349 research outputs found

    Revolution in Warfare? Air Power in the Persian Gulf

    Get PDF

    Reinventing grounded theory: some questions about theory, ground and discovery

    Get PDF
    Grounded theory’s popularity persists after three decades of broad-ranging critique. In this article three problematic notions are discussed—‘theory,’ ‘ground’ and ‘discovery’—which linger in the continuing use and development of grounded theory procedures. It is argued that far from providing the epistemic security promised by grounded theory, these notions—embodied in continuing reinventions of grounded theory—constrain and distort qualitative inquiry, and that what is contrived is not in fact theory in any meaningful sense, that ‘ground’ is a misnomer when talking about interpretation and that what ultimately materializes following grounded theory procedures is less like discovery and more akin to invention. The procedures admittedly provide signposts for qualitative inquirers, but educational researchers should be wary, for the significance of interpretation, narrative and reflection can be undermined in the procedures of grounded theory

    Evidential Deep Learning: Enhancing Predictive Uncertainty Estimation for Earth System Science Applications

    Full text link
    Robust quantification of predictive uncertainty is critical for understanding factors that drive weather and climate outcomes. Ensembles provide predictive uncertainty estimates and can be decomposed physically, but both physics and machine learning ensembles are computationally expensive. Parametric deep learning can estimate uncertainty with one model by predicting the parameters of a probability distribution but do not account for epistemic uncertainty.. Evidential deep learning, a technique that extends parametric deep learning to higher-order distributions, can account for both aleatoric and epistemic uncertainty with one model. This study compares the uncertainty derived from evidential neural networks to those obtained from ensembles. Through applications of classification of winter precipitation type and regression of surface layer fluxes, we show evidential deep learning models attaining predictive accuracy rivaling standard methods, while robustly quantifying both sources of uncertainty. We evaluate the uncertainty in terms of how well the predictions are calibrated and how well the uncertainty correlates with prediction error. Analyses of uncertainty in the context of the inputs reveal sensitivities to underlying meteorological processes, facilitating interpretation of the models. The conceptual simplicity, interpretability, and computational efficiency of evidential neural networks make them highly extensible, offering a promising approach for reliable and practical uncertainty quantification in Earth system science modeling. In order to encourage broader adoption of evidential deep learning in Earth System Science, we have developed a new Python package, MILES-GUESS (https://github.com/ai2es/miles-guess), that enables users to train and evaluate both evidential and ensemble deep learning

    Three red suns in the sky: A transiting, terrestrial planet in a triple M-dwarf system at 6.9 pc

    Get PDF
    We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of 1.380.12+0.13{1.38}_{-0.12}^{+0.13} R{R}_{\oplus }, an orbital period of 5.358820.00031+0.00030{5.35882}_{-0.00031}^{+0.00030} days, and an equilibrium temperature of 43327+28{433}_{-27}^{+28} K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3σ upper mass limit of 8.4 M{M}_{\oplus } on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co-planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.Accepted manuscrip

    Kepler eclipsing binary stars. VII. the catalogue of eclipsing binaries found in the entire Kepler data set

    Get PDF
    The primary Kepler Mission provided nearly continuous monitoring of ~200,000 objects with unprecedented photometric precision. We present the final catalog of eclipsing binary systems within the 105 deg2 Kepler field of view. This release incorporates the full extent of the data from the primary mission (Q0-Q17 Data Release). As a result, new systems have been added, additional false positives have been removed, ephemerides and principal parameters have been recomputed, classifications have been revised to rely on analytical models, and eclipse timing variations have been computed for each system. We identify several classes of systems including those that exhibit tertiary eclipse events, systems that show clear evidence of additional bodies, heartbeat systems, systems with changing eclipse depths, and systems exhibiting only one eclipse event over the duration of the mission. We have updated the period and galactic latitude distribution diagrams and included a catalog completeness evaluation. The total number of identified eclipsing and ellipsoidal binary systems in the Kepler field of view has increased to 2878, 1.3% of all observed Kepler targets

    Nursing heroism in the 21st Century'

