1,254 research outputs found
Brane world creation from flat or almost flat space in dynamical tension string theories
There is great interest in the construction of brane worlds, where matter and
gravity are forced to be effective only in a lower dimensional surface , the
brane . How these could appear as a consequence of string theory is a crucial
question and this has been widely discussed. Here we will examine a distinct
scenario that appears in dynamical tension theories and where string tension is
positive between two surfaces separated by a short distance and at the two
surfaces themselves the string tensions become infinite, therefore producing an
effective confinement of the strings and therefore of all matter and gravity to
the space between these to surfaces, which is in fact a new type of stringy
brane world scenario. The basic formulation for obtaining this scenario consist
of assuming two types of strings characterized by a different constant of
integration related to the spontaneous string tension generation. These string
tension multiplied by the embedding metric define conformally related metrics
that both satisfy Einsteins equation. The braneworlds appear very naturally
when these two metrics are both flat spaces related by a special conformal
transformation. The two types of string tensions are determined and they blow
up at two close expanding surfaces. A puzzling aspect appears then: the
construction is based on flat spaces, but then there are also strings with very
large tension near the boundaries of the braneworld,so can the back reaction
from the infinite tension strings destroy the flat space background?.
Fortunatelly that can be resolved using the mechanism Universe creation from
almost flat (or empty) spaces, which incorporates a gas of very large string
tensions in a membrane, studied before in 1+1 membranes in a 2+1 embedding
space and now is generalized for a 1+(D-2) membrane moving in a 1+(D-1) space.Comment: Motivated on our previous paper, arXiv:2107.08005 [hep-th], we study
a gravity picture that allows to understand those results from a different
angle, 1O pages, typos corrected, a subsection eliminated. This is the final
version of the paper which has been accepted for publication in the European
Physics Journal C. arXiv admin note: text overlap with arXiv:2105.0227
The MogR Transcriptional Repressor Regulates Nonhierarchal Expression of Flagellar Motility Genes and Virulence in Listeria monocytogenes
Flagella are surface structures critical for motility and virulence of many bacterial species. In Listeria monocytogenes, MogR tightly represses expression of flagellin (FlaA) during extracellular growth at 37 Ā°C and during intracellular infection. MogR is also required for full virulence in a murine model of infection. Using in vitro and in vivo infection models, we determined that the severe virulence defect of MogR-negative bacteria is due to overexpression of FlaA. Specifically, overproduction of FlaA in MogR-negative bacteria caused pleiotropic defects in bacterial division (chaining phenotype), intracellular spread, and virulence in mice. DNA binding and microarray analyses revealed that MogR represses transcription of all known flagellar motility genes by binding directly to a minimum of two TTTT-N(5)-AAAA recognition sites positioned within promoter regions such that RNA polymerase binding is occluded. Analysis of MogR protein levels demonstrated that modulation of MogR repression activity confers the temperature-specificity to flagellar motility gene expression. Epistasis analysis revealed that MogR repression of transcription is antagonized in a temperature-dependent manner by the DegU response regulator and that DegU further regulates FlaA levels through a posttranscriptional mechanism. These studies provide the first known example to our knowledge of a transcriptional repressor functioning as a master regulator controlling nonhierarchal expression of flagellar motility genes
Patterns of Pathogenesis: Discrimination of Pathogenic and Nonpathogenic Microbes by the Innate Immune System
The dominant conceptual framework for understanding innate immunity has been that host cells respond to evolutionarily conserved molecular features of pathogens called pathogen-associated molecular patterns (PAMPs). Here, we propose that PAMPs should be understood in the context of how they are naturally presented by pathogens. This can be experimentally challenging, since pathogens, almost by definition, bypass host defense. Nevertheless, in this review, we explore the idea that the immune system responds to PAMPs in the context of additional signals that derive from common āpatterns of pathogenesisā employed by pathogens to infect, multiply within, and spread among their hosts
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Recombinant Listeria promotes tumor rejection by CD8+ T cell-dependent remodeling of the tumor microenvironment.
