Vibrations Analysis on Tennis Racket String

The purpose of this project was to investigate and analyse the vibration of a tennis racket string when a ball is hit. This was done using concepts of mechanical vibrations and modelled using Microsoft Excel. The displacement of the tennis string over time was graphed for two different positions on the racket and two different relative speeds of the tennis ball. It was found that the position of the tennis ball on the racket has very little effect on the displacement of the strings. If the ball or racket is moving faster when the ball is hit, then the displacement of the strings is proportionally greater. There were a few factors in the modelling that were unlike the actual vibration of a tennis string. This model did not take in to account the fact that the tennis ball would deform when it is hit or the deflection of the tennis racket. The designed model will help compare different spring constants and ball speeds for different scenarios

Revealing the Structure of an Accretion Disk Through Energy Dependent X-ray Microlensing

We present results from monitoring observations of the gravitationally lensed quasar RX J1131-1231 performed with the Chandra X-ray Observatory. The X-ray observations were planned with relatively long exposures that allowed a search for energy-dependent microlensing in the soft (0.2-2 keV) and hard (2-10 keV) light curves of the images of RX J1131-1231. We detect significant microlensing in the X-ray light-curves of images A and D, and energy-dependent microlensing of image D. The magnification of the soft band appears to be larger than that in the hard band by a factor of ~ 1.3 when image D becomes more magnified. This can be explained by the difference between a compact, softer-spectrum corona that is producing a more extended, harder spectrum reflection component off the disk. This is supported by the evolution of the fluorescent iron line in image D over three consecutive time-averaged phases of the light curve. In the first period, a Fe line at E = 6.36(-0.16,+0.13) keV is detected (at > 99% confidence). In the second period, two Fe lines are detected, one at E = 5.47(-0.08,+0.06) keV (detected at > 99% confidence) and another at E = 6.02(-0.07,+0.09) keV (marginally detected at > 90% confidence), and in the third period, a broadened Fe line at 6.42(-0.15,+0.19) keV is detected (at > 99% confidence). This evolution of the Fe line profile during the microlensing event is consistent with the line distortion expected when a caustic passes over the inner disk where the shape of the fluorescent Fe line is distorted by General Relativistic and Doppler effects.Comment: 20 pages, includes 10 figures, submitted to Ap

From Textbooks To Safety Briefings: Helping Technical Writers Negotiate Complex Rhetorical Situations

In this dissertation, I analyze the organizational and political constraints that technical writers encounter when dealing with complex rhetorical situations, particularly within risk-management discourse. I ground my research in case studies of safety briefings that airlines provide to their passengers because these important documents have long been regarded as ineffective, yet they ve gone largely unchanged in the last 20 years. Airlines are required to produce these safety briefings, which must satisfy multiple audiences, such as corporate executives, federal safety inspectors, flight attendants, and passengers. Because space and time are limited when presenting safety information to passengers, the technical writers must negotiate constraints related to issues such as format, budget, audience education and language, passenger perceptions/fears, reproducibility, and corporate image/branding to name a few. The writers have to negotiate these constraints while presenting important (and potentially alarming) information in a way that s as informative, realistic, and tasteful as possible. But such constraints aren t unique to the airline industry. Once they enter the profession, many writing students will experience complex rhetorical situations that constrain their abilities to produce effective documentation; therefore, I am looking at the theories and skills that we re teaching our future technical communicators for coping with such situations. By applying writing-style and visual-cultural analyses to a set of documents, I demonstrate a methodology for analyzing complex rhetorical situations. I conclude by proposing a pedagogy that teachers of technical communication can employ for helping students assess and work within complex rhetorical situations, and I offer suggestions for implementing such practices in the classroom

A calibration of the stellar mass fundamental plane at z ~ 0.5 using the micro-lensing induced flux ratio anomalies of macro-lensed quasars

We measure the stellar mass surface densities of early type galaxies by observing the micro-lensing of macro-lensed quasars caused by individual stars, including stellar remnants, brown dwarfs and red dwarfs too faint to produce photometric or spectroscopic signatures. Instead of observing multiple micro-lensing events in a single system, we combine single epoch X-ray snapshots of ten quadruple systems, and compare the measured relative magnifications for the images with those computed from macro-models. We use these to normalize a stellar mass fundamental plane constructed using a Salpeter IMF with a low mass cutoff of 0.1 solar mass and treat the zeropoint of the surface mass density as a free parameter. Our method measures the graininess of the gravitational potential produced by individual stars, in contrast to methods that decompose a smooth total gravitational potential into two smooth components, one stellar and one dark. We find the median likelihood value for the normalization factor F by which the Salpeter stellar masses must be multiplied is 1.23, with a one sigma confidence range, dominated by small number statistics, of 0.77 < F < 2.10Comment: Revised in response to referee's suggestions and re-submitted to ApJ; changes to the adopted effective radii propagate to a new value of the factor F (by which Salpeter stellar masses must be multiplied) of 1.2

Regulatory Oversight and Financial Reporting Incentives: Evidence from SEC Budget Allocations

This study examines the determinants and consequences of regulatory oversight of corporate disclosures. I investigate the extent to which industry-level political activity influences the intensity of regulatory oversight, and whether variation in the intensity of oversight affects managers\u27 reporting incentives. I exploit variation in the allocation of budgetary resources between the SEC\u27s disclosure review offices as a source of variation in the oversight of financial reporting and disclosures. I find evidence of a significant relationship between industry-level political activity and visibility and the allocation of resources to each office. I then use the amount of budgetary resources allocated to each office as a proxy for the intensity of the SEC oversight that firms in a given industry face. I provide evidence that when SEC oversight is more intense managers report lower discretionary accruals, managers are less likely to issue financial reports that will be subsequently restated, and firms\u27 bid-ask spreads decrease. Overall, the results suggest that SEC oversight plays an important role in shaping managers\u27 reporting and disclosure incentives

X-ray Monitoring of Gravitational Lenses With Chandra

We present \emph{Chandra} monitoring data for six gravitationally lensed quasars: QJ 0158$-$4325, HE 0435$-$1223, HE 1104$-$1805, SDSS 0924+0219, SDSS 1004+4112, and Q 2237+0305. We detect X-ray microlensing variability in all six lenses with high confidence. We detect energy dependent microlensing in HE 0435$-$1223, SDSS 1004+4112, SDSS 0924+0219 and Q 2237+0305. We present a detailed spectral analysis for each lens, and find that simple power-law models plus Gaussian emission lines give good fits to the spectra. We detect intrinsic spectral variability in two epochs of Q 2237+0305. We detect differential absorption between images in four lenses. We also detect the \feka\ emission line in all six lenses, and the Ni XXVII K$\alpha$ line in two images of Q 2237+0305. The rest frame equivalent widths of the \feka\ lines are measured to be 0.4--1.2 keV, significantly higher than those measured in typical active galactic nuclei of similar X-ray luminosities. This suggests that the \feka\ emission region is more compact or centrally concentrated than the continuum emission region.Comment: 55 pages, 22 figure