bluuebunny/crossref_metadata_2025_split huggingface dataset:
تأثير أسلوبي الفارتلك والتلال (المتتالي والمتداخل) بأستخدام جهاز السير المتحرك في تطوير القوة العضلية للرجلين وإنجاز عدو (400) م لذوي الإعاقة البدنية فئة (46-47)
Authors: طاهر الديوان واثق ثامر , زعون الخزرجي ايمان عبد الامير 
Published: February 2021

هدفت الدراسة إلى إعداد تمرينات بأسلوبي الفارتلك والتلال (المتتالي والمتداخل) باستخدام جهاز السير المتحرك ، والتعرف على تأثير أسلوبي الفارتلك والتلال (المتتالي) ، وتأثير أسلوبي الفارتلك والتلال (المتداخل) في تطوير القوة العضلية للرجلين وانجاز عدو (400) متر لذوي الإعاقة البدنية فئة (46-47) ، وأنتهج الباحثان منهج البحث التجريبي بتصميم المجموعتين التجريبيتين على عينة راكضي المنتخب الوطني بألعاب القوى بعدو (400) متر لذوي الإعاقة البدنية فئة (46-47) ، المُستمرين بالتدريبات في الموسم الرياضي (2018/2019) البالغ عددهم (6) راكضين اختيروا عمدياً من مجتمعهم الأصل بنسبة (100%) من ثم قسموا إلى مجموعتين تجريبيتين متساويتي العدد ليكون راكضي المجموعة التجريبية الأولى يتلقون أسلوب الفارتلك والتلال (المتتالي) وراكضي المجموعة التجريبية الثانية يتلقون أسلوب الفارتلك والتلال (المتداخل) ، طُبِقت التمرينات الخاصة بكل من الأسلوبين حسب التنظيم المتتالي والمتداخل بواقع (16) وحدة تدريبية لكل مجموعة تجريبية طُبقت على مدى (8) أسابيع تدريبية ، وبعد انتهاء التجربة تم معالجة بيانات الاختبارات القبلية والبعدية باستعمال نظام الحقيبة الإحصائية الاجتماعية (SPSS) الإصدار (V25) ، لتكون استنتاجات الدراسة بأنه لأسلوبي الفارتلك والتلال (المتتالي والمتتالي) باستخدام جهاز السير المتحرك تأثير ايجابي في تطوير تحمل القوة العضلية الانتقالية بأفضلية لأسلوب الفارتلك والتلال (المتداخل) في هذا التطوير ، وتأثير ايجابي في تحسين إنجاز عدو (400) متر بأفضلية لأسلوب الفارتلك والتلال (المتداخل) في هذا التحسين لذوي الإعاقة البدنية فئة (46-47) ، وأوصى الباحثان بضرورة إلمام مدربي المعاقين بدمج الأساليب التدريبية وتنظيمها بما يلائم استعمال الاجهزة والادوات التدريبية ، ولابد من الاهتمام بإدخال تقنيات التكنولوجيا التدريبية ضمن الدورات التدريبية التي تقيمها اللجنة البارالمبية العراقية ، والتجهيز بحداثة التقنيات التكنولوجية للأجهزة الرياضية لما لها من مردودات ايجابية في تطوير القدرات وتحسين الانجاز الرقمي لعدو(400) متر .
A Educação de Jovens e Adultos em Cordel: o sistema de numeração decimal
Authors: Flôr Anildo Soares , Alencar Edvonete  Souza de , Furtado Alessandra Cristina 
Published: February 2021

Este artigo traz um recorte da dissertação “Literatura de Cordel para o Ensino do Sistema de Numeração Decimal” que teve como objetivo desenvolver uma sequência didática com a Literatura de Cordel para o ensino do sistema de numeração decimal em uma turma da Primeira Fase da Educação de Jovens e Adultos (EJA). Neste estudo, apresentaremos fragmentos do teste diagnóstico, do bloco dois das atividades da Unidade um e ao desenvolvimento dos alunos em relação a aprendizagem do conteúdo avaliado na atividade – do pós-teste. Esses dados nos ajudaram a compreender a questão de investigação: “Quais são as contribuições do uso da literatura de cordel para o ensino do sistema de numeração decimal na aprendizagem dos alunos em uma turma da 1ª Fase da EJA? Com o desenvolvimento da sequência didática foi possível constatar uma evolução da turma em relação a aprendizagem do sistema de numeração decimal passando de 75% de acertos no teste inicial para 90% no teste final. Evidenciando assim, o quanto é importante a utilização de novos meios que torne estes alunos protagonistas de sua aprendizagem.
Palavras-chave: Educação de jovens adultos. Educação matemática. Literatura de cordel. Sistema de numeração decimal.
Analysis of Previously Classified White Dwarf–Main-sequence Binaries Using Data from the APOGEE Survey
Authors: Corcoran Kyle A. , Lewis Hannah M. , Anguiano Borja , Majewski Steven R. , Kounkel Marina , McDonald Devin J , Stassun Keivan G. , Cunha Katia , Smith Verne , Prieto Carlos Allende , Badenes Carles , De Lee Nathan , Mazzola Christine N. , Longa-Peña Penélope , Roman-Lopes Alexandre 
Published: February 2021

