1,531 research outputs found

    Section Extension from Hyperbolic Geometry of Punctured Disk and Holomorphic Family of Flat Bundles

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    The construction of sections of bundles with prescribed jet values plays a fundamental role in problems of algebraic and complex geometry. When the jet values are prescribed on a positive dimensional subvariety, it is handled by theorems of Ohsawa-Takegoshi type which give extension of line bundle valued square-integrable top-degree holomorphic forms from the fiber at the origin of a family of complex manifolds over the open unit 1-disk when the curvature of the metric of line bundle is semipositive. We prove here an extension result when the curvature of the line bundle is only semipositive on each fiber with negativity on the total space assumed bounded from below and the connection of the metric locally bounded, if a square-integrable extension is known to be possible over a double point at the origin. It is a Hensel-lemma-type result analogous to Artin's application of the generalized implicit function theorem to the theory of obstruction in deformation theory. The motivation is the need in the abundance conjecture to construct pluricanonical sections from flatly twisted pluricanonical sections. We also give here a new approach to the original theorem of Ohsawa-Takegoshi by using the hyperbolic geometry of the punctured open unit 1-disk to reduce the original theorem of Ohsawa-Takegoshi to a simple application of the standard method of constructing holomorphic functions by solving the d-bar equation with cut-off functions and additional blowup weight functions

    Use of Plasmodium falciparum culture-adapted field isolates for in vitro exflagellation-blocking assay

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    International audienceA major requirement for malaria elimination is the development of transmission-blocking interventions. In vitro transmission-blocking bioassays currently mostly rely on the use of very few Plasmodium falciparum reference laboratory strains isolated decades ago. To fill a piece of the gap between laboratory experimental models and natural systems, the purpose of this work was to determine if culture-adapted field isolates of P. falciparum are suitable for in vitro transmission-blocking bioassays targeting functional maturity of male gametocytes: exflagellation. Plasmodium falciparum isolates were adapted to in vitro culture before being used for in vitro gametocyte production. Maturation was assessed by microscopic observation of gametocyte morphology over time of culture and the functional viability of male gametocytes was assessed by microscopic counting of exflagellating gametocytes. Suitability for in vitro exflagellation-blocking bioassays was determined using dihydroartemisinin and methylene blue. In vitro gametocyte production was achieved using two isolates from French Guiana and two isolates from Cambodia. Functional maturity of male gametocytes was assessed by exflagellation observations and all four isolates could be used in exflagellation-blocking bioassays with adequate response to methylene blue and dihydroartemisinin. This work shows that in vitro culture-adapted P. falciparum field isolates of different genetic background, from South America and Southeast Asia, can successfully be used for bioassays targeting the male gametocyte to gamete transition, exflagellation

    Lidar depolarization characterization using a reference system

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    In this study, we present a new approach for the determination of polarization parameters of the Nicosia Cimel CE376 lidar system, using the PollyXT in Limassol as a reference instrument. The method is applied retrospectively to the measurements obtained during the 2021 Cyprus Fall Campaign. Lidar depolarization measurements represent valuable information for aerosol typing and for the quantification of some specific aerosol types such as dust and volcanic ash. An accurate characterization is required for quality measurements and to remove instrumental artifacts. In this article, we use the PollyXT, a widely used depolarization lidar, as our reference to evaluate the CE376 system's gain ratio and channel cross-talk. We use observations of transported dust from desert regions for this approach, with layers in the free troposphere. Above the boundary layer and the highest terrain elevation of the region, we can expect that, for long-range transport of aerosols, local effects should not affect the aerosol mixture enough for us to expect similar depolarization properties at the two stations (separated by ∼ 60 km). Algebraic equations are used to derive polarization parameters from the comparison of the volume depolarization ratio measured by the two systems. The applied methodology offers a promising opportunity to evaluate the polarization parameters of a lidar system, in cases where a priori knowledge of the cross-talk parameters is not available, or to transfer the polarization parameters from one system to the other.</p

    Endometrial stromal cells of women with recurrent miscarriage fail to discriminate between high- and low-quality human embryos

