1,732 research outputs found
Superconducting Superstructure for the TESLA Collider
We discuss the new layout of a cavity chain (superstructure) allowing, we
hope, significant cost reduction of the RF system of both linacs of the TESLA
linear collider. The proposed scheme increases the fill factor and thus makes
an effective gradient of an accelerator higher. We present mainly computations
we have performed up to now and which encouraged us to order the copper model
of the scheme, still keeping in mind that experiments with a beam will be
necessary to prove if the proposed solution can be used for the acceleration.Comment: 11 page
Vitamin D status and risk of rheumatoid arthritis: systematic review and meta-analysis
Background Vitamin D is important for immunomodulation and may play a role in autoimmune diseases. Studies have reported a high prevalence of vitamin D deficiency in rheumatoid arthritis (RA) patients, and vitamin D status, assessed by circulating 25-hydroxyvitamin D [25(OH)D] concentration, is inversely associated with RA disease activity. However, it is unclear whether vitamin D deficiency increases the risk of later developing RA. We conducted a systematic review and meta-analysis of pre-diagnostic 25(OH)D concentrations and risk of RA. Methods Medline and Embase databases were searched in December 2021 using various keywords for ‘vitamin D’, ‘rheumatoid arthritis’, and ‘prospective study’. Publications identified from the search were screened for eligibility, studies were excluded if vitamin D status was measured at or after RA diagnosis, and data were extracted from relevant articles. Bayesian meta-analysis was used to estimate the summary relative risk (RR) and 95% credible interval (CrI) for risk of RA in relation to circulating 25(OH)D concentrations, as well as the between-study heterogeneity. Results The search strategy yielded 908 records, of which 4 publications reporting on 7 studies, involving a total of 15,604 participants and 1049 incident RA cases, were included in the meta-analysis. There was no suggestion of an association between 25(OH)D concentration and subsequent risk of RA. The pooled RR per 25 nmol/L increment in 25(OH)D was 0.96 (95% CrI 0.82–1.13; I2 = 52%). No associations were evident in men (RR = 1.02, 95% CrI 0.65–1.61; I2 = 77%, 2 studies) or women (RR = 0.94, 95% CrI 0.73–1.22; I2 = 71%, 4 studies). Conclusions This systematic review and meta-analysis did not identify evidence of an association between 25(OH)D and RA risk, but there was notable between-study heterogeneity and a lack of precision. Investigations in large-scale prospective studies with long follow-up or suitably designed Mendelian randomisation studies with consideration of potential non-linear relationships are needed to determine whether vitamin D is involved in RA aetiology
Progress on a spherical TPC for low energy neutrino detection
The new concept of the spherical TPC aims at relatively large target masses
with low threshold and background, keeping an extremely simple and robust
operation. Such a device would open the way to detect the neutrino-nucleus
interaction, which, although a standard process, remains undetected due to the
low energy of the neutrino-induced nuclear recoils. The progress in the
development of the fist 1 m prototype at Saclay is presented. Other physics
goals of such a device could include supernova detection, low energy neutrino
oscillations and study of non-standard properties of the neutrino, among
others.Comment: 3 pages, talk given at the 9th Workshop on Topics in Astroparticle
and Underground Physics, Zaragoza, September 10-1
CAST microbulk micromegas in the Canfranc Underground Laboratory
During the last taking data campaigns of the CAST experiment, the micromegas
detectors have achieved background levels of keVcms between 2 and 9 keV. This performance has
been possible thanks to the introduction of the microbulk technology, the
implementation of a shielding and the development of discrimination algorithms.
It has motivated new studies towards a deeper understanding of CAST detectors
background. One of the working lines includes the construction of a replica of
the set-up used in CAST by micromegas detectors and its installation in the
Canfranc Underground Laboratory. Thanks to the comparison between the
performance of the detectors underground and at surface, shielding upgrades,
etc, different contributions to the detectors background have been evaluated.
In particular, an upper limit keVcms
for the intrinsic background of the detector has been obtained. This work means
a first evaluation of the potential of the newest micromegas technology in an
underground laboratory, the most suitable environment for Rare Event Searches.Comment: 6 pages, 8 figures. To appear in the proceedings of the 2nd
International Conference on Technology and Instrumentation for Particle
Physics (TIPP 2011
X-ray detection with Micromegas with background levels below 10 keVcms
Micromegas detectors are an optimum technological choice for the detection of
low energy x-rays. The low background techniques applied to these detectors
yielded remarkable background reductions over the years, being the CAST
experiment beneficiary of these developments. In this document we report on the
latest upgrades towards further background reductions and better understanding
of the detectors' response. The upgrades encompass the readout electronics, a
new detector design and the implementation of a more efficient cosmic muon veto
system. Background levels below 10keVcms have been
obtained at sea level for the first time, demonstrating the feasibility of the
expectations posed by IAXO, the next generation axion helioscope. Some results
obtained with a set of measurements conducted in the x-ray beam of the CAST
Detector Laboratory will be also presented and discussed
Characterization of microbulk detectors in argon- and neon-based mixtures
A recent Micromegas manufacturing technique, so called Microbulk, has been
developed, improving the uniformity and stability of this kind of detectors.
