7,230 research outputs found
On the Perturbations of Viscous Rotating Newtonian Fluids
The perturbations of weakly-viscous, barotropic, non-self-gravitating,
Newtonian rotating fluids are analyzed via a single partial differential
equation. The results are then used to find an expression for the
viscosity-induced normal-mode complex eigenfrequency shift, with respect to the
case of adiabatic perturbations. However, the effects of viscosity are assumed
to have been incorporated in the unperturbed (equilibrium) model. This paper is
an extension of the normal-mode formalism developed by Ipser & Lindblom for
adiabatic pulsations of purely-rotating perfect fluids. The formulas derived
are readily applicable to the perturbations of thin and thick accretion disks.
We provide explicit expressions for thin disks, employing results from previous
relativistic analyses of adiabatic normal modes of oscillation. In this case,
we find that viscosity causes the fundamental p- and g- modes to grow while the
fundamental c-mode could have either sign of the damping rate.Comment: Accepted for publication by The Astrophysical Journal. 11 pages, no
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Design Principles for Sparse Matrix Multiplication on the GPU
We implement two novel algorithms for sparse-matrix dense-matrix
multiplication (SpMM) on the GPU. Our algorithms expect the sparse input in the
popular compressed-sparse-row (CSR) format and thus do not require expensive
format conversion. While previous SpMM work concentrates on thread-level
parallelism, we additionally focus on latency hiding with instruction-level
parallelism and load-balancing. We show, both theoretically and experimentally,
that the proposed SpMM is a better fit for the GPU than previous approaches. We
identify a key memory access pattern that allows efficient access into both
input and output matrices that is crucial to getting excellent performance on
SpMM. By combining these two ingredients---(i) merge-based load-balancing and
(ii) row-major coalesced memory access---we demonstrate a 4.1x peak speedup and
a 31.7% geomean speedup over state-of-the-art SpMM implementations on
real-world datasets.Comment: 16 pages, 7 figures, International European Conference on Parallel
and Distributed Computing (Euro-Par) 201
On the common origin of the AB Dor moving group and the Pleiades cluster
AB Dor is the nearest identified moving group. As with other such groups, the
age is important for understanding of several key questions. It is important,
for example, in establishing the origin of the group and also in comparative
studies of the properties of planetary systems, eventually surrounding some of
the AB Dor group members, with those existing in other groups. For AB Dor two
rather different estimates for its age have been proposed: a first one, of the
order of 50 Myr, by Zuckerman and coworkers from a comparison with
Tucana/Horologium moving group and a second one of about 100-125 Myr by Luhman
and coworkers from color-magnitude diagrams (CMD). Using this last value and
the closeness in velocity space of AB Dor and the Pleiades galactic cluster,
Luhman and coworkers suggested coevality for these systems. Because strictly
speaking such a closeness does not still guarantee coevality, here we address
this problem by computing and comparing the full 3D orbits of AB Dor, Pleiades,
alpha Persei and IC 2602. The latter two open clusters have estimated ages of
about 85-90 Myr and 50 Myr. The resulting age 119 20 Myr is consistent
with AB Dor and Pleiades being coeval. Our solution and the scenario of open
cluster formation proposed by Kroupa and collaborators suggest that the AB Dor
moving group may be identified with the expanding subpopulation (Group I)
present in this scenario. We also discuss other related aspects as iron and
lithium abundances, eventual stellar mass segregation during the formation of
the systems and possible fraction of debris discs in AB Dor group.Comment: 11 pages, 5 figures and 2 table
Use of a Simulation Model to Develop Feeding Strategies for Cattle at Pasture in Small Scale Dairy Farming Systems in the Highlands of Central Mexico: Methodological Frame Work
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Morphological Estimation of Cellularity on Neo-Adjuvant Treated Breast Cancer Histological Images
This paper describes a methodology that extracts key morphological features from histological breast cancer images in order to automatically assess Tumour Cellularity (TC) in Neo-Adjuvant treatment (NAT) patients. The response to NAT gives information on therapy efficacy and it is measured by the residual cancer burden index, which is composed of two metrics: TC and the assessment of lymph nodes. The data consist of whole slide images (WSIs) of breast tissue stained with Hematoxylin and Eosin (H&E) released in the 2019 SPIE Breast Challenge. The methodology proposed is based on traditional computer vision methods (K-means, watershed segmentation, Otsuâs binarisation, and morphological operations), implementing colour separation, segmentation, and feature extraction. Correlation between morphological features and the residual TC after a NAT treatment was examined. Linear regression and statistical methods were used and twenty-two key morphological parameters from the nuclei, epithelial region, and the full image were extracted. Subsequently, an automated TC assessment that was based on Machine Learning (ML) algorithms was implemented and trained with only selected key parameters. The methodology was validated with the score assigned by two pathologists through the intra-class correlation coefficient (ICC). The selection of key morphological parameters improved the results reported over other ML methodologies and it was very close to deep learning methodologies. These results are encouraging, as a traditionally-trained ML algorithm can be useful when limited training data are available preventing the use of deep learning approaches
Trigonometry of 'complex Hermitian' type homogeneous symmetric spaces
This paper contains a thorough study of the trigonometry of the homogeneous
symmetric spaces in the Cayley-Klein-Dickson family of spaces of 'complex
Hermitian' type and rank-one. The complex Hermitian elliptic CP^N and
hyperbolic CH^N spaces, their analogues with indefinite Hermitian metric and
some non-compact symmetric spaces associated to SL(N+1,R) are the generic
members in this family. The method encapsulates trigonometry for this whole
family of spaces into a single "basic trigonometric group equation", and has
'universality' and '(self)-duality' as its distinctive traits. All previously
known results on the trigonometry of CP^N and CH^N follow as particular cases
of our general equations. The physical Quantum Space of States of any quantum
system belongs, as the complex Hermitian space member, to this parametrised
family; hence its trigonometry appears as a rather particular case of the
equations we obtain.Comment: 46 pages, LaTe
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Estimation of cellularity in tumours treated with Neoadjuvant therapy: A comparison of Machine Learning algorithms
This paper describes a method for residual tumour cellularity (TC) estimation in Neoadjuvant treatment (NAT) of advanced breast cancer. This is determined manually by visual inspection by a radiologist, then an automated computation will contribute to reduce time workload and increase precision and accuracy. TC is estimated as the ratio of tumour area by total image area estimated after the NAT. The method proposed computes TC by using machine learning techniques trained with information on morphological parameters of segmented nuclei in order to classify regions of the image as tumour or normal. The data is provided by the 2019 SPIE Breast challenge, which was proposed to develop automated TC computation algorithms. Three algorithms were implemented: Support Vector Machines, Nearest K-means and Adaptive Boosting (AdaBoost) decision trees. Performance based on accuracy is compared and evaluated and the best result was obtained with Support Vector Machines. Results obtained by the methods implemented were submitted during ongoing challenge with a maximum of 0.76 of prediction probability of success
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