This paper reviews optical diagnostic methods and approaches applied to study the fundamentals of streamer discharges, considering the peculiarities of streamers developing in atmospheric gases at ...high (1 bar) as well as low (<10 mbar) pressures. A critical discussion is devoted to the cross-sections for electron-impact excitation/ionization/dissociation processes and corresponding rate constants in relation to methods used to probe streamer properties. The most important spectrometric signatures of radiative transitions of diatomic as well as atomic species are discussed on the basis of their synthetic models with a brief guide on how to simulate the most important emissions. Basic differences between UV-vis-NIR spectra produced by electron-impact and various heavy-particle energy-transfer processes during streamer evolution are presented and possible strategies based on 2D projections of cylindrically symmetric streamers to determine radial distributions of excited species within the streamer channel are discussed. The use of emission techniques to obtain the rotational temperatures and vibrational distributions of excited states of diatomics and laser-induced fluorescence techniques to probe the vibrational manifold of the lowest triplet metastable state of the nitrogen molecule is addressed.
Introduction and aim: Dental models are widely used in dentistry. The transmission of oral cavity situation outside patient's mouth brings us information in the field of diagnostics, treatment ...planning, and the fabrication planning of dental products. Dental models can be used in any dental field. They are particularly linked to prosthodontics, orthodontics, and maxillofacial surgery. The aim of this article is to report the benefits of the intraoral scanning in conjuction with 3D printing to the reader. Also, it describes their basic principles and presents the most useful technologies of 3D printing for production in dentistry according to the current literature. Materials and methods: The literature search and survey were focused on intraoral scanning and 3D printing. PubMed, Scopus, and Ebsco databases were used to find the articles. Their applicability in dentistry, the inclusion of a control group, and the age of the article within five years were essential for their subsequent selection. Conclusion: The included studies show that the technologies of direct intraoral scanning and 3D printing are already clinically usable today, and in the future we can expect their further development for everyday practice.
A numerical 0D kinetic model is developed here to simulate the detailed kinetics of the ground and excited electronic states of atmospheric gases occurring under streamer discharge conditions. The ...model is based on an extended kinetic scheme that involves state-to-state vibrational kinetics of the ground electronic states of N2, O2 and NO diatomics, including e-V, V-V and V-T energy transfers, and contains about 104 processes for more than 500 tracked state-specific states (including the higher excited and autoionising states of NI/OI atomic species), and also for state-non-specific species. This scheme takes into account the most important radiative processes occurring in N2 and N2-O2 mixtures that are of diagnostic interest, including the extreme ultraviolet and vacuum ultraviolet radiation produced by many excited and autoionising states of NI/OI. The dependence of the rates of electron-impact processes on the reduced electric field E/N is found by solving the Boltzmann equation for electrons in the two-term approximation using the Boltzmann equation solver Open Source library, BOLOS. We examine several test cases: pure nitrogen at 50 and 200 Torr and synthetic air at 10, 50 and 760 Torr, at a gas temperature of 300 K. The numerical results for pure nitrogen were compared with experimental results recently obtained by laser induced fluorescence for metastables. Good qualitative agreement was observed between numerical simulations and experiments at vibronic levels v = 2-5, giving important feedback on the appropriateness of the kinetic scheme. Numerical results were also used to find several general spectrometric signatures that might be helpful in the development of diagnostic procedures.
Efficient generation of ozone by cold atmospheric plasmas is interesting for sterilisation and decontamination of thermally-sensitive surfaces. This paper presents a study of robust coplanar ...dielectric barrier discharge (DBD) for generating atmospheric pressure plasma in synthetic air and in oxygen. The atmospheric plasma generated by coplanar DBD in synthetic air showed considerably high ozone production of 2.41 g/h (2.25 slm, 45 W), while the production yield and energy cost were 54 g/kWh and 40.9 eV/molecule. The use of oxygen instead of synthetic air, at much lower discharge power (2.25 slm, 17 W), maintained the ozone production of 2.35 g/h, whereas the production yield significantly increased to 138 g/kWh with a corresponding energy cost of 12.9 eV/molecule. The temperature of coplanar DBD ceramics in synthetic air (45 W) and oxygen (17 W) plasma generation (continuous alternating-current operation) showed temperatures below 70 °C and 30 °C, respectively. The rotational temperatures obtained from optical emission spectroscopy indicated similar gas temperatures in the thin plasma layer close to the surface of the DBD ceramics. The low temperature of the plasma–ceramics interface evidences the applicability of coplanar DBD for the contact treatment of thermally sensitive surfaces where a high concentration of ozone is required.
