Resistivity Saturation Research Articles

Growth pattern of dispersed methane hydrates in brine-saturated unconsolidated sediments via joint velocity and resistivity analysis

Although the different morphologies of methane hydrates have been identified in pore spaces, their growth mechanism has not yet been fully resolved. In this study, we performed two sets of experiments using dissolved methane in brine-saturated unconsolidated sediments composed of 95.5 wt% quartz sand and 4.5 wt% kaolin to simulate the formation of dispersed marine gas hydrates. The in situ ultrasonic velocities (VP and VS), electrical resistivity, and methane hydrate saturation (Sh) were simultaneously measured and were jointly analyzed and compared to elastic and electrical rock physics models of various hydrate morphologies in pore spaces to quantify the invisible dynamic evolution of the hydrates’ morphologies. The results indicate that the hydrate growth pattern is characterized by distinct stages as Sh increases. During the first set of experiments, the frame-strengthening morphology was dominant in all of the stages, the contact-cementing morphology occurred infrequently when Sh > 8%, and the pore-filling morphology gradually became identifiable when Sh > 25%. It is proposed that the frame-strengthening hydrates primarily grow on grain surfaces when Sh < 25%, then they extend toward the center of the pore, and finally they begin to plug the pores when Sh > 35%. In the second set of experiment, the geophysical responses were significantly affected by the presence of free gas, and the observed hydrate growth behavior was differed from that observed in the first set of experiments.

Analysis of zero-temperature coefficient behavior on vertically stacked double nanosheet nMOS devices

This work presents an experimental study of the zero-temperature coefficient (ZTC) bias point of vertically stacked gate-all-around (GAA) double nanosheet nMOS devices (GAA-NS) for different dimensions, operating in linear and saturation regions. The experimental data is also compared to a simple analytical ZTC model in order to better understand which electrical parameters impact the ZTC behavior. The variation of the threshold voltage with the temperature (ΔVTH/ΔT) and temperature transconductance degradation factor (c) are the two important aspects that most impact the gate to source voltage at ZTC (VZTC). Although the ZTC behavior of the GAA-NS nMOS devices studied in this paper is well described by the simple analytical ZTC model in linear region, at high drain bias, factors such as series resistance and carrier saturation velocity play a significant influence in the ZTC performance of GAA-NS nMOS devices examined in this study.

Exploring the efficiency limiting parameters trade-off at rear surface in passivated emitter rear contact (PERC) silicon solar cells

In recent years, there is a growing interest in reducing the various losses occurring at the rear surface of passivated emitter and rear contact (PERC) silicon solar cells through process optimization including chemical polishing, dielectric passivation and contact geometry etc. to realize the possible improvements in power conversion efficiency. In this contribution, a detailed investigation on recombination and resistive losses at rear surface of PERC solar cells using advanced imaging techniques for spatial distribution and allied characterization approaches are performed for better understanding of loss mechanisms and possible routes for their mitigation. Our analysis identifies that spreading resistance (Rspr) and reverse saturation current density due to first diode (J01) are the two key parameters in quantifying the efficiency improvement in PERC solar cells. For rear dielectric opening of 45 μm, optimized circular contact geometry was found to exhibit lower Rspr, as well as J01, when compared with the linear scheme. Our calculation also suggests an additional possible improvement of absolute 1.29% in power conversion efficiency through appropriate selection of starting wafer resistivity and improved passivation uniformity across the solar cell area.

Indirect Measurements of Acceleration Atelectasis and the Role of Inspired Oxygen Concentrations.

