Probe Measurements Research Articles

Archimedean Spiral Distribution of Energetic Particles in Earth's Inner Radiation Belt

AbstractArchimedean spirals are common in various fields such as biology, engineering, astronomy, and space physics. Here we report the discovery of patterns resembling the general Archimedean spirals in particle distributions in the Earth radiation belt. Our analytic theory and numerical simulations demonstrate that electrons with initially asymmetric spatial distributions form such spirals in the inner magnetosphere, where particles at smaller radial distances move more slowly in angular velocity. These spirals result in time‐varying peaks and valleys in particle fluxes, referred to as “zebra stripes,” which are well consistent with Van Allen Probes measurements. Although the initial asymmetric distribution may be seeded by the electric field in the magnetosphere, the spiral formation does not require them. Furthermore, we show that, due to the same fundamental motion of charged particles in regions dominated by dipole fields, this spiral phenomenon may also appear in the proton distributions, as well as in planetary magnetospheres.

Tuning the Microenvironment of Water Confined in Ti3C2Tx MXene by Cation Intercalation.

The local microenvironment has recently been found to play a major role in the electrocatalytic activity of nanomaterials. Modulating the microenvironment by adding alkali metal cations into the electrolyte can be used to either suppress hydrogen or oxygen evolution, thereby extending the electrochemical window of energy storage systems, or to tune the selectivity of electrocatalysts. MXenes are a large family of two-dimensional transition metal carbides, nitrides, and carbonitrides that have shown potential for use in electrochemical energy storage applications. Due to their negatively charged surfaces, MXenes can accommodate cations and water molecules between the layers. Nevertheless, the nature of the aqueous microenvironment in the MXene interlayer space is poorly understood. Here, we apply Fourier transform infrared spectroscopy (FTIR) to probe the hydrogen bonding of intercalated water in Ti3C2Tx as a function of intercalated cation and relative humidity. Substantial changes in the FTIR spectra after cation exchange demonstrate that the hydrogen bonding of water molecules confined between the MXene layers is strongly cation-dependent. Furthermore, the IR absorbance of the confined water correlates with resistivity estimated by 4-point probe measurements and interlayer distance calculated from XRD patterns. This work demonstrates that cation intercalation strongly modulates the confined microenvironment, which can be used to tune the activity or selectivity of electrochemical reactions in the interlayer space of MXenes in the future.

Characterization of elastomer degradation in O2/Ar plasma via mass and surface morphology changes

The degradation of fluoroelastomer, perfluoroelastomer (FFKM), and fluorosilicone materials were compared between three O2/Ar plasma conditions: full plasma (ions plus radicals), radical only, and ion only. These elastomer materials are used extensively in plasma processing equipment used to manufacture semiconductors, and understanding the plasma environments that enhance degradation will inform material choice and further material development. Langmuir probe measurements were made to quantify the electron temperature and plasma density; radical probe measurements were made to quantify the oxygen radical density. The results suggested that plasma radicals were required to drive significant mass loss rates, with ions speeding up the mass loss rate further in the full plasma case. Additionally, it was determined that plasma radicals were the main driver of surface changes of the elastomer, with similar surface roughening in plasma versus radical only conditions and less significant roughening in ion-only conditions. The O2/Ar plasma discharge had an electron temperature of 4.6 ± 0.1 eV and a plasma density of 2.9 ± 0.07 × 1016 m−3. It was observed that the fluorosilicone material had the lowest mass loss rate, the unfilled FFKM had the highest mass loss rate, and the silica-filled FFKM had the lowest mass loss rate among the FFKMs tested. The presence of oxygen radicals during exposure conditions significantly changed surface roughness.

Adaptive Ant Colony Optimization with Sub-Population and Fuzzy Logic for 3D Laser Scanning Path Planning.

For the precise measurement of complex surfaces, determining the position, direction, and path of a laser sensor probe is crucial before obtaining exact measurements. Accurate surface measurement hinges on modifying the overtures of a laser sensor and planning the scan path of the point laser displacement sensor probe to optimize the alignment of its measurement velocity and accuracy. This manuscript proposes a 3D surface laser scanning path planning technique that utilizes adaptive ant colony optimization with sub-population and fuzzy logic (SFACO), which involves the consideration of the measurement point layout, probe attitude, and path planning. Firstly, this study is based on a four-coordinate measuring machine paired with a point laser displacement sensor probe. The laser scanning four-coordinate measuring instrument is used to establish a coordinate system, and the relationship between them is transformed. The readings of each axis of the object being measured under the normal measuring attitude are then reversed through the coordinate system transformation, thus resulting in the optimal measuring attitude. The nominal distance matrix, which demonstrates the significance of the optimal measuring attitude, is then created based on the readings of all the points to be measured. Subsequently, a fuzzy ACO algorithm that integrates multiple swarm adaptive and dynamic domain structures is suggested to enhance the algorithm's performance by refining and utilizing multiple swarm adaptive and fuzzy operators. The efficacy of the algorithm is verified through experiments with 13 popular TSP benchmark datasets, thereby demonstrating the complexity of the SFACO approach. Ultimately, the path planning problem of surface 3D laser scanning measurement is addressed by employing the proposed SFACO algorithm in conjunction with a nominal distance matrix.

