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Reactive oxygen species (ROS) are important secondary messengers involved in a variety of cellular processes, including activation, proliferation, and differentiation. Hydrogen peroxide (H2O2) is a major ROS typically kept in low nanomolar range that causes cell and tissue damage at supraphysiological concentrations. While ROS have been studied in detail at molecular scale, little is known about their impact on cell mechanical properties as label-free biomarker for stress response. Here, we exposed human myeloid precursor cells, T-lymphoid cells and neutrophils to varying concentrations of H2O2 and show that elevated levels of mitochondrial superoxide are accompanied by an increased Young’s modulus. Mechanical alterations do not originate from global modifications in filamentous actin and microtubules but from cytosolic acidification due to lysosomal degradation. Finally, we demonstrate our findings to be independent of the presence of H2O2 and that stiffening seems to be a general response of cells to stress factors lowering cytosolic pH.
Introduction
Intracranial 4D flow MRI enables quantitative assessment of hemodynamics in patients with intracranial atherosclerotic disease (ICAD). However, quantitative assessments are still challenging due to the time-consuming vessel segmentation, especially in the presence of stenoses, which can often result in user variability. To improve the reproducibility and robustness as well as to accelerate data analysis, we developed an accurate, fully automated segmentation for stenosed intracranial vessels using deep learning.
Methods
154 dual-VENC 4D flow MRI scans (68 ICAD patients with stenosis, 86 healthy controls) were retrospectively selected. Manual segmentations were used as ground truth for training. For automated segmentation, deep learning was performed using a 3D U-Net. 20 randomly selected cases (10 controls, 10 patients) were separated and solely used for testing. Cross-sectional areas and flow parameters were determined in the Circle of Willis (CoW) and the sinuses. Furthermore, the flow conservation error was calculated. For statistical comparisons, Dice scores (DS), Hausdorff distance (HD), average symmetrical surface distance (ASSD), Bland-Altman analyses, and interclass correlations were computed using the manual segmentations from two independent observers as reference. Finally, three stenosis cases were analyzed in more detail by comparing the 4D flow-based segmentations with segmentations from black blood vessel wall imaging (VWI).
Results
Training of the network took approximately 10 h and the average automated segmentation time was 2.2 ± 1.0 s. No significant differences in segmentation performance relative to two independent observers were observed. For the controls, mean DS was 0.85 ± 0.03 for the CoW and 0.86 ± 0.06 for the sinuses. Mean HD was 7.2 ± 1.5 mm (CoW) and 6.6 ± 3.7 mm (sinuses). Mean ASSD was 0.15 ± 0.04 mm (CoW) and 0.22 ± 0.17 mm (sinuses). For the patients, the mean DS was 0.85 ± 0.04 (CoW) and 0.82 ± 0.07 (sinuses), the HD was 8.4 ± 3.1 mm (CoW) and 5.7 ± 1.9 mm (sinuses) and the mean ASSD was 0.22 ± 0.10 mm (CoW) and 0.22 ± 0.11 mm (sinuses). Small bias and limits of agreement were observed in both cohorts for the flow parameters. The assessment of the cross-sectional lumen areas in stenosed vessels revealed very good agreement (ICC: 0.93) with the VWI segmentation but a consistent overestimation (bias ± LOA: 28.1 ± 13.9%).
Discussion
Deep learning was successfully applied for fully automated segmentation of stenosed intracranial vasculatures using 4D flow MRI data. The statistical analysis of segmentation and flow metrics demonstrated very good agreement between the CNN and manual segmentation and good performance in stenosed vessels. To further improve the performance and generalization, more ICAD segmentations as well as other intracranial vascular pathologies will be considered in the future.
This work describes advanced neutral gas pressure gauges for the use in strong mag-netic fields during plasma operation of fusion devices, such as inside large stellarators and the International Thermonuclear Experimental Reactor (ITER; latin: way, path). In these environments, different factors compromise the performance of commercially available pressure gauges. Based on an existing design of the Axialsymmetrical Divertor-Experiment (ASDEX) pressure gauge, a manometer head with a novel cathode was developed. Differ-ent cathode geometries and materials, consisting of lanthanum hexaboride (LaB6), zirconi-um carbide (ZrC), hafnium carbide (HfC) and thoriated tungsten, were systematically in-vestigated to reveal their sensitivity in different gas atmospheres, magnetic field strengths and pressure ranges. In addition, thermo-mechanical loads and temperature limits were analyzed, as well as electrical stability as a function of the magnetic field and the condi-tioning properties. The focus lies in the development and characterization of novel elec-tron emitters and the understanding and optimization of their performance under typical operating conditions expected in large fusion devices.
