Kalkulo AS

Fornebu, Norway

Kalkulo AS

Fornebu, Norway
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Kriener B.,University of Texas at Austin | Kriener B.,Norwegian University of Life Sciences | Enger H.,Norwegian University of Life Sciences | Enger H.,Kalkulo AS | And 5 more authors.
Frontiers in Computational Neuroscience | Year: 2014

Random networks of integrate-and-fire neurons with strong current-based synapses can, unlike previously believed, assume stable states of sustained asynchronous and irregular firing, even without external random background or pacemaker neurons. We analyze the mechanisms underlying the emergence, lifetime and irregularity of such self-sustained activity states. We first demonstrate how the competition between the mean and the variance of the synaptic input leads to a non-monotonic firing-rate transfer in the network. Thus, by increasing the synaptic coupling strength, the system can become bistable: In addition to the quiescent state, a second stable fixed-point at moderate firing rates can emerge by a saddle-node bifurcation. Inherently generated fluctuations of the population firing rate around this non-trivial fixed-point can trigger transitions into the quiescent state. Hence, the trade-off between the magnitude of the population-rate fluctuations and the size of the basin of attraction of the non-trivial rate fixed-point determines the onset and the lifetime of self-sustained activity states. During self-sustained activity, individual neuronal activity is moreover highly irregular, switching between long periods of low firing rate to short burst-like states. We show that this is an effect of the strong synaptic weights and the finite time constant of synaptic and neuronal integration, and can actually serve to stabilize the self-sustained state. © 2014 Kriener, Enger, Tetzlaff, Plesser, Gewaltig and Einevoll.


Beitnes J.O.,University of Oslo | Klaeboe L.G.,University of Oslo | Karlsen J.S.,Kalkulo AS | Urheim S.,University of Oslo
International Journal of Cardiovascular Imaging | Year: 2015

The aim of the present study was to test the feasibility of analyzing 3D ultrasound data on a novel holographic display. An increasing number of mini-invasive procedures for mitral valve repair require more effective visualization to improve patient safety and speed of procedures. A novel 3D holographic display has been developed and may have the potential to guide interventional cardiac procedures in the near future. Forty patients with degenerative mitral valve disease were analyzed. All had complete 2D transthoracic (TTE) and transoesophageal (TEE) echocardiographic examinations. In addition, 3D TTE of the mitral valve was obtained and recordings were converted from the echo machine to the holographic screen. Visual inspection of the mitral valve during surgery or TEE served as the gold standard. 240 segments were analyzed by 2 independent observers. A total of 53 segments were prolapsing. The majority included P2 (31), the remaining located at A2 (8), A3 (6), P3 (5), P1 (2) and A1 (1). The sensitivity and specificity of the 3D display was 87 and 99 %, respectively (observer I), and for observer II 85 and 97 %, respectively. The accuracies and precisions were 96.7 and 97.9 %, respectively, (observer I), 94.3 and 88.2 % (observer II), and inter-observer agreement was 0.954 with Cohen’s Kappa 0.86. We were able to convert 3D ultrasound data to the holographic display. A very high accuracy and precision was shown, demonstrating the feasibility of analyzing 3D echo of the mitral valve on the holographic screen. © 2014, Springer Science+Business Media Dordrecht.


Said A.,Kalkulo AS | Moder C.,Kalkulo AS | Clark S.,Kalkulo AS | Abdelmalak M.M.,University of Oslo
Journal of African Earth Sciences | Year: 2015

