Double Probe Research Articles

Reliability of double probe measurements in nanodusty plasmas

Nonthermal plasmas are attractive sources for nanoparticles synthesis, however, their plasma properties are notoriously difficult to assess due to the chemically reactive environment and high nanoparticle concentrations. Here, we are using a floating double probe to measure the plasma properties of a nanoparticle-forming argon:silane plasma. We demonstrate good stability of current–voltage characteristics over several minutes of operation. However, unexpectedly larger electron temperatures are measured with increasing the silane mole fraction. To test the validity of these results, we developed a zero-dimensional global model to investigate the effect of the presence of nanoparticles on the plasma properties. Using this model, we show that increasing particle concentration leads to an increasing electronegativity of the plasma, causing an increase of the reduced electric field. However, this causes only a moderate increase in mean electron energy, in contrast to the much larger increase measured by the double probe. We argue that these large electron temperatures are based on the fact that a double probe measures an ‘apparent’ electron temperature, which is defined by the negative inverse slope of the logarithm of the electron energy probability function (EEPF) at an energy corresponding to the probe’s floating potential. As the silane mole fraction is increased, the plasma becomes more electronegative and the probe’s floating potential moves closer to the plasma potential. Combined with the strong non-Maxwellian EEPF, this leads to the large apparent electron temperatures obtained by the probe. Thus, the apparent electron temperatures measured with the double probe do not follow the trends in mean electron energy.

Miniaturized double transit magnetic field measurement probe using the Faraday rotation principle.

This paper presents the design and experimental results of a double transit magnetic field measurement probe based on the Faraday rotation principle using terbium doped borosilicate glass as a sensor element. When the magnetic field is applied in the direction of propagation of light through the glass, the Faraday effect produces non-reciprocal circular birefringence. This property of the Faraday effect adds rotations when the light beam is reflected using a mirror placed at the other end of the glass and passed through the glass, making double transit of light through the sensor element. Experiments were carried out to verify the characteristics of the designed probe by inserting it inside the solenoid load coil. The Verdet constant of the glass is determined using the slope of the linear least-squares fitted curve between the Faraday rotation angle and the applied magnetic field, obtained as 89.22r a d/(T⋅m) with a relative uncertainty of 2.43%. The magnetic field was measured with 0.28% accuracy. In the optics experiments, alignment of components is the major task. To the authors' knowledge, this is the first of its kind double transit miniaturized magnetic field measurement probe configuration in which components are aligned inside the single probe structure. The probe is easily portable and can be used in inaccessible locations in various applications such as accelerators, Z/θ pinch devices, or fusion reactors such as tokamaks, in which the magnetic field is one of the main parameters.

ON THE VALIDITY CONDITIONS OF THE SATO HYPOTHESIS

Many years ago, Sato and Sekoguchi proposed the additivity of inherent liquid turbulence and bubble-induced liquid pulsations (ordinarily pseudoturbulence) for two-phase bubbly flows. This hypothesis is often used in models of different two-phase flows and in the development of various flow codes, but the validity conditions of this hypothesis are not defined precisely. An electrodiffusional method involving eight double probes is used in this work to detect the wall shear stress in laminar and transitional upward two-phase bubble flows and check this hypothesis. Almost monodispersed spherical bubbles are used. The data show that for small bubbles the coupling of liquid turbulence and bubble pseudoturbulence can be more complex than the simple additivity proposed by Sato and Sekoguchi.

Double FIT hybridization probes - towards enhancing brightness, turn-on and specificity of RNA detection.

Efficient fluorogenic hybridization probes combine high brightness and specificity of fluorescence signaling with large turn-on of fluorescence. Herein, we present an approach to enhance signaling by combining two identical fluorescence base surrogates in FIT2 probes. Provided there is a suitable positioning of dyes, target-bound FIT2 probes emit brighter than mono dye probes, while dye-dye contact in the single stranded state provides opportunities for decreasing background fluorescence. The probes were used to explore the single nucleotide-specific detection of a C → U edited RNA of the glycine receptor (GlyR). We observed strong self-quenching upon single base mismatched hybridization of FIT2 probes, which helped in distinguishing edited from unedited RNA target in cell lysates.