The results presented here suggest that neutral gas manometers equipped with LaB6 emitters are best suited for use in W7-X and have already been selected to replace ma-nometers with tungsten cathodes. An evaluation of the use of LaB6 cathodes in ITER and future fusion facilities with planned deuterium-tritium (DT) operation requires a detailed study of the performance of the emitters under neutron bombardment, since LaB6 is known to have a large neutron cross section. The use of pure Boron-11 is proposed to avoid this.
Oxygen-containing plasmas are widely used in industry for a variety of applications, including thin-film deposition, etching, and other surface modification processes. Due to their high reactivity, oxygen atoms play a key role in most of these applications, and an accurate method for measuring their density is therefore of great importance, not only to gain a fundamental understanding of the chemistry in such plasmas, but also to improve industrial processes. However, existing techniques, such as two-photon absorption laser induced fluorescence (TALIF), vacuum ultraviolet (VUV) absorption spectroscopy, cavity ring-down spectroscopy (CRDS), and optical emission spectroscopy (OES), are all either bulky and expensive, experimentally challenging, or indirect and relying on a multitude of assumptions.
This work presents the first implementation of absorption spectroscopy in the terahertz (THz) spectral region as a novel diagnostic technique for measuring atomic oxygen densities in plasmas. It is based on the detection of the 3P1←3P2 fine structure transition at approximately 4.745 THz, using a newly developed tunable THz quantum cascade laser (QCL) as the radiation source. THz absorption spectroscopy allows for direct measurements (i.e. no calibration is required) of absolute ground-state atomic oxygen densities, and its accuracy depends almost exclusively on the accuracy to which the line strength of the transition is known. In addition, the narrow laser linewidth of just a few MHz makes it possible to determine the translational temperature from the detected absorption profiles as well. Furthermore, the experimental setup is relatively compact (especially compared to TALIF setups that typically involve bulky laser systems), vacuum conditions are not essential (as opposed to when working in the VUV), and the requirements for the optical alignment are not as strict as for CRDS. These features make THz absorption spectroscopy an attractive alternative to existing diagnostic techniques.
To confirm the accuracy of THz absorption spectroscopy, the obtained atomic oxygen densities were compared to those yielded by more established techniques. Therefore, TALIF and CRDS measurements of atomic oxygen densities were carried
out as well. All measurements were performed in the same capacitively coupled radio frequency (RF) oxygen discharge for a variation of the applied RF power (20 W to 100 W) and the gas pressure (0.7 mbar and 1.3 mbar). The atomic oxygen densities obtained with the three different diagnostic techniques (all of the order of 1*10^14 cm^-3) were found to be in excellent agreement, both qualitatively and quantitatively. This demonstrated that these techniques all allow for accurate measurements and can be used interchangeably as long as no spatial resolution is required. The novel technique of THz absorption spectroscopy is thus well suited for measuring atomic oxygen densities. It has the potential to turn into a standard diagnostic technique once tunable THz QCLs become commercially available and is of particular interest for industrial applications due to the simplicity and compactness of the experimental setup.
The Greifswald multi-reflection time-of-flight setup has been extended with a magnetron sputtering gas aggregation source for the production of atomic cluster ions with sizes ranging from a single to thousands of atoms. This source, combined with a newly added quadrupole mass filter and a linear Paul trap, opens up the possibility of many new atomic-cluster studies not feasible with the setup before. The new components and their interfacing with the previous setup are described, and benchmarking as well as the first experimental results are presented. The capability of the system to handle singly charged ions with masses of several ten thousand atomic mass units is demonstrated.
Spintronic THz emitters have attracted much attention due to their desirable properties, such as affordability, ultra-wideband capability, high efficiency, and tunable polarization. In this study, we investigate the characteristics of THz signals, including their frequency, bandwidth, and amplitude, emitted from a series of heterostructures with ferromagnetic (FM) and nonmagnetic (NM) materials. The FM layer consists of a wedge-shaped CoFeB layer with a thickness of 0 to 5 nm, while the NM materials include various metals such as Pt, Au, W, Ru, Pt%92Bi%8, and Ag%90Bi%10 alloys. Our experiments show that the emitter with the Pt-NM layer has the highest amplitude of the emitted THz signal. However, the PtBi-based emitter exhibits a higher central THz peak and wider bandwidth, making it a promising candidate for broadband THz emitters. These results pave the way for further exploration of the specific compositions of Pt1−x Bix for THz emitter design, especially with the goal of generating higher frequency and wider bandwidth THz signals. These advances hold significant potential for applications in various fields such as high-resolution imaging, spectroscopy, communications, medical diagnostics, and more.