Agents that remodel the tumor microenvironment (TME), prime functional tumor-specific T cells, and block inhibitory signaling pathways are essential components of effective immunotherapy. We are evaluating live-attenuated, double-deleted Listeria monocytogenes expressing tumor antigens (LADD-Ag) in the clinic. Here we show in numerous mouse models that while treatment with nonrecombinant LADD induced some changes in the TME, no antitumor efficacy was observed, even when combined with immune checkpoint blockade. In contrast, LADD-Ag promoted tumor rejection by priming tumor-specific KLRG1+PD1loCD62L- CD8+ T cells. These IFNĪ³-producing effector CD8+ T cells infiltrated the tumor and converted the tumor from an immunosuppressive to an inflamed microenvironment that was characterized by a decrease in regulatory T cells (Treg) levels, a proinflammatory cytokine milieu, and the shift of M2 macrophages to an inducible nitric oxide synthase (iNOS)+CD206- M1 phenotype. Remarkably, these LADD-Ag-induced tumor-specific T cells persisted for more than 2 months after primary tumor challenge and rapidly controlled secondary tumor challenge. Our results indicate that the striking antitumor efficacy observed in mice with LADD-based immunotherapy stems from TME remodeling which is a direct consequence of eliciting potent, systemic tumor-specific CD8+ T cells
The Universe out of an Elementary Particle?
We consider a model of an elementary particle as a 2 + 1 dimensional brane
evolving in a 3 + 1 dimensional space. Introducing gauge fields that live in
the brane as well as normal surface tension can lead to a stable "elementary
particle" configuration. Considering the possibility of non vanishing vacuum
energy inside the bubble leads, when gravitational effects are considered, to
the possibility of a quantum decay of such "elementary particle" into an
infinite universe. Some remarkable features of the quantum mechanics of this
process are discussed, in particular the relation between possible boundary
conditions and the question of instability towards Universe formation is
analyzed
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A Potent and Effective Suicidal Listeria Vaccine Platform.
Live-attenuated Listeria monocytogenes has shown encouraging potential as an immunotherapy platform in preclinical and clinical settings. However, additional safety measures will enable application across malignant and infectious diseases. Here, we describe a new vaccine platform, termed Lm-RIID (L. monocytogenes recombinase-induced intracellular death), that induces the deletion of genes required for bacterial viability yet maintains potent T cell responses to encoded antigens. Lm-RIID grows normally in broth but commits suicide inside host cells by inducing Cre recombinase and deleting essential genes flanked by loxP sites, resulting in a self-limiting infection even in immunocompromised mice. Lm-RIID vaccination of mice induces potent CD8+ T cells and protects against virulent challenges, similar to live L. monocytogenes vaccines. When combined with Ī±-PD-1, Lm-RIID is as effective as live-attenuated L. monocytogenes in a therapeutic tumor model. This impressive efficacy, together with the increased clearance rate, makes Lm-RIID ideal for prophylactic immunization against diseases that require T cells for protection
CP and related phenomena in the context of Stellar Evolution
We review the interaction in intermediate and high mass stars between their
evolution and magnetic and chemical properties. We describe the theory of
Ap-star `fossil' fields, before touching on the expected secular diffusive
processes which give rise to evolution of the field. We then present recent
results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that
magnetic fields of the kind seen on the main-sequence already exist during the
pre-main sequence phase, in agreement with fossil field theory, and that the
origin of the slow rotation of Ap/Bp stars also lies early in the pre-main
sequence evolution; we also present results confirming a lack of stars with
fields below a few hundred gauss. We then seek which macroscopic motions
compete with atomic diffusion in determining the surface abundances of AmFm
stars. While turbulent transport and mass loss, in competition with atomic
diffusion, are both able to explain observed surface abundances, the interior
abundance distribution is different enough to potentially lead to a test using
asterosismology. Finally we review progress on the turbulence-driving and
mixing processes in stellar radiative zones.Comment: Proceedings of IAU GA in Rio, JD4 on Ap stars; 10 pages, 7 figure
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