Single Probe Method Research Articles

Layer-dependent photoexcited carrier dynamics of WS2 observed using single pulse pump probe method

Understanding the ultrafast carrier dynamics and the mechanism of two-dimensional (2D) transition metal dichalcogenides (TMDs) is key to their applications in the field of optoelectronic devices. In this work, a single pulse pump probe method is introduced to detect the layer-dependent ultrafast carrier dynamics of monolayer and few-layer WS2 excited by a femtosecond pulse. Results show that the ultrafast carrier dynamics of the layered WS2 films can be divided into three stages: the fast photoexcitation phase with the characteristic time of 2–4 ps, the fast decay phase with the characteristic time of 4–20 ps, and the slow decay phase lasting several hundred picoseconds. Moreover, the layer dependency of the characteristic time of each stage has been observed, and the corresponding mechanism of free carrier dynamics has been discussed. It has been observed as well that the monolayer WS2 exhibits a unique rising time of carriers after photoexcitation. The proposed method can be expected to be an effective approach for studying the dynamics of the photoexcited carriers in 2D TMDs. Our results provide a comprehensive understanding of the photoexcited carrier dynamics of layered WS2, which is essential for its application in optoelectronics and photovoltaic devices.

Measurement of low sap flux density in plants using the single needle heat pulse probe

Heat pulse probes are used worldwide to quantify sap flow in plants. Probes consisting of a single needle inserted into a plant have a simple physical configuration relative to multi-probe methods. The single probe also minimizes physical damage to plant tissue. Single probe methods are therefore increasingly used for sap flux density measurements. However, at low sap flux density values, existing single probe heat pulse (SPHP) methods cannot be used for accurate measurements. To increase the sensitivity of SPHP to low sap flux densities, this paper describes and validates a simplified expression of sap flow and heat transport under various heat inputs and finite heat pulse time intervals. To test this theoretical development, measurements were collected from SPHP probes inserted into mature poplar forest trees (Populus tomentosa Carrière) during the 2020 growing season. The results show that the new method can successfully monitor low sap flux density: the lowest measured heat pulse velocity was 3 cm h−1, which is an improvement from the original SPHP method (20 cm h−1). The improved SPHP method had a root mean square deviation (RMSD) of 1.63 cm h−1 in comparison with the heat ratio (HR) method. The proposed SPHP method is therefore suitable for quantifying both low and high sap flux densities.

Measurement of Floating Potential and Ion Concentration in Arc Plasma at Atmospheric Pressure

Arc plasma is generated using low voltage dc power supply for the measurement of plasma parameters such as floating potential and ion-concentration in the plasma seeded with molybdenum. Langmuir moving probe is used in order to measure the probe current at different values of the dc potential applied on the probe. A graph is plotted between the probe current and the probe potential, based on data at the atmospheric pressure, using the experimental set up in the gas discharge chamber for the single probe method. The floating potential is calculated to be 32V, and the average ion-concentration to be 1.43 - 10e16m3.

Thermal Conductivity of Olive Cake Compost (OCC) as Affected by Moisture and Density: An Experimental and Mathematical Modeling

The behaviors of bioactive compounds treating gaseous pollutants in biofilters and in the compost used as soil amendment and in green roof buildings are controlled by their thermal properties. There is a lack of information on thermal conductivity of olive cake compost (OCC), K as affected by water content and bulk density. Thermal conductivities (K) of 40 samples of (OCC) were determined experimentally at bulk densities (400–950 kg/m3) and moisture contents (10%–90%) using a single thermal probe method. The results showed that thermal conductivity increased linearly as water content, and bulk density increased and with a decrease in air filled porosity. Simple linear relationships were developed between compost thermal conductivity and dry bulk density and the degree of saturation. The experimental values were close to those reported recently for leaf compost and green roof soils. The compost at water content of 90% showed the highest thermal conductivity (K) of 0.60 W/m.k, which indicate that compost, can be used as good cheep insulator in geothermal heat storage application and as an additional echo-friendly insulation layer in green roof building which might be considered as a good means of passive energy saving there.

