Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

The role of shear and elongation in the flow of solutions of semi-flexible polymers through porous media

Abstract: The rheological behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) and xanthan gum solutions has been characterized in simple shear flow, opposed-jets flow, and flow through porous media. Both polymers exhibit shear thinning in simple shear flow and apparent shear thinning in flow through porous media. Analysis of the results shows there is a direct correspondence between shear viscosities determined in simple shear experiments and apparent viscosities in porous media flow at relatively low shear rates. At high shear rates the extensional component of the flow in porous media appreciably increases the apparent viscosity over the simple shear values. This increase is shown to correlate with results obtained in opposed-jets experiments, and is attributed to formation of transient entanglements.

Dynamic Effects of CYP2D6 Genetic Variants in a Set of Poor Metaboliser Patients with Infiltrating Ductal Cancer Under Treatment with Tamoxifen.

Abstract: Breast cancer is a group of multigenic diseases. It is the most common cancer diagnosed among women worldwide and is often treated with tamoxifen. Tamoxifen is catalysed by cytochrome P450 2D6 (CYP2D6), and inter-individual variations in the enzyme due to single nucleotide polymorphisms (SNPs) could alter enzyme activity. We evaluated SNPs in patients from Colombia in South America who were receiving tamoxifen treatment for breast cancer. Allelic diversity in the CYP2D6 gene was found in the studied population, with two patients displaying the poor-metaboliser phenotype. Molecular dynamics and trajectory analyses were performed for CYP2D6 from these two patients, comparing it with the common allelic form (CYP2D6*1). Although we found no significant structural change in the protein, its dynamics differ significantly from those of CYP2D6*1, the effect of such differential dynamics resulting in an inefficient enzyme with serious implications for tamoxifen-treated patients, increasing the risk of disease relapse and ineffective treatment.

Toward a Systemic Notion of Information: Practical Consequences

Abstract: Introduction The meaning of "information systems" has been growing in diversity and complexity. Several authors have pointed out this fact, described the phenomena and tried to bring some order to the perceived chaos in the field. Cohen (1997, 1999, 2000), for example, after describing the attacks on the Information Systems (IS) field, for "its lack of tradition and focus" and the "misunderstandings of the nature of Information Systems," examines "the limitations of existing frameworks for defining IS" and reconceptualizes Information Systems and tries "to demonstrate that it has evolved to be part on an emerging discipline of fields, Informing Science" (Cohen, 2000). Our objective in this paper is to participate in the process of conceptualization and re-conceptualization required in the area of Information Systems and in Cohen's proposed Informing Science. We will try to do that making a first step in the description of a systemic notion of information, by identifying, first, the meaning of information. We are using the word "meaning" in its pragmatic sense, i.e. in the sense Peirce formulated when he pointed out that "in order to ascertain the meaning of an intellectual conception one should consider what practical consequences might conceivably result by necessity from the truth of that conception; and the sum of these consequences will constitute the entire meaning of the conception." (Peirce, 5.9.) When Peirce talks about "consequences," he is referring to the relation (consequentia) between the pair of antecedent and consequent, not just about the consequent (consequens). So, accordingly, we will try to analyze the antecedents, by means of Ackoff's approach to conceptual definitions (1962), then we will try to relate them to the respective consequents. In this way the meaning we will looking for the term "information" will be both its conceptual definition, as well as its respective practical consequences in the field of Information Systems and Informing Sciences. This will provide the input for establishing the direction of a systemic meaning of the notion of information. The term "information" has been widely and increasingly used, but not always with a clear idea about its meaning. As Dretske (1981) and Lewis (1991) pointed out, few books concerning information actually define it clearly. And Mingers (1997) adds, "Information systems could not exist without information and yet there is no secure agreement over what information actually is" (p. 73). The word "information" is one of the most used, and very abused, words. Different scientific disciplines and engineering fields provide diverse meanings to the word, which is becoming the umbrella of divergent, and sometimes dissimilar and incoherent homonyms. When concepts are not clear, the use of homonyms might be intellectually and pragmatically dangerous. We will try, here, to make an initial step, attempting first a conceptual definition. We are using "conceptual definition" with the meaning Ackoff (1962) described for it, and with the role he ascribed to it as a first step both in scientific inquiry and in systems analysis and synthesis. We will also follow the method suggested by Ackoff, but with the space restrictions of this paper. We can find, in the last years, a growing number of research studies directed to establish the meaning of "information." Some of these research studies will be cited below. In spite of the plurality of the approaches followed, we did not find studies oriented by Peirce's definition of "meaning" as applied to the concept "information", let alone studies where the defining process has the objective of finding practical consequences in the area of information systems development. We have no knowledge, either, of any kind of efforts made for the elaboration of a systemic notion of information. In our opinion, these two lacking aspects in the literature are very important, both from the intellectual and scientific perspective, as well as from the pragmatic one. …

Ecological and genetic data indicate recovery of the endangered coral Acropora palmata in Los Roques, Southern Caribbean

Abstract: The rapid decline of Acropora cervicornis and Acropora palmata has often been linked with coral reef deterioration in the Caribbean; yet, it remains controversial whether these species are currently recovering or still declining. In this study, the status of ten populations of A. palmata in Los Roques National Park (LRNP), Venezuela is presented. Six of these populations showed signs of recovery. Ten 80 m2 belt-transects were surveyed at each of the ten reef sites. Within belt-transects, each colony was measured (maximum diameter and height) and its status (healthy, diseased or injured) was recorded. Populations in recovery were defined by a dominance of small to medium-sized colonies in densities >1 colony per 10 m2, together with 75% undamaged colonies, a low prevalence of diseases (<10%), and a low density of predators (0.25 snails per colony). Based on allozyme analysis of seven polymorphic loci in four populations (N = 30), a moderate to high-genetic connectivity among these populations (F ST = 0.048) was found with a predominance of sexual over asexual reproduction (N* : N = 1; N go : N = 0.93–1). Both ecological and molecular data support a good prognosis for the recovery of this species in Los Roques.

Action selection for MDPs: anytime AO* versus UCT

Abstract: In the presence of non-admissible heuristics, A* and other best-first algorithms can be converted into anytime optimal algorithms over OR graphs, by simply continuing the search after the first solution is found. The same trick, however, does not work for best-first algorithms over AND/OR graphs, that must be able to expand leaf nodes of the explicit graph that are not necessarily part of the best partial solution. Anytime optimal variants of AO* must thus address an exploration-exploitation tradeoff: they cannot just "exploit", they must keep exploring as well. In this work, we develop one such variant of AO* and apply it to finite-horizon MDPs. This Anytime AO* algorithm eventually delivers an optimal policy while using non-admissible random heuristics that can be sampled, as when the heuristic is the cost of a base policy that can be sampled with rollouts. We then test Anytime AO* for action selection over large infinite-horizon MDPs that cannot be solved with existing off-line heuristic search and dynamic programming algorithms, and compare it with UCT.