Tangential projections and secant defective varieties

Going one step further in Zak's classification of Scorza varieties with secant defect equal to one, we characterize the Veronese embedding of $\P^n$ given by the complete linear system of quadrics and its smooth projections from a point as the only smooth irreducible complex and non-degenerate projective subvarieties of $\P^N$ that can be projected isomorphically into $\P^{2n}$ when $N\geq\binom{n+2}{2}-2$.Comment: To appear in Bulletin of the London Mathematical Societ

Initial and Advanced Stages of Microbiota Establishment within the Tsetse Fly

Symbiosis is a long-term physical association between two or more species, although little is known regarding its evolutionary origins, particularly at the genetic level. Tsetse flies are the vector of African trypanosomes, causative agents of Human and Animal African Trypanosomiases. Tsetse provide an ideal model for studying initial and advanced stages of symbiosis. Tsetse have a simple digestive tract microbiota primarily consisting of two bacteria; the ancient mutualist Wigglesworthia glossinidia and the recently acquired Sodalis glossinidius. This work presents a chronological study in evolutionary terms of the history of a microbial-insect association. First, I present concepts on symbiosis and comments on tsetse and their native microbiota. Second, I focus on early evolutionary transition of an environmental bacterium to a symbiotic lifestyle. I show that quorum sensing virulence suppression facilitates the establishment of Sodalis-allied symbionts in diverse insects. Third, I compare the metatranscriptome of teneral Glossina morsitans (high vector competence) to that of Glossina brevipalpis (low vector competence). The transcriptomes of Wigglesworthia and Sodalis reflect differences in the extent of co-evolution with tsetse and identify pathways that may contribute towards distinctions in vector competence. Fourth, I present a theoretical mechanism by which microbial symbionts may control gene expression in insect host via epigenetics. I propose a link between the folate provisioning roles of the microbiota and the health of blood-feeding insects, via DNA methylation. This work reflects the use of a combined approach to gain a comprehensive understanding of symbiosis evolution, its mechanisms and its potential to impact epidemiology

Ascorbic acid enhances the inhibitory effect of aspirin on neuronal cyclooxygenase-2-mediated prostaglandin E2 production.

Inhibition of neuronal cyclooxygenase-2 (COX-2) and hence prostaglandin E2 (PGE2) synthesis by non-steroidal anti-inflammatory drugs has been suggested to protect neuronal cells in a variety of pathophysiological situations including Alzheimer's disease and ischemic stroke. Ascorbic acid (vitamin C) has also been shown to protect cerebral tissue in a variety of experimental conditions, which has been attributed to its antioxidant capacity. In the present study, we show that ascorbic acid dose-dependently inhibited interleukin-1beta (IL-1beta)-mediated PGE2 synthesis in the human neuronal cell line, SK-N-SH. Furthermore, in combination with aspirin, ascorbic acid augmented the inhibitory effect of aspirin on PGE2 synthesis. However, ascorbic acid had no synergistic effect along with other COX inhibitors (SC-58125 and indomethacin). The inhibition of IL-1beta-mediated PGE2 synthesis by ascorbic acid was not due to the inhibition of the expression of COX-2 or microsomal prostaglandin E synthase (mPGES-1). Rather, ascorbic acid dose-dependently (0.1-100 microM) produced a significant reduction in IL-1beta-mediated production of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable indicator of free radical formation, suggesting that the effects of ascorbic acid on COX-2-mediated PGE2 biosynthesis may be the result of the maintenance of the neuronal redox status since COX activity is known to be enhanced by oxidative stress. Our results provide in vitro evidence that the neuroprotective effects of ascorbic acid may depend, at least in part, on its ability to reduce neuronal COX-2 activity and PGE2 synthesis, owing to its antioxidant properties. Further, these experiments suggest that a combination of aspirin with ascorbic acid constitutes a novel approach to render COX-2 more sensitive to inhibition by aspirin, allowing an anti-inflammatory therapy with lower doses of aspirin, thereby avoiding the side effects of the usually high dose aspirin treatment

Performance of alternative spatial models in empirical Douglas-fir and simulated datasets

Key message: Based on an empirical dataset originating from the French Douglas-fir breeding program, we showed that the bidimensional autoregressive and the two-dimensional P-spline regression spatial models clearly outperformed the classical block model, in terms of both goodness of fit and predicting ability. In contrast, the differences between both spatial models were relatively small. In general, results from simulated data were well in agreement with those from empirical data. Context: Environmental (and/or non-environmental) global and local spatial trends can lead to biases in the estimation of genetic parameters and the prediction of individual additive genetic effects. Aims: The goal of the present research is to compare the performances of the classical a priori block design (block) and two different a posteriori spatial models: a bidimensional first-order autoregressive process (AR) and a bidimensional P-spline regression (splines). Methods: Data from eight trials of the French Douglas-fir breeding program were analyzed using the block, AR, and splines models, and data from 8640 simulated datasets corresponding to 180 different scenarios were also analyzed using the two a posteriori spatial models. For each real and simulated dataset, we compared the fitted models using several performance metrics. Results: There is a substantial gain in accuracy and precision in switching from classical a priori blocks design to any of the two alternative a posteriori spatial methodologies. However, the differences between AR and splines were relatively small. Simulations, covering a larger though oversimplified hypothetical setting, seemed to support previous empirical findings. Both spatial approaches yielded unbiased estimations of the variance components when they match with the respective simulation data. Conclusion: In practice, both spatial models (i.e., AR and splines) suitably capture spatial variation. It is usually safe to use any of them. The final choice could be driven solely by operational reasons