Effects of Moisture Content on Thermal Properties of Adobe Bricks as a Sustainable Building Material

The adobe is a widely used traditional material in popular building construction in rural areas of Northeastern, Nigeria and more generally in African countries. In order to increase comfort and energy efficiency of buildings, it is necessary to better consider the thermal properties of the adobe. Adobes at different locations as a function of moisture content have been studied. Thermal conductivity and thermal resistivity were measured by means of a single probe method. Density was estimated by the ratio of mass to volume. The measured values of thermal conductivity and thermal resistivity of adobe soil are varying between 0.191 to 0.428 W/m K and 2.34 to 5.23 mK/W in the moisture content range 5-20% wet basis. However, the effect of moisture content increase by increasing the thermal conductivity and decreases the resistivity of soil samples. Regression analysis was carried out which could be used to reasonably estimate the values of the thermal conductivity and resistivity as a function of specified moisture content. For the adobe soils studied, thermal properties increased with increasing soil moisture content.

A Spherical Steady-State Method to Measure Soil Thermal Conductivity

The reliable prediction of coupled heat and moisture transfer in three-phase soils involves authentic estimation of soil thermal conductivity. In the current work, a steady-state method was developed to measure soil thermal conductivity. Soil samples for two soils were packed in a plastic of 6.6 cm inner diameter and 3 mm thickness. A 130 Ohm resistor as a heat generator being connected to 5 V electricity source was located in the center of the ball. Three thermocouples were installed at the distances of 0.5, 1.5, and 2.5 cm from the center, respectively. After unpacking the ball, thermal conductivity was measured using the single probe method. The thermal conductivity values measured by both methods were almost the same in air dry soils; overall, the observed differences between the two methods were less than 3%. However, in the intermediate moisture content ranges, the values measured by the steady-state method were slightly lower than those obtained by the single probe method. Considering the effect of convective vapor flux due to thermal expansion of soil air in the single probe method, values measured with the new steady-state method may be more reliable.

Complementary Characterization of Laser-Induced Plasmas by Optical Emission Spectroscopy and Triple Langmuir Probe

In this article, we study the temporal evolution of the electron density and temperature of carbon laser-produced plasmas (LPP) using a combination of optical emission spectroscopy (OES) and the triple Langmuir probe (TLP) method. OES has been widely used to characterize LPPs but it is limited to distances relatively close to the target. On the other hand, the main advantage of TLP over the single-probe method is that it allows to obtain simultaneous measurements of electron temperature ( $T_{e}$ ) and density ( $N_{e}$ ), without any voltage sweeping. In this article, we compare both techniques; measurements by OES were performed at distances from the target 5 cm. The plasma was generated by focusing nanosecond laser pulses onto a high purity graphite target placed inside a vacuum chamber. Our results show that the values of $T_{e}$ measured using both techniques predict decreasing exponential behavior. $N_{e}$ determined by the spectral line Stark broadening in OES ( 5 cm). This difference in the electron density can be explained by radiative recombination and the presence of different kinds of plasma species detected by the TLP technique. The results show that both methods are complementary and their combination can be used to characterize LPP in a wide range of distances and timescales.

Physical and mechanical properties of surface modified poly ethylene terephthalate films through low pressure plasma and ultra-violet light

The present work focussed on the effect of UV light radiation and Direct current glow Discharge Plasma (DC) on Polyethylene Terephthalate (PET) surface for food packaging applications. The PET was treated by three different plasma such as air, argon, and oxygen with a treatment time of 5–25 min and pressure kept as 3 Pa. The PET film was exposed by UV radiation using the wavelength between 200–400 nm UV light Lamp with a treatment time of 5–25 min. And also we measured the electron temperature (Te) and electron density (Ne) of the three different plasmas by Single Langmuir probe method. The surface properties of UV light radiated and plasma treated PET films were characterized by static contact angle, x-ray diffraction, Optical analysis (UV–vis), ATR-FTIR, Structural analysis (AFM)) and the results were compared. We observed that the bulk properties of the treated materials remained unchanged. This was confirmed by x-ray diffraction results. The new polar functional groups were also detected on the treated films by FTIR spectrum analysis. The surface roughness was calculated from AFM analysis for both untreated and treated PET films. The oxygen plasma treated sample showed higher roughness, which indicated that a large amount of oxygen containing polar groups appeared on the surface of the PET film. The obtained results reveal that the plasma treated PET films were more effective than the Ultra-violet (UV) light radiated film.

