Solar rejection in laser based underwater communication systems

This article provides a numerical study of the expected improvements in an underwater optical system given by a single-mode laser diode operating within a Fraunhofer line in a coastal water type. The system performance is examined for a silicon PIN direct-detection receiver in the euphotic zone. The solar irradiance, modelled as white noise, is evaluated when using a lithium niobate interference and a birefringent filter with different field-of-view (FOV) characteristics in a clear sky situation. The results of this analysis show the inverse dependence of the signal-to-noise (SNR) on the FOV, along with the significant improvement in the receiver sensitivity given by a narrow optical bandpass filter (OBPF)

Laser Based Underwater Communication Systems

We report on recent progress in the field of visible light communications including direct modulation of blue laser devices at data rates beyond 10 Gbit/s, and the transmission of 2.5 Gbit/s OOK data through water. We also discuss the advantages of operating with single mode laser devices and matched filtering at the receiver in the context of applications with significant solar background. The system performance for two types of direct-detection receivers, a PIN detector and less conventional silicon Photomultiplier technology will be presented

A Class of Eccentric Binaries with Dynamic Tidal Distortions Discovered with Kepler

We have discovered a class of eccentric binary systems within the Kepler data archive that have dynamic tidal distortions and tidally-induced pulsations. Each has a uniquely shaped light curve that is characterized by periodic brightening or variability at time scales of 4-20 days, frequently accompanied by shorter period oscillations. We can explain the dominant features of the entire class with orbitally-varying tidal forces that occur in close, eccentric binary systems. The large variety of light curve shapes arises from viewing systems at different angles. This hypothesis is supported by spectroscopic radial velocity measurements for five systems, each showing evidence of being in an eccentric binary system. Prior to the discovery of these 17 new systems, only four stars, where KOI-54 is the best example, were known to have evidence of these dynamic tides and tidally-induced oscillations. We perform preliminary fits to the light curves and radial velocity data, present the overall properties of this class and discuss the work required to accurately model these systems.Comment: 13 pages, submitted to Ap

Comparing the characteristics of snowboarders injured in a terrain park who present to the ski patrol, the emergency department or both

Ski patrol report forms are a common data source in ski/snowboard research, but it is unclear if those who only present to the emergency department (ED) are systematically different from those who see the ski patrol. To determine the proportion and characteristics of injured snowboarders who bypass the ski patrol before presenting to the ED, three groups of injured snowboarders were compared: presented to the ED only, ski patrol only and ski patrol and ED. Data were collected from ski patrol Accident Report Forms (ARFs), ED medical records and telephone interviews. There were 333 injured snowboarders (ED only: 34, ski patrol only: 107, both: 192). Ability, time of day, snow conditions or drugs/alcohol predicted ED only presentation. Concussions (RRR: 4.66; 95% CI: 1.83, 11.90), sprains/strains (RRR: 4.22; 95% CI: 1.87, 9.49), head/neck (RRR: 2.90; 95% CI: 1.48, 5.78), trunk (RRR: 4.17; 95% CI: 1.92, 9.09) or lower extremity (RRR: 3.65; 95% CI: 1.32, 10.07) injuries were significantly more likely to present to ski patrol only versus ski patrol and ED. In conclusion, snowboarders who presented to the ED only had similar injuries as those who presented to both

Feature-specific terrain park-injury rates and risk factors in snowboarders : a case–control study

Background : Snowboarding is a popular albeit risky sport and terrain park (TP) injuries are more severe than regular slope injuries. TPs contain man-made features that facilitate aerial manoeuvres. The objectives of this study were to determine overall and feature-specific injury rates and the potential risk factors for TP injuries. Methods : Case–control study with exposure estimation, conducted in an Alberta TP during two ski seasons. Cases were snowboarders injured in the TP who presented to ski patrol and/or local emergency departments. Controls were uninjured snowboarders in the same TP. κ Statistics were used to measure the reliability of reported risk factor information. Injury rates were calculated and adjusted logistic regression was used to calculate the feature-specific odds of injury. Results : Overall, 333 cases and 1261 controls were enrolled. Reliability of risk factor information was κ>0.60 for 21/24 variables. The overall injury rate was 0.75/1000 runs. Rates were highest for jumps and half-pipe (both 2.56/1000 runs) and lowest for rails (0.43/1000 runs) and quarter-pipes (0.24/1000 runs). Compared with rails, there were increased odds of injury for half-pipe (OR 9.63; 95% CI 4.80 to 19.32), jumps (OR 4.29; 95% CI 2.72 to 6.76), mushroom (OR 2.30; 95% CI 1.20 to 4.41) and kickers (OR 1.99; 95% CI 1.27 to 3.12). Conclusions : Higher feature-specific injury rates and increased odds of injury were associated with features that promote aerial manoeuvres or a large drop to the ground. Further research is required to determine ways to increase snowboarder safety in the TP