bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical investigation of laminar–turbulent transition in laminar separation bubbles: the effect of free-stream turbulence
Authors: Hosseinverdi Shirzad , Fasel Hermann F. 
Published: November 2018

The role of free-stream turbulence (FST) in the hydrodynamic instability mechanisms and transition to turbulence in laminar separation bubbles (LSBs) was investigated using direct numerical simulations (DNS). Towards this end, a set of highly resolved DNS have been carried out, where isotropic FST fluctuations with intensities from 0.1 % to 3 % are introduced to investigate the relevant physical mechanisms governing the interaction of separation and transition in LSBs. For disturbance-free simulations, i.e. without FST, laminar–turbulent transition involves a Kelvin–Helmholtz (KH) instability of the separated shear layer. For LSBs subjected to FST, vortical FST fluctuations penetrate the approaching attached laminar boundary layer upstream of the separation location and induce slowly growing low-frequency disturbances, so-called Klebanoff (K) modes, which cause a spanwise modulation with a distinct spanwise wavelength. Simultaneously, the FST enhances the initial levels of instability waves with frequencies in the frequency range of the KH instability, but at much smaller amplitude levels compared to the K-modes. Results from the calculations based on the linearized Navier–Stokes equations and comparison with DNS results reveal that the K-mode exhibits exponential growth in the separated shear layer until it reaches a peak amplitude. At the same time, two-dimensional (2D) disturbance waves are also exponentially amplified, in fact at larger growth rate compared to the K-mode, due to the primary (convective) shear-layer instability mechanism until they saturate downstream of the peak amplitude associated with the K-mode. Therefore, based on detailed spectral analysis and modal decompositions for the separation bubbles investigated, the transition process is the result of two different mechanisms: (i) strong amplification of high-frequency (order of the shedding frequency), essentially 2D or weakly oblique fluctuating disturbances and (ii) low-frequency, three-dimensional K-modes caused by FST. Depending on the intensity of the FST, one of these mechanisms would dominate the transition process, or both mechanisms act together and contribute simultaneously. The net effect of these two events is an acceleration of transition for an increased level of FST intensity, which in turn leads to a reduction of the extent of the separation bubble in streamwise and wall-normal directions. The ‘roll-up’ into spanwise large-scale vortical structures resulting from the shear-layer instability, and the eventual breakdown of these structures, strongly contribute to the reattachment process. The spanwise coherence of these ‘rollers’ deteriorates due to the presence of large-amplitude K-modes, thus effectively weakening their strength for high levels of FST intensities ($Tu>1\,\%$).
THE POLITICS OF RECOGNIZABILITY: GIVING AN ACCOUNT OF IRANIANGAYMEN’S LIVES UNDER REPRESSIVE CONDITIONS OF SEXUALITY GOVERNANCE
Authors: Martino Wayne , Kjaran Jón Ingvar 
Published: November 2018

AbstractIn this article we examine accounts of self-identifying Iranian gay men. We draw on a range of evidentiary sources—interpretive, historical, online, and empirical—to generate critical and nuanced insights into the politics of recognition and representation that inform narrative accounts of the lived experiences of self-identifiedgayIranian men, and the constitution of same-sex desire for these men under specific conditions of Iranian modernity. In response to critiques of existinggayinternationalist and liberationist accounts of the Iraniangaymale subject as a persecuted victim of the Islamic Republic of Iran's barbarism, we address interpretive questions of sexuality governance in transnational contexts. Specifically, we attend to human rights frameworks in weighing social justice and political claims made by and on behalf of sexual and gender minorities in such Global South contexts. In this sense, our article represents a critical engagement with the relevant literature on sexuality governance and the politics of same-sex desire for Iraniangaymen that is informed by empirical analysis.
Projection-operator methods for classical transport in magnetized plasmas. Part 2. Nonlinear response and the Burnett equations
Authors: Krommes John A. 
Published: November 2018