An improved single probe method for sap flow measurements using finite heating duration

Because of its low cost and simple fabrication, it is easy to advocate for the single probe method as a method of choice in sap flow studies. An improved single probe method with finite heating duration (F-SPHP) is verified both in cut stem segments and in the field using mature beech (Fagus sylvatica L.) trees. The F-SPHP method is based on an analytical solution of the partial differential equation for combined heat conduction and convection, which shows large relative sensitivity to thermal conductivity (K). The F-SPHP method is able to measure sap flux densities (SFD) between 2 and 36 cm3 cm−2 h−1 (heat pulse velocity (Vh): 3–60 cm h−1) in the cut stem segment experiment. This is an improvement compared to the instantaneous single probe heat pulse (I-SPHP) method which cannot accurately measure low (Vh < 20 cm h−1) sap flow. Sapflow+ (a four-needle heat pulse method) is used for field validation, and when compared with gravimetric measurements, slopes of 0.853 and 0.730 are obtained for F-SPHP and Sapflow+, respectively. Patterns measured with F-SPHP and Sapflow+ in mature beech trees in the forest are similar at all measurement positions and temperature correction is needed for both methods when natural temperature gradients are steep. Compared with multi-probe methods, the single probe method with finite heating duration has the advantage of causing less damage to conductive tissue.

(Invited) Atomic Level Investigation of Resistance Switching in 2D Memory Devices

The last few years have witnessed significant developments in non-volatile resistance switching (NVRS) devices which employ layered 2D materials such as hexagonal Boron Nitride (hBN) and Transitional Metal Dichalcogenides (TMDs) as the active medium. Among these developments, the demonstration of NVRS in vertical metal-insulator-metal (MIM) devices with single layer atomic sheets used as the insulating layer, is particularly intriguing. While it was long believed that leakage currents would prevent observation of this phenomenon for atomically thin insulating layers our previous studies on mesoscopic scale devices demonstrated stable unipolar and bipolar operations. Furthermore, these studies suggest that localized defects and other atomic-scale multiphysics mechanisms are likely to have a key role in NVRS observed in these 2D devices. Here, we present our current research on the atomic level details of the relationship between the NVRS and heterogeneities in 2D materials. For these investigations, we utilize both single probe and multi-probe scanning electron microscopy (STM) methods, first, to identify the atomic level details of the heterogeneity and then to conduct transport experiments in the vicinity of specific heterogeneities. These studies aim to provide one to one correlation between the structural properties of the heterogeneity and its role on the transport properties of the material. Through these studies, we seek to deduce which particular defect structures are most desirable for NVRS and utilize this information for the development of extremely high-density data storage devices as well as neuromorphic applications and low power RF switches.

