Latitudinal gradients in leaf litter decomposition in streams: Effects of leaf chemistry and temperature

Thesis (Ph.D.) University of Alaska Fairbanks, 1993Autumnal leaf litter that falls into streams of forested regions forms a major source of energy for stream food webs. The processing of this litter has been studied for many years, and two generalizations have come from this research: (1) nitrogen concentration is positively correlated with breakdown rate, and (2) temperature is negatively correlated with breakdown rate. Along with investigators in Michigan and Costa Rica, I examined these generalizations by estimating breakdown rates of litter of ten tree species with widely varying nutritional quality along the latitudinal gradient of Costa Rica to Michigan to Alaska. At each site, litter processing experiments were done using leaves of the same ten tree species and the same methods in streams with similar character. We found that (1) condensed tannin, a plant defense against herbivory, was more highly correlated (negatively) with breakdown rates than was nitrogen (positively correlated with breakdown), and (2) breakdown rate showed a complex response to water temperature (i.e., latitude). I propose a model of leaf litter breakdown in which the microbial contribution to litter breakdown is negatively correlated with latitude (i.e., temperature) and the invertebrate contribution to litter breakdown is positively correlated with latitude. In addition, I suggest that secondary compounds of low solubility, especially condensed tannin, should be considered along with nitrogen when evaluating a tree species for leaf litter quality

Monte-Carlo simulations and image reconstruction for novel imaging scenarios in emission tomography

AbstractEmission imaging incorporates both the development of dedicated devices for data acquisition as well as algorithms for recovering images from that data. Emission tomography is an indirect approach to imaging. The effect of device modification on the final image can be understood through both the way in which data are gathered, using simulation, and the way in which the image is formed from that data, or image reconstruction. When developing novel devices, systems and imaging tasks, accurate simulation and image reconstruction allow performance to be estimated, and in some cases optimized, using computational methods before or during the process of physical construction. However, there are a vast range of approaches, algorithms and pre-existing computational tools that can be exploited and the choices made will affect the accuracy of the in silico results and quality of the reconstructed images. On the one hand, should important physical effects be neglected in either the simulation or reconstruction steps, specific enhancements provided by novel devices may not be represented in the results. On the other hand, over-modeling of device characteristics in either step leads to large computational overheads that can confound timely results. Here, a range of simulation methodologies and toolkits are discussed, as well as reconstruction algorithms that may be employed in emission imaging. The relative advantages and disadvantages of a range of options are highlighted using specific examples from current research scenarios

Perceptual modalities guiding bat flight in a native habitat

Flying animals accomplish high-speed navigation through fields of obstacles using a suite of sensory modalities that blend spatial memory with input from vision, tactile sensing, and, in the case of most bats and some other animals, echolocation. Although a good deal of previous research has been focused on the role of individual modes of sensing in animal locomotion, our understanding of sensory integration and the interplay among modalities is still meager. To understand how bats integrate sensory input from echolocation, vision, and spatial memory, we conducted an experiment in which bats flying in their natural habitat were challenged over the course of several evening emergences with a novel obstacle placed in their flight path. Our analysis of reconstructed flight data suggests that vision, echolocation, and spatial memory together with the possible exercise of an ability in using predictive navigation are mutually reinforcing aspects of a composite perceptual system that guides flight. Together with the recent development in robotics, our paper points to the possible interpretation that while each stream of sensory information plays an important role in bat navigation, it is the emergent effects of combining modalities that enable bats to fly through complex spaces

Addressing Issues of Cloud Resilience, Security and Performance through Simple Detection of Co-locating Sibling Virtual Machine Instances

Most current Infrastructure Clouds are built on shared tenancy architectures, with resources shared amongst large numbers of customers. However, multi tenancy can lead to performance issues (so-called “noisy neighbours”) and also brings potential for serious security breaches such as hypervisor breakouts. Consequently, there has been a focus in the literature on identifying co-locating instances that are being affected by noisy neighbours or suggesting that such instances are vulnerable to attack. However, there is limited evidence of any such attacks in the wild. More beneficially, knowing that there is co-location amongst your own Virtual Machine instances (siblings) can help to avoid being your own worst enemy: avoiding your instances acting as your own noisy neighbours, building resilience through ensuring hostbased redundancy, and/or reducing exposure to a single compromised host. In this paper, we propose and demonstrate a test to detect co-locating sibling instances on Xen-based Clouds, as could help address such needs, and evaluate its efficacy on Amazon’s EC2

Perceptions of service quality of rural rail branchlines: a case study of southeast Benton County

