50 research outputs found
Optical sorting and detection of sub-micron objects in a motional standing wave
An extended interference pattern close to surface may result in both a
transmissive or evanescent surface fields for large area manipulation of
trapped particles. The affinity of differing particle sizes to a moving
standing wave light pattern allows us to hold and deliver them in a
bi-directional manner and importantly demonstrate experimentally particle
sorting in the sub-micron region. This is performed without the need of fluid
flow (static sorting). Theoretical calculations experimentally confirm that
certain sizes of colloidal particles thermally hop more easily between
neighboring traps. A new generic method is also presented for particle position
detection in an extended periodic light pattern and applied to characterization
of optical traps and particle behaviorComment: 5 pages, 6 figures, Optical Trapping pape
Synchronization of spin-driven limit cycle oscillators optically levitated in vacuum
We explore, experimentally and theoretically, the emergence of coherent
coupled oscillations and synchronization between a pair of non-Hermitian,
stochastic, opto-mechanical oscillators, levitated in vacuum. Each oscillator
consists of a polystyrene microsphere trapped in a circularly polarized,
counter-propagating Gaussian laser beam. Non-conservative, azimuthal forces,
deriving from inhomogeneous optical spin, push the micro-particles out of
thermodynamic equilibrium. For modest optical powers each particle shows a
tendency towards orbital circulation. Initially, their stochastic motion is
weakly correlated. As the power is increased, the tendency towards orbital
circulation strengthens and the motion of the particles becomes highly
correlated. Eventually, centripetal forces overcome optical gradient forces and
the oscillators undergo a collective Hopf bifurcation. For laser powers
exceeding this threshold, a pair of limit cycles appear, which synchronize due
to weak optical and hydrodynamic interactions. In principle, arrays of such
Non-Hermitian elements can be arranged, paving the way for opto-mechanical
topological materials or, possibly, classical time crystals. In addition, the
preparation of synchronized states in levitated optomechanics could lead to new
and robust sensors or alternative routes to the entanglement of macroscopic
objects
Observations of a PT-like phase transition and limit cycle oscillations in non-reciprocally coupled optomechanical oscillators levitated in vacuum
We explore the collective non-Hermitian dynamics of a pair of
non-conservatively coupled optomechanical oscillators. The oscillators consist
of silica nanoparticles optically levitated in vacuum in two parallel pairs of
interfering counter-propagating laser beams. By adjusting the relative phase,
polarization, and separation of the trapping laser beams, we set the optical
interaction between the particles to be purely non-reciprocal. Continuously
varying the relative power of the trapping beams over a predefined range takes
the system through transition, analogous to a parity-time (PT) phase
transition. Decreasing the dissipation rate within the non-equilibrium phase
induces a Hopf bifurcation resulting in the formation of collective limit cycle
oscillations similar to those observed in phonon lasers. Such systems provide a
novel platform for exceptional point optomechanical sensing and due to their
wide flexibility and tunability of the interactions can be extended to
multi-particle systems, paving the way for the development of topological
optomechanical media
Effect of an Aquatic Environment on Dual-Task Performance in Older Adults
Background: Older adults tend to have difficulty maintaining balance. It has been suggested that the aquatic environment may provide a safer and more challenging alternative to land for balance training. It has also been suggested that the performance of a dual cognitive-balance task paradigm may increase the competition for cortical resources needed to maintain balance. There is a need to evaluate the influence of an aquatic environment on the performance of a combined cognitive and motor task paradigm in older adults. Purpose: To assess the effects of an aquatic environment on the performance of cognitive and motor tasks in older adults using a dual-task paradigm. Methods: Twenty-one older adults performed a cognitive and motor task separately and simultaneously on land and in water. Cognitive and motor performance measures were number of listening errors and 95% ellipse area center of pressure (balance), respectively. Results: A significant main effect for environment on listening errors was observed (p = 0.001, effect size [ES] = 0.82). Participants made 37.5% (single-task) and 72.3% (dual-task) fewer listening errors when performing the auditory vigilance test in water versus land respectively. A significant main effect of environment on CoP sway was observed (p = 0.003, ES = -1.19). CoP sway areas were 58.3% (single-task) and 64.4% (dual-task) greater in water versus land respectively. Conclusion: Results suggest that older adults make fewer ‘cognitive’ errors when immersed in water compared to on land. This may be beneficial to older adults who are involved in aquatic-based exercise and rehabilitation
Identification of staphyloxanthin and derivates in yellow-pigmented Staphylococcus capitis subsp. capitis
Introduction: Staphylococcus capitis naturally colonizes the human skin but
as an opportunistic pathogen, it can also cause biofilm-associated infections
and bloodstream infections in newborns. Previously, we found that two strains
from the subspecies S. capitis subsp. capitis produce yellow carotenoids despite
the initial species description, reporting this subspecies as non-pigmented. In
Staphylococcus aureus, the golden pigment staphyloxanthin is an important
virulence factor, protecting cells against reactive oxygen species and modulating
membrane fluidity.
