Magnetic evolution of superactive regions. Complexity and potentially unstable magnetic discontinuities

In this work, we have studied the temporal evolution of some properties of a sample of superactive regions with the aim to single out the most significant for flare activity forecasting. We have investigated properties of 14 superactive regions, observed between January 1st 2000 and December 31st 2006 with MDI/SOHO instrument and characterized by a particularly intense flare activity during their passage on the solar disk. We have analyzed the temporal evolution of fractal and multifractal properties of photospheric magnetic fields, namely the generalized fractal dimension and the cntribution and dimensionality diversities, as well as the potential unstable volumes of magnetic discontinuities above the studied ARs. Correlations of these quantities with the flare index, which provides information about the flare activity of a region, have also been estimated. We found that in 50 % of our sample the generalized fractal dimension is correlated with the flare index computed over windows of 50 hours, while the contribution diversity and the dimensional diversity are anticorrelated with the same index. An increase of the potential unstable volume of magnetic discontinuities in the corona is observed before the phases characterized by more frequent and intense flares. We also found that the free energy distribution functions of unstable volumes of the analyzed superactive regions can be fitted with straight lines whose slope is larger than the values found in previous works for less active magnetic regions. The generalized fractal dimension and the potential unstable volume of magnetic discontinuities are the most suitable for statistical investigations of relations with flare activity over longer (50 hours) and shorter (few hours) time intervals, respectively

San Francisco Predictable Scheduling and Fair Treatment for Formula Retail Employees Ordinance

Economic and labor force changes since the Great Recession of 2007 have changed the way many American workers support themselves and their families. Today, Americans who would prefer full-time stable work are more likely to work in part-time jobs, and have little control over their work schedules. As employers seek new ways to maximize scheduling efficiency and profit, worker advocate groups have raised concerns about the implications of these scheduling practices on the lives of employees. This issue brief highlights some of the research on the growth of unstable work schedules, and describes the provisions of recently introduced legislation in San Francisco that seeks to increase predictable scheduling among certain retail and food service workers. San Francisco's is the first such legislation to be introduced at the local level in the natio

Competition of rotation and stratification in flux concentrations

In a strongly stratified turbulent layer, a uniform horizontal magnetic field can become unstable to spontaneously form local flux concentrations due to a negative contribution of turbulence to the large-scale (mean-field) magnetic pressure. This mechanism, called the negative effective magnetic pressure instability (NEMPI), is of interest in connection with dynamo scenarios where most of the magnetic field resides in the bulk of the convection zone, and not at the bottom. Recent work using the mean-field hydromagnetic equations has shown that NEMPI becomes suppressed at rather low rotation rates with Coriolis numbers as low as 0.1.}{Here we extend these earlier investigations by studying the effects of rotation both on the development of NEMPI and on the effective magnetic pressure. We also quantify the kinetic helicity from direct numerical simulations (DNS) and compare with earlier work.}{To calculate the rotational effect on the effective magnetic pressure we consider both DNS and analytical studies using the $\tau$ approach. To study the effects of rotation on the development of NEMPI we use both DNS and mean-field calculations of the 3D hydromagnetic equations in a Cartesian domain.}{We find that the growth rates of NEMPI from earlier mean-field calculations are well reproduced with DNS, provided the Coriolis number is below about 0.06. In that case, kinetic and magnetic helicities are found to be weak. For faster rotation, dynamo action becomes possible. However, there is an intermediate range of rotation rates where dynamo action on its own is not yet possible, but the rotational suppression of NEMPI is being alleviated.}{Production of magnetic flux concentrations through the suppression of turbulent pressure appears to be possible only in the upper-most layers of the Sun, where the convective turnover time is less than 2 hours.}Comment: 13 pages, 13 figures submitted to A&

Mechanisms producing different precipitation patterns over north‐eastern Italy: insights from HyMeX‐SOP1 and previous events

During the first HyMeX Special Observation Period (SOP1) field campaign, the target site of north‐eastern Italy (NEI) experienced a large amount of precipitation, locally exceeding the climatological values and distributed among several heavy‐rainfall episodes. In particular, two events that occurred during the last period of the campaign drew our attention. These events had common large‐scale patterns and a similar mesoscale setting, characterised by southerly low‐level flow interacting with the Alpine orography, but the precipitation distribution was very different. During Intensive Observing Period IOP18 (31 October–1 November 2012), convective systems were responsible for intense rainfall mainly located over a flat area of the eastern Po Valley, well upstream of the orography. Conversely, during IOP19 (4/5 November 2012), heavy precipitation affected only the Alpine area. In addition to IOP18 and IOP19, the present study analyses other heavy‐precipitation episodes that display similar characteristics and which occurred over NEI during the autumn of recent years. A high‐resolution (2 km grid spacing) non‐hydrostatic NWP model and available observations are used for this purpose. The two different observed precipitation patterns are explained in terms of interaction between the impinging flow and the Alps. Depending on the thermodynamic profile, convection can be triggered when the impinging flow is forced to rise over a pre‐existing cold‐air layer at the base of the orography. In this situation a persistent blocked‐flow condition and upstream convergence are responsible for heavy rain localized over the plain. Conversely, if convection does not develop, flow‐over conditions are established and heavy rain affects the Alps. Numerical parameters proposed in the literature are used to support the analysis. Finally, the role of evaporative cooling beneath the convective systems is evaluated. It turns out that the stationarity of the systems upstream of the Alps is mainly attributable to persistent blocked‐flow conditions, while convective outflow slightly modifies the location of precipitation

Current outcomes of blunt open pelvic fractures: how modern advances in trauma care may decrease mortality.

