286 research outputs found
De Sitter from T-branes
Hidden sector D7-branes with non-zero gauge flux are a generic feature of
type IIB compactifications. A non-vanishing Fayet-Iliopoulos term induced by
non-zero gauge flux leads to a T-brane configuration. Expanding the D7-brane
action around this T-brane background in the presence of three-form
supersymmetry breaking fluxes, we obtain a positive definite contribution to
the moduli scalar potential which can be used as an uplifting source for de
Sitter vacua. In this way we provide a higher-dimensional understanding of
known 4D mechanisms of de Sitter uplifting based on hidden sector F-terms which
are non-zero because of D-term stabilisation.Comment: 23 pages, 2 figure
Moduli Stabilisation with Nilpotent Goldstino: Vacuum Structure and SUSY Breaking
We study the effective field theory of KKLT and LVS moduli stabilisation
scenarios coupled to an anti-D3-brane at the tip of a warped throat. We
describe the presence of the anti-brane in terms of a nilpotent goldstino
superfield in a supersymmetric effective field theory. The introduction of this
superfield produces a term that can lead to a de Sitter minimum. We fix the
Kaehler moduli dependence of the nilpotent field couplings by matching this
term with the anti-D3-brane uplifting contribution. The main result of this
paper is the computation, within this EFT, of the soft supersymmetry breaking
terms in both KKLT and LVS for matter living on D3-brane (leaving the D7-brane
analysis to an appendix). A handful of distinct phenomenological scenarios
emerge that could have low energy implications, most of them having a split
spectrum of soft masses. Some cosmological and phenomenological properties of
these models are discussed. We also check that the attraction between the
D3-brane and the anti-D3-brane does not affect the leading contribution to the
soft masses and does not destabilise the system.Comment: 26+14 pages, 1 figure; references and clarifications added, typos
fixe
Thermodynamics of the Stephani Universes
We examine the consistency of the thermodynamics of the most general class of
conformally flat solution with an irrotational perfect fluid source (the
Stephani Universes). For the case when the isometry group has dimension
, the Gibbs-Duhem relation is always integrable, but if it is only
integrable for the particular subclass (containing FRW cosmologies)
characterized by and by admitting a conformal motion parallel to the
4-velocity. We provide explicit forms of the state variables and equations of
state linking them. These formal thermodynamic relations are determined up to
an arbitrary function of time which reduces to the FRW scale factor in the FRW
limit of the solutions. We show that a formal identification of this free
parameter with a FRW scale factor determined by FRW dynamics leads to an
unphysical temperature evolution law. If this parameter is not identified with
a FRW scale factor, it is possible to find examples of solutions and formal
equations of state complying with suitable energy conditions and reasonable
asymptotic behavior and temperature laws.Comment: 25 pages, Plain.TeX, four figure
En torno a Cultures. Revista Asturiana de Cultura
Among the journals of cultural anthropology that caters to regional studies, Cultures stands out not only because its editors chose to express its scientific production in the regional language, in this case Asturian, but also because they approach anthropological research from the standpoint of the particular traits of the culture out of which the social project underlying the journal grew. This approach, however, has not limited Cultures to exclusively Asturian topics.En el panorama de las revistas que se dedican a la antropologÃa cultural en un ámbito territorial regional. Cultures se distingue no sólo por haber tomado la opción de usar la propia lengua, en este caso el asturiano, como vehÃculo de expresión del conocimiento cientÃfico, sino también por enfocar el estudio antropológico a partir de la idiosincrasia y el carácter diferencial de la cultura particular de la que surge la iniciativa social de la revista, pero sin circunscribirse a una temática meramente asturiana
Repulsive regions in Lemaître–Tolman–Bondi gravitational collapse
We show that in the inhomogeneous Lemaître–Tolman–Bondi space–time there are specific regions in which repulsive gravity exists. To find these regions, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. In addition, we analyze the effects of repulsive gravity on the dynamics of the gravitational collapse. In particular, we investigate the collapse in the case of the parabolic solution for the effective scale factor of the Lemaître–Tolman–Bondi metric, corresponding to the marginally bound case. Exploring the corresponding cut-offs at which gravity becomes repulsive, we notice that black holes with dominant repulsive effects are not excluded a priori. Indeed, we demonstrate that the collapse leads, in general, to the formation of a central naked singularity; however, for particular values of the free parameters entering the model, black holes with dominant repulsive gravity can exist. We show that the expected physical process is not modified as the marginally bound condition is dropped out. Moreover, we show that this is true independently of the hypothesis that the energy–momentum tensor is built up in terms of pressureless matter. Further, we demonstrate that geodesic deviations can depend on the sign of the curvature eigenvalues. Finally, we give an astrophysical interpretation of black holes with dominant repulsive gravity. Indeed, we argue that compact objects with dominant repulsive gravity could be interpreted as progenitors of Gamma Ray Bursts
