1,452 research outputs found
Effects of electrical charging on the mechanical Q of a fused silica disk
We report on the effects of an electrical charge on mechanical loss of a
fused silica disk. A degradation of Q was seen that correlated with charge on
the surface of the sample. We examine a number of models for charge damping,
including eddy current damping and loss due to polarization. We conclude that
rubbing friction between the sample and a piece of dust attracted by the
charged sample is the most likely explanation for the observed loss.Comment: submitted to Review of Scientific Instrument
New energy-transfer upconversion process in Er(3+):ZBLAN mid-infrared fiber lasers
Abstract not availableOri Henderson-Sapir, Jesper Munch, and David J. Ottawa
Azabicyclo[3.2.0]heptan-7-ones (carbapenams) from pyrrole
The azabicyclo[3.2.0]heptan-7-ones 4, 10, 16 and 24 have been prepared from pyrrole. The same general
approach has been used for all these derivatives; namely, substitution of pyrrole at the 2- and 5-carbon
atoms, catalytic hydrogenation to produce pyrrolidine-2-acetic acid derivatives, and cyclisation
using tris(1,3-dihydro-2-oxobenzoxazol-3-yl)phosphine oxide 6. The catalytic hydrogenation of
2,5-disubstituted pyrroles gives only the corresponding cis-2,5-disubstituted pyrrolidines. The
hydrogenation proceeds more easily when the nitrogen atom bears a tert-butoxycarbonyl substituent.
The N-tert-butoxycarbonylpyrroles 8 and 21 bearing an á-substituent in the acetate side chain were
hydrogenated with a high degree of facial stereoselectivity. This allowed the 6-phthalimidoazabicyclo-
[3.2.0]heptan-7-one 24 to be isolated as a single diastereoisomer. The X-ray crystal structure of a
precursor, the triester, 22a, has been obtained
Versatile and widely tunable mid-infrared erbium doped ZBLAN fiber laser
We report on a long wavelength emitting rare earth doped fiber laser with
emission centered at 3.5 {\mu}m and tunable across 450 nm. The longest
wavelength emission was 3.78 {\mu}m, which is the longest emission from a fiber
laser operating at room temperature. In a simple optical arrangement employing
dielectric mirrors for feedback, the laser was capable of emitting 1.45 W of
near diffraction limited output power at 3.47 {\mu}m. These emission
characteristics compliment the emission from quantum cascade lasers and
demonstrate how all infrared dual wavelength pumping can be used to access high
lying rare earth ion transitions that have previously relied on visible
wavelength pumping
The Melanocortin-4 Receptor Integrates Circadian Light Cues and Metabolism
The melanocortin system directs diverse physiological functions from coat color to body weight homoeostasis. A commonality among melanocortin-mediated processes is that many animals modulate similar processes on a circannual basis in response to longer, summer days, suggesting an underlying link between circadian biology and the melanocortin system. Despite key neuroanatomical substrates shared by both circadian and melanocortin-signaling pathways, little is known about the relationship between the two. Here we identify a link between circadian disruption and the control of glucose homeostasis mediated through the melanocortin-4 receptor (Mc4r). Mc4r-deficient mice exhibit exaggerated circadian fluctuations in baseline blood glucose and glucose tolerance. Interestingly, exposure to lighting conditions that disrupt circadian rhythms improve their glucose tolerance. This improvement occurs through an increase in glucose clearance by skeletal muscle and is food intake and body weight independent. Restoring Mc4r expression to the paraventricular nucleus prevents the improvement in glucose tolerance, supporting a role for the paraventricular nucleus in the integration of circadian light cues and metabolism. Altogether these data suggest that Mc4r signaling plays a protective role in minimizing glucose fluctuations due to circadian rhythms and environmental light cues and demonstrate a previously undiscovered connection between circadian biology and glucose metabolism mediated through the melanocortin system
Power scalable TEM(oo) CW Nd: YAG laser with thermal lens compensation
We present finite-element analyzes and experimental results to validate our approach for building high-power single-mode Nd:YAG lasers. We show that the thermooptical and thermomechanical properties of a slab laser can be controlled. This is essential for the use of the proposed unstable resonator. We include demonstration of an efficient subscale laser operating at 20 W TEM00.D. Mudge, M. Ostermeyer, P. J. Veitch, J. Munch, B. Middlemiss, D. J. Ottaway and M. W. Hamilto
Stabilization of injection-locked lasers using spatial mode interference
We report the use of spatial-mode-interference, or tilt-locking, for the active stabilization of injection-locking of a Nd:YAG laser. We show that this control scheme is robust and adds negligible frequency noise to the injection-locked laserOttaway, D.J.; Gray, M.B.; Shaddock, D.A.; Hollitt, C.; Veitch, P.J.; Munch, J.; McClelland, David Ernes
Mid-IR laser for wavefront correction in gravitational wave detectors
The next-generation gravitational wave detectors aim to enhance our understanding of extreme phenomena in the Universe. The high-frequency sensitivity of these detectors will be maximized by injecting squeezed vacuum states into the detector. However, the performance advantages offered by squeezed state injection can be easily degraded by losses in the system. A significant source of loss is the mode mismatch between optical cavities within the interferometer. To overcome this issue, new actuators are required that can produce a highly spherical wavefront change, with minimal higher order aberrations, whist adding low phase noise to the incident beam
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