Classical Probe Research Articles

Drifting Plasma Collection by a Positive Biased Tether Wire in LEO-Like Plasma Conditions: Current Measurement and Plasma Diagnostic

BETs is a three-year project financed by the Space Program of the European Commission, aimed at developing an efficient deorbit system that could be carried on board any future satellite launched into Low Earth Orbit (LEO). The operational system involves a conductive tape-tether left bare to establish anodic contact with the ambient plasma as a giant Langmuir probe. As a part of this project, we are carrying out both numerical and experimental approaches to estimate the collected current by the positive part of the tether. This paper deals with experimental measurements performed in the IONospheric Atmosphere Simulator (JONAS) plasma chamber of the Onera-Space Environment Department. The JONAS facility is a 9- m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> vacuum chamber equipped with a plasma source providing drifting plasma simulating LEO conditions in terms of density and temperature. A thin metallic cylinder, simulating the tether, is set inside the chamber and polarized up to 1000 V. The Earth's magnetic field is neutralized inside the chamber. In a first time, tether collected current versus tether polarization is measured for different plasma source energies and densities. In complement, several types of Langmuir probes are used at the same location to allow the extraction of both ion densities and electron parameters by computer modeling (classical Langmuir probe characteristics are not accurate enough in the present situation). These two measurements permit estimation of the discrepancies between the theoretical collection laws, orbital motion limited law in particular, and the experimental data in LEO-like conditions without magnetic fields. In a second time, the spatial variations and the time evolutions of the plasma properties around the tether are investigated. Spherical and emissive Langmuir probes are also used for a more extensive characterization of the plasma in space and time dependent analysis. Results show the ion depletion because of the wake effect and the accumulation of ions upstream of the tether. In some regimes (at large positive potential), oscillations are observed on the tether collected current and on Langmuir probe collected current in specific sites.

Direct Electrochemical DNA Detection Originated from the Self-Redox Signal of Sulfonated Polyaniline Enhanced by Graphene Oxide in Neutral Solution

In this paper, a type of direct DNA impedance detection using the self-redox signal change of sulfonated polyaniline (SPAN) enhanced by graphene oxide (GNO) was reported, here SPAN is a copolymer obtained from aniline and m-aminobenzenesulfonic acid. The resulting nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The π-π planar structure of GNO and the carboxyl groups on the surface of GNO ensured it could act as an excellent substrate for adsorption and polymerization of aniline monomer. Because of the existence of GNO, the electrochemical activities of SPAN were enhanced obviously. Because of abundant sulfonic acid groups, the resulting nanocomposite showed obvious self-redox signal even at physiological pH, which is beneficial for biosensing field. DNA probes with amine groups could be covalently attached to the modified electrode surface through the acyl chloride cross-linking reaction of sulfonic groups and amines. When the flexible probe DNA was successfully grafted, the electrode was coated and electron transfer between electrode and buffer was restrained. Thus, the inner impedance value of SPAN (rather than using outer classic EIS probe, [Fe(CN)6](3-/4-)) increased significantly. After hybridization, the rigid helix opened the electron channel, which induced impedance value decreased dramatically. As an initial application of this system, the PML/RARA fusion gene sequence formed from promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARA) was successfully detected.

Parallax correction for precise near-wall flow investigations using particle imaging

For the basic understanding of turbulence generation in wall-bounded flows, precise measurements of the mean velocity profile and the mean velocity fluctuations very close to the wall are essential. Therefore, three techniques are established for high-resolution velocity profile measurements close to solid surfaces: (1) the nanoprobe sensor developed at Princeton University, which is a miniaturization of a classical hot-wire probe [Exp. Fluids 51, 1521 (2011)]; (2) the laser Doppler velocimetry (LDV) profile sensor, which allows measurement of the location of the particles inside the probe volume using a superposition of two fringe systems [Exp. Fluids 40, 473 (2006)]; and (3) the combination of particle image velocimetry and tracking techniques (PIV/PTV), which identify the location and velocity of submicrometer particles within the flow with digital imaging techniques [Exp. Fluids 52, 1641 (2006)]. The last technique is usually considered less accurate and precise than the other two. However, in addition to the measurement precision, the effect of the probe size, the position error, and errors due to vibrations of the model, test facility, or measurement equipment have to be considered. Taking these into account, the overall accuracy of the PTV technique can be superior, as all these effects can be compensated for. However, for very accurate PTV measurements close to walls, it is necessary to compensate the perspective error, which occurs for particles not located on the optical axis. In this paper, we outline a detailed analysis for this bias error and procedures for its compensation. To demonstrate the capability of the approach, we measured a turbulent boundary layer at Re(δ)=0.4×10(6) and applied the proposed methods.