Two-dimensional electron temperature and density profiles of Hall thruster plume plasmas using tomographically reconstructed optical emission spectroscopy

Two-dimensional electron temperature and density profiles in the plume region of 300 W-class Hall thruster Ar plasmas were obtained using tomographically reconstructed optical emission intensity profiles combined with a collisional-radiative (CR) model. A total of 1242 lines of sight were used by rotating the thruster to apply inverse Radon transform-based tomographic reconstructions and Abel inversion. The reconstruction accuracy of the developed diagnostic system was evaluated using a priori images derived from plasma pictures, and the reconstruction error was less than 1% in the region of interest, exhibiting higher accuracy than the Abel inversion. From the Ar Hall thruster plasma, more than 12 different two-dimensional profiles of Ar I emission intensity within a spectral range of 600–1000 nm were obtained 6 mm from the exit plane of the thruster. A CR model using 31 allowed transitions at 15 different states from the ground state to the 2p i states was incorporated with the tomographically reconstructed emission intensity sets. Consequently, two-dimensional electron temperature and density profiles in the range of 5–18 eV and 2.0 × 1016–4.7 × 1017 m−3 were obtained, respectively, exhibiting reasonable agreement with the double Langmuir probe measurements.

High‐aspect‐ratio oxide etching using CF4/C6F12O plasma in an inductively coupled plasma etching system with low‐frequency bias power

AbstractHigh‐aspect‐ratio (HAR) etch of SiO2 films was attempted using a low‐frequency (2 MHz) bias power in an inductively coupled plasma (ICP) system using heptafluoroisopropyl pentafluoroethyl ketone (C6F12O) gas, which has a lower global warming potential (GWP). Etching characteristics of the oxide film according to changes such as the CF4/C6F12O mixing ratio, source power (13.56 MHz), and bias power were derived. To understand the etching characteristics and mechanism, optical emission spectroscopy (OES), double Langmuir probe (DLP) measurement, and X‐ray photoelectron spectroscopy (XPS) analysis were performed. We observed the vertically etched profile of the 100 nm etched line pattern with a scanning electron microscope (SEM) and at first suggested that the HAR oxide etching process is feasible using the ICP system.

Unexpectedly High Prevalence of iAMP21 in Children with Acute Lymphoblastic Leukemia in Mexico: A Report from the "Mexico in Alliance with St. Jude” (MAS) Collaborative Group

