63 research outputs found
Delayed self-recognition in children with autism spectrum disorder.
This study aimed to investigate temporally extended self-awareness (awareness of oneâs place in and continued existence through time) in autism spectrum disorder (ASD), using the delayed self-recognition (DSR) paradigm (Povinelli et al., Child Development 67:1540â1554, 1996). Relative to age and verbal ability matched comparison children, children with ASD showed unattenuated performance on the DSR task, despite showing significant impairments in theory-of-mind task performance, and a reduced propensity to use personal pronouns to refer to themselves. The results may indicate intact temporally extended self-awareness in ASD. However, it may be that the DSR task is not an unambiguous measure of temporally extended self-awareness and it can be passed through strategies which do not require the possession of a temporally extended self-concept
A picogram and nanometer scale photonic crystal opto-mechanical cavity
We describe the design, fabrication, and measurement of a cavity
opto-mechanical system consisting of two nanobeams of silicon nitride in the
near-field of each other, forming a so-called "zipper" cavity. A photonic
crystal patterning is applied to the nanobeams to localize optical and
mechanical energy to the same cubic-micron-scale volume. The picrogram-scale
mass of the structure, along with the strong per-photon optical gradient force,
results in a giant optical spring effect. In addition, a novel damping regime
is explored in which the small heat capacity of the zipper cavity results in
blue-detuned opto-mechanical damping.Comment: 15 pages, 4 figure
Actuation of Micro-Optomechanical Systems Via Cavity-Enhanced Optical Dipole Forces
We demonstrate a new type of optomechanical system employing a movable,
micron-scale waveguide evanescently-coupled to a high-Q optical microresonator.
Micron-scale displacements of the waveguide are observed for
milliwatt(mW)-level optical input powers. Measurement of the spatial variation
of the force on the waveguide indicates that it arises from a cavity-enhanced
optical dipole force due to the stored optical field of the resonator. This
force is used to realize an all-optical tunable filter operating with sub-mW
control power. A theoretical model of the system shows the maximum achievable
force to be independent of the intrinsic Q of the optical resonator and to
scale inversely with the cavity mode volume, suggesting that such forces may
become even more effective as devices approach the nanoscale.Comment: 4 pages, 5 figures. High resolution version available at
(http://copilot.caltech.edu/publications/CEODF_hires.pdf). For associated
movie, see (http://copilot.caltech.edu/research/optical_forces/index.htm
Observation of Spontaneous Brillouin Cooling
While radiation-pressure cooling is well known, the Brillouin scattering of
light from sound is considered an acousto-optical amplification-only process.
It was suggested that cooling could be possible in multi-resonance Brillouin
systems when phonons experience lower damping than light. However, this regime
was not accessible in traditional Brillouin systems since backscattering
enforces high acoustical frequencies associated with high mechanical damping.
Recently, forward Brillouin scattering in microcavities has allowed access to
low-frequency acoustical modes where mechanical dissipation is lower than
optical dissipation, in accordance with the requirements for cooling. Here we
experimentally demonstrate cooling via such a forward Brillouin process in a
microresonator. We show two regimes of operation for the Brillouin process:
acoustical amplification as is traditional, but also for the first time, a
Brillouin cooling regime. Cooling is mediated by an optical pump, and scattered
light, that beat and electrostrictively attenuate the Brownian motion of the
mechanical mode.Comment: Supplementary material include
Tunable bipolar optical interactions between guided lightwaves
The optical binding forces between guided lightwaves in dielectric waveguides
can be either repulsive or attractive. So far only attractive force has been
observed. Here we experimentally demonstrate a bipolar optical force between
coupled nanomechanical waveguides. Both attractive and repulsive optical forces
are obtained. The sign of the force can be switched reversibly by tuning the
relative phase of the interacting lightwaves. This tunable, bipolar interaction
forms the foundation for the operation of a new class of light force devices
and circuits.Comment: 4 figure
Broadband Reconfiguration of OptoMechanical Filters
We demonstrate broad-band reconfiguration of coupled photonic crystal
nanobeam cavities by using optical gradient force induced mechanical actuation.
