arXiv subjects

Jiatong Jiang

Publications and source records attributed to Jiatong Jiang.

2 recordsLinked to original sources

arXiv2026

A Portable Multichannel Kilohertz Current Stimulator for Selective Peripheral Transcutaneous Stimulation

We present SineStim, a portable, 12-channel current stimulator for transcutaneous spinal cord stimulation and peripheral electrical stimulation at kilohertz frequencies. Each channel delivers independent, current-controlled sinusoidal waveforms with amplitudes from 0 to 50 mA (0.1 mA resolution) and frequencies from 0 to 50 kHz (0.1 Hz resolution), with burst modulation modes supported. A custom output stage with a high compliance voltage of $\pm$ 120 V was designed and developed, with galvanically isolated channels and independently programmable stimulation parameters for each channel. The stimulator performance was tested on both passive loads and human subjects. Benchtop characterisation on resistive and resistive-capacitive loads demonstrated a total harmonic distortion between 1 - 8 % across typical operating conditions. Multichannel functionality was demonstrated in two-channel human forearm stimulation experiments. Burst-modulated waveforms with differing channel amplitudes modulated inter-finger force ratios, and channels with small frequency offsets elicited temporal interference force patterns at the beat frequency. Smoothly enveloped bursts of kilohertz sinusoidal waveforms produced negligible stimulation artifacts at steady state in concurrent surface electromyography (sEMG) recordings at motor threshold, in contrast to conventional biphasic square wave stimulation. SineStim delivers precise, isolated, multichannel kilohertz stimulation through a portable device, with performance demonstrated on both benchtop loads and human participants. By combining multichannel spatial control with minimal-artifact sEMG compatibility, SineStim enables future precision non-invasive neural stimulation paradigms based on multichannel optimisation and real-time closed-loop control capabilities not available via existing single-channel stimulators.

eess.SP↗

arXiv2024

Crude Oil Displacement Enhanced by Interfacially Active Nanoparticles and Their Coupling Effect with Low-Salinity Brines

From the microscopic scale to the petroleum-reservoir scale, the interfacial phenomena of the crude oil-water-rock system crucially control an immiscible flow in a porous reservoir. One of the key mechanisms is crude oil droplet displacement dynamics, which can be optimized by manipulating the oil-water interfacial tension and the three-phase contact angle by means of chemical injection. The current study primarily investigated oil displacement enhanced by interfacially active nanoparticles, namely poly(N-isopropylacrylamide) or pNIPAM, which found an acceleration of oil droplet receding rate (5.66 degree/s) and a greater degree of oil droplet dewetted (37.0 degree contact angle). This was due to a contribution from the nanoparticle-induced structural disjoining pressures between the oil-water and water-solid interfaces. The coupling effect of pNIPAM nanoparticles with low-salinity brines was examined, which revealed a discrepancy in different brine valences. Coupling with divalent CaCl2 led to much slower oil droplet receding dynamics (2.58 degree/s, and 58.7 degree contact angle) since oil-substrate bridging is formulated and promoted by the divalent cation. However, positive synergy was observed with a monovalent NaCl blend. The crude oil dewetting dynamics were enhanced (9.55 degree/s) owing to the combined salt-induced hydration and nanoparticle-induced structural forces. The contact angle was as low as 21.5 degree before eventually detaching from the substrate for a relatively short period (156 s). These findings highlight the coupling effect of nanoparticles and low-salinity brine on the dewetting of heavy crude oil. Adding nanoparticles to an optimal brine could be an option for faster and greater fluid displacement, which is not limited to oil production applications but several others, such as detergency and other forms of geological storage.

physics.flu-dyn↗