AIP Advances最新文献

Stretchable RF coils offer the potential to improve MRI performance by conforming closely to patient anatomy, regardless of patient size, thereby enhancing both signal-to-noise ratio (SNR) and patient comfort. In this work, we investigate a stretchable receive array design based on the coaxial capacitor (COCA) coil for 7 T MRI, constructed primarily from ultra-flexible Litz wire stitched onto elastic fabric substrates. The COCA coil eliminates the need for lumped capacitors and maintains stable decoupling performance under transverse stretching, provided that the overlapped area and the coil area change proportionally as the coil is stretched. Bench tests and phantom imaging experiments demonstrate that elliptical COCA coils (in the non-stretched state) maintain consistent decoupling characteristics across stretch ratios up to ×1.3 and outperform fixed arrays in SNR across varying phantom sizes. The proposed design shows strong potential for integration into wearable coil arrays, enabling improved imaging quality and adaptability for diverse patient anatomies.

This paper aims to examine the ability to control a model of red blood cell (RBC) dynamics and the associated extracellular flow patterns in microfluidic channels via oscillatory flows. Our computational approach employs a hybrid continuum-particle coupling, in which the cell membrane and cytosol fluid are modeled using the dissipative particle dynamics method. The blood plasma is modeled as an incompressible fluid via the immersed boundary method. This coupling is novel because it provides an accurate description of RBC dynamics while the extracellular flow patterns around the RBCs are also captured in detail. Our coupling methodology is validated with available experimental and computational data in the literature and shows excellent agreement. We explore the controlling regimes by varying the shape of the oscillatory flow waveform at the channel inlet. Our simulation results show that a host of RBC morphological dynamics emerges depending on the channel geometry, the incoming flow waveform, and the RBC initial location. Complex dynamics of RBC are induced by the flow waveform. Our results show that the RBC shape is strongly dependent on its initial location. Our results suggest that the controlling of oscillatory flows can be used to induce specific morphological shapes of RBCs and the surrounding fluid patterns in bio-engineering applications.

Plasmonic heating of gold nanoparticles (GNPs) using pulsed lasers (PLs) enables microbubble generation for imaging, diagnostics, and microfluidics. However, aggregation and photomodification cause inconsistencies (variations) in microbubble formation and distribution, particularly in pool-like environments where GNPs undergo aggregation and photomodification. This study experimentally investigates microbubble generation by heating GNPs (532 nm, nanoseconds PL) of various sizes and concentrations, using high-speed imaging (20 kfps). Results show unpredictable variations in bubble formation area (BFA), even under similar energy absorption. Large individual microbubbles were observed at relatively low energy absorption, primarily due to aggregation. Boiling on the transparent surface occurred in multiple tests, a phenomenon linked to optical pulling forces that deposited GNPs on the surface. This produced well-defined semi-circular bubbles (∼600 μm) within 50 μs. MB formation was more concentrated near the backward facing surface than along the laser beam, highlighting the role of optical pulling. Dissolved gas release influenced microbubble growth, particularly in samples prone to aggregation. In addition, prior laser pulses impacted BFA through photomodification and aggregation, sometimes reducing BFA despite higher energy absorption. This study provides new insights into the factors influencing microbubble formation and distribution in the plasmonic heating of GNPs. Understanding these mechanisms can help improve the reliability and efficiency of photothermal applications, enabling better control over plasmonic bubble generation for various scientific and technological advancements.

Genetically encodable gas-filled particles, known as gas vesicles (GVs), have shown promise as a biomolecular contrast agent for ultrasound imaging and have the potential to be used as cavitation nuclei for ultrasound therapy. In this study, we used passive acoustic mapping techniques to characterize GV-seeded cavitation, utilizing 0.5 and 1.6 MHz ultrasound insonation over peak rarefactional pressures ranging from 100 to 2200 kPa. We found that GVs produce cavitation for the duration of the first applied pulse, up to at least 5000 cycles, but that bubble activity diminishes rapidly over subsequent pulses. At 0.5 MHz, the frequency content of cavitation emissions was predominantly broadband in nature, while at 1.6 MHz, narrowband content at harmonics of the main excitation frequency dominated. Simulations and high-speed camera imaging suggest that the received cavitation emissions come not from individual GVs but instead from the coalescence of GV-released gas into larger bubbles during the applied ultrasound pulse. These results will aid the future development of GVs as cavitation nuclei in ultrasound therapy.

We present simulation results for the Donnan equilibrium between a homogeneous bulk reservoir and inhomogeneous confining geometries with varying number of restricted dimensions, d _c. Planar slits (d _c = 1), cylindrical pores (d _c = 2), and spherical cavities (d _c = 3) are considered. The walls have a negative surface charge density. Because different dielectric constants are used in the reservoir and confined system, we used the Donnan grand canonical Monte Carlo method [Boda and Gillespie, J. Mol. Liq. 391, 123372 (2023)] to simulate the equilibrium. The systems with larger confining dimensionality produce greater adsorption of counterions (cations) into the confinements, so cation selectivity increases with increasing dimensionality. The systems with smaller dielectric constants produce more effective coion (anion) exclusion, so cation selectivity increases with decreasing dielectric constant. The combined effect of a more confining space and solvation penalty produces even more efficient anion exclusion and cation selectivity than each separately.

Diffusive adsorption/association is a fundamental step in almost all chemical reactions in diluted solutions, such as organic synthesis, polymerization, self-assembly, biomolecular interactions, electrode dynamics, catalysis, chromatography, air and water environmental dynamics, and social and market dynamics. However, predicting the rate of such a reaction is challenging using the equations established over 100 years ago. Several orders of magnitude differences between the theoretical predictions and experimental measurements for various systems, from self-assembled monolayers to protein-protein aggregations, make such calculations meaningless in many situations. I believe the major problem is that the time-dependent evolution curve of Fick's gradient is an ideal assumption in most cases, and its slope is significantly overestimated. This paper digs into Fick's gradient problem for 3D cases and provides a solution using the single-molecule diffusion probability density function discretely.