Simon Bolívar University
  • Nuestra Señora del Rosario de Baruta, Miranda, Venezuela
Recent publications
This short article shows an analysis of the effects of fault type and pre-fault load flow on the optimal coordination of directional overcurrent protections. A well-known case from the literature is taken as an example, because this case has been previously solved considering only three-phase faults and only one pre-fault load flow. The fault type and the pre-fault load flow have an influence on the results of short-circuit currents and, consequently, on the results of the optimal coordination of directional overcurrent protections. It is shown herein that the effects of pre-fault load flow and single-line-to-ground faults can be important on the results of optimal coordination. For the analyzed cases, the percentage changes in the optimal results of time delay settings can be considerably greater than the percentage changes in short-circuit currents. On the other hand, the percentage changes in optimal results of objective functions can be considerably lower than the percentage changes in short-circuit currents for the analyzed cases.
This paper presents a procedure to determine the cooling capacity distribution of the chillers composing a chiller plant using a statistical analysis of the building cooling demand. The mathematical-statistical procedure uses tools such as frequency histograms, box-and-whisker plots, stem-and-leaf plots, the generalized least squares method, and finally an iterative factorial procedure to generate from the processed information. Besides the manufacturer’s data, all possible chiller plant combinations considering design constraints. The procedure was verified in a hotel facility. Eight thermal demand profiles were simulated. Statistical analysis yielded a range of individual capacities between 100–353 kW. The procedure generated 189 refrigeration plant combinations between 2 to 5 chillers, with a safety factor (SF) between 10%–20%. The highest number of combinations considered plants comprising three and four chillers, reaching 50 and 70 chiller plant options, respectively.
Biological ocean science has a long history; it goes back millennia, whereas the related data services have emerged in the recent digital era of the past decades. To understand where we come from—and why data services are so important—we will start by taking you back to the rise in the study of marine biology—marine biodiversity—and its key players, before immersing ourselves in the data life cycle, past and present joint global initiatives, and systems that allow(ed) scientists to more easily access biological data, online services through some simple keyboard strokes, and the many challenges we still encounter on a daily basis when dealing with these types of data.
Purpose Systemic lupus erythematosus (SLE or lupus) is a chronic autoimmune disease, and kidney involvement with SLE, lupus nephritis (LN), is a frequent and severe complication of SLE that increases patient morbidity and mortalityis. The current gold standard for classifying LN progression is a renal biopsy, an invasive procedure with potential risks. Undergoing a series of biopsies for monitoring disease progression and treatments is unlikely suitable for patients with LN. Thus, there is an urgent need for non-invasive alternative biomarkers that can facilitate LN class diagnosis. Such biomarkers will be very useful in guiding intervention strategies to mitigate or treat patients with LN. The current study aims to explore new biomarker candidates for non-invasive diagnosis of LN and explore the pathogenic mechanisms that contribute to renal injury. Materials and Methods A metabolomics approach using LC-QTOF-MS in both positive and negative electrospray ionization (ESI) modes and GC-QTOF-MS was developed for comparison of urine metabolic profile of 23 LN patients, 16 SLE patients, and 10 healthy controls (HCs). Differential metabolites were evaluated with univariate (UVA) and multivariate (MVA) analysis using a nonparametric t test, principal component analysis (PCA) and orthogonal partial least squares regression (OPLS-DA). Results Both UVA and MVA showed a clear discrimination in the urinary metabolome between LN, SLE and HCs. The significant altered metabolites between LN and SLE correspond mainly to fatty acyls, amino acids, bile acids in particular methylglutamic acid, monopalmitin methyl-L-proline, 3-oxo-4-pentenoic acid, glutaric acid, 3-hydroxyglutaric acid, citraconic acid, glutamine, glycocholic acid and ureidoisobutyric acid. Analysis of metabolic pathways shows disturbances in biosynthesis of alanine, aspartate and glutamate metabolism, citrate cycle (TCA cycle) and glutamine and glutamate metabolism. Conclusions The urinary metabolome of SLE and LN patients made it possible to determine metabolic alterations and discriminate LN patients from SLE patients. If confirmed in larger studies, these urine metabolites may serve as biomarkers to help discriminate between SLE with and without renal involvement.
