188 research outputs found
Multi-color Cavity Metrology
Long baseline laser interferometers used for gravitational wave detection
have proven to be very complicated to control. In order to have sufficient
sensitivity to astrophysical gravitational waves, a set of multiple coupled
optical cavities comprising the interferometer must be brought into resonance
with the laser field. A set of multi-input, multi-output servos then lock these
cavities into place via feedback control. This procedure, known as lock
acquisition, has proven to be a vexing problem and has reduced greatly the
reliability and duty factor of the past generation of laser interferometers. In
this article, we describe a technique for bringing the interferometer from an
uncontrolled state into resonance by using harmonically related external fields
to provide a deterministic hierarchical control. This technique reduces the
effect of the external seismic disturbances by four orders of magnitude and
promises to greatly enhance the stability and reliability of the current
generation of gravitational wave detector. The possibility for using
multi-color techniques to overcome current quantum and thermal noise limits is
also discussed
Local-Oscillator Noise Coupling in Balanced Homodyne Readout for Advanced Gravitational Wave Detectors
The second generation of interferometric gravitational wave detectors are
quickly approaching their design sensitivity. For the first time these
detectors will become limited by quantum back-action noise. Several back-action
evasion techniques have been proposed to further increase the detector
sensitivity. Since most proposals rely on a flexible readout of the full
amplitude- and phase-quadrature space of the output light field, balanced
homodyne detection is generally expected to replace the currently used DC
readout. Up to now, little investigation has been undertaken into how balanced
homodyne detection can be successfully transferred from its ubiquitous
application in table-top quantum optics experiments to large-scale
interferometers with suspended optics. Here we derive implementation
requirements with respect to local oscillator noise couplings and highlight
potential issues with the example of the Glasgow Sagnac Speed Meter experiment,
as well as for a future upgrade to the Advanced LIGO detectors.Comment: 7 pages, 5 figure
Waveguide grating mirror in a fully suspended 10 meter Fabry-Perot cavity
We report on the first demonstration of a fully suspended 10m Fabry-Perot
cavity incorporating a waveguide grating as the coupling mirror. The cavity was
kept on resonance by reading out the length fluctuations via the
Pound-Drever-Hall method and employing feedback to the laser frequency. From
the achieved finesse of 790 the grating reflectivity was determined to exceed
99.2% at the laser wavelength of 1064\,nm, which is in good agreement with
rigorous simulations. Our waveguide grating design was based on tantala and
fused silica and included a ~20nm thin etch stop layer made of Al2O3 that
allowed us to define the grating depth accurately during the fabrication
process. Demonstrating stable operation of a waveguide grating featuring high
reflectivity in a suspended low-noise cavity, our work paves the way for the
potential application of waveguide gratings as mirrors in high-precision
interferometry, for instance in future gravitational wave observatories
Effects of static and dynamic higher-order optical modes in balanced homodyne readout for future gravitational waves detectors
With the recent detection of Gravitational waves (GW), marking the start of the new field of GW astronomy, the push for building more sensitive laser-interferometric gravitational wave detectors (GWD) has never been stronger. Balanced homodyne detection (BHD) allows for a quantum noise (QN) limited readout of arbitrary light field quadratures, and has therefore been suggested as a vital building block for upgrades to Advanced LIGO and third generation observatories. In terms of the practical implementation of BHD, we develop a full framework for analyzing the static optical high order modes (HOMs) occurring in the BHD paths related to the misalignment or mode matching at the input and output ports of the laser interferometer. We find the effects of HOMs on the quantum noise limited sensitivity is independent of the actual interferometer configuration, e.g. Michelson and Sagnac interferometers are effected in the same way. We show that misalignment of the output ports of the interferometer (output misalignment) only effects the high frequency part of the quantum noise limited sensitivity (detection noise). However, at low frequencies, HOMs reduce the interferometer response and the radiation pressure noise (back action noise) by the same amount and hence the quantum noise limited sensitivity is not negatively effected in that frequency range. We show that the misalignment of laser into the interferometer (input misalignment) produces the same effect as output misalignment and additionally decreases the power inside the interferometer. We also analyze dynamic HOM effects, such as beam jitter created by the suspended mirrors of the BHD. Our analyses can be directly applied to any BHD implementation in a future GWD. Moreover, we apply our analytical techniques to the example of the speed meter proof of concept experiment under construction in Glasgow. We find that for our experimental parameters, the performance of our seismic isolation system in the BHD paths is compatible with the design sensitivity of the experiment
Demonstration of a switchable damping system to allow low-noise operation of high-Q low-mass suspension systems
Low mass suspension systems with high-Q pendulum stages are used to enable
quantum radiation pressure noise limited experiments. Utilising multiple
pendulum stages with vertical blade springs and materials with high quality
factors provides attenuation of seismic and thermal noise, however damping of
these high-Q pendulum systems in multiple degrees of freedom is essential for
practical implementation. Viscous damping such as eddy-current damping can be
employed but introduces displacement noise from force noise due to thermal
fluctuations in the damping system. In this paper we demonstrate a passive
damping system with adjustable damping strength as a solution for this problem
that can be used for low mass suspension systems without adding additional
displacement noise in science mode. We show a reduction of the damping factor
by a factor of 8 on a test suspension and provide a general optimisation for
this system.Comment: 5 pages, 5 figure
Comparison of Airway Intubation Devices When Using a Biohazard Suit: A Feasibility Study
OBJECTIVES: We set out to compare emergency medicine residents\u27 intubating times and success rates for direct laryngoscopy (DL), GlideScope-assisted intubation (GS), and the Supraglottic Airway Laryngopharyngeal Tube (SALT) airway with and without biohazard gear.
