Current Flow Characteristics Research Articles

Detection Performance and Grading-Selection-Based Inversion of Low-Frequency Alternating Current Resistivity Logging in Moderate-High Resistance Formations

Summary With the development of high-angle/horizontal well technology, unconventional tight reservoirs with moderate/high resistivity have gradually become the focus of exploration and development. However, in moderate-high-resistance reservoir environments, distorted responses can be observed regularly in the array laterolog curves, which will lead to misjudgment for the oil-gas reservoirs. Therefore, the detection performance of the array lateral instrument powered by low-frequency alternating current urgently needs to be clarified and the true resistivity of the formation is necessary to be analyzed and extracted. In this paper, the reasons for distorted responses are investigated as well as the qualitative and quantitative assessments of the detection performance of low-frequency alternating current lateral instrument in moderate-high resistance formations. Moreover, a rapid inversion method is proposed based on the initial value grading optimization strategy to invert the anisotropic resistivities from the observed data with outliers. Numerical simulation results show that the current flow characteristics vary significantly across stratigraphic models and the distorted responses are primarily caused by the high-resistance characteristics and borehole enlargement. The combination of the initial value grading optimization strategy and the regularization inversion algorithm improves the accuracy of the inverted resistivities even further. Synthetic and field examples are analyzed to illustrate the detailed implementations and the performance of the proposed inversion method.

Toward Simultaneous Achievement of Outstanding Durability and Photoelectrochemical Reaction in Cu2O Photocathodes via Electrochemically Designed Resistive Switching

AbstractPhotoelectrochemical (PEC) cells using Cu2O, semiconductor photoabsorbers passivated by protection layers, show a trade‐off between high photocurrent and stability because of the thickness of the energy band transport along the conduction band. Based on nanofilaments with non‐volatile metal‐like current flow characteristics in resistance‐change memory devices, a strategically advanced conducting filament transport mechanism for vigorous and robust PEC operation is proposed. The breakdown‐like electrochemical forming behavior effectively occurs with a rapid increase in current at ≈2 V (vs RHE). The fundamental properties of filaments, such as diameter, density, and conductivity, are controlled by varying the artificial compliance currents. This process does not require any top electrodes that obstruct light‐harvesting and the injection of photo‐charges into electrolytes or individual forming process with point‐by‐point sweeping, and provides electrochemical forming sites with homogeneous and dense distribution. Additionally, some photocorrosive sites that induce photocurrent degradation are passivated by the preferential photoelectrodeposition of co‐catalysts. From the electrochemical filament forming process and selective Pt‐photoelectrodeposition on filaments, the Cu2O/AZO/TiO2 photocathodes exhibit an unprecedented photocurrent density of ≈11.9 mA cm−2 and open‐circuit potential of 0.73 V and produce vigorous hydrogen and oxygen evolutions for over 100 h, even when the TiO2 passivation film exceeds 100 nm in thickness.

Distribution, characteristics, and processes of formation of sediment waves along the Indian north-eastern continental margin

Muddy, upslope-migrating sediment waves, with their crestal lines parallel to the bathymetric contours, are the dominant geomorphic elements in the entire lower slope along the Indian north-eastern continental margin. Wave dimensions are maximum with high but differing degrees of sediment accretions on the upslope and downslope sides of wave crests and with most upslope wave migrations in the northeastern part of the study area, having relatively low seafloor gradients. The wave dimensions decrease with lower as well as differing degrees of sediment accretions on both sides of wave crests and with lower upslope wave migrations in the southwestern parts of the study area, having steeper seafloor gradients. Within each area of the lower slope, starting from updip, wave dimensions increase to their maximum at some distance downdip with optimal low seafloor gradients. Farther downdip, the wave dimensions decrease even with lower seafloor gradients continuing. Also, within each area, at the base of the wave intervals, the waves are small and grow into larger features with more sediment accretions in the upper intervals.The distribution and characteristics of sediment waves observed along the Indian margin are indicative of deposition by down-slope moving, unconfined turbidity currents that have evolved from other sediment gravity flows derived from several point sources updip. Along-slope bottom currents are least likely agents of wave deposition here. We interpret that the spatial and temporal variations in wave dimensions are due to the variations in seafloor gradients, turbidity current flow characteristics, frequency, duration and total number of flow events in space and time.

