The employability of the physically handicapped in manufacturing organizations in Boston, Massachusetts.

Thesis (M.S.)--Boston Universit

Systematic Mischaracterization of Exoplanetary System Dynamical Histories from a Model Degeneracy near Mean-motion Resonance

There is a degeneracy in the radial velocity exoplanet signal between a single planet on an eccentric orbit and a two-planet system with a period ratio of 2:1. This degeneracy could lead to misunderstandings of the dynamical histories of planetary systems as well as measurements of planetary abundances if the correct architecture is not established. We constrain the rate of mischaracterization by analysing a sample of 60 non-transiting, radial velocity systems orbiting main-sequence stars from the NASA Exoplanet Archive (NASA Archive) using a new Bayesian model comparison pipeline. We find that 15 systems (25 per cent of our sample) show compelling evidence for the two-planet case with a confidence level of 95 per cent

Turing pattern outside of the Turing domain

There are two simple solutions to reaction-diffusion systems with limit-cycle reaction kinetics, producing oscillatory behaviour. The reaction parameter $\mu$ gives rise to a ‘space-invariant’ solution, and $\mu$ versus the ratio of the diffusion coefficients gives rise to a ‘time-invariant’ solution. We consider the case where both solution types may be possible. This leads to a refinement of the Turing model of pattern formation. We add convection to the system and investigate its effect. More complex solutions arise that appear to combine the two simple solutions. The convective system sheds light on the underlying behaviour of the diffusive system

Limit cycles in the presence of convection, a first order analysis

We consider a diffusion model with limit cycle reaction functions. In an unbounded domain, diffusion spreads pattern outwards from the source. Convection adds instability to the reaction-diffusion system. We see the result of the instability in a readiness to create pattern. In the case of strong convection, we consider that the first-order approximation may be valid for some aspects of the solution behaviour. We employ the method of Riemann invariants and rescaling to transform the reduced system into one invariant under parameter change. We carry out numerical experiments to test our analysis. We find that most aspects of the solution do not comply with this, but we find one significant characteristic which is approximately first order. We consider the correspondence of the Partial Differential Equation with the Ordinary Differential Equation along rays from the initiation point in the transformed system. This yields an understanding of the behaviour

Improvement of indoor VLC network downlink scheduling and resource allocation

Indoor visible light communications (VLC) combines illumination and communication by utilizing the high-modulation-speed of LEDs. VLC is anticipated to be complementary to radio frequency communications and an important part of next generation heterogeneous networks. In order to make the maximum use of VLC technology in a networking environment, we need to expand existing research from studies of traditional point-to-point links to encompass scheduling and resource allocation related to multi-user scenarios. This work aims to maximize the downlink throughput of an indoor VLC network, while taking both user fairness and time latency into consideration. Inter-user interference is eliminated by appropriately allocating LEDs to users with the aid of graph theory. A three-term priority factor model is derived and is shown to improve the throughput performance of the network scheduling scheme over those previously reported. Simulations of VLC downlink scheduling have been performed under proportional fairness scheduling principles where our newly formulated priority factor model has been applied. The downlink throughput is improved by 19.6% compared to previous two-term priority models, while achieving similar fairness and latency performance. When the number of users grows larger, the three-term priority model indicates an improvement in Fairness performance compared to two-term priority model scheduling

A Reconsideration of the Effects of Unionism on Relative Wages and Employment in the United States, 1920-80

H. Gregg Lewis' estimates of the relative wage effect of unionism between 1920 and 1958 are routinely cited though they have rarely been subject to scrutiny. This paper extends Lewis' data to 1980 and, in particular, we construct a series on union membership that links up with the data available in the 1970's from the Current Population Surveys. We proceed to reexamine the effects of trade unions both on relative wages and on relative man hours worked.Our estimates of the relative wage effect are similar to Lewis' though these are not measured with precision and a wide range of estimates are consistent with the results. With respect to the effect of unionism on relative man hours worked, we are not at all satisfied that the analysis of these data clearly points to the existence of a negative effect.