1,398 research outputs found
Measurements of mechanical Q in levitated paramagnetic crystals
Thermal noise from test masses, arising both from internal noise in the test mass material and from losses in the suspension wires and their attachments, is a significant factor limiting sensitivity of interferometric gravity-wave detectors. To investigate ways of reducing these noise sources we are using magnetic levitation in place of suspension wires. A search for high-Q crystals with magnetic properties allowing tests in moderate field strengths has led us to paramagnetic crystals, and we report preliminary results with small levitated samples of Gadolinium Gallium Garnet (GGG) and Terbium Gallium Garnet (TGG). The technique seems the first to allow Q measurements with no mechanical contact, and may facilitate work aimed at reducing thermal noise
Analysis of a four-mirror cavity enhanced Michelson interferometer
We investigate the shot noise limited sensitivity of a four-mirror cavity
enhanced Michelson interferometer. The intention of this interferometer
topology is the reduction of thermal lensing and the impact of the
interferometers contrast although transmissive optics are used with high
circulating powers. The analytical expressions describing the light fields and
the frequency response are derived. Although the parameter space has 11
dimensions, a detailed analysis of the resonance feature gives boundary
conditions allowing systematic parameter studies
How many acres per hour?
MANY farm tractor operators don\u27t know exactly how much land is covered in an hour by implements drawn by their tractors. This information, useful on any farm where tractors are used, is of particular value in contract work.
The capacity of the machine or implement, or in other words, its rate of working, depends on the width of the machine, how fast it travels, how efficiently it is operated and the time it works
Passive and active seismic isolation for gravitational radiation detectors and other instruments
Some new passive and active methods for reducing the effects of seismic disturbances on suspended masses are described, with special reference to gravitational radiation detectors in which differential horizontal motions of two or more suspended test masses are monitored. In these methods it is important to be able to determine horizontal seismic accelerations independent of tilts of the ground. Measurement of changes in inclination of the suspension wire of a test mass, relative to a direction defined by a reference arm of long period of oscillation, makes it possible to carry this out over the frequency range of interest for earth-based gravitational radiation detectors. The signal obtained can then be used to compensate for the effects of seismic disturbances on the test mass if necessary. Alternatively the signal corresponding to horizontal acceleration can be used to move the point from which the test mass is suspended in such a way as to reduce the effect of the seismic disturbance and also damp pendulum motions of the suspended test mass. Experimental work with an active anti-seismic system of this type is described
Reducing the linewidth of a diode laser below 30 Hz by stabilization to a reference cavity with finesse above 10^5
An extended cavity diode laser operating in the Littrow configuration
emitting near 657 nm is stabilized via its injection current to a reference
cavity with a finesse of more than 10^5 and a corresponding resonance linewidth
of 14 kHz. The laser linewidth is reduced from a few MHz to a value below 30
Hz. The compact and robust setup appears ideal for a portable optical frequency
standard using the Calcium intercombination line.Comment: 8 pages, 4 figures on 3 additional pages, corrected version,
submitted to Optics Letter
The state of MIIND
MIIND (Multiple Interacting Instantiations of Neural Dynamics) is a highly modular multi-level C++ framework, that aims to shorten the development time for models in Cognitive Neuroscience (CNS). It offers reusable code modules (libraries of classes and functions) aimed at solving problems that occur repeatedly in modelling, but tries not to impose a specific modelling philosophy or methodology. At the lowest level, it offers support for the implementation of sparse networks. For example, the library SparseImplementationLib supports sparse random networks and the library LayerMappingLib can be used for sparse regular networks of filter-like operators. The library DynamicLib, which builds on top of the library SparseImplementationLib, offers a generic framework for simulating network processes. Presently, several specific network process implementations are provided in MIIND: the WilsonâCowan and OrnsteinâUhlenbeck type, and population density techniques for leaky-integrate-and-fire neurons driven by Poisson input. A design principle of MIIND is to support detailing: the refinement of an originally simple model into a form where more biological detail is included. Another design principle is extensibility: the reuse of an existing model in a larger, more extended one. One of the main uses of MIIND so far has been the instantiation of neural models of visual attention. Recently, we have added a library for implementing biologically-inspired models of artificial vision, such as HMAX and recent successors. In the long run we hope to be able to apply suitably adapted neuronal mechanisms of attention to these artificial models
Mutant Tau knock-in mice display frontotemporal dementia relevant behaviour and histopathology
Peer reviewedPostprin
A precision sidereal telescope drive based on a solar time crystal clock
A requirement arose for a sidereal drive for a small microwave radiometer on an equatorial mount, the equipment to run unattended to a precision of about 2 minutes in hour angle over a 7-day period. The installation already
included a solar-time crystal clock based on a IO MHz oscillator (type HCD 25), which through decade scalers could easily be arranged to operate a standard 50 Hz synchronous motor which would drive the mounting at one revolution per solar day. However, no suitable gearing was available to generate the required sidereal rate
Hydrologic Transport of Dissolved Inorganic Carbon and Its Control on Chemical Weathering
Chemical weathering is one of the major processes interacting with climate and tectonics to form clays, supply nutrients to soil microorganisms and plants, and sequester atmospheric CO2. Hydrology and dissolution kinetics have been emphasized as factors controlling chemical weathering rates. However, the interaction between hydrology and transport of dissolved inorganic carbon (DIC) in controlling weathering has received less attention. In this paper, we present an analytical model that couples subsurface water and chemical molar balance equations to analyze the roles of hydrology and DIC transport on chemical weathering. The balance equations form a dynamical system that fully determines the dynamics of the weathering zone chemistry as forced by the transport of DIC. The model is formulated specifically for the silicate mineral albite, but it can be extended to other minerals, and is studied as a function of percolation rate and water transit time. Three weathering regimes are elucidated. For very small or large values of transit time, the weathering is limited by reaction kinetics or transport, respectively. For intermediate values, the system is transport controlled and is sensitive to transit time. We apply the model to a series of watersheds for which we estimate transit times and identify the type of weathering regime. The results suggest that hydrologic transport of DIC may be as important as reaction kinetics and dilution in determining chemical weathering rates
New Observational Bounds to Quantum Gravity Signals
We consider a new set of effects arising from the quantum gravity corrections
to the propagation of fields, associated with fluctuations of the spacetime
geometry. Using already existing experimental data, we can put bounds on these
effects that are more stringent by several orders of magnitude than those
expected to be obtained in astrophysical observations. In fact these results
can be already interpreted as questioning the whole scenario of linear (in
) corrections to the dispersion relations for free fields in Lorentz
violating theories.Comment: Latex, to be published in PR
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