218 research outputs found
Pharmacological activation of endogenous protective pathways against oxidative stress under conditions of sepsis
Funding The study was funded entirely by institutional funds.Peer reviewedPostprin
Stable Umbral Chromospheric Structures
Aims. To understand the morphology of the chromosphere in sunspot umbra. We
investigate if the horizontal structures observed in the spectral core of the
Ca II H line are ephemeral visuals caused by the shock dynamics of more stable
structures, and examine their relationship with observables in the H-alpha
line. Methods. Filtergrams in the core of the Ca II H and H-alpha lines as
observed with the Swedish 1-m Solar Telescope are employed. We utilise a
technique that creates composite images and tracks the flash propagation
horizontally. Results. We find 0"15 wide horizontal structures, in all of the
three target sunspots, for every flash where the seeing was moderate to good.
Discrete dark structures are identified that are stable for at least two umbral
flashes, as well as systems of structures that live for up to 24 minutes. We
find cases of extremely extended structures with similar stability, with one
such structure showing an extent of 5". Some of these structures have a
correspondence in H-alpha but we were unable to find a one to one
correspondence for every occurrence. If the dark streaks are formed at the same
heights as umbral flashes then there are systems of structures with strong
departures from the vertical for all three analysed sunspots. Conclusions.
Long-lived Ca II H filamentary horizontal structures are a common and likely
ever-present feature in the umbra of sunspots. If the magnetic field in the
chromosphere of the umbra is indeed aligned with the structures, then the
present theoretical understanding of the typical umbra needs to be revisited.Comment: Accepted to Astronomy and Astrophysics. Online material (Fig3.mov and
Fig4.mov) will be available at A&
Ultrashort PW laser pulse interaction with target and ion acceleration
We present the experimental results on ion acceleration by petawatt
femtosecond laser solid interaction and explore strategies to enhance ion
energy. The irradiation of micrometer thick (0.2 - 6.0 micron) Al foils with a
virtually unexplored intensity regime (8x10^19 W/cm^2 - 1x10^21 W/cm^2)
resulting in ion acceleration along the rear and the front surface target
normal direction is investigated. The maximum energy of protons and carbon
ions, obtained at optimised laser intensity condition (by varying laser energy
or focal spot size), exhibit a rapid intensity scaling as I^0.8 along the rear
surface target normal direction and I^0.6 along the front surface target normal
direction. It was found that proton energy scales much faster with laser energy
rather than the laser focal spot size. Additionally, the ratio of maximum ion
energy along the both directions is found to be constant for the broad range of
target thickness and laser intensities. A proton flux is strongly dominated in
the forward direction at relatively low laser intensities. Increasing the laser
intensity results in the gradual increase in the backward proton flux and leads
to almost equalisation of ion flux in both directions in the entire energy
range. These experimental findings may open new perspectives for applications.Comment: 6 pages, 5 figures, 3rd EAAC worksho
Magnetism in Semiconducting Molybdenum Dichalcogenides
Transition metal dichalcogenides (TMDs) are interesting for understanding
fundamental physics of two-dimensional materials (2D) as well as for many
emerging technologies, including spin electronics. Here, we report the
discovery of long-range magnetic order below TM = 40 K and 100 K in bulk
semiconducting TMDs 2H-MoTe2 and 2H-MoSe2, respectively, by means of muon
spin-rotation (muSR), scanning tunneling microscopy (STM), as well as density
functional theory (DFT) calculations. The muon spin rotation measurements show
the presence of a large and homogeneous internal magnetic fields at low
temperatures in both compounds indicative of long-range magnetic order. DFT
calculations show that this magnetism is promoted by the presence of defects in
the crystal. The STM measurements show that the vast majority of defects in
these materials are metal vacancies and chalcogen-metal antisites which are
randomly distributed in the lattice at the sub-percent level. DFT indicates
that the antisite defects are magnetic with a magnetic moment in the range of
0.9-2.8 mu_B. Further, we find that the magnetic order stabilized in 2H-MoTe2
and 2H-MoSe2 is highly sensitive to hydrostatic pressure. These observations