Abstract
We present analyses of near-infrared spectroscopic data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey for 45 previously confirmed or candidate white dwarf–main-sequence (WDMS) binaries identified by the optical Sloan Digital Sky Survey (SDSS) and LAMOST surveys. Among these 45 systems, we classify three as having red giant primaries in the LAMOST sample and 14 as young stellar object contaminants in the photometrically identified SDSS sample. From among the subsample of 28 systems that we confirm to have MS primaries, we derive and place limits on orbital periods and velocity amplitudes for 14. Seven systems have significant velocity variations that warrant a post-common-envelope (PCE) binary classification, four of which are newly classified, three of which are newly confirmed, and five for which we can derive full orbital parameters. If confirmed, one of these newly discovered systems (2M14544500+4626456) will have the second-longest orbital period reported for a typical compact PCE WDMS binary (P = 15.1 days). In addition to the seven above, we also recover and characterize with APOGEE data the well-known PCE WDMS systems EG UMa and HZ 9. We also investigate the overall metallicity distribution of the WDMS sample, which is a parameter space not often explored for these systems. Of note, we find one system (2M14244053+4929580) to be extremely metal-poor ([Fe/H] = − 1.42) relative to the rest of the near-solar sample. Additionally, the PCE systems in our sample are found to be, on average, higher in metallicity than their wide-binary counterparts, though we caution that with this small number of systems, the sample may not be representative of the overall distribution of WDMS systems.
The Extreme Space Weather Event in 1941 February/March
Authors: Hayakawa Hisashi , Blake Sean P. , Bhaskar Ankush , Hattori Kentaro , Oliveira Denny M. , Ebihara Yusuke 
Published: February 2021

Abstract
Given the infrequency of extreme geomagnetic storms, it is significant to note the concentration of three extreme geomagnetic storms in 1941, whose intensities ranked fourth, twelfth, and fifth within the aa index between 1868–2010. Among them, the geomagnetic storm on 1941 March 1 was so intense that three of the four Dst station magnetograms went off scale. Herein, we reconstruct its time series and measure the storm intensity with an alternative Dst estimate (Dst*). The source solar eruption at 09:29–09:38 GMT on February 28 was located at RGO AR 13814 and its significant intensity is confirmed by large magnetic crochets of ∣35∣ nT measured at Abinger. This solar eruption most likely released a fast interplanetary coronal mass ejection with estimated speed 2260 km s−1. After its impact at 03:57–03:59 GMT on March 1, an extreme magnetic storm was recorded worldwide. Comparative analyses on the contemporary magnetograms show the storm peak intensity of minimum Dst* ≤ −464 nT at 16 GMT, comparable to the most and the second most extreme magnetic storms within the standard Dst index since 1957. This storm triggered significant low-latitude aurorae in the East Asian sector and their equatorward boundary has been reconstructed as 38.°5 in invariant latitude. This result agrees with British magnetograms, which indicate an auroral oval moving above Abinger at 53.°0 in magnetic latitude. The storm amplitude was even more enhanced in equatorial stations and consequently casts caveats on their usage for measurements of the storm intensity in Dst estimates.
Nearly 30,000 Late-type Main-sequence Stars with Stellar Age from LAMOST DR5
Authors: Zhang Jiajun , Zhao Jingkun , Oswalt Terry D. , Liang Xilong , Ye Xianhao , Zhao Gang 
Published: February 2021

Abstract
We construct a sample of nearly 30,000 main-sequence stars with 4500 K < T
eff < 5000 K and stellar ages estimated by the chromospheric activity−age relation. This sample is used to determine the age distribution in the R–Z plane of the Galaxy, where R is the projected Galactocentric distance in the disk midplane and Z is the height above the disk midplane. As ∣Z∣ increases, the percentage of old stars becomes larger. It is known that scale-height of Galactic disk increases as R increases, which is called a flare. A mild flare from R ∼ 8.0 to 9.0 kpc in stellar age distribution is found. We also find that the velocity dispersion increases with age as confirmed by previous studies. Finally we present spiral-shaped structures in Z–υ

