Phenomenological model of visual acuity

We propose in this work a model for describing visual acuity (VV) as a function of defocus and pupil diameter. Although the model is mainly based on geometrical optics, it also incorporates nongeometrical effects phenomenologically. Compared to similar visual acuity models, the proposed one considers the effect of astigmatism and the variability of best corrected VV among individuals; it also takes into account the accommodation and the “tolerance to defocus,” the latter through a phenomenological parameter. We have fitted the model to the VV data provided in the works of Holladay et al. and Peters, showing the ability of this model to accurately describe the variation of VV against blur and pupil diameter. We have also performed a comparison between the proposed model and others previously published in the literature. The model is mainly intended for use in the design of ophthalmic compensations, but it can also be useful in other fields such as visual ergonomics, design of visual tests, and optical instrumentation

Late Triassic and Early Jurassic palaeogeographic evolution and depositional cycles of the Western Tethys Iberian platform system (Eastern Spain)

Deposition of Upper Triassic and Lower Jurassic sediments on the Iberian platform system took place in a post-rift intraplate basin which formed part of the western Tethys shelf. Nevertheless, there is evidence for the tensional reactivation of a network of faults with associated magmatic activity. Early Jurassic palaeogeographic reconstructions, based on over 70 sections and 9 oil wells, reveal the presence of a series of highs and lows (depocentres). Two main highs, referred to as the El Maestrazgo High, in the east, and the La Mancha High, in the west, where condensed sections were deposited, were mainly controlled by syndepositional faults. The main depocentres were situated between these two highs areas, in a northwest trending belt in the central, northern and southern areas. Despite partial fault control, development of some Early Jurassic depocentres appears to be mainly controlled by thermal contraction of the lithosphere following Triassic main rifting pulse. The Upper Triassic–Lower Jurassic succession of the Iberian platform system was deposited during four transgressive and regressive cycles of 12 to 6 My duration. The lowermost cycle LJ-1 started in late Norian and lasted until the Sinemurian. The second cycle LJ-2 started in the Sinemurian and ended in the Pliensbachian (Davoei Zone), and can be subdivided into two minor cycles LJ2-1 and LJ2-2. The cycle LJ-3 started with an extensive upper Pliensbachian (Davoei Zone) transgression, whereas the top of its regressive cycle is dated to the Toarcian (Variablilis Zone). Within cycle LJ-3, three cycles can be distinguished. Maximum deepening was reached during the Bifrons Zone and active volcanism took place along the Teruel and Caudiel faults. The transgressive phase of the cycle LJ-4 started in the Thouarsense Zone and extended up to the Insigne Zone; its regressive phase developed during the upper Toarcian (Pseudoradiosa and Aalensis Zones) and part of the Aalenian (Opalinum and Murchisonae Zones). This cycle can be subdivided in two minor cycles, with their transgressive peaks occurring during the Insigne Zone, and the Aalensis Zone respectively. Palaeogeographically this corresponds with the expansion of the marginal carbonate platforms over hemipelagic deposits. The top of the cycle corresponds to a major unconformity with regional emersion during the Aalenian Murchisonae Zone

Warming-driven mass extinction in the Early Toarcian (Early Jurassic) of northern and central Spain. Correlation with other time-equivalent European sections

Causes of the major mass extinction recorded during the Early Toarcian (Early Jurassic) are controversial. Many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated Early Toarcian Oceanic Anoxic Event (ETOAE), supposedly synchronous in all basins and global in extent. Another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction. The results of the study of five sections of the uppermost Pliensbachian and Lower–Middle Toarcian deposits, located in northern and central Spain are presented. Detailed ammonite-based biostratigraphy, coupled with stable isotope analysis of belemnite calcite and bulk carbonates, as well as total organic carbon (TOC) analyses have been performed in all sections. Records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections. Results obtained in the Spanish outcrops have been compared and correlated with other European sections. The excellent mutual relation between the patterns of the Early Toarcian progressive warming and the concomitant progressive losses of species evidences a cause-and-effect relationship between the increase of temperature and the mass extinction. From an uppermost Pliensbachian cooling interval, warming started at the Lower Toarcian Tenuicostatum Zone. Increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic, planktonic and benthic organisms, representing the extinction interval. A prominent increase in seawater temperature occurred around the Lower Toarcian Tenuicostatum–Serpentinum zonal boundary. Average temperatures at the Serpentinum Zone increased about 7 °C, marking the extinction boundary. The high temperatures continued during the Middle Toarcian Bifrons Chronozone, representing the repopulation interval. The anoxia linked to the postulated ETOAE cannot be the responsible for the mass extinction, because it has been synchronously recorded in the oxygenated environments of many European and Northern African platforms. Deposition of laminated organic-rich black shale facies, above 5 wt.% TOC indicating anoxic environments, was mostly confined geographically to the Western Europe Euxinic Basin, and mainly deposited after the extinction event, during the interval of faunal recovery

