1,093 research outputs found
Quantum-limited amplification and parametric instability in the reversed dissipation regime of cavity optomechanics
Cavity optomechanical phenomena, such as cooling, amplification or
optomechanically induced transparency, emerge due to a strong imbalance in the
dissipation rates of the parametrically coupled electromagnetic and mechanical
resonators. Here we analyze the reversed dissipation regime where the
mechanical energy relaxation rate exceeds the energy decay rate of the
electromagnetic cavity. We demonstrate that this regime allows for
mechanically-induced amplification (or cooling) of the electromagnetic mode.
Gain, bandwidth, and added noise of this electromagnetic amplifier are derived
and compared to amplification in the normal dissipation regime. In addition, we
analyze the parametric instability, i.e. optomechanical Brillouin lasing, and
contrast it to conventional optomechanical phonon lasing. Finally, we propose
an experimental scheme that realizes the reversed dissipation regime using
parametric coupling and optomechanical cooling with a second electromagnetic
mode enabling quantum-limited amplification. Recent advances in high-Q
superconducting microwave resonators make the reversed dissipation regime
experimentally realizable.Comment: 5+3 pages, 5 figures, 1 tabl
Quantitative Margin Analysis in the Scanning Electron Microscope.
Interface between restorative materials and tooth hard substances must be morphologically as perfect as possible to avoid plaque accumulation and subsequent secondary caries or pulpal diseases. Therefore the marginal behavior of restorations is an important parameter to predict their longevity.
Morphologically, the quality of margins is characterized by different well defined criteria. Using a replica technique it is possible to assess the complete marginal circumference of restorations in the SEM. Margins of restorations show a large variety of their morphology. This publication describes a method to quantify the quality of dental restorations.
The restoration margins are traced on the SEM screen with a digitizer and an interface to measure the margin\u27s length. Simultaneously the margin quality is assessed and assigned to the corresponding lengths. The % distribution of the quality criteria for each restoration is then calculated. Using a comparative light microscope, the replicas are aligned and mounted identically in the SEM for longitudinal studies.
The results presented are limited to tests for the accuracy of the method. Using 5 criteria to characterize the margin quality, it was found that the difference between two measurements by the same operator, 4 weeks apart was 3% ± 2.6%. The largest difference for one group was 9%. In another accuracy test where 4 criteria for margin characterization were used, the difference between two measurements was 1.9% ± 0.9%. The largest difference between two groups found was 3.4%.
This method can be used for longitudinal studies in vivo, but also for in vitro screening tests with new materials
A new model of Holocene peatland net primary production, decomposition, water balance, and peat accumulation
Peatland carbon and water cycling are tightly coupled, so dynamic modeling of peat accumulation over decades to millennia should account for carbon-water feedbacks. We present initial results from a new simulation model of long-term peat accumulation, evaluated at a wellstudied temperate bog in Ontario, Canada. The Holocene Peat Model (HPM) determines vegetation community composition dynamics and annual net primary productivity based on peat depth (as a proxy for nutrients and acidity) and water table depth. Annual peat (carbon) accumulation is the net balance above- and below-ground productivity and litter/peat decomposition – a function of peat hydrology (controlling depth to and degree of anoxia). Peat bulk density is simulated as a function of degree of humification, and affects the water balance through its influence on both the growth rate of the peat column and on peat hydraulic conductivity and the capacity to shed water. HPM output includes both time series of annual carbon and water fluxes, peat height, and water table depth, as well as a final peat profile that can be “cored” and compared to field observations of peat age and