Keywords: acute lymphoblastic leukemia, intra-amplification of chromosome 21, genetic characterization. Mexico in Alliance with St. Jude (MAS) has carried out a multi-center collaboration for children with acute lymphoblastic leukemia (ALL) in Mexico since 2019. The "Bridge Project” has granted access to diagnostic tests that allow genetic characterization of children with ALL in participating centers. The Molecular Genetics Laboratory of Hospital Infantil Teleton de Oncologia (HITO) serves as the referral laboratory. 253 newly diagnosed ALL patients from 5 hospitals in Mexico have utilized a comprehensive diagnostic panel that includes cytogenetic and molecular tests to identify relevant abnormalities. iAMP21 is recognized by the 2017 World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues as a characteristic genetic alteration of B-lineage Leukemia/Lymphoma, with a reported incidence of up to 2-5%. It involves amplification of the RUNX1 gene and/or duplication of chromosome 21 dup(21q), and defines a relatively new cytogenetic subgroup in B-lineage ALL with poor prognosis, derived from the genetic instability of chromosome 21.The heterogeneity of iAMP21 contributes to the difficulty in its detection with the sole use of conventional cytogenetic techniques, rendering Fluorescent In Situ Hybridization (FISH) as a better strategy for the distinction between iAMP21 (amplification in tandem) and the sporadic gain of copies of the RUNX1 gene. METHODS: We performed a comprehensive diagnostic panel for 253 patients with ALL; the FISH B-cell lymphoid panel included (KMT2A, ETV6 (TEL)/RUNX1 (AML1), BCR/ ABL, E2A/(TCF3)/(PBX1) and the T-cell lymphoid panel included (MLL, BCR / ABL, E2A / (TCF3) / (PBX1), TLX1, TLX3, CDKN2A and TRA / D). Diagnosis of iAMP21 was made using the interphase FISH technique with the LSI ETV6/RUNX1 (Vysis®) double color double fusion probe (Abbott Molecular®, Ill), and Cytocell probe (OGT Company®, NY). A finding of ≥ 5 RUNX1 gene signals in interphase FISH and/or more than 3 signals within chromosome 21 was considered positive for the identification of iAMP21. Samples were processed according to the specifications to the AGT Cytogenetics Laboratory Manual. FISH analysis was performed by analyzing 200 interphase cells. When ETV6/ RUNX1 probes are used, samples of patients carrying iAMP21 usually show two normal copies of the ETV6 signal and multiple RUNX1 signals (three or more additional signals) and are negative for the ETV6-RUNX1 fusion gene. RESULTS: Among 253 patients with ALL, 233 cases were of lineage B (92%) and 20 (8%) were of lineage T. FISH was reported negative in 57 (23%) and positive in 185 (73%) cases, 11 results were not available (4.3%). We detected iAMP21 in 28 (11%); these cases were classified as high risk. We also report t(12;21) in 41 (16%), MLL gene disruption t(4;11) in 10 (4%), t(1;19) in 14 (6%), and t(9;22) in 7 (3%); 75 (30%) patients had nonspecific genetic gains. The T lineage showed CDKN2A del(9)(p21) in 6 (2.5%) and TRA/D(14)(q11.2) rearrangement in 4 (1.7%) cases. CONCLUSION: Our experience shows that FISH analysis with the ETV6/RUNX1 probe is useful for identifying iAMP21, a chromosomal abnormality with prognostic significance. Genetic risk factors in the Hispanic population that adversely impact survival in Latin America are not yet fully identified. The Molecular genetic analysis and the fluorescence in situ hybridization (FISH) technique are the basic methods used to detect the presence of the most common genetic abnormalities, the presence or absence of which has an impact on the patient's classification into the appropriate risk group. Our findings from this cohort point to an increased prevalence of iAMP21 in ALL patients in Mexico. We will soon incorporate gene sequencing to the diagnostic panel and improve the characterization of these patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Analysis of microRNAs by the Stem-Loop Real-Time Quantitative Reverse Transcription Polymerase Chain Reaction Using A Double Quencher Probe

Abstract Introduction/Objective We created a universal probe that can be used with mature micro RNAs (miRNAs) using a double quencher incorporating the ZEN quencher into the hydrolysis probe required for miRNA analysis by the real- time quantitative polymerase chain reaction (RT-qPCR) using a stem-loop primer. The main purpose of this approach was to improve sensitivity and convenience. Methods/Case Report We conducted studies on miR-21, miR-30a and miR-200c. To assess the relationship between the sequence interval and reactivity between the miRNA-specific sequence on the stem-loop primer and detection probe, various sequence patterns were examined using miRNA from K562 cells. The sensitivity and reactivity of the designed primers and probes were examined using each synthetic miRNA and transurethral resection of bladder tumor (TURBT) samples. The synthetic RNA was serially diluted in 10% increments. Twenty-seven TURBT cases were examined. The prepared samples were extracted with the FastGene RNA Basic Kit and FastGene miRNA Enhancer. After extraction, cDNA was prepared using FastGene Scriptase II. We performed quantitative analysis by the RT-qPCR using a ZEN double quencher probe. The samples were analyzed with the Taq Man miRNA assay. Results (if a Case Study enter NA) The probe and miRNA-specific sequences of the stem-loop primer showed better reactivity when the design contained less space within the sequences. Serial dilution of the samples using synthetic miRNA showed that linearity depended on the addition amount, and occurred at a concentration of log 7 or more. In the TURBT samples, the Δ of the mean Cp value, and the correlation coefficients of miR-21, miR-30a, and miR-200c, were 3.13 and 0.966; 1.10 and 0.991; and 0.39 and 0.997, respectively, compared with the TaqMan miRNA assay. Conclusion This demonstrates that our method has the same or higher sensitivity than the TaqMan miRNA assay. Overall, these findings suggest that the analysis of miRNA with a stem-loop primer using the double quencher probe is useful.