Genus Vibrio is involved in common pathologies of aquaculture fish species, being responsible for significant economic losses for that industrial activity. Microalgae and cyanobacteria have demonstrated to count on bioactive compounds able to diminish mortality and morbidity by their use as functional food supply or by addition of those bioactive compounds previously purified. The main goal of this work has been to evaluate the anti-microbian effect (growth of bacterial population measured as changes in optical density) of 25 microalgae extracts on the bacterial strain Vibrio anguillarum CECT 522T. Stock microalgae extracts were obtained from lyophilized biomass treated with methanol 99.9%. A total of thirteen extracts exhibited antibacterial activity. The highest activity corresponded to Monochrysis lutheri, followed by Hemiselmis cyclopea, Porphyridium cruentum, Tetraselmis rubens, Cryptomonas sp, Navicula sp. The anti-bacterial activity was not related to a taxonomic group, indicating species-specific or even strain-specific activity.
Teaching has often been linked to psychosocial problems, and is an occupation in which the implementation of strategies for the improvement, updating and promotion of the mental health of those involved is essential. Accordingly, this study assessed the effectiveness of a program aimed at improving psychological well-being, optimism, self-efficacy, and self-esteem as well as at reducing psychological distress in teachers. The study was quasi-experimental and comprised 24 teachers from technical, secondary, and elementary schools in Uruguay. The constructs were measured before and after the program, which was conducted during the COVID-19 pandemic and comprised 12 modules in a multicomponent intervention format. The results indicate a significantly low magnitude increase in well-being (F = 5.36, p = 0.033, Cohen’s d = 0.47) and a moderate increase in self-efficacy (F = 9.14, p = 0.008, Cohen’s d = 0.62). Similarly, a significant decrease was observed in psychological distress of mild effect (F = 5.80, p = 0.028, Cohen’s d = 0.49). To conclude, interventions based on positive psychology improve teachers’ well-being, enhance other psychological resources, and reduce psychosocial risks such as discomfort. Thus, these interventions can be devices for career development and teacher updating.
The importance of miRNAs in cellular processes and their dysregulation has taken significant importance in understanding different pathologies. Due to the constant increase in the prevalence of neurodegenerative diseases (ND) worldwide and their economic impact, mild cognitive impairment (MCI), considered a prodromal phase, is a logical starting point to study this public health problem. Multiple studies have established the importance of miRNAs in MCI, including astrocyte regulation during stressful conditions. Additionally, the protection mechanisms exerted by astrocytes against some damage in the central nervous system (CNS) lead to astrocytic reactivation, in which a differential expression of miRNAs has been shown. Nevertheless, excessive reactivation can cause neurodegeneration, and a clear pattern defining the equilibrium point between a neuroprotective or detrimental astrocytic phenotype is unknown. Therefore, the miRNA expression has gained significant attention to understand the maintenance of brain balance and improve the diagnosis and treatment at earlier stages in the ND. Here, we provide a comprehensive review of the emerging role of miRNAs in cellular processes that contribute to the loss of cognitive function, including lipotoxicity, which can induce chronic inflammation, also considering the fundamental role of astrocytes in brain homeostasis.
Sociosexuality refers to an individual’s disposition to have casual sex without establishing affective bonds and has been widely studied worldwide using the Revised Sociosexual Orientation Inventory (SOI-R; Penke & Asendorpf, 2008). Despite its many validations in different cultural contexts, no psychometric analyses of this instrument have been conducted in Spanish-speaking Latin American countries. To address this gap in the literature, we examined the psychometric properties of the SOI-R in Colombia. In a cross-sectional study with a large sample of participants (N = 812; 64% women), we conducted exploratory and confirmatory factor analyses to identify different factor structures and determine which had the best fit for our sample and examined the reliability of the scale. Results showed that a three-factor structure, with sociosexual behaviors, attitudes, and desire as first-order factors, and global sociosexuality as a second-order factor, had the best fit indexes. Each factor presented good reliability indexes. Replicating already established gender differences, we also found that men scored higher on each factor when compared to women. These findings show that the SOI-R is a reliable and valid instrument to assess sociosexuality in countries where sociosexuality research is underrepresented.
Several review articles about megachurch studies have been published recently concentrating their work on USA, Europe, and other parts of the world, with just a few references about Latin American megachurches. For that reason, this article aims to identify some of the characteristics of Latin American Evangelical megachurches by looking at relevant literature, especially that produced in the region, in Spanish and Portuguese, which is usually overlooked by researchers in the Global North. Since this research field is still limited in Latin America, areas where further work is necessary are identified. Three general catalysts for the emergence of megachurches in the region, church growth methodologies, Pentecostalization, and theologies of growth, serve as guides to organize the review process. The discussion shows that several potential areas of research in a variety of fields such as theology, ecclesiology, organizational theory, leadership, gender studies, and ethics, are proposed from the review.
