198 research outputs found
Scalable Parallel Numerical Constraint Solver Using Global Load Balancing
We present a scalable parallel solver for numerical constraint satisfaction
problems (NCSPs). Our parallelization scheme consists of homogeneous worker
solvers, each of which runs on an available core and communicates with others
via the global load balancing (GLB) method. The parallel solver is implemented
with X10 that provides an implementation of GLB as a library. In experiments,
several NCSPs from the literature were solved and attained up to 516-fold
speedup using 600 cores of the TSUBAME2.5 supercomputer.Comment: To be presented at X10'15 Worksho
The Petersen--Wilhelm conjecture on principal bundles
This paper studies Cheeger deformations on
principal bundles to obtain conditions for positive sectional curvature
submersion metrics. We conclude, in particular, a stronger version of the
Petersen--Wilhelm fiber dimension conjecture to the class of principal bundles.
We prove any principal bundle over a positively curved base admits a metric
of positive sectional curvature if, and only if, the submersion is fat, in
particular, . The proof combines the concept of ``good triples''
due to Munteanu and Tapp \cite{tappmunteanu2}, with a Chaves--Derdzisnki--Rigas
type condition to nonnegative curvature. Additionally, the conjecture is
verified for other classes of submersions.Comment: v4. follows anonymous referee suggestions to improve the exposition
significantly. Proofs were revised and simplified, and further results were
added. Comments are welcom
The complete dynamics description of positively curved metrics in the Wallach flag manifold
The family of invariant Riemannian manifolds in the Wallach flag manifold
is described by three parameters of
positive real numbers. By restricting such a family of metrics in the
\emph{tetrahedron} , in this paper, we describe all
regions admitting metrics with curvature properties
varying from positive sectional curvature to positive scalar curvature,
including positive intermediate curvature notion's. We study the dynamics of
such regions under the \emph{projected Ricci flow} in the plane ,
concluding sign curvature maintenance and escaping. In addition, we obtain some
results for positive intermediate Ricci curvature for a path of metrics on
fiber bundles over , further studying its
evolution under the Ricci flow on the base.Comment: 15 pages, 12 figures. arXiv admin note: text overlap with
arXiv:2305.0611
Predictors of affective commitment in Romanian educational organizations
The aim of this study consists in the analysis of relationship
between the level of psychological contract fulfillment, affective commitment and the satisfaction level of teachersâ needs. Data were collected from 168 teachers, 89.3% are women, 10.7% are men with age between 19 and 61 years. A cross-sectional survey research was used. All 4 hypotheses of the research were confirmed. The data shows that affective commitment has two significant predictors (degree of psychological needs satisfaction and intensity of psychological contract) on a sample of 168 teachers from preuniversity education. In our study, the need for autonomy dimension is approached in correlation with affective commitment and the fulfillmentâs degree of psychological contract. The autonomy feeling at workplace is extensively analysed in self-determination theory; the sense of choice for your own action in order to get a higher performance at workplace seems to become a major point of research in organizational psychology and human
resource management. The theoretical and applied underpinnings of this research are detailed in the conclusions
LINVIEW: Incremental View Maintenance for Complex Analytical Queries
Many analytics tasks and machine learning problems can be naturally expressed
by iterative linear algebra programs. In this paper, we study the incremental
view maintenance problem for such complex analytical queries. We develop a
framework, called LINVIEW, for capturing deltas of linear algebra programs and
understanding their computational cost. Linear algebra operations tend to cause
an avalanche effect where even very local changes to the input matrices spread
out and infect all of the intermediate results and the final view, causing
incremental view maintenance to lose its performance benefit over
re-evaluation. We develop techniques based on matrix factorizations to contain
such epidemics of change. As a consequence, our techniques make incremental
view maintenance of linear algebra practical and usually substantially cheaper
than re-evaluation. We show, both analytically and experimentally, the
usefulness of these techniques when applied to standard analytics tasks. Our
evaluation demonstrates the efficiency of LINVIEW in generating parallel
incremental programs that outperform re-evaluation techniques by more than an
order of magnitude.Comment: 14 pages, SIGMO
Tractography in the presence of multiple sclerosis lesions