Safety precautions for swimmers - A frequent whirlpool appearance at Pattaya Bay

Water current flow characteristics represent crucial information required for the management of coastal tourism destinations. Strong currents or strange flow patterns can pose risks to beach visitors. This research examined the currents at Pattaya Bay, one of the most famous beaches in the world. Numerical simulations were undertaken. Sophisticated simulation techniques were applied so that the calibrated simulation results were reliable. A whirlpool at the southern part of the bay was discovered, occurring every day during flood tides. The vortex rotated clockwise, with a magnitude between 0.34 and 0.41 m/s, and its radius could sometimes reach 500 m. The swirl was a natural phenomenon since it was created by the oblique orientation of the southern headland. The whirlpool was not deadly since its strength was normal for open coastal waters. However, care should not be neglected. This research raised awareness about the whirlpool's existence, so that proper management can be exercised.

Analysis of Droplet Generation in Electrospray Using a Carbon Fiber Based Microfluidic Emitter

This work presents simulation of jet break up in electrospray ionization using a microfluidic emitter. The emitter comprises a pointed carbon fiber located coaxial with a fused silica capillary of 360 microns OD and 75 microns ID, with its sharp tip extending 30 microns beyond the capillary terminus. The numerical model employs leaky-dielectric formulations for solving the electrodynamics and volume-of-fluid method for tracking the liquid-air interface. The existing leaky-dielectric model is modified to account for the presence of free charges inside the bulk of the liquid as well as at the interface. A small velocity perturbation is used at the capillary inlet to emulate the natural disturbance necessary for the jet break up. First, the model is validated by comparing model predictions with experimental results for a conventional emitter reported in literature. Then, it is applied to simulate the electrospray performance of the Carbon Fiber (CF) emitter including the Taylor cone and jet break up processes. Model predictions for CF emitter are compared with experimental results in terms of jet-length and current-flow characteristics. The influence of emitter geometry, operating conditions and liquid properties on the electrospray performance are investigated. Droplet diameter is correlated with flow rate and liquid properties and the correlation results are compared with that reported in literature.

A description of Ca2+ channels in human detrusor smooth muscle.

To characterize the Ca2+ channels in human detrusor smooth muscle and to investigate their contribution to spontaneous electrical activity. Isolated human detrusor smooth muscle myocytes were used to measure ionic currents under voltage-clamp or membrane potential under current-clamp. Membrane potential oscillations were analysed in terms of oscillation frequency and amplitude using fast Fourier transforms. Under voltage-clamp an inward current dependent on extracellular Ca2+ was recorded using Cs+-filled patch electrodes. The current could be separated into two components on the basis of their sensitivity to Ni2+, verapamil or nicardipine, and their dependence on holding and clamp potential. A Ni2+-sensitive component activated over a relatively negative range of potentials (-60 to -20 mV) comprised about a third of the total current and was designated a T-type Ca2+ current. A verapamil/nicardipine-sensitive component, activated at more positive potentials, was designated an l-type Ca2+ current. Using K+-based filling solutions spontaneous transient outward currents were recorded that had the characteristics of current flow through BK channels. Membrane potential oscillations, under current-clamp increased in frequency but not amplitude as the mean membrane potential was made less negative. The voltage-dependence of oscillation frequency was similar to that of the l-type, but not T-type, Ca2+ current activation curve. Furthermore oscillation frequency was slowed by verapamil but not Ni2+. The study showed, for the first time, the presence of both T- and L-type Ca2+ channels in human detrusor smooth muscle; we propose a role for these channels in spontaneous activity. The results suggest that the L-type Ca2+ current can control membrane potential oscillation frequency. The significance of this finding for spontaneous contractions is discussed.