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    Background The aetiology of recurrent miscarriage (RM) remains largely unexplained. Women with RM have a shorter time to pregnancy interval than normally fertile women, which may be due to more frequent implantation of non-viable embryos. We hypothesized that human endometrial stromal cells (H-EnSCs) of women with RM discriminate less effectively between high-and low-quality human embryos and migrate more readily towards trophoblast spheroids than H-EnSCs of normally fertile women. Methodology/Principal Findings Monolayers of decidualized H-EnSCs were generated from endometrial biopsies of 6 women with RM and 6 fertile controls. Cell-free migration zones were created and the effect of the presence of a high-quality (day 5 blastocyst, n = 13), a low-quality (day 5 blastocyst with three pronuclei or underdeveloped embryo, n = 12) or AC-1M88 trophoblast cell line spheroid on H-ESC migratory activity was analyzed after 18 hours. In the absence of a spheroid or embryo, migration of H-EnSCs from fertile or RM women was similar. In the presence of a low-quality embryo in the zone, the migration of H-EnSCs of control women was inhibited compared to the basal migration in the absence of an embryo (P<0.05) and compared to the migration in the presence of high-quality embryo (p<0.01). Interestingly, the migratory response H-EnSCs of women with RM did not differ between high- and low-quality embryos. Furthermore, in the presence of a spheroid their migration was enhanced compared to the H-EnSCs of controls (p<0.001). Conclusions H-EnSCs of fertile women discriminate between high- and low-quality embryos whereas H-EnSCs of women with RM fail to do so. H-EnSCs of RM women have a higher migratory response to trophoblast spheroids. Future studies will focus on the mechanisms by which low-quality embryos inhibit the migration of H-EnSCs and how this is deregulated in women with RM

    Dominance of excitation continuum in the longitudinal spectrum of weakly coupled Heisenberg S=1/2 chains

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    A low-field spin flop transition in the quasi one-dimensional antiferromagnet \ba is exploited to study the polarization dependence of low-energy magnetic excitations. The measured longitudinal spectrum is best described as single broad continuum, with no sharp ``longitudinal mode'', in apparent contradiction with the commonly used chain-MF/RPA theories. The observed behavior is also quite different than that previously seen in the related \kcuf material, presumably due to a large difference in the relative strength of inter-chain interactions. The results highlight the limitations of the chain-MF/RPA approach.Comment: 4 pages, 4 figures. To appear in Phys. Rev. Lett. Volume 89, issue 19, 19720

    Long-range-transported Canadian smoke plumes in the lower stratosphere over northern France

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    Long-range-transported Canadian smoke layers in the stratosphere over northern France were detected by three lidar systems in August 2017. The peaked optical depth of the stratospheric smoke layer exceeds 0.20 at 532&thinsp;nm, which is comparable with the simultaneous tropospheric aerosol optical depth. The measurements of satellite sensors revealed that the observed stratospheric smoke plumes were transported from Canadian wildfires after being lofted by strong pyro-cumulonimbus. Case studies at two observation sites, Lille (lat 50.612, long 3.142, 60&thinsp;m&thinsp;a.s.l.) and Palaiseau (lat 48.712, long 2.215, 156&thinsp;m&thinsp;a.s.l.), are presented in detail. Smoke particle depolarization ratios are measured at three wavelengths: over 0.20 at 355&thinsp;nm, 0.18–0.19 at 532&thinsp;nm, and 0.04–0.05 at 1064&thinsp;nm. The high depolarization ratios and their spectral dependence are possibly caused by the irregular-shaped aged smoke particles and/or the mixing with dust particles. Similar results are found by several European lidar stations and an explanation that can fully resolve this question has not yet been found. Aerosol inversion based on lidar 2α+3β data derived a smoke effective radius of about 0.33&thinsp;µm for both cases. The retrieved single-scattering albedo is in the range of 0.8 to 0.9, indicating that the smoke plumes are absorbing. The absorption can cause perturbations to the temperature vertical profile, as observed by ground-based radiosonde, and it is also related to the ascent of the smoke plumes when exposed in sunlight. A direct radiative forcing (DRF) calculation is performed using the obtained optical and microphysical properties. The calculation revealed that the smoke plumes in the stratosphere can significantly reduce the radiation arriving at the surface, and the heating rate of the plumes is about 3.5&thinsp;K&thinsp;day−1. The study provides a valuable characterization for aged smoke in the stratosphere, but efforts are still needed in reducing and quantifying the errors in the retrieved microphysical properties as well as radiative forcing estimates.</p

