Short wavelength operation of a 10 m perimeter ring laser gyroscope.

We report on the operation of a 10 m perimeter, helium-neon based ring laser gyroscope on the 3s 2→2p 6 (611.8 nm) and 3s 2→2p 10 (543.4 nm) transitions of neon. Cavity Q factors of 1.5×1012 and 3.8×1011 are obtained for 611.8 and 543.4 nm operation, inferred from measured ring-down times of 485 and 110 µs, respectively. For Sagnac frequencies, due to Earth rotation, of 205.14 and 230.96 Hz, minimum resolvable rotation rates of 80 and 226 prad/s are achieved for integration times of around 100 s. While environment limited performance is achieved for operation at 611.8 nm, it is found that a restrictive gas pressure regime must be utilized for the 543.4 nm lasing wavelength. As a consequence, the output photon count is low, which limits its intrinsic sensitivity for rotation rate measurements.

Gyroscopic performance and some seismic measurements made with a 10 meter perimeter ring laser gyro housed in the Ernest Rutherford building.

We describe the construction and operation of a large ring laser whose beam paths enclose an area of 6.25m2. The gyroscopic performance of this large laser interferometer was determined using laser operation at a wavelength of 632.8 nm. The laser cavity Q was inferred to be 1.1×1012 via a measured ring-down time of 375 µs, and the measured Sagnac frequency is 198.40 Hz due to Earth's rotation. The measured experimental sensitivity to rotation achieved is 7.9×10-12rad/s/Hz at an averaging interval of 512 s (being limited primarily by ambient building noise). The observation of microseismic activity in the 200 mHz region as well as local earthquakes is discussed.

The role of regional anaesthesia and multimodal analgesia in the prevention of chronic postoperative pain: a narrative review.

Effective prevention of chronic postoperative pain is an important clinical goal, informed by a growing body of studies. Peri-operative regional anaesthesia remains one of the most important tools in the multimodal analgesic toolbox, blocking injury-induced activation and sensitisation of both the peripheral and central nervous system. We review the definition and taxonomy of chronic postoperative pain, its mechanistic basis and the most recent evidence for the preventative potential of multimodal analgesia, with a special focus on regional anaesthesia. While regional anaesthesia targets several important aspects of the mechanistic pathway leading to chronic postoperative pain, evidence for its efficacy is still mixed, possibly owing to the heterogeneity of risk profiles within the surgical patient, but also to variation in techniques and medications reported in the literature.

Precision Angle Measurement Systems on the Basis of Ring Laser Gyro.

The main application of a ring laser gyroscope is navigation. It is currently the most widely used device for strapdown inertial navigation systems. However, it is also applicable for high-precision angle metrology systems. This paper discusses the properties of a laser dynamic goniometer (LDG) based on the ring laser gyroscope and designed for the calibration of optical polygons and digital angle converters, and for the measurement of angles between external mirrors (theodolite operating mode). We consider the main sources of uncertainty, such as the ring laser gyro bias due to an external magnetic field and the instability caused by the velocity of rotation along with applicable methods of their compensation. The reversal method providing separation of uncertainties of the LDG and the calibrated angle converter is analyzed in detail. The simplified cross-calibration method is also considered. The results of calibration of optical encoders of various designs-with and without their own rotors (on-axis and off-axis in Euramet terminology)-are presented. Some results of the dynamic goniometer for the measurement of angles between external mirrors are presented. It is shown that the LDG in this mode of operation demonstrates better accuracy than modern theodolites and total stations.

Gyroscopic operation on the 3s2→2p10 543.3 nm transition of neon in a 2.56 m2 ring cavity.

We report the development and initial operation of a 6.4 meter perimeter laser gyroscope employing the 543.3 nm, 3s2→2p10 transition of neon. Employing fused silica based supermirrors yielding a cavity Q of 3.9×1011 and an inferred lock in threshold below 1 µHz, the gyroscope unlocked on the bias provided by Earth rotation alone with a measured Sagnac frequency of approximately 133 Hz, which is 16% larger than that of the 632.8 nm transition.

Sensing Earth rotation with a helium-neon laser operating on three transitions in the visible region.