Methods: In this study, we used two pigmented (DSM 111179 and DSM 113836)
and two non-pigmented S. capitis subsp. capitis strains (DSM 20326T and DSM
31028) to identify the pigment, determine conditions under which pigmentproduction occurs and investigate whether pigmented strains show increased
resistance to ROS and temperature stress.
Results: We found that the non-pigmented strains remained colorless regardless
of the type of medium, whereas intensity of pigmentation in the two pigmented
strains increased under low nutrient conditions and with longer incubation
times. We were able to detect and identify staphyloxanthin and its derivates in
the two pigmented strains but found that methanol cell extracts from all four
strains showed ROS scavenging activity regardless of staphyloxanthin production.
Increased survival to cold temperatures (−20°C) was detected in the two
pigmented strains only after long-term storage compared to the non-pigmented
strains.
Conclusion: The identification of staphyloxanthin in S. capitis is of clinical
relevance and could be used, in the same way as in S. aureus, as a possible target
for anti-virulence drug design
Identification of staphyloxanthin and derivates in yellow-pigmented Staphylococcus capitis subsp. capitis
IntroductionStaphylococcus capitis naturally colonizes the human skin but as an opportunistic pathogen, it can also cause biofilm-associated infections and bloodstream infections in newborns. Previously, we found that two strains from the subspecies S. capitis subsp. capitis produce yellow carotenoids despite the initial species description, reporting this subspecies as non-pigmented. In Staphylococcus aureus, the golden pigment staphyloxanthin is an important virulence factor, protecting cells against reactive oxygen species and modulating membrane fluidity.MethodsIn this study, we used two pigmented (DSM 111179 and DSM 113836) and two non-pigmented S. capitis subsp. capitis strains (DSM 20326T and DSM 31028) to identify the pigment, determine conditions under which pigment-production occurs and investigate whether pigmented strains show increased resistance to ROS and temperature stress.ResultsWe found that the non-pigmented strains remained colorless regardless of the type of medium, whereas intensity of pigmentation in the two pigmented strains increased under low nutrient conditions and with longer incubation times. We were able to detect and identify staphyloxanthin and its derivates in the two pigmented strains but found that methanol cell extracts from all four strains showed ROS scavenging activity regardless of staphyloxanthin production. Increased survival to cold temperatures (−20°C) was detected in the two pigmented strains only after long-term storage compared to the non-pigmented strains.ConclusionThe identification of staphyloxanthin in S. capitis is of clinical relevance and could be used, in the same way as in S. aureus, as a possible target for anti-virulence drug design
Three-dimensional holographic optical manipulation through a high-numerical-aperture soft-glass multimode fibre
Holographic optical tweezers (HOT) hold great promise for many applications in biophotonics, allowing the creation and measurement of minuscule forces on biomolecules, molecular motors and cells. Geometries used in HOT currently rely on bulk optics, and their exploitation in vivo is compromised by the optically turbid nature of tissues. We present an alternative HOT approach in which multiple three-dimensional (3D) traps are introduced through a high-numerical-aperture multimode optical fibre, thus enabling an equally versatile means of manipulation through channels having cross-section comparable to the size of a single cell. Our work demonstrates real-time manipulation of 3D arrangements of micro-objects, as well as manipulation inside otherwise inaccessible cavities. We show that the traps can be formed over fibre lengths exceeding 100 mm and positioned with nanometric resolution. The results provide the basis for holographic manipulation and other high-numerical-aperture techniques, including advanced microscopy, through single-core-fibre endoscopes deep inside living tissues and other complex environments
Imaging via multimode optical fiber: recovery of a transmission matrix using internal references
Current research of life shows a great desire to study the mechanics of biological processes\ndirectly within the complexity of living organisms. However, majority of practical techniques\nused nowadays for tissue visualization can only reach depths of a few tens of micrometres as\nthe issue obscures deep imaging due to the random light scattering. Several imaging\ntechniques deal with this problems from different angels, such as optical coherence\ntomography, light sheet microscopy or structured light illumination A different and promising strategy to overcome the turbid nature of scattering tissues is to employ multimode optical fibers (MMF) as minimally invasive light guides or endoscopes to provide optical access inside. Although the theoretical description of light propagation through such fibers has been developed a long time ago it is frequently considered inadequate to describe real MMF. The inherent randomization of light propagating through MMFs is typically attributed to undetectable deviations from the ideal fiber structure. It is a commonly believed that this\nadditional chaos is unpredictable and that its influence grows with the length of the fiber.\nDespite this, light transport through MMFs remains deterministic and can be characterized by a transmission matrix (TM) which connects the intensity and phase patterns on the fiber input and output facets. Once the TM is known it can be used to create focus in any desired 3D\ncoordinates beyond the distal fiber facet, see figure 1, and perform e.g. fluorescence based\nlaser scanning microscopy or optical trapping