355 research outputs found
Graphene-based active slow surface plasmon polaritons
Finding new ways to control and slow down the group velocity of light in media remains a major challenge in the field of optics. For the design of plasmonic slow light structures, graphene represents an attractive alternative to metals due to its strong field confinement, comparably low ohmic loss and versatile tunability. Here we propose a novel nanostructure consisting of a monolayer graphene on a silicon based graded grating structure. An external gate voltage is applied to graphene and silicon, which are separated by a spacer layer of silica. Theoretical and numerical results demonstrate that the structure exhibits an ultra-high slowdown factor above 450 for the propagation of surface plasmon polaritons (SPPs) excited in graphene, which also enables the spatially resolved trapping of light. Slowdown and trapping occur in the mid-infrared wavelength region within a bandwidth of similar to 2.1 mu m and on a length scale less than 1/6 of the operating wavelength. The slowdown factor can be precisely tuned simply by adjusting the external gate voltage, offering a dynamic pathway for the release of trapped SPPs at room temperature. The presented results will enable the development of highly tunable optoelectronic devices such as plasmonic switches and buffers
Detection of paramagnetic spins with an ultrathin van der Waals quantum sensor
Detecting magnetic noise from small quantities of paramagnetic spins is a
powerful capability for chemical, biochemical, and medical analysis. Quantum
sensors based on optically addressable spin defects in bulk semiconductors are
typically employed for such purposes, but the 3D crystal structure of the
sensor inhibits the sensitivity by limiting the proximity of the defects to the
target spins. Here we demonstrate the detection of paramagnetic spins using
spin defects hosted in hexagonal boron nitride (hBN), a van der Waals material
which can be exfoliated into the 2D regime. We first create negatively charged
boron vacancy (V) defects in a powder of ultrathin hBN nanoflakes
(~atomic monolayers thick on average) and measure the longitudinal spin
relaxation time () of this system. We then decorate the dry hBN nanopowder
with paramagnetic Gd ions and observe a clear quenching, under
ambient conditions, consistent with the added magnetic noise. Finally, we
demonstrate the possibility of performing spin measurements including
relaxometry using solution-suspended hBN nanopowder. Our results highlight the
potential and versatility of the hBN quantum sensor for a range of sensing
applications, and pave the way towards the realisation of a truly 2D,
ultrasensitive quantum sensor.Comment: 19 pages, 11 figure
Peroxisome Proliferator-Activated Receptor alpha (PPAR alpha) down-regulation in cystic fibrosis lymphocytes
Background: PPARs exhibit anti-inflammatory capacities and are potential modulators of the inflammatory response. We hypothesized that their expression and/or function may be altered in cystic fibrosis (CF), a disorder characterized by an excessive host inflammatory response.
Methods: PPARα, β and γ mRNA levels were measured in peripheral blood cells of CF patients and healthy subjects via RT-PCR. PPARα protein expression and subcellular localization was determined via western blot and immunofluorescence, respectively. The activity of PPARα was analyzed by gel shift assay.
Results: In lymphocytes, the expression of PPARα mRNA, but not of PPARβ, was reduced (-37%; p < 0.002) in CF patients compared with healthy persons and was therefore further analyzed. A similar reduction of PPARα was observed at protein level (-26%; p < 0.05). The transcription factor was mainly expressed in the cytosol of lymphocytes, with low expression in the nucleus. Moreover, DNA binding activity of the transcription factor was 36% less in lymphocytes of patients (p < 0.01). For PPARα and PPARβ mRNA expression in monocytes and neutrophils, no significant differences were observed between CF patients and healthy persons. In all cells, PPARγ mRNA levels were below the detection limit.