Data from 23 wells were used to quantify the sedimentary budgets in the Tanzania coastal basin in order to unravel the uplift chronology of the sourcing area located in the East African Rift System. We quantified the siliciclastic sedimentary volumes preserved in the Tanzania coastal basin corrected for compaction and in situ (e.g., carbonates) production. We found that the drainage areas, which supplied sediments to this basin, were eroded in four episodes: (1) during the middle Jurassic, (2) during the Campanian-Palaeocene, (3) during the middle Eocene and (4) during the Miocene. Three of these high erosion and sedimentation periods are more likely related to uplift events in the East African Rift System and earlier rift shoulders and plume uplifts. Indeed, rapid cooling in the rift system and high denudation rates in the sediment source area are coeval with these recorded pulses. However, the middle Eocene pulse was synchronous with a fall in the sea level, a climatic change and slow cooling of the rift flanks and thus seems more likely due to climatic and eustatic variations. We show that the rift shoulders of the East African rift system have inherited their present relief from at least three epeirogenic uplift pulses of middle Jurassic, Campanian-Palaeocene, and Miocene ages. © 2015 Elsevier Ltd.


Gillberg T.,Simula Research Laboratory | Gillberg T.,Kalkulo AS | Sourouri M.,Simula Research Laboratory | Sourouri M.,University of Oslo | And 2 more authors.
Procedia Computer Science | Year: 2012

We present a novel method for 3D anisotropic front propagation and apply it to the simulation of geological folding. The new iterative algorithm has a simple structure and abundant parallelism, and is easily adapted to multithreaded architectures using OpenMP. Moreover, we have used the automated C-to-CUDA source code translator, Mint, to achieve greatly enhanced computing speed on GPUs. Both OpenMP and CUDA implementations have been tested and benchmarked on several examples of 3D geological folding. © 2012 Published by Elsevier Ltd.


Noack M.,Kalkulo AS | Noack M.,Simula Research Laboratory | Noack M.,University of Oslo
Journal of Computational Science | Year: 2015

Wave form modeling is used in a vast number of applications. Therefore, different methods have been developed that exhibit different strengths and weaknesses in accuracy, stability and computational cost. The latter remains a problem for most applications. Parallel programming has had a large impact on wave field modeling since the solution of the wave equation can be divided into independent steps. The finite difference solution of the wave equation is particularly suitable for GPU acceleration; however, one problem is the rather limited global memory current GPUs are equipped with. For this reason, most large-scale applications require multiple GPUs to be employed. This paper proposes a method to optimally distribute the workload on different GPUs by avoiding devices that are running idle. This is done by using a list of active sub-domains so that a certain sub-domain is activated only if the amplitude inside the sub-domain exceeds a given threshold. During the computation, every GPU checks if the sub-domain needs to be active. If not, the GPU can be assigned to another sub-domain. The method was applied to synthetic examples to test the accuracy and the efficiency of the method. The results show that the method offers a more efficient utilization of multi-GPU computer architectures. © 2015 The Author.


Gillberg T.,Simula Research Laboratory | Hjelle O.,Kalkulo AS | Bruaset A.M.,Simula Research Laboratory | Bruaset A.M.,University of Oslo
Computational Geosciences | Year: 2012

Motivated by the needs for creating fast and accurate models of complex geological scenarios, accuracy and efficiency of three stencils for the isotropic eikonal equation on rectangular grids are evaluated using a fast marching implementation. The stencils are derived by direct modelling of the wave front, resulting in new and valuable insight in terms of improved upwind and causality conditions. After introducing a method for generalising first-order upwind stencils to higher order, a new second-order diagonal stencil is presented. Similarly to the multistencil fast marching approach, the diagonal stencil makes use of nodes in the diagonal directions, whereas the traditional Godunov stencil uses solely edge-connected neighbours. The diagonal stencil uses nodes close to each other, reaching upwind, to get a more accurate estimate of the angle of incidence of the arriving wave front. Although the stencils are evaluated in a fast marching setting, they can be adapted to other efficient eikonal solvers. All first- and second-order stencils are evaluated in a range of tests. The first test case models a folded structure from the Zagros fold belt in Iran. The other test cases are constructed to investigate specific properties of the examined stencils. The numerical investigation considers convergence rates and CPU times for non-constant and constant speed first-arrival computations. In conclusion, the diagonal stencil is the most efficient and accurate of the three alternatives. © 2012 Springer Science+Business Media B.V.