Promising near-infrared non-targeted probes: benzothiazole heptamethine cyanine dyes

A series of benzothiazole heptamethine cyanine dyes have been synthesized and their photophysical properties evaluated in relation to their structural features. These have been compared against two classical probes of this type: Indocyanine Green (IGC) and New Indocyanine Green (IR-820). Growth inhibitory studies were also performed using a eukaryotic, unicellular organism, fission yeast Schizosaccharomyces pombe. Herein we highlight some potentially interesting candidates with improved fluorescence quantum yields when compared with ICG and IR-820.

Measurement of the plasma and neutral gas flow velocities in a low-pressure hollow-cathode plasma jet sputtering system

We present results from two mutually independent measurements of plasma and neutral gas flow velocities in a plasma jet deposition system. Operation of a hollow-cathode discharge within the plasma jet nozzle in the pulse regime enables the simple use of a classical Langmuir probe for the plasma flow velocity measurement. In this method, we assume that the plasma is generated solely inside the nozzle during the power impulse and we measure the time of flight of the ions along a known distance between the nozzle end and the probe. The plasma velocity at the plasma jet axis is then determined by differentiation of the dependence of the distance covered by ions on time. As the second method the well-known Pitot tube is used for measurement of the neutral gas velocity. By comparison of both methods we have experimentally proved that the neutral gas flow velocity is almost unaffected by the presence of the plasma, i.e. it does not substantially depend on whether the discharge is switched on or off. The results of both methods correspond well; detected differences are qualitatively explained. It is documented that the plasma jet can be operated both in a subsonic and in a supersonic regime. We present the dependences of the plasma and neutral gas flow velocity on the distance from the cathode, on the pressure in the reactor chamber, and on the flow rate of the working gas.

Performance of μ-XRF with SEM/EDS for trace analysis on the example of RoHS relevant elements – measurement, optimisation and prediction of the detection limits

For ten years μ-XRF (micro-focus X-ray fluorescence) analysis has been performed with SEM/EDS (scanning electron microscope with an energy dispersive X-ray detector) so that non-destructive analysis of elements at trace level concentrations below 100 μg g−1 becomes possible. This can be considered as a valuable completion of the classical electron probe microanalysis by EDS, an analytical method “suffering” from rather poor limits of detection in the range of one to two orders of magnitude higher than those of μ-XRF. Based on a representative actual application, namely analysis of RoHS relevant elements at trace concentration levels, the performance of the rather new analytical method with respect to its limits of detection is systematically evaluated. CRMs (certified reference materials) specially prepared to support the quantitative XRF analysis of RoHS relevant elements were employed. On the other side, based on calculations of μ-XRF spectra according to a recently developed physical model the optimization of the analytical performance is also successfully undertaken.

CLASSICAL CEPHEIDS REQUIRE ENHANCED MASS LOSS

Measurements of rates of period change of Classical Cepheids probe stellar physics and evolution. Additionally, better understanding of Cepheid structure and evolution provides greater insight into their use as standard candles and tools for measuring the Hubble constant. Our recent study of the period change of the nearest Cepheid, Polaris, suggested that it is undergoing enhanced mass loss when compared to canonical stellar evolution model predictions. In this work, we expand the analysis to rates of period change measured for about 200 Galactic Cepheids and compare them to population synthesis models of Cepheids including convective core overshooting and enhanced mass loss. Rates of period change predicted from stellar evolution models without mass loss do not agree with observed rates whereas including enhanced mass loss yields predicted rates in better agreement with observations. This is the first evidence that enhanced mass loss as suggested previously for Polaris and delta Cephei must be a ubiquitous property of Classical Cepheids.