Initiation and evolution of turbidity current sediment waves in the Magdalena turbidite system

This study describes an extensive sediment–wave field in the Magdalena Turbidite System, Caribbean Sea, Colombia, which occupies an area of at least 15 000 km2 on the continental slope (3330–>3800 m). The waves display wavelengths up to 1.9 km, wave heights up to 18 m, and crestlines that are aligned roughly parallel to the regional bathymetric contours. Preferential deposition on the upslope wave flank has led to upslope migration, in the manner of antidunes. The Magdalena sediment waves are interpreted as forming beneath unconfined turbidity currents, which may result from the downslope evolution of slumps and mass flows. The unconfined turbidity currents are derived from several point sources along the continental slope and spread laterally as they flow downslope. This has led to the formation of a laterally extensive sediment–wave field. Simple numerical modelling estimates that the turbidity currents responsible for wave generation were near- or super-critical, with flow thickness and velocity estimated at 40–160 m, and 36–82 cm s−1 respectively. However, later phases of wave growth were not dependent on specific flow conditions. The most important aspect of this study is that the entire sediment–wave unit, from the basal boundary to the present-day seafloor, has been investigated using ultra high-resolution seismic profiles. The sediment–wave unit rests upon an irregular discontinuity that marks a recent change in the sedimentary regime of the Magdalena Turbidite System, from channelised to unchannelised gravity flows. Above this boundary, the sediment waves display a growth pattern characterised by an increase in wave dimensions. In addition, the wave dimensions appear to become more regular through time. However, breaks of slope in the lower bounding surface of the wave field have produced variations in wave morphology that are still visible at the present-day seafloor. This indicates that there is a close relationship between variations in slope angle and turbidity current flow characteristics, which in turn leads to variations in wave morphology.

Turbidity current sediment waves on irregular slopes: observations from the Orinoco sediment–wave field

The Orinoco sediment–wave field covers an area of at least 29 000 km2 on the southern margin of the Orinoco Valley, at a water depth of 4400–4825 m. Wave dimensions are highly variable across the wave field, with wavelengths of 110–2600 m, and wave heights of 1–15 m. Slope gradients are also very variable, with values of 0.14–0.48°. Overall, the sedimentary sequence on the upslope wave flanks is about 40% thicker than that on the downslope flanks, leading to upslope wave migration in the manner of antidunes. In addition, reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks, suggesting that a higher proportion of coarser sediment occurs on the upslope flank. An unconfined turbidity current origin is proposed for the Orinoco sediment waves, based upon detailed analysis of regional stratigraphic/seismic facies, and sediment wave distribution, morphology and dimensions. Sediment waves are not related to flows passing along (or spilling out of) the Orinoco Valley, or to bottom currents flowing parallel to the slope. Turbidity currents responsible for wave generation are interpreted as originating from slope failures on the adjacent Venezuela, Guyana and Suriname continental margins. Simple numerical modelling has enabled turbidity current flow characteristics across the Orinoco sediment waves to be estimated: internal Froude number=0.7–1.1, flow thickness=24–645 m, and flow velocity=31–82 cm s−1. A key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in wave dimensions across the wave field. The irregular gradient of the present-day wave field is partly a reflection of the irregular bounding surface of the sediment waves, which is represented by mass-flow deposits and associated mud diapirs. The changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents, which in turn control the wave dimensions. Generally, on lower gradients beyond minor breaks of slope, flow thickness increases and flow velocity decreases, leading to an increase in wavelength and a decrease in height.

On the multifrequency method of the range dependent transversal current monitoring

Transverse flow of inhomogeneous current produces fluctuations of the acoustic signal passing through it. These fluctuations vary with the signal frequency due to the variation of the Fresnel zone size. Respectively, fluctuations of signals at two different frequencies are coherent in a low-frequency range of the spectrum and noncoherent in the high-frequency band when ocean inhomogeneities are smaller than the transverse size of the Fresnel zone. The frequency cutoff of the coherence function of signals at different frequencies depends on current flow characteristics. Di Iorio and Farmer [J. Acoust. Soc. Am. 100, 814–834 (1996)] describe high-frequency acoustic scintillation measurements in a tidally forced flow through a Cordova Channel specifically designed to characterize the two-dimensional angle of arrival fluctuations in terms of the mean and turbulent properties of sound speed and current. We present new results from this data set which was collected in an alternating dual frequency mode. The multifrequency technique gives results which are consistent with previous results, but eventually will allow the measurement of current profiles across the channel.