BACKGROUND: A growing number of symptom reports suggestive of acceleration atelectasis in fast jet aircrew have raised the question as to whether traditional guidelines on inspired gas composition remain valid. The aim of this study was to assess the effects of inspired O₂ concentration on the development of acceleration atelectasis when wearing modern anti-G garments. METHODS: There were 14 nonaircrew subjects who completed 5 centrifuge exposures to +5 Gz lasting 90 s. During exposures subjects breathed a gas mixture containing 21, 35, 45, 60, or 75% O₂. To assess the extent of atelectasis post-Gz, forced inspiratory vital capacity (FIVC), regional FIVC (EITFIVC), shunt, respiratory resistance, reactance, and compliance and peripheral O₂ saturation during a hypoxic exposure were measured. RESULTS: Compared with baseline, FIVC was not statistically significantly altered. EITFIVC was 14.4% lower after the 75% O₂ exposure only with a greater symptom reporting with higher FIO₂ in some individuals. A significantly greater shunt (3>6%) followed the 60 and 75% O₂ exposures. O₂ concentration during Gz had no effect on respiratory resistance, reactance, compliance, or hypoxemia. DISCUSSION: There is evidence of mild acceleration atelectasis present when breathing 60% O₂, particularly in susceptible individuals, with 75% O₂ causing more obvious physiological compromise. An inspired oxygen concentration of <60% will prevent the majority of individuals from developing acceleration atelectasis. Pollock RD, Gates SD, Radcliffe JJ, Stevenson AT. Indirect measurements of acceleration atelectasis and the role of inspired oxygen concentrations. Aerosp Med Hum Perform. 2021; 92(10):780785.

Li2CaSi2N4:Sm3+: A nitride-based red phosphor with excellent temperature sensitivity and cathodoluminescence for temperature sensor and FED

Temperature sensor and field emission displays (FED) are the intensive topics for Sm3+ activated red phosphor. In this study, a novel lithium nitride red phosphor Li2CaSi2N4:Sm3+ was successfully prepared by solid phase method. The photoluminescence and cathodoluminescence performances were systematically studied to explore the possibility in FED and temperature sensor applications. The results indicate that the Li2CaSi2N4:Sm3+ phosphor features intense red emission under the UV light and cathode ray excitations. The phosphor also has a long red afterglow with an afterglow time of 12.7 min. Most importantly, Li2CaSi2N4:Sm3+ exhibits excellent temperature sensitivity with the relative sensitivity of 4.8% K−1 @473 K, which is higher than other temperature sensor materials. The thermal quenching mechanism was proposed based on a configurational-coordinate model. Moreover, excellent cathode ray saturation and aging resistance were observed in Li2CaSi2N4:Sm3+. The results indicate that Li2CaSi2N4:Sm3+ is a potential temperature sensor and FED materials.

Strongly correlated electrons in the ferroelectric metal LiOsO3

The metallic $\mathrm{LiOs}{\mathrm{O}}_{3}$ undergoes a transition to a polar phase below ${T}_{s}\ensuremath{\approx}140\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This unusual property provides a unique opportunity to study the interaction between free electrons and electric dipoles. We report a suite of measurements of physical properties in $\mathrm{LiOs}{\mathrm{O}}_{3}$ as a function of temperature, including resistivity and magnetoresistance down to 0.16 K, thermoelectric power, high-precision magnetization, specific heat, and thermal conductivity on textured single-crystal samples. Enhancements from the electron contribution to the specific heat and the paramagnetic susceptibility indicate that electrons in $\mathrm{LiOs}{\mathrm{O}}_{3}$ are highly correlated. An anomalously large Kadowaki-Woods ratio also supports the argument of strongly correlated electrons in $\mathrm{LiOs}{\mathrm{O}}_{3}$. In the nonpolar phase above ${T}_{s}$, electrons are coupled strongly to the lattice vibrations, which leads to the resistivity saturation at high temperatures and eventually a crossover to the hopping conduction. The data of thermal conductivity and specific heat are consistent with an order-disorder transition at ${T}_{s}$. The analysis of critical behavior in the resistivity, specific heat, and the thermal conductivity provides useful information for understanding the electron-dipole interaction in $\mathrm{LiOs}{\mathrm{O}}_{3}$.

Extrinsic and Intrinsic Anomalous Metallic States in Transition Metal Dichalcogenide Ising Superconductors.