Thermal conductivity of unfrozen and partially frozen managed peat soils

Detailed, accurate information on soil temperature is crucial for understanding processes leading to solute leaching and greenhouse gas (GHG) emissions from managed peat soils, but few studies have attempted to study these processes in detail. Drained peat soils have different characteristics from pristine peat. Cultivated peat soils, in particular, have high mineral matter content in the plough layer, due to mineralisation of peat and, sometimes, addition of mineral material. This study examined the effect of mineral matter content on thermal conductivity (λ) in partially frozen and unfrozen peat samples. Effect of change in temperature from −3 °C to −10 °C on thermal conductivity was also estimated. Three existing models for estimating the thermal conductivity of organic soils were assessed for their suitability for cultivated drained peat soils. The thermal conductivity of peat samples with three different levels of mineral matter content was determined, using the single probe method, in the saturated state and when subjected to at least two different matric potentials at five different temperatures (+10 °C, + 1 °C, −3 °C, −5 °C and −10 °C). The results showed that λ values differed between peat soils depending on mineral matter content, ice content and moisture content. The samples with the highest mineral matter content and bulk density had higher thermal conductivity at positive temperatures and to a lesser extent, at freezing temperatures, when volumetric water content and volume of water-free pores was similar. Most soil samples, especially those with no added mineral soil, were not fully frozen at −3 °C and −5 °C, but this had minor effect on thermal conductivity compared with values measured at −10 °C. The Brovka-Rovdan model proved reasonably good at predicting frozen thermal conductivity in sand-enriched peat soils, while the de Vries model proved best at estimating thermal conductivity for unfrozen peat samples. We provide a first estimate of the thermal conductivity of (partially) frozen cultivated peat measured using undisturbed samples. These results can be used to parameterise numerical heat transport models for simulating soil processes and GHG emissions.

Characterization of Arc Plasma by Movable Single and Double Langmuir Probes

In this work, plasma is produced by arc discharge between two copper electrodes and is characterized by a movable single probe and a double Langmuir probe. The movable Langmuir single-probe technique has a reference point since it is biased with reference to one of the electrodes of the plasma-producing system. In some situations such as radio-frequency discharges, no reference point is available to bias the movable single probe. In the double-probe method, each probe is biased with respect to each other and allowed to move through the arc plasma. Depending on the magnitude of the biasing potential, charges are collected by the probes, and the probe current flowing to the circuit is calculated. After that, we obtain the electron temperature and plasma density of the arc plasma. By using the double-probe method, the value of the plasma density is more precise than with the single-probe method. Hence, the double-probe method is more appropriate than the single-probe method.

Experimental set up for the study of plasma parameters in seeded arc plasma using Langmuir Probes inside low-cost vacuum chamber

In this piece of study, the design and development of a low cost vacuum chamber with different ports are mentioned. I-V characteristic of Langmuir Probe is obtained using the primary data of the experimental set up for ‘single probe method’ in nitrogen seeded arc plasma at atmospheric pressure The floating potential was found to be 36V and the electron density to be 1.24 ´ 104 K. Variation in electron density of the arc plasma with probe potential is also studied at low pressure range from 10 Nm-2 (0.10 mbar) to 20 Nm-2.BIBECHANA 16 (2019) 1-6

Temporal separation of Cerenkov radiation and scintillation using artificial neural networks in Clinical LINACs

The irradiation of scintillator-fiber optic dosimeters by clinical LINACs results in the measurement of scintillation and Cerenkov radiation. In scintillator-fiber optic dosimetry, the scintillation and Cerenkov radiation responses are separated to determine the dose deposited in the scintillator volume. Artificial neural networks (ANNs) were trained and applied in a novel single probe method for the temporal separation of scintillation and Cerenkov radiation. Six dose profiles were measured using the ANN, with the dose profiles compared to those measured using background subtraction and an ionisation chamber. The average dose discrepancy of the ANN measured dose was 2.2% with respect to the ionisation chamber dose and 1.2% with respect to the background subtraction measured dose, while the average dose discrepancy of the background subtraction dose was 1.6% with respect to the ionisation chamber dose. The ANNs performance was degraded when compared with background subtraction, arising from an inaccurate model used to synthesise ANN training data.

Polymerase-free measurement of microRNA-122 with single base specificity using single molecule arrays: Detection of drug-induced liver injury.