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Seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the Toarcian (Early Jurassic) in Central and Northern Spain. Comparison with other European sections

The Early Toarcian mass extinction marks one of the critical events in the history of the Earth. Many of these events have been linked to important climate changes. Two sections of the Toarcian showing high-resolution ammonite-based biostratigraphy are studied in Central and Northern Spain. Stable isotope datasets, based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates, allowed the construction of δ13C curves and a δ18O-based palaeotemperature. Comparison of the extinction pattern with other sections in Europe and northern Africa shows that the Early Toarcian mass extinction boundary occurred at the Tenuicostatum–Serpentinum transition, and that the organic-rich facies linked to the Oceanic Anoxic Event and the associated negative δ13C excursion are diachronous. From a latest Pliensbachian cooling interval, a first increment of seawater temperature averaging about 4.5 °C, started around the Pliensbachian–Toarcian boundary and developed during the earliest Toarcian Tenuicostatum Biochron, marking the beginning of the main extinction interval. From the Tenuicostatum–Serpentinum transition up to the Bifrons Biochron, a rise in seawater temperature averaging 5.7 °C to 7.8 °C was recorded. This warming interval, which started rapidly and which seems to be synchronous at least in Western Europe, is considered one of the main factors responsible for mass extinction. For some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere, but it does not seem to be recorded in belemnite calcite, and the origin of these possible gases is largely debated in the literature. Additional isotope excursions were found in the studied sections in Spain during the Middle and Late Toarcian. A negative δ13Cbel excursion has been recorded at the latest Bifrons Biochron. Above this shift, the Illustris–Vitiosa subzones thermal peak, which represents a 2–3 °C ΔT, could be linked to one of the tectonomagmatic activity peaks recorded in the Karoo Basin. A renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in NW Europe and Western Tethys. An interesting thermal peak has also been detected in belemnites of the Insigne Subzone. ΔT is in the order of 3 °C, and in both sections the thermal peak is included into a δ13Cbel negative excursion of about −1.5‰. Relative synchrony with the new age for the Karoo main magmatic activity (178–180 Ma) indicates that the δ13C negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases. At this short interval, noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of NW Europe and Tethys are observed. The uppermost Levesquei Subzone thermal peak has only been recognized in the deposits of the section located in Central Spain and coincides with a positive δ13C excursion

Proyecto de innovación educativa: límite y continuidad

Se explica un proyecto sencillo de innovación educativa para introducir de manera intuitiva la caracterización épsilon-delta de límite a estudiantes de bachillerato

Stress Increases Vulnerability to Inflammation in the Rat Prefrontal Cortex

Inflammation could be involved in some neurodegenerative disorders that accompany signs of inflammation. However, because sensitivity to inflammation is not equal in all brain structures, a direct relationship is not clear. Our aim was to test whether some physiological circumstances, such as stress, could enhance susceptibility to inflammation in the prefrontal cortex (PFC), which shows a relative resistance to inflammation. PFC is important in many brain functions and is a target for some neurodegenerative diseases. We induced an inflammatory process by a single intracortical injection of 2 μg of lipopolysaccharide (LPS), a potent proinflammogen, in nonstressed and stressed rats. We evaluated the effect of our treatment on inflammatory markers, neuronal populations, BDNF expression, and behavior of several mitogen-activated protein (MAP) kinases and the transcription factor cAMP response element-binding protein. Stress strengthens the changes induced by LPS injection: microglial activation and proliferation with an increase in the levels of the proinflammatory cytokine tumor necrosis factor-α; loss of cells such as astroglia, seen as loss of glial fibrillary acidic protein immunoreactivity, and neurons, studied by neuronal-specific nuclear protein immunohistochemistry and GAD67 and NMDA receptor 1A mRNAs expression by in situ hybridization. A significant increase in the BDNF mRNA expression and modifications in the levels of MAP kinase phosphorylation were also found. In addition, we observed a protective effect from RU486 [mifepristone (11β-[p-(dimethylamino)phenyl]-17β-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one)], a potent inhibitor of the glucocorticoid receptor activation. All of these data show a synergistic effect between inflammation and stress, which could explain the relationship described between stress and some neurodegenerative pathologies.España,Ministerio de Educación y Ciencia Grants SAF2002-01952 and SAF2004-0660

Critical elements of proper discrete Morse functions

The aim of this paper is to study the notion of critical element of a proper discrete Morse function defined on non-compact graphs and surfaces. It is an extension to the non-compact case of the concept of critical simplex which takes into account the monotonous behaviour of a function at the ends of a complex. We show how the number of critical elements are related to the topology of the complex.Plan Nacional de Investigación (Ministerio de Educación y Ciencia