    Get PDF
    Abstract Background The Vivian Bullwinkel Oration honours the life and work of an extraordinary nurse. Given her story and that of her World War II colleagues, the topic of nursing heroism in the 21st century could not be more germane. Discussion Is heroism a legitimate part of nursing, or are nurses simply 'just doing their job' even when facing extreme personal danger? In this paper I explore the place and relevance of heroism in contemporary nursing. I propose that nursing heroism deserves a broader appreciation and that within the term lie many hidden, 'unsung' or 'unrecorded' heroisms. I also challenge the critiques of heroism that would condemn it as part of a 'militarisation' of nursing. Finally, I argue that nursing needs to be more open in celebrating our heroes and the transformative power of nursing achievements. Summary The language of heroism may sound quaint by 21st Century standards but nursing heroism is alive and well in the best of our contemporary nursing ethos and practice.</p

    Tidal Disruption Event Demographics with the Zwicky Transient Facility: Volumetric Rates, Luminosity Function, and Implications for the Local Black Hole Mass Function

    Full text link
    We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete sample of 33 TDEs is constructed using the Zwicky Transient Facility over three years (from October 2018 to September 2021). We infer the black hole (BH) mass (MBHM_{\rm BH}) with host galaxy scaling relations, showing that the sample MBHM_{\rm BH} ranges from 105.1M10^{5.1}\,M_\odot to 108.2M10^{8.2}\,M_\odot. We developed a survey efficiency corrected maximum volume method to infer the rates. The rest-frame gg-band luminosity function (LF) can be well described by a broken power-law of ϕ(Lg)[(Lg/Lbk)0.3+(Lg/Lbk)2.6]1\phi (L_g)\propto [(L_g / L_{\rm bk})^{0.3} + (L_g / L_{\rm bk})^{2.6}]^{-1}, with Lbk=1043.1ergs1L_{\rm bk}=10^{43.1}\,{\rm erg\,s^{-1}}. In the BH mass regime of 105.3(MBH/M)107.310^{5.3}\lesssim (M_{\rm BH}/M_\odot) \lesssim 10^{7.3}, the TDE mass function follows ϕ(MBH)MBH0.25\phi(M_{\rm BH})\propto M_{\rm BH}^{-0.25}, which favors a flat local BH mass function (dnBH/dlogMBHconstantdn_{\rm BH}/d{\rm log}M_{\rm BH}\approx{\rm constant}). We confirm the significant rate suppression at the high-mass end (MBH107.5MM_{\rm BH}\gtrsim 10^{7.5}\,M_\odot), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of Mgal1010MM_{\rm gal}\sim 10^{10}\,M_\odot, the average optical TDE rate is 3.2×105galaxy1yr1\approx 3.2\times 10^{-5}\,{\rm galaxy^{-1}\,yr^{-1}}. We constrain the optical TDE rate to be [3.7, 7.4, and 1.6]×105galaxy1yr1]\times 10^{-5}\,{\rm galaxy^{-1}\,yr^{-1}} in galaxies with red, green, and blue colors.Comment: Replaced following peer-review process. 38 pages, 23 figures. Accepted for publication in ApJ

    A Conserved Behavioral State Barrier Impedes Transitions between Anesthetic-Induced Unconsciousness and Wakefulness: Evidence for Neural Inertia

    Get PDF
    One major unanswered question in neuroscience is how the brain transitions between conscious and unconscious states. General anesthetics offer a controllable means to study these transitions. Induction of anesthesia is commonly attributed to drug-induced global modulation of neuronal function, while emergence from anesthesia has been thought to occur passively, paralleling elimination of the anesthetic from its sites in the central nervous system (CNS). If this were true, then CNS anesthetic concentrations on induction and emergence would be indistinguishable. By generating anesthetic dose-response data in both insects and mammals, we demonstrate that the forward and reverse paths through which anesthetic-induced unconsciousness arises and dissipates are not identical. Instead they exhibit hysteresis that is not fully explained by pharmacokinetics as previously thought. Single gene mutations that affect sleep-wake states are shown to collapse or widen anesthetic hysteresis without obvious confounding effects on volatile anesthetic uptake, distribution, or metabolism. We propose a fundamental and biologically conserved concept of neural inertia, a tendency of the CNS to resist behavioral state transitions between conscious and unconscious states. We demonstrate that such a barrier separates wakeful and anesthetized states for multiple anesthetics in both flies and mice, and argue that it contributes to the hysteresis observed when the brain transitions between conscious and unconscious states
    corecore