8 research outputs found
Synchronization in pairs of opto-thermally driven mechanically coupled micro-oscillators
We study the phenomenon of synchronization in pairs of doubly clamped,
mechanically coupled silicon micro-oscillators. A continuous-wave laser beam is
used to drive the micro-beams into limit cycle oscillations and to detect the
oscillations using interferometry. Devices of different dimensions are used to
introduce frequency detuning, and short silicon bridges connecting the
micro-beams are used as mechanical coupling between the oscillators. The region
of synchronization is plotted for the MEMS system in the detuning vs. coupling
parameter space and compared with the numerical analysis of a corresponding,
lumped-parameter model. Three states of oscillations are observed i.e. the
drift state, quasi-periodic state, and the synchronized state. The numerical
model also distinguishes between in-phase and out-of-phase synchronization
where out-of-phase synchronization is observed at low coupling strengths and
low frequency detuning. We also show that the experimentally measured frequency
fluctuations of the system reduce with an increase in coupling strength.Comment: 8 pages, 7 figure
Driver Selection for Mechanical Drive Service
TutorialThis panel will cover different types of drivers for mechanical drive service including steam and gas turbines, electric motors and heat recovery cycles. Panel members will discuss the different technologies available, and how they fit into a decision matrix for different projects. The discussion will be technology neutral, with a focus only on approaches for driver selection, technical aspects, pros and cons of different technologies, and a brief discussion relating to key issues such as life cycle costs, reliability, efficiency, maintenance, larger driver sizes, new technologies and trends in the Oil and Gas Industry
The Arizona CDFS Environment Survey (ACES): A Magellan/IMACS Spectroscopic Survey of the Chandra Deep Field-South
We present the Arizona CDFS Environment Survey (ACES), a recently-completed
spectroscopic redshift survey of the Chandra Deep Field South (CDFS) conducted
using IMACS on the Magellan-Baade telescope. In total, the survey targeted 7277
unique sources down to a limiting magnitude of R = 24.1, yielding 5080 secure
redshifts across the ~30' x 30' extended CDFS region. The ACES dataset delivers
a significant increase to both the spatial coverage and the sampling density of
the spectroscopic observations in the field. Combined with
previously-published, spectroscopic redshifts, ACES now creates a
highly-complete survey of the galaxy population at R < 23, enabling the local
galaxy density (or environment) on relatively small scales (~1 Mpc) to be
measured at z < 1 in one of the most heavily-studied and data-rich fields in
the sky. Here, we describe the motivation, design, and implementation of the
survey and present a preliminary redshift and environment catalog. In addition,
we utilize the ACES spectroscopic redshift catalog to assess the quality of
photometric redshifts from both the COMBO-17 and MUSYC imaging surveys of the
CDFS.Comment: resubmitted to MNRAS; 12 pages, 12 figures, and 3 tables; updated
redshift catalog available at http://mur.ps.uci.edu/~cooper/ACES
Bistability in coupled opto-thermal micro-oscillators
In this work, we experimentally investigate the dynamics of pairs of
opto-thermally driven, mechanically coupled, doubly clamped, silicon
micromechanical oscillators, and numerically investigate the dynamics of the
corresponding lumped-parameter model. Coupled limit cycle oscillators exhibit
striking nonlinear dynamics and bifurcations in response to variations in
system parameters. We show that the input laser power influences the frequency
detuning between two non-identical oscillators. As the laser power is varied,
different regimes of oscillations such as the synchronized state, the drift
state, and the quasi-periodic state are mapped at minimal and high coupling
strengths. For non-identical oscillators, coexistence of two states, the
synchronized state and the quasi-periodic state, is demonstrated at high
coupling and high laser power. Experimentally, this bistability manifests as
irregular oscillations as the system rapidly switches between the two states
due to the system's sensitive dependence on initial conditions in the presence
of noise. We provide a qualitative comparison of the experimental and numerical
results to elucidate the behavior of the system.Comment: 9 pages, 8 figures, revised Figs. 2, 5, 6, and 7 and associated tex
A bright-lensed galaxy at z = 5.4 with strong Ly α emission
We present a detailed study of an unusually bright, lensed galaxy at z = 5.424 discovered within the CFHTLS imaging survey. With an observed flux ofiAB =23.0, J141446.82+544631.9 is one of the brightest galaxies known at z > 5. It is characterized by strong Ly α emission, reaching a peak in (observed) flux density of >10−16erg s−1 cm−2Å−1. A deep optical spectrum from the Large Binocular Telescope places strong constraints on NV and C IV emission, disfavouring an Active Galactic Nucleus (AGN) source for the emission. However, a detection of the NIV] λ1486 emission line indicates a hard ionizing continuum, possibly from hot, massive stars. Resolved imaging from HST deblends the galaxy from a foreground interloper; these observations include narrowband imaging of the Ly α emission, which is marginally resolved on approximately few kpc scales and has EW0 ∼ 260 Å. The Ly α emission extends over ∼2000 km s−1 and is broadly consistent with expanding shell models. Spectral energy distribution fitting that includes Spitzer/IRAC photometry suggests a complex star formation history that includes both a recent burst and an evolved population. J1414+5446 lies 30 arcsec from the centre of a known lensing cluster in the CFHTLS; combined with the foreground contribution, this leads to a highly uncertain estimate for the lensing magnification in the range 5 μ 25. Because of its unusual brightness, J1414+5446 affords unique opportunities for detailed study of an individual galaxy near the epoch of re-ionization and a preview of what can be expected from upcoming wide-area surveys that will yield hundreds of similar objects
The Portland region: Where city and suburbs talk to each other ... and sometimes agree
Portland, OR, is often cited as an example of successful regional governance and planning. The metropolitan area appears to match many of the precepts of the popular compact city model of urban growth and to demonstrate the capacity of local and state government to shape growing metropolitan regions. Given this reputation, it is important to evaluate the relevance of the Portland experience for other communities, distinguishing unique local circumstances form generalizable characteristics. This analysis explores the spatial character of metropolitan Portland in the 1990s, summarizes the politics of regional planning, examines weaknesses in the Portland approach, and offers suggestions for other metropolitan areas. The study finds that many of Portland\u27s accomplishments center on urban design, but that the region\u27s most distinguishing characteristics is its attention to political process. The discussion concludes with suggestions about the value of extensive civic discourse,incremental policy making, and institution building