We demonstrate an active Sagnac ring interferometer that operates on the previously unexploited 3s2→2p6 (611.8 nm), 3s2→2p7 (604.6 nm), and 3s2→2p8 (593.9 nm) neon transitions, in a helium-neon gain medium. The cavity was constructed using state-of-the-art ion-beam sputtered, ultralow-loss supermirrors designed to yield greater transmission loss at lower optical frequency, which partially compensates for the gain differential across the three transitions. For an optimized cavity fill of 0.3 mbar partial pressure of neon (50% Ne20 and 50% Ne22) and a total gas pressure of 2 mbar, for laser operation at 611.8 nm, the cavity Q is 1.2×1011, having a cold cavity ringdown time of 38 µs. The laser yielded a stable Sagnac frequency of 117.4 Hz due to the Earth's rotation. The usable gyroscopic sensitivity is determined to be 8.8×10-9 rad/s for a measurement time of 128 s.

The Macek and Davis experiment revisited: a large ring laser interferometer operating on the 2s2 → 2p4 transition of neon.

We operate a large helium-neon-based ring laser interferometer with single-crystal GaAs/AlGaAs optical coatings on the 2s2→2p4 transition of neon at a wavelength of 1.152276 µm. For either single longitudinal- or phase-locked multi-mode operation, the preferable gas composition for gyroscopic operation is 0.2 and 0.3 mbar of 50:50 neon with total pressures between 6-12 mbar. The Earth rotation bias is sufficient to unlock the device, yielding a Sagnac frequency of approximately 60 Hz.

All-in-fiber SESAM based comb oscillator with an intra-cavity electro-optic modulator for coherent high bandwidth stabilization.

We demonstrate the stabilization of an all-in-fiber polarization maintaining semi-conductor saturable absorber mirror (SESAM) mode locked frequency comb oscillator with an intra-cavity waveguide electro-optic phase modulator (EOM) to a narrow linewidth HeNe laser over 46 hours. The high feedback bandwidth of the EOM allows a coherent optical lock with an in-loop integrated phase noise of 1.12 rad (integrated from 10 Hz to 3 MHz) from the carrier signal. No piezo fiber stretcher was required to guarantee long-term stabilization, preventing mechanical degradation of the optical fibers and enabling a long lifetime of the oscillator. As an application a hybrid stabilization scheme is presented, where a comb tooth is phase locked to a longitudinal mode of the large ring laser "G" located at the Geodatic Observatory Wettzell. The hybrid stabilization scheme describes the optical lock of the frequency comb to the G laser and the simultaneous compensation of the ring laser frequency drift by comparing the comb repetition rate against an active H-maser reference. In this context the ring laser reached a fractional Allan deviation of 5 · 10-16 at an integration time of 16384 s.

The risk of ischaemic stroke in primary antiphospholipid syndrome patients: a prospective study.

BACKGROUND AND PURPOSE: The most common neurological manifestation of antiphospholipid syndrome (APS) is ischaemic stroke. Identifying patients with APS at high risk for developing any thrombotic event remains a major challenge. In this study, the aim was to identify predictive factors of ischaemic stroke in a cohort of primary APS (PAPS) patients who presented with new onset symptoms suggestive of acute stroke. METHODS: This prospective multicentre study included 36 consecutive PAPS patients who presented with new onset symptoms suggestive of an acute stroke. Patients were prospectively followed up for 12 months. RESULTS: In 10 (28%) out of 36 PAPS patients [mean age 41 years (SD 13.4), 70% female], the suspicion of an acute stroke was confirmed by brain magnetic resonance imaging. Sixty per cent of these patients were <50 years old. Eight of the 10 patients had a history of previous venous thrombosis and were receiving vitamin K antagonist (VKA), with international normalized ratio target 2-3; one patient had a history of a previous arterial event receiving treatment with VKA target international normalized ratio 2-3 plus low dose aspirin; and one patient had a history of previous pregnancy morbidity receiving only low dose aspirin. Time in the therapeutic range for patients receiving VKA was 77.7% (SD 6.6%). Hypercholesterolaemia was significantly higher in patients with confirmed stroke compared to those without (P < 0.05). Similarly, a significantly higher rate of anti-ß2 glycoprotein-I (ß2GPI) antibodies (immunoglobulin G/immunoglobulin M; P < 0.05) and higher adjusted global APS score (aGAPSS) values were found in patients with a confirmed stroke [mean aGAPSS 8.9 (SD 4.7) vs. mean aGAPSS 6.4 (SD 2.5); P < 0.05]. CONCLUSIONS: Patients with PAPS, including young patients, have a high risk of recurrent thrombosis despite anticoagulation treatment. A careful risk assessment is mandatory to identify patients at risk for recurrence.

Abnormal vaginal bleeding in women of reproductive age treated with edoxaban or warfarin for venous thromboembolism: a post hoc analysis of the Hokusai-VTE study.

