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Search Results: 1 - 10 of 12561 matches for " Christopher Kellner "
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Bryophyte mass to stem length ratio: A potential metric for eco-physiological response to land use  [PDF]
Jason A. Hubbart, Elliott Kellner
Open Journal of Ecology (OJE) , 2013, DOI: 10.4236/oje.2013.31001

Methods of analysis are needed that quantitatively characterize the response of organisms to anthropogenic disturbance. Herein a method is presented that characterizes bryophyte morphological variability in response to timber harvest treatments (clearcut and partial cut). Samples (n = 6196) of the semi-aquatic bryophyte Brachythecium frigidum were collected from clearcut, partial cut and full forest stream reaches between August 2003 and October 2005 and analyzed to obtain mass to stem length ratios (M:SL). Results show that relative to a full forest (i.e. full canopy cover condition), average M:SL ratios were reduced approximately 18% in the partial cut and 37% in the clearcut, indicating a decrease in biomass per unit stem length with increasing harvest intensities. Increased light intensities and higher air temperatures resulting from decreased canopy cover in the harvest treatments corresponded to lower M:SL ratios (0.31 and 0.24 for the partial cut and clearcut, respectively). Results quantify the morphological response of B. frigidum to habitat perturbation, thereby validating the method as a useful assessment of anthropogenic disturbance in post-timber harvest environments. Additional work should be conducted to test the method in other physiographic regions and to isolate bryophyte response to alterations of distinct environmental variables.

