527 research outputs found
Interferometric length metrology for the dimensional control of ultra-stable Ring Laser Gyroscopes
We present the experimental test of a method for controlling the absolute
length of the diagonals of square ring laser gyroscopes. The purpose is to
actively stabilize the ring cavity geometry and to enhance the rotation sensor
stability in order to reach the requirements for the detection of the
relativistic Lense-Thirring effect with a ground-based array of optical
gyroscopes. The test apparatus consists of two optical cavities 1.32 m in
length, reproducing the features of the ring cavity diagonal resonators of
large frame He-Ne ring laser gyroscopes. The proposed measurement technique is
based on the use of a single diode laser, injection locked to a frequency
stabilized He-Ne/Iodine frequency standard, and a single electro-optic
modulator. The laser is modulated with a combination of three frequencies
allowing to lock the two cavities to the same resonance frequency and, at the
same time, to determine the cavity Free Spectral Range (FSR). We obtain a
stable lock of the two cavities to the same optical frequency reference,
providing a length stabilization at the level of 1 part in , and the
determination of the two FSRs with a relative precision of 0.2 ppm. This is
equivalent to an error of 500 nm on the absolute length difference between the
two cavities
Interpretação de imagens de satélite para mapeamento preliminar de uso e ocupação da terra: Bacia Hidrográfica do Paracatu, MG.
O projeto Agrohidro visa detectar impactos da agricultura e das mudanças climáticas nos recursos hídricos, e elaborar propostas de adaptação e mitigação em bacias hidrográficas nos diferentes Biomas brasileiros
Laser induced fluorescence for axion dark matter detection: a feasibility study in YLiF:Er
We present a detection scheme to search for QCD axion dark matter, that is
based on a direct interaction between axions and electrons explicitly predicted
by DFSZ axion models. The local axion dark matter field shall drive transitions
between Zeeman-split atomic levels separated by the axion rest mass energy . Axion-related excitations are then detected with an upconversion scheme
involving a pump laser that converts the absorbed axion energy (
hundreds of eV) to visible or infrared photons, where single photon
detection is an established technique. The proposed scheme involves rare-earth
ions doped into solid-state crystalline materials, and the optical transitions
take place between energy levels of electron configuration. Beyond
discussing theoretical aspects and requirements to achieve a cosmologically
relevant sensitivity, especially in terms of spectroscopic material properties,
we experimentally investigate backgrounds due to the pump laser at temperatures
in the range K. Our results rule out excitation of the upper Zeeman
component of the ground state by laser-related heating effects, and are of some
help in optimizing activated material parameters to suppress the
multiphonon-assisted Stokes fluorescence.Comment: 8 pages, 5 figure
A laser gyroscope system to detect the Gravito-Magnetic effect on Earth
Large scale square ring laser gyros with a length of four meters on each side
are approaching a sensitivity of 1x10^-11 rad/s/sqrt(Hz). This is about the
regime required to measure the gravitomagnetic effect (Lense Thirring) of the
Earth. For an ensemble of linearly independent gyros each measurement signal
depends upon the orientation of each single axis gyro with respect to the
rotational axis of the Earth. Therefore at least 3 gyros are necessary to
reconstruct the complete angular orientation of the apparatus. In general, the
setup consists of several laser gyroscopes (we would prefer more than 3 for
sufficient redundancy), rigidly referenced to each other. Adding more gyros for
one plane of observation provides a cross-check against intra-system biases and
furthermore has the advantage of improving the signal to noise ratio by the
square root of the number of gyros. In this paper we analyze a system of two
pairs of identical gyros (twins) with a slightly different orientation with
respect to the Earth axis. The twin gyro configuration has several interesting
properties. The relative angle can be controlled and provides a useful null
measurement. A quadruple twin system could reach a 1% sensitivity after 3:2
years of data, provided each square ring has 6 m length on a side, the system
is shot noise limited and there is no source for 1/f- noise.Comment: 9 pages, 6 figures. 2010 Honourable mention of the Gravity Research
Foundation; to be published on J. Mod. Phys.