Human papillomavirus 31 (HPV31) is the fourth most frequent high-risk HPV (HR-HPV) genotype identified in cervical cancer (CC) worldwide and in Mexico. It has been recently classified into three lineages (A, B, and C) and eight sublineages (A1, A2, B1, B2, and C1 – C4). Here, we report the complete genomic sequences of 14 HPV31 isolates from cervical samples, and these were compared with viral genome sequences from the GenBank database for phylogenetic and genetic distance analysis. The formation of two novel clades within the C lineage (proposed as C5 and C6) was observed, with a well-defined variant-specific mutational pattern. The smallest average pairwise distance was 0.71% for lineages A and B, 0.94% for lineages A and C, and 1.01% for lineages B and C, and between sublineages, these values were 0.21% for clade A, 0.29% for clade B, and 0.24% for clade C. The isolates were grouped into the sublineages A1, B2, C1-C3, and C6. This is the first report on the whole-genome diversity of HPV31 in Mexico.
Twitter is one of the most popular sources of information available on the internet. Thus, many studies have proposed tools and models to analyze the credibility of the information shared. The credibility analysis on Twitter is generally supported by measures that consider the text, the user, and the social impact of text and user. More recently, identifying the topic of tweets is becoming an interesting aspect for many applications that analyze Twitter as a source of information, for example, to detect trends, to filter or classify tweets, to identify fake news, or even to measure a tweet’s credibility. In most of these cases, the hashtags represent important elements to consider to identify the topics. In a previous work, we presented a credibility model based on text, user, and social credibility measures, and a framework called T-CREo, implemented as an extension of Google Chrome. In this paper, we propose an extension of our previous credibility model by integrating the detection of the topic in the tweet and calculating the topic credibility measure by considering hashtags. To do so, we evaluate and compare different topic detection algorithms, to finally integrate in our framework T-CREo, the one with better results. To evaluate the performance improvement of our extended credibility model and show the impact of hashtags, we performed experiments in the context of fake news detection using the PHEME dataset. Results demonstrate an improvement in our extended credibility model with respect to the original one, with up to 3.04% F1 score when applying our approach to the whole PHEME dataset and up to 9.60% F1 score when only considering tweets that contain hashtags from PHEME dataset, demonstrating the impact of hashtags in the topic detection process.
is research aims to provide a general visualization of studies focused on the intellectual capital developed in Colombia. Firstly, detailed information on research articles on this topic was obtained from the Scopus database. Secondly, the information was analyzed using Excel through the direct comparison and analysis of graphs with references and theories related to intellectual capital. Finally, the results exposed that Colombian scienti c production is associated with 32 public universities, representing 45,029 elaborate documents by 9,758 authors on three relevant topics: physics and astronomy, agricultural and biological science, and medicine. Also, the data obtained exposed that 56.61% of the institutions are above the average considering the overall public institutions. However, this behavior depends on the institution's number of researchers and full-time teachers related to intellectual capital. Finally, the hypotheses agree with the results obtained, considering that the quantity and quantity of intellectual capital signi cantly in uence scienti c production, the size and location of the public universities of Colombia, and the national and international scienti c collaboration.
The increasing evolution of computing technologies has fostered the new intelligent concept of Ubiquitous computing (Ubicomp). Ubicomp environments encompass the introduction of new paradigms, such as Internet of Things (IoT), Mobile computing, and Wearable computing, into communication networks, which demands more efficient strategies to deliver tasks and services, considering heterogeneity, scalability, reliability, and efficient energy consumption of the connected devices. Middlewares have a crucial role to deal with all these aspects, by implementing efficient load balancing methods based on the hardware characterization and the computational cost of the queries and tasks. However, most existing solutions do not take into account both considerations in conjunction. In this context, we propose a methodology to characterize distributed servers, services, and network delays in Ubicomp environments, based on the Server Ability to Answer a Query (SAAQ). To evaluate our SAAQ-based methodology, we implemented a simple middleware in a museum context, in which different IoT devices (e.g., social robots, mobile devices) and distributed servers with different capabilities can participate, and performed a set of experiments in scenarios with diverse hardware and software characteristics. Results show that the middleware is able to distribute queries to servers with adequate capacity, freeing from service requests to devices with hardware restrictions; thus, our SAAQ-based middleware has a good performance regarding throughput (22.52 ms for web queries), end-to-end delay communications (up to 193.30 ms between San Francisco and Amsterdam), and good management of computing resources (up to 80% of CPU consumption).
