3,521 research outputs found
Assessment of Land Cover Change in North Eastern Nigeria
No full textLand cover change provides a means of understanding and managing the problems of
degradation and shortage of land and water resources and the conflicts therewith in
the north eastern Nigeria. This research assessed how tree, shrub grass, bare ground
changed from 1986 to 2005 using the NigeriaSat-1 and Landsat images calibrated
with field survey data. Thirteen subclasses of the land cover were spectrally analysed
and classified severally, however uncertainties in the classification made the merger
into four classes necessary. Changes were analysed according to persistence,
swapping, loss and gain analysis, multi-year transition of each land cover in
succession, location of intensive change, and regional change density. Uncertainties
were analysed by confusion and transition error matrices. The overall accuracies of
the classifications were between 60% and 75%, and the transition and change
accuracies were between 45% and 60%. Approximately 60% of the area of study
remained unchanged during the period. Of the remainder, approximately 11% of the
area interchanged between shrub grass and bare ground. Shrub grass was found to be
the most unstable category and the source of most misclassification. The loss of tree
was general but more intensive in the Fadama making it the most vulnerable. How
local people perceived land cover change was sought through group interview and the
results concurred generally with the assessment of the changes. NigeriaSat-1 imagery
was tested for its quality and whether the addition of the middle infrared wavebands
improved the classification. NigeriaSat-1 failed to classify the 13 classes and the
middle infrared did not improve the classification, thus comparable to Landsat data,
although the test was done with dry season images and the result may likely be
different for wet season imagery. The 8 km AHVRR-NDVI was found to be useful in
assessing the timing of image acquisition, but the data could not provide sufficient
spatial resolution to warrant its usage for local scale studies
Application of remote sensing and GIS for modeling and assessment of land use/cover change in Amman/Jordan
No full textModeling and assessment of land use/cover and its impacts play a crucial role in land use planning and formulation of sustainable land use policies. In this study, remote sensing data were used within geographic information system (GIS) to map and predict land use/cover changes near Amman, where half of Jordan's population is living. Images of Landsat TM, ETM+ and OLI were processed and visually interpreted to derive land use/cover for the years 1983, 1989, 1994, 1998, 2003 and 2013. The output maps were analyzed using GIS and cross-tabulated to quantify land use/cover changes for the different periods. The main changes that altered the character of land use/cover in the area were the expansion of urban areas and the recession of forests, agricultural areas (after 1998) and rangelands. The Markov Chain was used to predict future land use/cover, based on the historical changes during 1983-2013. Results showed that prediction of land use/cover would depend on the time interval of the multi-temporal satellite imagery from which the probability of change was derived. The error of prediction was in the range of 2% - 5%, with more accurate prediction for urbanization and less accurate prediction for agricultural areas. The trends of land use/cover change showed that urban areas would expand at the expense of agricultural land and would form 33% of the study area (50km x 60km) by year 2043. The impact of these land use/cover changes would be the increased water demand and wastewater generation in the future
Structure of the Helicobacter pylori Cag type IV Secretion System
No full textBacterial type IV secretion systems (T4SSs) are molecular machines that can mediate interbacterial DNA transfer through conjugation and delivery of effector molecules into host cells. The Helicobacter pylori Cag T4SS translocates CagA, a bacterial oncoprotein, into gastric cells, contributing to gastric cancer pathogenesis. We report the structure of a membrane-spanning Cag T4SS assembly, which we describe as three sub-assemblies: a 14-fold symmetric outer membrane core complex (OMCC), 17-fold symmetric periplasmic ring complex (PRC), and central stalk. Features that differ markedly from those of prototypical T4SSs include an expanded OMCC and unexpected symmetry mismatch between the OMCC and PRC. This structure is one of the largest bacterial secretion system assemblies ever reported and illustrates the remarkable structural diversity that exists among bacterial T4SSs.National Institute of Allergy and Infectious Diseases AI118932 Timothy L Cover Melanie D Ohi
National Cancer Institute CA116087 Timothy L Cover
U.S. Department of Veterans Affairs 1I01BX004447 Timothy L Cover
National Institute of General Medical Sciences GM103310 Melanie D Oh
Patterns and Rates of Land Use Land Cover Change: A Case Study of Ambos Nogales (Arizona and Sonora), 1985-2004
