Statement of James Perley and Mary Burgan Before the Commission on the Future of Worker-Management Relations

Testimony_Perley_and_Burgan_081094.pdf: 197 downloads, before Oct. 1, 2020

Kaman 40 kW wind turbine generator - control system dynamics

The generator design incorporates an induction generator for application where a utility line is present and a synchronous generator for standalone applications. A combination of feed forward and feedback control is used to achieve synchronous speed prior to connecting the generator to the load, and to control the power level once the generator is connected. The dynamics of the drive train affect several aspects of the system operation. These were analyzed to arrive at the required shaft stiffness. The rotor parameters that affect the stability of the feedback control loop vary considerably over the wind speed range encountered. Therefore, the controller gain was made a function of wind speed in order to maintain consistent operation over the whole wind speed range. The velocity requirement for the pitch control mechanism is related to the nature of the wind gusts to be encountered, the dynamics of the system, and the acceptable power fluctuations and generator dropout rate. A model was developed that allows the probable dropout rate to be determined from a statistical model of wind gusts and the various system parameters, including the acceptable power fluctuation

Burst of the Century? A Case Study of the Afterglow of Nearby Ultra-Bright GRB 130427A

GRB 130427A is the brightest gamma-ray burst observed by any satellite in almost 30 years and one of the most thoroughly observed. I will present a summary of the worldwide campaign to monitor the afterglow of this event from GHz to TeV energies and from seconds to years after the explosion. Remarkably, the entire data set can be described to good agreement using standard synchrotron afterglow theory, providing strong support for the validity the basic model in describing the evolution of this event and for GRB afterglows generally. Distinct forward and reverse shock components are resolved in both the SED and multifrequency light curves; the late-time high-energy emission seen by LAT is produced by the forward shock. We also infer a tenuous, wind-stratified medium surrounding this burst, suggesting a massive, low-metallicity progenitor. While GRB 130427A was an incredibly rare and fortuitous event its properties are probably not intrinsically unusual, and it provides lessons for what might be routinely achieved in the future with faster and deeper multiwavelength follow-up of gamma-ray bursts

Book review: Charlemagne by Johannes Fried

In Charlemagne, Johannes Fried offers a new account of the life of the Frankish king and emperor, one of the most influential figures in European history. Although the limited surviving resources from the period make the book more of an in-depth account of the socio-political context of Charlemagne’s reign rather than a strict biography, Sara Perley welcomes this as a well-researched and engaging read that will foster curiosity about both Charlemagne and this lesser known period of history

High-Fidelity VLA Imaging of the Radio Structure of 3C273

3C273, the nearest bright quasar, comprises a strong nuclear core and a bright, one-sided jet extending ~ 23 arcseconds to the SW. The source has been the subject of imaging campaigns in all wavebands. Extensive observations of this source have been made with the Very Large Array and other telescopes as part of a campaign to understand the jet emission mechanisms. Partial results from the VLA radio campaign have been published, but to date, the complete set of VLA imaging results has not been made available. We have utilized the VLA to determine the radio structure of 3C273 in Stokes I, Q, and U, over the widest possible frequency and resolution range. The VLA observed the source in all four of its configurations, and with all eight of its frequency bands, spanning 73.8 MHz to 43 GHz. The data were taken in a pseudo-spectral line mode to minimize the VLA's correlator errors, and were fully calibrated with subsequent self-calibration techniques to maximise image fidelity. Images in Stokes parameters I, Q, and U, spanning a resolution range from 6 arcseconds to 88 milliarcseconds are presented. Spectral index images, showing the evolution of the jet component are shown. Polarimetry demonstrates the direction of the magnetic fields responsible for the emission, and rotation measure maps show the RM to be very small with no discernible trend along or across the jet. This paper presents a small subset of these images to demonstrate the major characteristics of the source emission. A library of all ~500 images has been made available for open, free access by interested parties.Comment: 9 pages, 17 figure