A Method for Modeling Low-Probability, High- Consequence Risk Events: Vessel Traffic on the Lower Mississippi River

[Excerpt] A variety of commodities, from chlorine to corn and petroleum to passengers, are transported on the lower Mississippi River regularly. Corn, wheat and coal are the most commonly carried commodities. From a human health and safety perspective, these are relatively benign products in that a vessel accident and spill of these are not directly hazardous to people, whatever other ecological disturbances may ensue. However, over eighty million tons of petroleum products are transported on the river annually. Over a million tons of liquid natural gas traverse the river through the center of New Orleans. Additionally, over 400,000 tons of ammonium nitrate2 pass through the center of Baton Rouge annually. The potential for a technological disaster is certainly present […] The vast majority of the literature relevant to the question of vessel accident risk concerns the question of on-board causes of vessel accidents. It is assumed that the predictors of which vessel will have an accident are on-board the vessel (i.e., vessel and crew characteristics). The most commonly cited on-board hazards include: the size of the vessel; the age of the vessel; the length of the vessel; whether the vessel is single or double hulled; the maintenance of the vessel; the classification society under which the vessel is registered; the type of ownership; the history of ownership; where the vessel is flagged (i.e., flag of convenience or traditional maritime nation); license qualifications of mates and engineers; the vessel’s casualty history; the vessel’s history of violations; whether the vessel has system (e.g., steering) redundancy; and personnel history (including manning levels and the comparison of the present levels of manning with that of the vessel in the past and with similar type vessels)

Collide and Conquer: Constraints on Simplified Dark Matter Models using Mono-X Collider Searches

The use of simplified models as a tool for interpreting dark matter collider searches has become increasingly prevalent, and while early Run II results are beginning to appear, we look to see what further information can be extracted from the Run I dataset. We consider three `standard' simplified models that couple quarks to fermionic singlet dark matter: an $s$-channel vector mediator with vector or axial-vector couplings, and a $t$-channel scalar mediator. Upper limits on the couplings are calculated and compared across three alternate channels, namely mono-jet, mono-$Z$ (leptonic) and mono-$W/Z$ (hadronic). The strongest limits are observed in the mono-jet channel, however the computational simplicity and absence of significant $t$-channel model width effects in the mono-boson channels make these a straightforward and competitive alternative. We also include a comparison with relic density and direct detection constraints.Comment: 32 pages, 8 figures; v2: minor changes, conclusion unchanged, matches published versio

Rapid Design of Gravity Assist Trajectories

Several International Solar Terrestrial Physics (ISTP) missions require the design of complex gravity assisted trajectories in order to investigate the interaction of the solar wind with the Earth's magnetic field. These trajectories present a formidable trajectory design and optimization problem. The philosophy and methodology that enable an analyst to design and analyse such trajectories are discussed. The so called 'floating end point' targeting, which allows the inherently nonlinear multiple body problem to be solved with simple linear techniques, is described. The combination of floating end point targeting with analytic approximations with a Newton method targeter to achieve trajectory design goals quickly, even for the very sensitive double lunar swingby trajectories used by the ISTP missions, is demonstrated. A multiconic orbit integration scheme allows fast and accurate orbit propagation. A prototype software tool, Swingby, built for trajectory design and launch window analysis, is described

Preliminary navigation accuracy analysis for the TDRSS Onboard Navigation System (TONS) experiment on EP/EUVE

A Tracking and Data Relay Satellite System (TDRSS) Onboard Navigation System (TONS) is currently being developed by NASA to provide a high accuracy autonomous navigation capability for users of TDRSS and its successor, the Advanced TDRSS (ATDRSS). The fully autonomous user onboard navigation system will support orbit determination, time determination, and frequency determination, based on observation of a continuously available, unscheduled navigation beacon signal. A TONS experiment will be performed in conjunction with the Explorer Platform (EP) Extreme Ultraviolet Explorer (EUVE) mission to flight quality TONS Block 1. An overview is presented of TONS and a preliminary analysis of the navigation accuracy anticipated for the TONS experiment. Descriptions of the TONS experiment and the associated navigation objectives, as well as a description of the onboard navigation algorithms, are provided. The accuracy of the selected algorithms is evaluated based on the processing of realistic simulated TDRSS one way forward link Doppler measurements. The analysis process is discussed and the associated navigation accuracy results are presented

An Empirical Examination of Two Models of Cultural Causation

The traditional macroscopic model of cultural causation advanced by Weber and modified by Parsons assumes that values provide orientation for human action. Thus, values are conceptualized as the intervening link between culture and behavior and in general, are viewed as predictive of human action. Swidler (1986) contends that values are a poor predictor of behavior. As an a/tentative model, Swidler asserts that cultures provide actors with a limited array of behavioral options. Because this array is finite and indicative of a particular cultural setting, inuacultural behavioral similatities are observable. We empirically test the link between culture and behavior in a situation which Swidler defines as "unsettled lives." Our findings offer little support for the traditionally assumed link between values and behavior. The theoretical implications of our findings are discussed and an expansion of Swidler's model is offered

Autonomous Navigation With Ground Station One-Way Forward-Link Doppler Data

The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) has spent several years developing operational onboard navigation systems (ONS's) to provide real time autonomous, highly accurate navigation products for spacecraft using NASA's space and ground communication systems. The highly successful Tracking and Data Relay Satellite (TDRSS) ONS (TONS) experiment on the Explorer Platform/Extreme Ultraviolet (EP/EUV) spacecraft, launched on June 7, 1992, flight demonstrated the ONS for high accuracy navigation using TDRSS forward link communication services. In late 1994, a similar ONS experiment was performed using EP/EUV flight hardware (the ultrastable oscillator and Doppler extractor card in one of the TDRSS transponders) and ground system software to demonstrate the feasibility of using an ONS with ground station forward link communication services. This paper provides a detailed evaluation of ground station-based ONS performance of data collected over a 20 day period. The ground station ONS (GONS) experiment results are used to project the expected performance of an operational system. The GONS processes Doppler data derived from scheduled ground station forward link services using a sequential estimation algorithm enhanced by a sophisticated process noise model to provide onboard orbit and frequency determination. Analysis of the GONS experiment performance indicates that real time onboard position accuracies of better than 125 meters (1 sigma) are achievable with two or more 5-minute contacts per day for the EP/EUV 525 kilometer altitude, 28.5 degree inclination orbit. GONS accuracy is shown to be a function of the fidelity of the onboard propagation model, the frequency/geometry of the tracking contacts, and the quality of the tracking measurements. GONS provides a viable option for using autonomous navigation to reduce operational costs for upcoming spacecraft missions with moderate position accuracy requirements