Background:Open pelvic fracture, caused by a blunt mechanism, is an uncommon injury with a high mortality rate. In 2008, evidence-based algorithm for managing pelvic fractures in unstable patients was published by the Western Trauma Association (WTA). The use of massive transfusion protocols has become widespread as has the availability and use of pelvic angiography. The purpose of this study was to evaluate the outcome of open pelvic fractures in association with related advances in trauma care. Methods:A retrospective review was performed, at an American College of Surgeon verified level I trauma center, of patients with blunt open pelvic fractures from January 2010 to April 2016. The WTA algorithm, including massive transfusion protocol, and pelvic angiography were uniformly used. Data collected included injury severity score, demographic data, transfusion requirements, use of pelvic angiography, length of stay, and disposition. Data were compared with a similar study from 2005. Results:During the study period, 1505 patients with pelvic fractures were analyzed; 87 (6%) patients had open pelvic fractures. Of these, 25 were from blunt mechanisms and made up the study population. Patients in both studies had similar injury severity scores, ages, Glasgow Coma Scale, and gender distributions. Use of angiography was higher (44% vs. 16%; P=0.011) and mortality was lower (16% vs. 45%; P=0.014) than in the 2005 study. Conclusions:Changes in trauma care for patients with open blunt pelvic fracture include the use of an evidence-based algorithm, massive transfusion protocols and increased use of angioembolization. Mortality for open pelvic fractures has decreased with these advances. Level of evidence:Level IV

Fiscal policy and indeterminacy in models of endogenous growth

This paper investigates the dynamic behavior of two-sector models of endogenous growth with sector-specific external effects, and government expenditure financed by distortionary taxation. When this type of external effect is combined with a sufficient degree of capital taxation in a Lucas–Uzawa endogenous growth model, continua of equilibria will emerge in the region of the balanced growth paths. By contrast, indeterminacy is not possible when either sector-specific external effects or factor taxation are added to the model in isolation. In the second part of the paper, we demonstrate that if labor supply is endogenous, indeterminacy can be consistent with much lower degrees of increasing returns to scale. Furthermore, certain types of fiscal policy will be associated with multiple balanced growth paths and the existence of a poverty trap. Finally, in the last part of the paper, we demonstrate that if physical capital is employed in both sectors of the economy, indeterminacy will emerge for varying combinations of factor taxation and external effects, even when returns to scale are constant at the social level

Long lasting instabilities in granular mixtures

We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and spatio-temporal graphs are created. We report the occurence of instabilities which can last several hours. We stress that those instabilities originate from the competition between axial and radial segregations. We put into evidence the occurence of giant fluctuations in the fraction of grain species along the surface during the unstable periods.Comment: 10 pages, 10 figures, (2002

Diurnal cycle RANS simulations applied to wind resource assessment

Microscale computational fluid dynamics (CFD) models can be used for wind resource assessment on complex terrains. These models generally assume neutral atmospheric stratification, an assumption that can lead to inaccurate modeling results and to large uncertainties at certain sites. We propose a methodology for wind resource evaluation based on unsteady Reynolds averaged Navier‐Stokes (URANS) simulations of diurnal cycles including the effect of thermal stratification. Time‐dependent boundary conditions are generated by a 1D precursor to drive 3D diurnal cycle simulations for a given geostrophic wind direction sector. Time instants of the cycle representative of four thermal stability regimes are sampled within diurnal cycle simulations and combined with masts time series to obtain the wind power density (WPD). The methodology has been validated on a complex site instrumented with seven met masts. The WPD spatial distribution is in good agreement with observations with the mean absolute error improving 17.1% with respect to the neutral stratification assumption.This work has been partially supported by the three EU H2020 projects, New European Wind Atlas ERA‐NET PLUS (NEWA, FP7‐ENERGY.2013.10.1.2, European Commission's grant agreement 618122), High Performance Computing for Energy (HPC4E, grant agreement 689772), and the Energy oriented Centre of Excellence (EoCoE, grant agreement 676629), and the SEDAR (“Simulación eólica de alta resolución”) project. Jordi Barcons is grateful to a PhD fellowship from the Industrial Doctorates Plan of the Government of Catalonia (Ref. eco/2497/2013). We also thank Iberdrola Renovables Energa S.A. and Impulsora Latinoamericana de Energa Renovables S.A. for providing the access to Puebla met masts data for validation and to Luis Prieto and Daniel Paredes for their help. We also thank the reviewers for their productive comments and observations.Peer ReviewedPostprint (published version