23,030 research outputs found
The Influence of Dual-Recycling on Parametric Instabilities at Advanced LIGO
Laser interferometers with high circulating power and suspended optics, such
as the LIGO gravitational wave detectors, experience an optomechanical coupling
effect known as a parametric instability: the runaway excitation of a
mechanical resonance in a mirror driven by the optical field. This can saturate
the interferometer sensing and control systems and limit the observation time
of the detector. Current mitigation techniques at the LIGO sites are
successfully suppressing all observed parametric instabilities, and focus on
the behaviour of the instabilities in the Fabry-Perot arm cavities of the
interferometer, where the instabilities are first generated. In this paper we
model the full dual-recycled Advanced LIGO design with inherent imperfections.
We find that the addition of the power- and signal-recycling cavities shapes
the interferometer response to mechanical modes, resulting in up to four times
as many peaks. Changes to the accumulated phase or Gouy phase in the
signal-recycling cavity have a significant impact on the parametric gain, and
therefore which modes require suppression.Comment: 9 pages, 11 figures, 2 ancillary file
Why Do Adults Engage in Cyberbullying on Social Media? An Integration of Online Disinhibition and Deindividuation Effects with the Social Structure and Social Learning Model
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Monoamine oxidase-A modulates apoptotic cell death induced by staurosporine in human neuroblastoma cells
Monoamine oxidases (MAOs) are mitochondrial enzymes which control the levels of neurotransmitters in the brain and dietary amines in peripheral tissues via oxidative deamination. MAO has also been implicated in cell signalling. In this study, we describe the MAO-A isoform as functional in apoptosis induced by staurosporine (STS) in human dopaminergic neuroblastoma cells (SH-SY5Y). Increased levels of MAO-A activity were induced by STS, accompanied by increased MAO-A protein and activation of the initiator of the intrinsic pathway, caspase 9, and the executioner caspase 3. MAO-A mRNA levels were unaffected by STS, suggesting that changes in MAO-A protein are due to post-transcriptional events. Two unrelated MAO-A inhibitors reduced caspase activation. STS treatment resulted in sustained activation of the mitogen-activated protein kinase pathway enzymes extracellular regulated kinase, c-jun terminal kinase and p38, and depletion of the anti-apoptotic protein Bcl-2. These changes were significantly reversed by MAO inhibition. Production of reactive oxygen species was increased following STS exposure, which was blocked by both MAO inhibition and the antioxidant N-acetylcysteine. Therefore our data provide evidence that MAO-A, through its production of reactive oxygen species as a by-product of its catalytic activity on the mitochondrial surface, is recruited by the cell to enhance apoptotic signalling
Neuraminidase Activity in \u3cem\u3eDiplococcus pneumoniae\u3c/em\u3e
Kelly, R. T. (Marquette University School of Medicine, Milwaukee, Wis.), D. Greiff, and S. Farmer. Neuraminidase activity in Diplococcus pneumoniae. J. Bacteriol. 91:601–603. 1966.—A method for the quantitation of neuraminidase in the presence of N-acetylneuraminic acid aldolase is described. The neuraminidase content of Diplococcus pneumoniae was found to be dependent on the media employed for growth; the highest enzyme activity per milligram of bacterial protein was obtained with Todd-Hewitt broth. Neuraminidase production was stimulated in D. pneumoniae by the addition of N-acetylneuraminlactose, N-acetylneuraminic acid, or N-acetylmannosamine to the growth medium. Three rough strains of D. pneumoniae, which were nonpathogenic for mice, lacked neuraminidase activity. Seven of 12 smooth strains contained neuraminidase; enzyme activity was not detected in the remaining 5 smooth strains. There was no correlation between the presence of neuraminidase activity and the capsular type or between neuraminidase production and animal virulence
Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington
Context. Near-Earth asteroid-comet transition object 107P/ (4015)
Wilson-Harrington is a possible target of the joint European Space Agency (ESA)
and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return
mission. Physical studies of this object are relevant to this mission, and also
to understanding its asteroidal or cometary nature. Aims. Our aim is to obtain
significant new constraints on the surface thermal properties of this object.
Methods. We present mid-infrared photometry in two filters (16 and 22 microns)
obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results
from the application of the Near Earth Asteroid Thermal Model (NEATM).We
obtained high S/N in two mid-IR bands allowing accurate measurements of its
thermal emission. Results. We obtain a well constrained beaming parameter (eta
= 1.39 +/- 0.26) and obtain a diameter and geometric albedo of D = 3.46 +/-
0.32 km, and pV = 0.059 +/- 0.011. We also obtain similar results when we apply
this best-fitting thermal model to single-band mid-IR photometry reported by
Campins et al. (1995), Kraemer et al. (2005) and Reach et al. (2007).
Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those
of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough
lower limit for the thermal inertia of W-H of 60 Jm^-2s^(-0.5)K^-1 when it is
at r=1AU, which is slightly over the limit of 30 Jm^-2s^(-0.5)K-1 derived by
Groussin et al. (2009) for the thermal inertia of the nucleus of comet
22P/Kopff.Comment: 4 pages, 1 figure and 3 tables. Paper accepted for publicatio
High dynamic range spatial mode decomposition
Accurate readout of low-power optical higher-order spatial modes is of
increasing importance to the precision metrology community. Mode sensors are
used to prevent mode mismatches from degrading quantum and thermal noise
mitigation strategies. Direct mode analysis sensors (MODAN) are a promising
technology for real-time monitoring of arbitrary higher-order modes. We
demonstrate MODAN with photo-diode readout to mitigate the typically low
dynamic range of CCDs. We look for asymmetries in the response our sensor to
break degeneracies in the relative alignment of the MODAN and photo-diode and
consequently improve the dynamic range of the mode sensor. We provide a
tolerance analysis and show methodology that can be applied for sensors beyond
first-order spatial modes
A new approach to modelling impacts on rubble pile asteroid simulants
Many asteroids with low bulk densities must have a rubble pile structure and internal voids. Although little is known about their internal structure, numerical simulations of impact events on these asteroids rely on assumptions on how the voids are distributed. We present a new approach to model impacts on rubble pile asteroids that explicitly takes into account their internal structure. The formation of the asteroid is modelled as a rubble pile aggregate of spherical pebbles of different sizes. This aggregate is then converted into a high-resolution smoothed particle hydrodynamics (SPH) model, accounting for macroporosity inside the pebbles. We compare impact-event outcomes for a large set of internal configurations to explore the parameter space of our model-building process. The analysis of the fragment size distribution and the disruption threshold quantifies the specific influence of each input parameter. The size distribution of the pebbles used in our model is a simple power law, containing three free parameters: the slope α, the lower cut-off radius rmin and the upper cut-off radius rmax. The influence of all three parameters on the outcome is assessed in this paper. The existence of void space in our model increases the resistance against collisional disruption, a behaviour previously reported based on numerical simulations using a continuum description of porous material (Holsapple 2009). We show, for a set of asteroid collisions typical for small asteroids in the main belt, that no a priori knowledge of the exact size distribution of the pebbles inside the asteroid is needed, as the choice of the corresponding parameters does not directly correlate with the impact outcome
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