50 research outputs found

    Invasive and non-invasive diagnostics of High Power Impulse Magnetron Sputtering (HiPIMS) discharges

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    HiPIMS discharges operated with a titanium and an aluminium-doped zinc target sputtered with the working gas argon were investigated by means of optical 2d-imaging in combination with Abel-inversion. By using optical bandpass filters, the spatial and temporal evolution of the plasma-induced emission of argon atoms and ions and metal atoms and ions were studied. The discharge ignition was found to be accompanied by an intensity maximum observed remote from the target, followed by an asymmetric intensity profile. During the stage of high discharge current, the intensity distribution indicates strong rarefaction of the working gas, efficient ionisation of the sputtered particles above the target and a wider sputter distribution. The off-time is characterised by an initial drop of the intensity by 4 - 6 orders of magnitude and a transition from electron-impact excitation to excitation by electron-electron-ion recombination. Decay constants in the order of 1 ms and the spatial distribution of the emission suggest the loss of electrons and ions due to ambipolar diffusion across the magnetic field. Plasma potential measurements by means of emissive probe revealed strongly negative space potentials of up to -300 V and electric fields in the order of 10000 V/m during discharge ignition, caused by strong charge separation due to the extended sheath. The plasma potential increases to a stable level of more than -25 V during the second half of the discharge pulse, while the electric field is largely reduced to maximal 1500 V/m. It was found that the space potential is consistently 5 V lower when the substrate is kept floating compared to a grounded substrate, which can be explained by the reduced electron loss rate to the substrate due to the potential barrier. This is confirmed by spatially resolved Langmuir probe measurements, showing a density maximum of 1019 m-3 in the confined plasma zone, and an increased density in the vicinity of the floating substrate of 1.3 × �1018 m-3 compared to 0.8 × �1018 m-3 for a grounded substrate. The electron temperature was found to be spatially uniform ranging from 1 eV to 3 eV. A quasi-continuous transport model for sputtered particles confirmed the high degree of ionisation of the sputtered particles of about 90 % and revealed a return probability for titanium ions to the target of 80 % for Ti+ and 96 % for Ti2+. Varying the force caused by a modified two-stream instability [1], showed an increasing sideway defletion of ions also increasing the kinetic energy observed for these particles. The spatial distribution of the relative density confirmed efficient ionisation of sputtered particles in the dense plasma zone adjacent to the target. Average azimuthal velocities of the drifting ion fluid of 3�000 m/s for Ti+ and 7�000 m/s for Ti2+ were obtained

    Differentiation of benign and malignant vertebral fractures using a convolutional neural network to extract CT-based texture features.

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    PURPOSE To assess the diagnostic performance of three-dimensional (3D) CT-based texture features (TFs) using a convolutional neural network (CNN)-based framework to differentiate benign (osteoporotic) and malignant vertebral fractures (VFs). METHODS A total of 409 patients who underwent routine thoracolumbar spine CT at two institutions were included. VFs were categorized as benign or malignant using either biopsy or imaging follow-up of at least three months as standard of reference. Automated detection, labelling, and segmentation of the vertebrae were performed using a CNN-based framework ( https://anduin.bonescreen.de ). Eight TFs were extracted: Varianceglobal, Skewnessglobal, energy, entropy, short-run emphasis (SRE), long-run emphasis (LRE), run-length non-uniformity (RLN), and run percentage (RP). Multivariate regression models adjusted for age and sex were used to compare TFs between benign and malignant VFs. RESULTS Skewnessglobal showed a significant difference between the two groups when analyzing fractured vertebrae from T1 to L6 (benign fracture group: 0.70 [0.64-0.76]; malignant fracture group: 0.59 [0.56-0.63]; and p = 0.017), suggesting a higher skewness in benign VFs compared to malignant VFs. CONCLUSION Three-dimensional CT-based global TF skewness assessed using a CNN-based framework showed significant difference between benign and malignant thoracolumbar VFs and may therefore contribute to the clinical diagnostic work-up of patients with VFs

    Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

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    A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

    Measurements of top-quark pair differential cross-sections in the eμe\mu channel in pppp collisions at s=13\sqrt{s} = 13 TeV using the ATLAS detector

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    Measurement of the W boson polarisation in ttˉt\bar{t} events from pp collisions at s\sqrt{s} = 8 TeV in the lepton + jets channel with ATLAS

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    Measurement of jet fragmentation in Pb+Pb and pppp collisions at sNN=2.76\sqrt{{s_\mathrm{NN}}} = 2.76 TeV with the ATLAS detector at the LHC

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    Search for single production of vector-like quarks decaying into Wb in pp collisions at s=8\sqrt{s} = 8 TeV with the ATLAS detector

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    Measurement of the charge asymmetry in top-quark pair production in the lepton-plus-jets final state in pp collision data at s=8TeV\sqrt{s}=8\,\mathrm TeV{} with the ATLAS detector

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    Measurement of the bbb\overline{b} dijet cross section in pp collisions at s=7\sqrt{s} = 7 TeV with the ATLAS detector

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    Charged-particle distributions at low transverse momentum in s=13\sqrt{s} = 13 TeV pppp interactions measured with the ATLAS detector at the LHC

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