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Characteristics of glow-discharge LIBS in a rarefied environment
Full text linkThere is a trade-off between the signal level and bandwidth of the atomic lines in laser-induced breakdown spectroscopy (LIBS). The LIBS plasma plume is a dense plasma, with linewidths of spectral features enlarged by Stark broadening. Narrow linewidths can be detected at delays of some μs with respect to the laser pulse, but this comes at the cost of low signal intensity. This demand becomes urgent when spectral separation is necessary, as in the application of LIBS for in situ detection of atomic deuterium (D) and atomic tritium (T) in walls exposed to the plasma of a Tokamak. The D and T Balmer lines need to be well separated from the atomic hydrogen (H) lines that are present as contaminants in the LIBS spectra. Clearly, solving for the signal-bandwidth tradeoff can be of more general interest than the Balmer lines issue only. In this work, we report an investigation of LIBS signal enhancement with a low-pressure (some Torr), pulsed glow-discharge. The discharge produces a low-density plasma that has a negligible effect on the linewidth. The possibility of signal enhancement instead relies on the long duration of the discharge compared with that of the plume, allowing for long time-integration of the atomic emissions. The concept can be stressed to the limit in which the laser shot just ablates the material, whereas the electronic excitation of the material is obtained by the non-equilibrium gas discharge ignited in a background gas in the region where the laser-induced plasma plume expands
Effect of dielectric Barrier Discharge Plasma on Alumina electrodes evidenced by Thermoluminescence and Optically Stimulated Luminescence analysis
No full text2D Thermoluminescence imaging of dielectric surface long term charge memory of plasma surface interaction in DBD discharges
No full textThe charge trapping effect due to the exposure of alumina surfaces to plasma has been studied
in a volume dielectric barrier discharge (DBD) in Ar and He noble gases. The long lasting
charge trapping of alumina dielectric plates, used as barriers in DBDs, is evidenced by an ex
situ thermoluminescence (TL) experiment performed with a standard and a custom
two-dimensional (2D)-TL apparatus. The spatial density of trapped surface charges is found to
be strongly correlated to the plasma morphology, and the surface spatial memory lasted for
several minutes to hours after plasma exposure. In the case of Ar, the plasma channel impact
signature on the surface shows a higher equivalent radiation dose with respect to the surface
plasma wave and the post-discharge species signature. As a consequence, for the development
of discharges, inside the dielectric surface the availability of lower energy trapped electrons is
larger in the first region of plasma impact. The reported spatial memory increases the
likelihood of the occurrence of plasma filaments in the same position in different runs. In He
plasmas, the dielectric barrier shows an almost uniform distribution of trapped charges,
meaning that there is no preferred region for the development of the discharge. In all cases a
slight asymmetry was shown in the direction of the gas flow. This can be interpreted as being due to the long-living species moving in the direction of the gas flow, corresponding with the
TL side experiment on the sample exposed to the plasma afterglow. The maximum values and the integral of the 2D-TL images showed a linear relation with the total charge per ac cycle,
corresponding with findings for the TL glow curve. In conclusion, 2D-TL images allow the retrieval of information regarding the plasma surface interaction such as the plasma
morphology, trap sites and their activation temperature
Sensitivity Analysis of Differential Absorption Lidar Measurements in the Mid-Infrared Region
No full textThe availability of new laser sources that are tunable in the IR spectral region opens new perspectives for differential absorption lidar (DIAL) measurements. A region of particular interest is located in the near IR, where some of the atmospheric pollutants have absorption lines that permit monitoring of emissions from industrial plants and in urban areas. In DIAL measurements, the absorption lines for the species to be measured must be carefully chosen to prevent interference from other molecules, to minimize the dependence of the absorption cross section on temperature, and to optimize the measurements with respect to the optical depth. We analyze the influence of these factors and discuss a set of criteria for selecting the best pairs of wavelengths (λon and λoff) to be used in DIAL measurements of several molecular species (HCl, CO, CO2, NO2, CH4, H2O, and O2). Moreover, a sensitivity study has been carried out for selected lines in three different regimes: clean air, urban polluted air, and emission from an incinerator stack
Recognition of healthy and cancerous breast cells: Sensing the differences by dielectric spectroscopy