The metallic ground state in two-dimensional (2D) superconductors has attracted much attention but is still under intense scrutiny. Especially, the measurements in the ultralow temperature region are challenging for 2D superconductors due to the sensitivity to external perturbations. In this work, the resistance saturation induced by external noise, named as the "extrinsic anomalous metallic state", is observed in 2D transition metal dichalcogenide (TMD) superconductor 4Ha-TaSe2 nanodevices. However, with further decreasing temperature, credible evidence of the intrinsic anomalous metallic state is obtained by adequately filtering external radiation. Our work indicates that, at ultralow temperatures, the anomalous metallic state can be experimentally revealed as the quantum ground state in 2D crystalline TMD superconductors. Besides, Ising superconductivity revealed by ultrahigh in-plane critical field (Bc2∥) going beyond the Pauli paramagnetic limit (Bp) is detected in 4Ha-TaSe2, from the one-unit-cell device to the bulk situation, which might be due to the weak coupling between the TaSe2 submonolayers.

Influence of geological reservoir heterogeneity on exploitation conditions of Garadagh field / underground gas storage (Azerbaijan)

Underground oil and gas reservoirs (formations) are characterized by spatial variability of their structure, material composition and petrophysical properties of its constituent rocks: particle size distribution, porosity, permeability, structure and texture of the pore space, carbonate content, electrical resistivity, oil and water saturation and other properties. When assessing development and exploitation conditions for underground gas storages, created in depleted underground oil and gas reservoirs, the inherited nature of the reservoir development should be taken into account. Therefore, identifying the features of variations in well productivity is a crucial task, solution of which can contribute to the creation of more efficient system for underground gas storage exploitation. The paper presents the findings of comparative analysis of spatial variations in well productivity during the exploitation of the Garadagh underground gas storage (Azerbaijan), created in the depleted gas condensate reservoir. An uneven nature of the variations in well productivity was established, which was connected with the reservoir heterogeneity (variations in the reservoir lithological composition and poroperm properties). The research was based on the analysis of spatial variations of a number of reservoir parameters: the reservoir net thickness, lithological composition and poroperm properties. The analysis of variations in the net thickness and poroperm properties of the VII horizon of the Garadagh gas condensate field was carried out based on the data of geophysical logging of about 40 wells and studying more than 90 core samples. The data on of more than 90 wells formed the basis for the spacial productivity variation analysis. The analysis of productivity variation in the space of well technological characteristics (based on data from 18 wells) in the Garadagh underground gas storage (UGS) was carried out through the example of the volume of cyclic gas injection and withdrawal in 2020–2021 season. The studies allowed revealing non-uniform spacial variations in the volumes of injected and withdrawn gas at the Garadagh UGS, created in the corresponding depleted gas condensate reservoir. The features of the UGS exploitation conditions are in good agreement with the features of the reservoir development conditions (variations in the well productivity). The inherited nature of the reservoir development and the underground gas storage exploitation is substantiated by the reservoir heterogeneity caused by the spatial variability of the reservoir lithological composition and poroperm properties. Assessing and taking into account the reservoir heterogeneity when designing underground gas storage exploitation conditions should be an important prerequisite for increasing UGS exploitation efficiency.

Evaluation of micro-structural and magnetic properties of nickel nano-ferrite and Mn2+ substituted nickel nano-ferrite

The spinel ferrites have remarkable applications in electronic technology owing to their elevated saturation magnetization, steadiness, resistivity and little loss energy over a broad array of frequencies. The features with respect to structure and magnetism of manganese doped NiFe2O4 nano ferrite are extensively probed. The lattice parameter value and volume of unit cell rises with manganese substitution. The cation distribution indicates that the Ni2+ ions inhabit B-sites and Mn2+ ions dwell in tetrahedral A-spot and the Mn2+ ions swap Ni2+ from tetrahedral spot. The saturation magnetization and magnetic moment of the NiFe2O4 is lower than the manganese substituted ferrite. Spectra pertaining to electron spin resonance exhibit a lone signal wide enough showing the occurrence of Fe3+, Ni2+ and Mn2+ ions with a 'g' approximately equal to 2.00.

Maintaining oxygen delivery is crucial to prevent intestinal ischemia in critical ill patients.