The circumstellar medium of the peculiar supernova SN1997ab

We report the detection of the slow moving wind into which the compact supernova remnant SN 1997ab is expanding. Echelle spectroscopy provides clear evidence for a well resolved narrow (Full Width at Zero Intensity, FWZI ~ 180 km/s) P-Cygni profile, both in Ha and Hb, superimposed on the broad emission lines of this compact supernova remnant. From theoretical arguments we know that the broad and strong emission lines imply a circumstellar density (n ~ 10^7 cm^-3). This, together with our detection, implies a massive and slow stellar wind experienced by the progenitor star shortly prior to the explosion.Comment: 10 pages, 2 figures, acepted for publication in MNRAS. Uses referee.sty, psfig.sty and mn.sty. A postscript file can also be retrieved at http://www.strw.LeidenUniv.nl/~salamanc/latest.htm

A reexamination of the effective fine structure constant of graphene, as measured in graphite

We present a refined and improved study of the influence of screening on the effective fine structure constant of graphene, $\alpha^*$, as measured in graphite using inelastic x-ray scattering. This follow-up to our previous study [J. P. Reed, et al., Science 330, 805 (2010)] was carried out with two times better energy resolution, five times better momentum resolution, and improved experimental setup with lower background. We compare our results to RPA calculations and evaluate the relative importance of interlayer hopping, excitonic corrections, and screening from high energy excitations involving the $\sigma$ bands. We find that the static, limiting value of $\alpha^*$ falls in the range 0.25 to 0.35, which is higher than our previous result of 0.14, but still below the value expected from RPA. We show the reduced value is not a consequence of interlayer hopping effects, which were ignored in our previous analysis, but of a combination of excitonic effects in the $\pi \rightarrow \pi^*$ particle-hole continuum, and background screening from the $\sigma$-bonded electrons. We find that $\sigma$-band screening is extremely strong at distances of the order of a few nm, and should be highly effective at screening out short-distance, Hubbard-like interactions in graphene, as well as other carbon allotropes.Comment: 23 pages, 5 figure

Universidad virtual mixta: modelo de posicionamiento múltiple EDMIX para nichos en riesgo

The multiple positioning of the blended virtual superior education service (EDMIX) or simultaneous positioning, both in the enrolment niche as in the co-producers suppliers, associates in their minds the educative service with the attribute that satisfies each one of them, when more value or priority is perceived in it than in other options of life or occupation, considered in the same category of belonging. For the niche (capable young people, interested, economically vulnerables, no enroled), the perception of the benefits provided by superior education (ES), influenced by the cultural pattern that an profissional academic with a diploma has job, better quality of life and social status, is not enough to position EDMIX, at least that will guarantee: support to attenuate its economic vulnerability, terminal efficacy and vinculation to the productive sector; however, these attributes desired in the educative service need to be positioned in the several co-producers. Under a mixed methodological perspective, a forecaster exploratory design supported in hybrid methods and techniques for the collecting, analysis and interpretation of data, a model of multiple positioning that aligns the interests of each one of the involved towards the strategic objetive of reach a quality service is proposed. The community hopes that the effort invested in a superior preparation will produce, proportionally, human development, at least for the profissional itself; the municipal administration, as facilitator partner of the local instalations and equipment, could enhance and optimize with minimum investment the development of human and social capital; the professors and administrators, could consolidate their professional and vocational expectations; and the students, directly benefited, could obtain what explicitly or implicitly demand: the effectiveness of the project in which they have decided to participate. The sinergy of the quality promoves sustentability; but the disagreement, desertion and/or the positioning no desired of discredit.El posicionamiento múltiple del servicio de educación superior virtual mixto (EDMIX) o posicionamiento simultaneo, tanto en el nicho de matrícula como en los coproductores oferentes, asocia en sus mentes el servicio educativo con el atributo que satisface a cada uno de ellos, cuando en él perciben mayor valor o prioridad que en el de otras opciones de vida u ocupación, consideradas en la misma categoría de pertenencia. Para el nicho (jóvenes capaces, interesados, vulnerables económicamente, no matriculados), la percepción de los beneficios que proporciona la educación superior (ES), influenciada por el patrón cultural de que un profesionista universitario titulado tiene trabajo, mejor calidad de vida y estatus social, no es suficiente para posicionar EDMIX, al menos que garantizara: apoyos para atenuar su vulnerabilidad económica, eficacia terminal y vinculación al sector productivo; sin embargo, estos atributos deseados en el servicio educativo precisan de ser posicionados en los diversos coproductores. Bajo una perspectiva metodológica mixta, un diseño exploratorio pronosticador apoyados en métodos y técnicas híbridas para la recolección, análisis e interpretación de datos, se propone un modelo de posicionamiento múltiple que alinea los intereses de cada uno de los implicados hacia el objetivo estratégico de alcanzar un servicio de calidad. La comunidad espera que el esfuerzo invertido en una preparación superior reditúe proporcionalmente en desarrollo humano, al menos para el propio profesionista; la administración municipal, como socio facilitador de las instalaciones y equipos locales, que se potencie y optimice con mínima inversión el desarrollo de capital humano y social; los docentes y administrativos, que concreten sus expectativas profesional y de vocación, por supuesto los estudiantes directamente beneficiados, obtengan lo que explícita e implícitamente demandan: la efectividad del proyecto en el cual han decidido participar. La sinergia de calidad promueve sustentabilidad; pero la disconformidad, deserción y/o un posicionamiento no deseado de descrédito