Z
phase space in three stellar age bins. The spiral is clearly seen in the age bin of [0, 1] Gyr, which suggests that a vertical perturbation to the disk probably took place within the last ∼1.0 Gyr.
A New Cosmic-Ray-driven Instability
Authors: Shalaby Mohamad , Thomas Timon , Pfrommer Christoph 
Published: February 2021

Abstract
Cosmic-ray-driven (CR-driven) instabilities play a decisive role during particle acceleration at shocks and CR propagation in galaxies and galaxy clusters. These instabilities amplify magnetic fields and modulate CR transport so that the intrinsically collisionless CR population is tightly coupled to the thermal plasma and provides dynamical feedback. Here, we show that CRs with a finite pitch angle drive electromagnetic waves (along the background magnetic field) unstable on intermediate scales between the gyroradii of CR ions and electrons as long as CRs are drifting with a velocity less than half of the Alfvén speed of electrons. By solving the linear dispersion relation, we show that this new instability typically grows faster by more than an order of magnitude in comparison to the commonly discussed resonant instability at the ion gyroscale. We find the growth rate for this intermediate-scale instability and identify the growing modes as background ion-cyclotron modes in the frame that is comoving with the CRs. We confirm the theoretical growth rate with a particle-in-cell simulation and study the nonlinear saturation of this instability. We identify three important astrophysical applications of this intermediate-scale instability, which is expected to (1) modulate CR transport and strengthen CR feedback in galaxies and galaxy clusters, (2) enable electron injection into the diffusive shock acceleration process, and (3) decelerate CR escape from the sites of particle acceleration, which would generate gamma-ray halos surrounding CR sources such as supernova remnants.
In the Trenches of the Solar–Stellar Connection. II. Extreme Ultraviolet Flux–Flux Correlations across Solar Cycle 24
Authors: Ayres Thomas R. 
Published: February 2021

Abstract
Solar extreme-ultraviolet (EUV: 100–1100 Å) radiation rises in the 104 K upper chromosphere and hotter layers extending into the million-degree corona. Much of the EUV normally is not visible in other stars owing to interstellar H i absorption. The present study derived power-law scaling relations for EUV species based on irradiance spectra from the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory, over the rise and fall of recent sunspot Cycle 24. These relations not only can test solar models, but also allow “invisible” stellar EUV emissions to be reconstructed from more accessible ultraviolet (UV: 1100–3000 Å) proxies, with implications for heating, ionization, and erosion of exoplanet atmospheres by Sun-like hosts. Hot EUV coronal tracers like Si xii 520 Å (8 MK) show strongly curved power laws relative to chromospheric H i 1025 Å Lyβ, as was seen in Paper I for 0.2–2 keV soft X-rays versus Mg ii 2800 Å. The brightest EUV feature, He ii 303 Å, exhibits a nearly 1:1 correlation with Lyβ (and H i 1215 Lyα, but slightly steeper than 1:1 relative to Mg ii). The second brightest, C iii 977 Å, has a shallower power-law slope of ∼0.5. Correlations for low first ionization potential species, such as Mg, Si, and Fe, might be affected by cycle-dependent chemical fractionation. Parameterized flux–flux relations are presented for most of the strong EUV (and selected UV) features, together with fluxes of individual lines and broad EUV wavelength bands at the highs and lows of Cycle 24.
Aurora Sightings Observed in Chinese History Caused by CIRs or Great-storm CMEs
Authors: Wang Guowei , Yao Shuo , Yu Yiqun , Wei Dong , Di Fei , Bao Xiujuan , Zhang Shihong , Liu Jianjun 
Published: February 2021