Intestinal ischemia is a common complication with obscure pathophysiology in critically ill patients. Since insufficient delivery of oxygen is discussed, we investigated the influence of oxygen delivery, hemoglobin, arterial oxygen saturation, cardiac index and the systemic vascular resistance index on the development of intestinal ischemia. Furthermore, we evaluated the predictive power of elevated lactate levels for the diagnosis of intestinal ischemia. In a retrospective case-control study data (mean oxygen delivery, minimum oxygen delivery, systemic vascular resistance index) of critical ill patients from 02/2009-07/2017 were analyzed using a proportional hazard model. General model fit and linearity were tested by likelihood ratio tests. The components of oxygen delivery (hemoglobin, arterial oxygen saturation and cardiac index) were individually tested in models. 59 out of 874 patients developed intestinal ischemia. A mean oxygen delivery less than 250ml/min/m2 (LRT vs. null model: p = 0.018; LRT for non-linearity: p = 0.012) as well as a minimum oxygen delivery less than 400ml/min/m2 (LRT vs null model: p = 0.016; LRT for linearity: p = 0.019) were associated with increased risk of the development of intestinal ischemia. We found no significant influence of hemoglobin, arterial oxygen saturation, cardiac index or systemic vascular resistance index. Receiver operating characteristics analysis for elevated lactate levels, pH, CO2 and central venous saturation was poor with an area under the receiver operating characteristic of 0.5324, 0.52, 0.6017 and 0.6786. There was a significant correlation for mean and minimum oxygen delivery with the incidence of intestinal ischemia for values below 250ml/min/m2 respectively 400ml/min/m2. Neither hemoglobin, arterial oxygen saturation, cardiac index, systemic vascular resistance index nor elevated lactate levels could be identified as individual risk factors.

Multiscale evaluation of a thin-bed reservoir

A thin-bed laminated shaly-sand reservoir of the Miocene formation was evaluated using two methods: high resolution microresistivity data from the XRMI tool and conventional well logs. Based on high resolution data, the Earth model of the reservoir was defined in a way that allowed the analyzed interval to be subdivided into thin layers of sandstones, mudstones, and claystones. Theoretical logs of gamma ray, bulk density, horizontal and vertical resistivity were calculated based on the forward modeling method to describe the petrophysical properties of individual beds and calculate the clay volume, porosity, and water saturation. The relationships amongst the contents of minerals were established based on the XRD data from the neighboring wells; hence, the high-resolution lithological model was evaluated. Predicted curves and estimated volumes of minerals were used as an input in multimineral solver and based on the assumed petrophysical model the input data were recalculated, reconstructed and compared with the predicted curves. The volumes of minerals and input curves were adjusted during several runs to minimalize the error between predicted and recalculated variables. Another approach was based on electrofacies modeling using unsupervised self-organizing maps. As an input, conventional well logs were used. Then, the evaluated facies model was used during forward modeling of the effective porosity, horizontal resistivity and water saturation. The obtained results were compared and, finally, the effective thickness of the reservoir was established based on the results from the two methods.

Robust anomalous metallic states and vestiges of self-duality in two-dimensional granular In-InOx composites

Many experiments investigating magnetic-field tuned superconductor-insulator transition (H-SIT) often exhibit low-temperature resistance saturation, which is interpreted as an anomalous metallic phase emerging from a ‘failed superconductor’, thus challenging conventional theory. Here we study a random granular array of indium islands grown on a gateable layer of indium-oxide. By tuning the intergrain couplings, we reveal a wide range of magnetic fields where resistance saturation is observed, under conditions of careful electromagnetic filtering and within a wide range of linear response. Exposure to external broadband noise or microwave radiation is shown to strengthen the tendency of superconductivity, where at low field a global superconducting phase is restored. Increasing magnetic field unveils an ‘avoided H-SIT’ that exhibits granularity-induced logarithmic divergence of the resistance/conductance above/below that transition, pointing to possible vestiges of the original emergent duality observed in a true H-SIT. We conclude that anomalous metallic phase is intimately associated with inherent inhomogeneities, exhibiting robust behavior at attainable temperatures for strongly granular two-dimensional systems.

