100 research outputs found
Remote Sensing of Arctic Vegetation: Relations between the NDVI, Spatial Resolution and Vegetation Cover on Boothia Peninsula, Nunavut
Arctic tundra environments are thought to be particularly sensitive to changes in climate, whereby alterations in ecosystem functioning are likely to be expressed through shifts in vegetation phenology, species composition, and net ecosystem productivity (NEP). Remote sensing has shown potential as a tool to quantify and monitor biophysical variables over space and through time. This study explores the relationship between the normalized difference vegetation index (NDVI) and percent-vegetation cover in a tundra environment, where variations in soil moisture, exposed soil, and gravel till have significant influence on spectral response, and hence, on the characterization of vegetation communities. IKONOS multispectral data (4 m spatial resolution) and Landsat 7 ETM+ data (30 m spatial resolution) were collected for a study area in the Lord Lindsay River watershed on Boothia Peninsula, Nunavut. In conjunction with image acquisition, percent cover data were collected for twelve 100 m Ă 100 m study plots to determine vegetation community composition. Strong correlations were found for NDVI values calculated with surface and satellite sensors, across the sample plots. In addition, results suggest that percent cover is highly correlated with the NDVI, thereby indicating strong potential for modeling percent cover variations over the region. These percent cover variations are closely related to moisture regime, particularly in areas of high moisture (e.g., water-tracks). These results are important given that improved mapping of Arctic vegetation and associated biophysical variables is needed to monitor environmental change.On croit que les environnements de la toundra arctique sont particuliĂšrement sensibles aux changements climatiques, en ce sens que toute altĂ©ration du fonctionnement de lâĂ©cosystĂšme est susceptible dâĂȘtre exprimĂ©e dans le rĂ©arrangement de la phĂ©nologie de la vĂ©gĂ©tation, de la composition des espĂšces et de la productivitĂ© nette de lâĂ©cosystĂšme (PNĂ). La tĂ©lĂ©dĂ©tection sâavĂšre un outil efficace de quantification et de surveillance des variables biophysiques dans le temps et dans lâespace. Cette Ă©tude explore la relation entre lâindice dâactivitĂ© vĂ©gĂ©tale et le pourcentage de couverture vĂ©gĂ©tale en milieu de toundra, oĂč les variations propres Ă lâhumiditĂ© du sol, au sol exposĂ© et au till de gravier ont une influence considĂ©rable sur la rĂ©ponse spectrale et, par consĂ©quent, sur la caractĂ©risation des communautĂ©s vĂ©gĂ©tales. Des donnĂ©es multispectrales IKONOS (rĂ©solution spatiale de 4 m) et des donnĂ©es ETM+ de Landsat 7 (rĂ©solution spatiale de 30 m) ont Ă©tĂ© recueillies pour une zone dâĂ©tude visĂ©e par la ligne de partage des eaux Ă la hauteur de la riviĂšre Lord Lindsay, dans la pĂ©ninsule de Boothia, au Nunavut. De concert avec lâacquisition dâimages, les donnĂ©es relatives au pourcentage de couverture ont Ă©tĂ© recueillies pour douze terrains dâĂ©tude de 100 m sur 100 m dans le but de dĂ©terminer la composition de la communautĂ© vĂ©gĂ©tale. De fortes corrĂ©lations ont Ă©tĂ© dĂ©notĂ©es dans le cas des valeurs de lâindice dâactivitĂ© vĂ©gĂ©tale calculĂ©es Ă lâaide de dĂ©tecteurs de surface et de dĂ©tecteurs satellisĂ©s et ce, Ă lâĂ©chelle des terrains ayant servi dâĂ©chantillon. Par ailleurs, les rĂ©sultats laissent entendre que le pourcentage de couverture est hautement corrĂ©lĂ© avec lâindice dâactivitĂ© vĂ©gĂ©tale, ce qui indique une forte possibilitĂ© de modĂ©lisation des variations de pourcentage de couverture dans la rĂ©gion. Ces variations du pourcentage de couverture sont Ă©troitement liĂ©es au rĂ©gime dâhumiditĂ©, particuliĂšrement dans les rĂ©gions oĂč lâhumiditĂ© est Ă©levĂ©e (comme les traces dâeau). Ces rĂ©sultats revĂȘtent de lâimportance Ă©tant donnĂ© quâil y a lieu dâamĂ©liorer le mappage de la vĂ©gĂ©tation arctique et les variables biophysiques connexes afin de surveiller la modification de lâenvironnement
An Incidence of Multi-Year Sediment Storage on Channel Snowpack in the Canadian High Arctic