The addressing characteristics of an alternating current plasma display panel adopting a ramping reset pulse

The characteristics of the address discharge of an alternating current plasma display panel (ac PDP) adopting a ramping reset pulse were studied using two-dimensional (2-D) numerical simulation. We investigated the principal parameters of the reset pulse for a successful address discharge. In this paper, we suggest a new parameter, the terminal voltage of the ramping reset pulse, and its effects on the minimum address voltage and current flow characteristics during the address discharge. The minimum addressing voltage decreased with increase in the ramping-down time and with increase in the terminal voltage of the ramping reset pulse, which were explained with the wall charge characteristics obtained by a 2-D simulation and confirmed through an ac PDP experiment.

Characteristics of current flow in composites made from a high-temperature superconductor and the low-temperature superconducting metal oxide Ba(PbBi)O3

Composites are prepared from a high-temperature superconductor with the 1-2-3 structure and the low-temperature oxide BaPb3/4Bi1/4O3 with various volume concentrations of the high-temperature and low-temperature superconductors. The temperature dependences of the electrical resistivities and critical current densities of the composites are measured. It is shown experimentally that these composites comprise a synthetically created network of Josephson weak links (with a specified degree of coupling).

Electromechanics and fluidization characteristics of co-flow type electrofluidized beds

Experimental study of fluidization and current flow characteristics was conducted. The result shows that the pressure overshoot at the incipient fluidization under electric field was slightly influenced by applied electric potential, while a significant influence on the minimum fluidization velocity was observed. The process of the initiating fluidization was also analyzed through axial pressure drop profiles.

A study on the current density distribution in the circular contact surface

The distribution of the current density in the circular contact surface between two conducting semi-infinite bodies is theoretically analyzed. The current flow characteristics in the contact surface are simulated by solving a set of simultaneous equations derived from an analogy to the electrostatic charge distribution problem. The current density distribution is measured for uniform size of microcontacts by using enamel-coated copper wires and electrolyte, and the experimental results are compared with the calculated current density for various densities of the microcontact. It is revealed that the experimental and theoretical results are in good agreement. By using the proposed theoretical model the current density can be calculated also for circular contacts with arbitrary size and distribution of microcontacts, if the size and distribution of microcontacts are given from experimental or theoretical studies. Therefore, the proposed model can be used effectively to determine the current density distribution in the circular-shaped contact surface with multiple microcontacts.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrical conduction through thermal and anodic oxides of InSb

The characteristics of current flow through thermally and anodically grown oxides of vapor deposited and bulk InSb are reported. The magnitude of the current though the thermal and anodic oxides are found to be markedly different. The thermally grown oxides have very low resistance similar to In2O3. The anodic oxides are insulating and the current flow is characteristic of Schottky emission. The anodic oxides grown on bulk single crystals (BSC) and on thin films deposited at 150° and 350°C have essentially the same current−voltage characteristics. The breakdown strength of the BSC oxides is approximately 50% greater than of the thin film oxides.

Rectification by Anodic Oxide Films on Zirconium

The electrical conduction characteristics of anodic oxide films on zirconium were studied using evaporated metal and aqueous electrolyte contacts. All the films tested showed electrolytic rectification. In the dry systems rectification was not observed, but asymmetry in conduction was pronounced in the case of films grown in the nitric acid solution. Capacitance measurements under an applied d‐c bias provided no positive evidence for the presence of a p‐n junction either in the bulk oxide or at the oxide‐electrolyte boundary. The conduction characteristics were influenced by the anodizing electrolyte used: (i) the relatively flaw‐free films grown in gave nonohmic but nearly symmetrical I–V curves; (ii) a porous and hydrated oxide film, essentially monoclinic zirconia, grown in resulted in asymmetric conduction; and (iii) phosphate ion incorporation in oxides grown in a solution containing phosphoric acid led to space charge limited current flow characteristics.