macrofossil composition. A stochastic 8500-yr, annual precipitation time series was constrained by a published Holocene climate reconstruction for southern Quebec. HPM simulated 5.4 m of ´ peat accumulation (310 kg C m−2 ) over 8500 years, 6.5% of total NPP over the period. Vascular plant functional types accounted for 65% of total NPP over 8500 years but only 35% of the final (contemporary) peat mass. Simulated age-depth and carbon accumulation profiles were compared to a radiocarbon dated 5.8 m, c.9000-yr core. The simulated core was younger than observations at most depths, but had a similar overall trajectory; carbon accumulation rates were generally higher in the simulation and were somewhat more variable than observations. HPM results were sensitive to centuryscale anomalies in precipitation, with extended drier periods (precipitation reduced ∼10%) causing the peat profile to lose carbon (and height), despite relatively small changes in NP
EPIQR-TOBUS: a new generation of refurbishment decision aid methods
In a large majority of European countries, the amount of maintenance and refurbishment works represents nearly 50% of the total amount spent in the building sector. New requirements are being added to the necessity of maintaining or re-establishing the building stock's usage value. They are linked to the determination to reduce energy consumption, pollutant emissions, work site wastes, to improve the Indoor Environment Quality (IEQ) and all the modern conveniences inside buildings. Two European projects, EPIQR (réf. nr.: JOR3-CT96-0044) and TOBUS (réf. nr.: JOR3-CT98-Û235), developed in the IIIrd and IVth framework programs put the foundations of a new generation of refurbishment decision aid tools. A structured diagnosis scheme covering the state of deterioration of the building elements, energy performance, indoor environment quality, functional obsolescence offer a new concept which helps architects and engineers to approach the building refurbishment with a global view of the whole process, to take informed decisions, to construct coherent refurbishment scenarii and calculate a reasonable investment budget in the very first stage of the refurbishment project. EPIQR project addresses residential buildings and it has been finished in 1998, TOBUS addresses office buildings and it is still in course. The support of these methods is a multimedia computer program. Several modules help the users to treat the data collected during a diagnosis survey, to set up refurbishment scenarii and calculate their cost or energy performance, and finally to visualise the results in a comprehensive way and to prepare quality reports. This paper presents the structure and the main features of the method and softwar
`Natural Masslessness Conservation' for neutrinos in two Higgs-doublet models
We present a model which supplements the Standard Electroweak Model with
three right-handed neutrinos and one extra scalar doublet which does not
develop a vacuum expectation value. With the aid of a discrete symmetry the
neutrinos are kept strictly massless. This model has several interesting
features. It has unsuppressed lepton flavour violating processes, in particular
, hinting at the possibility that these may soon be
within experimental reach. The and interactions become non-diagonal at
one loop level. In particular, a non-trivial leptonic mixing matrix is seen to
arise from the clash between the charged gauge boson and the charged scalar
interactions.Comment: (Latex file, 12 pages. Two figures available upon request).
CMU-preprin
Resonant conversions of extremely high energy neutrinos in dark matter halos
We study the effect of adiabatically resonant conversion in galactic halos of
neutrinos at the highest energies ( - eV), when the
source is in the center of a galaxy. Using the standard neutrino
properties and the standard cosmological scenario for the hot dark part of
matter, we find that interesting conversions may take place just for neutrino
parameters relevant to the solar and atmospheric neutrino problem. The effect
is due to the large enhancement in the density in galactic halos and to
the form of the effective matter potential both below and above the pole of the
resonance.Comment: 8 pages, revtex, some comments and references added, to appear in
Phys. Rev.
