Abstract
Imaging X-ray Polarimetry Explorer (IXPE) is a Small Explorer mission that was launched at the end of 2021 to measure the polarization of X-ray emission from tens of astronomical sources. ...Its focal-plane detectors are based on the Gas Pixel Detector, which measures the polarization by imaging photoelectron tracks in a gas mixture and reconstructing their initial directions. The quality of the single track, and then the capability of correctly determining the original direction of the photoelectron, depends on many factors, e.g., whether the photoelectron is emitted at low or high inclination with respect to the collection plane or the occurrence of a large Coulomb scattering close to the generation point. The reconstruction algorithm used by IXPE to obtain the photoelectron emission direction also calculates several properties of the shape of the tracks that characterize the process. In this paper we compare several such properties and identify the best one to weight each track on the basis of the reconstruction accuracy. We demonstrate that significant improvement in sensitivity can be achieved with this approach and for this reason it will be the baseline for IXPE data analysis.
Ring Laser Gyroscopes, based on the Sagnac effect, are currently the most sensitive rotation sensors. GINGERINO, a RLG installed underground, shows a proved sensitivity that enters the few frad/s ...regime in about 2.5 days of integration time. On one hand, this sensitivity is well below the shot–noise–level as predicted applying to GINGERINO the so called independent beam model. On the other hand, it paves the way to the use of RLG in fundamental and quantum physics research. Indeed, high sensitivity rotation measurement opens to test general relativity and alternative theory of gravity. Moreover, it make possible to study the interplay between quantum effects in the optical domain and non-inertial reference frames.
The GINGER (gyroscopes in general relativity) project foresees the construction of an array of large frame ring laser gyroscopes, rigidly connected to the Earth. Large frame ring laser gyroscopes are ...high-sensitivity instruments used to measure angular velocity with respect to the local inertial frame. In particular, they can provide sub-daily variations in the Earth rotation rate, a measurement relevant for geodesy and for fundamental physics at the same time. Sensitivity is the key point in determining the relevance of this instrument for fundamental science. The most recent progress in sensitivity evaluation, obtained on a ring laser prototype, indicates that GINGER should reach the level of 1 part in 1011 of the Earth’s rotation rate. The impact on fundamental physics of this kind of apparatus is reviewed.
•Generalized turbulent models for breakage and coalescence are proposed.•The PBE-based 0D model accounts for reactor inhomogeneity and for fluid viscosity.•The model is able to predict droplets ...evolution in and out of the inertial subrange.•The improvement over classical kernels is highlighted by various experimental data.
A generalized model for breakage and coalescence kernels valid for the entire spectrum of turbulence is proposed and validated. Most of the available kernels in the literature indeed assume that in a turbulent liquid-liquid dispersion, the dispersed droplets have dimension in the inertial subrange, and are affected by eddies with size in the same subrange. These kernels are based on the Kolmogorov second-order structure function, which is valid only in the inertial subrange. However, in most industrially encountered situations, many droplets may have a size in the dissipation range, where the Kolmogorov second-order structure function does not apply. Therefore, a more general description of the energy transferred between these droplets and the turbulent eddies is needed to properly model breakage and coalescence events.
In this work, the Coulaloglou and Tavlarides (1977) breakage and coalescence kernels have been modified through the implementation of the second-order structure function proposed by Davidson (2004), along with the Pope (2000) energy spectrum. Turbulent liquid-liquid dispersion experiments at high continuous phase viscosity are performed to test and validate the model. The generalized model is able to predict the experimental Sauter mean diameters at different viscosities, turbulent conditions and dispersed-phase volume fraction without any adjustment of the kernel parameters.
•A novel PBM-based model is introduced to simulate extraction column hydrodynamics.•Interfacial area and holdup are predicted from the turbulent energy distribution.•The sensitivity of the results to ...the empirical parameters of the model is studied.•The effect of geometry and operating parameters is well reflected by the model.