Correlation between weak localization effects and resistivity saturation in dilute Ti-Al alloys

Resistivity saturation in Ti-Al alloys has been studied by fitting empirical functions of temperature, T, to 20 sets of literature data. By replacing the commonly used temperature-independent saturation term by a term in T−1/2, to model weak localization effects at high temperature, the quality of the fits improved significantly and physically acceptable values were obtained for the fitted parameters. A linear correlation was found between the fitted high-T weak localization parameters and experimental data for the corresponding low-T weak localization conduction terms. No such correlation could be detected when using constant saturation terms. The results suggest that weak localization is a possible cause for resistivity saturation in Ti-Al alloys.

Synthesis and characterization of natural zeolite-clay as resistive humidity detection

Zeolite-clay was successfully employed in as resistance type humidity sensor. Zeolite-clay humidity sensor was synthesized by crushing into powder and soaked into 6% H2SO4while stirred for two hours using a magnetic stirrer. The solution was filtered, washed using aquadest and dried at 100°C for 5 hours with the mixture process of zeolite and clay were varied into 10%:0%, 9.5%:0.5%, 9%:1%, 8.5%:1.5%, and 8%:2%. The result pressed with a size of 3x3x1 cm3 using a hydraulic under 3 tons pressure for 10 minutes and heated at temperatures of 800°C.Zeolite-clay was placed in a testing chamber equipped with the electrode that connected to an electrical supply of 3 Volt. The electrical resistance was recorded using Multimeter Hydra Series III Fluke when exposed with humidity in range of 18.5-99% RH. Zeolite 8%-clay 2% sensor exhibits the highest sensitivity properties, which indicate saturated resistance value at 99% RH.Meanwhile, Zeolite 8.5 gr-clay 1.5 gr revealed the highest response value at 54.3 Mega Ohm. Based on SEM and EDX characterization, the ratio of Si/Al and microstructure surface have an effect towards humidity detection process. The results indicate enhancement than previous research on zeolite as a sensor, and therefore Zeolite-Clay has proved the capability to detect humidity.

Oxygen migration induced effective magnetic and resistive switching boosted by graphene quantum dots

Graphene materials have attracted considerable research interest owing to their applications in memristor and prospective spintronic devices. In this work, the bifunctional resistive and magnetic switching effect is investigated in Ag/graphene quantum dots (GQDs): graphene oxide (GO)/ITO device: (1) In the low-resistance state, the conductive filaments are formed by oxygen migration away inducing the C–C sp2 groups. (2) In the high-resistance state, the directions of magnetic moment align by increasing the C–O sp3 group. The resistive switching ratios and saturation magnetization of GQDs memristor are shown to be approximately 20 and 2.2 times higher than that of GQDs-free memristor, respectively. Tunable magnetic switching makes GO-based memristive devices boosted by GQDs a promising candidate to future voltage-controlled, low-power, and high-density spintronics devices.

Resistivity saturation in an electron-doped cuprate

We report the observation of resistivity saturation in lightly doped ($x\sim 0.10)$ as-grown samples of the electron-doped cuprate La$_{2-x}$Ce$_x$CuO$_4$ (LCCO). The saturation occurs at resistivity values roughly consistent with the phenomenological Mott-Ioffe-Regel criterion once the low effective carrier density of these materials is included in the analysis. These results imply that, at least for light doping, the high-temperature metallic phase of these materials is not necessarily strange and may be understood as simply a low-density metal.