sve 'te Hastane Kütüphaneleri
Bernard Kellner
Türk Kütüphanecili?i , 1968,
Even more simple cardinal invariants
Jakob Kellner
Mathematics , 2007, DOI: 10.1007/s00153-008-0094-2
Abstract: Using GCH, we force the following: There are continuum many simple cardinal characteristics with pairwise different values.
Containment Problems for Projections of Polyhedra and Spectrahedra
Kai Kellner
Mathematics , 2015,
Abstract: Spectrahedra are affine sections of the cone of positive semidefinite matrices which form a rich class of convex bodies that properly contains that of polyhedra. While the class of polyhedra is closed under linear projections, the class of spectrahedra is not. In this paper we investigate the problem of deciding containment of projections of polyhedra and spectrahedra based on previous works on containment of spectrahedra. The main concern is to study these containment problems by formulating them as polynomial nonnegativity problems. This allows to state hierarchies of (sufficient) semidefinite conditions by applying (and proving) sophisticated Positivstellens\"atze. We also extend results on a solitary sufficient condition for containment of spectrahedra coming from the polyhedral situation as well as connections to the theory of (completely) positive linear maps.
Preserving Non-Null with Suslin+ forcing
Jakob Kellner
Mathematics , 2002, DOI: 10.1007/s00153-006-0008-0
Abstract: We introduce the notion of effective Axiom A and use it to show that some popular tree forcings are Suslin+. We introduce transitive nep and present a simplified version of Shelah's "preserving a little implies preserving much": If I is a Suslin ccc ideal (e.g. Lebesgue-null or meager) and P is a transitive nep forcing (e.g. P is Suslin+) and P doesn't make any I-positive Borel set small, then P doesn't make any I-positive set small.
Non-elementary proper forcing
Jakob Kellner
Mathematics , 2009,
Abstract: We introduce a simplified framework for ord-transitive models and Shelah's non elementary proper (nep) theory. We also introduce a new construction for the countable support nep iteration.
Update on the natural history of intracranial atherosclerotic disease: A critical review
Ricardo J Komotar, Christopher P Kellner, Daniel M Raper, Dorothea Strozyk, Randall T Higashida, Philip M Meyers
World Journal of Radiology , 2010,
Abstract: Intracranial atherosclerotic disease (ICAD) contributes to a significant number of ischemic strokes. There is debate in the recent literature concerning the impact of the location of stenosis in ICAD on outcome. Some reports have suggested that disease processes and outcomes vary by vessel location, potentially altering the natural history and indications for intervention. Here we have performed a comprehensive, critical review of the natural history of ICAD by vessel in an attempt to assess the differences in disease specific to each of the vascular territories. Our assessment concludes that only minor differences exist between patients with different vessels affected in vessel-specific ICAD. We have found that middle cerebral artery disease confers a lower mortality than vessel-specific ICAD in other intracranial vessels, asymptomatic disease follows a more benign course than symptomatic disease, and that plaque progression or the detection of microemboli on transcranial Doppler may predict poor outcome. Given the expanding indications for treatment of ICAD and rapidly developing endovascular techniques to confront this disease, a thorough understanding of the natural history of ICAD aids the interventional neuroradiologist in determining when to treat and how to predict outcome in this patient population.
Forest Canopy Gap Distributions in the Southern Peruvian Amazon
Gregory P. Asner, James R. Kellner, Ty Kennedy-Bowdoin, David E. Knapp, Christopher Anderson, Roberta E. Martin
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0060875
Abstract: Canopy gaps express the time-integrated effects of tree failure and mortality as well as regrowth and succession in tropical forests. Quantifying the size and spatial distribution of canopy gaps is requisite to modeling forest functional processes ranging from carbon fluxes to species interactions and biological diversity. Using high-resolution airborne Light Detection and Ranging (LiDAR), we mapped and analyzed 5,877,937 static canopy gaps throughout 125,581 ha of lowland Amazonian forest in Peru. Our LiDAR sampling covered a wide range of forest physiognomies across contrasting geologic and topographic conditions, and on depositional floodplain and erosional terra firme substrates. We used the scaling exponent of the Zeta distribution (λ) as a metric to quantify and compare the negative relationship between canopy gap frequency and size across sites. Despite variable canopy height and forest type, values of λ were highly conservative (λ mean = 1.83, s = 0.09), and little variation was observed regionally among geologic substrates and forest types, or at the landscape level comparing depositional-floodplain and erosional terra firme landscapes. λ-values less than 2.0 indicate that these forests are subjected to large gaps that reset carbon stocks when they occur. Consistency of λ-values strongly suggests similarity in the mechanisms of canopy failure across a diverse array of lowland forests in southwestern Amazonia.
Computational Fluid Dynamics and Its Impact on Flow Measurements Using Phase-Contrast MR-Angiography  [PDF]
Claus Kiefer, Frauke Kellner-Weldon
Open Journal of Medical Imaging (OJMI) , 2012, DOI: 10.4236/ojmi.2012.21004
Abstract: Rationale and Objectives: Computational fluid dynamic (CFD) simulations are discussed with respect to their potential for quality assurance of flow quantification using commercial software for the evaluation of magnetic resonance phase contrast angiography (PCA) data. Materials and Methods: Magnetic resonance phase contrast angiography data was evaluated with the Nova software. CFD simulations were performed on that part of the vessel system where the flow behavior was unexpected or non-reliable. The CFD simulations were performed with in-house written software. Results: The numerical CFD calculations demonstrated that under reasonable boundary conditions, defined by the PCA velocity values, the flow behavior within the critical parts of the vessel system can be correctly reproduced. Conclusion: CFD simulations are an important extension to commercial flow quantification tools with regard to quality assurance.
The Improvement of Mental Rotation Performance in Second Graders after Creative Dance Training  [PDF]
Petra Jansen, Jan Kellner, Cornelia Rieder
Creative Education (CE) , 2013, DOI: 10.4236/ce.2013.46060

The study presented here investigated the influence of creative dance training on mental rotation performance. Two groups of second graders solved a paper-pencil mental rotation test and a motor performance test. Afterwards one group received five weeks of normal physical education lessons, while the other group received five weeks of creative dance training. At the end of the training period all children solved the mental rotation again. The results show that the dance-training group improved their mental rotation performance more than the physical education group. Further studies should investigate whether this positive effect of creative dance training transfers to cognitive, social, and emotional skills, such as a possible enhancement of self-esteem.

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