ASAS-EULAR recommendations for the management of axial spondyloarthritis: 2022 update
Objectives: To update the Assessment of SpondyloArthritis international Society (ASAS)-EULAR recommendations for the management of axial spondyloarthritis (axSpA).
Methods: Following the EULAR Standardised Operating Procedures, two systematic literature reviews were conducted on non-pharmacological and pharmacological treatment of axSpA. In a task force meeting, the evidence was presented, discussed, and overarching principles and recommendations were updated, followed by voting.
Results: Five overarching principles and 15 recommendations with a focus on personalised medicine were agreed: eight remained unchanged from the previous recommendations; three with minor edits on nomenclature; two with relevant updates (#9, 12); two newly formulated (#10, 11). The first five recommendations focus on treatment target and monitoring, non-pharmacological management and non-steroidal anti-inflammatory drugs (NSAIDs) as first-choice pharmacological treatment. Recommendations 6-8 deal with analgesics and discourage long-term glucocorticoids and conventional synthetic disease-modifying antirheumatic drugs (DMARDs) for pure axial involvement. Recommendation 9 describes the indication of biological DMARDs (bDMARDs, that is, tumour necrosis factor inhibitors (TNFi), interleukin-17 inhibitors (IL-17i)) and targeted synthetic DMARDs (tsDMARDs, ie, Janus kinase inhibitors) for patients who have Ankylosing Spondylitis Disease Activity Score ≥2.1 and failed ≥2 NSAIDs and also have either elevated C reactive protein, MRI inflammation of sacroiliac joints or radiographic sacroiliitis. Current practice is to start a TNFi or IL-17i. Recommendation 10 addresses extramusculoskeletal manifestations with TNF monoclonal antibodies preferred for recurrent uveitis or inflammatory bowel disease, and IL-17i for significant psoriasis. Treatment failure should prompt re-evaluation of the diagnosis and consideration of the presence of comorbidities (#11). If active axSpA is confirmed, switching to another b/tsDMARD is recommended (#12). Tapering, rather than immediate discontinuation of a bDMARD, can be considered in patients in sustained remission (#13). The last recommendations (#14, 15) deal with surgery and spinal fractures.
Conclusions: The 2022 ASAS-EULAR recommendations provide up-to-date guidance on the management of patients with axSpA.
Keywords: Biological Therapy; Spondyloarthritis; Therapeutic
Feedback cooling of the normal modes of a massive electromechanical system to submillikelvin temperature
We apply a feedback cooling technique to simultaneously cool the three
electromechanical normal modes of the ton-scale resonant-bar gravitational wave
detector AURIGA. The measuring system is based on a dc Superconducting Quantum
Interference Device (SQUID) amplifier, and the feedback cooling is applied
electronically to the input circuit of the SQUID. Starting from a bath
temperature of 4.2 K, we achieve a minimum temperature of 0.17 mK for the
coolest normal mode. The same technique, implemented in a dedicated experiment
at subkelvin bath temperature and with a quantum limited SQUID, could allow to
approach the quantum ground state of a kilogram-scale mechanical resonator.Comment: 4 pages, 4 figure
Optimization of the geometrical stability in square ring laser gyroscopes
Ultra sensitive ring laser gyroscopes are regarded as potential detectors ofthe general relativistic frame-dragging effect due to the rotation of theEarth: the project name is GINGER (Gyroscopes IN GEneral Relativity), aground-based triaxial array of ring lasers aiming at measuring the Earthrotation rate with an accuracy of 10^-14 rad/s. Such ambitious goal is nowwithin reach as large area ring lasers are very close to the necessarysensitivity and stability. However, demanding constraints on the geometricalstability of the laser optical path inside the ring cavity are required. Thuswe have started a detailed study of the geometry of an optical cavity, in orderto find a control strategy for its geometry which could meet the specificationsof the GINGER project. As the cavity perimeter has a stationary point for thesquare configuration, we identify a set of transformations on the mirrorpositions which allows us to adjust the laser beam steering to the shape of asquare. We show that the geometrical stability of a square cavity stronglyincreases by implementing a suitable system to measure the mirror distances,and that the geometry stabilization can be achieved by measuring the absolutelengths of the two diagonals and the perimeter of the ring
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