Additive factors and stages of mental processes in task networks.

To perform a task a subject executes mental processes. An experimental manipulation, such as a change in stimulus intensity, is said to selectively influence a process if it changes the duration of that process leaving other process durations unchanged. For random process durations a definition of a factor selectively influencing a process by increments is given in terms of stochastic dominance (also called “the usual stochastic order”. A technique for analyzing reaction times, Sternberg\u27s Additive Factor Method, assumes all the processes are in series. When all processes are in series, each process is called a stage. With the Additive Factor Method, if two experimental factors selectively influence two different stages by increments, the factors will have additive effects on reaction time. An assumption of the Additive Factor Method is that if two experimental factors interact, then they influence the same stage. We consider sets of processes in which some pairs of processes are sequential and some are concurrent (i. e., the processes are partially ordered). We propose a natural definition of a stage for such sets of processes. For partially ordered processes, with our definition of a stage, if two experimental factors selectively influence two different processes by increments, each within a different stage, then the factors have additive effects. If each process selectively influenced by increments is in the same stage, then an interaction is possible, although not inevitable

Paleotectonic and paleogeographic significance of the Calaveras Complex, western Sierra Nevada, California

The Calaveras Complex of the western Sierra Nevada, as defined here, consists of a 375 km long, 35 km wide belt of metasedimentary and metavolcanic rocks, bounded on the west by the Melones fault zone and Kings-Kaweah suture, and on the east by the Sierra Nevada batholith. The Calaveras Complex forms a continuous northwest-trending belt between the Placerville area and the Merced River area. South of the Merced River the belt extends in numerous roof pendants at least as far south as the Tule River. A sequence of four lithologic units is recognized, each of which is thousands of meters thick. Precise original stratigraphic thicknesses cannot be measured because of intense soft-sediment and post-consolidation deformation. The lowest unit consists of mafic pillow lava, breccia, tuff, and argilllte, and may represent layer 2 of oceanic crust. This basal unit is overlain by a predominantly chaotic unit of argillite with variable amounts of chert and siltstone often occurring as clasts in a diamictite. Olistoliths of shallow water limestone are locally an important component of this argillite unit. The overlying chert unit contains abundant large olistoliths of rhythmically bedded chert and locally important limestone olistoliths in a matrix of streaky argillite and diamictite. The highest unit included within the Calaveras Complex contains abundant, well-bedded quartzite with abundant interbedded olistostromes containing quartzite clasts and limes tone olistoliths. Fossils from limestone olistoliths reported here indicate a maximum Permo-Carboniferous age for the upper part of the argillite unit, and a maximum late Permian age for the over lying chert unit. Published fossil data indicate the upper parts of the quartzite unit are late Triassic to early Jurassic. The argillite and chert units apparently comprise numerous olistostromes that accumulated on oceanic crust in a marginal basin that was broad enough to have been relatively free of elastic detritus derived from the basin margins. Olistostromes apparently were shed from tectonically elevated areas within the marginal basin that were denuded of their pelagic and hemi pelagic cover. The quartzite unit may represent an early Mesozoic northwestward progradation of mature continent-derived sand across the western end of the late Paleozoic marginal basin. The marginal basin is considered to have been situated between the Cordilleran miogeocline to the southeast and a volcanic arc terrane to the northwest. The late Paleozoic Havallah sequence of north-central Nevada is believed to have accumulated in the same marginal basin. The Melones fault zone and Kings-Kaweah suture represent a zone of early Mesozoic tectonic truncation a long which the Calaveras Complex is juxtaposed against upper Paleozoic ophiolitic rocks and Jurassic volcanic and epiclastic rocks. Thus, we infer that the Calaveras Complex represents the westernmost exposure of the late Paleozoic marginal basin

A Randomized Trial of Nighttime Physician Staffing in an Intensive Care Unit

Background Increasing numbers of intensive care units (ICUs) are adopting the practice of nighttime intensivist staffing despite the lack of experimental evidence of its effectiveness. Methods We conducted a 1-year randomized trial in an academic medical ICU of the effects of nighttime staffing with in-hospital intensivists (intervention) as compared with nighttime coverage by daytime intensivists who were available for consultation by telephone (control). We randomly assigned blocks of 7 consecutive nights to the intervention or the control strategy. The primary outcome was patients’ length of stay in the ICU. Secondary outcomes were patients’ length of stay in the hospital, ICU and in-hospital mortality, discharge disposition, and rates of readmission to the ICU. For length-of-stay outcomes, we performed time-to-event analyses, with data censored at the time of a patient’s death or transfer to another ICU. Results A total of 1598 patients were included in the analyses. The median Acute Physiology and Chronic Health Evaluation (APACHE) III score (in which scores range from 0 to 299, with higher scores indicating more severe illness) was 67 (interquartile range, 47 to 91), the median length of stay in the ICU was 52.7 hours (interquartile range, 29.0 to 113.4), and mortality in the ICU was 18%. Patients who were admitted on intervention days were exposed to nighttime intensivists on more nights than were patients admitted on control days (median, 100% of nights [interquartile range, 67 to 100] vs. median, 0% [interquartile range, 0 to 33]; P\u3c0.001). Nonetheless, intensivist staffing on the night of admission did not have a significant effect on the length of stay in the ICU (rate ratio for the time to ICU discharge, 0.98; 95% confidence interval [CI], 0.88 to 1.09; P=0.72), ICU mortality (relative risk, 1.07; 95% CI, 0.90 to 1.28), or any other end point. Analyses restricted to patients who were admitted at night showed similar results, as did sensitivity analyses that used different definitions of exposure and outcome. Conclusions In an academic medical ICU in the United States, nighttime in-hospital intensivist staffing did not improve patient outcomes. (Funded by University of Pennsylvania Health System and others; ClinicalTrials.gov number, NCT01434823.

Managing the Interface of Sedation, Weakness and ICU Rehabilitation

Overall Goals and Objectives: 1. To review the epidemiology of weakness acquired by patients with critical illness. 2. To describe the relationship between immobility, sedation and ICU-acquired weakness. 3. To detail pivotal clinical studies of early exercise and mobilization in ICU patients. 4. To discuss practical implementation of an early exercise and mobilization program, including criteria for consultation, therapy progression, and tracking outcomes