Hjelle O.,Kalkulo AS | Petersen S.A.,Statoil | Bruaset A.M.,Simula Research Laboratory | Bruaset A.M.,University of Oslo
Mathematical Geosciences | Year: 2013

A numerical framework for modeling folds in structural geology is presented. This framework is based on a novel and recently published Hamilton-Jacobi formulation by which a continuum of layer boundaries of a fold is modeled as a propagating front. All the fold classes from the classical literature (parallel folds, similar folds, and other fold types with convergent and divergent dip isogons) are modeled in two and three dimensions as continua defined on a finite difference grid. The propagating front describing the fold geometry is governed by a static Hamilton-Jacobi equation, which is discretized by upwind finite differences and a dynamic stencil construction. This forms the basis of numerical solution by finite difference solvers such as fast marching and fast sweeping methods. A new robust and accurate scheme for initialization of finite difference solvers for the static Hamilton-Jacobi equation is also derived. The framework has been integrated in simulation software, and a numerical example is presented based on seismic data collected from the Karama Block in the North Makassar Strait outside Sulawesi. © 2013 International Association for Mathematical Geosciences.


Clark S.R.,Simula Research Laboratory | Skogseid J.,Statoil | Stensby V.,Kalkulo AS | Smethurst M.A.,Simula Research Laboratory | And 4 more authors.
Computers and Geosciences | Year: 2012

This paper presents the 4DPlates, an application designed to display high resolution data and reconstruct their positions in the geologic past. 4DPlates makes use of level of detail (LoD) grids with a 4-8 tree structure to store the data so only the required resolution for a particular viewpoint is used. This facility means that the user can interact with large data sets on the fly, achieving between 30 and 50 frames per second with a large test data set. The article presents the design and functionality of the application from view-dependent visualization to the ability to reconstruct data in the distant past. Finally, we apply the application in two geoscientific settings. In the first, we calculate the tectonic subsidence from sediment loading and test the variation of the sediment density to the resulting subsidence grid. Secondly, we examine two South Atlantic reconstructions and highlight minor differences between them visible in the closeness of the fit of the topographic grids. The application excels at providing an interactive manipulation of high resolution data, whether it be reconstructing the data, setting the lighting angle or vertical exaggeration, or modifying parameters in the underlying formulas. © 2012 Elsevier Ltd.


Gillberg T.,Kalkulo AS | Hjelle O.,Kalkulo AS | Bruaset A.M.,Kalkulo AS
74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources | Year: 2012

A 3D front propagation algorithm for the simulation of geological folding is presented. The algorithm is implemented on multicore and GPU architectures. Numerical experiments based on OpenMP show an almost perfect scaling. Using the automatic code translator Mint, Cuda code is created from seqential C code. On a GPU the Cuda code runs 67-95 times faster than sequential code, and allows large 3D grids to be computed at interactive times.


Said A.,Kalkulo AS | Moder C.,Kalkulo AS | Clark S.,Kalkulo AS | Ghorbal B.,Kalkulo AS
Journal of African Earth Sciences | Year: 2015

In this study, data from 41 wells were used to quantify the evolution of the sedimentary budget in the Southern Mozambique passive margin basin, with a high temporal resolution for the Cenozoic period. We found that the drainage areas, which supplied sediments to the Southern Mozambique Basin, were eroded in two episodes. The first, of Mid-Late Cretaceous in age, is concordant with both thermochronological datation and sedimentary fluxes estimated by other studies in the Namibian and South African and Northern Mozambique margins. This erosion episode ended when the African surface, as defined by Burke and Gunnel (2008), had become flat and low-lying over most of the South African Plateau by ~65. Ma. Carbonate sediment deposition became more important in the shallow waters of the Mozambique basin after that time. The second erosion episode began at ~23. Ma and is likely due to an uplift event of the North-eastern part of the South African Plateau. It seems that the Limpopo catchment and the whole area sourcing the studied basin have inherited their present relief from two epeirogenic uplift pulses of Late Cretaceous and Miocene ages. © 2015 Elsevier Ltd.

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