Abstract
Auroras observed at middle and low geographic latitudes are related to external inputs and varying geomagnetic fields. This work aims to exclude corotating interaction region (CIR) storms and identify strong coronal mass ejection (CME) storms according to historical auroral records when the geomagnetic field varies substantially. An existing catalog of the aurora records in Chinese history reported by Zeng & Jin from 193 B.C. to 1911 A.D. is used. Archaeomagnetic field models are adopted to estimate the variation of the dipole field. According to the empirical relation between the equatorward boundary of the auroral oval, Dst index, and geomagnetic field intensity, the auroras caused by CIRs can be excluded, and those caused by strong CMEs are identified. After 1500 A.D., China’s magnetic latitude decreased substantially due to the pole shift. This shift provides a better opportunity to investigate the existence of great-level storms. These great-storm CMEs occurred in both solar maximum and minimum. The space weather modeling framework is used to calculate the cusp area and the downward ion flux through the cusp for varied geomagnetic field and solar wind. For the present solar wind condition and tilt angle <15°, stronger geomagnetic field tends to generate a larger cusp area and higher ion flux through the cusp. For the weaker solar wind in the Maunder minimum, the ion flux is lower, but the cusp area is similar to that at present.
A Large Population of Luminous Active Galactic Nuclei Lacking X-Ray Detections: Evidence for Heavy Obscuration?
Authors: Carroll Christopher M. , Hickox Ryan C. , Masini Alberto , Lanz Lauranne , Assef Roberto J. , Stern Daniel , Chen Chien-Ting J. , Ananna Tonima T. 
Published: February 2021

Abstract
We present a large sample of infrared-luminous candidate active galactic nuclei (AGNs) that lack X-ray detections in Chandra, XMM-Newton, and NuSTAR fields. We selected all optically detected SDSS sources with redshift measurements, combined additional broadband photometry from WISE, UKIDSS, 2MASS, and GALEX, and modeled the spectral energy distributions (SEDs) of our sample sources. We parameterize nuclear obscuration in our SEDs with

and uncover thousands of powerful obscured AGNs that lack X-ray counterparts, many of which are identified as AGN candidates based on straightforward WISE photometric criteria. Using the observed luminosity correlation between rest-frame 2–10 keV (

) and rest-frame AGN

(

), we estimate the intrinsic X-ray luminosities of our sample sources and combine these data with flux limits from X-ray catalogs to determine lower limits on nuclear obscuration. Using the ratio of intrinsic-to-observed X-ray luminosity (

), we find a significant fraction of sources with column densities approaching

cm–2, suggesting that multiwavelength observations are necessary to account for the population of heavily obscured AGNs. We simulate the underlying

distribution for the X-ray non-detected sources in our sample through survival analysis, and confirm the presence of AGN activity via X-ray stacking. Our results point to a considerable population of extremely obscured AGNs undetected by current X-ray observatories.
Timing Calibration of the NuSTAR X-Ray Telescope
Authors: Bachetti Matteo , Markwardt Craig B. , Grefenstette Brian W. , Gotthelf Eric V. , Kuiper Lucien , Barret Didier , Cook W. Rick , Davis Andrew , Fürst Felix , Forster Karl , Harrison Fiona A. , Madsen Kristin K. , Miyasaka Hiromasa , Roberts Bryce , Tomsick John A. , Walton Dominic J. 
Published: February 2021

Abstract
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission is the first focusing X-ray telescope in the hard X-ray (3–79 keV) band. Among the phenomena that can be studied in this energy band, some require high time resolution and stability: rotation-powered and accreting millisecond pulsars, fast variability from black holes and neutron stars, X-ray bursts, and more. Moreover, a good alignment of the timestamps of X-ray photons to UTC is key for multi-instrument studies of fast astrophysical processes. In this paper, we describe the timing calibration of the NuSTAR mission. In particular, we present a method to correct the temperature-dependent frequency response of the on-board temperature-compensated crystal oscillator. Together with measurements of the spacecraft clock offsets obtained during downlinks passes, this allows a precise characterization of the behavior of the oscillator. The calibrated NuSTAR event timestamps for a typical observation are shown to be accurate to a precision of ∼65 μs.
A Possible Selection Rule for Flares Causing Sunquakes
Authors: Chen Ruizhu , Zhao Junwei 
Published: February 2021

Abstract
Sunquakes are helioseismic power enhancements initiated by solar flares, but not all flares generate sunquakes. It is curious why some flares cause sunquakes while others do not. Here we propose a hypothesis to explain the disproportionate occurrence of sunquakes: during a flare’s impulsive phase when the flare’s impulse acts upon the photosphere, delivered by shock waves, energetic particles from higher atmosphere, or by downward Lorentz Force, a sunquake tends to occur if the background oscillation at the flare footpoint happens to oscillate downward in the same direction with the impulse from above. To verify this hypothesis, we select 60 strong flares in Solar Cycle 24, and examine the background oscillatory velocity at the sunquake sources during the flares’ impulsive phases. Since the Doppler velocity observations at sunquake sources are usually corrupted during the flares, we reconstruct the oscillatory velocity in the flare sites using helioseismic holography method with an observation-based Green’s function. A total of 24 flares are found to be sunquake active, giving a total of 41 sunquakes. It is also found that in 3–5 mHz frequency band, 25 out of 31 sunquakes show net downward oscillatory velocities during the flares’ impulsive phases, and in the 5–7 mHz frequency band, 33 out of 38 sunquakes show net downward velocities. These results support the hypothesis that a sunquake more likely occurs when a flare impacts a photospheric area with a downward background oscillation.
Tracing Dark Energy History with Gamma-Ray Bursts
Authors: Muccino M. , Izzo L. , Luongo O. , Boshkayev K. , Amati L. , Della Valle M. , Pisani G. B. , Zaninoni E. 
Published: February 2021