Wind-Induced Response Assessment of CAARC Building Based on LBM and FSI Simulation

It is very important for the wind-resistant design of high-rise buildings to assess wind-induced vibrations efficiently. The Lattice Boltzmann Method-based Large Eddy Simulation and Fluid–Structure Interaction techniques are used to identify the surface wind pressure and wind-induced dynamic response of a CAARC standard high-rise building. Compared with wind tunnel tests, a detailed analysis of the accuracy of simulated wind pressures and base moments of the CAARC model are discussed under multiple wind direction angles. The differences between one-way and two-way Fluid–Structure Interaction simulations are compared under two different reduced wind velocities. The research results show that the simulated mean surface wind pressures of building under seven wind direction conditions have an error within 15% compared to probe measurements, and the average and root mean square base bending moments agree well with the wind tunnel tests. The top transverse wind-induced vibrations of the buildings are significantly larger when the reduced wind velocity reaches 4.6, indicating that aerodynamic damping effects on structural responses should not be overlooked. The research findings of this article provide valuable technical references for the application of LBM methods in the wind load effect assessments of high-rise buildings.

Revisitation of reactive direct current magnetron sputtering discharge: Investigation of Mg–CF4, Mg–O2, and Ti–O2 discharges by probe measurements

The reactive direct current (DC) magnetron sputtering discharges of Mg–CF4, Mg–O2, and Ti–O2 were investigated using probe measurements as a function of reactive gas flow ratio. The emission spectroscopy, which was conducted before the probe measurements, demonstrates that all the three DC discharges transit from nonreactive to reactive discharge mode with increasing reactive gas flow ratio. The probe measurements show that the plasma potentials of the Mg–O2 and Ti–O2 DC discharges slightly increase or remain almost constant with increasing reactive gas flow ratio, whereas that of the Mg–CF4 DC discharge drastically decreases at the mode transition. For the same change in reactive gas flow ratio, the discharge voltage of the Mg–CF4 DC discharge slightly increases and that of the Mg–O2 DC discharge drastically increases at the mode transition, whereas that of the Ti–O2 DC discharge slightly decreases at the mode transition. The changes in the cathode sheath potential difference at the mode transition differ between the Mg–CF4 and Ti–O2 DC discharges and the Mg–O2 DC discharge because of the difference in the probability of secondary electron emission at the cathode surface; furthermore, the changes in the anode sheath potential difference at the mode transition differ between the Mg–CF4 DC discharge and the Mg–O2 and Ti–O2 DC discharges because of the difference in the probability of negative-ion formation in the plasma bulk. The most informative results obtained in this study were the differences in the potential differences at the cathode and anode sheaths among the Mg–CF4, Mg–O2, and Ti–O2 DC discharges. They well demonstrated the effects of the change in secondary-emitted species at the cathode surface and the change in reactive gas concentration in the plasma on the potential configuration.

Magneto-optical characterization of TCO films using standard and enhanced configurations

Thin film samples like transparent conducting oxides (TCO) are typically investigated using measurements like Hall Effect and 4-point probe measurements. We use a sensitive AC Faraday rotation (FR) setup to study thin film samples for which a magneto-optic response is challenging to characterize. The experimental setup employs a stabilized He-Ne laser (633 nm) along with an AC magnetic field that enables lock-in detection. We investigate a series of TCO samples that are deposited on a glass substrate. The TCO samples include the more widely used Indium Tin Oxide (ITO) and the relatively newer Fluorine doped Tin Oxide films, usually referred to as FTO. These films have a magneto-optic response due to the presence of free carrier concentration and therefore measurement of this response (Verdet constant) could allow one to determine the carrier concentration of these films. Given that magneto optic responses like FR depend on the length of the sample length traveled by light, these sub-micron films pose considerable challenges in trying to extract the FR response of the film from that of the much thicker glass substrate. Furthermore, we present details of the design and FR characterization of samples using a Michelson interferometer-based measurement setup which enhances the Faraday rotation and affords a new means of studying harmonic peaks of the recorded optical signal in response to a sinusoidally-varying applied magnetic field. We compare some early results from this setup to the typical “single-pass” setup to highlight the difference in the recorded signals from the two setups. To showcase the advantages of the proposed measurements, we also include some early results from a very different type of sample, namely superparamagnetic nanoparticles (SNPs).