METHODS: Each resident passed through 2 sets of 3 testing stations (DL, GS, SALT) in succession, intubating Laerdal mannequin heads with the 3 modalities after randomization to start with or without biohazard gear.
RESULTS: Thirty-seven residents participated, and 27 were male (73%); 14 (37.8%) had prior experience intubating in biohazard suits. There was a statistically significant difference in those who had prior intubation experience between DL (37, 100%), GS (32, 86.5%), and SALT (12, 32.4%) (P \u3c .001) and in median time to intubation (48 seconds, no suit; 57 seconds, with suits) (P = .03). There was no statistically significant difference between the overall times to intubate for the 3 devices. First-pass success was highest for DL (91.2%, no suit; 83.7%, suit) followed by GS (89%, no suit; 78.3%, suit) and SALT (51%, no suit; 67.6%, suit).
CONCLUSION: A minority of participants had prior experience intubating in biohazard suits. Use of biohazard suits extends time to successful intubation. There was no difference in time to intubation for the 3 devices, but first-pass success was highest for DL (with or without biohazard gear)
Stereocilia-staircase spacing is influenced by myosin III motors and their cargos espin-1 and espin-like
Hair cells tightly control the dimensions of their stereocilia, which are actin-rich protrusions with graded heights that mediate mechanotransduction in the inner ear. Two members of the myosin-III family, MYO3A and MYO3B, are thought to regulate stereocilia length by transporting cargos that control actin polymerization at stereocilia tips. We show that eliminating espin-1 (ESPN-1), an isoform of ESPN and a myosin-III cargo, dramatically alters the slope of the stereocilia staircase in a subset of hair cells. Furthermore, we show that espin-like (ESPNL), primarily present in developing stereocilia, is also a myosin-III cargo and is essential for normal hearing. ESPN-1 and ESPNL each bind MYO3A and MYO3B, but differentially influence how the two motors function. Consequently, functional properties of different motor-cargo combinations differentially affect molecular transport and the length of actin protrusions. This mechanism is used by hair cells to establish the required range of stereocilia lengths within a single cell
Stereocilia-staircase spacing is influenced by myosin III motors and their cargos espin-1 and espin-like
Hair cells tightly control the dimensions of their stereocilia, which are actin-rich protrusions with graded heights that mediate mechanotransduction in the inner ear. Two members of the myosin-III family, MYO3A and MYO3B, are thought to regulate stereocilia length by transporting cargos that control actin polymerization at stereocilia tips. We show that eliminating espin-1 (ESPN-1), an isoform of ESPN and a myosin-III cargo, dramatically alters the slope of the stereocilia staircase in a subset of hair cells. Furthermore, we show that espin-like (ESPNL), primarily present in developing stereocilia, is also a myosin-III cargo and is essential for normal hearing. ESPN-1 and ESPNL each bind MYO3A and MYO3B, but differentially influence how the two motors function. Consequently, functional properties of different motor-cargo combinations differentially affect molecular transport and the length of actin protrusions. This mechanism is used by hair cells to establish the required range of stereocilia lengths within a single cell
Stereocilia-staircase spacing is influenced by myosin III motors and their cargos espin-1 and espin-like
Hair cells tightly control the dimensions of their stereocilia, which are actin-rich protrusions with graded heights that mediate mechanotransduction in the inner ear. Two members of the myosin-III family, MYO3A and MYO3B, are thought to regulate stereocilia length by transporting cargos that control actin polymerization at stereocilia tips. We show that eliminating espin-1 (ESPN-1), an isoform of ESPN and a myosin-III cargo, dramatically alters the slope of the stereocilia staircase in a subset of hair cells. Furthermore, we show that espin-like (ESPNL), primarily present in developing stereocilia, is also a myosin-III cargo and is essential for normal hearing. ESPN-1 and ESPNL each bind MYO3A and MYO3B, but differentially influence how the two motors function. Consequently, functional properties of different motor-cargo combinations differentially affect molecular transport and the length of actin protrusions. This mechanism is used by hair cells to establish the required range of stereocilia lengths within a single cell
'To live and die [for] Dixie': Irish civilians and the Confederate States of America
Around 20,000 Irishmen served in the Confederate army in the Civil War. As a result, they left behind, in various Southern towns and cities, large numbers of friends, family, and community leaders. As with native-born Confederates, Irish civilian support was crucial to Irish participation in the Confederate military effort. Also, Irish civilians served in various supporting roles: in factories and hospitals, on railroads and diplomatic missions, and as boosters for the cause. They also, however, suffered in bombardments, sieges, and the blockade. Usually poorer than their native neighbours, they could not afford to become 'refugees' and move away from the centres of conflict. This essay, based on research from manuscript collections, contemporary newspapers, British Consular records, and Federal military records, will examine the role of Irish civilians in the Confederacy, and assess the role this activity had on their integration into Southern communities. It will also look at Irish civilians in the defeat of the Confederacy, particularly when they came under Union occupation. Initial research shows that Irish civilians were not as upset as other whites in the South about Union victory. They welcomed a return to normalcy, and often 'collaborated' with Union authorities. Also, Irish desertion rates in the Confederate army were particularly high, and I will attempt to gauge whether Irish civilians played a role in this. All of the research in this paper will thus be put in the context of the Drew Gilpin Faust/Gary Gallagher debate on the influence of the Confederate homefront on military performance. By studying the Irish civilian experience one can assess how strong the Confederate national experiment was. Was it a nation without a nationalism
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