Social comparison in the workplace: evidence from a field experiment

We conducted a randomized field experiment to examine how workers respond to wage cuts, and whether their response depends on the wages paid to coworkers. Workers were assigned to teams of two, performed identical individual tasks, and received the same performance‐independent hourly wage. Cutting both team members’ wages caused a substantial decrease in performance. When only one team member’s wage was cut, the performance decrease for the workers who received the cut was more than twice as large as the individual performance decrease when both workers’ wages were cut. This finding indicates that social comparison processes among workers affect effort provision because the only difference between the two wage cut conditions is the other team member’s wage level. In contrast, workers whose wage was not cut but who witnessed their team member’s pay being cut displayed no change in performance relative to the baseline treatment in which both workers’ wages remained unchanged, indicating that social comparison exerts asymmetric effects on effort.Compensation, fairness, field experiment, social comparison

Investigation of site-specific wind field parameters and their effect on loads of offshore wind turbines

The main contributing factors to unsteady loading of Offshore Wind Turbines (OWT) are wind shear, turbulence, and waves. In the present paper, the turbulence intensity and the wind shear exponent are investigated. Using data from the FINO 1 research platform, these parameters are analyzed and compared with the proposed wind field parameters in the IEC standard 61400-3. Based on this analysis, aeroelastic simulations are performed to determine the effect of wind field parameters on the fatigue and the extreme loads on the rotor blades. For the investigations, the aeroelastic model of a 5 MW OWT is used with a focus on design load cases in an operating state (power production). The fatigue loads are examinedby means of the damage-equivalent load-range approach. In order to determine the extreme loads with a recurrence period of 50 years, a peak over threshold extrapolation method and a novel method based on average conditional exceedance ratesare used. The results show that the requirements of the IEC standard are very conservative for the design of the rotor blades. Therefore, there could be a large optimization potential for the reduction of weight and cost of the rotor blades.Ministry for Science and Culture in Lower SaxonyFederal Maritime and Hydrographic Agency (BSH)Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU

Horizontal secondary gas injection in fluidized beds: Solids concentration and velocity in multiphase jets

Secondary gas injection into fluidized beds is used in many industrial applications to control the particle size (1) or to introduce a reactant gas (2). Also in fluidized bed opposed jet mills a highly expanded gas can be used to grind particles into the submicron range. To model and improve processes which use secondary gas injection, a better understanding of the multiphase flow inside the jets is indispensable. A contribution to this is the analysis of the particle velocity via particle image velocimetry (PIV). These experiments were carried out in a semicircle fluidized bed with optical access, so that the morphology, particle acceleration and entrainment behavior can be visualized. These results can be compared to a simple model for the calculation of particle velocities in free jets and give a good agreement. Additionally, the solids concentrations in the particle laden gas jets are investigated with capacitance probes, an invasive measurement technique (3). Thus a solid concentration profile of the jet area can be determined and together with the PIV-data the solid mass flow can be estimated. This information is important for the calculation of the residence time in a reaction zone or the load condition in a jet mill. Parameters for those studies were the particle-size-distributions, the nozzle diameter, secondary gas velocity or the fluidization velocity. The measurements as well as the comparisons with calculations and models have discovered some unexpected insights in the multiphase flow of gas jets into fluidized beds and in the comminution process in fluidized bed opposed jet mills. REFERENCES J. McMillan, C. Briens, F.Berruti, and E.Chan. High velocity attrition nozzles in fluidized beds. Powd. Techn., 175:133-141, 2007. L. Chen, and H. Weinstein. Shape and extent of the void formed by a horizontal jet in a fluidized bed. AIChE. Journ., 39(12):1901-1909, 1993. M. Richtberg, R. Richter, and K.-E. Wirth. Characterization of the flow patterns in a pressurized circulating fluidized bed. Powd. Techn., 155:145-152, 2005

Effect of Geometric Uncertainties on the Aerodynamic Characteristic of Offshore Wind Turbine Blades

Offshore wind turbines operate in a complex unsteady flow environment which causes unsteady aerodynamic loads. The unsteady flow environment is characterized by a high degree of uncertainty. In addition, geometry variations and material imperfections also cause uncertainties in the design process. Probabilistic design methods consider these uncertainties in order to reach acceptable reliability and safety levels for offshore wind turbines. Variations of the rotor blade geometry influence the aerodynamic loads which also affect the reliability of other wind turbine components. Therefore, the present paper is dealing with geometric uncertainties of the rotor blades. These can arise from manufacturing tolerances and operational wear of the blades. First, the effect of geometry variations of wind turbine airfoils on the lift and drag coefficients are investigated using a Latin hypercube sampling. Then, the resulting effects on the performance and the blade loads of an offshore wind turbine are analyzed. The variations of the airfoil geometry lead to a significant scatter of the lift and drag coefficients which also affects the damage-equivalent flapwise bending moments. In contrast to that, the effects on the power and the annual energy production are almost negligible with regard to the assumptions made.Ministry for Science and Culture in Lower Saxony/ForWin

Aerodynamic behavior of an airfoil with morphing trailing edge for wind turbine applications