Langmuir-probe measurement through the plasma grid aperture of hydrogen negative ion source

The extraction physics of negative-ion sources is still unknown because of the complication of the plasma-beam boundary (meniscus), which includes electronegative plasma, the magnetic field, and a surface production of negative ions. This paper shows results from Langmuir probe measurements inside of the extraction aperture (EA) and the criteria for locating the meniscus. The criteria are defined by the appearance and disappearance of Maxwellian feature of plasma. The result gives direct information on the location and shape of the plasma-beam boundary.

Tailoring the surface properties of molybdenum oxytelluride thin films by its compositional ratio

In this work, RF magnetron co‐sputtering was used to fabricate molybdenum oxytelluride thin films with different atomic ratios. Scanning electron micrographs and atomic force micrographs revealed that pure Mo thin films were segregated. Thin films with 40% Te content portrayed needle‐like structures and thus had the largest Rq value of 2.48 nm. Contact angle measurements further supported the findings as the thin films with 40% Te content were the most hydrophobic. X‐ray photoelectron spectroscopy results revealed that the major oxidation states of Mo from Te‐poor to Te‐rich TFs were changed from high (+6) to low (+4 and/or +2). X‐ray diffraction data showed that peaks pertaining to molybdenum oxide species appeared, notably at 33.048° and 33.115°. Ultraviolet photoelectron spectroscopy and Kelvin probe measurements evinced that the work function increases with increasing Te content. Four‐point probe measurements revealed that molybdenum oxytelluride thin films tend to have higher electrical conductivity than pure Mo and Te thin films.

Irrigation and Thermal Buffering Using Mathematical Modeling

Two methods of irrigation, drip, and sprinkler were studied to determine the response of the Javits green roof to irrigation. The control study was dry unirrigated plots. Drip irrigation consisted of irrigation tubes running through the green roof that would water the soil throughout and sprinkler irrigation used a sprinkler system to irrigate the green roof from above. In all cases, the irrigated roofs had increased the soil moisture, reduced temperatures of both the upper and lower surfaces, reduced growing medium temperatures and reduced air temperatures above the green roof relative to the unirrigated roof. The buffered temperature fluctuations were also studied via air conditioner energy consumption. There was a 28% reduction in air conditioner energy consumption and a 33% reduction in overall energy consumption between dry and irrigated plots. Values of thermal resistance or S were determined for accuracy and for this study, there was little change which is ideal. A series of infra-red and thermal probe measurements were used to determine temperatures in the air and sedum. It was determined that the sprinkler irrigation did a better job than the drip irrigation in keeping cooler temperatures within the green roof. A Mann-Whitney U test was performed to verify the variation in moisture temperatures buffering energy consumption. By getting a p-value < 0.05, it indicates that the model is accurate for prediction and medium temperatures were statistically different.

Estimating the turbulent kinetic energy dissipation rate from one-dimensional velocity measurements in time

Abstract. The turbulent kinetic energy dissipation rate is one of the most important quantities characterizing turbulence. Experimental studies of a turbulent flow in terms of the energy dissipation rate often rely on one-dimensional measurements of the flow velocity fluctuations in time. In this work, we first use direct numerical simulation of stationary homogeneous isotropic turbulence at Taylor-scale Reynolds numbers 74≤Rλ≤321 to evaluate different methods for inferring the energy dissipation rate from one-dimensional velocity time records. We systematically investigate the influence of the finite turbulence intensity and the misalignment between the mean flow direction and the measurement probe, and we derive analytical expressions for the errors associated with these parameters. We further investigate how statistical averaging for different time windows affects the results as a function of Rλ. The results are then combined with Max Planck Variable Density Turbulence Tunnel hot-wire measurements at 147≤Rλ≤5864 to investigate flow conditions similar to those in the atmospheric boundary layer. Finally, practical guidelines for estimating the energy dissipation rate from one-dimensional atmospheric velocity records are given.