Abstract
Observations of gamma-ray bursts up to z ∼ 9 are best suited to study the possible evolution of the universe equation of state at intermediate redshifts. We apply the Combo relation to a sample of 174 gamma-ray bursts to investigate possible evidence of evolving dark energy parameter w(z). We first build a gamma-ray burst Hubble’s diagram and then we estimate the set (Ω
m
, ΩΛ) in the framework of flat and non-flat ΛCDM paradigm. We then get bounds over the wCDM model, where w is thought to evolve with redshift, adopting two priors over the Hubble constant in tension at 4.4σ, i.e., H
0 = (67.4 ± 0.5) km s−1 Mpc−1 and H
0 = (74.03 ± 1.42) km s−1 Mpc−1. We show our new sample provides tighter constraints on Ω
m
since at z ≤ 1.2 we see that w(z) agrees within 1σ with the standard value w = −1. The situation is the opposite at larger z, where gamma-ray bursts better fix w(z) that seems to deviate from w = −1 at 2σ and 4σ level, depending on the redshift bins. In particular, we investigate the w(z) evolution through a piecewise formulation over seven redshift intervals. From our fitting procedure we show that at z ≥ 1.2 the case w < −1 cannot be fully excluded, indicating that dark energy’s influence is not negligible at larger z. We confirm the Combo relation as a powerful tool to investigate cosmological evolution of dark energy. Future space missions will significantly enrich the gamma-ray burst database even at smaller redshifts, improving de facto the results discussed in this paper.
Identifying Candidate Optical Variables Using Gaia Data Release 2
Authors: Andrew Shion , Swihart Samuel J. , Strader Jay 
Published: February 2021

Abstract
Gaia is undertaking a deep synoptic survey of the Galaxy, but photometry from individual epochs has, as of yet, only been released for a minimal number of sources. We show that it is possible to identify variable stars in Gaia Data Release 2 by selecting stars with unexpectedly large photometric uncertainties given their brightness and number of observations. By comparing our results to existing catalogs of variables, we show that information on the amplitude of variability is also implicitly present in the Gaia photometric uncertainties. We present a catalog of about 9.3 million candidate variable stars, and discuss its limitations and prospects for future tests and extensions.
Elliptical Accretion Disk as a Model for Tidal Disruption Events
Authors: Liu F. K. , Cao C. Y. , Abramowicz M. A. , Wielgus M. , Cao R. , Zhou Z. Q. 
Published: February 2021

Abstract
Elliptical accretion disk models for tidal disruption events (TDEs) have been recently proposed and independently developed by two groups. Although these two models are characterized by a similar geometry, their physical properties differ considerably. In this paper, we further investigate the properties of the elliptical accretion disk of the nearly uniform distribution of eccentricity within the disk plane. Our results show that the elliptical accretion disks have distinctive hydrodynamic structures and spectral energy distributions, associated with TDEs. The soft X-ray photons generated at pericenter and nearby are trapped in the disk and advected around the ellipse because of large electron scattering opacity. They are absorbed and reprocessed into emission lines and low-frequency continuum via recombination and bremsstrahlung emission. Because of the rapid increase of bound–free and free–free opacities with radius, the low-frequency continuum photons become trapped in the disk at large radius and are advected through apocenter and back to the photon-trapping radius. Elliptical accretion disks predict sub-Eddington luminosities and emit mainly at the photon-trapping radius of thousands of Schwarzschild radii with a blackbody spectrum of nearly single temperature of typically about 3 × 104 K. Because of the self-regulation, the photon-trapping radius expands and contracts following the rise and fall of accretion rate. The radiation temperature is nearly independent of BH mass and accretion rate and varies weakly with the stellar mass and the viscosity parameter. Our results are well consistent with the observations of optical/UV TDEs.