OBJECTIVE: To investigate the characteristics and outcome of abnormal vaginal bleeding in women receiving edoxaban or warfarin for treatment of venous thromboembolism (VTE). DESIGN AND SETTING: Post hoc analysis of the Hokusai-VTE study, a multicentre, randomised, double-blind trial comparing edoxaban with warfarin for acute symptomatic VTE. POPULATION: Women below 50 years receiving edoxaban or warfarin for treatment of VTE. METHODS: We collected data on diagnostic measures, treatment, and clinical outcome of abnormal vaginal bleeding events. MAIN OUTCOME MEASURES: Occurrence of major and clinically relevant nonmajor (CRNM) abnormal vaginal bleeding events. RESULTS: In all, 628 women aged under 50 years were treated with edoxaban and 665 with warfarin. The rate of abnormal vaginal bleeding was 15/100 person-years (py) (95% CI 11-19) in women receiving edoxaban and 9/100 py (95% CI 6-12) in the warfarin group (hazard ratio: 1.7, 95% CI 1.1-2.5). Major abnormal vaginal bleeding occurred in eight (1.3%) women on edoxaban and in three (0.9%) women receiving warfarin [odds ratio (OR) 2.8; 95% CI 0.8-10.8], and CRNM abnormal vaginal bleeding occurred in 53 (8.4%) women treated with edoxaban and in 37 (5.6%) on warfarin therapy (OR 1.6, 95% CI 1.0-2.4). Over 85% of all vaginal bleeds were characterised by heavy menstrual bleeding. Major bleeds frequently required treatment, and in more than 75% of patients anticoagulant therapy was adjusted. The severity of clinical presentation and course of major and CRNM bleeds was mild in most patients. CONCLUSIONS: Abnormal vaginal bleeding occurred more frequently in women treated with edoxaban than with warfarin. Reassuringly, most events could be managed conservatively and had a mild outcome. TWEETABLE ABSTRACT: Abnormal vaginal bleeding occurred more frequently in women treated with edoxaban than with warfarin.

High-accuracy absolute rotation rate measurements with a large ring laser gyro: establishing the scale factor.

Large ring lasers have exceeded the performance of navigational gyroscopes by several orders of magnitude and have become useful tools for geodesy. In order to apply them to tests in fundamental physics, remaining systematic errors have to be significantly reduced. We derive a modified expression for the Sagnac frequency of a square ring laser gyro under Earth rotation. The modifications include corrections for dispersion (of both the gain medium and the mirrors), for the Goos-Hänchen effect in the mirrors, and for refractive index of the gas filling the cavity. The corrections were measured and calculated for the 16 m2 Grossring laser located at the Geodetic Observatory Wettzell. The optical frequency and the free spectral range of this laser were measured, allowing unique determination of the longitudinal mode number, and measurement of the dispersion. Ultimately we find that the absolute scale factor of the gyroscope can be estimated to an accuracy of approximately 1 part in 108.

Pregnancies in women with systemic lupus erythematosus and antiphospholipid antibodies.

Systemic lupus erythematosus (SLE) has preponderance in women in their childbearing years; consequently pregnancy has always been an important issue of concern for the patient and the treating physician. Based upon numerous reports on successful pregnancy outcomes in the past decades, the initial advice against pregnancy in the 1950s has been replaced by a common understanding that women with SLE often have successful pregnancy outcomes, and clinicians therefore advise on pregnancy planning, including possible drug adjustments, timing and close surveillance. The recently published Predictors of Pregnancy Outcome: Biomarkers in Antiphospholipid Antibody Syndrome and Systemic Lupus Erythematosus (PROMISSE) study, so far the largest multicentre cohort study of pregnant women with underlying stable SLE, has given some important answers to long-discussed questions. Future studies on data collected from the PROMISSE cohort will hopefully identify serological biomarkers, possibly genes, and in addition, give valuable information about underlying disease mechanisms.

Sensing earth's rotation with a helium-neon ring laser operating at 1.15 µm.

We report on the operation of a 2.56 m2 helium-neon based ring laser interferometer at a wavelength of 1.152276 µm using crystalline coated intracavity supermirrors. This work represents the first implementation of crystalline coatings in an active laser system and expands the core application area of these low-thermal-noise cavity end mirrors to inertial sensing systems. Stable gyroscopic behavior can only be obtained with the addition of helium to the gain medium as this quenches the 1.152502 µm (2s4→2p7) transition of the neon doublet which otherwise gives rise to mode competition. For the first time at this wavelength, the ring laser is observed to readily unlock on the bias provided by the earth's rotation alone, yielding a Sagnac frequency of approximately 59 Hz.