During June 2005, we identified the presence of sediment buried within multi-year channel snowpack of a small river located near Cape Bounty, Melville Island, Nunavut (74°55' N, 109°35' W). Photographic evidence indicates that the sediment was deposited during the 2003 season by the initial meltwater flowing on the snowpack, which was dammed by snow upstream of a channel constriction. The resulting pond covered a minimum area of 180 m2 and contained an estimated minimum 27 Mg of sediment. Suspended sediment measurements during the 2003 season indicate that deposition on the snowpack at this location represented 49%â65% of the sediment transport prior to the ponding and emplacement of the sediment on the snow, and approximately 20% of the measured sediment flux for the entire season. Multi-year snow accumulations immediately downstream exhibited similar sediment deposition on snow, but no evidence of multi-year sediment storage was present. By contrast, a similar stream in an adjacent watershed channelized rapidly, with minimal sediment deposition on the snow, and delivered a large pulse of sediment to the downstream lake. These results provide quantitative evidence for the magnitude of sediment storage on snowpack and point to the unique role that snow plays in the fluvial geomorphology of High Arctic watersheds.En juin 2005, nous avons dĂ©notĂ© la prĂ©sence de sĂ©diment enterrĂ© dans une plaque de neige datant de plusieurs annĂ©es dâune petite riviĂšre situĂ©e prĂšs de cap Bounty, sur lâĂźle Melville, au Nunavut (74°55' N, 109°35' O). DâaprĂšs des preuves photographiques, le sĂ©diment a Ă©tĂ© dĂ©posĂ© pendant la saison 2003 par lâeau de fusion initiale sâĂ©coulant sur la plaque de neige, qui avait Ă©tĂ© endiguĂ©e par la neige en amont dâun canal confinĂ©. LâĂ©tang qui en a dĂ©coulĂ© recouvrait une aire minimale de 180 m2 et contenait, selon les estimations, au moins 27 Mg de sĂ©diment. Les mesures de sĂ©diment en suspension pendant la saison 2003 indiquent que ce dĂ©pĂŽt sur la plaque de neige Ă cet endroit reprĂ©sentait entre 49 % et 65 % du transport de sĂ©diment avant lâaccumulation dâeau et lâemplacement de sĂ©diment sur la neige, et environ 20 % du flux de sĂ©diment mesurĂ© pour toute la saison. Les accumulations de neige de plusieurs annĂ©es immĂ©diatement en aval comptaient des dĂ©pĂŽts de sĂ©diment semblables sur la neige, quoi quâaucun emmagasinage de sĂ©diment sur plusieurs annĂ©es nâĂ©tait prĂ©sent. Par contraste, un cours dâeau similaire dâun bassin hydrographique adjacent sâest canalisĂ© rapidement, avec peu de dĂ©pĂŽts de sĂ©diment sur la neige, puis a laissĂ© une grande quantitĂ© de sĂ©diment au lac en aval. Ces rĂ©sultats fournissent des preuves quantitatives quant Ă lâampleur de lâemmagasinage de sĂ©diment sur la plaque de neige et laissent envisager le rĂŽle unique que joue la neige sur la gĂ©omorphologie fluviale des bassins hydrographiques de lâExtrĂȘme-Arctique
USE OF GROWTH ANALYSIS TO EVALUATE GENETIC MECHANISMS AFFECTING ACHENE YIELD FORMATION OF SUNFLOWER
The main objective of this study was to investigate the process of dry matter accumulation (DMA) in achenes during the grain-filling period of fifty sunflower genotypes by using the functional method of growth analysis in a field trial at Bicsérd, Hungary. The Hunt-formula of lnY= P0 + P1*X + P2*X2 was fitted to data. Maximum yield (Ymax), the average of the absolute growth rate (AGRavg), maximum growth rate (AGRmax), date of the maximum growth rate (Xagrmax), and the average of the relative growth rate (RGRavg) were calculated from growth curves for hybrids and replications. Significant differences among hybrids and their interaction with sampling dates indicate hybrid differences in the intensity of DMA
accumulation. The strongest correlation was observed between the parameters of Ymax and AGRmax
Spatial variability in carbon dioxide exchange processes within wet sedge meadows in the Canadian High Arctic
Wet sedge meadows are the most productive plant communities in the High Arctic. However, the controls on carbon dioxide (CO2) exchange processes within wet sedge communities â and the scale at which they operate â are poorly understood. Here, the factors controlling CO2 exchange of wet sedge meadows experiencing different moisture regimes are examined. Environmental data are used to create predictive models of CO2 exchange on multiple temporal scales. Automated chamber systems recorded CO2 fluxes at 30-minute intervals at wet sedge sites in the Canadian High Arctic from June to August in 2014 and 2015. Static chambers were also deployed over a larger spatial extent in 2014. Our results show that wet sedge communities were strong CO2 sinks during the growing season (â7.67 to â44.36 g C·mâ2). CO2 exchange rates in wetter and drier areas within wet sedge meadows differed significantly (Wilcoxon, p<0.001), suggesting that soil moisture regimes within vegetation types influence net CO2 balance. Random Forest models explained a significant amount of the variability in CO2 flux rates over time (R2=0.46 to 0.90). The models showed that the drivers of CO2 exchange in these communities vary temporally. Variable moisture regimes indirectly influenced CO2 fluxes given that they exhibit different vegetation and temperature-response characteristics. We suggest that the response of a single vegetation type to environmental changes may vary depending on microenvironment variability within that community
An individual differences approach to semantic cognition:Divergent effects of age on representation, retrieval and selection
