Dynamical masses and non-homology of massive elliptical galaxies grown by dry mergers

We study whether dry merger-driven size growth of massive elliptical galaxies depends on their initial structural concentration, and analyse the validity of the homology hypothesis for virial mass determination in massive ellipticals grown by dry mergers. High-resolution simulations of a few realistic merger trees, starting with compact progenitors of different structural concentrations (S\'ersic indices n), show that galaxy growth has little dependence on the initial S\'ersic index (larger n leads to slightly larger size growth), and depends more on other particulars of the merger history. We show that the deposition of accreted matter in the outer parts leads to a systematic and predictable breaking of the homology between remnants and progenitors, which we characterize through the evolution, during the course of the merger history, of virial coefficients K = GM/Re \sigma^2 associated to the most commonly-used dynamical and stellar mass parameters. The virial coefficient for the luminous mass, K , is about 50 per cent larger at the z = 2 start of the merger evolution than in z = 0 remnants. Ignoring virial evolution leads to biased virial mass estimates. We provide K corresponding to a variety of dynamical and stellar mass parameters, and provide recipes for the dynamical determination of galaxy masses. For massive, non-compact ellipticals, the popular expression M = 5 Re \sigma^2 / G underestimates the dynamical mass within the luminous body by factors of up to 4; it instead provides an approximation to the total stellar mass with smaller uncertainty than current stellar population models

16PF Traits and Work Performance Among Restaurant Workers

Personality traits have been linked to work performance in a variety of jobs. For as many restaurants as there are in every major city, little is known about the traits that characterize the success of their personnel. Personality traits are thought to be especially relevant to restaurant work because, in the case of the wait staff, interaction with the public is a major part of the job. In the case of the kitchen staff, it is necessary to work under conditions of heat and work load stress, while at the same time make each meal turn out exactly the way it was intended on the menu. The restaurant trade is also susceptible to high turnover, suggesting that the person-job fit for most employees is less than adequate

Efficient detection for multifrequency dynamic phasor analysis

Analysis of harmonic and interharmonic phasors is a promising smart grid measurement and diagnostic tool. This creates the need to deal with multiple phasor components having different amplitudes, including interharmonics with unknown frequency locations. The Compressive Sensing Taylor-Fourier Multifrequency (CSTFM) algorithm provides very accurate results under demanding test conditions, but is computationally demanding. In this paper we present a novel frequency search criterion with significantly improved effectiveness, resulting in a very efficient revised CSTFM algorithm

PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications

In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be largely employed in Wide Area Monitoring, Protection and Control (WAMPAC) applications. However, a standard approach towards ROCOF measurements is still missing. In this paper, we investigate the feasibility of Phasor Measurement Units (PMUs) deployment in ROCOF-based applications, with a specific focus on Under-Frequency Load-Shedding (UFLS). For this analysis, we select three state-of-the-art window-based synchrophasor estimation algorithms and compare different signal models, ROCOF estimation techniques and window lengths in datasets inspired by real-world acquisitions. In this sense, we are able to carry out a sensitivity analysis of the behavior of a PMU-based UFLS control scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters, as long as the harmonic and inter-harmonic distortion within the measurement pass-bandwidth is scarce. In the presence of transient events, the synchrophasor model looses its appropriateness as the signal energy spreads over the entire spectrum and cannot be approximated as a sequence of narrow-band components. Finally, we validate the actual feasibility of PMU-based UFLS in a real-time simulated scenario where we compare two different ROCOF estimation techniques with a frequency-based control scheme and we show their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE Transactions on Instrumentation and Measurement (acceptance date: 9 March 2019

Composite Likelihood Function in State Space Models.

In general state space models, where the computational effort required in the evaluation of the full likelihood function is infeasible, we analyze the problem of static parameter estimation based on composite likelihood functions, in particular pairwise likelihood functions. We discuss consistency and efficiency properties of the estimators obtained by maximizing these functions in state space scenario, linking these properties to the characteristics of the model. We empirically compare the efficiency between maximum pairwise likelihood and maximum full likelihood estimators. We suggest the existence of a ‘best’ distance between pairs of observations, in terms of variance of the maximum pairwise likelihood estimator