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We develop a novel ‘moving-capacitor’ dynamic network model to simulate immiscible fluid–fluid displacement in porous media. Traditional network models approximate the pore geometry as a network of fixed resistors, directly analogous to an electrical circuit. Our model additionally captures the motion of individual fluid–fluid interfaces through the pore geometry by completing this analogy, representing interfaces as a set of moving capacitors. By incorporating pore-scale invasion events, the model reproduces, for the first time, both the displacement pattern and the injection-pressure signal under a wide range of capillary numbers and substrate wettabilities. We show that at high capillary numbers the invading patterns advance symmetrically through viscous fingers. In contrast, at low capillary numbers the flow is governed by the wettability-dependent fluid–fluid interactions with the pore structure. The signature of the transition between the two regimes manifests itself in the fluctuations of the injection-pressure signal.

Carbon film resistors have the characteristics of high precision, wide resistance range, high voltage rating, good stability, negative temperature coefficient of resistance, good high-frequency characteristics, and good pulse load capability, and have a wide range of applications. In this research, experimental research was conducted on the electrical conductivity and influencing factors of carbon film resistors, providing a scientific basis for optimizing the preparation process of carbon film and improving its conductivity performance. In addition, the resistance value of carbon film resistors is greatly affected by temperature. Leveraging the negative temperature coefficient of resistance characteristic of carbon film resistors, they are widely used in temperature measurement.

This paper studies the relationship between the value of temperature variation and the resistance value of each type of general resistors as well as also determines the temperature coefficient value of each resistor type. All obtained results will be compared to build a guideline for selecting the resistor to apply in any applications accurately and properly. Each type of 1 k-ohm resistor that has different power is used to study its properties and is controlled its temperature variation to be in range of 20 to 30 degree Celsius. An experimental setup to control the temperature variation of the resistors in this paper is that the resistors are put into an oil bath controlled its temperature after that measuring the changed resistance value of the resistors following oil temperature in the bath. The experimental result demonstrates that the temperature variation affects to change the resistance value of Carbon Film type the most but affects to change the resistance value of Wire Wound type with low power the least.

Temperature gradient is an important performance indicator of a stirred liquid bath. Its evaluation requires measuring the temperature differences between different bath positions. A common way to do that is to place two SPRTs at two positions and measure their resistances against a standard resistor ( R SPRT1 / R S and R SPRT2 / R S ) sequentially (the sequential method). A drawback of this method is the existence of a time gap between the two measurements rendering the results susceptible to temporal temperature variation. The instantaneous comparisons method offers a better solution by measuring the resistance ratio of two SPRTs directly ( R SPRT1 / R SPRT2 ) and deriving their temperature difference at the same moment eliminating the time gap. To implement this method at the Standards and Calibration Laboratory (SCL) of Hong Kong, the resistance ratio of SPRT1 to a standard resistor ( R SPRT1 / R s ) is firstly measured to determine the initial bath temperature. After that, the resistance ratios of SPRT1 to SPRT2 ( R SPRT1 / R SPRT2 ) are measured with the two SPRTs placed at different positions and immersion depths in the bath. This paper describes the derivation of the temperature difference from the SPRT resistance ratio using the ITS-90 reference equations and the estimation of the measurement uncertainties. The potential of reducing the uncertainties of measured temperature gradient by leveraging the correlation of the two SPRTs calibrated at the same set of temperature fixed points is discussed. The paper also compares the calibration results obtained by the instantaneous comparisons method and the sequential method.

Direct printing of functional inks is critical for applications in diverse areas including electrochemical energy storage, smart electronics and healthcare. However, the available printable ink formulations are far from ideal. Either surfactants/additives are typically involved or the ink concentration is low, which add complexity to the manufacturing and compromises the printing resolution. Here, we demonstrate two types of two-dimensional titanium carbide (Ti 3 C 2 T x ) MXene inks, aqueous and organic in the absence of any additive or binary-solvent systems, for extrusion printing and inkjet printing, respectively. We show examples of all-MXene-printed structures, such as micro-supercapacitors, conductive tracks and ohmic resistors on untreated plastic and paper substrates, with high printing resolution and spatial uniformity. The volumetric capacitance and energy density of the all-MXene-printed micro-supercapacitors are orders of magnitude greater than existing inkjet/extrusion-printed active materials. The versatile direct-ink-printing technique highlights the promise of additive-free MXene inks for scalable fabrication of easy-to-integrate components of printable electronics. Printing functional inks is attractive for applications in electrochemical energy storage and smart electronics, among others. Here the authors report highly concentrated, additive-free, aqueous and organic MXene-based inks that can be used for high-resolution extrusion and inkjet printing.