The time-independent projection-operator formalism of Breyet al. (PhysicaA, vol. 109, 1981, pp. 425–444) for the derivation of Burnett equations is extended and considered in the context of multispecies and magnetized plasmas. The procedure provides specific formulas for transport coefficients in terms of two-time correlation functions involving both two and three phase-space points. It is shown how to calculate those correlation functions in the limit of weak coupling. The results are used to demonstrate, with the aid of a particular non-trivial example, that the Chapman–Enskog methodology employed by Catto & Simakov (CS) (Phys. Plasmas, vol. 11, 2004, pp. 90–102) to calculate the contributions to the parallel viscosity driven by temperature gradients is consistent with formulas previously derived from the two-time formalism by Brey (J. Chem. Phys., vol. 79, 1983, pp. 4585–4598). The work serves to unify previous work on plasma kinetic theory with formalism usually applied to turbulence. Additional contributions include discussions of (i) Braginskii-order interspecies momentum exchange from the point of view of two-time correlations; and (ii) a simple stochastic model, unrelated to many-body theory, that exhibits Burnett effects. Insights from that model emphasize the role of non-Gaussian statistics in the evaluation of Burnett transport coefficients, including the effects calculated by CS that stem from the nonlinear collision operator. Together, Parts 1 and 2 of this series provide an introduction to projection-operator methods that should be broadly useful in theoretical plasma physics.
Bias-contingent attention bias modification and attention control training in treatment of PTSD: a randomized control trial
Authors: Lazarov Amit , Suarez-Jimenez Benjamin , Abend Rany , Naim Reut , Shvil Erel , Helpman Liat , Zhu Xi , Papini Santiago , Duroski Ariel , Rom Rony , Schneier Franklin R. , Pine Daniel S. , Bar-Haim Yair , Neria Yuval 
Published: November 2018

AbstractBackgroundRandomized control trials (RCTs) comparing attention control training (ACT) and attention bias modification (ABM) in posttraumatic stress disorder (PTSD) have shown mixed results. The current RCT extends the extant literature by comparing the efficacy of ACT and a novel bias-contingent-ABM (BC-ABM), in which direction of training is contingent upon the direction of pre-treatment attention bias (AB), in a sample of civilian patients with PTSD.MethodsFifty treatment-seeking civilian patients with PTSD were randomly assigned to either ACT or BC-ABM. Clinician and self-report measures of PTSD and depression, as well as AB and attention bias variability (ABV), were acquired pre- and post-treatment.ResultsACT yielded greater reductions in PTSD and depressive symptoms on both clinician-rated and self-reported measures compared with BC-ABM. The BC-ABM condition successfully shifted ABs in the intended training direction. In the ACT group, there was no significant change in ABV or AB from pre- to post-treatment.ConclusionsThe current RCT extends previous results in being the first to apply ABM that is contingent upon AB at pre-treatment. This personalized BC-ABM approach is associated with significant reductions in symptoms. However, ACT produces even greater reductions, thereby emerging as a promising treatment for PTSD.
THE CORPORATION'S GOVERNMENTAL PROVENANCE AND ITS SIGNIFICANCE
Authors: Singer Abraham A. 
Published: November 2018

Abstract:Corporations cannot exist, scholars rightly note, without being constituted by government. However, many take a further step, claiming that corporations are normatively distinct from other market actors because of this governmental provenance. They are mistaken. Like corporations, markets and contracts also require government for their creation. Governmental provenance does not distinguish corporations normatively because our coercive social institutions are pro tanto justified in re-arranging both corporate and non-corporate market activities on behalf of social and political values. The corporation is distinct only practically and prudentially, in that it represents a more proximate instrument for effecting morality in the economy.
Inequality and Political Trust in China: The Social Volcano Thesis Re-examined
Authors: Zhou Yingnan Joseph , Jin Shuai 
Published: November 2018

