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  1. Abstract

    Ionospheric scintillation and fading events over low‐latitude regions are often caused by severely depleted geomagnetic field‐aligned structures known as Equatorial Plasma Bubbles. These events are subject of interest to scientific investigations and concern to technological applications. Over the past several years, most of scintillation studies have focused on the dependence of these events on density gradients, location, local time, geomagnetic conditions, and so forth. This work presents a discussion about the role of the alignment between the signal propagation path and the depleted structures or, equivalently, the geomagnetic field lines, on the observed scintillation and deep fading characteristics. Data from three stations (dip latitudes: 16.13°S, 19.87°S, and 22.05°S) located around the Equatorial Ionization Anomaly (EIA) region were used to assess the amplitude scintillation severity and the deep fading events features under aligned and nonaligned conditions. The results show that the alignment condition plays a crucial role in the occurrence of strong scintillation. The study also revealed that, as stations far from the crests of the EIA are considered, the alignment influence seems to increase, and that a combination of strong plasma density fluctuation and increased aligned path is, presumably, the configuration under which the most severe scintillation and drastic deep fading events are observed. The results indicate that this conjunction is typically met in regions somewhat distinct from that with largest plasma density background over the Brazilian region, therefore, strongest scintillation and largest deep fading rates were observed by a station slightly off‐the EIA peak.

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  2. Abstract

    While low and high‐latitude ionospheric scintillation have been extensively reported, significantly less information is available about the properties of and conditions leading to mid‐latitude scintillations. Here, we report and discuss scintillation observations made in the Southern United States (UT Dallas, 32.99°N, 96.76°W, 43.2°N dip latitude) on June 1st, 2013. The measurements were made by a specialized dual‐frequency GPS‐based scintillation monitor which allowed us to determine main properties of this mid‐latitude scintillation event. Additionally, simultaneous airglow observations and ionospheric total electron content (TEC) maps provided insight on the conditions leading to observed scintillations. Moderate amplitude scintillations (S4>∼0.4) occurred in both L1 and L2C signals, and severe (S4 > ∼0.8) events occurred in L2C signals at low (<30°) elevation angles. Phase scintillation accompanied amplitude fadings, with maximum σϕvalues exceeding 0.5 radians in L2C. We also show that the observed phase scintillation magnitudes increased with amplitude scintillation severity. Decorrelation times were mostly between 0.25 and 1.25 s, with mean value around 0.65 s for both L1 and L2C. Frequency scaling of S4matched fairly well the predictions of weak scattering theory but held for observations of moderate and strong amplitude scintillation as well. Scintillation occurred during the main phase of a modest magnetic storm that, nevertheless, prompted an extreme equatorward movement of the mid‐latitude trough and large background TEC enhancements over the US. Scintillations, however, occurred within TEC and airglow depletions observed over Texas. Finally, scintillation properties including severity and rapidity, and associated TEC signatures are comparable to those associated with equatorial spread F.

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  3. Abstract

    We report the proposal and results of a low‐cost, easy‐to‐build GPS‐based sensor for detection and monitoring ionospheric irregularities through the detection of amplitude scintillation. The system is based on the Raspberry Pi single‐board computer combined with an Adafruit Ultimate GPS peripheral, which is capable of measuring (at 10‐Hz rate) the intensity of the L1 signals transmitted by GPS satellites. We introduce and discuss results of short‐ and long‐term observations obtained with a prototype of this system deployed in Presidente Prudente, a low magnetic latitude site in Brazil. The deployment and observations were carried out to test the ability of the system to detect ionospheric scintillations and, therefore, monitor the occurrence of ionospheric irregularities associated with equatorial spreadF. Our results show that this low‐cost sensor is indeed capable of detecting scintillation events associated with equatorial spreadF. Comparison with simultaneous, collocated measurements made by a commercial scintillation monitor are also presented. The joint observations allowed us to quantify the performance of the low‐cost monitor and to identify sources of potential limitations. While the sensor cannot (and it was not intended to) substitute commercial scintillation monitors, the low cost allows its use in studies of ionospheric irregularities (space weather) that require observations made by distributed arrays of small instruments (DASI). Furthermore, the simplicity of the sensor design stimulates its use in educational and citizen science initiatives.

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  4. Abstract

    After sunset, in the equatorial regions ionospheric plasma irregularities are generated due to the generalized Rayleigh‐Taylor instability. Under favorable conditions these irregularities develop in the equatorial region while mapping along the magnetic field lines giving rise to large plasma depletion structures called Equatorial Plasma Bubbles with embedded smaller structures on their walls. The global navigation satellite system (GNSS) L1 band frequency is sensitive to irregularities of the size of 300–400 m in the first Fresnel zone, which cause scattering and diffraction of the signal and produce amplitude and/or phase scintillation. Severe scintillation of GNSS signals can in turn cause loss of lock of the receiver code and/or carrier loops. As a result, GNSS navigation and positioning solution can be adversely affected by the ionospheric scintillation. There are multiple GNSS receivers designed to monitor scintillations. These receivers are based on different hardware designs and use different methodologies to process the raw data. When using simultaneous data from different GNSS scintillation monitors it is important to evaluate and compare their performances under similar scintillation conditions. The scintillation monitoring techniques may be useful for many applications that use GNSS signal. The aim of this work is to evaluate the performance of six different GNSS receivers located at São José dos Campos (23.1°S, 45.8°W, dip latitude 17.3°S) during moderate and strong scintillation activity. The amplitude (S4) and phase (σϕ) scintillation indexes from these receivers were analyzed and compared for the nights February 20–21 and November 27–28, 2013.

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  5. Free, publicly-accessible full text available December 1, 2024
  6. A<sc>bstract</sc>

    A search for new physics in top quark production with additional final-state leptons is performed using data collected by the CMS experiment in proton-proton collisions at$$ \sqrt{s} $$s= 13 TeV at the LHC during 2016–2018. The data set corresponds to an integrated luminosity of 138 fb1. Using the framework of effective field theory (EFT), potential new physics effects are parametrized in terms of 26 dimension-six EFT operators. The impacts of EFT operators are incorporated through the event-level reweighting of Monte Carlo simulations, which allows for detector-level predictions. The events are divided into several categories based on lepton multiplicity, total lepton charge, jet multiplicity, and b-tagged jet multiplicity. Kinematic variables corresponding to the transverse momentum (pT) of the leading pair of leptons and/or jets as well as thepTof on-shell Z bosons are used to extract the 95% confidence intervals of the 26 Wilson coefficients corresponding to these EFT operators. No significant deviation with respect to the standard model prediction is found.

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    Free, publicly-accessible full text available December 1, 2024
  7. Free, publicly-accessible full text available November 1, 2024
  8. Abstract

    A description is presented of the algorithms used to reconstruct energy deposited in the CMS hadron calorimeter during Run 2 (2015–2018) of the LHC. During Run 2, the characteristic bunch-crossing spacing for proton-proton collisions was 25 ns, which resulted in overlapping signals from adjacent crossings. The energy corresponding to a particular bunch crossing of interest is estimated using the known pulse shapes of energy depositions in the calorimeter, which are measured as functions of both energy and time. A variety of algorithms were developed to mitigate the effects of adjacent bunch crossings on local energy reconstruction in the hadron calorimeter in Run 2, and their performance is compared.

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    Free, publicly-accessible full text available November 1, 2024
  9. Free, publicly-accessible full text available November 1, 2024
  10. Free, publicly-accessible full text available November 1, 2024