156 research outputs found
Towards a new generation axion helioscope
We study the feasibility of a new generation axion helioscope, the most
ambitious and promising detector of solar axions to date. We show that large
improvements in magnetic field volume, x-ray focusing optics and detector
backgrounds are possible beyond those achieved in the CERN Axion Solar
Telescope (CAST). For hadronic models, a sensitivity to the axion-photon
coupling of \gagamma\gtrsim {\rm few} \times 10^{-12} GeV is
conceivable, 1--1.5 orders of magnitude beyond the CAST sensitivity. If axions
also couple to electrons, the Sun produces a larger flux for the same value of
the Peccei-Quinn scale, allowing one to probe a broader class of models. Except
for the axion dark matter searches, this experiment will be the most sensitive
axion search ever, reaching or surpassing the stringent bounds from SN1987A and
possibly testing the axion interpretation of anomalous white-dwarf cooling that
predicts of a few meV. Beyond axions, this new instrument will probe
entirely unexplored ranges of parameters for a large variety of axion-like
particles (ALPs) and other novel excitations at the low-energy frontier of
elementary particle physics.Comment: 37 pages, 11 figures, accepted for publication in JCA
CAST solar axion search with 3^He buffer gas: Closing the hot dark matter gap
The CERN Axion Solar Telescope (CAST) has finished its search for solar
axions with 3^He buffer gas, covering the search range 0.64 eV < m_a <1.17 eV.
This closes the gap to the cosmological hot dark matter limit and actually
overlaps with it. From the absence of excess X-rays when the magnet was
pointing to the Sun we set a typical upper limit on the axion-photon coupling
of g_ag < 3.3 x 10^{-10} GeV^{-1} at 95% CL, with the exact value depending on
the pressure setting. Future direct solar axion searches will focus on
increasing the sensitivity to smaller values of g_a, for example by the
currently discussed next generation helioscope IAXO.Comment: 5 pages, 2 figures. Last version uploade
The International Axion Observatory (IAXO)
The International Axion Observatory (IAXO) is a new generation axion
helioscope aiming at a sensitivity to the axion-photon coupling of a few
10 GeV, i.e. 1 - 1.5 orders of magnitude beyond the one currently
achieved by CAST. The project relies on improvements in magnetic field volume
together with extensive use of x-ray focusing optics and low background
detectors, innovations already successfully tested in CAST. Additional physics
cases of IAXO could include the detection of electron-coupled axions invoked to
solve the white dwarfs anomaly, relic axions, and a large variety of more
generic axion-like particles (ALPs) and other novel excitations at the
low-energy frontier of elementary particle physics. This contribution is a
summary of our paper [1] to which we refer for further details.Comment: 4 pages, 2 figures. To appear in the proceedings of the 7th Patras
Workshop on Axions, WIMPs and WISPs, Mykonos, Greece, 201
New solar axion search in CAST with He filling
The CERN Axion Solar Telescope (CAST) searches for conversion in
the 9 T magnetic field of a refurbished LHC test magnet that can be directed
toward the Sun. Two parallel magnet bores can be filled with helium of
adjustable pressure to match the X-ray refractive mass to the axion
search mass . After the vacuum phase (2003--2004), which is optimal for
eV, we used He in 2005--2007 to cover the mass range of
0.02--0.39 eV and He in 2009--2011 to scan from 0.39--1.17 eV. After
improving the detectors and shielding, we returned to He in 2012 to
investigate a narrow range around 0.2 eV ("candidate setting" of our
earlier search) and 0.39--0.42 eV, the upper axion mass range reachable with
He, to "cross the axion line" for the KSVZ model. We have improved the
limit on the axion-photon coupling to (95% C.L.), depending on the pressure settings. Since 2013, we
have returned to vacuum and aim for a significant increase in sensitivity.Comment: CAST Collaboration 6 pages 3 figure
CAST constraints on the axion-electron coupling
In non-hadronic axion models, which have a tree-level axion-electron
interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton
scattering, and axio-recombination, the "BCA processes." Based on a new
calculation of this flux, including for the first time axio-recombination, we
derive limits on the axion-electron Yukawa coupling g_ae and axion-photon
interaction strength g_ag using the CAST phase-I data (vacuum phase). For m_a <
10 meV/c2 we find g_ag x g_ae< 8.1 x 10^-23 GeV^-1 at 95% CL. We stress that a
next-generation axion helioscope such as the proposed IAXO could push this
sensitivity into a range beyond stellar energy-loss limits and test the
hypothesis that white-dwarf cooling is dominated by axion emission
Active Suppression of Early Immune Response in Tobacco by the Human Pathogen Salmonella Typhimurium