The impact of glial neurotransmitter receptors in vivo is still elusive. In the cerebellum, Bergmann glial (BG) cells express α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)—type ...glutamate receptors (AMPARs) composed exclusively of GluA1 and/or GluA4 subunits. With the use of conditional gene inactivation, we found that the majority of cerebellar GluA1/A4-type AMPARs are expressed in BG cells. In young mice, deletion of BG AMPARs resulted in retraction of glial appendages from Purkinje cell (PC) synapses, increased amplitude and duration of evoked PC currents, and a delayed formation of glutamatergic synapses. In adult mice, AMPAR inactivation also caused retraction of glial processes. The physiological and structural changes were accompanied by behavioral impairments in fine motor coordination. Thus, BG AMPARs are essential to optimize synaptic integration and cerebellar output function throughout life.
The evolution of N(4S) species produced by filamentary streamer discharge was investigated by two-photon absorption laser-induced fluorescence technique. A triggered single streamer filament was ...periodically produced in pure nitrogen at pressures of 20, 50, 100 and 200 Torr, and N(4S) species were monitored in the center of the discharge gap during the streamer formation, decay and afterglow. Under all of the investigated pressures, the population maxima of nitrogen atoms were observed in a microsecond timescale; i.e. well after the extinction of the streamer event. The concentration of nitrogen atoms increased with pressure. The maximum N(4S) concentration measured at 20 Torr was about 1013 cm−3, while it exceeded 1015 cm−3 at 200 Torr. After reaching maxima, atomic densities exhibit hyperbolic decay, which was followed up to the post-discharge time of 0.5 ms. Our results show that only a small part of N(4S) is produced during the streamer transit or within 200 ns after the transit (20%-25% increase with respect to the background density), while most of the nitrogen N(4S) atoms are produced during the streamer channel decay in timescales from units to several tens of microseconds.
Many studies proved that non-equilibrium discharges generated at atmospheric pressure are highly effective for the bio-decontamination of surfaces of various materials. One of the key processes that ...leads to a desired result is plasma etching and thus the evaluation of etching rates of organic materials is of high importance. However, the comparison of reported results is rather difficult if impossible as different authors use diverse sources of atmospheric plasma that are operated at significantly different operational parameters. Therefore, we report here on the systematic study of the etching of nine different common polymers that mimic the different structures of more complicated biological systems, bovine serum albumin (BSA) selected as the model protein and spores of Bacillus subtilis taken as a representative of highly resistant micro-organisms. The treatment of these materials was performed by means of atmospheric pressure dielectric barrier discharge (DBD) sustained in open air at constant conditions. All tested polymers, BSA and spores, were readily etched by DBD plasma. However, the measured etching rates were found to be dependent on the chemical structure of treated materials, namely on the presence of oxygen in the structure of polymers.
The formation of N2(A3Σu+) metastable species, produced by cathode-directed streamer discharge, was investigated using the technique of laser-induced fluorescence. A triggered single streamer ...filament was periodically produced in pure nitrogen (and in nitrogen with admixtures of oxygen) at total pressure of 50 Torr and metastable species were monitored during the streamer channel decay in the centre of the discharge gap. We revealed the dynamics of individual vibrational (v = 0-8) levels of N2(A3Σu+) for various oxygen admixtures (0-20%). In pure nitrogen, the observed evolution of the N2(A3Σu+) during the decaying streamer channel is evidence of initial vibrational relaxation of high vibrational levels towards the v = 2 and 3 levels, followed by a delayed increase of terminal (v = 0, 1) levels. A calibration procedure based on the rate of energy-pooling processes was used to place all detected vibronic levels in pure nitrogen on the absolute scale. Population maxima exceeding 1 × 1014 cm−3 were fixed for the v = 2 and 3 vibrational levels, while the lowest v = 0 level reaches only 3 × 1013 cm−3. Populations of v = 2-5 vibrational levels were also estimated for N2 + O2 mixtures after scaling of laser-induced fluorescence signals obtained at various oxygen admixtures. The total N2(A3Σu+) population in an air-like mixture is formed mainly by v = 3-4 vibronic levels with the population maximum of ~3 × 1013 cm−3 fixed at the shortest analyzed delay. This observation, together with the fact that we were unable to detect v = 0 and 1 levels (fluorescence signals below detection threshold), gives a strong evidence of the inhibition of Δv = 2 vibrational relaxation towards terminal v = 0 and 1 levels, causing much lower populations of the lowest v = 0-1 levels. By analyzing data obtained in pure nitrogen and in nitrogen with three different oxygen admixtures, we have estimated the quenching rate constants of N2(A3Σu+, v) + O2 and N2(A3Σu+, v) + N2 processes for v = 2-6 vibrational levels which are consistent with data from the literature. Quenching rate constants for nitrogen reflect the N2(A3Σu+, v) → N2(A3Σu+, v − 2) relaxation process, however the v = 2 rate constant shows a much larger value compared with the published data.