Dielectric covered hairpin probe for its application in reactive plasmas

The hairpin probe is a well known technique for measuring local electron density in low temperature plasmas. In reactive plasmas, the probe characteristics are affected by surface sputtering, contamination, and secondary electron emission. At higher densities, the plasma absorbs the entire electromagnetic energy of hairpin and hence limits the density measurements. These issues can be resolved by covering the hairpin surface with a thin layer of dielectric. In this letter, the dielectric contribution to the probe characteristics is incorporated in a theory which is experimentally verified. The dielectric covering improves the performance of probe and also allows the hairpin tip to survive in reactive plasma where classical electrical probes are easily damaged.

Registration of gas impurities in nonlocal plasma of helium microdischarge by an additional electrode — sensor

Identification of gas impurities in helium by selective registration of groups of fast electrons created in Penning ionization of impurities atoms or molecules by metastable helium atoms at pressures of 7–40 Torr is realized. The collisional electron spectroscopy (CES) method is applied and is experimentally verified. Identification of impurities atoms and molecules is accomplished in collisional regime of movement of the particles, where the different groups of electrons have no time to relax in energy by collisions in the volume and behave independently of each other. An original design of microplasma gas analyzer is proposed, containing only nonlocal negative glow plasma of a short dc microdischarge. Registration of the energy spectra of penning electrons by means of an additional electrode-sensor, located at the boundary of the discharge volume is performed. The sensor has large collecting area compared to classical Langmuir probes, contributing to significant enhancement in the measurements sensitivity. Maxima in the EEDF are recorded in helium with small admixtures of krypton, argon and air. The obtained maxima appear at low discharge currents and at characteristic energies corresponding exactly to the expected maxima for penning electrons of the known gas impurities used. The gas analyser is compact, simple in technical performance, has high sensitivity and its size is dramatically reduced compared to the existing devices for gas analysis. This work is an approach to the development of microdischarge gas analyzers for gas impurities detection like poison gases, gas pollutions in the atmosphere or in the industry etc.

Highly sensitive electrochemical impedance sensing of PEP gene based on integrated Au–Pt alloy nanoparticles and polytyramine

Fabrication of an electrochemical impedimetric DNA biosensor based on the integration of Au–Pt alloy nanoparticles (Au–PtNPs) and electropolymerized polytyramine (Pty) film for the detection of phosphoenolpyruvate carboxylase (PEP) gene is described in this article, where Pty films acted as an ideal combination platform for Au–PtNPs via electrostatic adsorption. The electrochemical properties of the Au–PtNPs/Pty, the characteristics of the immobilization and hybridization of DNA were investigated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy (EIS), respectively. Primary study indicated that Au–PtNPs/Pty had a synergistic effect on the electrochemical signal of [Fe(CN)6]3−/4−, which served as the classic redox probe in the most electrochemical impedimetric sensors. DNA sequence-specific of PEP transgene existed in some transgenic crops was detected by this EIS protocol. The dynamic detection range of this DNA electrochemical biosensor to the DNA target sequence was from 1.0×10−12M to 1.0×10−7M. The detection limit was measured to be 3.6×10−13M. The DNA biosensor also had good selectivity, stability and reproducibility.

Comparative Ultrasound: novel finger probe versus classic probe

INTRODUCTIONUltrasonography (USS) is the stethoscope of the future. USS probes have evolved to improve structural identification. This study investigated a novel shaped probe used by first‐year medical students (FMS) conducting a clinical procedure.METHODSLiterature search was conducted on texts, specialty journals and websites regarding the use USS finger probe by FMS performing invasive techniques. FMS performed timed USS‐guided cannulation to the internal jugular (IJV) and subclavian (SCV) veins on a blue phantom torso, and identified them on a volunteer using a novel USS finger and a classic probe. A questionnaire asked about probe preference.RESULTSLiterature search revealed no studies comparing finger and classic probes, nor USS‐guided central line techniques being conducted by FMS. FMS identified and cannulated the IJV and SCV using both probes within 6 minutes with statistical significance. Questionnaire revealed FMS preferred the finger probe.DISCUSSIONUSS is a safe, non‐invasive imaging medium proven successful for invasive procedures. This study demonstrated FMS could interpret USS while conducting a common procedure. Finger probe proved successful in structure identification and was preferred to the classic probe due to its combined tactile presence.CONCLUSIONThis pilot study of a novel finger USS probe was successful identifying structures by FMS, suggesting future studies.