Conclusion: Lymphocytes are important regulators of the inflammatory response by releasing cytokines and antibodies. The diminished lymphocytic expression and activity of PPARα may therefore contribute to the inflammatory processes that are observed in CF
The effect of discrete wavelengths of visible light on the developing murine embryo
Open Access funding enabled and organized by CAUL and its Member Institutions KRD is supported by a Mid-Career Fellowship from the Hospital Research Foundation (C-MCF-58–2019). KD is supported by funding from the UK Engineering and Physical Sciences Research Council (EP/P030017/1) and the Australian Research Council (FL210100099). CC acknowledges the support of a PhD scholarship jointly from the University of Adelaide and University of Nottingham. This study was funded by the Australian Research Council Centre of Excellence for Nanoscale BioPhotonics (CE140100003). PR acknowledges funding through the RMIT Vice-Chancellor’s Research Fellowship and ARC DECRA Fellowship scheme (DE200100279).Purpose A current focus of the IVF field is non-invasive imaging of the embryo to quantify developmental potential. Such approaches use varying wavelengths to gain maximum biological information. The impact of irradiating the developing embryo with discrete wavelengths of light is not fully understood. Here, we assess the impact of a range of wavelengths on the developing embryo. Methods Murine preimplantation embryos were exposed daily to wavelengths within the blue, green, yellow, and red spectral bands and compared to an unexposed control group. Development to blastocyst, DNA damage, and cell number/allocation to blastocyst cell lineages were assessed. For the longer wavelengths (yellow and red), pregnancy/fetal outcomes and the abundance of intracellular lipid were investigated. Results Significantly fewer embryos developed to the blastocyst stage when exposed to the yellow wavelength. Elevated DNA damage was observed within embryos exposed to blue, green, or red wavelengths. There was no effect on blastocyst cell number/lineage allocation for all wavelengths except red, where there was a significant decrease in total cell number. Pregnancy rate was significantly reduced when embryos were irradiated with the red wavelength. Weight at weaning was significantly higher when embryos were exposed to yellow or red wavelengths. Lipid abundance was significantly elevated following exposure to the yellow wavelength. Conclusion Our results demonstrate that the impact of light is wavelength-specific, with longer wavelengths also impacting the embryo. We also show that effects are energy-dependent. This data shows that damage is multifaceted and developmental rate alone may not fully reflect the impact of light exposure.Publisher PDFPeer reviewe
Multi-species optically addressable spin defects in a van der Waals material
Optically addressable spin defects hosted in two-dimensional van der Waals
materials represent a new frontier for quantum technologies, promising to lead
to a new class of ultrathin quantum sensors and simulators. Recently, hexagonal
boron nitride (hBN) has been shown to host several types of optically
addressable spin defects, thus offering a unique opportunity to simultaneously
address and utilise various spin species in a single material. Here we
demonstrate an interplay between two separate spin species within a single hBN
crystal, namely boron vacancy defects and visible emitter spins. We
unambiguously prove that the visible emitters are spins and
further demonstrate room temperature coherent control and optical readout of
both spin species. Importantly, by tuning the two spin species into resonance
with each other, we observe cross-relaxation indicating strong inter-species
dipolar coupling. We then demonstrate magnetic imaging using the
defects, both under ambient and cryogenic conditions, and
leverage their lack of intrinsic quantization axis to determine the anisotropic
magnetic susceptibility of a test sample. Our results establish hBN as a
versatile platform for quantum technologies in a van der Waals host at room
temperature
Fano resonances in plasmonic core-shell particles and the Purcell effect
Despite a long history, light scattering by particles with size comparable
with the light wavelength still unveils surprising optical phenomena, and many
of them are related to the Fano effect. Originally described in the context of
atomic physics, the Fano resonance in light scattering arises from the
interference between a narrow subradiant mode and a spectrally broad radiation
line. Here, we present an overview of Fano resonances in coated spherical
scatterers within the framework of the Lorenz-Mie theory. We briefly introduce
the concept of conventional and unconventional Fano resonances in light
scattering. These resonances are associated with the interference between
electromagnetic modes excited in the particle with different or the same
multipole moment, respectively. In addition, we investigate the modification of
the spontaneous-emission rate of an optical emitter at the presence of a
plasmonic nanoshell. This modification of decay rate due to electromagnetic
environment is referred to as the Purcell effect. We analytically show that the
Purcell factor related to a dipole emitter oriented orthogonal or tangential to
the spherical surface can exhibit Fano or Lorentzian line shapes in the near
field, respectively.Comment: 28 pages, 10 figures; invited book chapter to appear in "Fano
Resonances in Optics and Microwaves: Physics and Application", Springer
Series in Optical Sciences (2018), edited by E. O. Kamenetskii, A. Sadreev,
and A. Miroshnichenk
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