The length of wind turbine rotor blades has been increased during the last decades. Higher stresses arise especially at the blade root because of the longer lever arm. One way to reduce unsteady blade-root stresses caused by turbulence, gusts, or wind shear is to actively control the lift in the blade tip region. One promising method involves airfoils with morphing trailing edges to control the lift and consequently the loads acting on the blade. In the present study, the steady and unsteady behavior of an airfoil with a morphing trailing edge is investigated. Two-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations are performed for a typical thin wind turbine airfoil with a morphing trailing edge. Steady-state simulations are used to design optimal geometry, size, and deflection angles of the morphing trailing edge. The resulting steady aerodynamic coefficients are then analyzed at different angles of attack in order to determine the effectiveness of the morphing trailing edge. In order to investigate the unsteady aerodynamic behavior of the optimal morphing trailing edge, time-resolved RANS-simulations are performed using a deformable grid. In order to analyze the phase shift between the variable trailing edge deflection and the dynamic lift coefficient, the trailing edge is deflected at four different reduced frequencies for each different angle of attack. As expected, a phase shift between the deflection and the lift occurs. While deflecting the trailing edge at angles of attack near stall, additionally an overshoot above and beyond the steady lift coefficient is observed and evaluated.BMWi/Smart BladesGerman Aerospace Center (DLR)LUI

Wind turbine rotor blade monitoring using digital image correlation: a comparison to aeroelastic simulations of a multi-megawatt wind turbine

Optical full-field measurement methods such as Digital Image Correlation (DIC) provide a new opportunity for measuring deformations and vibrations with high spatial and temporal resolution. However, application to full-scale wind turbines is not trivial. Elaborate preparation of the experiment is vital and sophisticated post processing of the DIC results essential. In the present study, a rotor blade of a 3.2 MW wind turbine is equipped with a random black-and-white dot pattern at four different radial positions. Two cameras are located in front of the wind turbine and the response of the rotor blade is monitored using DIC for different turbine operations. In addition, a Light Detection and Ranging (LiDAR) system is used in order to measure the wind conditions. Wind fields are created based on the LiDAR measurements and used to perform aeroelastic simulations of the wind turbine by means of advanced multibody codes. The results from the optical DIC system appear plausible when checked against common and expected results. In addition, the comparison of relative out-of-plane blade deflections shows good agreement between DIC results and aeroelastic simulations.Ministry of Science and Culture of Lower Saxon

Cybersecurity in Power Grids: Challenges and Opportunities

Increasing volatilities within power transmission and distribution force power grid operators to amplify their use of communication infrastructure to monitor and control their grid. The resulting increase in communication creates a larger attack surface for malicious actors. Indeed, cyber attacks on power grids have already succeeded in causing temporary, large-scale blackouts in the recent past. In this paper, we analyze the communication infrastructure of power grids to derive resulting fundamental challenges of power grids with respect to cybersecurity. Based on these challenges, we identify a broad set of resulting attack vectors and attack scenarios that threaten the security of power grids. To address these challenges, we propose to rely on a defense-in-depth strategy, which encompasses measures for (i) device and application security, (ii) network security, and (iii) physical security, as well as (iv) policies, procedures, and awareness. For each of these categories, we distill and discuss a comprehensive set of state-of-the art approaches, as well as identify further opportunities to strengthen cybersecurity in interconnected power grids

Four and a half LIM protein 1C (FHL1C)

Four-and-a-half LIM domain protein 1 isoform A (FHL1A) is predominantly expressed in skeletal and cardiac muscle. Mutations in the FHL1 gene are causative for several types of hereditary myopathies including X-linked myopathy with postural muscle atrophy (XMPMA). We here studied myoblasts from XMPMA patients. We found that functional FHL1A protein is completely absent in patient myoblasts. In parallel, expression of FHL1C is either unaffected or increased. Furthermore, a decreased proliferation rate of XMPMA myoblasts compared to controls was observed but an increased number of XMPMA myoblasts was found in the G(0)/G(1) phase. Furthermore, low expression of K(v1.5), a voltage-gated potassium channel known to alter myoblast proliferation during the G(1) phase and to control repolarization of action potential, was detected. In order to substantiate a possible relation between K(v1.5) and FHL1C, a pull-down assay was performed. A physical and direct interaction of both proteins was observed in vitro. In addition, confocal microscopy revealed substantial colocalization of FHL1C and K(v1.5) within atrial cells, supporting a possible interaction between both proteins in vivo. Two-electrode voltage clamp experiments demonstrated that coexpression of K(v1.5) with FHL1C in Xenopus laevis oocytes markedly reduced K(+) currents when compared to oocytes expressing K(v1.5) only. We here present the first evidence on a biological relevance of FHL1C

Thickness dependence of the anomalous Hall effect in thin films of the topological semimetal Co2_2MnGa

Topological magnetic semimetals promise large Berry curvature through the distribution of the topological Weyl nodes or nodal lines and further novel physics with exotic transport phenomena. We present a systematic study of the structural and magnetotransport properties of Co$_2$MnGa films from thin (20 nm) to bulk like behavior (80 nm), in order to understand the underlying mechanisms and the role on the topology. The magnetron sputtered Co$_2$MnGa films are $L$$2_{\mathrm {1}}$-ordered showing very good heteroepitaxy and a strain-induced tetragonal distortion. The anomalous Hall conductivity was found to be maximum at a value of 1138 S/cm, with a corresponding anomalous Hall angle of 13 %, which is comparatively larger than topologically trivial metals. There is a good agreement between the theoretical calculations and the Hall conductivity observed for the 80 nm film, which suggest that the effect is intrinsic. Thus, the Co$_2$MnGa compound manifests as a promising material towards topologically-driven spintronic applications.Comment: 7 pages, 5 figures, 1 tabl