McGill wetland model: evaluation of a peatland carbon simulator developed for global assessments
We developed the McGill Wetland Model (MWM) based on the general structure of the Peatland Carbon Simulator (PCARS) and the Canadian Terrestrial Ecosystem Model. Three major changes were made to PCARS: (1) the light use efficiency model of photosynthesis was replaced with a biogeochemical description of photosynthesis; (2) the description of autotrophic respiration was changed to be consistent with the formulation of photosynthesis; and (3) the cohort, multilayer soil respiration model was changed to a simple one box peat decomposition model divided into an oxic and anoxic zones by an effective water table, and a one-year residence time litter pool. MWM was then evaluated by comparing its output to the estimates of net ecosystem production (NEP), gross primary production (GPP) and ecosystem respiration (ER) from 8 years of continuous measurements at the Mer Bleue peatland, a raised ombrotrophic bog located in southern Ontario, Canada (index of agreement [dimensionless]: NEP = 0.80, GPP = 0.97, ER = 0.97; systematic RMSE [g C m<sup>−2</sup> d<sup>−1</sup>]: NEP = 0.12, GPP = 0.07, ER = 0.14; unsystematic RMSE: NEP = 0.15, GPP = 0.27, ER = 0.23). Simulated moss NPP approximates what would be expected for a bog peatland, but shrub NPP appears to be underestimated. Sensitivity analysis revealed that the model output did not change greatly due to variations in water table because of offsetting responses in production and respiration, but that even a modest temperature increase could lead to converting the bog from a sink to a source of CO<sub>2</sub>. General weaknesses and further developments of MWM are discussed
Decaying neutron propagation in the Galaxy and the Cosmic Ray anisotropy at 1 EeV
We study the cosmic ray arrival distribution expected from a source of
neutrons in the galactic center at energies around 1 EeV and compare it with
the anisotropy detected by AGASA and SUGAR. Besides the point-like signal in
the source direction produced by the direct neutrons, an extended signal due to
the protons produced in neutron decays is expected. This associated proton
signal also leads to an excess in the direction of the spiral arm. For
realistic models of the regular and random galactic magnetic fields, the
resulting anisotropy as a function of the energy is obtained. We find that for
the anisotropy to become sufficiently suppressed below E\sim 10^{17.9}eV, a
significant random magnetic field component is required, while on the other
hand, this also tends to increase the angular spread of the associated proton
signal and to reduce the excess in the spiral arm direction. The source
luminosity required in order that the right ascension anisotropy be 4% for the
AGASA angular exposure corresponds to a prediction for the point-like flux from
direct neutrons compatible with the flux detected by SUGAR. We also analyse the
distinguishing features predicted for a large statistics southern observatory.Comment: 14 pages, 6 figures, minor changes to match published versio
McGill Wetland Model: evaluation of a peatland carbon simulator developed for global assessments
International audienceWe developed the McGill Wetland Model (MWM) based on the general structure of the Peatland Carbon Simulator (PCARS) and the Canadian Terrestrial Ecosystem Model. Three major changes were made to PCARS: 1. the light use efficiency model of photosynthesis was replaced with a biogeochemical description of photosynthesis; 2. the description of autotrophic respiration was changed to be consistent with the formulation of photosynthesis; and 3. the cohort, multilayer soil respiration model was changed to a simple one box peat decomposition model divided into an oxic and anoxic zones by an effective water table, and a one-year residence time litter pool. MWM was then evaluated by comparing its output to the estimates of net ecosystem production (NEP), gross primary production (GPP) and ecosystem respiration (ER) from 8 years of continuous measurements at the Mer Bleue peatland, a raised ombrotrophic bog located in southern Ontario, Canada (index of agreement [dimensionless]: NEP=0.80, GPP=0.97, ER=0.97; systematic RMSE [g C m?2 d?1]: NEP=0.12, GPP=0.07, ER=0.14; unsystematic RMSE [g C m?2 d?1]: NEP=0.15, GPP=0.27, ER=0.23). Simulated moss NPP approximates what would be expected for a bog peatland, but shrub NPP appears to be underestimated. Sensitivity analysis revealed that the model output did not change greatly due to variations in water table because of offsetting responses in production and respiration, but that even modest temperature increases could lead to converting the bog from a sink to a source of CO2. General weaknesses and further developments of MWM are discussed
Wear of human teeth: a tribological perspective
The four main types of wear in teeth are attrition (enamel-on-enamel contact), abrasion (wear due to abrasive particles in food or toothpaste), abfraction (cracking in enamel and subsequent material loss), and erosion (chemical decomposition of the tooth). They occur as a result of a number of mechanisms including thegosis (sliding of teeth into their lateral position), bruxism (tooth grinding), mastication (chewing), toothbrushing, tooth flexure, and chemical effects. In this paper the current understanding of wear of enamel and dentine in teeth is reviewed in terms of these mechanisms and the major influencing factors are examined. In vitro tooth wear simulation and in vivo wear measurement and ranking are also discussed
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