Compressed Multi-Row Storage Format for Sparse Matrices on Graphics Processing Units

A new format for storing sparse matrices is proposed for efficient sparse matrix-vector (SpMV) product calculation on modern graphics processing units (GPUs). This format extends the standard compressed row storage (CRS) format and can be quickly converted to and from it. Computational performance of two SpMV kernels for the new format is determined for over 130 sparse matrices on Fermi-class and Kepler-class GPUs and compared with that of five existing generic algorithms and industrial implementations, including Nvidia cuSparse CSR and HYB kernels. We found the speedup of up to $\approx 60$ over the best of the five alternative kernels

How to Calculate Tortuosity Easily?

Tortuosity is one of the key parameters describing the geometry and transport properties of porous media. It is defined either as an average elongation of fluid paths or as a retardation factor that measures the resistance of a porous medium to the flow. However, in contrast to a retardation factor, an average fluid path elongation is difficult to compute numerically and, in general, is not measurable directly in experiments. We review some recent achievements in bridging the gap between the two formulations of tortuosity and discuss possible method of numerical and an experimental measurements of the tortuosity directly from the fluid velocity field.Comment: 6 pages, 8 figure

Power exponential velocity distributions in disordered porous media

Velocity distribution functions link the micro- and macro-level theories of fluid flow through porous media. Here we study them for the fluid absolute velocity and its longitudinal and lateral components relative to the macroscopic flow direction in a model of a random porous medium. We claim that all distributions follow the power exponential law controlled by an exponent $\gamma$ and a shift parameter $u_0$ and examine how these parameters depend on the porosity. We find that $\gamma$ has a universal value $1/2$ at the percolation threshold and grows with the porosity, but never exceeds 2.Comment: 4 pages, 3 figure

Self-reported psychosocial health in obese patients before and after weight loss

Psychosocial profiles were examined in 255 morbidly obese patients attending a hospital service offering access to standard weight loss therapies. 129 patients were reassessed after at least 6-month follow-up. At baseline, 51.8% and 32.7% of patients, respectively, had evidence of anxiety and depressive disorders, 24% had severe impairments in self esteem, and 29.7% had an increased risk of eating disorders. At follow-up, weight loss from baseline was significant in all 3 therapies: diet only is 0.74±1.8 kg; pharmacotherapy is 6.7±4.2 kg; and surgery is 20.1±13.6 kg. Anxiety scores improved in all three groups (P<.05). Patients having pharmacotherapy or surgery had significant improvements in physical and work function and public distress compared to those having dietary treatment only (P<.05). Our observational data suggest that weight management services can lead to psychosocial benefit in morbidly obese patients. Well-designed studies are necessary to examine the link between weight loss and emotional health

Wall Orientation and Shear Stress in the Lattice Boltzmann Model

The wall shear stress is a quantity of profound importance for clinical diagnosis of artery diseases. The lattice Boltzmann is an easily parallelizable numerical method of solving the flow problems, but it suffers from errors of the velocity field near the boundaries which leads to errors in the wall shear stress and normal vectors computed from the velocity. In this work we present a simple formula to calculate the wall shear stress in the lattice Boltzmann model and propose to compute wall normals, which are necessary to compute the wall shear stress, by taking the weighted mean over boundary facets lying in a vicinity of a wall element. We carry out several tests and observe an increase of accuracy of computed normal vectors over other methods in two and three dimensions. Using the scheme we compute the wall shear stress in an inclined and bent channel fluid flow and show a minor influence of the normal on the numerical error, implying that that the main error arises due to a corrupted velocity field near the staircase boundary. Finally, we calculate the wall shear stress in the human abdominal aorta in steady conditions using our method and compare the results with a standard finite volume solver and experimental data available in the literature. Applications of our ideas in a simplified protocol for data preprocessing in medical applications are discussed.Comment: 9 pages, 11 figure