8,808 research outputs found
Microscale application of column theory for high resolution force and displacement sensing
We present the design, fabrication and experimental validation of a novel
device that exploits the amplification of displacement and attenuation of
structural stiffness in the post-buckling deformation of slender columns to
obtain pico-Newton force and nanometer displacement resolution even under an
optical microscope. The extremely small size, purely mechanical sensing scheme
and vacuum compatibility of the instrument makes it compatible with existing
visualization tools of nanotechnology. The instrument has a wide variety of
potential applications ranging from electro-mechanical characterization of one
dimensional solids to single biological cells
Isochronal synchronization of delay-coupled systems
We consider small network models for mutually delay-coupled systems which
typically do not exhibit stable isochronally synchronized solutions. We show
that for certain coupling architectures which involve delayed self feedback to
the nodes, the oscillators become isochronally synchronized. Applications are
shown for both incoherent pump coupled lasers and spatio-temporal coupled fiber
ring lasers.Comment: 5 pages, accepted for publication in Physical Review
Modelling the dynamics of turbulent floods
Consider the dynamics of turbulent flow in rivers, estuaries and floods. Based on the widely used k-epsilon model for turbulence, we use the techniques of centre manifold theory to derive dynamical models for the evolution of the water depth and of vertically averaged flow velocity and turbulent parameters. This new model for the shallow water dynamics of turbulent flow: resolves the vertical structure of the flow and the turbulence; includes interaction between turbulence and long waves; and gives a rational alternative to classical models for turbulent environmental flows
Complete chaotic synchronization in mutually coupled time-delay systems
Complete chaotic synchronization of end lasers has been observed in a line of
mutually coupled, time-delayed system of three lasers, with no direct
communication between the end lasers. The present paper uses ideas from
generalized synchronization to explain the complete synchronization in the
presence of long coupling delays, applied to a model of mutually coupled
semiconductor lasers in a line. These ideas significantly simplify the analysis
by casting the stability in terms of the local dynamics of each laser. The
variational equations near the synchronization manifold are analyzed, and used
to derive the synchronization condition that is a function of the parameters.
The results explain and predict the dependence of synchronization on various
parameters, such as time-delays, strength of coupling and dissipation. The
ideas can be applied to understand complete synchronization in other chaotic
systems with coupling delays and no direct communication between synchronized
sub-systems.Comment: 22 pages, 6 figure
On the Rotation Period of (90377) Sedna
We present precise, ~1%, r-band relative photometry of the unusual solar
system object (90377) Sedna. Our data consist of 143 data points taken over
eight nights in October 2004 and January 2005. The RMS variability over the
longest contiguous stretch of five nights of data spanning nine days is only
1.3%. This subset of data alone constrain the amplitude of any long-period
variations with period P to be A<1% (P/20 days)^2. Over the course of any given
5-hour segment, the data exhibits significant linear trends not seen in a
comparison star of similar magnitude, and in a few cases these segments show
clear evidence for curvature at the level of a few millimagnitudes per hour^2.
These properties imply that the rotation period of Sedna is O(10 hours), cannot
be 10 days, unless the intrinsic light curve has
significant and comparable power on multiple timescales, which is unlikely. A
sinusoidal fit yields a period of P=(10.273 +/- 0.002) hours and semi-amplitude
of A=(1.1 +/- 0.1)%. There are additional acceptable fits with flanking periods
separated by ~3 minutes, as well as another class of fits with P ~ 18 hours,
although these later fits appear less viable based on visual inspection. Our
results indicate that the period of Sedna is likely consistent with typical
rotation periods of solar system objects, thus obviating the need for a massive
companion to slow its rotation.Comment: 7 pages, 4 figures, 2.5 tables. Final ApJL version, minor changes.
Full light curve data in tex
Deep MMT Transit Survey of the Open Cluster M37 IV: Limit on the Fraction of Stars With Planets as Small as 0.3 R_J
We present the results of a deep (15 ~< r ~< 23), 20 night survey for
transiting planets in the intermediate age open cluster M37 (NGC 2099) using
the Megacam wide-field mosaic CCD camera on the 6.5m MMT. We do not detect any
transiting planets among the ~1450 observed cluster members. We do, however,
identify a ~ 1 R_J candidate planet transiting a ~ 0.8 Msun Galactic field star
with a period of 0.77 days. The source is faint (V = 19.85 mag) and has an
expected velocity semi-amplitude of K ~ 220 m/s (M/M_J). We conduct Monte Carlo
transit injection and recovery simulations to calculate the 95% confidence
upper limit on the fraction of cluster members and field stars with planets as
a function of planetary radius and orbital period. Assuming a uniform
logarithmic distribution in orbital period, we find that < 1.1%, < 2.7% and <
8.3% of cluster members have 1.0 R_J planets within Extremely Hot Jupiter (EHJ,
0.4 < T < 1.0 day), Very Hot Jupiter (VHJ, 1.0 < T < 3.0 days) and Hot Jupiter
(HJ, 3.0 < T < 5.0 days) period ranges respectively. For 0.5 R_J planets the
limits are < 3.2%, and < 21% for EHJ and VHJ period ranges, while for 0.35 R_J
planets we can only place an upper limit of < 25% on the EHJ period range. For
a sample of 7814 Galactic field stars, consisting primarily of FGKM dwarfs, we
place 95% upper limits of < 0.3%, < 0.8% and < 2.7% on the fraction of stars
with 1.0 R_J EHJ, VHJ and HJ assuming the candidate planet is not genuine. If
the candidate is genuine, the frequency of ~ 1.0 R_J planets in the EHJ period
range is 0.002% < f_EHJ < 0.5% with 95% confidence. We place limits of < 1.4%,
< 8.8% and < 47% for 0.5 R_J planets, and a limit of < 16% on 0.3 R_J planets
in the EHJ period range. This is the first transit survey to place limits on
the fraction of stars with planets as small as Neptune.Comment: 61 pages, 19 figures, 5 tables, replaced with the version accepted
for publication in Ap
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