824 research outputs found
Rotational sensitivity of the "G-Pisa" gyrolaser
G-Pisa is an experiment investigating the possibility to operate a high
sensitivity laser gyroscope with area less than for improving the
performances of the mirrors suspensions of the gravitational wave antenna
Virgo. The experimental set-up consists in a He-Ne ring laser with a 4 mirrors
square cavity. The laser is pumped by an RF discharge where the RF oscillator
includes the laser plasma in order to reach a better stability. The contrast of
the Sagnac fringes is typically above 50% and a stable regime has been reached
with the laser operating both single mode or multimode. The effect of hydrogen
contamination on the laser was also checked. A low-frequency sensitivity, below
, in the range of has been
measured.Comment: 6 pages, 6 figures, presented at the EFTF-IFCS joint conference 200
OPA1-related auditory neuropathy: site of lesion and outcome of cochlear implantation.
Hearing impairment is the second most prevalent clinical feature after optic atrophy in Dominant Optic Atrophy associated with mutations in the OPA1 gene. In this study we characterized the hearing dysfunction in OPA1-linked disorders and provided effective rehabilitative options to improve speech perception.
We studied two groups of OPA1 subjects, one comprising 11 patients (7 males; age range 13-79 years) carrying OPA1 mutations inducing haploinsufficiency, the other, 10 subjects (3 males; age range 5-58 years) carrying OPA1 missense mutations. Both groups underwent audiometric assessment with pure tone and speech perception evaluation, and otoacoustic emissions and auditory brainstem response recording. Cochlear potentials were recorded through transtympanic electrocochleography from the group of patients harboring OPA1 missense mutations and were compared to recordings obtained from 20 normally-hearing controls and from 19 subjects with cochlear hearing loss. Eight patients carrying OPA1 missense mutations underwent cochlear implantation. Speech perception measures and electrically-evoked auditory nerve and brainstem responses were obtained after one year of cochlear implant use.
Nine out of 11 patients carrying OPA1 mutations inducing haploinsufficiency had normal hearing function. In contrast, all but one subject harboring OPA1 missense mutations displayed impaired speech perception, abnormal brainstem responses and presence of otoacoustic emissions consistent with auditory neuropathy. In electrocochleography recordings, cochlear microphonic had enhanced amplitudes while summating potential showed normal latency and peak amplitude consistent with preservation of both outer and inner hair cell activities. After cancelling the cochlear microphonic, the synchronized neural response seen in both normally-hearing controls and subjects with cochlear hearing loss was replaced by a prolonged, low-amplitude negative potential that decreased in both amplitude and duration during rapid stimulation consistent with neural generation. The use of cochlear implant improved speech perception in all but one patient. Brainstem potentials were recorded in response to electrical stimulation in five subjects out of six, whereas no compound action potential was evoked from the auditory nerve through the cochlear implant.
These findings indicate that underlying the hearing impairment in patients carrying OPA1 missense mutations is a disordered synchrony in auditory nerve fiber activity resulting from neural degeneration affecting the terminal dendrites. Cochlear implantation improves speech perception and synchronous activation of auditory pathways by by-passing the site of lesion
Geometrical scale-factor stabilization of square cavity ring laser gyroscopes
Large frame ring laser gyros performances are ultimately limited by the instabilities of their geometrical parameters. We present the experimental activity on the GP2 ring laser gyro. GP2 is a ring laser gyro devoted to develop advanced stabilization techniques of the ring cavity geometrical scale-factor. A method based on optical interferometry has been developed for canceling the deformations of the resonator. The method is based on the measurement and stabilization of the absolute length of the cavity perimeter and of the resonators formed by the opposite cavity mirrors. The optical frequency reference in the experiment is an iodine-stabilized He-Ne laser, with a relative frequency stability of 10-11. The measurement of the absolute length of the two resonators has been demonstrated up to now on a test bench. We discuss the experimental results on GP2: the present performances as a ring laser gyro and the stabilization scheme to be implemented in the near future
A high sensitivity tool for geophysical applications: A geometrically locked Ring Laser Gyroscope
This work demonstrates that a middle size ring laser gyroscope (RLG) can be a
very sensitive and robust instrument for rotational seismology, even if it
operates in a quite noisy environment. The RLG has a square cavity, m, and it lies in a plane orthogonal to the Earth rotational axis.
The Fabry-Perot optical cavities along the diagonals of the square were
accessed and their lengths were locked to a reference laser. Through a quite
simple locking circuit, we were able to keep the sensor fully operative for 14
days. The obtained long term stability is of the order of 3~nanorad/s and the
short term sensitivity close is to 2~nanorad/sHz. These results
are limited only by the noisy environment, our laboratory is located in a
building downtown.Comment: 9 pages, 4 figures, 25 reference
Length measurement and stabilization of the diagonals of a square area laser gyroscope
Large frame ring laser gyroscopes are top sensitivity inertial sensors able to measure absolute angular rotation rate below prad s-1 in few seconds. The GINGER project is aiming at directly measuring the Lense-Thirring effect with an 1% precision on an Earth based experiment. GINGER is based on an array of large frame ring laser gyroscopes. The mechanical design of this apparatus requires a micrometric precision in the construction and the geometry must be stabilized in order to keep constant the scale factor of the instrument. The proposed control is based on square cavities, and relies on the length stabilization of the two diagonals, which must be equal at micrometric level. GP2 is the prototype devoted to the scale factor control test. As a first step, the lengths of the diagonals of the ring cavity have been measured through an interferometric technique with a statistical accuracy of some tens of nanometers, and they have been locked to the wavelength of a reference optical standard. Continuous operation has been obtained over more than 12 h, without loss of sensitivity. GP2 is located in a laboratory with standard temperature stabilization, with residual fluctuations of the order of 1 C. Besides the demonstration of the control effectiveness, the analysis of the Sagnac frequency demonstrates that relative small and low-cost ring lasers (around one meter of side) can also achieve a sensitivity of the order of nrad s-1 in the range 0.01-10 Hz in a standard environment, which is the target sensitivity in many different applications, such as rotational seismology and next generation gravitational waves detectors
Deep-well ultrafast manipulation of a SQUID flux qubit
Superconducting devices based on the Josephson effect are effectively used
for the implementation of qubits and quantum gates. The manipulation of
superconducting qubits is generally performed by using microwave pulses with
frequencies from 5 to 15 GHz, obtaining a typical operating clock from 100MHz
to 1GHz. A manipulation based on simple pulses in the absence of microwaves is
also possible. In our system a magnetic flux pulse modifies the potential of a
double SQUID qubit from a symmetric double well to a single deep well
condition. By using this scheme with a Nb/AlOx/Nb system we obtained coherent
oscillations with sub-nanosecond period (tunable from 50ps to 200ps), very fast
with respect to other manipulating procedures, and with a coherence time up to
10ns, of the order of what obtained with similar devices and technologies but
using microwave manipulation. We introduce the ultrafast manipulation
presenting experimental results, new issues related to this approach (such as
the use of a feedback procedure for cancelling the effect of "slow"
fluctuations), and open perspectives, such as the possible use of RSFQ logic
for the qubit control.Comment: 9 pages, 7 figure
- …