Background Visceral pain (VP) following laparoscopic sleeve gastrectomy remains a substantial problem. VP is associated with autonomic symptoms, especially nausea and vomiting, and is unresponsive to traditional pain management algorithms aimed at alleviating somatic (incisional) pain. The present study was performed to evaluate the safety and effectiveness of laparoscopic paragastric autonomic neural blockade (PG-ANB) in managing the symptoms associated with VP following sleeve gastrectomy. Study Design This prospective, double-blinded, randomized clinical trial involved patients undergoing laparoscopic sleeve gastrectomy at two high-volume institutions. The patients were randomized to laparoscopic transversus abdominis plane block with or without PG-ANB. The primary outcome was patient-reported pain scores assessed at 1, 8, and 24 h postoperatively. The secondary outcome measures were analgesic requirements, nausea, vomiting, hiccups, and hemodynamic changes immediately after PG-ANB and postoperatively. Results In total, 145 patients (block group, n = 72; control group, n = 73) were included in the study. The heart rate and mean arterial pressure significantly decreased 10 min after PG-ANB. The visual analog scale score for pain was significantly lower in the PG-ANB than in the control group at 1 h postoperatively (p < 0.001) and 8 h postoperatively (p < 0.001). Vomiting, nausea, sialorrhea, and hiccups were significantly less prevalent in the PG-ANB group. Patients in the PG-ANB group received fewer cumulative doses of analgesics at 1 h postoperatively (p = 0.003) and 8 h postoperatively (p < 0.001). No differences between the groups were detected at 24 h (p = 0.298). No complications related to PG-ANB occurred. Conclusion PG-ANB safely and effectively reduces early VP, associated autonomic symptoms, and analgesic requirements after laparoscopic sleeve gastrectomy. Graphical abstract
The primary and secondary distribution grids are typically designed separately and operated with a radial configuration; therefore, specialized load flow methods only applicable to radial or weakly meshed networks are normally used. However, projections indicate that the distribution grids will be more interconnected in the future, mainly because of the inclusion of distributed generation, voltage and reliability optimization, as well as an efficiency improvement when the primary and secondary networks are considered in an integrated way. For this new meshed grids scenario, the efficient and precise typically used load flow methods for distribution networks are no longer applicable and it becomes necessary using load flow algorithms that are also applicable for meshed configurations, such as the ones classically used for transmission networks like the Newton-Raphson, Gauss-Seidel and Gauss Implicit Z-bus methods, while also procuring to avoid potential singularity problems which may arise when dealing with long radial grids. In this work, variations of the Gauss-Seidel and Gauss Implicit Z-bus methods are presented, that are adequate for low and medium voltage grids regardless of the network configuration. Additionally, a linear, direct, and non-iterative load flow variation is presented as well as a comparison between different possible convergence criteria for the classical methods.
Quantifying the effect of human-wildlife interactions, and particularly those where negative perceptions exist, can have a benefit towards the conservation of species. The negative perceptions surrounding human-shark interactions can be put forward as a case in point. In this work, we use six relevant statements questions to test human perceptions before and after controlled human interactions with the white shark, Carcharodon carcharias. Questions were adapted from Kellert's typology of human attitudes towards animals. A total of 322 tourists participating in white shark cage diving tours in Gansbaai, South Africa were exposed to two surveys (pre and post-experience) to assess whether a shift in perception can happen. We focused the work on measuring the effect of the shark cage diving tourism activities to change negative perceptions towards white sharks in people who dare to cage diving with sharks. To determine the underlying structure of the statements involved in shark perception, exploratory factor analyses were performed. Two attitudes, Dominionistic and Ecologistic-Scientific explained 52.8% of the variance. In addition, analyses of differences between pre and post-surveys in participants of White Shark cage diving tours indicated a positive change in perception towards white sharks after the activity. No age, gender, or transcultural differences were found, and possible psychological and political approaches were addressed. Controlled human-shark interaction can aid in a positive shift of the attitudes towards this animal, which can have significant potential implications. Ultimately, exposure to sharks could be a valuable tool for promoting public attitudes, especially when paired with the correct interpretation of shark behavior and its impact on the ecosystem.
