror in a fully suspended 10 meter Fabry-Perot cavity

We report on the first demonstration of a fully suspended 10m Fabry-Perot cavity incorporating a waveguide grating as the coupling mirror. The cavity was kept on resonance by reading out the length fluctuations via the Pound-Drever-Hall method and employing feedback to the laser frequency. From the achieved finesse of 790 the grating reflectivity was determined to exceed 99.2% at the laser wavelength of 1064\,nm, which is in good agreement with rigorous simulations. Our waveguide grating design was based on tantala and fused silica and included a ~20nm thin etch stop layer made of Al2O3 that allowed us to define the grating depth accurately during the fabrication process. Demonstrating stable operation of a waveguide grating featuring high reflectivity in a suspended low-noise cavity, our work paves the way for the potential application of waveguide gratings as mirrors in high-precision interferometry, for instance in future gravitational wave observatories

¿Qué leían los cruzados argentinos? : Las lecturas del nacionalismo católico a través de 'Cabildo' (1973-1976)

En el siguiente artículo se aborda la revista nacionalista católica Cabildo desde una perspectiva sensible a la historia intelectual. El objetivo es ampliar y completar, a partir de las lecturas promocionadas en las publicidades y de los libros reseñados, el universo de representaciones políticas y religiosas. Luego de presentar la revista, largamente estudiada por la historiografía, se analizan las publicidades identificando redes intelectuales locales, pero también transnacionales. En forma posterior se examinan tres reseñas dedicadas a la lectura de la historia, la ciencia ficción y la guerra contrarrevolucionaria. Se concluye que el nacionalismo católico, lejos de impugnar la modernidad en un nivel ontológico, trazó un diálogo práctico bajo la condición de corregir sus peligrosas derivas.En el següent article s'aborda la revista nacionalista catòlica Cabildo des d'una perspectiva sensible a la història intel·lectual. L'objectiu és ampliar i completar, a partir de les lectures promocionades en les publicitats i dels llibres ressenyats, l'univers de representacions polítiques i religioses. Després de presentar la revista, llargament estudiada per la historiografia, s'analitzen les publicitats tot identificant xarxes intel·lectuals locals, però també transnacionals. Més endavant s'examinen tres ressenyes dedicades a la lectura de la història, la ciència-ficció i la guerra contrarevolucionària. Es conclou que el nacionalisme catòlic, lluny d'impugnar la modernitat en un nivell ontològic, va traçar un diàleg pràctic sota la condició de corregir les seves perilloses derives.The following paper focuses on the Catholic nationalist magazine Cabildo from an Intellectual History standpoint. The aim is to expand and complete, from the reading matter promoted in its advertisements and the books reviewed, the universe of its political and religious representations. After a brief introduction to the magazine, long studied in the literature, the advertisements are analyzed and transnational as well as local intellectual networks are identified. Later, three book reviews, focusing on the interpretation of Argentine history, science fiction, and the counterrevolutionary war, are examined. It is concluded that, far from challenging modernity on an ontological level, Cabildo entered into a practical dialogue with it without accepting its dangerous deviations

Investigation of mechanical losses of thin silicon flexures at low temperatures

The investigation of the mechanical loss of different silicon flexures in a temperature region from 5 to 300 K is presented. The flexures have been prepared by different fabrication techniques. A lowest mechanical loss of $3\times10^{-8}$ was observed for a 130 $\mu$m thick flexure at around 10 K. While the mechanical loss follows the thermoelastic predictions down to 50 K a difference can be observed at lower temperatures for different surface treatments. This surface loss will be limiting for all applications using silicon based oscillators at low temperatures. The extraction of a surface loss parameter using different results from our measurements and other references is presented. We focused on structures that are relevant for gravitational wave detectors. The surface loss parameter $\alpha_s$ = 0.5 pm was obtained. This reveals that the surface loss of silicon is significantly lower than the surface loss of fused silica.Comment: 16 pages, 7 figure

Pound-Drever-Hall error signals for the length control of three-port grating coupled cavities

Gratings enable light coupling into an optical cavity without transmission through any substrate. This concept reduces light absorption and substrate heating and was suggested for light coupling into the arm cavities of future gravitational wave detectors. One particularly interesting approach is based on all-reflective gratings with low diffraction efficiencies and three diffraction orders (three ports). However, it was discovered that, generally, three-port grating coupled cavities show an asymmetric resonance profile that results in asymmetric and low quality Pound–Drever–Hall error signals for cavity length control. We experimentally demonstrate that this problem is solved by the detection of light at both reflection ports of the cavity and the postprocessing of the two demodulated electronic signals