SHG nanoprobes: Advancing harmonic imaging in biology

Second harmonic generating (SHG) nanoprobes have recently emerged as versatile and durable labels suitable for in vivo imaging, circumventing many of the inherent drawbacks encountered with classical fluorescent probes. Since their nanocrystalline structure lacks a central point of symmetry, they are capable of generating second harmonic signal under intense illumination - converting two photons into one photon of half the incident wavelength - and can be detected by conventional two-photon microscopy. Because the optical signal of SHG nanoprobes is based on scattering, rather than absorption as in the case of fluorescent probes, they neither bleach nor blink, and the signal does not saturate with increasing illumination intensity. When SHG nanoprobes are used to image live tissue, the SHG signal can be detected with little background signal, and they are physiologically inert, showing excellent long-term photostability. Because of their photophysical properties, SHG nanoprobes provide unique advantages for molecular imaging of living cells and tissues with unmatched sensitivity and temporal resolution.

Modification of the electron energy distribution function during lithium experiments on the National Spherical Torus Experiment

The National Spherical Torus Experiment (NSTX) has recently studied the use of a liquid lithium divertor (LLD). Divertor Langmuir probes have also been installed for making measurements of the local plasma conditions. A non-local probe interpretation method is used to supplement the classical probe interpretation and obtain measurements of the electron energy distribution function (EEDF) which show the occurrence of a hot-electron component. Analysis is made of two discharges within a sequence that exhibited changes in plasma fueling efficiency. It is found that the local electron temperature increases and that this increase is most strongly correlated with the energy contained within the hot-electron population. Preliminary interpretative modeling indicates that kinetic effects are likely in the NSTX scrape-off layer (SOL) plasma. The decrease in plasma fueling efficiency, increase in local temperature, and increase in hot-electron fraction are all consistent with an absorbing surface intercepting the SOL plasma.