High-quality dense ZnO thin films: work function and photo/electrochemical properties

Compact ZnO (wurtzite) thin films are prepared on four different substrates by (i) spray pyrolysis or (ii) pulsed reactive magnetron sputtering combined with a radio frequency electron cyclotron wave resonance plasma. Films are characterized by AFM, XRD, Kelvin probe, cyclic voltammetry, electrochemical impedance spectroscopy, and UV photoelectrochemistry. Film morphologies, defect concentrations, crystallite size, and orientation provided specific fingerprints for the electronic structure of ZnO close to the conduction band minimum. Fabricated films are referenced, if relevant, to a model system based on a wurtzite single crystal with either Zn-face or O-face termination. Kelvin probe measurements of the ZnO/air interface distinguished effects of annealing and UV excitation, which are attributed to removal of oxygen vacancies close to the surface. In turn, the work function, at the electrochemical interface, specifically addressed the growth protocol of the ZnO electrodes but not the effects of crystallinity and annealing. Finally, high photocurrents of water oxidation are observed exclusively on virgin films. This effect is then discussed in terms of photocorrosion, and work function changes due to UV light.Graphical

Towards quantification of doping in gallium arsenide nanostructures by low-energy scanning electron microscopy and conductive atomic force microscopy.

We calculate a universal shift in work function of 59.4 meV per decade of dopant concentration change that applies to all doped semiconductors and from this use Monte Carlo simulations to simulate the resulting change in secondary electron yield for doped GaAs. We then compare experimental images of doped GaAs layers from scanning electron microscopy and conductive atomic force microscopy. Kelvin probe force microscopy allows to directly measure and map local work function changes, but values measured are often smaller, typically only around half, of what theory predicts for perfectly clean surfaces.

Significant Oxygen Underestimation When Quantifying Barium-Doped SrTiO Layers by Atom Probe Tomography.

In this paper, the capability for quantifying the composition of Ba-doped SrTiO layers from an atom probe measurement was explored. Rutherford backscattering spectrometry and time-of-flight/energy elastic recoil detection were used to benchmark the composition where the amount of titanium was intentionally varied between samples. The atom probe results showed a significant divergence from the benchmarked composition. The cause was shown to be a significant oxygen underestimation (≳14 at%). The ratio between oxygen and titanium for the samples varied between 2.6 and 12.7, while those measured by atom probe tomography were lower and covered a narrower range between 1.4 and 1.7. This difference was found to be associated with the oxygen and titanium predominantly field evaporating together as a molecular ion. The evaporation fields and bonding chemistries determined showed inconsistencies for explaining the oxygen underestimation and ion species measured. The measured ion charge state was in excellent agreement with that predicted by the Kingham postionization theory. Only by considering the measured ion species, their evaporation fields, the coordination chemistry, the analysis conditions, and some recently reported density functional theory modeling for oxide field emission were we able to postulate a field emission and oxygen neutral desorption process that may explain our results.

Spontaneous Combustion in Coal Stockpiles with Different Particle Sizes

In this study, the spontaneous combustion behavior of stocks created with coals of 3 different particle sizes (0-18/18-28/25-100 mm) was examined for 2 months and the results were analyzed. For this purpose, daily temperaturechanges in the stockpiles were recorded by means of temperature measurement probes placed in the stocks designed in2x3x10 m size. According to the results obtained; Coal stocks with grain sizes of 18-25 and 25-100 mm started to catchfire before the end of the first month of storage. While no open flame ignition was observed in the stock with the finestgrain size (0-18 mm), at the end of the 2nd month, a temperature increase was observed only at a single point accordingto the wind direction.

Passivating Polycrystalline Copper with an Ultrathin Samarium Layer

Herein, it is reported that how a layer of samarium (Sm) with a thickness equivalent to ≈2 atoms (0.8 nm) deposited by thermal evaporation is remarkably effective at passivating polycrystalline copper (Cu) toward oxidation in ambient air. To monitor the rate of Cu oxidation in real time, slablike Cu films with a thickness of 9 nm are fabricated on glass modified with a layer of 3‐mercaptopropyl silatrane, which immobilizes condensing Cu atoms by reaction with the thiol moiety, promoting slablike film formation at very low thickness. Upon exposure to ambient air the rate of increase in electrical resistance due to reaction with oxygen and water is slowed by more than an order of magnitude when the Cu film is capped with the ultrathin Sm layer. After 1 year, the resistance increases by ≈30% as compared to ≈190% for Cu films without an ultrathin Sm layer. Photoelectron spectroscopy, atomic force microscopy, and Kelvin probe measurements shed light on the underlying mechanism of passivation. Additionally, the ultrathin Sm layer is greatly lowering the work function of polycrystalline Cu films making this approach attractive for applications requiring a low‐work‐function electrode with high stability in air.

