587 research outputs found
Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes
We show that when a microsphere is illuminated by an evanescent wave, the
optical forces on- and off- whispering gallery mode (WGM) resonance can differ
by several orders of magnitude. Such size selective force allows one to
selectively manipulate the resonating particles, while leaving those particles
at off-resonance untouched. As WGM resonances have very high-Q's, this kind of
force could be deployed for size-selective manipulation with a very high
accuracy (~1/Q), as well as simultaneous particle-sorting according to their
size or resonant frequency.Comment: 11 pages, 2 figure
Localized vibrational modes in optically bound structures
We show, through analytical theory and rigorous numerical calculations, that
optical binding can organize a collection of particles into stable
one-dimensional lattice. This lattice, as well as other optically-bound
structures, are shown to exhibit spatially localized vibrational eigenmodes.
The origin of localization here is distinct from the usual mechanisms such as
disorder, defect, or nonlinearity, but is a consequence of the long-ranged
nature of optical binding. For an array of particles trapped by an interference
pattern, the stable configuration is often dictated by the external light
source, but our calculation revealed that inter-particle optical binding forces
can have a profound influence on the dynamics.Comment: 4 pages, Optical Bindin
Negative Optical Torque
Maxwell noted that light carries angular momentum, and as such it can exert
torques on material objects. This was subsequently proved by Beth in 1936.
Applications of these opto-mechanical effects were limited initially due to
their smallness in magnitude, but later enabled by the invention of laser.
Novel and practical approaches for harvesting light for particle rotation have
been demonstrated, where the structure is subjected to a positive optical
torque along a certain axis21 if the incident angular momentum has a positive
projection on the same axis. We report here a counter-intuitive phenomenon of
negative optical torque, meaning that incoming photons carrying angular
momentum rotate an object in the opposite sense. Surprisingly this can be
realized quite straightforwardly in simple planar structures. Field retardation
is a necessary condition. The optimal conditions are explored and explained.Comment: 15 pages, 3 figure
Illusion optics: The optical transformation of an object into another object
We propose to use transformation optics to generate a general illusion such
that an arbitrary object appears to be like some other object of our choice.
This is achieved by using a remote device that transforms the scattered light
outside a virtual boundary into that of the object chosen for the illusion,
regardless of the profile of the incident wave. This type of illusion device
also enables people to see through walls. Our work extends the concept of
cloaking as a special form of illusion to the wider realm of illusion optics.Comment: Including a paper and its auxiliary materia
Epigenetics involvement in Parkinson’s disease and manganese-induced neurotoxicity
Parkinson's disease (PD) is a progressive neurological disorder of CNS and one of the most common neurodegenerative diseases. The exact mechanisms underlying PD has been unclear but it is believed that multiple factors are involved. Excessive exposure to manganese (Mn) can causes its accumulation in the human brain and subsequent neural damage and even development of PD-like movement disorder, referred to as manganism. Although recent studies indicated the pathologic and clinical distinction between PD and Mn-induced neurotoxicity, genetically they have been shown some common features and associations. In recent years, the role of epigenetic changes has been well studied in brain development as well as different brain diseases including PD. Meanwhile, environmental agents including Mn have been found to damage the developing and mature nervous system through altering epigenetic regulatory pathways such as DNA methylation. The aim of this contribution was to review the epigenetic involvement in the etiology of PD and Mn-induced neurotoxicity. Other aspects of these syndromes were also discussed. Several lines of evidence have indicated that epigenetic modulation of gene plays more important roles in PD processes. On the other hand, Maternal Mn exposure has been found to be able to cause epigenetic changes in genes associated with neurodegeneration. The current data is very limited to show the association of MN-induced epigenetic changes and PD etiology. Although conclusion about the relationship between PD and Mn exposure need more consolidated studies, studying the molecular mechanisms of the effect of Mn, genetically and epigenetically will be helpful to understand the etiology of PD which is essential for therapeutic strategies of this disease
Strong optical force induced by morphology dependent resonances
We consider the resonant optical force acting on a pair of transparent
microspheres by the excitation of the Morphology Dependent Resonance (MDR). The
bonding and anti-bonding modes of the MDR correspond to strong attractions and
repulsions respectively. The dependence of the force on separation and the role
of absorption are discussed. At resonance, the force can be enhanced by orders
of magnitude so that it will dominate over other relevant forces. We find that
a stable binding configuration can be induced by the resonant optical force.Comment: 4 pages, 4 figure
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