Search

The California Fish and Game Commission listed the Swainson's Hawk (Buteo swainsoni) as a state threatened species in 1983 in response to population reductions and habitat loss across the state. Human population increases, urbanization, and shifts in agricultural land use have the potential to affect California's Swainson's Hawk population. In 2005 and 2006, we conducted surveys to estimate the abundance and density of Swainson's Hawk breeding pairs in California's Great (Central) Valley, using a random sampling design stratified across dense, medium, and sparse nesting density strata. The sampling units comprised 2.59-km2 (1-mile2) US Public Land Survey System Sections, and the 2-yr survey covered an aggregate total of 682 sampling units (268 in 2005, 414 in 2006). Separate surveyors conducted independent surveys of 29 sampling units in 2006; based on these data, the estimated probability of detecting a single pair (if present) following the multiple-visits protocol was 0.81 (95% CI: 0.58–0.93). After applying this detection-probability correction and using generalized linear modeling of habitat associations to extrapolate density estimates throughout the study area, we estimated that the Great Valley supported 3218 (95% CI: 2271–4165) breeding pairs of Swainson's Hawks in 2005–2006. Our modeling of habitat associations showed crop diversity, alfalfa, and native vegetation as positively associated with the density of Swainson's Hawk breeding pairs, and orchards/vineyards negatively associated. Counts of breeding pairs were also highest in the middle latitudes of the Great Valley, which spans approximately 660 km from north to south. The predictive density model results had some areas of disagreement with the density strata used as basis for the stratified sampling design. To monitor the population status of this species throughout California, we recommend that our 2-yr sampling approach be expanded throughout the state and repeated every 5–10 yr. We also suggest this approach be used to monitor other special status raptor species to track population trend and distributional changes over time. [ABSTRACT FROM AUTHOR]

A rich tradition in developmental psychology explores physical reasoning in infancy. However, no research to date has investigated whether infants can reason about physical objects that behave probabilistically, rather than deterministically. Physical events are often quite variable, in that similar-looking objects can be placed in similar contexts with different outcomes. Can infants rapidly acquire probabilistic physical knowledge, such as some leaves fall and some glasses break by simply observing the statistical regularity with which objects behave and apply that knowledge in subsequent reasoning? We taught 11-month-old infants physical constraints on objects and asked them to reason about the probability of different outcomes when objects were drawn from a large distribution. Infants could have reasoned either by using the perceptual similarity between the samples and larger distributions or by applying physical rules to adjust base rates and estimate the probabilities. Infants learned the physical constraints quickly and used them to estimate probabilities, rather than relying on similarity, a version of the representativeness heuristic. These results indicate that infants can rapidly and flexibly acquire physical knowledge about objects following very brief exposure and apply it in subsequent reasoning. [ABSTRACT FROM AUTHOR]

This investigation presents results of the statistical and probabilistic analyses of 3,269 normal weight concrete cylinder compression tests used for recently constructed highway bridges in California. A new model for in-place strength of concrete structures is proposed as a function of the specified compressive strength, the normalized 28-day cylinder strength, and age of the structure based on a realistic strength-age relation for hardened concrete. The model prediction indicates that concretes in cast-in-place bridge structures designed with specified compressive strengths of 25 MPa (3.6 ksi), 28 MPa (4.0 ksi), and 35 MPa (5.0 ksi) reach their maximum strengths at about 40 years, with approximately 98% of the maximum strength occurring during the first 10 years. Also, through significance testing on the 28-day cylinder strengths, it was established that the California Department of Transportation practice of using an expected concrete strength instead of the specified strength for seismic design of bridge components is justified. An expression for predicting the 28-day strength of concrete cylinders as a function of the strength of companion cylinders, also proposed herein, could prove a useful tool for quality control of concrete during construction. [ABSTRACT FROM AUTHOR]

Probabilistic assessments of the seismic ductility demand for hysteretic bilinear single-degree-of-freedom systems have been reported in the literature. However, a systematic assessment of possible differences in the estimated ductility demand for different earthquake types using recorded ground motions is not available, although ground motion prediction equations for different earthquake types are developed. The assessment of the differences can be important for estimating structural reliability and expected damage cost under seismic excitations since partial damage and collapse could be related to the ductility demand. Therefore, if the differences are significant one must use consistent sets of ground motion prediction equation and ductility demand relation for each earthquake type affecting a site of interest to evaluate the seismic hazard and risk. To assess the differences of the ductility demand, 413 records for Mexican interplate earthquakes, 275 records for Mexican inslab earthquakes, and 592 records for California earthquakes are employed. The evaluation considers ranges of values of natural vibration periods and ratios of initial to postyield stiffness. The obtained results indicate that the statistics of displacement ductility demand differs for different earthquake types. The results are used to develop empirical relations for predicting the expected displacement ductility demand. [ABSTRACT FROM AUTHOR]

Ground motions recorded during earthquakes are often used to assess the seismic performance of structures affected by those ground motions. However, it is necessary to first establish the return period of the recorded ground motion, because structures are expected to perform better for frequently occurring ground motions than for rare ground motions. A systematic approach is presented to establish the return period of ground motion recorded at the base of the Templeton Community Hospital during the 2003 San Simeon California Earthquake. A similar approach can be used for any other ground motion. [ABSTRACT FROM AUTHOR]