Stealth Acceleration and Modified Gravity

We show how to construct consistent braneworld models which exhibit late time acceleration. Unlike self-acceleration, which has a de Sitter vacuum state, our models have the standard Minkowski vacuum and accelerate only in the presence of matter, which we dub ``stealth-acceleration''. We use an effective action for the brane which includes an induced gravity term, and allow for an asymmetric set-up. We study the linear stability of flat brane vacua and find the regions of parameter space where the set-up is stable. The 4-dimensional graviton is only quasi-localised in this set-up and as a result gravity is modified at late times. One of the two regions is strongly coupled and the scalar mode is eaten up by an extra symmetry that arises in this limit. Having filtered the well-defined theories we then focus on their cosmology. When the graviton is quasi-localised we find two main examples of acceleration. In each case, we provide an illustrative model and compare it to LambdaCDM.Comment: 32 pages, 5 figure

Genes de virulencia y bacteriocinas en cepas de Enterococcus faecalis aisladas desde diferentes muestras clínicas en la Región del Maule, Chile

Padilla, C (reprint author), Univ Talca, Dept Microbiol, Talca, Chile.The presence of virulence genes (VG) and bacteriocins from different clinical samples was studied in Enterococcus faecalis isolated from urinary tract infections (UTI), bacteremia and endodontitis and was correlated with haemolysin and gelatinase activity. We evaluated the presence of VG by PCR in 150 strains of E. faecalis including cylA, aggA, efaA, eep, gelE, esp, as-48, bac31, entL50 A/B, entA, ent P, entB, enlA and ent1071. Haemolysin and gelatinase activity was studied. gelE and cylA genes expressed hemolysin and gelatinase, respectively. This activity was observed in some strains of bacteremia, UTI and endodontitis. The highest number of VG was detected in bacteremic strains, being aggA and entA genes the most frequent. efaA, esp, entA, entL50A/B were associated with their clinical origin (p <0.05). The most common genetic profile was aggA-eep-enlA-entL50A/B. E. faecalis from UTI, bacteremia and endodontitis presented different gene combinations. Some of the genes studied were related to their clinical origin. The results obtained in this study are similar to those reported in other countries

Analysis of social performance of the industrial tomatoes food chain in Algeria

International audienceThe social life cycle assessment approach is used to measure the social performance of companies, using the rules of international labor as a reference. Our purpose is to measure the social performance of sub-sectors of the industrial tomatoes food chain in Algeria. Among the different currents of this approach, the method of attributes was adopted. The system boundaries include a nursery, 150 farms and the biggest cannery of the country. The working conditions are clearly in favour of the cannery and the nursery. At farm level, the hard and precarious work, the absence of social protection and the impossibility to constitute or join a trade union, as well as child labour, determine low social performance. There is a mismatch between the labor time needed at each stage of production and the value assigned to each of these steps.La démarche d’analyse sociale de cycle de vie sert à mesurer la performance sociale des entreprises au regard des règles internationales du travail. Notre objectif est précisément de mesurer les performances sociales des sous secteurs d’activités de la filière tomates industrielles en Algérie. Parmi les divers courants de cette démarche, nous avons adopté la méthode des attributs. Le périmètre de notre système inclut une pépinière, 150 exploitations agricoles et une conserverie. Les conditions de travail sont très favorables à la conserverie et à la pépinière. Au niveau des exploitations agricoles, la pénibilité du travail, la précarité du poste, l’absence de toute protection sociale et l’impossibilité de se constituer en syndicat, le fort emploi des enfants, engendrent une faible performance sociale. Il y a inadéquation entre le temps de travail nécessaire à chaque stade de la production et la valeur attribuée à chacune de ces étapes

Resonance in Asymmetric Warped Geometry

We study the spectrum of an asymmetric warped braneworld model with different AdS curvatures on either side of the brane. In addition to the RS-like modes we find a resonance state. Its mass is proportional to the geometric mean of the two AdS curvature scales, while the difference between them determines the strength of the resonance peak. There is a complementarity between the RS zero-mode and the resonance: making the asymmetry stronger weakens the zero-mode but strengthens the resonance, and vice versa. We calculate numerically the braneworld gravitational potential and discuss the holographic correspondence for the asymmetric model.Comment: 17 pages, 9 figures; v2 references with comments added; v3 two references added, JHEP versio

Effects of tacky mat contamination on bond degradation for Chemlok/liner and NBR/liner bonds

Tacky mats are placed by the rubber lay-up areas for the solid rocket motor segments. These mats dust off the shoes prior to entering the platform where the lay-up work is performed. The possibility exists that a tacky mat could be touched with gloved hands prior to handling the uncured nitride butadiene rubber (NBR). Tests were run to determine if NBR were accidentally touched would there be any degradation of the liner/NBR bond. The tacky mats were judged solely on the basis of bond degradation caused by either direct or indirect contamination. Test results all indicate that there was no notable NBR/Chemlok or liner/NBR bond degradation on samples that came into contact with the tacky mat material. Testing procedures are described. The tacky mat adhesive composition does not contain fluorocarbons or release agents that would affect bonding

Infra-red modification of gravity from asymmetric branes

We consider a single Minkowski brane sandwiched in between two copies of anti-de Sitter space. We allow the bulk Planck mass and cosmological constant to differ on either side of the brane. Linearised perturbations about this background reveal that gravity can be modified in the infra-red. At intermediate scales, the braneworld propagator mimics four-dimensional GR in that it has the correct momentum dependance. However it has the wrong tensor structure. Beyond a source dependant scale, we show that quadratic brane bending contributions become important, and conspire to correct the tensor structure of the propagator. We argue that even higher order terms can consistently be ignored up to very high energies, and suggest that there is no problem with strong coupling. We also consider scalar and vector perturbations in the bulk, checking for scalar ghosts.Comment: Version appearing in CQ

Ghosts in asymmetric brane gravity and the decoupled stealth limit

We study the spectrum of gravitational perturbations around a vacuum de Sitter brane in a 5D asymmetric braneworld model, with induced curvature on the brane. This generalises the stealth acceleration model proposed by Charmousis, Gregory and Padilla (CGP) which realises the Cardassian cosmology in which power law cosmic acceleration can be driven by ordinary matter. Whenever the bulk has infinite volume we find that there is always a perturbative ghost propagating on the de Sitter brane, in contrast to the Minkowski brane case analysed by CGP. We discuss the implication of this ghost for the stealth acceleration model, and identify a limiting case where the ghost decouples as the de Sitter curvature vanishes.Comment: 21 page

Electronically Tunable Phase Response for Phased array Patches

The design and prototyping of radiating elements with tunable phase response, for reconfigurable patch array antennas, is presented. Different options are found in the technical literature to obtain feasible reconfigurable array antennas: placing the active circuitry in the transmission lines or directly over the radiating element, obtaining the desired phase shift for each radiating element of the array. In this reported work, the second option is selected and active radiating elements at 12 GHz are designed and prototyped