    Hormonal Signal Amplification Mediates Environmental Conditions during Development and Controls an Irreversible Commitment to Adulthood

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    Many animals can choose between different developmental fates to maximize fitness. Despite the complexity of environmental cues and life history, different developmental fates are executed in a robust fashion. The nematode Caenorhabditis elegans serves as a powerful model to examine this phenomenon because it can adopt one of two developmental fates (adulthood or diapause) depending on environmental conditions. The steroid hormone dafachronic acid (DA) directs development to adulthood by regulating the transcriptional activity of the nuclear hormone receptor DAF-12. The known role of DA suggests that it may be the molecular mediator of environmental condition effects on the developmental fate decision, although the mechanism is yet unknown. We used a combination of physiological and molecular biology techniques to demonstrate that commitment to reproductive adult development occurs when DA levels, produced in the neuroendocrine XXX cells, exceed a threshold. Furthermore, imaging and cell ablation experiments demonstrate that the XXX cells act as a source of DA, which, upon commitment to adult development, is amplified and propagated in the epidermis in a DAF-12 dependent manner. This positive feedback loop increases DA levels and drives adult programs in the gonad and epidermis, thus conferring the irreversibility of the decision. We show that the positive feedback loop canalizes development by ensuring that sufficient amounts of DA are dispersed throughout the body and serves as a robust fate-locking mechanism to enforce an organism-wide binary decision, despite noisy and complex environmental cues. These mechanisms are not only relevant to C. elegans but may be extended to other hormonal-based decision-making mechanisms in insects and mammals

    PvDBPII elicits multiple antibody-mediated mechanisms that reduce growth in a Plasmodium vivax challenge trial

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    The receptor-binding domain, region II, of the Plasmodium vivax Duffy binding protein (PvDBPII) binds the Duffy antigen on the reticulocyte surface to mediate invasion. A heterologous vaccine challenge trial recently showed that a delayed dosing regimen with recombinant PvDBPII SalI variant formulated with adjuvant Matrix-MTM reduced the in vivo parasite multiplication rate (PMR) in immunized volunteers challenged with the Thai P. vivax isolate PvW1. Here, we describe extensive analysis of the polyfunctional antibody responses elicited by PvDBPII immunization and identify immune correlates for PMR reduction. A classification algorithm identified antibody features that significantly contribute to PMR reduction. These included antibody titre, receptor-binding inhibitory titre, dissociation constant of the PvDBPII-antibody interaction, complement C1q and Fc gamma receptor binding and specific IgG subclasses. These data suggest that multiple immune mechanisms elicited by PvDBPII immunization are likely to be associated with protection and the immune correlates identified could guide the development of an effective vaccine for P. vivax malaria. Importantly, all the polyfunctional antibody features that correlated with protection cross-reacted with both PvDBPII SalI and PvW1 variants, suggesting that immunization with PvDBPII should protect against diverse P. vivax isolates

    Dynamics of an anisotropic Haldane antiferromagnet in strong magnetic field

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    We report the results of elastic and inelastic neutron scattering experiments on the Haldane gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) performed at mK temperatures in a wide range of magnetic field applied parallel to the S = 1 spin chains. Even though this geometry is closest to an ideal axially symmetric configuration, the Haldane gap closes at the critical field Hc~4T, but reopens again at higher fields. The field dependence of the two lowest magnon modes is experimentally studied and the results are compared with the predictions of several theoretical models. We conclude that of several existing theories, only the recently proposed model [Zheludev et al., cond-mat/0301424 ] is able to reproduce all the features observed experimentally for different field orientations.Comment: 11 pages 8 figures submitted to Phys. Rev.
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