The Kunene Complex (KC) represents a large Mesoproterozoic igneous body, mainly composed of anorthosites and gabbroic rocks that extends from SW Angola to NW Namibia (18000 km², N-S trend, and ca. 350 km long and 25–50 km wide). Although the KC has been studied from a cartographic and geochemical point of view, little is known about its structure at depth below the sedimentary deposits of the Kalahari basin. Hence, we use available satellite gravity data to estimate its extent and to unravel its morphology at depth. The Bouguer anomaly map depicts a gravity gradient from the coast (+200 mGal) towards eastern Angola (-150 mGal), which is explained by the transition from a young, dense and thin basaltic oceanic crust, formed during the Mesozoic Atlantic rifting, to an old, light and thick Archaean to Proterozoic continental crust (Congo Craton), to the east. The outcropping KC interrupts the gravity trend, showing at the western, southwestern and northeastern sides, several positive and isolated gravity anomalies linked to gabbroic intrusions associated to KC (ca. 50 km wavelength and −90 mGal). In contrast, the anomalies found at the central part of the massif (50 km wavelength and < -110 mGal) correspond to the dominant anorthositic members, according to the spatial correlation of the mapping. Five 2.5D gravity profiles have been modelled to investigate the unexposed eastern boundary, reconstructing the surface crustal structure (between 0 and 15 km depth) overlaid by the thin sedimentary cover of the Kalahari basin. The gravity modelling helps us to show that the KC was emplaced in the Upper Crust and extends in depth up to ca. 6 km, showing a lobular geometry and following a large NE-SW to NNE-SSW linear trend, presumably inherited from older Palaeoproterozoic structures. The lateral continuation of the KC to the east (between 50 and 125 km) beneath the Kalahari sediments suggests an overall size of at least twice the outcropping dimension (about 42500 km²). This statement clearly influences in the economic potential of this massif, related to the prospecting of raw materials and certain types of economic mineralization (Fe-Ti oxides, metallic sulphides or platinum group minerals).
The complex rheological response of chocolates of different compositions was analyzed in depth from stationary shear flow curves and large amplitude oscillatory shear tests. The samples have a wide range of cocoa content that controls the rheological behavior characterized by a yielding response. The strain amplitude at which the chocolates changed from elastic-dominated to viscous-dominated behavior ranged from 0.2 to 0.4%. In this region, the stress response to the applied sinusoidally oscillating shear strain showed transient overshoots whose values were similar to yield stress calculated using the Casson equation in continuous flow. The nonlinear response at the steady-state was analyzed. The Q 0 nonlinearity parameter, obtained from Fourier Transform analysis, increases as the concentration of the solids conferring bimodality to the particle size distribution increases. In the study of intracycle nonlinearities, the analysis of the third-order Chebyshev elastic and viscous coefficients showed that the sample which contains the highest amount of solids different from cocoa exhibited the lowest strain-stiffening and the highest shear-thinning behaviors. Stress bifurcation analysis identified the beginning of the yielding transition and evidenced a nonlinear solid-like behavior before the solid-liquid transition. Analysis of Lissajous–Bowditch curves allowed the static and dynamic contributions of the yielding transition to be identified, and the full Sequence of Physical Process quantitative analysis captures the time-dependent nonlinear response of chocolates over the history of applied deformations.
Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a multisystem and progressive neurodegenerative mitochondrial disease, caused by point nucleotide changes in the mtDNA where 80% of cases have the mutation m.3243A>G in the MT-TL1 gene. In this work, we described the clinical, biochemical and molecular analysis of three Venezuelan patients affected with MELAS syndrome. All cases showed lactic acidosis, cortical cerebral atrophy on magnetic resonance imaging and muscular system deficit, and in two of the cases alteration of urine organic acid levels was also registered. A screening for the mutation m.3243A>G in different patients’ body samples confirmed the presence of this mutation with variable degrees of heteroplasmy (blood=7-41%, buccal mucosa=14-53%, urine=58-94%). The mitochondrial haplogroups for the three patients were different (H, C1b, and A2), indicating an independent origin for the mutation.
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2,472 members
Luis Rojas-Solórzano
  • Departamento de Conversión y Transporte de Energía
Marlene Goncalves
  • Department of Computer Science and Information Technology
Neudo Urdaneta
  • Departamento de Química
Maria I Camejo
  • Departamento de Biología de Organismos
Marisol Castrillo
  • Departamento de Biología de Organismos
Sartenejas, Nuestra Señora del Rosario de Baruta, Miranda, Venezuela
Head of institution
Universidad Simón Bolívar
+58 212 9063111