Cascaded Raman slow light and optical spatial solitons in Kerr media

International audienceWe provide a complete experimental and numerical investigation of nonlinear beam propagation in a carbon disulfide liquid-filled Kerr slab waveguide using picosecond pulsed light. A first spatial analysis shows the generation of a multicolor solitary wave through the combined effects of cascaded Raman scattering and crossphase modulation. The impact of temporal effects on this self-trapped optical beam is further studied through a spatiotemporal analysis. It is shown in particular how cascaded Raman slow light induces optical delays between the solitonic components which prevents higher-order spatial soliton and provides a remarkable beam stability. Experimental observations are in very good agreement with numerical simulations of the spatiotemporal (1+1D) nonlinear Schr¨odinger equation including the Raman scattering

Interactions with M Cells and Macrophages as Key Steps in the Pathogenesis of Enterohemorragic Escherichia coli Infections

Enterohemorrhagic Escherichia coli (EHEC) are food-borne pathogens that can cause serious infections ranging from diarrhea to hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Translocation of Shiga-toxins (Stx) from the gut lumen to underlying tissues is a decisive step in the development of the infection, but the mechanisms involved remain unclear. Many bacterial pathogens target the follicle-associated epithelium, which overlies Peyer's patches (PPs), cross the intestinal barrier through M cells and are captured by mucosal macrophages. Here, translocation across M cells, as well as survival and proliferation of EHEC strains within THP-1 macrophages were investigated using EHEC O157:H7 reference strains, isogenic mutants, and 15 EHEC strains isolated from HC/HUS patients. We showed for the first time that E. coli O157:H7 strains are able to interact in vivo with murine PPs, to translocate ex vivo through murine ileal mucosa with PPs and across an in vitro human M cell model. EHEC strains are also able to survive and to produce Stx in macrophages, which induce cell apoptosis and Stx release. In conclusion, our results suggest that the uptake of EHEC by M cells and underlying macrophages in the PP may be a critical step in Stx translocation and release in vivo. A new model for EHEC infection in humans is proposed that could help in a fuller understanding of EHEC-associated diseases

Open Problems and Fundamental Limitations of Reinforcement Learning from Human Feedback

Reinforcement learning from human feedback (RLHF) is a technique for training AI systems to align with human goals. RLHF has emerged as the central method used to finetune state-of-the-art large language models (LLMs). Despite this popularity, there has been relatively little public work systematizing its flaws. In this paper, we (1) survey open problems and fundamental limitations of RLHF and related methods; (2) overview techniques to understand, improve, and complement RLHF in practice; and (3) propose auditing and disclosure standards to improve societal oversight of RLHF systems. Our work emphasizes the limitations of RLHF and highlights the importance of a multi-faceted approach to the development of safer AI systems

E. coli-mediated gut inflammation in genetically predisposed Crohn's disease patients

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Beam steering using optical parametric amplification in Kerr medium: a space-time analogy of parametric slow-light

International audienceIn a way analogous to a light pulse that can be optically delayed via slow light propagation in Kerr-type nonlinear media, we theoretically demonstrate that beam steering and spatial walk-off compensation can be achieved in noncollinear optical parametric amplification. We identify this effect as a result of the quadratic phase shift induced by parametric amplification that leads to the cancellation of the spatial walk-off and collinear propagation of all beams though they have different wavevectors. Experimental evidence is reported of a soliton array steering in a Kerr slab waveguide

The cyclopropene radical cation: Rovibrational level structure at low energies from high-resolution photoelectron spectra

ISSN:0021-9606ISSN:1089-769

Importance of Bacteria as Trigger in Inflammatory Bowel Disease

International audienceInflammatory bowel diseases (IBD) provide a complex model of host-microbe interactions underpinning disease pathogenesis. Although there is no widespread agreement on the aetiology of IBD, there is evidence that microorganisms lead to the often severe inflammatory response characteristic of the disease. IBD is thought to result from an inappropriate and continuing inflammatory response to pathobionts microbes in a genetically susceptible host. In this review, we discuss the complex microbial ecosystem of the mammalian gut, the underlying genetic factors that predispose to IBD, and how these gene variants may alter host-microbe interactions and propagate inflammation. Incentive should be given to research that will promote a better understanding of host-microbial interactions in the intestine and lay the foundations for new therapeutic approaches to both treat and prevent onset and relapse of intestinal inflammation in genetically susceptible hosts