No full textPurpose: The response of human cells to applied electrical signals depends on the cellular health status, because it is influenced by the composition and structure of the main cellular components. Therefore, electrical impedance-based techniques can be considered as sensitive tools to investigate healthy or disease state at cellular level. The goal of this study is to show that different types of in vitro cellular lines, related to different health status, can be differentiated using impedance spectra analysis. Methods: Three different types of human breast cell line, corresponding to healthy, cancerous, and metastatic adenocarcinoma cells, were measured by means of electrical impedance spectroscopy. By modeling the investigated cells with proper resistive and capacitive circuital elements, the magnitude of the cell electrical components and spectra of real and imaginary part of dielectric permittivity were obtained. The latter were subsequently examined with a commonly adopted mathematical model, in order to estimate the values of specific dielectric parameters for the three different cellular lines. Results: The relative variation of cellular capacitance with respect to that of the culture medium, estimated at 100 Hz, has a larger value for the two types of cancerous cells with respect to the noncancerous type. Furthermore, the ratio between the real and imaginary part of the dielectric permittivity function has larger values for metastatic cells with respect to the normal and nonmetastatic ones. Therefore, the mentioned relative capacitance allows to discriminate between normal and cancerous cells, whereas the results obtained for the dielectric function can discriminate between metastatic and nonmetastatic cells. Conclusions: This study can be considered as an exploratory investigation of evaluating in vitro the health status of humans cells using selected electrical impedance parameters as potential markers. The obtained results highlight that a standard cultureware system, provided with interdigitated electrodes and appropriate impedance parameters, that is, cellular capacitance and the ratio between the imaginary and real part of cellular dielectric function, can be used to discriminate between healthy and cancerous breast cell lines, as well as different malignancy degrees
Role of direct and inverted undoped spiro-OMeTAD-perovskite architectures in determining solar cells performances: An investigation: Via electrical impedance spectroscopy
No full textThe present study involved an investigation on the reasoning behind the dependence of the perovskite solar cells photovoltaic efficiencies on the relative position of the undoped spiro-OMeTAD hole-transport material with respect to the perovskite in the device. We adopted impedance spectroscopy to investigate the modification of the carrier transport mechanisms across the spiro-OMeTAD/perovskite interface constituting the active part where the main device processes occur. We investigated two interface structures, referred to as the direct (or regular, n-i-p) and the inverted (p-i-n) configuration. This work also intended to further stress the possible adoption of alternative device structures working with undoped hole-transport materials
Keratinocyte cellular damage induced by pesticide doses below the cytotoxic level evidenced by electrical impedance and broadband dielectric spectroscopy
No full textThe cellular response of a normal human keratinocyte cell line exposed to non-cytotoxic doses of a deltamethrin-based pesticide was investigated by means of two different electrical impedance data spectroscopy approaches: Nyquist plot and broadband dielectric spectroscopy. The measurements have shown that the membrane capacity increases with pesticide concentration and this facilitates the electric current through cell membranes. Furthermore, the impedance of the extracellular matrix also increases with pesticide concentration, thus reducing the electric current outside the cell. Dielectric permittivity changes in the cellular samples at frequencies larger than 100 Hz. Fluorescence (FL) measurements emphasized an increase in neutral membrane lipids as a consequence of the pesticide exposure. Comparison of FL response of pesticide exposed cells with the control ones showed a time increase in the emission intensity, suggesting the existence of a membrane lipid response aimed at repairing the cell damage due to pesticide exposure. Therefore, both spectroscopic techniques have been demonstrated as potential means to investigate the response to cell stress and damage. This opens up new possibilities in the early diagnosis of cellular modifications related to the pesticide exposure of cells
Early Altered Cells Health Status Detection via Label Free Impedance and Broadband dielectric Spectroscopy
No full textHuman cells are able to respond to applied electrical signals and their response is different according to cell health status. In this framework, the electrical bio-impedance can be sensitive tools to monitor cellular health status in addition to other commonly adopted biological methods. Here we show that in vitro cellular lines affected by inflammatory processes or outside insult can be identified by using impedance and broadband dielectric spectroscopy analysis. The analysis of specific parameters of the electrical response evidences modification in the cells compartments. The features of the cell electrical response allow to discriminate between the different processes involved
Thermoluminescence study of the trapped charge at an alumina surface electrode in different dielectric barrier discharge regimes
No full textIn this study, the charge trapping effect in alumina dielectric surfaces has been deeply investigated by means of a dedicated dielectric barrier discharge apparatus in different discharge regimes and gas mixtures. This work further validates our previous findings in the case of air discharges in a filamentary regime. Long lasting charge trapping has been
evidenced by ex situ thermoluminescence characterizations of alumina dielectric barrier plates
exposed to a plasma. The density of trapped surface charges was found to be higher in the glow discharge with respect to pseudo-glow and filamentary regimes, and for all regimes the minimum trap activation temperature was 390K and the trap energy was less than or around 1 eV. This implies that in the case of glow discharges a higher reservoir of electrons is present.
