10,855 research outputs found
Principal components analysis in the space of phylogenetic trees
Phylogenetic analysis of DNA or other data commonly gives rise to a
collection or sample of inferred evolutionary trees. Principal Components
Analysis (PCA) cannot be applied directly to collections of trees since the
space of evolutionary trees on a fixed set of taxa is not a vector space. This
paper describes a novel geometrical approach to PCA in tree-space that
constructs the first principal path in an analogous way to standard linear
Euclidean PCA. Given a data set of phylogenetic trees, a geodesic principal
path is sought that maximizes the variance of the data under a form of
projection onto the path. Due to the high dimensionality of tree-space and the
nonlinear nature of this problem, the computational complexity is potentially
very high, so approximate optimization algorithms are used to search for the
optimal path. Principal paths identified in this way reveal and quantify the
main sources of variation in the original collection of trees in terms of both
topology and branch lengths. The approach is illustrated by application to
simulated sets of trees and to a set of gene trees from metazoan (animal)
species.Comment: Published in at http://dx.doi.org/10.1214/11-AOS915 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
An L^2-Index Theorem for Dirac Operators on S^1 * R^3
An expression is found for the -index of a Dirac operator coupled to a
connection on a vector bundle over . Boundary
conditions for the connection are given which ensure the coupled Dirac operator
is Fredholm. Callias' index theorem is used to calculate the index when the
connection is independent of the coordinate on . An excision theorem due
to Gromov, Lawson, and Anghel reduces the index theorem to this special case.
The index formula can be expressed using the adiabatic limit of the
-invariant of a Dirac operator canonically associated to the boundary. An
application of the theorem is to count the zero modes of the Dirac operator in
the background of a caloron (periodic instanton).Comment: 14 pages, Latex, to appear in the Journal of Functional Analysi
Testing Observational Techniques with 3D MHD Jets in Clusters
Observations of X-ray cavities formed by powerful jets from AGN in galaxy
cluster cores are commonly used to estimate the mechanical luminosity of these
sources. We test the reliability of observationally measuring this power with
synthetic X-ray observations of 3-D MHD simulations of jets in a galaxy cluster
environment. We address the role that factors such as jet intermittency and
orientation of the jets on the sky have on the reliability of observational
measurements of cavity enthalpy and age. An estimate of the errors in these
quantities can be made by directly comparing ``observationally'' derived values
with values from the simulations. In our tests, cavity enthalpy, age and
mechanical luminosity derived from observations are within a factor of two of
the simulation values.Comment: 4 pages, 3 figures; to appear in proceedings of The Monster's Fiery
Breath: Feedback in Galaxies, Groups, and Clusters (AIP conference series
Real-World Repetition Estimation by Div, Grad and Curl
We consider the problem of estimating repetition in video, such as performing
push-ups, cutting a melon or playing violin. Existing work shows good results
under the assumption of static and stationary periodicity. As realistic video
is rarely perfectly static and stationary, the often preferred Fourier-based
measurements is inapt. Instead, we adopt the wavelet transform to better handle
non-static and non-stationary video dynamics. From the flow field and its
differentials, we derive three fundamental motion types and three motion
continuities of intrinsic periodicity in 3D. On top of this, the 2D perception
of 3D periodicity considers two extreme viewpoints. What follows are 18
fundamental cases of recurrent perception in 2D. In practice, to deal with the
variety of repetitive appearance, our theory implies measuring time-varying
flow and its differentials (gradient, divergence and curl) over segmented
foreground motion. For experiments, we introduce the new QUVA Repetition
dataset, reflecting reality by including non-static and non-stationary videos.
On the task of counting repetitions in video, we obtain favorable results
compared to a deep learning alternative
Modelling Glacial Lake Outburst Flood Discharge in the Rio Huemules, Northern Patagonian Icefield
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Characterization of lipoprotein composition and function in pediatric psoriasis reveals a more atherogenic profile
Garnet–monazite rare earth element relationships in sub-solidus metapelites: a case study from Bhutan
A key aim of modern metamorphic geochronology is to constrain precise and accurate rates and timescales of tectonic processes. One promising approach in amphibolite and granulite-facies rocks links the geochronological information recorded in zoned accessory phases such as monazite to the pressure–temperature information recorded in zoned major rock-forming minerals such as garnet. Both phases incorporate rare earth elements (REE) as they crystallize and their equilibrium partitioning behaviour potentially provides a useful way of linking time to temperature. We report REE data from sub-solidus amphibolite-facies metapelites from Bhutan, where overlapping ages, inclusion relationships and Gd/Lu ratios suggest that garnet and monazite co-crystallized. The garnet–monazite REE relationships in these samples show a steeper pattern across the heavy (H)REE than previously reported. The difference between our dataset and the previously reported data may be due to a temperature-dependence on the partition coefficients, disequilibrium in either dataset, differences in monazite chemistry or the presence or absence of a third phase that competed for the available REE during growth. We urge caution against using empirically-derived partition coefficients from natural samples as evidence for, or against, equilibrium of REE-bearing phases until monazite–garnet partitioning behaviour is better constrained
Intention to adopt Cloud-based e-Learning in Nigerian Educational Institutions
Institutions of higher education must utilize innovative information and communication technologies for teaching in Nigeria. Thus, cloud-based e-Learning is essential to curtail educational challenges such as limited infrastructure, funds, and student-to-lecturer ratio. Recently, there has been widespread enthusiasm regarding Cloud computing for e-Learning; adopting and strategically utilizing these technologies remains a significant challenge for higher education institutions. Furthermore, there is a limited understanding of how cloud-based e-learning can transform Nigerian educational establishments. Cloud-based e-Learning systems' technological components have been the subject of numerous study studies, but little is known about how they operate from an organizational perspective. Accordingly, using the Technology-Organization-Environment theory, the goal of this study is to investigate the variables that influence the adoption of cloud-based e-learning. The findings of the research show that relative benefit and competing pressure have a big impact on whether cloud-based e-learning is adopted. However, compatibility, security, and top management commitment do not appear to be significant determinants. These findings will help Nigerian education institutions, the ministry of education, and practitioners to understand the critical factors for adopting this technology for improved education
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