Disposable bioreactors: from process development to production

Single-use bioreactors are commonly used for seeding stainless steel bioreactors or for producing material. The profitability of these equipments has been well demonstrated on more that decade. But few data on its scalability have been published. In 2010-2011, Merck Serono Biodevelopment performed a study in order to evaluate the performance of several disposable bioreactors. As different technologies and scales were available, this study compared the performance of several types of mixing in single-use bioreactors for process development and pilot scale production. In addition, the evaluation was performed for both seeding applications and for clinical material production. Thus the feature of this study is the comparison of 3 to 50L disposable bioreactors with internal mixing system or external agitation (Table ​(Table1).1). In order to compare their performance with traditional bioreactors, gas flow rate applied in disposable bioreactors was scaled-down from seeding and production stainless steel bioreactors. Furthermore the ratio working volume on total volume and the power input applied to the 3L disposable bioreactor were similar to those in glass bioreactors. Table 1 Description of the different disposable bioreactors assessed. In order to compare the 5 different types of disposable bioreactors, a fed-batch process producing a highly glycosylated molecule was performed. The cell growth during the amplification phase was similar reflected by the doubling time of the cells. It was similar between traditional bioreactors (21h in 250L stainless steel seeding bioreactor) and disposable bioreactors (from 17h in the Nucleo and the Orbital to 19h in the STR) The quality of the molecule together with the molecule titer and the cell growth were compared in the 5 single use technologies during a production process. The process performance was also compared in 250L and 1.25kL bioreactors and to a 3.6L glass development bioreactor. The overall production process performance was similar in traditional and disposable bioreactors (Figure ​(Figure11). Figure 1 Quantity of highly glycosylated molecule produced in different bioreactors This study was completed by a characterization of liquid/liquid and gas/liquid transfers inside each disposable bioreactor in order to estimate their potential in terms of cell culture. These cells did not require a lot of oxygen. A low kLa (0.44h–1 in the Nucleo) was sufficient to run this process. The air-flow rates applied in the orbital shaking bioreactor during the process were defined according to Merck Serono Biodevelopment and supplier experience. These flow rates should have been decreased as kLa was higher (3.6h-1) than in traditional bioreactors (2.6 h-1). Mixing time was measured in phosphate saline buffer at the maximum working volume and the agitation speed applied during production process. Mixing time was measured by injecting concentrated sodium hydroxide from the top of the bag and from the bottom of the bag. The Nucleo and the CellReady 3L system have classical probes, while the Orbital, the RM and the STR bioreactors have optical probes. Optical probes were more stable because they took a measure every five seconds. Classical probes were less stable and showed variations of around 0.03 pH unit even a few minutes after injection in the Nucleo. Nevertheless, mixing times on all disposable bioreactors (from 15s in CellReady 3L to 100s in Orbital) were higher than in traditional bioreactors (12s in 3.6L glass bioreactor to 28s in 1250L stainless steel bioreactor). For the STR, the mixing time was close to one minute, which is the recommended maximum for mammalian cell culture. The Orbital and the Nucleo had a mixing time below two minutes. Howerver, after sodium hydroxide injection, pH measured below or close to the final pH value. The disposable bioreactor which has a mixing time closest to traditional bioreactors is the CellReady 3L. Finally, an evaluation grid was applied to choose the best disposable bioreactor. All these comparisons allowed Merck Serono Biodevelopment to come to a conclusion about disposable bioreactor use and on the scalability (up and down) of these disposable systems. It also enabled us to highlight critical points for disposable bioreactor implementation such as tubing size and length, use of disposable or reusable probes or factory.

Mass spectrometry diagnosis of ion species in low-pressure plasmas

This work proposes a method to measure the I–V characteristic of a plane probe for each one of the ion species present in a low-pressure plasma, by using as the ammeter a mass spectrometer whose probe entrance can be biased at an arbitrary electric potential. From the I–V characteristic, the corresponding ion energy probability distribution function of each ion species in the plasma is obtained. Moreover, the corresponding ion temperature and the plasma potential are obtained. These results are in good agreement with those obtained from classical Langmuir probes and mass spectrometry methods.

Microwave discharge as a remote source of neutral oxygen atoms

The late flowing afterglow of an oxygen plasma was used as a remote source of neutral oxygen atoms. Plasma was created via a microwave discharge in a narrow quartz glass tube with an inner diameter of 6 mm at powers between 50 W and 300 W. The tube was connected to a wider perpendicular tube with an inner diameter of 36 mm. The density of neutral oxygen atoms was measured in the wide tube about 70 cm from the discharge using a classical nickel catalytic probe. The oxygen atom density as a function of gas pressure had a well-defined maximum. The oxygen atom density can be as large as 11 × 1020 m-3. At the lowest power tested (50 W), the maximum was obtained at a pressure of about 30 Pa. However, at higher powers, the maximum shifted to higher pressures. As a result, at 300 W the maximum appeared at 60 Pa. The results can be explained through collision phenomena in gas phase and surfaces in both discharge and flowing afterglow regions, and strong pressure gradients along the narrow tube.

Spectral characteristics of scalar higher-dimensional bremsstrahlung

We consider scalar higher-dimensional bremsstrahlung to explore the possibility of classical probes of extra dimensions, since higher-dimensional Minkowski space-time is a flat limit of cosmological backgrounds. The applicability of this results to models of ADD type has been proven by Galtsov, Kofinas, Spirin, and Tomaras in a number of papers. We develop classical perturbation theory which describes interaction between point particles moving on the observable 3-dimensional space, that simulates a 3-brane, and mediated by scalar fields. Applying this to the scattering problem, we find that the scattering angle is finite and contrary to the corresponding quantum result. Then we calculate scalar bremsstrahlung from ultrarelativistic particles colliding in D-dimensional Minkowski space and show that the radiation loss increases as a power of the Lorentz factor γ of the collision, increasing with D.

