Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three ...orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network, alongside the two Advanced LIGO detectors in the US and GEO HF in Germany, with the goal of contributing to the early detection of gravitational waves and to opening a new window of observation on the universe. In this paper we describe the main features of the Advanced Virgo detector and outline the status of the construction.
Polypyrimidine tract-binding proteins (PTBPs) are RNA binding proteins that regulate a number of posttranscriptional events. Human PTBP1 transits between the nucleus and cytoplasm and is thought to ...regulate RNA processes in both. However, information about
mRNA isoforms and regulation of PTPB1 expression remains incomplete. Here we mapped the major
mRNA isoforms in HEK293T cells and identified alternative 5' and 3' untranslated regions (5'-UTRs, 3'-UTRs), as well as alternative splicing patterns in the protein coding region. We also assessed how the observed
mRNA isoforms contribute to PTBP1 expression in different phases of the cell cycle. Previously,
mRNAs were shown to crosslink to eukaryotic translation initiation factor 3 (eIF3). We find that eIF3 binds differently to each
mRNA isoform in a cell cycle dependent manner. We also observe a strong correlation between eIF3 binding to
mRNAs and repression of PTBP1 levels during the S phase of the cell cycle. Our results provide evidence of translational regulation of PTBP1 protein levels during the cell cycle, which may affect downstream regulation of alternative splicing and translation mediated by PTBP1 protein isoforms.
On 14 September 2015, a gravitational wave signal from a coalescing black hole binary system was observed by the Advanced LIGO detectors. This paper describes the transient noise backgrounds used to ...determine the significance of the event (designated GW150914) and presents the results of investigations into potential correlated or uncorrelated sources of transient noise in the detectors around the time of the event. The detectors were operating nominally at the time of GW150914. We have ruled out environmental influences and non-Gaussian instrument noise at either LIGO detector as the cause of the observed gravitational wave signal.
The first observing run of Advanced LIGO spanned 4 months, from 12 September 2015 to 19 January 2016, during which gravitational waves were directly detected from two binary black hole systems, ...namely GW150914 and GW151226. Confident detection of gravitational waves requires an understanding of instrumental transients and artifacts that can reduce the sensitivity of a search. Studies of the quality of the detector data yield insights into the cause of instrumental artifacts and data quality vetoes specific to a search are produced to mitigate the effects of problematic data. In this paper, the systematic removal of noisy data from analysis time is shown to improve the sensitivity of searches for compact binary coalescences. The output of the PyCBC pipeline, which is a python-based code package used to search for gravitational wave signals from compact binary coalescences, is used as a metric for improvement. GW150914 was a loud enough signal that removing noisy data did not improve its significance. However, the removal of data with excess noise decreased the false alarm rate of GW151226 by more than two orders of magnitude, from 1 in 770 yr to less than 1 in 186 000 yr.
Parameter estimates of GW150914 were obtained using Bayesian inference, based on three semi-analytic waveform models for binary black hole coalescences. These waveform models differ from each other ...in their treatment of black hole spins, and all three models make some simplifying assumptions, notably to neglect sub-dominant waveform harmonic modes and orbital eccentricity. Furthermore, while the models are calibrated to agree with waveforms obtained by full numerical solutions of Einstein's equations, any such calibration is accurate only to some non-zero tolerance and is limited by the accuracy of the underlying phenomenology, availability, quality, and parameter-space coverage of numerical simulations. This paper complements the original analyses of GW150914 with an investigation of the effects of possible systematic errors in the waveform models on estimates of its source parameters. To test for systematic errors we repeat the original Bayesian analysis on mock signals from numerical simulations of a series of binary configurations with parameters similar to those found for GW150914. Overall, we find no evidence for a systematic bias relative to the statistical error of the original parameter recovery of GW150914 due to modeling approximations or modeling inaccuracies. However, parameter biases are found to occur for some configurations disfavored by the data of GW150914: for binaries inclined edge-on to the detector over a small range of choices of polarization angles, and also for eccentricities greater than 0.05. For signals with higher signal-to-noise ratio than GW150914, or in other regions of the binary parameter space (lower masses, larger mass ratios, or higher spins), we expect that systematic errors in current waveform models may impact gravitational-wave measurements, making more accurate models desirable for future observations.