AbstractThe social volcano thesis states that the rising inequality in China threatens regime stability. This idea, although widely held in the media and in academia, is backed by little positive evidence but by much negative evidence. Two primary pieces of negative evidence are that the Chinese people trust the central government and that they are highly tolerant of inequality. This paper discusses the shortcomings of the negative evidence and re-examines the thesis in a rigorous and direct way. Our multilevel analysis shows that provincial inequality has negative effects on individuals’ trust in the local government but not in the central government, and this negative effect holds for both the rich and the poor. Because distrust in the local government implies distrust in the central government, we conclude that a social volcano exists.
When Voluntary Donations Meet the State Monopoly: Understanding Blood Shortages in China
Authors: Guan Yue 
Published: November 2018

AbstractChina's blood-borne HIV catastrophe in the 1990s prompted the government to adopt a blood-collection system that combines voluntary donations with the state's monopoly on blood services. Juxtaposing fieldwork and survey data, this study examines how the intricate interplay between government manoeuvres and citizen reactions has led to blood shortages that are serious yet manageable. This article reveals that even though voluntary blood donations are adversely affected by a public distrust of state-run collection agencies, owing to political concerns healthcare officials shirk from engaging with citizens to overcome the distrust. It also finds that the blood shortages are nevertheless largely manageable because the authorities have the capacity to recruit captive donors through work units, with the caveat that such captive practices are used sparingly. Overall, this study argues that the lack of state–society synergy in voluntary donations, while exacerbated by government involvement, is also partially remedied by the government's mobilization of captive donors.
Comparing Hydrological Postprocessors Including Ensemble Predictions Into Full Predictive Probability Distribution of Streamflow
Authors: Biondi D. , Todini E. 
Published: November 2018

AbstractAlthough not matching the formal definition of the predictive probability distribution, meteorological and hydrological ensembles have been frequently interpreted and directly used to assess flood‐forecasting predictive uncertainty. With the objective of correctly assessing the predictive probability of floods, this paper introduces ways of taking into account the measures of uncertainty provided in the form of ensemble forecasts by modifying a number of well‐established uncertainty postprocessors, such as Bayesian Model Averaging and Model Conditional Processor. The uncertainty postprocessors were developed on the assumption that the future unknown quantity (predictand) is uncertain while model forecasts (predictors) are given, which imply that they are perfectly known. With this in mind, we propose to relax this assumption by considering ensemble predictions, in analogy to measurement errors, as expressions of errors in model predictions to be integrated in the postprocessors coefficients estimation process. The analyses of the methodologies proposed in this work are conducted on a real case study based on meteorological ensemble predictions for the Po River at Pontelagoscuro in Italy. After showing how improper can be the direct use of ensemble predictions to describe the predictive probability distribution, results from the modified postprocessors are compared and discussed.
Tropical Ionization Trough in the Ionosphere Seen by Swarm‐A Satellite
Authors: Lee Woo Kyoung , Kil Hyosub , Paxton Larry J. 
Published: November 2018

AbstractA new type of ionization trough, the tropical ionization trough, is identified in the tropical F region from the Swarm‐A satellite observations in December 2013 to January 2017. The trough is formed around midnight near 25° magnetic latitudes in the winter hemisphere during the solstices. The trough is pronounced around 330°E longitude in the Southern Hemisphere (negative magnetic declination) during the June solstices and around 210°E longitude in the Northern Hemisphere (positive magnetic declination) during the December solstices. Weak signatures of the trough also appear at those locations during the equinoxes. We interpret the formation of the trough in the winter hemisphere during the solstices by the convergence of meridional winds in the winter tropics. The longitudinal variation of the trough intensity is explained by the magnetic declination control of the zonal wind effect and the longitudinal variation of the meridional wind velocity.
Toward Data‐Driven Weather and Climate Forecasting: Approximating a Simple General Circulation Model With Deep Learning
Authors: Scher S. 
Published: November 2018

AbstractIt is shown that it is possible to emulate the dynamics of a simple general circulation model with a deep neural network. After being trained on the model, the network can predict the complete model state several time steps ahead—which conceptually is making weather forecasts in the model world. Additionally, after being initialized with an arbitrary model state, the network can through repeatedly feeding back its predictions into its inputs create a climate run, which has similar climate statistics to the climate of the general circulation model. This network climate run shows no long‐term drift, even though no conservation properties were explicitly designed into the network.
Effect of the Reconnection Electric Field on Electron Distribution Functions in the Diffusion Region of Magnetotail Reconnection
Authors: Bessho N. , Chen L.‐J. , Wang S. , Hesse M. 
Published: November 2018

