Desiccation and recolonization of phytobenthos in a regulated desert river: Colorado River at Lees Ferry,Arizona, USA

We tested the recolonization of the phytobenthic community in the tailwaters of Glen Canyon Dam following long- and short-term experimentally induced desiccation. The response of Cladophora glomerata, Oscillatoria spp., miscellaneous phytobenthos species and periphyton was studied over 18 weeks using three treatments: (1) undisturbed control cobbles from the submerged zone; (2) cobbles desiccated and replaced into the submerged zone; and (3) cobbles desiccated and replaced into the varial zone. Periphyton density and compositional response resulting from these treatments were also examined. Desiccation treatments were significantly different in biomass from controls throughout the study. The biomass of desiccated and replaced river cobbles averaged <30% of the controls for C. glomerata and periphyton during the 18-week recolonization period. In contrast, the biomass of the control Oscillatoria and miscellaneous phytobenthos species averaged only 3 and 50% of that in the desiccation treatments, respectively. Cladophora, the dominant alga, comprised 77% of the phytobenthic biomass. A significant positive relationship between discharge, Cladophora and periphyton biomass was present in all treatments, while there was a negative relationship with discharge for Oscillatoria and miscellaneous phytobenthos species. There was a significant inverse correlation, as well as a pattern of separate biomass dominance, between C. glomerata and Oscillatoria. Cladophora was the dominant phytobenthos species on cobbles below the baseflow and Oscillatoria was dominant on cobbles in the varial zone. In general, the Cladophora biomass decreased under intermittent drying conditions, while Oscillatoria declined under permanently wet conditions. Diatom composition was not significantly different between treatments; however, their density was lower on desiccated cobbles. Diatom density on desiccated cobbles in the submerged and varial zones averaged 69 and 42% of that of the controls, respectively. Recovery and maintenance of benthic resources are hindered by fluctuating flow regimes driven by electricity and irrigation requirements. Repeated desiccation of the phytobenthos has major effects on the bottom-up interactions in the Colorado River ecosystem. © 1998 John Wiley & Sons, Ltd.     

Synthesizing mixed-phase TiO2 nanocomposites using a hydrothermal method for photo-oxidation and photoreduction applications

Mixed-phase titanium dioxide (TiO₂) materials, such as Degussa P25, show high photocatalytic activity due largely to the synergistic effect between anatase and rutile phases, in which spatial charge separation hinders charge recombination. Our previous studies indicate that a particular nanostructured assembly of anatase and rutile crystallites is necessary for the synergy. In this paper, we apply this structure-function understanding to the synthesis of highly active TiO₂ nanocomposite photocatalysts. Using simple synthetic procedures, we demonstrate an ability to design a highly active nanocomposite that shows enhanced photoactivity in both oxidative and reductive chemistry. Studies by electron paramagnetic resonance spectroscopy indicate the existence of the critical nanostructured assembly and thus the optimization of charge transfer between anatase and rutile phases in the synthesized nanocomposite. These results illustrate the potential of rationally designing photocatalysts for energy applications.     

Study of the material properties and suitability of plasma-deposited fluorine-doped silicon dioxides for low dielectric constant interlevel dielectrics

A major challenge for back-end interconnection technology as device geometries shrink is the development of low dielectric constant materials with good gap-filling properties that are suitable for microelectronics manufacturing. Recently, there has been much interest in fluorine-doped silicon dioxides (SiOF) as such a material. The advantages of a silicon dioxide based film from an integration standpoint make these films very attractive for manufacturing.

In this study, SiOF films have been prepared in a conventional parallel-plate dual-frequency plasma-enhanced chemical vapor deposition reactor. By varying the deposition parameters, SiOF films with indices of refraction from 1.38 to 1.46 and corresponding changes of as much as 20% in the dielectric constants have been produced. Fourier transform infrared data for these films have been correlated with fluorine concentration by secondary ion mass spectroscopy measurements. The presence of fluorine can also be observed in the capacitance-voltage (CV) characteristics for the films. Fluorine interface states trap electrons which delay the onset of accumulation in the CV measurements for p-type silicon. In a similar way, the fluorine-induced trap states affect the onset of inversion for n-type silicon.

Some films with high fluorine concentrations have been observed to be unstable with respect to moisture absorption. The reliability and stability data for these films are presented.     

Information Security Threats and Practices in Small Businesses

This article focuses on how small businesses (fewer than 500 employees) are managing information security and the associated risks. Our findings indicate that the businesses interviewed for this study are taking many of the typical steps that are indicative of best security practices. However, there are also several areas of concern that could potentially leave their systems open to threats.     

Neural synchrony in stochastic resonance, attention, and consciousness.

We describe briefly three of our lab's ongoing projects studying the role of neural synchrony in human perception and cognition. These projects arise from two main interests: the role of noise both in human perception and in neural synchrony, and neural synchrony as a basis for integration of functional modules in the brain. Our experimental work on these topics began with a study of the possibility that noise-influenced neural synchrony might be responsible for the fact that small amounts of noise added to weak signals can enhance their detectability (stochastic resonance). We are also studying the role of neural synchrony in attention and consciousness in several paradigms. On the basis of our own and related work by others, we conclude that (1) neural synchrony plays an important role in the integration of functional modules in the brain and (2) neural synchrony is profoundly affected and possibly regulated, in part, by the "noisiness" of the brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preventing disability from work-related low-back pain. New evidence gives new hope--if we can just get all the players onside

Tumor necrosis factor (TNF) is a proinflammatory cytokine playing a central role in the expression of endothelial adhesion molecules required for the recruitment of inflammatory cells. Proliferative glomerulonephritis induced by anti-glomerular basement membrane (GBM) antibody is characterized by the recruitment of inflammatory cells in the glomerulus followed by capillary damage and crescent formation. The glomerular pathology may be due to a large extent to TNF induction. We therefore tested this hypothesis in TNF-deficient mice. Anti-GBM antibody administration in sensitized wild-type mice resulted in deposition of immune complexes, followed by increased intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression, as well as the influx of polymorphonuclear neutrophils (PMNs), lymphocytes, and macrophages. Distinct proteinuria preceded proliferative glomerulonephritis characterized by crescent formation. In the absence of TNF, the development of proteinuria was delayed and the formation of crescents was almost completely prevented. Although the deposition of immune complexes in glomeruli was comparable in both groups, the up-regulation of ICAM-1 and VCAM-1, as well as the influx of PMNs and lymphocytes, but not of monocytes, was dramatically reduced in TNF-deficient mice. Therefore, we conclude that TNF plays a key role in the recruitment of inflammatory cells and in the subsequent development of proliferative glomerulonephritis.     

Pre-service teachers’ perspectives on using scenario-based virtual worlds in science education

This paper presents the findings of a study on the current knowledge and attitudes of pre-service teachers on the use of scenario-based multi-user virtual environments in science education. The 28 participants involved in the study were introduced to Virtual Singapura, a multi-user virtual environment, and completed an open-ended questionnaire. Data from the questionnaire indicated that gender and current computer game use were likely to affect the perceived benefits of using virtual worlds in a classroom setting. Behavior management was seen as being a constraining factor on a pre-service teacher’s willingness to use a virtual world in the future. Overall, the results of the study indicate that pre-service teachers as a result of their use of Virtual Singapura are both aware of virtual worlds and have a reasonable understanding of both their potential advantages and disadvantages within a classroom setting.