Abstract
The three advanced Virgo and LIGO gravitational wave detectors participated to the third observing run (O3) between 1 April 2019 15:00 UTC and 27 March 2020 17:00 UTC, leading to several ...gravitational wave detections per month. This paper describes the advanced Virgo detector calibration and the reconstruction of the detector strain
h
(
t
) during O3, as well as the estimation of the associated uncertainties. For the first time, the photon calibration technique as been used as reference for Virgo calibration, which allowed to cross-calibrate the strain amplitude of the Virgo and LIGO detectors. The previous reference, so-called free swinging Michelson technique, has still been used but as an independent cross-check.
h
(
t
) reconstruction and noise subtraction were processed online, with good enough quality to prevent the need for offline reprocessing, except for the two last weeks of September 2019. The uncertainties for the reconstructed
h
(
t
) strain, estimated in this paper in a 20–2000 Hz frequency band, are frequency independent: 5% in amplitude, 35 mrad in phase and 10
μ
s in timing, with the exception of larger uncertainties around 50 Hz.
Charge-exchange processes in collisions between H+ projectiles and a three-monolayer C60 film grown on Cu(111) are experimentally and theoretically analyzed for a wide range of energies (2–8 keV) in ...the low-energy regime. The negative, positive, and total projectile scattered ion fractions are experimentally determined by using the low-energy ion scattering technique. Two different collisional setups are studied for a fixed backscattering angle of 135°: 45/90° and 67.5/67.5° incoming/exit angles, determined with respect to the target surface plane. Total ion fractions between 10 and 20% are experimentally found in the whole energy range analyzed, with a slight but sustained increase with the projectile incoming energy. Positive ions were measured to be the majority of the total scattered charged projectiles in almost the whole energy range analyzed. Only for very low incoming energies (2–3 keV), the positive and negative ion fractions become comparable. A first-principle-based theoretical model is used to describe the dynamic charge-exchange processes taking place in the experimental collisional situation. A good description of the experimental results is obtained in the studied energy range. The theoretical and experimental results are also analyzed in comparative terms with previous measurements in the H+/highly oriented pyrolytic graphite (HOPG) system. The differences in the measured ion fractions can be directly related to differences in the electronic structures of C60 and HOPG.
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The low-energy ion scattering (LEIS) technique was used to experimentally determine the formation of positive and negative ions in the scattering of protons by a Cu(111) surface for a large ...scattering angle in the backscattering configuration and a wide range of incoming energies (2–8 keV). Two different collisional geometries were analyzed for a 135° fixed scattering angle: 45°/90° and 67.5°/67.5° incoming/exit angles measured with respect to the target surface. The total fraction of backscattered ions ranges from 10% to 25%, and a peculiarly high yield of negative ions, which always exceeds that of positive ions, was detected for the whole energy range analyzed. A strong dependence of the measured ion fractions with the geometrical conditions was experimentally found. On the theoretical side, a first-principles quantum-mechanical formalism that takes into account the three possible final charge states of the H+ in a correlated way and the fine details of the band structure of the Cu(111) surface was applied to describe the charge transfer processes involved in the experimental situation. The theoretical calculation leads to a nonmonotonous dependence with the incoming energy that properly describes the experimental results, especially the negative ion fraction in the specular collisional geometry. The oscillatory behavior predicted by the theory in the range of low energies is clear evidence of the charge exchange between localized states, that is, the situation related with the presence of the surface state immersed in the L-gap present in the Cu(111) surface. The positive ion fraction is discussed for the first time for this collisional system. The differences found between the measurements and the theory seem to indicate that the neutralization to excited states and also the formation of excited negative hydrogen ions are possible charge exchange channels in the dynamic process analyzed.
Full text
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
So far, the sensitivity of gravitational-wave (GW) detectors, in the low-frequency and mid-frequency regions of its bandwidth, has been limited by technical noises. The re-injection of ...sensing and control noises can be one of the main limitations. After the end of the third observing run O3, in preparation for the fourth observing run O4, an upgrade phase started among all the km-scale GW detectors, namely LIGO, Virgo and KAGRA, with the aim of improving their sensitivity. In particular, for the case of Advanced Virgo, one of the most significant upgrades is the installation of a signal recycling (SR) mirror, introducing the SR cavity. The main target of this SR mirror is to shape the sensitivity curve of the detector. The installation of a SR mirror adds an extra optical cavity and, thus, extra DoFs (longitudinal and angular), that should be controlled to keep its working point, ultimately increasing the complexity of the whole control strategy. In order to have an accurate description of the interferometer, we have implemented a multiple-input multiple-output (MIMO) model in the frequency domain. The target of this paper, after showing the Advanced Virgo configuration for the next observing run, is to describe the control scheme used for the main longitudinal degrees of freedom using a MIMO approach. In particular, we detail a useful matrix representation for the modeled system. Finally, we use the implemented model to project the sensing and control noises on the sensitivity curve. Following the obtained results, we propose noise subtraction filters to achieve the low control noise target in the low-frequency region of the sensitivity curve. Additionally, using this model, we have implemented the core of a noise budget tool, which will allow to estimate the contribution of all the known sources of noise on the measured sensitivity.
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