Universidad del Norte, Colombia

About: Universidad del Norte, Colombia is a education organization based out in Barranquilla, Colombia. It is known for research contribution in the topics: Population & Context (language use). The organization has 3562 authors who have published 4355 publications receiving 37861 citations. The organization is also known as: University of the North, Colombia & Uninorte.

A parallel ensemble Kalman filter implementation based on modified Cholesky decomposition

Abstract: This paper discusses an efficient parallel implementation of the ensemble Kalman filter based on the modified Cholesky decomposition. The proposed implementation starts with decomposing the domain into sub-domains. In each sub-domain a sparse estimation of the inverse background error covariance matrix is computed via a modified Cholesky decomposition; the estimates are computed concurrently on separate processors. The sparsity of this estimator is dictated by the conditional independence of model components for some radius of influence. Then, the assimilation step is carried out in parallel without the need of inter-processor communication. Once the local analysis states are computed, the analysis sub-domains are mapped back onto the global domain to obtain the analysis ensemble. Computational experiments are performed using the Atmospheric General Circulation Model (SPEEDY) with the T-63 resolution on the Blueridge cluster at Virginia Tech. The number of processors used in the experiments ranges from 96 to 2,048. The proposed implementation outperforms in terms of accuracy the well-known local ensemble transform Kalman filter (LETKF) for all the model variables. The computational time of the proposed implementation is similar to that of the parallel LETKF method (where no covariance estimation is performed). Finally, for the largest number of processors, the proposed parallel implementation is 400 times faster than the serial version of the proposed method.

Connective Tissue Nevi: A Review of the Literature

Abstract: Connective tissue nevi (CTN) are hamartomas of the dermis, with the 3 main components being collagen, elastin, and proteoglycans. Each subtype can present as a solitary lesion or multiple lesions. They could present as part of systemic diseases or inherited disorders. This article provides a comprehensive literature review of the different types of CTN, their clinical presentations, associations, and treatment options. Treatment options for 56 lesions were reviewed. Fifty-two percent of lesions were present in males, and the age range at the time of presentation was wide (1.6-80 years). Management varied according to CTN subtypes. Most lesions (14) received topical or intralesional treatment with corticosteroids, followed by surgical removal of lesions (12), whereas the remaining lesions were clinically monitored.

Culture of Gracilaria sp. in outdoor tanks: productivity

Abstract: Gracilaria is one of the main commercial seaweeds exploited along the Chilean coast. In 1983, 10.6 x 105 tonnes of this alga were exported as raw material, returning a revenue of 7 x 106 dollars (Servicio Nacional de Pesca, 1983). Gracilaria has been planted on sandy bottoms in protected bays with normally calm water using uncomplicated methods. The plantations have been affected by storms and currents which cut portions of the thalli or completely bury the plants in the sand (Santelices et al., 1984). Ocean currents may deposit the seaweeds on beaches distant from their original locations. The steepness of shores and unpredictability of water movements affect most of the highly productive Chilean coast, restricting possible seaweed cultivation to only a few bays. An alternative method of culture for this alga which avoids natural stresses involves open-circuit outdoor tanks. We now report on 14 months of experience in culture of Gracilaria in tanks where light and the flow of water and air were controlled, and where productivity of Gracilaria was routinely measured under varied conditions.