Gravitational signal propagation in the double pulsar studied with the MeerKAT telescope

The double pulsar PSR J0737−3039A/B has offered a wealth of gravitational experiments in the strong-field regime, all of which general relativity has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the double pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in the future, the Square Kilometre Array (SKA) can greatly improve the accuracy of current tests and facilitate tests of next-to-leading-order (NLO) contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737−3039A, made using the MeerKAT telescope over the last three years. The increased timing precision offered by MeerKAT yields a measurement of Shapiro delay parameter s that it twice as good, and an improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16 yr data by a factor of 1.65. These effects include the retardation effect due to the movement of the companion and the deflection of the signal by the gravitational field of the companion. We also investigate the novel effects that have been expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line of sight due to latitudinal signal deflection, and we find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the double pulsar system that meets the timing precision expected from future instruments such as the full SKA.

Bacillus anthracis strain differentiation based on SNP and VNTR loci.

Bacillus anthracis is the anthrax causative agent. For its epidemiology, it is important not only to identify the etiological agent but also to determine the patterns of its evolution and spread. Modern methods of molecular biology make it possible to detect a number of genetic markers suitable for indicating and differentiating the strains of B. anthracis, including the loci arranged as variable number tandem repeats (VNTRs) and SNPs, one nucleotide-sized differences in the DNA sequence of the loci being compared. The objective of the present study was to examine the effectiveness of SNP analysis and PCR amplif ication of VNTR loci combined with the high-resolution amplicon melting analysis for identif ication and differentiation of the anthrax agent strains. In the study, seven strains of B. anthracis obtained from soil samples and animal carcasses were investigated using vaccine strain STI-1 as a reference. For molecular genetic characterization of these bacteria, analysis of 12 SNPs and variability analysis of eight VNTR loci were carried out. To detect the differences between the strains, their PCR product melting points were measured in the presence of the EvaGreen (Sintol, Russia) intercalating dye. For SNP detection, a PCR assay with double TaqMan probes was applied. It was found that the studied virulent strains, except for B. anthracis No. 1 and 3, could not be attributed to any phylogenetic subgroup of the anthrax agents. The proposed method made it possible to differentiate four out of the seven investigated strains. Strains No. 5–7 had identical SNP and HRM prof iles and, as a result, formed a single cluster. Our investigation has conf irmed that the proposed method can be successfully used for preliminary analysis of an epizootic situation in the case of anthrax.

Rational design of a symmetric double rotor-based fluorescent probe for revealing LDs viscosity changes during ferroptosis

Investigation of lipid droplets (LDs) viscosity is vital for revealing the function of LDs and the pathogenesis of related diseases. Thus, the development of fluorescent probes that can detect LDs viscosity variations is highly desired. Inspired by the traditional Chinese dragon boat, a symmetric double-rotor-based LDs-specific fluorescent probe PBBA was fabricated. The probe PBBA ((2E,2′E)-3,3'-(1,4-phenylene)bis(2-(benzo[d]thiazol-2-yl) acrylonitrile), C26H14N4S2) exhibited high selectivity and favorable sensitivity for viscosity changes with low interference from other factors. Cell imaging with PBBA at a concentration of only 2 μM presented obvious viscosity increases in LDs during erastin- or RSL3-induced ferroptosis, while nearly no change was observed when the inhibitor ferrostatin 1 (Fer-1) was added simultaneously. This study provides a new strategy for the design of viscosity-sensitive probes and contributes to a robust molecular tool to promote an in-depth understanding of the Fenton reaction and lipid peroxidation in LDs during ferroptosis.