We have developed a single probe method for detecting microRNA from human serum using single molecule arrays, with sequence specificity down to a single base, and without the use of amplification by polymerases. An abasic peptide nucleic acid (PNA) probe—containing a reactive amine instead of a nucleotide at a specific position in the sequence—for detecting a microRNA was conjugated to superparamagnetic beads. These beads were incubated with a sample containing microRNA, a biotinylated reactive nucleobase—containing an aldehyde group—that was complementary to the missing base in the probe sequence, and a reducing agent. When a target molecule with an exact match in sequence hybridized to the capture probe, the reactive nucleobase was covalently attached to the backbone of the probe by a dynamic covalent chemical reaction. Single molecules of the biotin-labeled probe were then labeled with streptavidin-β-galactosidase (SβG), the beads were resuspended in a fluorogenic enzyme substrate, loaded into an array of femtoliter wells, and sealed with oil. The array was imaged fluorescently to determine which beads were associated with single enzymes, and the average number of enzymes per bead was determined. The assay had a limit of detection of 500 fM, approximately 500 times more sensitive than a corresponding analog bead-based assay, with target specificity down to a single base mis-match. This assay was used to measure microRNA-122 (miR-122)—an established biomarker of liver toxicity—extracted from the serum of patients who had acute liver injury due to acetaminophen, and control healthy patients. All patients with liver injury had higher levels of miR-122 in their serum compared to controls, and the concentrations measured correlated well with those determined using RT-qPCR. This approach allows rapid quantification of circulating microRNA with single-based specificity and a limit of quantification suitable for clinical use.

Interpretation of Double Langmuir Probe I-V Characteristics at Different Ionospheric Plasma Temperatures

Where the plasma potential is fluctuating significantly, Single Langmuir probe method is not relevant to determine the plasma characteristics. This weakness was overcome by the development of the floating double probe. A distortion of the probe characteristics due to varying potential is eliminated, while the whole probe system is floating. This supports probe operation also in discharges with strongly varying potential. Double Langmuir probes provide valuable information on the behavior of space plasmas including ionospheres and the interstellar medium. This research paper focuses on the study of Spherical Double Langmuir Probe I-V characteristics in Maxwellian interstellar plasma. To generate the exact plasma conditions of the experimental testing environments computational procedures is adopted. The investigations address the development of a technique to model Maxwellian plasma. Three different ionospheric plasma temperatures are theoretically taken and its effects on floating potential are studied in this research. The variation of floating potential and ion saturation current due to temperature is clearly depicted. A noticeable trail in the I-V curves is the bump that occurs right after the floating potential. This feature in the transition region affects ability to determine the electron temperature, ion saturation current and plasma potential. Symmetric characteristic when both tips are of equal geometry is an important advantage of the double probe. Generally, all surfaces adjacent to the plasma become contaminated with deposits, so also does any probe. Here I have also deliver some sense of how one might proceed to use these results in the analysis of experimental I-V curves acquired in space.

An extensive cocktail approach for rapid risk assessment of in vitro CYP450 direct reversible inhibition by xenobiotic exposure

Acute exposure to environmental factors strongly affects the metabolic activity of cytochrome P450 (P450). As a consequence, the risk of interaction could be increased, modifying the clinical outcomes of a medication. Because toxic agents cannot be administered to humans for ethical reasons, in vitro approaches are therefore essential to evaluate their impact on P450 activities.In this work, an extensive cocktail mixture was developed and validated for in vitro P450 inhibition studies using human liver microsomes (HLM). The cocktail comprised eleven P450-specific probe substrates to simultaneously assess the activities of the following isoforms: 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 2J2 and subfamily 3A. The high selectivity and sensitivity of the developed UHPLC-MS/MS method were critical for the success of this methodology, whose main advantages are: (i) the use of eleven probe substrates with minimized interactions, (ii) a low HLM concentration, (iii) fast incubation (5min) and (iv) the use of metabolic ratios as microsomal P450 activities markers. This cocktail approach was successfully validated by comparing the obtained IC50 values for model inhibitors with those generated with the conventional single probe methods. Accordingly, reliable inhibition values could be generated 10-fold faster using a 10-fold smaller amount of HLM compared to individual assays. This approach was applied to assess the P450 inhibition potential of widespread insecticides, namely, chlorpyrifos, fenitrothion, methylparathion and profenofos. In all cases, P450 2B6 was the most affected with IC50 values in the nanomolar range. For the first time, mixtures of these four insecticides incubated at low concentrations showed a cumulative inhibitory in vitro effect on P450 2B6.