No full textAbstract The continued expansion of the paired U.S.–Mexican border cities of Ambos Nogales presents many environmental management and urban planning challenges. This study focuses on a comparative study of spatial patterns and rates of land-use and land-cover change, in relation to land degradation, deforestation, and urban growth over different time periods. Based on historical data the study suggests that both cities have experi- enced high land degradation; however, land on the Arizona-side has been more stable and less degraded. However, there were more severely degraded areas found in Nogales, Arizona, than in Nogales, Sonora. The delineation of land use change and the severity of land degradation provide important information to planners about areas that should be targeted for development and other areas that require restoration to natural settings. Keywords: Nogales, land use land cover, urban growth, land degradation Resumen La expansión continua de las ciudades gemelas de Ambos Nogales (USA-Mexico) presenta muchos desafÃos de planificación urbana y manejo ambiental. Este estudio se concentra en un análisis comparativo de los patrones espaciales y velocidad de cambios de uso del suelo con relación a la degradación del terreno, deforestación, y crecimiento urbano durante distintos perÃodos de tiempo. Basado en datos históricos el estudio sugiere que ambas ciudades han experimentado alta degradación de tierra, pero la tierra en el lado de Arizona ha sido más estable y menos degradada. Sin embargo, en Nogales Arizona, habÃan áreas severamente más degradadas que en Nogales, Sonora. Palabras clave: Nogales, crecimiento urbano, uso de suelo, degradación de tierra
Simplifying nondeterministic finite cover automata
No full textThe concept of Deterministic Finite Cover Automata (DFCA) was introduced at WIA '98, as a more compact representation than Deterministic Finite Automata (DFA) for finite languages. In some cases representing a finite language, Nondeterministic Finite Automata (NFA) may significantly reduce the number of states used. The combined power of the succinctness of the representation of finite languages using both cover languages and non-determinism has been suggested, but never systematically studied. In the present paper, for nondeterministic finite cover automata (NFCA) and l-nondeterministic finite cover automaton (l-NFCA), we show that minimization can be as hard as minimizing NFAs for regular languages, even in the case of NFCAs using unary alphabets. Moreover, we show how we can adapt the methods used to reduce, or minimize the size of NFAs/DFCAs/l-DFCAs, for simplifying NFCAs/l-NFCAs
Management for network diversity speeds evolutionary adaptation to climate change
No full textEcosystems around the world are reorganizing due to climate change1, motivating management responses to facilitate spe- cies persistence and maintain ecological functions. Spatial management actions are generally undertaken to relieve local stressors on populations and have recently been suggested as an approach to facilitate species range shifts, provide refugia and enhance resilience to climate change2,3. Efforts to iden- tify which habitats to protect, however, typically assume that organisms do not evolve in response to shifting environmental conditions4,5 despite growing evidence that rapid evolutionary responses occur under new selective regimes in the wild6,7. It is not clear whether conservation strategies would be differ- ent if evolutionary dynamics were considered during conser- vation planning. Here, we show that evolutionary responses fundamentally change recommendations for conservation actions. With spatially explicit simulations of a simple three- species coral reef ecosystem, we show that the preferred management strategies changed from those focusing on ther- mal refugia when evolutionary capacity was absent to those prioritizing trait and habitat diversity or high cover when adaptive evolution was possible. Prioritizing habitat diversity protects heat resistant populations and protects cooler ref- uges and the stepping stones between them. The protection of habitat heterogeneity and connectivity also produced sub- stantially larger benefits outside reserves than refugia-based strategies, providing conservation planners an opportunity to facilitate adaptation to ongoing and unpredictable change.Peer reviewe
Cover Story piece profiling Linda Greenlaw, 40, of Isle au Haut, author of Th
No full textCover Story piece profiling Linda Greenlaw, 40, of Isle au Haut, author of The Hungry Ocean
Protein-Protein Interactions Required for CagA Recruitment and Secretion by the Helicobacter pylori Cag Type IV Secretion System
No full textHelicobacter pylori strains that contain the cag pathogenicity island (PAI) utilize the Cag type IV secretion system (T4SS) to deliver a bacterial effector protein (CagA) and non-protein substrates into human gastric cells. The Cag T4SS outer membrane core complex (OMCC) contains multiple copies of five proteins, two of which are species-specific proteins. Additional species-specific proteins encoded by the cag PAI are required for Cag T4SS activity, but their localization within the Cag T4SS is undefined. By using optimized mass spectrometric methods and modifications of a previously described OMCC immunopurification method, we have identified four cag PAI-encoded proteins (CagW, CagL, CagI, and CagH) that co-purify with the Cag T4SS OMCC. Analysis of immunopurified samples by size exclusion chromatography revealed that CagW, CagL, CagI and CagH co-elute with OMCC components. These four Cag proteins are copurified