Shaping the lens of the atom probe: Fabrication of site specific, oriented specimens and application to grain boundary analysis

The random sampling provided by classical atom probe sample preparation methods is one of the major factors limiting the types of problems that can be addressed using this powerful technique. A focused ion beam enables not only site-specific preparation, but can also be used to give the specimen, which acts as the lens in an atom probe experiment, a specific shape. In this paper we present a technique that uses low accelerating voltages (10 and 5 kV) in the focused ion beam (FIB) to reproducibly produce specimens with selected grain boundaries <100 nm from the tip at any desired orientation. These tips have a high rate of successfully running in the atom probe and no Ga contamination within the region of interest. This technique is applied to the analysis of grain boundaries in a high purity iron wire and a strip-cast steel. Lattice resolution is achieved around the boundary in certain areas. Reconstruction of these datasets reveals the distribution of light and heavy elements around the boundary. Issues surrounding the uneven distribution of certain solute elements as a result of field-induced diffusion are discussed.

Use of a New Rectal Probe in Laparoscopic Pelvic Surgery

Pelvic surgical interventions that involve rectal dissection such as in endometriosis surgery, oncology procedures or adhesiolysis necessitate rectal identification. This can be done through trans anal introduction of a rectal probe to manipulate the rectum and identify its location. Rectal safety testing to check rectal parietal integrity is mandatory to diagnose rectosigmoid perforation and minimize the risk of fistula formation. These tests require air and coloured solution (blue dye or betadine) injection in the rectum through a transanal rectal catheter. Sterile manipulation and minimizing leakage of air and fluid through the anus are challenging issues in performing this procedure. We developed a disposable rectal probe that can be used for exposure and testing purposes paying attention to reduce manipulation in non sterile environment. This video shows the use of this probe with some tips and tricks to optimise its use compared to the classical rectal probe and rectal catheter. Pelvic surgical interventions that involve rectal dissection such as in endometriosis surgery, oncology procedures or adhesiolysis necessitate rectal identification. This can be done through trans anal introduction of a rectal probe to manipulate the rectum and identify its location. Rectal safety testing to check rectal parietal integrity is mandatory to diagnose rectosigmoid perforation and minimize the risk of fistula formation. These tests require air and coloured solution (blue dye or betadine) injection in the rectum through a transanal rectal catheter. Sterile manipulation and minimizing leakage of air and fluid through the anus are challenging issues in performing this procedure. We developed a disposable rectal probe that can be used for exposure and testing purposes paying attention to reduce manipulation in non sterile environment. This video shows the use of this probe with some tips and tricks to optimise its use compared to the classical rectal probe and rectal catheter.

Second harmonic generating (SHG) nanoprobes for in vivo imaging

Fluorescence microscopy has profoundly changed cell and molecular biology studies by permitting tagged gene products to be followed as they function and interact. The ability of a fluorescent dye to absorb and emit light of different wavelengths allows it to generate startling contrast that, in the best cases, can permit single molecule detection and tracking. However, in many experimental settings, fluorescent probes fall short of their potential due to dye bleaching, dye signal saturation, and tissue autofluorescence. Here, we demonstrate that second harmonic generating (SHG) nanoprobes can be used for in vivo imaging, circumventing many of the limitations of classical fluorescence probes. Under intense illumination, such as at the focus of a laser-scanning microscope, these SHG nanocrystals convert two photons into one photon of half the wavelength; thus, when imaged by conventional two-photon microscopy, SHG nanoprobes appear to generate a signal with an inverse Stokes shift like a fluorescent dye, but with a narrower emission. Unlike commonly used fluorescent probes, SHG nanoprobes neither bleach nor blink, and the signal they generate does not saturate with increasing illumination intensity. The resulting contrast and detectability of SHG nanoprobes provide unique advantages for molecular imaging of living cells and tissues.