A Fluorescent Probe with a Double Reaction Site for Hydrazine Detection in Water Samples

AbstractA double reaction site fluorescent probe (probe PPEO) was developed. The probe detects hydrazine by reaction with an α, β‐unsaturated ketone and o‐aminophenyl. Probe PPEO was a rare two reaction site hydrazine fluorescent probe. The strategy of double reaction sites can improve the atomic utilization of the probe. The limit of detection (LOD) of probe PPEO for hydrazine was 10.40 nM, which below the limited standard. The fluorescence of the probe solution changes from colourless to yellowish‐brown with different concentrations of N2H4. Furthermore, probe PPEO can be used to detect the content of N2H4 in tap water, river water and mineral water.

The Performance of the Uterine Artery Resistance Index following Stimulation of the Cervix in the Diagnosis of Endometriosis: A Prospective Study

Background: We speculated that stimulating the uterine cervix of patients may increase blood flow resistance of the uterine artery more significantly in women with endometriosis than those without. Accordingly, the resistance index (RI) of the uterine artery following stimulation of the cervix may offer a novel and promising non-invasive method for diagnosing endometriosis. In this prospective study, the aim was to determine the performance of the uterine artery resistance index (RI) following stimulation of the cervix in the diagnosis of endometriosis. Methods: This prospective cohort study included 270 patients with non-uterine diseases who were scheduled for laparoscopic surgery. Each patient underwent Doppler sonography for peak systolic velocity (PSV), end diastolic velocity (EDV), and RI before and after stimulation of the cervix, in addition to conventional ultrasound examination one day prior to laparoscopic surgery. The cervix was stimulated using a double convex array electronic vaginal probe for real-time tissue elastography. Results: Laparoscopic surgical evaluation revealed endometriosis in 91 (33.7%) patients. Following stimulation of the cervix, the RI of the uterine artery was significantly increased in the endometriosis group (p = 0.00), but no significant increase in the RI was observed in the control group (p = 0.45). The sensitivity and specificity of the post-stimulation RI for diagnosing endometriosis (using a cut off of 0.83) were 85.71% (95% confidence interval (CI): 76.45–91.88) and 88.83% (95% CI: 83.05–92.87), respectively. For peritoneal endometriosis (PEM), sensitivity and specificity were 86.96% (95% CI: 65.33–96.57) and 88.83% (95% CI: 83.05–92.87), respectively. The sensitivity and specificity of transvaginal ultrasonography (TVU) for diagnosing endometriosis were 63.74% (95% CI: 52.93–73.37) and 94.41% (95% CI: 89.68–97.14), respectively. The positive rate for TVU in diagnosing all endometrioses was 63.7%, and this was lower than that for the post-stimulation RI (84.6%, p = 0.001). Conclusions: Stimulation of the cervix leads to a significant decrease in uterine blood perfusion in women with endometriosis. TVU is a sensitive and specific method for the diagnosis of endometrioma, while the RI is a more sensitive parameter for diagnosing PEM than TVU. For the diagnosis of endometriosis, especially for PEM, the post-stimulation RI may prove to be a promising non-invasive diagnostic technique.

