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Abstract
The laser photodetachment experiment in a diffuse helium–oxygen barrier discharge is evaluated by a 1D fluid simulation. As in the experiment, the simulated discharge operates in helium with
400
ppm
oxygen admixture at
500
mbar
inside a discharge gap of
3
mm
. The laser photodetachment is included by the interaction of negative ions with a temporally and spatially dependent photon flux. The simulation with the usually applied set of reactions and rate coefficients provides a much lower negative ion density than needed to explain the impact on the discharge characteristics in the experiment. Further processes for an enhanced negative ion formation and their capabilities of reproducing the experimental results are discussed. These further processes are additional attachment processes in the volume and the negative ion formation at the negatively charged dielectric. Both approaches are able to reproduce the measured laser photodetachment effect partially, but the best agreement with the experimental results is achieved with the formation of negative ions at the negatively charged dielectric.
Abstract
Single self-stabilized discharge filaments were investigated in the plane-parallel electrode configuration. The barrier discharge was operated inside a gap of 3 mm shielded by glass plates to both electrodes, using helium-nitrogen mixtures and a square-wave feeding voltage at a frequency of 2 kHz. The combined application of electrical measurements, ICCD camera imaging, optical emission spectroscopy and surface charge diagnostics via the electro-optic Pockels effect allowed the correlation of the discharge development in the volume and on the dielectric surfaces. The formation criteria and existence regimes were found by systematic variation of the nitrogen admixture to helium, the total pressure and the feeding voltage amplitude. Single self-stabilized discharge filaments can be operated over a wide parameter range, foremost, by significant reduction of the voltage amplitude after the operation in the microdischarge regime. Here, the outstanding importance of the surface charge memory effect on the long-term stability was pointed out by the recalculated spatio-temporally resolved gap voltage. The optical emission revealed discharge characteristics that are partially reminiscent of both the glow-like barrier discharge and the microdischarge regime, such as a Townsend pre-phase, a fast cathode-directed ionization front during the breakdown and radially propagating surface discharges during the afterglow.
Abstract
This work reports on the spatio-temporal characterization of the multiple current pulse regime of diffuse barrier discharges driven by sine-wave feeding voltage at a frequency of 2 kHz in helium with small nitrogen admixtures. The discharge gap of 3 mm is bounded by glass plates on both plane electrodes. Priority is given to the lateral discharge inhomogeneities, underlying volume- and surface-memory effects, and the breakdown mechanism. Therefore, relevant processes in the discharge volume and on the dielectric surfaces were investigated by ICCD camera imaging and optical emission spectroscopy in combination with electrical measurements and surface charge diagnostics using the electro-optic Pockels effect of a bismuth silicon oxide crystal. The number of current pulses per half-cycle of the sine-wave voltage rises with increasing nitrogen admixture to helium due to the predominant role of the Penning ionization. Here, the transition from the first glow-like breakdown to the last Townsend-like breakdown is favored by residual species from the former breakdowns which enhance the secondary electron emission during the pre-phase of the later breakdowns. Moreover, the surface charge measurements reveal that the consecutive breakdowns occur alternately at central and peripheral regions on the electrode surface. These spatial inhomogeneities are conserved by the surface charge memory effect as pointed out by the recalculated spatio-temporal development of the gap voltage.
Surface charge measurements on different dielectrics in diffuse and filamentary barrier discharges
(2017)
Abstract
Previously, we reported on the measurement of surface charges during the operation of barrier discharges (BDs) using the electro-optic Pockels effect of a bismuth silicon oxide (BSO) crystal. With the present work, the next milestone is achieved by making this powerful method accessible to various dielectrics which are typically used in BD configurations. The dynamics and spatial distribution of positive and negative surface charges were determined on optically transparent borosilicate glass, mono-crystalline alumina and magnesia, respectively, covering the BSO crystal. By variation of the nitrogen admixture to helium and the pressure between 500 mbar and 1 bar, both the diffuse glow-like BD and the self-stabilized discharge filaments were operated inside of a gas gap of 3 mm. The characteristics of the discharge and, especially, the influence of the different dielectrics on its development were studied by surface charge diagnostics, electrical measurements and ICCD camera imaging. Regarding the glow-like BD, the breakdown voltage changes significantly by variation of the cathodic dielectric, due to the different effective secondary electron emission (SEE) coefficients. These material-specific SEE yields were estimated using Townsend’s criterion in combination with analytical calculations of the effective ionization coefficient in helium with air impurities. Moreover, the importance of the surface charge memory effect for the self-stabilization of discharge filaments was quantified by the recalculated spatio-temporal behavior of the gap voltage.