An original one dimensional population balance model (PBM)-based model of liquid–liquid extraction columns is reported. Compared to existing simulators, ColHySE implements a more realistic description of the flow patterns in the contactor, and predicts its effect on the local droplet–droplet interactions (i.e. breakage and coalescence rates). Proper turbulent properties, extracted from single-phase flow CFD simulations, are used in the source terms of the PBM to evaluate locally the inhomogeneous breakage and coalescence rates, using the averaged Coulaloglou and Tavlarides kernels (Castellano et al., 2018). The sensitivity of the predicted droplets mean diameter, d32, and the holdup, φ, to the parameters of the used empirical and phenomenological models, on the one hand, and to the operating conditions of the column, on the other hand, was studied. Although some model parts must be refined, and an experimental validation remains necessary, the results confirm that the 1D-PBM methodology used in ColHySE is relevant for predicting the interfacial area in the pulsed column as a function of the operating conditions and geometry, hence highlighting its relevance to study the hydrodynamic stability and tendency to flooding. The sensitivity analysis has moreover highlighted the needs for an improved slip velocity model.
Introdução: O ritmo acelerado de vida dos professores em seu ambiente de trabalho, associado às múltiplas funções desempenhadas, conferem a essa categoria um elevado nível de esforço, sendo ...considerada uma das profissões com maior vulnerabilidade a problemas de saúde.Objetivo: Avaliar os motivos de não adesão à prática habitual de atividade física (PHAF) em professores da Educação Básica.Métodos: Estudo seccional, de abordagem qualitativa, com amostragem por conveniência composta por 193 docentes da cidade de Uberaba-MG. Foi desenvolvido um questionário estruturado para o estudo, constituído por perguntas sobre características sociodemográficas, de saúde e quanto aos motivos da não adesão à PHAF.Resultados: Todos os professores trabalhavam em duas escolas e ministravam, em média, 34 aulas por semana. O principal motivo para a não adesão à PHAF apontado foi a falta de tempo (78,2%), seguido de cansaço (8,8%), falta de ânimo (4,6%), dinheiro (3,6%), comodismo (2,0%), preguiça (1,5%) e falta de hábito (1,0%).Conclusão: A falta de tempo e os fatores secundários estão intimamente interligados e podem estar vinculados ao estresse relacionado à atividade docente afetando a motivação em praticar exercícios. Sugere-se que sejam realizados estudos longitudinais para que seja possível inferir causalidade quanto à associação de hábitos e comportamentos ativos dos professores com a falta de aderência à PHAF. Reasons for non-Adherence to Physical Exercise in Teachers of Basic Education: A Qualitative Sectional Study Introduction: The school work environment imposes on Brazilian teachers an accelerated pace of life, which combined with the multiple functions performed lead to high levels of effort. Therefore, that profession is considered one of the most vulnerable to health problems.Objective: To evaluate the reasons for not adhering to the habitual physical activity (HPA) in Basic Education teachers.Methods: A sectional study, with a qualitative approach, with convenience sampling composed of 193 basic education teachers from the city of Uberaba-MG. A structured questionnaire was developed for the study, consisting of questions about socio-demographic characteristics, health, and reasons for non-adherence to PHAF.Results: All teachers worked in two schools and taught, on average, 34 classes per week. The main reason for not adhering to the PHAF was lack of time (78.2%), followed by fatigue (8.8%), lack of mood (4.6%), money (3.6%), (2.0%), laziness (1.5%) and lack of habit (1.0%).Conclusion: Lack of time and secondary factors are closely intertwined and may be linked to stress related to teacher activity affecting motivation in exercising. It is suggested that longitudinal studies be performed in order to infer causality regarding the association of teachers' active habits and behaviors with the lack of adherence to PHAF.
•The properties of oil-water emulsions are simulated through population balance models.•Volume-averaged breakup and coalescence kernels are computed and validated.•The 0D model based on ...volume-averaged kernel accounts for turbulent inhomogeneity.•Kernels are based on turbulent dissipation rate distributions predicted by CFD.•The improvement over classical kernels is highlighted by various experimental data.