Excellent energy resolutions have been obtained, reaching values as low as 11%
FWHM at 5.9 keV in Ar+5%iC4H10. This detector has other advantages like its
flexible structure, low material budget and high radio-purity. Two microbulk
detectors with gaps of 50 and 25 um have been characterized in argon- and
neon-based mixtures with ethane, isobutane and cyclohexane. The results will be
presented and discussed. The gain curves have been fitted to the Rose-Korff
gain model and dependences of the electron mean free path and the threshold
energy for ionization have been obtained. The possible relation between these
two parameters and the energy resolution will be also discussed.Comment: Submitted to the Journal of Instrumentatio
Lowering the background level and the energy threshold of Micromegas x-ray detectors for axion searches
Axion helioscopes search for solar axions by their conversion in x-rays in
the presence of high magnetic fields. The use of low background x-ray detectors
is an essential component contributing to the sensitivity of these searches. In
this work, we review the recent advances on Micromegas detectors used in the
CERN Axion Solar Telescope (CAST) and proposed for the future International
Axion Observatory (IAXO). The actual setup in CAST has achieved background
levels below 10 keV cm s, a factor 100 lower than
the first generation of Micromegas detectors. This reduction is based on active
and passive shielding techniques, the selection of radiopure materials, offline
discrimination techniques and the high granularity of the readout. We describe
in detail the background model of the detector, based on its operation at CAST
site and at the Canfranc Underground Laboratory (LSC), as well as on Geant4
simulations. The best levels currently achieved at LSC are low than 10
keV cm s and show good prospects for the application of
this technology in IAXO. Finally, we present some ideas and results for
reducing the energy threshold of these detectors below 1 keV, using
high-transparent windows, autotrigger electronics and studying the cluster
shape at different energies. As a high flux of axion-like-particles is expected
in this energy range, a sub-keV threshold detector could enlarge the physics
case of axion helioscopes.Comment: Proceedings of 3rd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2014
The Study of TeV Variability and Duty Cycle of Mrk 421 from 3 Years of Observations with the Milagro Observatory
TeV flaring activity with time scales as short as tens of minutes and an
orphan TeV flare have been observed from the blazar Markarian 421 (Mrk 421).
The TeV emission from Mrk 421 is believed to be produced by leptonic
synchrotron self-Compton (SSC) emission. In this scenario, correlations between
the X-ray and the TeV fluxes are expected, TeV orphan flares are hardly
explained and the activity (measured as duty cycle) of the source at TeV
energies is expected to be equal or less than that observed in X-rays if only
SSC is considered. To estimate the TeV duty cycle of Mrk 421 and to establish
limits on its variability at different time scales, we continuously observed
Mrk 421 with the Milagro observatory. Mrk 421 was detected by Milagro with a
statistical significance of 7.1 standard deviations between 2005 September 21
and 2008 March 15. The observed spectrum is consistent with previous
observations by VERITAS. We estimate the duty cycle of Mrk 421 for energies
above 1 TeV for different hypothesis of the baseline flux and for different
flare selections and we compare our results with the X-ray duty cycle estimated
by Resconi et al. 2009. The robustness of the results is discussed.Comment: 27 pages, 6 figures, ApJ accepte
Preventing type 2 diabetes mellitus in Qatar by reducing obesity, smoking, and physical inactivity: mathematical modeling analyses.
BACKGROUND: The aim of this study was to estimate the impact of reducing the prevalence of obesity, smoking, and physical inactivity, and introducing physical activity as an explicit intervention, on the burden of type 2 diabetes mellitus (T2DM), using Qatar as an example. METHODS: A population-level mathematical model was adapted and expanded. The model was stratified by sex, age group, risk factor status, T2DM status, and intervention status, and parameterized by nationally representative data. Modeled interventions were introduced in 2016, reached targeted level by 2031, and then maintained up to 2050. Diverse intervention scenarios were assessed and compared with a counter-factual no intervention baseline scenario. RESULTS: T2DM prevalence increased from 16.7% in 2016 to 24.0% in 2050 in the baseline scenario. By 2050, through halting the rise or reducing obesity prevalence by 10-50%, T2DM prevalence was reduced by 7.8-33.7%, incidence by 8.4-38.9%, and related deaths by 2.1-13.2%. For smoking, through halting the rise or reducing smoking prevalence by 10-50%, T2DM prevalence was reduced by 0.5-2.8%, incidence by 0.5-3.2%, and related deaths by 0.1-0.7%. For physical inactivity, through halting the rise or reducing physical inactivity prevalence by 10-50%, T2DM prevalence was reduced by 0.5-6.9%, incidence by 0.5-7.9%, and related deaths by 0.2-2.8%. Introduction of physical activity with varying intensity at 25% coverage reduced T2DM prevalence by 3.3-9.2%, incidence by 4.2-11.5%, and related deaths by 1.9-5.2%. CONCLUSIONS: Major reductions in T2DM incidence could be accomplished by reducing obesity, while modest reductions could be accomplished by reducing smoking and physical inactivity, or by introducing physical activity as an intervention
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