American railroads have faced a declining share of freight traffic relative to other modes. Although a variety of reasons have been identified for this decline, most experts agree that a contributing problem is that the rail system is overdeveloped with unprofitable branchlines. Many economic models have been utilized to analyze relative branchline value, but the literature is insufficient in defining quality of service from the user viewpoint. The principal objective of this paper is to determine the rail service needs of shippers on rural branchlines, using a segment of the West Side Branchline located in Southeast Benton County, Oregon as a case study. Personal interviews were conducted with the shippers on this rural branchline to identify rail service attributes and deficiencies in meeting the transport requirements of various resource commodities, particularly agricultural products, wood products and Christmas trees. Several techniques were employed to compare and interpret the responses of the shippers. A "trade-off analysis" by monotone analysis of variance, was used experimentally in this study and proved to be a useful technique in quantifying judgemental data. It was found that shippers of like commodities expressed similar preferences regarding service needs, often in contradiction to the findings of other studies. Overall rates, total transit time and car availability were of highest concern to most shippers

Role of magnetic resonance spectroscopy in cerebral glutathione quantification for youth mental health:A systematic review

AIM: Oxidative stress is strongly implicated in many psychiatric disorders, which has resulted in the development of new interventions to attempt to perturb this pathology. A great deal of attention has been paid to glutathione, which is the brain's dominant antioxidant and plays a fundamental role in removing free radicals and other reactive oxygen species. Measurement of glutathione concentration in the brain in vivo can provide information on redox status and potential for oxidative stress to develop. Glutathione might also represent a marker to assess treatment response. METHODS: This paper systematically reviews studies that assess glutathione concentration (measured using magnetic resonance spectroscopy) in various mental health conditions. RESULTS: There is limited evidence showing altered brain glutathione concentration in mental disorders; the best evidence suggests glutathione is decreased in depression, but is not altered in bipolar disorder. The review then outlines the various methodological options for acquiring glutathione data using spectroscopy. CONCLUSIONS: Analysis of the minimum effect size measurable in existing studies indicates that increased number of participants is required to measure subtle but possibly important differences and move the field forward

Low pressure radiofrequency balloon angioplasty: Evaluation in porcine peripheral arteries

AbstractObjectives. The purpose of this study was to evaluate the efficacy of radiofrequency-powered thermal balloon angioplasty in an in vivo porcine model.Background. Various modes of thermal energy used adjunctively during balloon angioplasty have demonstrated the potential to enhance the results of acute lumen dilation.Methods. In normal pigs, 75 peripheral arteries were dilated with a newly designed, radiofrequency-powered, thermal angioplasty balloon. All inflations were performed at 2-atm pressure for 85 s. Dilations were performed either with (hot) or without (cold) the application of heat. Lumen dimensions and vessel morphology were assessed with intravascular ultrasonography. At the end of each study, dilated arterial segments were harvested for histologic examination.Results. Single cold balloon inflations resulted in a 12.7% increase in arterial cross-sectional area whereas single hot inflations resulted in a 22.9% increase (p < 0.03). Similarly, when multiple cold inflations were compared with multiple hot inflations, two, three and four sequential hot inflations resulted in a significantly greater increase in cross-sectional area than an equivalent number of cold inflations (p < 0.03).Histologic examination demonstrated a temperaturedependent effect on the depth of medial necrosis and extent of arterial wall thinning (p < 0.001) as well as evidence for uniform alteration of elastic tissue fibers at temperatures of ≥60 °C (p < 0.03).Conclusions. Low pressure radiofrequency thermal balloon angioplasty results in a greater increase in cross-sectional area in porcine peripheral arteries than does nonheated conventional balloon angioplasty. The pathologic basis for this enhanced dilation may be a temperature-dependent effect on medial necrosis, thinning of the arterial wall or alteration of vascular elastic fibers, alone or in combination

The open-air site of Tolbor 16 (Northern Mongolia): Preliminary results and perspectives.

Numerous questions remain regarding the timing and the context of Upper Paleolithic emergence in Northeast Asia. Available data allow the recognition of a form of Initial Upper Paleolithic (IUP) documented in the Altai circa 45e40 ka 14C BP, and in the Cis- and Transbaikal around �37 ka 14C BP. In Northern Mongolia, a series of assemblages show intriguing similarities with IUP laminar assemblages from South Siberia and suggest long distance contact/movements of population during the first half of MIS3. These contacts are potentially enabled by the main river that drains into Lake Baikal, the Selenga. By cutting through the Sayan and the Yablonovy mountain ranges, the Selenga drainage system provides a potential corridor connecting South Siberia with the plains of Mongolia. The Tolbor 16 site (Ikh Tulberiin Gol, Northern Mongolia) is located circa 13 km from the confluence with the Selenga. The first results presented here suggest that the lithic assemblage and the ornaments discovered at Tolbor 16 document the early appearance of Upper Paleolithic in the region. This newly discovered site offers the possibility to generate high-resolution contextual data on the first appearance of the blade assemblages in Mongolia and to test the ‘Selenga corridor hypothesis’