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Biomedical subjects

A Arenas

Publications and source records attributed to A Arenas.

At least 19 recordsLinked to original sources
PubMed2002

Modeling diffusion of innovations in a social network.

A simple model of diffusion of innovations in a social network with upgrading costs is introduced. Agents are characterized by a single real variable, their technological level. According to local information, agents decide whether to upgrade their level or not, balancing their possible benefit with the upgrading cost. A critical point where technological avalanches display a power-law behavior is also found. This critical point is characterized by a macroscopic observable that turns out to optimize technological growth in the stationary state. Analytical results supporting our findings are found for the globally coupled case.

Journal Article↗
PubMed2001

Communication in networks with hierarchical branching.

We present a simple model of communication in networks with hierarchical branching. We analyze the behavior of the model from the viewpoint of critical systems under different situations. For certain values of the parameters, a continuous phase transition between a sparse and a congested regime is observed and accurately described by an order parameter and the power spectra. At the critical point the behavior of the model is totally independent of the number of hierarchical levels. Also scaling properties are observed when the size of the system varies. The presence of noise in the communication is shown to break the transition. The analytical results are a useful guide to forecasting the main features of real networks.

Communication↗
PubMed2000

Neural network based quantitative structural property relations (QSPRs) for predicting boiling points of aliphatic hydrocarbons

Quantitative structural property relations (QSPRs) for boiling points of aliphatic hydrocarbons were derived using a back-propagation neural network and a modified Fuzzy ARTMAP architecture. With the back-propagation model, the selected molecular descriptors were capable of distinguishing between diastereomers. The QSPRs were obtained from four valance molecular connectivity indices (1chiv,2chiv,3chiv,4chiv), a second-order Kappa shape index (2kappa), dipole moment, and molecular weight. The inclusion of dipole moment proved to be particularly useful for distinguishing between cis and trans isomers. A back-propagation 7-4-1 architecture predicted boiling points for the test, validation, and overall data sets of alkanes with average absolute errors of 0.37% (1.65 K), 0.42% (1.73 K), and 0.37% (1.54 K), respectively. The error for the test and overall data sets decreased to 0.19% (0.81 K) and 0.31% (1.30 K), respectively, using the modified Fuzzy ARTMAP network. A back-propagation alkene model, with a 7-10-1 architecture, yielded predictions with average absolute errors for the test, validation, and overall data sets of 1.96% (6.79 K), 1.83% (6.45 K), and 1.25% (4.42 K), respectively. Fuzzy ARTMAP reduced the errors for the test and overall data sets to 0.19% (0.73 K) and 0.25% (0.95 K), respectively. The back-propagation composite model for aliphatic hydrocarbons, with a 7-9- architecture, yielded boiling points with average absolute errors for the test, validation, and overall set of 1.74% (6.09 K), 1.25% (4.68 K), and 1.37% (4.85 K), respectively. The error for the test and overall data sets using the Fuzzy ARTMAP composite model decreased to 0.84% (1.15 K) and 0.35% (1.35 K), respectively. Performance of the QSPRs, developed from a simple set of molecular descriptors, displayed accuracy well within the range of expected experimental errors and of better accuracy than other regression analysis and neural network-based boiling points QSPRs previously reported in the literature.

Journal Article↗
PubMed2000

Self-organized evolution in a socioeconomic environment.

We propose a general scenario to analyze technological changes in socio-economic environments. We illustrate the ideas with a model that incorporating the main trends is simple enough to extract analytical results and, at the same time, sufficiently complex to display a rich dynamic behavior. Our study shows that there exists a macroscopic observable that is maximized in a regime where the system is critical, in the sense that the distribution of events follow power laws. Computer simulations show that, in addition, the system always self-organizes to achieve the optimal performance in the stationary state.

Computer Simulation↗
PubMed1999

Maternal care and attachment security in ordinary and emergency contexts.

One of the foundations of attachment theory is the notion that early care plays a key role in determining the quality of child-caregiver attachment relationships. Studies have consistently shown relations between maternal sensitivity and infant security. Further research is required to resolve issues arising from modest correlations, focus on research in stressful as opposed to ordinary contexts, and questions about the generality of results across cultures and social contexts and about the context specificity of caregiving behavior. This article addressed these issues in 2 studies of child care in home and hospital contexts. Q-sort scores derived from extended naturalistic observations were used. Results are discussed in terms of links between methodology and effect sizes, the generality of links between maternal care and child security, the need for further research on caregiving in ordinary and emergency situations, and the context sensitivity of maternal behavior.

Adult↗
PubMed1999

Outbreak of septicaemic colibacillosis in Japanese quail (Coturnix coturnix japonica).

We have carried out an aetiological and pathological study of an outbreak of septicaemia caused by the O165 serogroup of Escherichia coli in Japanese quail (Coturnix coturnix japonica) which resulted in high mortality (90%). After treatment with amoxicilin in drinking water (200 mg/l), morbility and mortality rates dropped markedly. Microbiological studies showed that the organism responsible was an atypical E. coli strain, on the basis of the non-fermentation of lactose (ONPG-), which belonged to the O165 serogroup and was highly virulent for 1-day-old chickens.

Animals↗
PubMed1998

Malignant schwannoma in a red deer (Cervus elaphus).

