Field emission-driven microdischarges

For over half a century, it has been known that the onset of field emission can lead to anomalous breakdown for electrode gaps spaced \u3c10 μm apart. In adddition, field emission can serve as a substantial source of primary electrons in a microdischarge operating well below the breakdown threshold at atmospheric pressure. To better understand the role of field emission in a microdischarge, we have developed kinetic simulations and fluid models. Theoretical results from both our simulations and models have shown that the anomalous breakdown at the microscale is due to ion-enhanced field emission. In addition, they predict an entirely new prebreakdown regime – the field emission-driven microdischarge – in which field-emitted electrons interact with the surrounding gas to produce ions and excited metastables. Experiments conducted in our lab agree well with the predictions of our simulations and fluid model for parallel plate electrode spacings ranging from 4.8 to 14 μm

Decoupling Interfacial Reactions between Plasmas and Liquids: Charge Transfer vs Plasma Neutral Reactions

Plasmas (gas discharges) formed at the surface of liquids can promote a complex mixture of reactions in solution. Here, we decouple two classes of reactions, those initiated by electrons (electrolysis) and those initiated by gaseous neutral species, by examining an atmospheric-pressure microplasma formed in different ambients at the surface of aqueous saline (NaCl) solutions. Electrolytic reactions between plasma electrons and aqueous ions yield an excess of hydroxide ions (OH^–), making the solution more basic, while reactions between reactive neutral species formed in the plasma phase and the solution lead to nitrous acid (HNO₂), nitric acid (HNO₃), and hydrogen peroxide (H₂O₂), making the solution more acidic. The relative importance of either reaction path is quantified by pH measurements, and we find that it depends directly on the composition of the ambient background gas. With a background gas of oxygen or argon, electron transfer reactions yielding excess OH^– dominate, while HNO₂ and HNO₃ formed in the plasma and by the dissolution of nitrogen oxide (NO_<i>x</i>) species dominate in the case of air and nitrogen. For pure nitrogen (N₂) gas, we observe a unique coupling between both reactions, where oxygen (O₂) gas formed via water electrolysis reacts in the bulk of the plasma to form NO_<i>x</i>, HNO₂, and HNO₃

Sunlight exposure exerts immunomodulatory effects to reduce multiple sclerosis severity

Multiple sclerosis (MS) disease risk is associated with reduced sunexposure. This study assessed the relationship between measures of sun exposure (vitamin D [vitD], latitude) and MS severity in the setting of two multicenter cohort studies (n(NationMS) = 946, n(BIONAT) = 990). Additionally, effect-modification by medication and photosensitivity-associated MC1R variants was assessed. High serum vitD was associated with a reduced MS severity score (MSSS), reduced risk for relapses, and lower disability accumulation over time. Low latitude was associated with higher vitD, lower MSSS, fewer gadolinium-enhancing lesions, and lower disability accumulation. The association of latitude with disability was lacking in IFN-beta-treated patients. In carriers of MC1R:rs1805008(T), who reported increased sensitivity toward sunlight, lower latitude was associated with higher MRI activity, whereas for noncarriers there was less MRI activity at lower latitudes. In a further exploratory approach, the effect of ultraviolet (UV)-phototherapy on the transcriptome of immune cells of MS patients was assessed using samples from an earlier study. Phototherapy induced a vitD and type I IFN signature that was most apparent in monocytes but that could also be detected in B and T cells. In summary, our study suggests benefidal effects of sun exposure on established MS, as demonstrated by a correlative network between the three factors: Latitude, vitD, and disease severity. However, sun exposure might be detrimental for photosensitive patients. Furthermore, a direct induction of type I IFNs through sun exposure could be another mechanism of UV-mediated immune-modulation in MS