A sensing strategy combining T7 promoter-contained DNA probe with CRISPR/Cas13a for detection of bacteria and human methyltransferase

Abnormal DNA methylation is closely related to the occurrence and development of many diseases. The determination of human DNA methyltransferase activity and the screening of its inhibitors are extreme important for the diagnosis and the treatment of methylation-related diseases in clinic. Most of the current detection methods have the disadvantages of sophisticated design, high cost and low detection limit. By combining T7 promoter-contained DNA probe as the substrate for methyltransferase with CRISPR/Cas13a sensing strategy, a novel fluorescent sensing platform is designed to achieve simple, specific, sensitive detection of bacteria DNA methyltransferase (DNA-(N-6-adenine)-methyltransferase, Dam MTase) and also human methyltransferase (DNA (cytosine-5)-methyltransferase 1, Dnmt1). A hairpin DNA probe designed for Dam MTase and a double strand DNA probe for Dnmt1 are both methylated followed by the methylation-dependent site-specific cleavage, which result a T7 promoter-contained product and a T7 promoter-free one to respectively open and close the transcription and subsequent CRISPR/Cas13a target-initiated cleavage of fluorescence-labeled reporter RNA. In virtue of the specificity of methylation-dependent cleavage of probe, the efficient transcription amplification and CRISPR/Cas13a sequence-specific sensing, this strategy exhibited remarkable specificity and sensitivity, with the limit of detection of 3.10 × 10−5 U/mL for Dam MTase. Moreover, Dnmt1 activity in MCF-7 cells was detected and the inhibition of Apt. #9 was evaluated. This strategy for methyltransferase detection is convenient and efficient for inhibitor discovery and early cancer diagnosis.

Excited state double proton transfer efficient probe: Theoretical investigation and sensing ability towards Pb2+ and Al3+ ions

Dual ESIPT efficient Schiff-base probe possessing multiple binding sites was synthesized which is capable of showing Aggregation Induced Emission (AIE) properties. Probe 1 behaves as a fluorescence “turn-on” chemosensor, showing interactions with Pb2+ and Al3+ ions in H2O-CH3CN solvent at pH≈7. The binding constant and detection limit for all the ions were calculated. The binding properties of probe 1 with all the ions were checked by Job's plot and the 1H NMR titration method. Further, the presence of dual intramolecular hydrogen bonding was confirmed theoretically by geometrical parameters and FTIR analysis. The potential energy curves (PECs) calculations for proton transfer coordinates verified that probe 1 shows a single ESIPT process. Thus with good selectivity and sensitivity and fast response time, a highly efficient platform for simultaneous detection of Pb2+ ions was generated using a simple molecule.

Application of a dual-thermopile radical probe to expanding hydrogen plasmas

We compare the performance of a hydrogen radical probe to historic data determined via two-photon absorption laser induced fluorescence using a comparable cascaded arc source under similar operating conditions. This probe has dual heat flux sensors (DHFS) each coated with materials with different catalytic properties for hydrogen atoms. In the ideal situation, the hydrogen radical flux can be deduced based on the difference between the heat loads measured by these two sensors. The influence of DHFS temperature on the performance was also assessed. The experimental results showed measurement errors of <10% could be obtained regardless of the probe temperature during plasma exposures. To convert heat fluxes into atomic fluxes, we calibrated the difference of the recombination coefficients using a vacuum ultraviolet absorption technique, which is more reliable than modeled values based on assumptions or scattered values reported in literature. As a result, we measured the hydrogen plasma and radical parameters at various settings using both a double Langmuir probe and the DHFS. The typical atom flux in the 1022 m−2s−1 range was in good agreement with those obtained using optical techniques. We also observed that the ion and atom fluxes are both sensitive to the background gas pressure. These findings validate application of the DHFS to the cascaded arc source, and could pave the way for optimization of the source performance in the plasma material processing experiments.