Correction of backscatter-induced systematic errors in ring laser gyroscopes.

In ring laser gyroscopes, backscatter coupling between the counterpropagating beams leads to systematic errors in measured rotation rates. We show the errors can be derived from the nearly independent optical frequency perturbations of the separate beams. In a process of double backscatter each beam is scattered first into the other beam direction, then rescattered back into itself, giving phase and amplitude perturbations. The analysis proceeds from a purely passive ring cavity, through inclusion of a gain medium and gain saturation. The rotation rate errors may be estimated and corrected from the modulations of the counterpropagating beams. The method is demonstrated with real data.

Closed-loop locking of an optical frequency comb to a large ring laser.

We report on the frequency locking of a 16 m2 ring laser to a single tooth of an optical frequency comb referenced to a hydrogen maser, obtaining a frequency stability of 1 kHz over several days. In common mode operation, where the counterpropagating laser beams run on the same longitudinal mode index, a sensitivity to rotation of 3×10(-9) relative to Earth's rotation is obtained. To test a proposal to bypass time-varying backscatter-induced readout errors in large ring laser gyroscopes, we have operated the laser on adjacent longitudinal cavity modes. The Sagnac frequency due to Earth's rotation obtained in this fashion was strongly influenced by atmospheric pressure changes because the counterpropagating beams within the cavity are affected differently by geometric cavity fluctuations.

NfL and GFAP in serum are associated with microstructural brain damage in progressive multiple sclerosis.

BACKGROUND: The potential of neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) as biomarkers of disease activity and severity in progressive forms of multiple sclerosis (MS) is unclear. OBJECTIVE: To investigate the relationship between serum concentrations of NfL, GFAP, and magnetic resonance imaging (MRI) in progressive MS. METHODS: Serum concentrations of NfL and GFAP were measured in 32 healthy controls and 32 patients with progressive MS from whom clinical and MRI data including diffusion tensor imaging (DTI) were obtained during three years of follow-up. RESULTS: Serum concentrations of NfL and GFAP at follow-up were higher in progressive MS patients than in healthy controls and serum NfL correlated with the EDSS score. Decreasing fractional anisotropy (FA) in normal-appearing white matter (NAWM) correlated with worsening EDSS scores and higher serum NfL. Higher serum NfL and increasing T2 lesion volume correlated with worsening paced autitory serial addition test scores. In multivariable regression analyses with serum GFAP and NfL as independent factors and DTI measures of NAWM as dependent factors, we showed that high serum NfL at follow-up was independently associated with decreasing FA and increasing MD in NAWM. Moreover, we found that high serum GFAP was independently associated with decreasing MD in NAWM and with decreasing MD and increasing FA in cortical gray matter. CONCLUSION: Serum concentrations of NfL and GFAP are increased in progressive MS and are associated with distinct microstructural changes in NAWM and CGM.

Long-term frequency stabilization of a 16 m(2) ring laser gyroscope.

A 16 m(2) helium-neon-based ring laser gyroscope has been frequency stabilized to within 60 kHz over a period of three months. This is achieved using the beat frequency of the ring laser and an iodine-stabilized reference laser as a feedback signal on a pressure vessel enclosing the entire laser, under servo control. We demonstrate that we can compensate for, and thereby negate the influence of, atmospheric pressure variations, which are considerable sources of long-term instability.

Mode selection in an ultralarge ring laser gyro.

A significant operational difficulty with very large ring laser gyroscopes is the length of time required to achieve the desired single-mode configuration. A control technique has been developed where the order of mode splitting between corotating beams is alternated. Theoretical advantages to this are the elimination of noise caused by variations in perimeter and systematic error caused by Adler pulling. External seeding of mode configurations has been proposed to allow the technique to work fast enough to eliminate known sources of perimeter perturbations. While investigating the intensity requirements for this concept, we found that the operating mode of a large ring laser can be successfully self-seeded with seed beams of near (6±3) single photon cavity mode population.

How to detect the Chandler and the annual wobble of the Earth with a large ring laser gyroscope.

We demonstrate a 16 m(2) helium-neon ring laser gyroscope with sufficient sensitivity and stability to directly detect the Chandler wobble of the rotating Earth. The successful detection of both the Chandler and the annual wobble is verified by comparing the time series of the ring laser measurements against the "C04 series" of Earth rotation data from the International Earth Rotation and Reference System Service.