Protection of shallow marine ecosystems in Galapagos by permanent moorings
We describe a new system of permanent moorings designed for tour boats, to be installed throughout Galapagos, and the deployment of a research and monitoring vessel to Wolf Island
Review: computer vision applied to the inspection and quality control of fruits and vegetables
This is a review of the current existing literature concerning the inspection of fruits and vegetables with the application of computer vision, where the techniques most used to estimate various properties related to quality are analyzed. The objectives of the typical applications of such systems include the classification, quality estimation according to the internal and external characteristics, supervision of fruit processes during storage or the evaluation of experimental treatments. In general, computer vision systems do not only replace manual inspection, but can also improve their skills. In conclusion, computer vision systems are powerful tools for the automatic inspection of fruits and vegetables. In addition, the development of such systems adapted to the food industry is fundamental to achieve competitive advantages
A database of Calabi-Yau orientifolds and the size of D3-tadpoles
The classification of 4D reflexive polytopes by Kreuzer and Skarke allows for a systematic construction of Calabi-Yau hypersurfaces as fine, regular, star triangulations (FRSTs). Until now, the vastness of this geometric landscape remains largely unexplored. In this paper, we construct Calabi-Yau orientifolds from holomorphic reflection involutions of such hypersurfaces with Hodge numbers h(1,1) <= 12. In particular, we compute orientifold configurations for all favourable FRSTs for h(1,1) <= 7, while randomly sampling triangulations for each pair of Hodge numbers up to h(1,1) = 12. We find explicit string compactifications on these orientifolded Calabi-Yaus for which the D3-charge contribution coming from Op-planes grows linearly with the number of complex structure and Kahler moduli. We further consider non-local D7-tadpole cancellation through Whitney branes. We argue that this leads to a significant enhancement of the total D3-tadpole as compared to conventional SO(8) stacks with (4 + 4) D7-branes on top of 07-planes. In particular, before turning-on worldvolume fluxes, we find that the largest D3-tadpole in this class occurs for Calabi-Yau threefolds with (h(+)(1,1), h(-)(1,2) ) = (11, 491) with D3-brane charges vertical bar Q(D3)vertical bar = 504 for the local D7 case and vertical bar Q(D3)vertical bar = 6, 664 for the non-local Whitney branes case, which appears to be large enough to cancel tadpoles and allow fluxes to stabilise all complex structure moduli. Our data is publicly available under the following link https://github.com/AndreasSchachner/CY_Orientifold_database
Palacios del Sil: relatu etnográficu
Nesti trabayu faise un relatu de los rasgos fundamentales
de la cultura ya las instituciones sociales propias del concechu de
Palacios del Sil, asitiáu al norte de la provincia de L.lión. Esti relatu
faise con un repasu de los trabachos de campu, cono métodu de
la observación participante, ya la bibliografÃa que l’autor d’esti estudiu
vien fayendo dende cuantayá. Escomiénzase estudiando los
aspeutos de la ganaderÃa, na que la vaca tien un puestu mui importante
que chega a tolos ámbitos culturales, como’l mundu simbólicu
ya las emociones coleutivas. Por supuestu, outros aspeutos de
la ganaderÃa son bien relevantes ya compleméntanse cona actividá
agrÃcola, también de muita importancia social ya económica. Tras
l’estudiu de los trabachos de recolección, que tradicionalmente
tenÃan una importancia decisiva na vida diaria, estúdiase’l mundu
máxicu, especialmente en cuantas al tema del mal de güechu ya
los ritos de curación en xeneral. Al final trátase la cuestión de la
tradición oral, que yÃa mui rica en cuentos populares, l.leendas ya
mitos, que se tienen pañao ya axeitao l.literariamente nuna interesante
literatura local
Diseño de una antena impresa de ranura plegada sintonizable
In this Project the design and manufacturing of a folded slot frequency tunable antenna is described, doing it using
a squared geometry printed antenna. The working frequency of the antenna is 1 GHz. A coplanar transmission
line with an impedance of 50 Ohms performs the electrical power supply. To obtain the tunable effect, the design
includes two varactor diodes working as electronic ballasts. With the diodes is possible to vary the resonance
frequency from the entrance tension. The main objective of this Project is to obtain a relative bandwidth above the
15% within the diodes frequency range.IngenierÃa de Sistemas de Comunicacione
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