establish 2H-MoTe2 and 2H-MoSe2 as a new class of magnetic semiconductors and
opens a path to studying the interplay of 2D physics and magnetism in these
interesting semiconductors.Comment: 13 pages, 10 Figure
Experimental evaluation of the response of micro-channel plate detector to ions with 10s of MeV energies
Spatial resolution and refractive index contrast of resonant photonic crystal surfaces for biosensing
By depositing a resolution test pattern on top of a Si3N4 photonic crystal resonant surface, we have measured the dependence of spatial resolution on refractive index contrast \Delta n. Our experimental results and finite-difference time-domain (FDTD) simulations at different refractive index contrasts show that the spatial resolution of our device reduces with reduced contrast, which is an important consideration in biosensing, where the contrast may be of order 10{-2} . We also compare 1-D and 2-D gratings, taking into account different incidence polarizations, leading to a better understanding of the excitation and propagation of the resonant modes in these structures, as well as how this contributes to the spatial resolution. At \Delta n = 0.077, we observe resolutions of 2 and 6 \mu\hbox{m} parallel to and perpendicular to the grooves of a 1-D grating, respectively, and show that for polarized illumination of a 2-D grating, resolution remains asymmetrical. Illumination of a 2-D grating at 45 ^{\circ} results in symmetric resolution. At very low index contrast, the resolution worsens dramatically, particularly for \Delta n\ <\ 0.01, where we observe a resolution exceeding 10 \mu\hbox{m} for our device. In addition, we measure a reduction in the resonance linewidth as the index contrast becomes lower, corresponding to a longer resonant mode propagation length in the structure and contributing to the change in spatial resolution
Ultrashort PW laser pulse interaction with target and ion acceleration
We present the experimental results on ion acceleration by petawatt femtosecond laser solid interaction and explore strategies to enhance ion energy. The irradiation of micrometer thick (0.2-6.0 mu m) Al foils with a virtually unexplored intensity regime (8 x 10(19) W/cm(2) - 1 x 10(21) W/cm(2)) resulting in ion acceleration along the rear and the front surface target normal direction is investigated. The maximum energy of protons and carbon ions, obtained at optimized laser intensity condition (by varying laser energy or focal spot size), exhibit a rapid intensity scaling as I-0.8 along the rear surface target normal direction and I-0.6 along the front surface target normal direction. It was found that proton energy scales much faster with laser energy rather than the laser focal spot size. Additionally, the ratio of maximum ion energy along the both directions is found to be constant for the broad range of target thickness and laser intensities. A proton flux is strongly dominated in the forward direction at relatively low laser intensities. Increasing the laser intensity results in the gradual increase in the backward proton flux and leads to almost equalization of ion flux in both directions in the entire energy range. These experimental findings may open new perspectives for applications
Ion acceleration in electrostatic field of charged cavity created by ultra-short laser pulses of 1020–1021 W/cm2
Surface modulation and back reflection from foil targets irradiated by a Petawatt femtosecond laser pulse at oblique incidence
Surface modulation and back reflection from foil targets irradiated by a Petawatt femtosecond laser pulse at oblique incidence
A significant level of back reflected laser energy was measured during the interaction of ultra-short, high contrast PW laser pulses with solid targets at 30 degrees incidence. 2D PIC simulations carried out for the experimental conditions show that at the laser-target interface a dynamic regular structure is generated during the interaction, which acts as a grating (quasi-grating) and reflects back a significant amount of incident laser energy. With increasing laser intensity above 1018 W/cm(2) the back reflected fraction increases due to the growth of the surface modulation to larger amplitudes. Above 1020 W/cm(2) this increase results in the partial destruction of the quasi-grating structure and, hence, in the saturation of the back reflection efficiency. The PIC simulation results are in good agreement with the experimental findings, and, additionally, demonstrate that in presence of a small amount of pre-plasma this regular structure will be smeared out and the back reflection reduced. (C) 2016 Optical Society of Americ
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