48 research outputs found
Towards Minkowski Vacua in Type II String Compactifications
We study the vacuum structure of compactifications of type II string theories
on orientifolds with SU(3)xSU(3) structure. We argue that generalised geometry
enables us to treat these non-geometric compactifications using a supergravity
analysis in a way very similar to geometric compactifications. We find
supersymmetric Minkowski vacua with all the moduli stabilised at weak string
coupling and all the tadpole conditions satisfied. Generically the value of the
moduli fields in the vacuum is parametrically controlled and can be taken to
arbitrarily large values.Comment: 33 pages; v2 minor corrections, references added, version to appear
in JHE
Towards mirror symmetry \`a la SYZ for generalized Calabi-Yau manifolds
Fibrations of flux backgrounds by supersymmetric cycles are investigated. For
an internal six-manifold M with static SU(2) structure and mirror \hat{M}, it
is argued that the product M x \hat{M} is doubly fibered by supersymmetric
three-tori, with both sets of fibers transverse to M and \hat{M}. The mirror
map is then realized by T-dualizing the fibers. Mirror-symmetric properties of
the fluxes, both geometric and non-geometric, are shown to agree with previous
conjectures based on the requirement of mirror symmetry for Killing
prepotentials. The fibers are conjectured to be destabilized by fluxes on
generic SU(3)xSU(3) backgrounds, though they may survive at type-jumping
points. T-dualizing the surviving fibers ensures the exchange of pure spinors
under mirror symmetry.Comment: 30 pages, 3 figures, LaTeX; v2: references adde
DBI Inflation in the Tip Region of a Warped Throat
Previous work on DBI inflation, which achieves inflation through the motion
of a brane as it moves through a warped throat compactification, has
focused on the region far from the tip of the throat. Since reheating and other
observable effects typically occur near the tip, a more detailed study of this
region is required. To investigate these effects we consider a generalized warp
throat where the warp factor becomes nearly constant near the tip. We find that
it is possible to obtain 60 or more e-folds in the constant region, however
large non-gaussianities are typically produced due to the small sound speed of
fluctuations. For a particular well-studied throat, the Klebanov-Strassler
solution, we find that inflation near the tip may be generic and it is
difficult to satisfy current bounds on non-gaussianity, but other throat
solutions may evade these difficulties.Comment: 26 pages, 1 figure. v1. references added, typos corrected v2.
clarifications mad
Warped Reheating in Multi-Throat Brane Inflation
We investigate in some quantitative details the viability of reheating in
multi-throat brane inflationary scenarios by estimating and comparing the time
scales for the various processes involved. We also calculate within
perturbative string theory the decay rate of excited closed strings into KK
modes and compare with that of their decay into gravitons; we find that in the
inflationary throat the former is preferred. We also find that over a small but
reasonable range of parameters of the background geometry, these KK modes will
preferably tunnel to another throat (possibly containing the Standard Model)
instead of decaying to gravitons due largely to their suppressed coupling to
the bulk gravitons. Once tunneled, the same suppressed coupling to the
gravitons again allows them to reheat the Standard Model efficiently. We also
consider the effects of adding more throats to the system and find that for
extra throats with small warping, reheating still seems viable.Comment: 29 pages, 4 figures, discussions on closed string decay expanded,
references adde
Perdas de solo e nutrientes por erosão num Argissolo com resÃduos vegetais de cana-de-açúcar
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
Effects of spironolaetone on the plasma binding and unbound levels of testosterone and oestradiol in healthy men
Rate constants for hydrogen abstraction from alkoxides by a perfluoroalkyl radical. An oxyanion accelerated process
A combination of laser flash photolysis and competitive kinetic methods has been used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in water from a series of fluorinated alkoxides and aldehyde hydrates by the perfluoroalkyl radical, CF2CF2OCF 2CF2SO3 -Na+. The bimolecular rate constants observed for the \u3b2-fluorinated alkoxides were in the 105 M-1 s-1 range, such rates representing enhancements (relative to the respective alcohols) of between 100 and almost 1000-fold, depending on the reactivity of the alkoxide. Likewise, the monobasic sodium salts of chloral and fluoral hydrate exhibit similar rate enhancements, relative to their respective hydrates.Peer reviewed: YesNRC publication: Ye
Rate constants for hydrogen abstraction from alkoxides by a perfluoroalkyl radical. An oxyanion accelerated process
A combination of laser flash photolysis and competitive kinetic methods has been used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in water from a series of fluorinated alkoxides and aldehyde hydrates by the perfluoroalkyl radical, CF2CF2OCF 2CF2SO3 -Na+. The bimolecular rate constants observed for the \u3b2-fluorinated alkoxides were in the 105 M-1 s-1 range, such rates representing enhancements (relative to the respective alcohols) of between 100 and almost 1000-fold, depending on the reactivity of the alkoxide. Likewise, the monobasic sodium salts of chloral and fluoral hydrate exhibit similar rate enhancements, relative to their respective hydrates.Peer reviewed: YesNRC publication: Ye