Factors Contributing to the Catastrophe in Mexico City During the Earthquake of September 19, 1985

The extensive damage to high‐rise buildings in Mexico City during the September 19, 1985 earthquake is primarily due to the intensity of the ground shaking exceeding what was previously considered credible for the city by Mexican engineers. There were two major factors contributing to the catastrophe, resonance in the sediments of an ancient lake that once existed in the Valley of Mexico, and the long duration of shaking compared with other coastal earthquakes in the last 50 years. Both of these factors would be operative again if the Guerrero seismic gap ruptured in a single earthquake

Disjunct Lake Michigan Populations of Two Atlantic Coast Spiders, \u3ci\u3eDisembolus Bairdi\u3c/i\u3e and \u3ci\u3eGrammonota Pallipes\u3c/i\u3e (Araneae: Linyphiidae)

Two species of linyphiid spiders, Disembolus bairdi Edwards, 1999 and Grammonota pallipes Banks, 1895, were discovered along the southwestern coast of Lake Michigan in Lake County, Illinois representing an Atlantic Coastal Plain disjunct distribution. A brief discussion of known collection sites, habitat preferences, and possible modes of dispersal are given

Recursive estimation of possibly misspecified MA(1) models: Convergence of a general algorithm

We introduce a recursive algorithm of conveniently general form for estimating the coefficient of a moving average model of order one and obtain convergence results for both correct and misspecified MA(1) models. The algorithm encompasses Pseudolinear Regression (PLR--also referred to as AML and $RML_1$) and Recursive Maximum Likelihood ($RML_2$) without monitoring. Stimulated by the approach of Hannan (1980), our convergence results are obtained indirectly by showing that the recursive sequence can be approximated by a sequence satisfying a recursion of simpler (Robbins-Monro) form for which convergence results applicable to our situation have recently been obtained.Comment: Published at http://dx.doi.org/10.1214/074921706000000932 in the IMS Lecture Notes Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

The effect of toxic Microcystis aeruginosa on four different populations of Daphnia

Cyanobacteria reduce the fitness of many Daphnia species, and blooms in eutrophic lakes may place strong selective pressure upon these primary consumers. This study examines the ability of daphnids to resist the deleterious effects of toxic Microcystis and determine if this resistance is related to the trophic conditions of their native lakes. Three populations of Daphnia pulex/pulicaria were examined; D. pulicaria from eutrophic Klamath Lake in Oregon, D. pulex from eutrophic Old Durham Reservoir in New Hampshire, and D. pulicaria from oligotrophic Russell Pond in New Hampshire. D. carinata from meso-oligotrophic Lake Rotoaira in New Zealand was used as a known cyanobacteria-sensitive species. Ten-day old 5th-6th instar animals were exposed to a mixture of Microcystis aeruginosa and Chlorella vulgaris (25% and 100% M. aeruginosa). Body length, lipid index, reproductive index and clearance rate were assessed for each population after 120 hours of treatment. A feeding bioassay response quantifying the energetic (feeding rate) cost of post abdominal rejections was also determined for a gradient of M. aeruginosa concentrations from 0% to 100%. The four populations of Daphnia exhibited different rates of decline in overall fitness when exposed to Microcystis. Populations exposed to Microcystis exhibited reduced thoracic beat rate, lower lipid and reproductive indexes, and higher cost of post abdominal rejections in comparison to daphnids in the control Chlorella. Length was not a sensitive indicator of fitness level. D. pulex from eutrophic Klamath Lake had a mean clearance rate in 100% Microcystis that was three to four times higher than D. pulicaria from oligotrophic Russell Pond. In general, daphnids from oligotrophic lakes exhibited a more drastic decline in fitness than daphnids from eutrophic lakes. This suggests that taxonomically related populations of Daphnia have evolved a suite of adaptations to Microcystis depending upon their history of exposure

Viscous damped space structure for reduced jitter

A technique to provide modal vibration damping in high performance space structures was developed which uses less than one once of incompressible fluid. Up to 50 percent damping can be achieved which can reduce the settling times of the lowest structural mode by as much as 50 to 1. This concept allows the designers to reduce the weight of the structure while improving its dynamic performance. Damping by this technique is purely viscous and has been shown by test to be linear over 5 orders of input magnitude. Amplitudes as low as 0.2 microinch were demonstrated. Damping in the system is independent of stiffness and relatively insensitive to temperature

An RF interference mitigation methodology with potential applications in scheduling

Software tools for interference analysis and mitigation were developed in the Communications Link Analysis and Simulation System (CLASS) environment for: communications performance evaluation; and mission planning. Potential applications are seen in analysis, evaluation, and optimization of user schedules. Tools producing required separation angles and potential interference intervals can be used as an aid to mutual interference mitigation within a scheduling system

Flight-testing of the self-repairing flight control system using the F-15 highly integrated digital electronic control flight research facility

Flight tests conducted with the self-repairing flight control system (SRFCS) installed on the NASA F-15 highly integrated digital electronic control aircraft are described. The development leading to the current SRFCS configuration is highlighted. Key objectives of the program are outlined: (1) to flight-evaluate a control reconfiguration strategy with three types of control surface failure; (2) to evaluate a cockpit display that will inform the pilot of the maneuvering capacity of the damage aircraft; and (3) to flight-evaluate the onboard expert system maintenance diagnostics process using representative faults set to occur only under maneuvering conditions. Preliminary flight results addressing the operation of the overall system, as well as the individual technologies, are included

A method for interference mitigation in space communications scheduling

Increases in the number of user spacecraft and data rates supported by NASA's Tracking and Data Relay Satellite System (TDRSS) in the S and Ku bands could result in communications conflicts due to mutual interference. A method to mitigate interference while minimizing unnecessary scheduling restrictions on both TDRSS network and user resources, based on consideration of all relevant communications parameters, was developed. The steps of this method calculate required separation angles at TDRS and produce interference intervals, which can be used in the production of schedules free of unacceptable interference. The method can also be used as a basis for analysis, evaluation, and optimization of user schedules with respect to communications performance. Described here are the proposed method and its potential application to scheduling in space communications. Test cases relative to planned missions, including the Earth Observing System, the Space Station Manned Base, and the Space Shuttle are discussed