6-OHDA-induced dopaminergic neurodegeneration in <i>Caenorhabditis elegans</i> is promoted by the engulfment pathway and inhibited by the transthyretin-related protein TTR-33
<div><p>Oxidative stress is linked to many pathological conditions including the loss of dopaminergic neurons in Parkinsonâs disease. The vast majority of disease cases appear to be caused by a combination of genetic mutations and environmental factors. We screened for genes protecting <i>Caenorhabditis elegans</i> dopaminergic neurons from oxidative stress induced by the neurotoxin 6-hydroxydopamine (6-OHDA) and identified the <u>t</u>rans<u>t</u>hyretin-<u>r</u>elated gene <i>ttr-33</i>. The only described <i>C</i>. <i>elegans</i> transthyretin-related protein to date, TTR-52, has been shown to mediate corpse engulfment as well as axon repair. We demonstrate that TTR-52 and TTR-33 have distinct roles. TTR-33 is likely produced in the posterior arcade cells in the head of <i>C</i>. <i>elegans</i> larvae and is predicted to be a secreted protein. TTR-33 protects <i>C</i>. <i>elegans</i> from oxidative stress induced by paraquat or H<sub>2</sub>O<sub>2</sub> at an organismal level. The increased oxidative stress sensitivity of <i>ttr-33</i> mutants is alleviated by mutations affecting the KGB-1 MAPK kinase pathway, whereas it is enhanced by mutation of the JNK-1 MAPK kinase. Finally, we provide genetic evidence that the <i>C</i>. <i>elegans</i> cell corpse engulfment pathway is required for the degeneration of dopaminergic neurons after exposure to 6-OHDA. In summary, we describe a new neuroprotective mechanism and demonstrate that TTR-33 normally functions to protect dopaminergic neurons from oxidative stress-induced degeneration, potentially by acting as a secreted sensor or scavenger of oxidative stress.</p></div
On-line bioaffinity-electrospray mass spectrometry for simultaneous detection, identification, and quantification of protein-ligand interactions
Elderly with Autism: Executive Functions and Memory
Cognitive autism research is mainly focusing on children and young adults even though we know that autism is a life-long disorder and that healthy aging already has a strong impact on cognitive functioning. We compared the neuropsychological profile of 23 individuals with autism and 23 healthy controls (age range 51â83Â years). Deficits were observed in attention, working memory, and fluency. Aging had a smaller impact on fluency in the high functioning autism (HFA) group than in the control group, while aging had a more profound effect on visual memory performance in the HFA group. Hence, we provide novel evidence that elderly with HFA have subtle neuropsychological deficits and that the developmental trajectories differ between elderly with and without HFA in particular cognitive domains
The cross-sectional GRAS sample: A comprehensive phenotypical data collection of schizophrenic patients
<p>Abstract</p> <p>Background</p> <p>Schizophrenia is the collective term for an exclusively clinically diagnosed, heterogeneous group of mental disorders with still obscure biological roots. Based on the assumption that valuable information about relevant genetic and environmental disease mechanisms can be obtained by association studies on patient cohorts of ℠1000 patients, if performed on detailed clinical datasets and quantifiable biological readouts, we generated a new schizophrenia data base, the GRAS (Göttingen Research Association for Schizophrenia) data collection. GRAS is the necessary ground to study genetic causes of the schizophrenic phenotype in a 'phenotype-based genetic association study' (PGAS). This approach is different from and complementary to the genome-wide association studies (GWAS) on schizophrenia.</p> <p>Methods</p> <p>For this purpose, 1085 patients were recruited between 2005 and 2010 by an invariable team of traveling investigators in a cross-sectional field study that comprised 23 German psychiatric hospitals. Additionally, chart records and discharge letters of all patients were collected.</p> <p>Results</p> <p>The corresponding dataset extracted and presented in form of an overview here, comprises biographic information, disease history, medication including side effects, and results of comprehensive cross-sectional psychopathological, neuropsychological, and neurological examinations. With >3000 data points per schizophrenic subject, this data base of living patients, who are also accessible for follow-up studies, provides a wide-ranging and standardized phenotype characterization of as yet unprecedented detail.</p> <p>Conclusions</p> <p>The GRAS data base will serve as prerequisite for PGAS, a novel approach to better understanding 'the schizophrenias' through exploring the contribution of genetic variation to the schizophrenic phenotypes.</p
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