Cobalt nickel oxide films are deposited on Si(111) or fluorine-doped tin-oxide-coated (FTO) glass substrates employing a pulsed hollow-cathode discharge. The hollow cathode is operated with argon gas flowing through the nozzle and with O2 gas admitted to the vacuum chamber. Three different cathode compositions (Co20Ni80, Co50Ni50, and Co80Ni20) are investigated. Deposited and annealed thin films are characterized by X-ray diffraction, infrared (Raman) spectroscopy, and ellipsometry. As-deposited films consist of a single mixed cobalt nickel oxide phase. Upon annealing at 600 °C, the mixed cobalt nickel oxide phase separates into two cystalline sub-phases which consist of cubic NiO and cubic Co3O4. Annealed films are investigated by spectroscopic ellipsometry and the optical bandgaps are determined.
In this work, an overview of the neutral gas pressures and particle exhaust in the subdivertor of the stellarator Wendelstein 7-X during the last two experimental campaigns is presented for different magnetic field configurations.
The particle exhaust, which depends on the neutral gas pressure as well as the available pumping capacity was analyzed regarding the newly installed cryo-vacuum pumping system after characterizing its pumping speed for different gases in the current neutral gas pressure regime of Wendelstein 7-X. The analysis of the neutral gas pressures shows that the pressures currently reached in the subdivertor of Wendelstein 7-X correspond to the molecular flow regime, in which the cryo-vacuum pumps are not operated efficiently.
A variety of tools has been developed to simulate the neutral gas pressure and particle exhaust in the current divertor geometry and in the future, modified divertor geometries in order to improve the divertor geometry with respect to its particle exhaust properties. Direct Simulation Monte Carlo calculations as well as a ray-tracing approach used to simulate the neutral gas pressure in the molecular flow regime confirm the neutral gas pressures measured during plasma operation. A multi-chamber model of the subdivertor based on the conductance of the subdivertor space is presented as an analytical method to assess the neutral gas pressures in different parts of the subdivertor region without the need of a complete computer-aided design of the subdivertor geometry.
Apart from modifications to the divertor geometry, the extended two-point model for
stellarators has been used to explore how varying upstream plasma parameters affect
the plasma density at the divertor targets—and consequently, the neutral gas pressure and particle exhaust in the subdivertor. These findings can be utilized to develop plasma scenarios that facilitate particle exhaust.
Quite a many electron transport problems in condensed matter physics are analyzed with a quasiparticle Boltzmann equation. For sufficiently slowly varying weak external potentials it can be derived from the basic equations of quantum kinetics, provided quasiparticles can be defined and lead to a pole in the quantum‐mechanical propagators. The derivation breaks down, however, in the vicinity of an interface which constitutes an abrupt strong perturbation of the system. In this contribution we discuss in a tutorial manner a particular technique to systematically derive, for a planar, nonideal interface, matching conditions for the quasi‐particle Boltzmann equation. The technique is based on pseudizing the transport problem by two auxiliary interface‐free systems and matching Green functions at the interface. Provided quasiparticles exist in the auxiliary systems, the framework can be put onto the semiclassical level and the desired boundary conditions result. For ideal interfaces, the conditions can be guessed from flux conservation, but for complex interfaces this is no longer the case. The technique presented in this work is geared toward such interfaces.
Broadband Alfvénic excitation & mode characterization in the Wendelstein 7-X stellarator plasmas
(2024)
Shear Alfvén waves (SAWs) can be important in plasma magnetohydrodynam-
ics (MHD) stability. In the Wendelstein 7-X (W7-X) stellarator plasmas, Alfvénic
fluctuations have been identified in routine plasma scenarios of the opera-
tional phase (OP) known as OP1.2b. Magnetic fluctuations between f = 100 −
200 kHz are measured using a system of Mirnov coils. The work presented
in the thesis aims to contribute to the physics understanding of SAWs in fu-
sion plasmas without externally driven fast ions. The dynamics of a broad
frequency range of SAWs in W7-X plasmas are analyzed. The time variations
of frequency, amplitude, and width of frequency bands of the magnetic fluc-
tuations’ spectra are determined using a new analysis method, the so-called
tracking method. The SAW variations are correlated to global plasma param-
eters during W7-X plasmas. The new tracking method enabled determining
the role of different plasma parameters in the observed variations of the SAW
spectral properties. This thesis furthermore discusses potential couplings be-
tween SAWs and ITG-driven turbulent modes to explain amplitude variations
of SAWs.