133 research outputs found
Observations on fluxes near anti-branes
We revisit necessary conditions for gluing local (anti-)D3 throats into flux
throats with opposite charge. These consistency conditions typically reveal
singularities in the three-form fluxes whose meaning is being debated. In this
note we prove, under well-motivated assumptions, that unphysical singularities
can potentially be avoided when the anti-branes polarise into spherical NS5
branes with a specific radius. If a consistent solution can then indeed be
found, our analysis seems to suggests a rather large correction to the radius
of the polarization sphere compared to the probe result. We furthermore comment
on the gluing conditions at finite temperature and point out that one specific
assumption of a recent no-go theorem can be broken if anti-branes are indeed to
polarise into spherical NS5 branes at zero temperature.Comment: 17 pages, 2 figures, v2: error corrected and text extende
A new class of de Sitter vacua in type IIB large volume compactifications
We construct a new class of metastable de Sitter vacua of flux
compactifications of type IIB string theory. These solutions provide a natural
extension of the `Large Volume Scenario' anti-de Sitter vacua, and can
analogously be realised at parametrically large volume and weak string
coupling, using standard supergravity. For these new vacua, a
positive vacuum energy is achieved from the inclusion of a small amount of
flux-induced supersymmetry breaking in the complex structure and axio-dilaton
sector, and no additional `uplift' contribution (e.g.~from anti-branes) is
required. We show that the approximate no-scale structure of the effective
theory strongly influences the spectrum of the stabilised moduli: one complex
structure modulus remains significantly lighter than the supersymmetry breaking
scale, and metastability requires only modest amounts of tuning. After
discussing these general results, we provide a recipe for constructing de
Sitter vacua on a given compactification manifold, and give an explicit example
of a de Sitter vacuum for the compactification on the Calabi-Yau orientifold
realised in . Finally, we note that these solutions have
intriguing implications for phenomenology, predicting no superpartners in the
spectrum below 50 TeV, and no WIMP dark matter.Comment: 34 page
Identifying the factors that determine ecosystem services provision in Pampean agroecosystems (Argentina) using a data-mining approach
Ecosystem services (ES) have become a key concept in the assessment of natural resources, as a way to connect human well-being and ecosystems degradation. However, ES quantification is considered a basic problem because provision varies considerably as a result of land use change and site-specific characteristics (i.e. climate, soil, topography, and time). Thus, more detailed studies are needed to assess whether these changes affect ecological variables. We explored the use of environmental and crop management variables in predicting the provision of four ES (soil C balance, soil N balance, N2O emission control and groundwater contamination control) in three agroecosystems located in the Pampa region (Argentina). Data-mining, represented by k-means cluster and classification trees, was used to identify the dependence of ES provision on the variation of both environmental and crop management factors. We used plot level crop management and environmental field information stored in a large database during a 10-year period. The k-means method selected five different clusters. The final configuration showed two contrasting clusters: one with the lowest ES provision, and another one with the highest ES provision. The five clusters were represented in the terminal nodes of the final classification tree. Regarding the predictive power of the variables, crop and year were the most important predictors. Then, differences observed in ES provision resulted from changes in land use (variable “crop”) and crop season (variable “year”). These results are meant to enlighten stakeholders in terms of how to manage Pampean agroecosystems in order to positively influence ES provision.Fil: Rositano, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; ArgentinaFil: Bert, Federico Esteban. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Piñeiro, Gervasio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Ecología; ArgentinaFil: Ferraro, Diego Omar. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin
Method and system for the automatic recognition of lesions in a set of breast magnetic resonance images
A method of identification of potential lesions of a breast from tomographic image datasets of a chest region of a patient, the- datasets comprising a plurality of voxels (2) each having an intensity value, the images including a region of interest (10) which comprises at least one breast (6). The method comprises the steps of: acquiring a set of images after the administration of a contrast agent to the patient; normalizing (254) the intensity of voxels (2) belonging to the region of interest (10) of the acquired images according to at least one normalization factor; classifying (255) each of the normalized voxels (2) on the basis of a classification criterion, in such a way as to identify regions (40) representing potential lesions. The method is characterized in that the normalization factor is based on normalization voxels (2) corresponding to an anatomical structure (34), the normalization voxels (2) having intensity values enhanced due to the administration of the contrast agent
Terabyte-scale supervised 3D training and benchmarking dataset of the mouse kidney
The performance of machine learning algorithms, when used for segmenting 3D biomedical images, does not reach the level expected based on results achieved with 2D photos. This may be explained by the comparative lack of high-volume, high-quality training datasets, which require state-of-the-art imaging facilities, domain experts for annotation and large computational and personal resources. The HR-Kidney dataset presented in this work bridges this gap by providing 1.7 TB of artefact-corrected synchrotron radiation-based X-ray phase-contrast microtomography images of whole mouse kidneys and validated segmentations of 33 729 glomeruli, which corresponds to a one to two orders of magnitude increase over currently available biomedical datasets. The image sets also contain the underlying raw data, threshold- and morphology-based semi-automatic segmentations of renal vasculature and uriniferous tubules, as well as true 3D manual annotations. We therewith provide a broad basis for the scientific community to build upon and expand in the fields of image processing, data augmentation and machine learning, in particular unsupervised and semi-supervised learning investigations, as well as transfer learning and generative adversarial networks
Terabyte-scale supervised 3D training and benchmarking dataset of the mouse kidney
The performance of machine learning algorithms, when used for segmenting 3D
biomedical images, does not reach the level expected based on results achieved
with 2D photos. This may be explained by the comparative lack of high-volume,
high-quality training datasets, which require state-of-the-art imaging
facilities, domain experts for annotation and large computational and personal
resources. The HR-Kidney dataset presented in this work bridges this gap by
providing 1.7 TB of artefact-corrected synchrotron radiation-based X-ray
phase-contrast microtomography images of whole mouse kidneys and validated
segmentations of 33 729 glomeruli, which corresponds to a one to two orders of
magnitude increase over currently available biomedical datasets. The image sets
also contain the underlying raw data, threshold- and morphology-based
semi-automatic segmentations of renal vasculature and uriniferous tubules, as
well as true 3D manual annotations. We therewith provide a broad basis for the
scientific community to build upon and expand in the fields of image
processing, data augmentation and machine learning, in particular unsupervised
and semi-supervised learning investigations, as well as transfer learning and
generative adversarial networks
The baryon vertex with magnetic flux
In this letter we generalise the baryon vertex configuration of AdS/CFT by
adding a suitable instantonic magnetic field on its worldvolume, dissolving
D-string charge. A careful analysis of the configuration shows that there is an
upper bound on the number of dissolved strings. This should be a manifestation
of the stringy exclusion principle. We provide a microscopical description of
this configuration in terms of a dielectric effect for the dissolved strings.Comment: 17 pages, 2 figures. V2: reference added. V3: version to appear in
JHE
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