A five-year-old female red deer (Cervus elaphus) was in poor condition and severely lame on the left hindleg owing to a 19.4 cm x 15.9 cm mass involving and destroying the distal end (head) of metatarsal bones III and IV, the proximal sesamoid bones and the first phalanges (III and IV). The histopathological analysis revealed a spindle cell tumour with frequent palisade arrangement (Antoni type A pattern), and with highly anaplastic tumour cells in some areas. Structures resembling peripheral nerves were identified within the tumour. The neoplastic cells reacted with vimentin in a cytoplasmic pattern, and almost all of them reacted with S-100 protein in a nuclear and cytoplasmic pattern and did not express neurofilament, glial fibrillary acidic protein or keratins. This immunophenotype and the histopathological features were consistent with a diagnostic of malignant schwannoma. It was atypical because of the species affected, the location and the local malignancy.

Animals↗
PubMed1997

Equine pulmonary mycosis due to Aspergillus niger and Rhizopus stolonifer.

Invasive pulmonary mycosis caused by Aspergillus niger and Rhizopus stolonifer is reported in a 2-year-old horse, one of three that died after being housed in a disused, uncleaned stable. Lesions were characterized by thrombosis of the blood vessels with haemorrhage and tissue necrosis. Fungal hyphae were observed both in thrombosed vessels and in adjacent necrotic tissue. In culture media inoculated with lung samples and samples from the bedding hay, two types of colony were recorded and identified as A. niger and R. stolonifer. This study is the first description of equine pulmonary mucormycosis and of A. niger as an aetiological agent in the horse.

Animals↗
PubMed1996

Identification of coherent structures in turbulent shear flows with a fuzzy artmap neural network.

An implementation of a Fuzzy Artmap neural network is used to detect and to identify (recognise) structures (patterns) embedded in the velocity field of a turbulent wake behind a circular cylinder. The net is trained to recognise both clockwise and anticlockwise eddies present in the u and v velocity fields at 420 diameters downstream of the cylinder that generates the wake, using a pre-processed part of the recorded velocity data. The phase relationship that exists between the angles of the velocity vectors of an eddy pattern is used to reduce the number of classes contained in the data, before the start of the training procedure. The net was made stricter by increasing the vigilance parameter within the interval [0.90, 0.95] and a set of net-weights were obtained for each value. Full data files were scanned with the net classifying patterns according to their phase characteristics. The net classifies about 27% of the recorded signals as eddy motions, with the strictest vigilance parameter and without the need to impose external initial templates. Spanwise distances (homogeneous direction of the flow) within the centres of the eddies identified suggest that they form pairs of counter-rotating vortices (double rollers). The number of patterns selected with Fuzzy Artmap is lower than that reported for template matching because the net classifies eddies according to the recirculating pattern present at the core or central region, while template matching extends the region over which correlation between data and template is performed. In both cases, the topology of educed patterns is in agreement.

Air Movements↗
PubMed1995

Serological survey for avian paramyxoviruses from wildfowl in aquatic habitats in Andalusia.

A serological survey for a range of avian paramyxoviruses (PMV) was carried out among wildfowl from southern Spain, 1990 to 1992, using the hemagglutination inhibition technique. We collected 579 sera from 24 avian families (18 aquatic and six non-aquatic). Antibodies were detected to all paramyxoviruses in waterfowl, with a notable prevalence of antibodies to PMV-8 (43%) and to a lesser extent PMV-6 (21%). By contrast, in non-aquatic species high antibody prevalences were detected only to PMV-2 (60%), particularly in sparrows (68%), while antibody prevalences to other PMV's were moderate or low.

Animals↗
PubMed1994

An indirect fluorescent antibody technique for detection of anti-Dermatophilus congolensis antibodies in sheep.

An indirect fluorescent antibody (IFA) technique has been developed for detection of anti-Dermatophilus antibodies in sheep. Sera from 25 bacteriologically confirmed clinically affected sheep and from 10 negative non affected lambs were used. Whole cell antigen from brain heart infusion cultures of D. congolensis was used and all sera were tested in the same way for cross-reactivity against antigens obtained from cultures of Actinomyces viscosus, Micrococcus luteus, Nocardia asteroides, and Corynebacterium pseudotuberculosis. Sera from Dermatophilus-infected sheep gave positive results with D. congolensis antigen and negative results with the antigens from other bacteria. The whole cell antigens employed were simple to prepare and easy to recognise by microscopy. Cross-reactivity was further tested using the D. congolensis culture whole cell antigen and 3 sera from sheep with bacteriologically confirmed natural infections due to Corynebacterium pseudotuberculosis, Actinomyces pyogenes and Nocardia asteroides. None of these sera showed positive reactions. The authors recommend this technique for serological surveys and research on dermatophilosis.

Actinomycetales↗
PubMed1994

Prevalence of antibodies to different Leptospira interrogans serovars in pigs on large farms.

A seroepidemiological survey was carried out in the province of Badajoz (south-western Spain) in order to determine the presence and spread of Leptospira interrogans. The 521 sera tested were drawn from breeding sows on 28 large farms (15 with fewer than 60 and 13 with over 60 breeders). Immunological testing was performed using the Martin-Pettit micro-agglutination technique. Pigs with titres equal to or greater than 1:100 were considered positive. Haemolysed and/or contaminated test sera were reprocessed following filter-paper treatment. A total of 10.56% of pigs tested proved positive, 39.28% of farms being affected. The following L. interrogans serovars were detected: pomona (6.53%), castellonis (1.15%), sejroe (1.15%), grippotyphosa (0.96%), australis (0.38%), hebdomadis (0.19%) and icterohaemorrhagiae (0.19%).

Animals↗