Neuromorphic perception systems inspired by biology have tremendous potential in efficiently processing multi-sensory signals from the physical world, but a highly efficient hardware element capable of sensing and encoding multiple physical signals is still lacking. Here, we report a spike-based neuromorphic perception system consisting of calibratable artificial sensory neurons based on epitaxial VO 2 , where the high crystalline quality of VO 2 leads to significantly improved cycle-to-cycle uniformity. A calibration resistor is introduced to optimize device-to-device consistency, and to adapt the VO 2 neuron to different sensors with varied resistance level, a scaling resistor is further incorporated, demonstrating cross-sensory neuromorphic perception component that can encode illuminance, temperature, pressure and curvature signals into spikes. These components are utilized to monitor the curvatures of fingers, thereby achieving hand gesture classification. This study addresses the fundamental cycle-to-cycle and device-to-device variation issues of sensory neurons, therefore promoting the construction of neuromorphic perception systems for e-skin and neurorobotics. A highly efficient hardware element capable of sensing and encoding multiple physical signals is still lacking. Here, the authors report a spike-based neuromorphic perception system consisting of tunable and highly uniform artificial sensory neurons based on epitaxial VO 2 capable of hand gesture classification.

Masks are an effective tool in combatting the spread of COVID-19, but some people still resist wearing them and mask-wearing behavior has not been experimentally studied in the United States. To understand the demographics of mask wearers and resistors, and the impact of mandates on mask-wearing behavior, we observed shoppers (n = 9935) entering retail stores during periods of June, July, and August 2020. Approximately 41% of the June sample wore a mask. At that time, the odds of an individual wearing a mask increased significantly with age and was also 1.5x greater for females than males. Additionally, the odds of observing a mask on an urban or suburban shopper were ~4x that for rural areas. Mask mandates enacted in late July and August increased mask-wearing compliance to over 90% in all groups, but a small percentage of resistors remained. Thus, gender, age, and location factor into whether shoppers in the United States wear a mask or face covering voluntarily. Additionally, mask mandates are necessary to increase mask wearing among the public to a level required to mitigate the spread of COVID-19.

The accumulation and extrusion of Ca 2+ in the pre- and postsynaptic compartments play a critical role in initiating plastic changes in biological synapses. To emulate this fundamental process in electronic devices, we developed diffusive Ag-in-oxide memristors with a temporal response during and after stimulation similar to that of the synaptic Ca 2+ dynamics. In situ high-resolution transmission electron microscopy and nanoparticle dynamics simulations both demonstrate that Ag atoms disperse under electrical bias and regroup spontaneously under zero bias because of interfacial energy minimization, closely resembling synaptic influx and extrusion of Ca 2+ , respectively. The diffusive memristor and its dynamics enable a direct emulation of both short- and long-term plasticity of biological synapses, representing an advance in hardware implementation of neuromorphic functionalities. Calcium ions play a vital role in enabling synaptic plasticity in biological systems. The dynamic behaviour of these ions has now been emulated in a metal atom diffusion-based memristor.

We study infinite resistor networks perturbed by line defects, in which the resistances are periodically modified along a single line. Using the Sherman–Morrison identity applied to the lattice Laplace operator, we develop a general analytical framework for computing the Green’s function and the equivalent resistance between arbitrary nodes. The resulting expression is a one-dimensional integral that is evaluated exactly in special cases. While our analysis is carried out for the square lattice, the method readily extends to other lattice geometries and networks with general impedances. Therefore, this framework is useful for studying the boundary behavior of topolectrical circuits, which serve as classical analogs of topological insulators.

As a new development direction of the domestic medium voltage distribution network, the flexible grounding method has a rapid expansion trend, and accordingly, the ground fault protection scheme needs to follow up quickly. This paper calculates and analyzes the distribution characteristics of transient electric quantities in the system under different fault conditions by establishing the transient equivalent model of shunt small resistor casting and cutting in the flexible grounding system. It is found that if transition resistance is small, the application of parallel small resistors will cause the transient zero sequence current amplitude of the faulty line to be maximum and have opposite polarity to the healthy line. When transition resistance is high, distribution characteristics of the transient zero sequence current projection component are also the same. Based on the above features, a flexible grounding system ground fault routing method is proposed, which can cope with a variety of ground fault situations in engineering practice with high reliability, and the correctness of the method is verified through simulation.