with the OMCC in immunopurifications from a Δcag3 mutant strain (lacking peripheral OMCC components), but not from a ΔcagX mutant strain (defective in OMCC assembly). Mutant strains with deletions of cagW, cagL, cagI, or cagH lacked T4SS activity but retained the ability to assemble OMCCs. Furthermore, by targeting several different Cag proteins and adding crosslinkers to the bacteria prior to immunopurification, we improved our ability to isolate multiple Cag proteins, providing further insight into protein-protein interactions among cag PAI-encoded proteins. We also generated H. pylori strains that produce CagA N-terminal fusion proteins (APEX2-CagA, GFP-CagA) and found that these fusion proteins retained the ability to interact with the Cag T4SS OMCC. In summary, the experiments described in my dissertation provide new insights into protein-protein interactions relevant to the structural organization of the Cag T4SS
On the dangers of decentralization
No full textThe author highlights some of the dangers of decentralizations. The benefits of decentralization in allocative efficiency are not as obvious as suggested by the standard theory of fiscal federalism. The assumptions of this theory are fragile. These doubtful benefits might carry a cost in production efficiency, but more empirical research is needed on this point. What is not doubtful is that decentralization runs counter to redistribution and stabilization. Decentralization makes redistributive policies, whether interpersonal or interjurisdictional, more difficult, if not impossible. Decentralization also makes macroeconomic stabilization programs more difficult to implement because subnational government fiscal policies can run counter to national policies. Serious drawbacks or potential drawbacks should be considered in designing any decentralization program. The arguments that the author develops make it easier to understand some of the real choices. These choices are not so much whether to decentralize in general but rather what functions to decentralize - in which sectors, and in which regions. Guidelines can be provided on this. Often, the problem is not so much whether a certain service should be provided by a central, regional, or local government, since the service often has to be provided with the intervention of all three levels of government. The real challenge is how to organize the joint production of the service. Decentralization refers simultaneously to a state and to a process. The virtues and dangers of decentralization are often discussed simultaneously for both concepts. This is a dangerous confusion because decentralization is path-dependent. What is desirable in a given country at a certain point in time depends on the present state of decentralization and the speed at which it has been reached. Much more work, particularly empirical work, is needed -- in review of decentralization (or centralization) experiences in general, as well as those encouraged or supported by the World Bank.National Governance,Banks&Banking Reform,Municipal Financial Management,Economic Theory&Research,Pharmaceuticals&Pharmacoeconomics
Revealing the Interactions of Clostridioides difficile Toxin B With Epithelial Receptors
No full textClostridioides difficile is a Gram-positive, spore-forming bacterium and the leading cause of hospital-acquired diarrhea in the United States. Upon colonizing the colon of susceptible hosts, C. difficile causes disease through two secreted protein toxins, toxin A (TcdA) and toxin B (TcdB). The glucosyltransferase activity of the toxins inactivates small Rho-family GTPases involved in cell signaling to promote inflammation, fluid secretion, and cell death. While multiple proteins have been identified to bind each toxin in vitro, the significance of these interactions remains unclear for mediating disease. In this dissertation, I investigated the roles of chondroitin sulfate proteoglycan 4 (CSPG4), Frizzled (FZD), and Nectin-3, three receptors proposed to mediate the endocytosis of TcdB. Using a rectal instillation mouse model of C. difficile toxins, I show that FZD interactions with TcdB are not essential for mediating pathologies. Furthermore, I show that ribotype 027 C. difficile, an epidemic C. difficile ribotype, produces a TcdB that is unable to interact with FZD proteins but is still capable of promoting fulminant disease in hosts. Mechanistically, I propose that TcdB promotes injuries to the colonic epithelium through interactions with Nectin-3 and CSPG4. By developing a method to visualize TcdB on cells using fluorescent microscopy, I demonstrate that both Nectin-3 and CSPG4 colocalize with TcdB on 18Co cells. On host colonic tissue, I observed novel localization of Nectin-3 within the brush border of epithelial cells and CSPG4 localization along the epithelial cell junction. As colonic epithelial cells do not express CSPG4, I propose that this CSPG4 signal is likely mediated by shed forms of CSPG4 produced by stromal cells along the crypt-surface axis. In support of this model, I show that shed forms of CSPG4 can be endocytosed by epithelial cells, a concept that TcdB can exploit to potentiate its activity. Collectively, my study provides new insights into how TcdB utilizes receptor interactions to intoxicate colonic epithelial cells to cause disease
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