Effect of Pressure and Hot Filament Cathode on Some Plasma Parameters of Hollow Anode Argon Glow Discharge Plasma

The present study represents a review article and a complementary study to a published paper of direct current hot cathode and hollow anode argon glow discharge plasma at different pressures in the range 0.05 - 0.8 mbar. The glow discharge usually obtained by applying a high voltage between the electrodes sufficient to occurring breakdown of argon gas and sustaining the discharge. Additional estimation of some plasma parameters, ion temperature, degree of ionization and electron energy distribution function as well as some characteristics of glow discharge under the influence of pressure and filament current has been done. Plasma parameters have been calculated using single probe method at fixed discharge current Id=1.88mA and diameter of hollow anode. Furthermore a computer MATLAB program is applied for this purpose. Results show that the average discharge voltage increases while its average discharge current decreases according to the increasing of the filament current. On the Contrary the average discharge voltage decrease nearly exponentially whiles its average discharge current increases according to increasing of the gas pressure. Degree of ionization starts to increase from low pressure to medium and then tends to decrease toward high pressure investigated. However it starts to increase to maximum value at filament current 0.9A then tends to decrease at higher current and low pressure. While for high pressures there is no significance change. Ion temperature increases slowly with filament current up to 0.9A and then sharply increases to maximum value at 1.5A. But it decreases for pressures in the range 0.05 - 0.09 mbar and then increases with gas pressure. Electron energy distribution function (EEDFs) decrease according to increases filament current, however, it starts to increase from low pressure to maximum value at medium pressure then tends to increase according to further increases of pressure.

COMPARISON OF HEAT TRANSFER PROPERTIES OF DRY SAND AND MAGNESIUM OXIDE POWDER BY SINGLE-PROBE METHOD

The use of magnesium oxide (MgO) powder in electrical heating appliances is based on its thermal and electrical insulating properties. However, dry sand, which is readily available and free on the surface horizon than MgO powder also possesses good thermal and electrical insulating properties that could be utilized in the fabrication of electrical heating devices. In this study, we determined and compared heat transfer properties of dry fine-medium sand (0.125-0.50 mm) and dry coarse sand (0.50-1.00 mm) with those of MgO powder, using the single-probe method. Electrical heating equipment was designed and fabricated with a heating element that generated a heat flux of 18.05Wm-1. From the results obtained, the thermal conductivities of dry fine-medium sand, dry coarse sand and MgO powder were found to be 0.21 m-1K-1, 0.22 Wm-1K-1 and 0.36 Wm-1K-1 respectively. Temperature increase per second were also obtained and found to be 4.75 × 10-2 Ks-1 in dry fine-medium sand, 4.28 × 10-2 Ks-1 in dry coarse sand and 2.03 × 10-2 Ks-1 in MgO powder. Thus, while it took MgO powder 472 s to warm from 30 oC to 40 oC, it took dry coarse sand and dry fine-medium sand only 229 s and 205 s respectively to warm through the same temperature range.

Investigation of Hot Cathode and Hollow Anode of Argon Glow Discharge Plasma

Hot cathode and hollow anode argon DC glow discharge plasma at different pressures of (0.04, 0.05, 0.06, 0.07, 0.09, 0.2, 0.4, and 0.8 mbar) has been investigated. The experiments were carried out under the influence of pressure and filament cathode current on voltage – current characteristics of glow discharge and its breakdown voltage. Plasma parameters have been measured and obtained using single probe method at fixed discharge current (Id=1.88 mA) and hollow anode diameter. A computer MATLAB program is performed for this purpose. It was shown that the discharge voltage – current characteristics curve has a positive resistance and represents an abnormal glow region at pressure (0.04 and 0.06) mbar for different filament current. The breakdown voltage increases as the filament current is increased. In different pressure, electron temperature shows different behavior with increasing filament current. Electron density varies nearly inversely with the filament current, but it is increase due to increase of pressure from (1 to 3 mbar), then tends to decrease for the higher pressure. There are two groups of electrons according to the two peaks of (EEDFs), and the peaks amplitude decrease, with the increases of both filament current and gas pressure.