Background: Although 20-30% of all strokes occur in the posterior circulation, few studies have explored the characteristics of patients with strokes in the posterior compared to the anterior circulation so far. Especially data on young patients is missing. Methods: In this secondary analysis of data of the prospective multi-centre European sifap1 study that investigated stroke and transient ischemic attack (TIA) patients aged 18-55 years, we compared vascular risk factors, stroke aetiology, presence of white matter hyperintensities (WMH) and cerebral microbleeds (CMB) between patients with ischaemic posterior circulation stroke (PCS) and those having suffered from anterior circulation stroke (ACS) based on cerebral MRI. Results: We diagnosed PCS in 612 patients (29.1%, 407 men, 205 women) and ACS in 1,489 patients (70.9%). Their age (median 46 vs. 47 years, p = 0.205) and stroke severity (modified Rankin Scale: both 2, p = 0.375, Barthel Index 90 vs. 85, p = 0.412) were similar. PCS was found to be more frequent among the male gender (66.5 vs. 60.1% with ACS, p = 0.003). Vertebral artery (VA) dissection was more often the cause of PCS (16.8%) than was carotid artery dissection of ACS (7.9%, p < 0.001). Likewise, small vessel disease (Trial of Org 10172 in Acute Stroke Treatment [TOAST] = 3, PCS: 14.7%, ACS: 11.8%) and stroke of other determined aetiology (TOAST = 4, PCS: 24.5%, ACS: 16.0%) were more frequent in those with PCS. Furthermore, patent foramen ovale (PFO; PCS: 31.1%, ACS: 25.4%, p = 0.029) was more often detected in patients with PCS. In contrast, large-artery atherosclerosis (TOAST = 1, PCS: 15.4%, ACS: 22.2%) and cardio-embolic stroke (TOAST = 2, PCS: 15.6%, ACS: 18.0%) were less frequent in those with PCS (p < 0.001) as were preceding cerebrovascular events (10.1 vs. 14.1%, p = 0.014), TIA (4.8 vs. 7.7%, p = 0.016) and smoking (53.2 vs. 61.0%, p = 0.001). The presence, extent, and location of WMH and CMB did not differ between the 2 groups. Conclusions: Our data suggested a different pattern of aetiology and risk factors in young patients with PCS compared to those with ACS. These findings especially call for a higher awareness of VA dissection and potentially for more weight of a PFO as a risk factor in young patients with PCS. Clinical trial registration-URL: http://www.clinicaltrials.gov; NCT00414583.
Synopsis
Polyanionic metal clusters are produced by electron attachment in both Paul and Penning traps. After size and charge-state selection, the cluster properties are further investigated by various methods including photo-dissociation. Depending on the particular cluster species various decay modes are observed.
Depression und Adipositas sind weit verbreitet und eng miteinander verbunden. Brain-
derived neurotrophic factor und Vitamin D stehen in Diskussion an neuronaler Plastizität beteiligt zu sein, insbesondere bei Depression. Es wurde berichtet, dass niedrige BDNF und Vitamin D Spiegel auch mit Adipositas assoziiert. Auch bei Adipositas scheint Neuroplastizität eine Rolle zu spielen. Serum Neuronen-spezifische Enolase, wird als Marker für neuronale Schädigung diskutiert. Über das Zusammenspiel von BDNF und Vitamin D ist bisher wenig bekannt. In der vorliegenden Dissertation wurden die vermuteten Zusammenhänge und Interaktionen von BDNF und Vitamin D mit Depression und Adipositas in einer großen, bevölkerungsbasierten Kohorte untersucht. Dabei wird auch auf den Zusammenhang zwischen sNSE und Adipositas eingegangen. Die Daten kamen aus der epidemiologischen Study of Health in Pomerania (SHIP)-Trend. Die logistischen Regressionsmodelle erbrachten eine negative Assoziation von Vitamin D mit Depression und Adipositas. Zwischen BDNF und Depression oder Adipositas zeigte sich in der logistischen Regression kein signifikanter Zusammenhang. Allerdings erbrachten multivariable lineare Regressionsmodelle einen U-förmigen Zusammenhang zwischen BDNF und WHR. Die Interaktion von BDNF und Vitamin D in Bezug auf Depression zeigte keine statistische Signifikanz (p-Wert=0,065). sNSE Spiegel und BMI waren nicht linear assoziiert, es zeigte sich ein parabelförmiger Zusammenhang mit fallenden sNSE Werten ab einem BMI von >25 kg/m2. Zusammenfassend lässt sich sagen, dass Vitamin D negativ mit Depression und Adipositas assoziiert war. BDNF zeigte einen Zusammenhang mit Adipositas, aber nicht mit Depression. In Übereinstimmung mit anderen Studien scheint es im Frühstadium von
Adipositas zu akuten neuronalen Schäden zu kommen, wobei die Auswirkungen auf das Gehirn mit steigendem Körperfett zunehmen. Um die Auswirkungen von Depression und Adipositas auf neuronale Schädigung und Differenzierung besser beurteilen zu können und BDNF, Vitamin D und sNSE als Biomarker für diese Prozesse einsetzen zu können, sind weitere Studien nötig. Im klinischen Alltag könnten sich so neue, wirksame Diagnostik- und Therapiestrategien ableiten lassen.
Antibodies recognizing complexes of the chemokine platelet factor 4 (PF4/CXCL4) and polyanions (P) opsonize PF4-coated bacteria hereby mediating bacterial host defense. A subset of these antibodies may activate platelets after binding to PF4/heparin complexes, causing the prothrombotic adverse drug reaction heparin-induced thrombocytopenia (HIT). In autoimmune-HIT, anti-PF4/P-antibodies activate platelets in the absence of heparin. Here we show that antibodies with binding forces of approximately 60–100 pN activate platelets in the presence of polyanions, while a subset of antibodies from autoimmune-HIT patients with binding forces Z100 pN binds to PF4 alone in the absence of polyanions. These antibodies with high binding forces cluster PF4-molecules forming antigenic complexes which allow binding of polyanion-dependent anti-PF4/P-antibodies. The resulting immunocomplexes induce massive platelet activation in the absence of heparin. Antibody-mediated changes in endogenous proteins that trigger binding of otherwise non-pathogenic (or cofactor-dependent) antibodies may also be relevant in other antibody-mediated autoimmune disorders.
Abstract
Der Beitrag richtet sich an Studenten, die sich im Schwerpunkt oder aus Interesse mit dem Kartellrecht beschäftigen. Er will den Einstieg in die Materie erleichtern und auch dem Wiederholenden noch einmal die wichtigsten Denkbrücken zur Lösung eines kartellrechtlichen Falles nach dem GWB aufzeigen. Dabei orientiert er sich nach den möglichen Einstiegsmöglichkeiten in eine Klausur und erläutert Schritt für Schritt die wesentlichen Tatbestandsmerkmale und Probleme.