9 research outputs found
Deformed General Relativity and Effective Actions from Loop Quantum Gravity
Canonical methods can be used to construct effective actions from deformed
covariance algebras, as implied by quantum-geometry corrections of loop quantum
gravity. To this end, classical constructions are extended systematically to
effective constraints of canonical quantum gravity and applied to model systems
as well as general metrics, with the following conclusions: (i) Dispersion
relations of matter and gravitational waves are deformed in related ways,
ensuring a consistent realization of causality. (ii) Inverse-triad corrections
modify the classical action in a way clearly distinguishable from curvature
effects. In particular, these corrections can be significantly larger than
often expected for standard quantum-gravity phenomena. (iii) Finally, holonomy
corrections in high-curvature regimes do not signal the evolution from collapse
to expansion in a "bounce," but rather the emergence of the universe from
Euclidean space at high density. This new version of signature-change cosmology
suggests a natural way of posing initial conditions, and a solution to the
entropy problem.Comment: 44 page
A no-singularity scenario in loop quantum gravity
Canonical methods allow the derivation of effective gravitational actions
from the behavior of space-time deformations reflecting general covariance.
With quantum effects, the deformations and correspondingly the effective
actions change, revealing dynamical implications of quantum corrections. A new
systematic way of expanding these actions is introduced showing as a first
result that inverse-triad corrections of loop quantum gravity simplify the
asymptotic dynamics near a spacelike collapse singularity. By generic quantum
effects, the singularity is removed.Comment: 10 page
Mosquito Infection Responses to Developing Filarial Worms
Human lymphatic filariasis is a mosquito-vectored disease caused by the nematode parasites Wuchereria bancrofti, Brugia malayi and Brugia timori. These are relatively large roundworms that can cause considerable damage in compatible mosquito vectors. In order to assess how mosquitoes respond to infection in compatible mosquito-filarial worm associations, microarray analysis was used to evaluate transcriptome changes in Aedes aegypti at various times during B. malayi development. Changes in transcript abundance in response to the different stages of B. malayi infection were diverse. At the early stages of midgut and thoracic muscle cell penetration, a greater number of genes were repressed compared to those that were induced (20 vs. 8). The non-feeding, intracellular first-stage larvae elicited few differences, with 4 transcripts showing an increased and 9 a decreased abundance relative to controls. Several cecropin transcripts increased in abundance after parasites molted to second-stage larvae. However, the greatest number of transcripts changed in abundance after larvae molted to third-stage larvae and migrated to the head and proboscis (120 induced, 38 repressed), including a large number of putative, immunity-related genes (∼13% of genes with predicted functions). To test whether the innate immune system of mosquitoes was capable of modulating permissiveness to the parasite, we activated the Toll and Imd pathway controlled rel family transcription factors Rel1 and Rel2 (by RNA interference knockdown of the pathway's negative regulators Cactus and Caspar) during the early stages of infection with B. malayi. The activation of either of these immune signaling pathways, or knockdown of the Toll pathway, did not affect B. malayi in Ae. aegypti. The possibility of LF parasites evading mosquito immune responses during successful development is discussed