46 research outputs found
Spin-Polarized Electrons in Monolayer MoS
The optical susceptibility is a local, minimally-invasive and spin-selective
probe of the ground state of a two-dimensional electron gas. We apply this
probe to a gated monolayer of MoS. We demonstrate that the electrons are
spin polarized. Of the four available bands, only two are occupied. These two
bands have the same spin but different valley quantum numbers. We argue that
strong Coulomb interactions are a key aspect of this spontaneous symmetry
breaking. The Bohr radius is so small that even electrons located far apart in
phase space interact, facilitating exchange couplings to align the spins
Quantum confined Stark effect in a MoS monolayer van der Waals heterostructure
The optics of dangling-bond-free van der Waals heterostructures containing
transition metal dichalcogenides are dominated by excitons. A crucial property
of a confined exciton is the quantum confined Stark effect (QCSE). Here, such a
heterostructure is used to probe the QCSE by applying a uniform vertical
electric field across a molybdenum disulfide (MoS) monolayer. The
photoluminescence emission energies of the neutral and charged excitons shift
quadratically with the applied electric field provided the electron density
remains constant, demonstrating that the exciton can be polarized. Stark shifts
corresponding to about half the homogeneous linewidth were achieved. Neutral
and charged exciton polarizabilities of (7.8~\pm~1.0)\times
10^{-10}~\tr{D~m~V}^{-1} and (6.4~\pm~0.9)\times 10^{-10}~\tr{D~m~V}^{-1} at
relatively low electron density (8 \times 10^{11}~\tr{cm}^{-2}) have been
extracted, respectively. These values are one order of magnitude lower than the
previously reported values, but in line with theoretical calculations. The
methodology presented here is versatile and can be applied to other
semiconducting layered materials as well
Optical second harmonic generation in encapsulated single-layer InSe
We report the observation of optical second harmonic generation (SHG) in
single-layer indium selenide (InSe). We measure a second harmonic signal of
under nonresonant excitation using a home-built
confocal microscope and a standard pulsed pico-second laser. We demonstrate
that polarization-resolved SHG serves as a fast, non-invasive tool to determine
the crystal axes in single-layer InSe and to relate the sharp edges of the
flake to the armchair and zigzag edges of the crystal structure. Our experiment
determines these angles to an accuracy better than .
Treating the two-dimensional material as a nonlinear polarizable sheet, we
determine a second-order nonlinear sheet polarizability for single-layer InSe, corresponding to an effective nonlinear
susceptibility value of accounting for the sheet
thickness ( ). We demonstrate that the SHG
technique can also be applied to encapsulated samples to probe their crystal
orientations. The method is therefore suitable for creating high quality van
der Waals heterostructures with control over the crystal directions
Persistent Oxytetracycline Exposure Induces an Inflammatory Process That Improves Regenerative Capacity in Zebrafish Larvae
BACKGROUND: The excessive use of antibiotics in aquaculture can adversely affect not only the environment, but also fish themselves. In this regard, there is evidence that some antibiotics can activate the immune system and reduce their effectiveness. None of those studies consider in detail the adverse inflammatory effect that the antibiotic remaining in the water may cause to the fish. In this work, we use the zebrafish to analyze quantitatively the effects of persistent exposure to oxytetracycline, the most common antibiotic used in fish farming. METHODOLOGY: We developed a quantitative assay in which we exposed zebrafish larvae to oxytetracycline for a period of 24 to 96 hrs. In order to determinate if the exposure causes any inflammation reaction, we evaluated neutrophils infiltration and quantified their total number analyzing the Tg(mpx:GFP)(i114) transgenic line by fluorescence stereoscope, microscope and flow cytometry respectively. On the other hand, we characterized the process at a molecular level by analyzing several immune markers (il-1β, il-10, lysC, mpx, cyp1a) at different time points by qPCR. Finally, we evaluated the influence of the inflammation triggered by oxytetracycline on the regeneration capacity in the lateral line. CONCLUSIONS: Our results suggest that after 48 hours of exposure, the oxytetracycline triggered a widespread inflammation process that persisted until 96 hours of exposure. Interestingly, larvae that developed an inflammation process showed an improved regeneration capacity in the mechanosensory system lateral line
Extended lubrication theory: Improved estimates of flow in channels with variable geometry
Lubrication theory is broadly applicable to the flow characterization of thin fluid films and the motion of particles near surfaces. We offer an extension to lubrication theory by starting with Stokes equations and considering higher-order terms in a systematic perturbation expansion to describe the fluid flow in a channel with features of a modest aspect ratio. Experimental results qualitatively confirm the higher-order analytical solutions, while numerical results are in very good agreement with the higherorder analytical results. We show that the extended lubrication theory is a robust tool for an accurate estimate of pressure drop in channels with shape changes on the order of the channel height, accounting for both smooth and sharp changes in geometry
Worm-like instability of a vibrated sessile drop
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