5,308 research outputs found
Arm cavity resonant sideband control for laser interferometric gravitational wave detectors
We present a new optical control scheme for a laser interferometric gravitational wave detector that has a high degree of tolerance to interferometer spatial distortions and noise on the input light. The scheme involves resonating the rf sidebands in an interferometer arm cavity
Grouting to Control Deep Foundation Settlement
An 18-story reinforced concrete building under construction in South Florida reached 16th floor level when significant differential settlement presented an unanticipated foundation problem. The foundation consisted of a structural mat supported by 14-in. concrete piles 24 to 75 ft long. Surprisingly, the longest piles were within the area of greatest settlement. Investigation revealed a previously undisclosed semi-cavernous zone from 120 to 175 ft below ground surface, and level surveys using deep benchmarks confirmed that zone to be the source of movement. Injection grouting first accelerated and then controlled the settlement, allowing the building to be completed on schedule. Temperature probes and weekly precise level surveys were key control devices contributing to the correction of the problem
Atom lithography using MRI-type feature placement
We demonstrate the use of frequency-encoded light masks in neutral atom
lithography. We demonstrate that multiple features can be patterned across a
monotonic potential gradient. Features as narrow as 0.9 microns are fabricated
on silicon substrates with a metastable argon beam. Internal state manipulation
with such a mask enables continuously adjustable feature positions and feature
densities not limited by the optical wavelength, unlike previous light masks.Comment: 4 pages, 4 figure
Control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry
We present the first demonstration of real-time closed-loop control and
deterministic tuning of an independently suspended Fabry-Perot optical cavity
using digitally-enhanced heterodyne interferometry, realising a peak
sensitivity of 10 pm over the 10-1000 Hz frequency
band. The methods presented are readily extensible to multiple coupled
cavities. As such, we anticipate that refinements of this technique may find
application in future interferometric gravitational-wave detectors
GaAs monolithic frequency doublers with series connected varactor diodes
GaAs monolithic frequency doublers using series connected varactor diodes have been fabricated for the first time. Output powers of 150 mW at 36.9 GHz with 24% efficiency and 300 mW at 24.8 GHz with 18% efficiency have been obtained. Peak efficiencies of 35% at output power levels near 100 mW have been achieved at both frequencies. Both K-band and Ka-band frequency doublers are derived from a lower power, single-diode design by series connection of two diodes and scaling to achieve different power and frequency specifications. Their fabrication was accomplished using the same process sequence
Numerical wave optics and the lensing of gravitational waves by globular clusters
We consider the possible effects of gravitational lensing by globular
clusters on gravitational waves from asymmetric neutron stars in our galaxy. In
the lensing of gravitational waves, the long wavelength, compared with the
usual case of optical lensing, can lead to the geometrical optics approximation
being invalid, in which case a wave optical solution is necessary. In general,
wave optical solutions can only be obtained numerically. We describe a
computational method that is particularly well suited to numerical wave optics.
This method enables us to compare the properties of several lens models for
globular clusters without ever calling upon the geometrical optics
approximation, though that approximation would sometimes have been valid.
Finally, we estimate the probability that lensing by a globular cluster will
significantly affect the detection, by ground-based laser interferometer
detectors such as LIGO, of gravitational waves from an asymmetric neutron star
in our galaxy, finding that the probability is insignificantly small.Comment: To appear in: Proceedings of the Eleventh Marcel Grossmann Meetin
Causes of Differences in Soil Series of the Missouri River Bottomlands of Monona County
The current soil survey of Monona County has revealed many differences in the alluvial deposits occurring in the Missouri River bottomlands. As a consequence the soils developed from these different deposits show numerous dissimilarities. It is the purpose of this paper to describe and explain the causes of the differences encountered. The principal factors in soil formation are climate, organisms, topography, parent material and time. In the Missouri River bottomlands of Monona County it can be assumed that climate and organisms are not important causes of soil differences. In general, differences in topography are closely related to differences in parent material. Thus parent material or time of deposition or both, must be the principal cause or causes of soil differences. The soils found on the Missouri River bottomlands are, for the most part, formed from alluvial materials. Some coarser alluvium may have been resorted by wind action subsequent to deposition but areas showing evidence of wind action are not extensive. The principal source of alluvium is the Missouri River; next, the tributary rivers and streams; and, of least importance, the steep bluffs that form the sides of the valley
Photothermal Fluctuations as a Fundamental Limit to Low-Frequency Squeezing in a Degenerate Optical Parametric Amplifier
We study the effect of photothermal fluctuations on squeezed states of light
through the photo-refractive effect and thermal expansion in a degenerate
optical parametric amplifier (OPA). We also discuss the effect of the
photothermal noise in various cases and how to minimize its undesirable
consequences. We find that the photothermal noise in the OPA introduces a
significant amount of noise on phase squeezed beams, making them less than
ideal for low frequency applications such as gravitational wave (GW)
interferometers, whereas amplitude squeezed beams are relatively immune to the
photothermal noise and may represent the best choice for application in GW
interferometers
Arm-length stabilisation for interferometric gravitational-wave detectors using frequency-doubled auxiliary lasers
Residual motion of the arm cavity mirrors is expected to prove one of the
principal impediments to systematic lock acquisition in advanced
gravitational-wave interferometers. We present a technique which overcomes this
problem by employing auxiliary lasers at twice the fundamental measurement
frequency to pre-stabilise the arm cavities' lengths. Applying this approach,
we reduce the apparent length noise of a 1.3 m long, independently suspended
Fabry-Perot cavity to 30 pm rms and successfully transfer longitudinal control
of the system from the auxiliary laser to the measurement laser
Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
The Binary Population and Spectral Synthesis (BPASS) suite of binary stellar
evolution models and synthetic stellar populations provides a framework for the
physically motivated analysis of both the integrated light from distant stellar
populations and the detailed properties of those nearby. We present a new
version 2.1 data release of these models, detailing the methodology by which
BPASS incorporates binary mass transfer and its effect on stellar evolution
pathways, as well as the construction of simple stellar populations. We
demonstrate key tests of the latest BPASS model suite demonstrating its ability
to reproduce the colours and derived properties of resolved stellar
populations, including well- constrained eclipsing binaries. We consider
observational constraints on the ratio of massive star types and the
distribution of stellar remnant masses. We describe the identification of
supernova progenitors in our models, and demonstrate a good agreement to the
properties of observed progenitors. We also test our models against photometric
and spectroscopic observations of unresolved stellar populations, both in the
local and distant Universe, finding that binary models provide a
self-consistent explanation for observed galaxy properties across a broad
redshift range. Finally, we carefully describe the limitations of our models,
and areas where we expect to see significant improvement in future versions.Comment: 69 pages, 45 figures. Accepted for publication in PASA. Accompanied
by a full, documented data release at http://bpass.auckland.ac.nz and
http://warwick.ac.uk/bpas
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