• Energy Research

One of t h e l e a s t understood aspec t s of e l e c t r i c a l conduction through ionized gases i s t h e tendency of t h e c u r r e n t t o concentra te i n s m a l l a r eas or f i laments , p a r t i c u l a r l y i n the v i c i n i t y of e l e c t r o d e surfaces . There are reasons t o be l i eve t h a t t h i s cu r ren t c o n s t r i c t i o n c o n s t i t u t e s one of t h e major causes of e l e c t r o d e degradat ion, both i n a r c devices and i n MHD power genera t ion experiments. While some q u a l i t a t i v e explanat ions e x i s t f o r t h e c o n s t r i c t i o n a t t h e cathode su r face , genera l cons ide ra t ions of the condi t ions f o r a uniform o r d i f f u s e d ischarge do not appear t o exist i n t h e l i t e ra tu re . The purpose of t h i s communication is t o set down a few o f t h e s e condi t ions based on an elementary s t a b i l i t y considera t ion. The i n s t a b i l i t y mechanism t o be invoked i n t h e p resen t communication i s t h a t due t o t h e coupling of t h e plasma energy equation wi th t h e equat ions governing e l e c t r i c a l conduction. It s h a l l not be implied t h a t t h e author considers t h i s t h e only mechanism responsible f o r c u r r e n t c o n s t r i c t i o n , nor even n e c e s s a r i l y the major one. It i s encouraging t o no te , however, t h a t q u a l i t a t i v e e x t r a p o l a t i o n s of t h e conclusions of t h e p resen t s tudy appear t o be i n agreement wi th t h e w e l l known behavior of a r c e lec t rodes . I n t h e s imples t form, t h e above mentioned i n s t a b i l i t y can be explained by considering e l e c t r i c a l conduction i n a gas whose e lect r ical conduct iv i ty inc reases r a p i d l y with temperature. I f a pe r tu rba t ion e x i s t s i n t h e form of a l o c a l ho t spo t , t h e hot spot may disappear i n t i m e due t o heat conduction, o r it may i n t e n s i f y due t o increased Jou le heat ing, which is a r e s u l t of t h e h igher e l e c t r i c a l conduct i v i t y . The l a t t e r case represen t s an i n s t a b i l i t y which may grow u n t i l an e n t i r e l y d i f f e r e n t d ischarge conf igurat ion, such as a f i lamentary a r c column, i s a t t a ined . S imi la r processes may occur i n the v i c i n i t y of e l e c t r o d e s , al though they can no longer be expressed i n such simple t e r m s due t o t h e a d d i t i o n a l complications of shea th and emission c h a r a c t e r i s t i c s . Cursory examinations i n d i c a t e t h a t t h e phenomenon probably would be most pronounced i n cases where t h e charge c a r r i e r d e n s i t y is s t rong ly dependent on temperat u r e , a s is i n t h e case of p a r t i a l l y ionized gases of s u f f i c i e n t d e n s i t y t o insure a degree of i o n i z a t i o n equil ibrium. The major i ty of engineering l abora to ry plasma f a l l i n t o t h i s category. For t h i s reason, t h e formulation adopted f o r t h i s a n a l y s i s is more i n keeping wi th a onef l u i d equi l ibr ium gas, f o r which t h e o r e t i c a l understanding is poor, r a t h e r than a frozen gas , f o r which se l fcons i s t en t t h e o r i e s are becoming ava i l ab le . I n o rde r t o by-pass t h e mult i tude of t h e o r e t i c a l complications which surround t h e s o l i d plasma i n t e r f a c e and t h e f l u i d mechanical boundary l a y e r , and place t h e emphasis only on t h e i n s t a b i l i t y a spec t s of t h e problem, w e r e s t r i c t our a t t e n t i o n t o t h e simple problem of a motionless plasma between two plane surfaces . E i t h e r o r both of t h e su r faces could be an e l e c t r o d e surface . Other major assumptions are : (1) Except i n t h e sheaths , t h e plasma & v # = O with e l e c t r i c a l conduct iv i ty dei s considered t o obey t h e simple Ohms l a w : 0 pendent on temperature only. This assumpt i o n can e a s i l y be modified t o include t h e case of nonequilibrium i o n i z a t i o n by adding t h e cur ren t dependence of 4 . (2) Radiation and convective hea t l o s s e s i n t h e plasma are considered negl ig i b l e , with hea t t r a n s f e r governed by Four ier ' s l a w of heat conduction. Thermal conduct iv i ty s h a l l be considered temperature dependent but K / p C p s h a l l be assumed con-

Scars are a common disfiguring sequela of various events such as acne, hidradenitis suppurativa, surgery, trauma, and burns, which can lead to serious psychosocial problems with a negative effect on the quality of life. Many conventional approaches have been proposed for the treatment of scars, including surgical techniques, dermabrasion, chemical peels, topical silicone gel, 5-fluorouracile and dermal fillers injection or autologous fat transfer for atrophic scars, and corticosteroids injection for hypertrophic and keloid scars; however, they have sporadic effects. Ablative lasers, such as carbon dioxide laser or Erbium Yag laser, are associated with many collateral effects limiting their application. Non-ablative laser treatments have been shown to be safer and to have fewer side effects, but they have a reduction of clinical efficacy compared to ablative lasers and a minimal improvement of scars. The demand for minimal invasive and safe technology for the treatment of a scars has stimulated the search for more effective novel therapy with fewer collateral effects. Plasma radiofrequency ablation is a new technique consisting of the generation of plasma energy through the production of ionized energy, which thermally heats tissue in a uniform and controlled manner, through a plasma radiofrequency device, inducing a sublimation of the tissue. The aim of this study is to evaluate the effectiveness of P-RF ablation in the treatment of scars performed with D.A.S. Medical device (Technolux, Italia), which is a tool working with the long-wave plasma radiofrequency principle.

Abstract The investigation of graphene and porous silicon (PS) composite materials for low work function PETE (photon-enhanced thermionic emission for solar concentrator systems) energy systems synthesis is performed in this article. These two types of materials are suggested for further development and study due to noteworthy physical effects taking place in the aforementioned structures. The nature of low-work function phenomenon is interpreted as related to the influence of functionalization and synthesis parameters on the surface structure of composite materials. The Raman spectroscopy technique is used to characterize porous silicon based nanostructured composite layers (PS/Ag). The interpretation of PS/Ag Raman spectra is suggested. The significant decrease in the effective electron work function to a value of 1 eV is registered in a perforated graphene-covered nickel anode intercalated with Cs atoms. SEM X-ray microanalysis of the anode surface is performed, the interpretation of the anode work function lowering effect is proposed.