University of California

About: University of California is a education organization based out in Oakland, California, United States. It is known for research contribution in the topics: Population & Layer (electronics). The organization has 55175 authors who have published 52933 publications receiving 1491169 citations. The organization is also known as: UC & University of California System.

Thresholds, memory, and seasonality: understanding pulse dynamics in arid/semi-arid ecosystems

Abstract: Changes in resource availability can alter the functioning of ecosystems, especially with regard to both population dynamics and the cycling of organic matter and nutrients. At perhaps one end of the spectrum, arid and semi-arid ecosystems represent an extreme in which essential resource availability (e.g., water) is discontinuously available and the availability of these resources impact the ecosystem as discreet pulse events interspersed among long periods of limited resource availability. The objective of the special section that follows is to contribute to our understanding of how pulsed events shape population dynamics, species interactions, and ecosystem processes in arid and semi-arid ecosystems. There has been a renewed interest in recent years in the relationships between precipitation and ecosystem processes in arid and semi-arid lands. For many years, studies focused on the effects of mean precipitation, averaged at annual, seasonal, or monthly time scales. These studies suggested broad-scale relationships between precipitation amounts and seasonal distribution and the productivity of ecosystems (Le Houerou 1984; Le Houerou et al. 1988), or the plant functional type composition of water-limited systems (e.g., Neilson 1995; Smith et al. 1997). Though some researchers asked questions about the effects of single rainfall events early on (e.g., Went and Westergaard 1949; Beatley 1974; Sala and Lauenroth 1982), this perspective received wider attention only in the last decade, in part through the development of stable isotope tracer methods in plant ecology (e.g., Caldwell et al. 1985; Ehleringer et al. 1991; Lin et al. 1996). More recently, studies also have begun to focus on intra-seasonal precipitation patterns, asking whether variability in rainfall event size, frequency, and timing alone affect the biological processes in water-limited ecosystems (e.g., Goldberg and Novoplansky 1997; Knapp et al. 2002; Schwinning et al. 2003). With a view to addressing these questions, an international workshop was held at the University of Arizona in Tucson, USA (http://ag.arizona.edu/research/schwinn/ workshop.html). This special issue contains both peerreviewed synthesis papers that were generated through the collaboration of workshop participants, as well as original research contributions related to pulse dynamics in arid and semi-arid ecosystems. A generation ago, two major paradigms for understanding rainfall effects in water-limited ecosystems were published: (1) the pulse-reserve paradigm of Noy-Meir (1974) and co-workers, and (2) Walter’s (1971) two-layer soil water-partitioning model. Our understanding has advanced significantly since then, moving from the largely conceptual paradigms to an invariably more complex body of data and theory. Reynolds et al. (2004) critically review both paradigms, concluding that the accurate description of soil moisture dynamics is pivotal for addressing the dynamics of primary production and soil water partitioning. While Walter (1971) envisioned water partitioning in vertical space to govern major patterns of plant functional type distribution, Ehleringer et al. (1991) and Lin et al. (1996) have provided strong evidence of this spatial partitioning. Evidence is mounting that partitioning over time may be at least as important (Reynolds et al. 2004; Schwinning et al. 2004a, b). However, the consequences of the hydraulic redistribution of water for species S. Schwinning (*) School of Natural Resources, University of Arizona, Biological Sciences East 325, Tucson, AZ, 85721 e-mail: schwinn@Ag.arizona.edu

Diversifying Science: Underrepresented Student Experiences in Structured Research Programs.

Abstract: Targeting four institutions with structured science research programs for undergraduates, this study focuses on how underrepresented students experience science. Several key themes emerged from focus group discussions: learning to become research scientists, experiences with the culture of science, and views on racial and social stigma. Participants spoke of essential factors for becoming a scientist, but their experiences also raised complex issues about the role of race and social stigma in scientific training. Students experienced the collaborative and empowering culture of science, exhibited strong science identities and high self-efficacy, while developing directed career goals as a result of “doing science” in these programs.

Method and device for retrieving materials from body lumens

Abstract: A retrieval catheter (10) for removing deleterious materials (S) from body lumens comprises an elongate catheter body (12) having a slack net (26) at its distal end (16). The slack net may be collapsed to facilitate introduction into the body lumen and opened in situ to permit capture and retrieval of the deleterious materials. A method for removing ureteral stones from the ureter is described.

Lunar Reconnaissance Orbiter Overview: The Instrument Suite and Mission

Abstract: NASA’s Lunar Precursor Robotic Program (LPRP), formulated in response to the President’s Vision for Space Exploration, will execute a series of robotic missions that will pave the way for eventual permanent human presence on the Moon. The Lunar Reconnaissance Orbiter (LRO) is first in this series of LPRP missions, and plans to launch in October of 2008 for at least one year of operation. LRO will employ six individual instruments to produce accurate maps and high-resolution images of future landing sites, to assess potential lunar resources, and to characterize the radiation environment. LRO will also test the feasibility of one advanced technology demonstration package. The LRO payload includes: Lunar Orbiter Laser Altimeter (LOLA) which will determine the global topography of the lunar surface at high resolution, measure landing site slopes, surface roughness, and search for possible polar surface ice in shadowed regions, Lunar Reconnaissance Orbiter Camera (LROC) which will acquire targeted narrow angle images of the lunar surface capable of resolving meter-scale features to support landing site selection, as well as wide-angle images to characterize polar illumination conditions and to identify potential resources, Lunar Exploration Neutron Detector (LEND) which will map the flux of neutrons from the lunar surface to search for evidence of water ice, and will provide space radiation environment measurements that may be useful for future human exploration, Diviner Lunar Radiometer Experiment (DLRE) which will chart the temperature of the entire lunar surface at approximately 300 meter horizontal resolution to identify cold-traps and potential ice deposits, Lyman-Alpha Mapping Project (LAMP) which will map the entire lunar surface in the far ultraviolet. LAMP will search for surface ice and frost in the polar regions and provide images of permanently shadowed regions illuminated only by starlight. Cosmic Ray Telescope for the Effects of Radiation (CRaTER), which will investigate the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background space radiation. The technology demonstration is an advanced radar (mini-RF) that will demonstrate X- and S-band radar imaging and interferometry using light weight synthetic aperture radar. This paper will give an introduction to each of these instruments and an overview of their objectives.

The role of the prefrontal cortex in dynamic filtering

Abstract: Functional neuroimaging and neuropsychological methods have broadened our understanding of the human prefrontal cortex. Converging evidence suggests that this brain region contributes to executive control of information processing. Both cognitive and neural-based models have attempted to delineate the manner in which the prefrontal cortex mediates executive control. An analysis of these findings and models suggests four prominent aspects of executive control—selecting, maintaining, updating, and rerouting information processing. These four aspects are couched in terms of dynamic filtering theory, which proposes that the prefrontal cortex acts as a selective gating or filtering mechanism that controls information processing.