AbstractElectron distribution functions in the electron diffusion region during symmetric magnetic reconnection are investigated by means of theory and fully kinetic simulations. Crescent‐like striations are formed in distribution functions in the velocity plane perpendicular to the magnetic field. Using an analytical current sheet, we solve the equation of motion for electrons, and derive the shape of a crescent distribution, as a function of the distance from the neutral line, field gradients, and the reconnection electric field. Each crescent is tilted in the velocity plane because of the acceleration by the reconnection electric field, and multiple stripes appear due to multiple meandering bounces. Applying the theory to distribution functions observed in Earth's magnetotail, we deduce the amplitude of the reconnection electric field.
The Energetics of Extensive Meltwater Flooding of Level Arctic Sea Ice
Authors: Diaz A. , Ehn J. K. , Landy J. C. , Else B. G. T. , Campbell K. , Papakyriakou T. N. 
Published: November 2018

AbstractDuring the spring‐to‐summer transition, the snow cover on Arctic sea ice melts and meltwater pools on the surface to form melt ponds; however, the timing and extent of the ponding vary between years. In Dease Strait (Nunavut), this transition was particularly dramatic in 2014 when on 18 June meltwater had flooded >95% of the surface. In this study, continuous surface energy balance measurements throughout the transition highlight how the timing of transient weather events influenced seasonal shifts in distinct ice melt stages. The keys to the extensive flooding were (1) the level ice cover, (2) a strong low‐pressure system on 24 May that deposited ~10 cm of snow, and (3) freeze‐thaw cycling and a subsequent return to subzero air temperatures on 30 May that led to superimposed and interposed ice formation. Without these, melt ponds would have likely developed within days from an initial melt onset on 28 May. After a 2‐week delay, snow‐melt resumed and lead to near‐complete flooding of the surface for 4 days. The albedo of the flooded ice remained high (0.35–0.40), as a result of the bubble‐laden superimposed ice layer. Once this layer eroded, the albedo over melt ponds decreased to a more typical level (~0.20). Our observations suggest that the formation of superimposed and interposed ice prevented the vertical drainage of meltwater to the ocean. Future challenges remain to measure the presence of these layers and understand their effect on sea ice permeability and pond evolution, while sea ice temperatures are near the melting point.
Observations of Reduced Turbulence and Wave Activity in the Arctic Middle Atmosphere Following the January 2015 Sudden Stratospheric Warming
Authors: Triplett Colin C. , Li Jintai , Collins Richard L. , Lehmacher Gerald A. , Barjatya Aroh , Fritts David C. , Strelnikov Boris , Lübken Franz‐Josef , Thurairajah Brentha , Harvey V. Lynn , Hampton Donald L. , Varney Roger H. 
Published: November 2018