Also, the effect was found to persist for several days after running the discharge
Low-temperature plasma and plasma-activated water as alternative novel technologies for postharvest disease control
No full textThe need for new sustainable technologies to reduce losses and maintain the quality of fruits and vegetables during postharvest storage has grown during recent years. Low-Temperature Plasma (LTP) and Plasma-Activated Water (PAW) are currently proposed as promising tools for inactivation of microbial contaminants, including foodborne pathogens and microorganisms responsible for postharvest decay. The effects of both direct and indirect applications of atmospheric air plasma against major fungal pathogens (Botrytis cinerea, Monilinia fructicola, Fusarium graminearum, Aspergillus carbonarius, Penicillium italicum, Penicillium digitatum, Alternaria alternata) and contaminant bacteria (e.g., Bacillus subtilis) were investigated in in-vitro assays using different treatment conditions and exposure times. Three different plasma sources, i.e., Surface Dielectric Barrier Discharge (SDBD), Atmospheric Pressure Plasma Jet (APPJ), and Volume Dielectric Barrier Discharge (VDBD), were applied. Albino mutants of Botrytis cinerea and Aspergillus carbonarius were used to explore the protective role of fungal melanin on sensitivity to plasma exposure, with mutants showing higher sensitivity to treatments compared to the melanized wild-type strains. As expected, inhibitory effects increased with higher exposure times. The complete spore inactivation was obtained after a few seconds (VDBD) or minutes (SDBD and APPJ) of exposure. Major structural damages to the conidia surface after plasma treatment were assessed by Scanning Electron Microscopy (SEM) analysis. An early etching and later perforation of cell walls up to complete cell disruption was observed. A decrease in viability of conidia and an increase in their membrane permeability was assessed by fluorescence-based assays. Differences in the response to plasma among species that could be related to the fungal cell structure and composition were observed, with the strongly melanized conidia of A. carbonarius and A. alternata showing the lowest sensitivity to the treatments. Antibacterial and antifungal activities of PAW having different contents in reactive species (hydrogen peroxide, nitrite and nitrate), pH, and ORP under different treatment conditions (i.e., plasma source, exposure time, gas flow) were evaluated. Results revealed a close correlation between chemical properties of PAW and inhibition rates for bacteria and fungi. Furthermore, inhibitory effect of PAW against all the tested microbial species was proved stable, with a persistence of at least 30 min after water activation. The efficacy of PAW was also tested on fruits of Citrus sinensis cv. Fukumoto artificially inoculated with P. italicum with a total inhibition of the infection development and symptoms appearance recorded on treated fruit. Experiments on cherry fruits artificially inoculated with B. cinerea and M. fructicola and exposed to SDBD air plasma demonstrated that the application of cold plasma on fruits may significantly extend their shelf life by direct inactivation of fungi and possible activation of plant defense responses
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