Propagating waveguide modes that exist over wide wavelength range are used to
actuate the structures and in that way control the resonance of localized
cavity mode. Using this all-optical approach, more than 18 linewidths of tuning
range is demonstrated. Using on-chip temperature self-referencing method that
we developed, we determined that 20 % of the total tuning was due to
optomechanical reconfiguration and the rest due to thermo-optic effects.
Independent control of mechanical and optical resonances of our structures, by
means of optical stiffening, is also demonstrated
Observation of unidirectional backscattering-immune topological electromagnetic states
One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems subject to a large magnetic field applied perpendicular to the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal fabricated in the microwave regime. We demonstrate that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems
Stimulated optomechanical excitation of surface acoustic waves in a microdevice
Stimulated Brillouin interaction between sound and light, known to be the
strongest optical nonlinearity common to all amorphous and crystalline
dielectrics, has been widely studied in fibers and bulk materials but rarely in
optical microresonators. The possibility of experimentally extending this
principle to excite mechanical resonances in photonic microsystems, for sensing
and frequency reference applications, has remained largely unexplored. The
challenge lies in the fact that microresonators inherently have large free
spectral range, while the phase matching considerations for the Brillouin
process require optical modes of nearby frequencies but with different
wavevectors. We rely on high-order transverse optical modes to relax this
limitation. Here we report on the experimental excitation of mechanical
resonances ranging from 49 to 1400 MHz by using forward Brillouin scattering.
These natural mechanical resonances are excited in ~100 um silica microspheres,
and are of a surface-acoustic whispering-gallery type
Lower bound for the spatial extent of localized modes in photonic-crystal waveguides with small random imperfections
Light localization due to random imperfections in periodic media is paramount in photonics research. The group index is known to be a key parameter for localization near photonic band edges, since small group velocities reinforce light interaction with imperfections. Here, we show that the size of the smallest localized mode that is formed at the band edge of a one-dimensional periodic medium is driven instead by the effective photon mass, i.e. the flatness of the dispersion curve. Our theoretical prediction is supported by numerical simulations, which reveal that photonic-crystal waveguides can exhibit surprisingly small localized modes, much smaller than those observed in Bragg stacks thanks to their larger effective photon mass. This possibility is demonstrated experimentally with a photonic-crystal waveguide fabricated without any intentional disorder, for which near-field measurements allow us to distinctly observe a wavelength-scale localized mode despite the smallness (âŒ1/1000 of a wavelength) of the fabrication imperfections
The Wnt Receptor Ryk Reduces Neuronal and Cell Survival Capacity by Repressing FOXO Activity During the Early Phases of Mutant Huntingtin Pathogenicity
The Wnt receptor Ryk is an evolutionary-conserved protein important during neuronal differentiation through several mechanisms, including Îł-secretase cleavage and nuclear translocation of its intracellular domain (Ryk-ICD). Although the Wnt pathway may be neuroprotective, the role of Ryk in neurodegenerative disease remains unknown. We found that Ryk is up-regulated in neurons expressing mutant huntingtin (HTT) in several models of Huntington's disease (HD). Further investigation in Caenorhabditis elegans and mouse striatal cell models of HD provided a model in which the early-stage increase of Ryk promotes neuronal dysfunction by repressing the neuroprotective activity of the longevity-promoting factor FOXO through a noncanonical mechanism that implicates the Ryk-ICD fragment and its binding to the FOXO co-factor ÎČ-catenin. The Ryk-ICD fragment suppressed neuroprotection by lin-18/Ryk loss-of-function in expanded-polyQ nematodes, repressed FOXO transcriptional activity, and abolished ÎČ-catenin protection of mutant htt striatal cells against cell death vulnerability. Additionally, Ryk-ICD was increased in the nucleus of mutant htt cells, and reducing Îł-secretase PS1 levels compensated for the cytotoxicity of full-length Ryk in these cells. These findings reveal that the Ryk-ICD pathway may impair FOXO protective activity in mutant polyglutamine neurons, suggesting that neurons are unable to efficiently maintain function and resist disease from the earliest phases of the pathogenic process in HD. © 2014 Tourette et al
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