AbstractMeasurements of turbulence and waves were made as part of the Mesosphere‐Lower Thermosphere Turbulence Experiment (MTeX) on the night of 25–26 January 2015 at Poker Flat Research Range, Chatanika, Alaska (65°N, 147°W). Rocket‐borne ionization gauge measurements revealed turbulence in the 70‐ to 88‐km altitude region with energy dissipation rates between 0.1 and 24 mW/kg with an average value of 2.6 mW/kg. The eddy diffusion coefficient varied between 0.3 and 134 m2/s with an average value of 10 m2/s. Turbulence was detected around mesospheric inversion layers (MILs) in both the topside and bottomside of the MILs. These low levels of turbulence were measured after a minor sudden stratospheric warming when the circulation continued to be disturbed by planetary waves and winds remained weak in the stratosphere and mesosphere. Ground‐based lidar measurements characterized the ensemble of inertia‐gravity waves and monochromatic gravity waves. The ensemble of inertia‐gravity waves had a specific potential energy of 0.8 J/kg over the 40‐ to 50‐km altitude region, one of the lowest values recorded at Chatanika. The turbulence measurements coincided with the overturning of a 2.5‐hr monochromatic gravity wave in a depth of 3 km at 85 km. The energy dissipation rates were estimated to be 3 mW/kg for the ensemble of waves and 18 mW/kg for the monochromatic wave. The MTeX observations reveal low levels of turbulence associated with low levels of gravity wave activity. In the light of other Arctic observations and model studies, these observations suggest that there may be reduced turbulence during disturbed winters.
Vertical Characterization of Aerosol Particle Composition in Beijing, China: Insights From 3‐Month Measurements With Two Aerosol Mass Spectrometers
Authors: Zhou Wei , Sun Yele , Xu Weiqi , Zhao Xiujuan , Wang Qingqing , Tang Guiqian , Zhou Libo , Chen Chen , Du Wei , Zhao Jian , Xie Conghui , Fu Pingqing , Wang Zifa 
Published: November 2018

AbstractDespite extensive studies for characterization of aerosol chemistry near ground level, long‐term vertical characterization of aerosol particle composition in Beijing is very limited. In this work, non‐refractory submicron aerosol (NR‐PM1) species were simultaneously measured at ground level and 260 m on a meteorological tower from 14 October 2014 to 18 January 2015 in Beijing using two aerosol mass spectrometers. Our results showed overall lower concentrations of NR‐PM1 at 260 m by 2%–36% than ground level in both heating and non‐heating seasons, and also larger vertical gradients during clean periods than polluted episodes. The vertical ratios and correlations of aerosol species between ground level and 260 m presented higher values in daytime and lower ones at nighttime mainly due to the influences of planetary boundary layer and local source emissions, respectively. Nitrate showed ubiquitously higher ratio of 260 m to ground (ratio260m/ground) than sulfate due to a higher formation potential from gas‐particle partitioning and heterogeneous reactions at higher heights. A detailed analysis of vertical evolution showed relatively stable ratios260m/ground for secondary aerosol species during the early formation stage of haze episodes, which decreased simultaneously along with mixing layer height during the later severely polluted periods with NR‐PM1 concentration above 150 μg/m3. Our results demonstrated that the evolution of vertical differences in megacities is subject to the influences from both physical (e.g., regional transport, mountain‐valley winds, inversions of temperature and relative humidity, and mixing layer height) and chemical processes (e.g., gas‐particle partitioning and aqueous‐phase processing).
Effects of Langmuir Turbulence on Upper Ocean Carbonate Chemistry
Authors: Smith K. M. , Hamlington P. E. , Niemeyer K. E. , Fox‐Kemper B. , Lovenduski N. S. 
Published: November 2018

AbstractEffects of wave‐driven Langmuir turbulence on the air‐sea flux of carbon dioxide (CO2) are examined using large eddy simulations featuring actively reacting carbonate chemistry in the ocean mixed layer at small scales. Four strengths of Langmuir turbulence are examined with three types of carbonate chemistry: time‐dependent chemistry, instantaneous equilibrium chemistry, and no reactions. The time‐dependent model is obtained by reducing a detailed eight‐species chemical mechanism using computational singular perturbation analysis, resulting in a quasi steady state approximation for hydrogen ion (H+); that is, fixed pH. The reduced mechanism is then integrated in two half‐time steps before and after the advection solve using a Runge‐Kutta‐Chebyshev scheme that is robust for stiff systems of differential equations. The simulations show that as the strength of Langmuir turbulence increases, CO2 fluxes are enhanced by rapid overturning of the near‐surface layer, which rivals the removal rate of CO2 by time‐dependent reactions. Equilibrium chemistry and nonreactive models are found to bring more and less carbon, respectively, into the ocean as compared to the more realistic time‐dependent model. These results have implications for Earth system models that either neglect Langmuir turbulence or use equilibrium, instead of time‐dependent, chemical mechanisms.