181 research outputs found
Multimaterial coatings with reduced thermal noise
The most sensitive measurements of time and space are made with resonant optical cavities, and these measurements are limited by coating thermal noise. The mechanical and optical performance requirements placed on coating materials, especially for interferometric gravitational wave detectors, have proven extremely difficult to meet despite a lengthy search. In this paper we propose a new approach to high performance coatings, the use of multiple materials at different depths in the coating. To support this we generalize previous work on thermal noise in two-material coatings to an arbitrary multimaterial stack, and develop a means of estimating absorption in these multimaterial coatings. This new approach will allow for a broadening of the search for high performance coating materials.National Science Foundation (U.S.)Laser Interferometer Gravitational Wave Observatory (Cooperative Agreement PHY-0757058
Continuously tunable modulation scheme for precision control of optical cavities with variable detuning
We present a scheme for locking optical cavities with arbitrary detuning by many linewidths from resonance using an electro-optic modulator that can provide arbitrary ratios of amplitude-to-phase modulation. We demonstrate our scheme on a Fabry–Perot cavity, and show that a well-behaved linear error signal can be obtained by demodulating the reflected light from a cavity that is detuned by several linewidths.National Science Foundation (U.S.) (PHY-0757058
Equivalent electric circuit of a carbon nanotube based molecular conductor
We apply our first-principles method to simulate the transient electrical
response through carbon nanotube based conductors under time-dependent bias
voltages, and report the dynamic conductance for a specific system. We find
that the electrical response of the carbon nanotube device can be mapped onto
an equivalent classical electric circuit. This is confirmed by studying the
electric response of a simple model system and its equivalent circuit.Comment: 10 pages, 4 figure
Exploring the Optical Transient Sky with the Palomar Transient Factory
The Palomar Transient Factory (PTF) is a wide-field experiment designed to
investigate the optical transient and variable sky on time scales from minutes
to years. PTF uses the CFH12k mosaic camera, with a field of view of 7.9 deg^2
and a plate scale of 1 asec/pixel, mounted on the the Palomar Observatory
48-inch Samuel Oschin Telescope. The PTF operation strategy is devised to probe
the existing gaps in the transient phase space and to search for theoretically
predicted, but not yet detected, phenomena, such as fallback supernovae,
macronovae, .Ia supernovae and the orphan afterglows of gamma-ray bursts. PTF
will also discover many new members of known source classes, from cataclysmic
variables in their various avatars to supernovae and active galactic nuclei,
and will provide important insights into understanding galactic dynamics
(through RR Lyrae stars) and the Solar system (asteroids and near-Earth
objects). The lessons that can be learned from PTF will be essential for the
preparation of future large synoptic sky surveys like the Large Synoptic Survey
Telescope. In this paper we present the scientific motivation for PTF and
describe in detail the goals and expectations for this experiment.Comment: 15 pages, 6 figures, submitted to PAS
Intramolecular azide-diene cycloadditions. An approach to fused bicyclic 3-pyrrolines based on a one-pot nitrene-diene cycloaddition equivalent.
Cyclization of heterosubstituted [omega]-azidodienes 11 provides fused bicyclic 3-pyrrolines 12 in one operation. These pyrrolines are potentially useful intermediates for natural products synthesis, as illustrated by further functionalization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26464/1/0000552.pd
RCW 86: A Type Ia Supernova in a Wind-Blown Bubble
We report results from a multi-wavelength analysis of the Galactic SNR RCW
86, the proposed remnant of the supernova of 185 A.D. We report new infrared
observations from {\it Spitzer} and {\it WISE}, where the entire shell is
detected at 24 and 22 m. We fit the infrared flux ratios with models of
collisionally heated ambient dust, finding post-shock gas densities in the
non-radiative shocks of 2.4 and 2.0 cm in the SW and NW portions of the
remnant, respectively. The Balmer-dominated shocks around the periphery of the
shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact
remnant support a Type Ia origin for this remnant. From hydrodynamic
simulations, the observed characteristics of RCW 86 are successfully reproduced
by an off-center explosion in a low-density cavity carved by the progenitor
system. This would make RCW 86 the first known case of a Type Ia supernova in a
wind-blown bubble. The fast shocks ( km s) observed in the NE
are propagating in the low-density bubble, where the shock is just beginning to
encounter the shell, while the slower shocks elsewhere have already encountered
the bubble wall. The diffuse nature of the synchrotron emission in the SW and
NW is due to electrons that were accelerated early in the lifetime of the
remnant, when the shock was still in the bubble. Electrons in a bubble could
produce gamma-rays by inverse-Compton scattering. The wind-blown bubble
scenario requires a single-degenerate progenitor, which should leave behind a
companion star.Comment: Accepted for publication in ApJ. 50 pages, 9 figure
Short gamma-ray bursts from dynamically-assembled compact binaries in globular clusters: pathways, rates, hydrodynamics and cosmological setting
We present a detailed assessment of the dynamical pathways leading to the
coalescence of compact objects in Globular Clusters (GCs) and Short Gamma-Ray
Burst (SGRB) production. We consider primordial binaries, dynamically formed
binaries (through tidal two-body and three-body exchange interactions) and
direct impacts of compact objects (WD/NS/BH). We show that if the primordial
binary fraction is small, close encounters dominate the production rate of
coalescing compact systems. We find that the two dominant channels are the
interaction of field NSs with dynamically formed binaries, and two-body
encounters. We then estimate the redshift distribution and host galaxy
demographics of SGRB progenitors, and find that GCs can provide a significant
contribution to the overall observed rate.
We have carried out hydrodynamical modeling of evolution of close stellar
encounters with WD/NS/BH, and show that there is no problem in accounting for
the energy budget of a typical SGRB. The particulars of each encounter are
variable and lead to interesting diversity: the encounter characteristics are
dependent on the impact parameter, in contrast to the merger scenario; the
nature of the compact star itself can produce very different outcomes; the
presence of tidal tails in which material falls back onto the central object at
later times is a robust feature of these calculations, with the mass involved
being larger than for binary mergers. It is thus possible to account
generically in this scenario for a prompt episode of energy release, as well as
for activity many dynamical time scales later (abridged).Comment: Accepted for publication in ApJ (24 pages, 19 figures
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