The evolution of individual v = 0-10 vibrational levels of N2(A3) metastable species produced by filamentary streamer discharge was investigated by the laser-induced fluorescence technique. Triggered ...single streamer filament was periodically produced in pure nitrogen at a pressure of 200 torr and metastable species were monitored during the streamer channel decay in the centre of the discharge gap. The observed dynamics of N2(A3) vibrational levels follow two very different scenarios: while higher (v > 6) vibronic levels decay exponentially in hundreds of nanoseconds, the populations of lower levels (v ≤ 6) definitely increase, first reaching a local maximum on a microsecond timescale and then decreasing afterwards. Population maxima of N2(A3, v ≤ 6) levels occur after the streamer onset with a certain delay, which decreases with increasing vibrational number. Interpretation of experimental observation based on a 0D kinetic model of the post-discharge period takes into account the most important processes redistributing populations between the N2(A3), N2 and N2 vibronic levels. The model reproduces experimental observations fairly well, including observed maxima delays occurring due to the collisional cascade, which transfers metastable species from higher even/odd vibrational levels towards v = 0/v = 1 terminal levels through the Δv = 2 vibrational relaxation mechanism. A calibration procedure based on the rate of energy-pooling processes was used to determine absolute populations of the v = 0 and 1 levels from LIF data, and the model results were utilized to place on an absolute scale all the higher (v > 1) measured vibronic levels. Vibrational distributions obtained from calibrated LIF data at selected instants show a reasonable qualitative agreement with model predictions. Population maxima exceeding 3 × 1014 cm−3 were fixed for v = 2 and 3 vibrational levels, while the lowest v = 0 level reaches only 8-9 × 1013 cm−3. Lastly, we show that the observed rate of the v = 2 level decay is not compatible with published rate constants for the v = 2 → v = 0 vibrational relaxation.
The initial stages of transient luminous events (TLEs) occurring in the upper atmosphere of the Earth are, in a certain pressure range, controlled by the streamer mechanism. This paper presents the ...results of the first laboratory experiments to study the TLE streamer phenomena under conditions close to those of the upper atmosphere. Spectrally and highly spatiotemporally resolved emissions originating from radiative states N2(C3Πu) (second positive system) and N2+(B2Σu+) (first negative system) have been recorded from the positive streamer discharge. Periodic ionizing events were generated in a barrier discharge arrangement at a pressure of 4 torr of synthetic air, i.e. simulating the pressure conditions at altitudes of 37 km. Employing Abel inversion on the radially scanned streamer emission and a 2D fitting procedure, access was obtained to the local spectral signatures within the over 106 m s−1 fast propagating streamers. The reduced electric field strength distribution within the streamer head was determined from the ratio of the N2+/N2 band intensities with peak values up to 500 Td and overall duration of about 10 ns. The 2D profiles of the streamer head electric fields were used as an experimentally obtained input for kinetic simulations of the streamer-induced air plasma chemistry. The radial and temporal computed distribution of the ground vibrational levels of the radiative states involved in the radiative transitions analyzed (337.1 nm and 391.5 nm), atomic oxygen, nitrogen, nitric oxide and ozone concentrations are vizualized and discussed in comparison with available models of the streamer phase of Blue Jet discharges in the stratosphere.