The persistence of enteric pathogens on plants has been studied extensively, mainly due to the potential hazard of human pathogens such as Salmonella enterica being able to invade and survive in/on plants. Factors involved in the interactions between enteric bacteria and plants have been identified and consequently it was hypothesized that plants may be vectors or alternative hosts for enteric pathogens. To survive, endophytic bacteria have to escape the plant immune systems, which function at different levels through the plant-bacteria interactions. To understand how S. enterica survives endophyticaly we conducted a detailed analysis on its ability to elicit or evade the plant immune response. The models of this study were Nicotiana tabacum plants and cells suspension exposed to S. enterica serovar Typhimurium. The plant immune response was analyzed by looking at tissue damage and by testing oxidative burst and pH changes. It was found that S. Typhimurium did not promote disease symptoms in the contaminated plants. Live S. Typhimurium did not trigger the production of an oxidative burst and pH changes by the plant cells, while heat killed or chloramphenicol treated S. Typhimurium and purified LPS of Salmonella were significant elicitors, indicating that S. Typhimurium actively suppress the plant response. By looking at the plant response to mutants defective in virulence factors we showed that the suppression depends on secreted factors. Deletion of invA reduced the ability of S. Typhimurium to suppress oxidative burst and pH changes, indicating that a functional SPI1 TTSS is required for the suppression. This study demonstrates that plant colonization by S. Typhimurium is indeed an active process. S. Typhimurium utilizes adaptive strategies of altering innate plant perception systems to improve its fitness in the plant habitat. All together these results suggest a complex mechanism for perception of S. Typhimurium by plants
Effects of C282Y, H63D, and S65C HFE gene mutations, diet, and life-style factors on iron status in a general Mediterranean population from Tarragona, Spain
Mutations in the HFE gene result in iron overload and can produce hereditary hemochromatosis (HH), a disorder of iron metabolism characterized by increased intestinal iron absorption. Dietary quality, alcoholism and other life-style factors can increase the risk of iron overload, especially among genetically at risk populations. Polymorphisms of the HFE gene (C282Y, H63D and S65C) were measured together with serum ferritin (SF), transferrin saturation (TS) and hemoglobin, to measure iron status, in randomly-selected healthy subjects living in the Spanish Mediterranean coast (n = 815; 425 females, 390 males), 18 to 75 years of age. The intake of dietary components that affect iron absorption was calculated from 3-day dietary records. The presence of C282Y/H63D compound heterozygote that had a prevalence of 2.8% in males and 1.2% in females was associated with an elevated TS and SF. No subject was homozygous for C282Y or S65C. The C282Y heterozygote, H63D heterozygote and homozygote and H63D/S65C compound heterozygote genotypes were associated with increased TS relative to the wild type in the general population. These genotypes together with the alcohol and iron intake increase the indicators of iron status, while calcium intake decreases them. We did not observe any affect of the S65C heterozygote genotype on these levels. All the HFE genotypes except for the S65C heterozygote together with the alcohol, iron and calcium intake affect the indicators of iron status. The C282Y/H63D compound heterozygote genotype has the higher phenotypic expression in our Spanish Mediterranean population
Mechanism of effector capture and delivery by the type IV secretion system from Legionella pneumophila
Legionella pneumophila is a bacterial pathogen that utilises a Type IV secretion (T4S) system to inject effector proteins into human macrophages. Essential to the recruitment and delivery of effectors to the T4S machinery is the membrane-embedded T4 coupling complex (T4CC). Here, we purify an intact T4CC from the Legionella membrane. It contains the DotL ATPase, the DotM and DotN proteins, the chaperone module IcmSW, and two previously uncharacterised proteins, DotY and DotZ. The atomic resolution structure reveals a DotLMNYZ hetero-pentameric core from which the flexible IcmSW module protrudes. Six of these hetero-pentameric complexes may assemble into a 1.6-MDa hexameric nanomachine, forming an inner membrane channel for effectors to pass through. Analysis of multiple cryo EM maps, further modelling and mutagenesis provide working models for the mechanism for binding and delivery of two essential classes of Legionella effectors, depending on IcmSW or DotM, respectively
The role of enzyme replacement therapy in severe Hunter syndrome—an expert panel consensus
Intravenous enzyme replacement therapy (ERT) with idursulfase for Hunter syndrome has not been demonstrated to and is not predicted to cross the blood–brain barrier. Nearly all published experience with ERT with idursulfase has therefore been in patients without cognitive impairment (attenuated phenotype). Little formal guidance is available on the issues surrounding ERT in cognitively impaired patients with the severe phenotype. An expert panel was therefore convened to provide guidance on these issues. The clinical experience of the panel with 66 patients suggests that somatic improvements (e.g., reduction in liver volume, increased mobility, and reduction in frequency of respiratory infections) may occur in most severe patients. Cognitive benefits have not been seen. It was agreed that, in general, severe patients are candidates for at least a 6–12-month trial of ERT, excluding patients who are severely neurologically impaired, those in a vegetative state, or those who have a condition that may lead to near-term death. It is imperative that the treating physician discuss the goals of treatment, methods of assessment of response, and criteria for discontinuation of treatment with the family before ERT is initiated. Conclusion: The decision to initiate ERT in severe Hunter syndrome should be made by the physician and parents and must be based on realistic expectations of benefits and risks, with the understanding that ERT may be withdrawn in the absence of demonstrable benefits
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