Simulations of the Performance of Maximum Power Point Tracking Algorithms Based on Experimental Data According to the Topologies of DC-DC Converters

Maximum Power Point Tracking (MPPT) algorithms are now widely used in PV systems independently of the weather conditions. In function of the application, a DC-DC converter topology is chosen without any previous performance test under normal weather conditions. This paper proposes an experimental evaluation of MPPT algorithms according to DC-DC converters topologies, under normal operation conditions. Four widely used MPPT algorithms i.e. Perturb and Observe (P & O), Hill Climbing (HC), Fixed step Increment of Conductance (INCF) and Variable step Increment of Conductance (INCV) are implemented using two topologies of DC-DC converters i.e. buck and boost converters. As input variables to the PV systems, recorded irradiance and temperature, and extracted photovoltaic parameters (ideality factor, series resistance and reverse saturation current) were used. The obtained results show that buck converter has a lot of power losses when controlled by each of the four MPPT algorithms. Meanwhile, boost converter presents a stable output power during the whole day. Once more, the results show that INCV algorithm has the best performance.

A New Method for Obtaining Irreductive Water Saturation and Other Parameters

The results show that the resistivity and water saturation data from a core obtained by core electrical experiments are power functions, which can reflect the conductivity characteristics of pore water in rock. Further research shows that when the resistivity data of power function shows a gentle change trend, it shows that the change of movable water pores affects the resistivity data, and when the resistivity data shows a drastic change trend, it shows that the irreducible water conductivity plays a leading role. Therefore, parameters such as irreducible water saturation and movable oil saturation can be determined from the morphological changes of the curve, just as the porosity lower limit of rocks can be determined. Compared with the irreducible water saturation data obtained by mercury injection and other data, a new method is proposed to determine the irreducible water saturation of a core by the cutoff value of slope of power function curve, and the movable oil saturation can be determined by the maximum curvature value of power function curve, which can further obtain the residual oil saturation. The preliminary application shows that the absolute error of irreducible water saturation and other parameters is within 5% and can be used in practice.

Preparation and Superior Absorbing of Electroless Deposited Ni-P-Fe3O4 Composite Powders

In this study, the Ni-P-Fe3O4 composite powders containing about 10% phosphorus were prepared by hydrothermal method. The phase, composition and morphology of the powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The wave absorption properties of the Ni-P-Fe3O4 composite powders were estimated by vector network analyzer (VNA). The results showed that the saturation magnetization and resistivity of the as-obtained Ni-P-Fe3O4 composite powders were significantly reduced, however their dispersion as well as conductivity were improved. The electromagnetic wave absorbed by Ni-P-Fe3O4 composite powders was mainly attributed to the dielectric loss, and the absorption of electromagnetic wave in the low frequency can reach to 90% (the reflection loss is less than -10 dB).

Premedication with intravenous midazolam for neonatal endotracheal intubation: A double blind randomized controlled trial.

Background:Pain during the neonatal period has been associated with immediate and long-term adverse effects. One of the most frequent painful procedures that neonates face in neonatal intensive care unit is the endotracheal intubation. Midazolam has been a candidate for premedication before neonatal intubation. Our aim was to evaluate the effects of midazolam as the premedication on endotracheal intubation of premature infants during surfactant administration.Materials and Methods:In a double-blind clinical trial, 80 preterm infants were undertaken for tracheal intubation following the use of atropine associated to either midazolam or placebo. Patient's vital signs and general conditions were constantly monitored, and pain was assessed using premature infant pain profile (PIPP) score.Results:The mean ± standard deviation for postnatal age was 95.38 ± 50.04 and 111.63 ± 49.4 min in control and midazolam groups, respectively. The patients in the midazolam group had significantly better outcomes across several intubation outcome measures such as duration of endotracheal intubation (23.5 ± 6.7 vs. 18.8 ± 4.8 s, P = 0.001), oxygen saturation level (88.05% ±13.7 vs. 95.1 ± 1.8%, P = 0.002), intubation failure (34.2% vs. 2.5%, P = 0.0001), awake and resistance during intubation (95% vs. 20%, P = 0.0001), and excellent patient condition during intubation (0% vs. 82.5%, P = 0.0001). In addition, PIPP score was significantly lower in the midazolam group (5.2 ± 2.06 vs. 12.9 ± 2.9, P = 0.0001).Conclusion:Premedication with midazolam in newborns before intubation, can hold promising effects that manifests as better overall outcomes, less complications, better vital signs, more comfortable situation, and lesser pain for these patients.