Mitigation of Side-Effect Modulation in Optical OFDM VLC Systems

Side-effect modulation (SEM) has the potential to be a significant source of interference in future visible light communication (VLC) systems. SEM is a variation in the intensity of the light emitted by a luminaire and is usually a side-effect caused by the power supply used to drive the luminaires. For LED luminaires powered by a switched mode power supply, the SEM can be at much higher frequencies than that emitted by conventional incandescent or fluorescent lighting. It has been shown that the SEM caused by commercially available LED luminaires is often periodic and of low power. In this paper, we investigate the impact of typical forms of SEM on the performance of optical OFDM VLC systems; both ACO-OFDM and DCO-OFDM are considered. Our results show that even low levels of SEM power can significantly degrade the bit-error-rate performance. To solve this problem, an SEM mitigation scheme is described. The mitigation scheme is decision-directed and is based on estimating and subtracting the fundamental component of the SEM from the received signal. We describe two forms of the algorithm; one uses blind estimation while the other uses pilot-assisted estimation based on a training sequence. Decision errors, resulting in decision noise, limit the performance of the blind estimator even when estimation is based on very long signals. However, the pilot system can achieve more accurate estimations, thus better performance. Results are first presented for typical SEM waveforms for the case where the fundamental frequency of the SEM is known. The algorithms are then extended to include a frequency estimation step and the mitigation algorithm is shown also to be effective in this case

Trends and Disparities in TB among U.S.-born Black and White Chicago Residents, 1998-2008

ABSTRACT OBJECTIVE: To describe the decline of tuberculosis (TB) cases among U.S.-born non-Hispanic (NH) black and white Chicago residents. METHODS: Data from the National TB Surveillance System was used to analyze trends and characteristics of reported TB cases among U.S.-born NH black and U.S.-born NH white Chicago residents from 1998-2008. RESULTS: Chicago reported a total of 3,821 TB cases over the 11-year time period. Of these, 1,916 were U.S.-born NH black and 235 were U.S.-born NH white. The proportion of cases attributable to U.S.-born NH blacks was 63% (294/469) in 1998 and 34% in 2008 (72/213). Analysis for trends from 2000-2008 revealed a greater than predicted decrease in rates among U.S.-born NH blacks (p CONCLUSION: Despite more TB risk factors in Chicago’s U.S.-born black population, there was a narrowing of TB case disparity in Chicago from 1998-2008. Continued focused strategies aimed at controlling TB are needed

Transitions to Nematic states in homogeneous suspensions of high aspect ratio magnetic rods

Isotropic-Nematic and Nematic-Nematic transitions from a homogeneous base state of a suspension of high aspect ratio, rod-like magnetic particles are studied for both Maier-Saupe and the Onsager excluded volume potentials. A combination of classical linear stability and asymptotic analyses provides insight into possible nematic states emanating from both the isotropic and nematic non-polarized equilibrium states. Local analytical results close to critical points in conjunction with global numerical results (Bhandar, 2002) yields a unified picture of the bifurcation diagram and provides a convenient base state to study effects of external orienting fields.Comment: 3 Figure

Data Combinations Accounting for LISA Spacecraft Motion

LISA is an array of three spacecraft in an approximately equilateral triangle configuration which will be used as a low-frequency gravitational wave detector. We present here new generalizations of the Michelson- and Sagnac-type time-delay interferometry data combinations. These combinations cancel laser phase noise in the presence of different up and down propagation delays in each arm of the array, and slowly varying systematic motion of the spacecraft. The gravitational wave sensitivities of these generalized combinations are the same as previously computed for the stationary cases, although the combinations are now more complicated. We introduce a diagrammatic representation to illustrate that these combinations are actually synthesized equal-arm interferometers.Comment: 10 pages, 3 figure

Simultaneous observations of solar protons inside and outside the magnetosphere Progress report

Simultaneous observations of solar protons inside and outside magnetosphere by Explorer XXXIII AND Injun I

Solar particle observations inside the magnetosphere during the 7 July 1966 event

Injun satellite observations of solar particles inside magnetospher

Disproportionate School Disciplinary Responses: An Exploration of Prisonization and Minority Threat Hypothesis Among Black, Hispanic, and Native American Students

This research tests two potential explanations of school disciplinary responses: minority threat hypothesis and prisonization of schools. Data from the Arizona Safe and Drug-Free Schools (SDFS) survey and Arizona Youth Survey (AYS) are analyzed using ordinary least squares (OLS) regressions. Findings demonstrate that the percentage of Black, Hispanic, and Native American students was not associated with exclusionary responses to school misconduct, but was linked to decreases in mild and restorative disciplinary practices. Findings support the hypothesis that minority threat reduces access to mild and restorative disciplinary responses. Although, further research is needed on the roles of mental health professionals and counselors in school disciplinary procedures to better guide policy and school administrator expectations

TDIR: Time-Delay Interferometric Ranging for Space-Borne Gravitational-Wave Detectors

Space-borne interferometric gravitational-wave detectors, sensitive in the low-frequency (mHz) band, will fly in the next decade. In these detectors, the spacecraft-to-spacecraft light-travel times will necessarily be unequal and time-varying, and (because of aberration) will have different values on up- and down-links. In such unequal-armlength interferometers, laser phase noise will be canceled by taking linear combinations of the laser-phase observables measured between pairs of spacecraft, appropriately time-shifted by the light propagation times along the corresponding arms. This procedure, known as time-delay interferometry (TDI), requires an accurate knowledge of the light-time delays as functions of time. Here we propose a high-accuracy technique to estimate these time delays and study its use in the context of the Laser Interferometer Space Antenna (LISA) mission. We refer to this ranging technique, which relies on the TDI combinations themselves, as Time-Delay Interferometric Ranging (TDIR). For every TDI combination, we show that, by minimizing the rms power in that combination (averaged over integration times $\sim 10^4$ s) with respect to the time-delay parameters, we obtain estimates of the time delays accurate enough to cancel laser noise to a level well below the secondary noises. Thus TDIR allows the implementation of TDI without the use of dedicated inter-spacecraft ranging systems, with a potential simplification of the LISA design. In this paper we define the TDIR procedure formally, and we characterize its expected performance via simulations with the \textit{Synthetic LISA} software package.Comment: 5 pages, 2 figure

Testing the Influence of Community Characteristics on School Misconduct

This study examines the effect of dynamic and structural community characteristics on school misconduct. Data include over 45,000 students in the eighth, tenth, or twelfth grade in 237 schools. Hierarchical linear models tested the direct and interactive effects of community measures, while accounting for student and school characteristics. Community substance abuse norms as well as perceptions of community crime and disorder mediated the influence of concentrated disadvantage on school misconduct. Interaction effects demonstrated that community substance abuse norms were more influential for students enrolled in schools that had a less positive school climate although individual and school characteristics remained robust predictors of school misconduct. School misconduct is influenced by the characteristics of the surrounding community and school context, as well as the interaction between those contexts. Research relying on census data measures of community characteristics may underestimate community influence on school misconduct, and omit proximal community influences on school misconduct