A zero-dimensional homogenous Population Balance Model (PBM) based on the evaluation of the volume-averaged coalescence and breakup rates is here adopted for the first time to fit the model parameter values through experiments carried out on a water-oil emulsion. The method accounts for the spatial inhomogeneities in mixing, namely for the probability density function of the turbulent kinetic energy dissipation in the apparatus, but avoids the use of coupling the PBM with computational fluid dynamics (CFD) or compartmentalization, thus ensuring fast computational time. In order to demonstrate the advantage of the proposed model over traditional ones based on the volume-averaged turbulent kinetic energy dissipation rate, the operating conditions were varied, including the mixing rate, the disperse phase fraction as well as considering inverse emulsions (water in oil and oil in water). The new model was found to be more generalizable to different operating conditions.
A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric ...observation of the XRB Cygnus X-1 using the Imaging X-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray–emitting region. The polarization degree is 4.01 ± 0.20% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. These observations reveal that hot x-ray–emitting plasma is spatially extended in a plane perpendicular to, not parallel to, the jet axis.
x-ray polarization of Cygnus X-1
A black hole in a binary system can rip material off of its companion star, which heats up and forms an accretion disk. The disc emits light in the optical and x-ray bands, forming an x-ray binary (XRB) system. Some XRBs also launch a jet of fast-moving material that is visible at radio wavelengths. Krawczynski
et al
. observed the x-ray polarization of Cygnus X-1, a black hole XRB with a radio jet. By comparing the measured polarization properties with several competing XRB models, they eliminated some hypothesized geometries and determined that the x-ray–emitting region extends parallel to the accretion disc. —KTS
x-ray polarization measurements determine the geometric arrangement of hot material accreting onto a black hole.
Abstract
While X-ray spectroscopy, timing, and imaging have improved much since 1962 when the first astronomical nonsolar source was discovered, especially wi the launch of the Newton/X-ray ...Multi-Mirror Mission, Rossi/X-ray Timing Explorer, and Chandra/Advanced X-ray Astrophysics Facility, the progress of X-ray polarimetry has been meager. This is in part due to the lack of sensitive polarization detectors, which in turn is a result of the fate of approved missions and because celestial X-ray sources appear less polarized than expected. Only one positive measurement has been available until now: the Orbiting Solar Observatory measured the polarization of the Crab Nebula in the 1970s. The advent of microelectronics techniques has allowed for designing a detector based on the photoelectric effect of gas in an energy range where the optics are efficient at focusing in X-rays. Here we describe the instrument, which is the major contribution of the Italian collaboration to the Small Explorer mission called IXPE, the Imaging X-ray Polarimetry Explorer, which will launch in late 2021. The instrument is composed of three detector units based on this technique and a detector service unit. Three mirror modules provided by Marshall Space Flight Center focus X-rays onto the detectors. We show the technological choices, their scientific motivation, and results from the calibration of the instrument. IXPE will perform imaging, timing, and energy-resolved polarimetry in the 2–8 keV energy band opening this window of X-ray astronomy to tens of celestial sources of almost all classes.
The results obtained with the total exposure of 1.04 ton × yr collected by DAMA/LIBRA-phase1 deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. during 7 annual cycles are ...summarized. The DAMA/LIBRA-phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton × yr, corresponding to 14 annual cycles) give evidence at 9.3 σ C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radiopure NaI(Tl) target. The modulation amplitude of the single-hit events in the (2–6) keV energy interval is 0.0112 ± 0.0012 cpd/kg/keV; the measured phase is 144 ± 7 days and the measured period is 0.998 ± 0.002 yr; values are in a good well in agreement with those expected for DM particles. No systematic or side reactions able to mimic the exploited DM signature have been found or suggested by anyone over more than a decade. Some of the perspectives of the presently running DAMA/LIBRA-phase2 are outlined.
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