A strategy to distinguish cancers from normal cells through lysosomal targeted double site fluorescent probe for lipase and hydrogen sulfide

For tumor resection, the key step is to distinguish normal from tumor cells accurately. In this article, a lysosome targeting double site fluorescent probe T was reported for porcine pancreatic lipase (PPL) and hydrogen sulfide (H2S). In PBS solution, T could be hydrolyzed by PPL and emitted yellow fluorescence, but no fluorescence change could be observed by H2S only. While in the coexistence of PPL and H2S, a double site chemical reaction was activated, and blue fluorescence was found in the end. The concentration of H2S in some cancer cells is high enough to trigger this dual-site chemical reaction for T. This phenomenon can be repeated in cell experiments: T emits yellow fluorescence in normal cells (MPC) and blue fluorescence in cancer cells (HeLa and SMCC-7721). It illuminates a fact that a vast amount of H2S existed in these cancer cells. As a result, probe T could be used to distinguish cancer cells from normal cells with different fluorescence colors.

Three-dimensional reconstruction of large non-uniform surface wave plasma using multi-lens array attached to a single viewing port

A new passive monitoring system applied to large surface wave plasmas (SWP) is experimentally tested. In the first experiment, spatial distributions of the electron density and temperature are measured using double probes. Subsequently, integral photography with deconvolution techniques is applied to identify the three-dimensional emissivity distribution of SWP. The result obtained from the first experiment seems to identify the localization of SWP around the antenna launching an 860 MHz microwave.

Measurement of Low-Pressure Plasma Parameters by the Floating Double Probe Method for Dry Air and Helium Gas in a Capillary Glow Discharge

The electrical continuous glow discharge is in the capillary tubes. It has gained great interest especially in the applications of liquid crystals as well as display plasmas and soft x-ray lasers. In the present work, an electrical discharge system was designed consisting of a capillary tube and two electrodes. The cathode takes on a hollow geometric shape from nickel material to obtain a high current density. The anode electrode is a tungsten material. The inter-electrodes distance was taken as 12 cm. The floating Langmuir double probe was used as a diagnostic Tool to measure the plasma parameters at different ranges of gas pressure for dry air and helium as working gases. The current-voltage characteristics of the double probe were measured at gas pressure 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 torr. All measurements are conducted at a constant power of 0.6 watt. Electron temperature and ion saturation current were extracted from the I-V characteristics curves. The electron density, Debye length, and plasma frequency were calculated. It was observed that the electron temperature decreases with increasing working gas pressure. The influence of pressure on electron density and ion saturation current gave a clear similarity to the variation in them with pressure in both gases used. Comparisons of the effect of pressure on plasma parameters in working gases were illustrated. The results were in reasonable agreement with previous research.

Eddy Current Techniques for Detecting Hidden Subsurface Defects in Multilayer Aircraft Structures

Abstract In-service non-destructive inspection (NDI) is a very important part of the aircraft maintenance program that minimizes aircraft breakdowns due to the fracture of critical components. The eddy current (EC) NDI method is one of the most applicable methods for this purpose, due to its high sensitivity to fatigue cracks and corrosion damage in the main structural materials. In this paper, selective double differential type EC probes characterized by the enhanced possibility of detecting subsurface cracks initiated by fatigue or stress corrosion phenomena are presented. For different applications, a family of double differential type EC probes was developed with different sizes (from 5 to 33 mm) and different spatial resolutions. These types of probes are characterized by different operational frequencies in a wide frequency range (from 0.2 kHz to 1.0 MHz), high penetration depth and unique sensitivity to subsurface defects of different types (like elongated fatigue cracks or local corrosive pitting), and a high level of specific noise suppression concerned with the scanning inspection procedures. The EC probes proposed were investigated as effective tools for characteristic aircraft applications concerned with subsurface defect detection in multilayer structures, such as the detection of cracks in the second layer of a riveted two-layer structure or cracks initiated on the side surface of a multilayer structure with the suppression of the reinforcing hoop influence; the detection of subsurface defects in arc welding with a rough surface; the detection of cracks through repair patches fabricated from aluminum alloy or carbon fiber reinforced plastic, etc. These techniques create remarkable possibilities for the well-timed detection of dangerous damage without disassembling the aircraft structure or removing protective coating.