In-situ generation of Au–carbon–TiO2 Ohmic junction from Ti3C2 MXene for efficient photocatalytic H2 evolution

Photogenerated charge separation is a challenging step in semiconductor-based photosynthesis. Though numerous efforts have been devoted to developing multi-component photocatalyst heterostructures for improving charge separation efficiency, the short distance between electrons and holes-aggregated regions still leads to undesirable charge recombination. Herein, a facile and commercial in-situ synthesis method was designed to directly prepare a three-component Au–carbon–TiO2 photocatalyst from Ti3C2 MXene, air, CO2, and HAuCl4, in which the carbon layer bridged Au and TiO2 nanoparticles for stable and efficient photocatalytic hydrogen production. Kelvin probe measurements and density functional theory (DFT) calculations demonstrated that a multi-interfacial charge transmission network was successfully constructed to achieve a directional and long-distance spatial charge separation/transfer channel between TiO2 and Au through carbon layer, desirably inhibiting the recombination of photogenerated charge carriers. The hydrogen production rate of the formed three-component Au/C–TiO2 (CTA) photocatalyst was demonstrated to be 27 times higher than that of Au–TiO2, which also surpassed many reported Ti3C2 MXene-derived carbon–TiO2 photocatalysts. This work sheds light on the ingenious use of 2D MXene to form a well-behaved TiO2-based photocatalytic system and helps to propose future design principles in accelerating charge transfer.

Validation of a spring loaded probe for single and repeat pressure pain testing, including public domain specifications for design and manufacture.

Temporal summation of pressure pain is technically more challenging than simple pressure pain thresholds. The current study describes the design, manufacture and validation of a simple mechanical test apparatus to assess the temporal summation of deep pressure pain. We release design details into the public domain with the intention of providing free access for researchers especially in low income countries. Utility and validity of the probes were assessed by pressure application in three different experimental setups: A. Identifying potential issues which needed to be addressed to ensure a reliable test procedure (189 tests with 24 testers using four different probes). B. Selecting the most reliable target force curve (one tester conducted 20 tests). C. Estimating classic inter and intra-examiner reliability and comparing probe measures to other QST measures (repeated measures study with counterbalancing). We make recommendations on best use of the probes. Pressure pain thresholds assessed using probes were affected by anatomical test site and testing tool, but not by tester, day or session. Temporal summation of pressure pain was significantly greater than that of a single pressure application. We found no correlation between temporal summation using the probes on the Infra-Spinatus muscle and temporal summation using a pneumatic cuff on the lower leg. The probe was a useful tool for assessing pain intensity and temporal summation of pressure pain intensity, but not for pain thresholds. A number of caveats need to be considered when using the probe, including but not limited to audio cues and target ideal wave function.

Self-Assembly and Antimicrobial Activity of Lipopeptides Containing Lysine-Rich Tripeptides.

The conformation and self-assembly of two pairs of model lipidated tripeptides in aqueous solution are probed using a combination of spectroscopic methods along with cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). The palmitoylated lipopeptides comprise C16-YKK or C16-WKK (with two l-lysine residues) or their respective derivatives containing d-lysine (k), i.e., C16-Ykk and C16-Wkk. All four molecules self-assemble into spherical micelles which show structure factor effects in SAXS profiles due to intermicellar packing in aqueous solution. Consistent with micellar structures, the tripeptides in the coronas have a largely unordered conformation, as probed using spectroscopic methods. The molecules are found to have good cytocompatibility with fibroblasts at sufficiently low concentrations, although some loss of cell viability is noted at the highest concentrations examined (above the critical aggregation concentration of the lipopeptides, determined from fluorescence dye probe measurements). Preliminary tests also showed antimicrobial activity against both Gram-negative and Gram-positive bacteria.

Coherence of Elsässer Variables in the slow solar wind from 0.1 au to 0.3 au

The highly Alfvénic fluctuations (AF) and magnetic-velocity alignment structures (MVAS) are two distinguished components in the near-Sun slow solar wind observed by Parker Solar Probe. The amplitudes of the Elsässer Variables z± of AF and MVAS show distinct features. However, how these fluctuations contribute to the slow solar wind turbulence remains unknown. Here we investigate the coherence between z+ and z− for the first time using the Parker Solar Probe measurements with a high resolution 0.8738 s in the slow solar wind from 0.1–0.3 au. We find that the coherence spectra of z+ and z− in the perpendicular directions for MVAS are remarkable higher than that for AF, in particular at large scale. There exists a break around 10 di (di is the ion inertial length) where the coherence decreases to a lower level for MVAS. A bump around 10 di appears on the coherence spectra of all three components for AF. The coherence of z+ and z− may relate to the possible nonlinear interactions reflected by the time series, the power spectra, and the self-correlation functions. These results help to understand the roles of AF and MVAS in the slow solar wind turbulence.