Accurate anatomical localisation of specific white matter tracts and the quantification of their tract-specific microstructural damage in conditions such as multiple sclerosis (MS) can contribute to a better understanding of symptomatology, disease evolution and intervention effects. Diffusion MRI-based tractography is being used increasingly to segment white matter tracts as regions-of-interest for subsequent quantitative analysis. Since MS lesions can interrupt the tractography algorithmâs tract reconstruction, clinical studies frequently resort to atlas-based approaches, which are convenient but ignorant to individual variability in tract size and shape. Here, we revisit the problem of individual tractography in MS, comparing tractography algorithms using: (i) The diffusion tensor framework; (ii) constrained spherical deconvolution (CSD); and (iii) damped Richardson-Lucy (dRL) deconvolution. Firstly, using simulated and in vivo data from 29 MS patients and 19 healthy controls, we show that the three tracking algorithms respond differentially to MS pathology. While the tensor-based approach is unable to deal with crossing fibres, CSD produces spurious streamlines, in particular in tissue with high fibre loss and low diffusion anisotropy. With dRL, streamlines are increasingly interrupted in pathological tissue. Secondly, we demonstrate that despite the effects of lesions on the fibre orientation reconstruction algorithms, fibre tracking algorithms are still able to segment tracts that pass through areas with a high prevalence of lesions. Combining dRL-based tractography with an automated tract segmentation tool on data from 131 MS patients, the cortico-spinal tracts and arcuate fasciculi could be reconstructed in more than 90% of individuals. Comparing tract-specific microstructural parameters (fractional anisotropy, radial diffusivity and magnetisation transfer ratio) in individually segmented tracts to those from a tract probability map, we show that there is no systematic disease-related bias in the individually reconstructed tracts, suggesting that lesions and otherwise damaged parts are not systematically omitted during tractography. Thirdly, we demonstrate modest anatomical correspondence between the individual and tract probability-based approach, with a spatial overlap between 35 and 55%. Correlations between tract-averaged microstructural parameters in individually segmented tracts and the probability-map approach ranged between
r=.53
(
p<.001
) for radial diffusivity in the right cortico-spinal tract and
r=.97
(
p<.001
) for magnetisation transfer ratio in the arcuate fasciculi. Our results show that MS white matter lesions impact fibre orientation reconstructions but this does not appear to hinder the ability to anatomically reconstruct white matter tracts in MS. Individual tract segmentation in MS is feasible on a large scale and could prove a powerful tool for investigating diagnostic and prognostic markers
Wind Data Mining by Kohonen Neural Networks
Time series of Circulation Weather Type (CWT), including daily averaged wind direction and vorticity, are self-classified by similarity using Kohonen Neural Networks (KNN). It is shown that KNN is able to map by similarity all 7300 five-day CWT sequences during the period of 1975â94, in London, United Kingdom. It gives, as a first result, the most probable wind sequences preceding each one of the 27 CWT Lamb classes in that period. Inversely, as a second result, the observed diffuse correlation between both five-day CWT sequences and the CWT of the 6(th) day, in the long 20-year period, can be generalized to predict the last from the previous CWT sequence in a different test period, like 1995, as both time series are similar. Although the average prediction error is comparable to that obtained by forecasting standard methods, the KNN approach gives complementary results, as they depend only on an objective classification of observed CWT data, without any model assumption. The 27 CWT of the Lamb Catalogue were coded with binary three-dimensional vectors, pointing to faces, edges and vertex of a âwind-cube,â so that similar CWT vectors were close
A Comparison of Wood Density between Classical Cremonese and Modern Violins
Classical violins created by Cremonese masters, such as Antonio Stradivari and Giuseppe Guarneri Del Gesu, have become the benchmark to which the sound of all violins are compared in terms of their abilities of expressiveness and projection. By general consensus, no luthier since that time has been able to replicate the sound quality of these classical instruments. The vibration and sound radiation characteristics of a violin are determined by an instrument's geometry and the material properties of the wood. New test methods allow the non-destructive examination of one of the key material properties, the wood density, at the growth ring level of detail. The densities of five classical and eight modern violins were compared, using computed tomography and specially developed image-processing software. No significant differences were found between the median densities of the modern and the antique violins, however the density difference between wood grains of early and late growth was significantly smaller in the classical Cremonese violins compared with modern violins, in both the top (Spruce) and back (Maple) plates (pâ=â0.028 and 0.008, respectively). The mean density differential (SE) of the top plates of the modern and classical violins was 274 (26.6) and 183 (11.7) gram/liter. For the back plates, the values were 128 (2.6) and 115 (2.0) gram/liter. These differences in density differentials may reflect similar changes in stiffness distributions, which could directly impact vibrational efficacy or indirectly modify sound radiation via altered damping characteristics. Either of these mechanisms may help explain the acoustical differences between the classical and modern violins
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