Journal of Applied Physics

Directional fluid flow in perivascular spaces surrounding cerebral arteries is hypothesized to play a key role in brain solute transport and clearance. While various drivers for a pulsatile flow, such as cardiac or respiratory pulsations, are well quantified, the question remains as to which mechanisms could induce a directional flow within physiological regimes. To address this question, we develop theoretical and numerical reduced-order models to quantify the directional (net) flow induceable by peristaltic pumping in periarterial networks...

Cardiac muscle contraction is initiated by an elementary Ca signal (called Ca spark) which is achieved by collective action of Ca release channels in a cluster. The mechanism of this synchronization remains uncertain. We approached Ca spark activation as an emergent phenomenon of an interactive system of release channels. We constructed a weakly lumped Markov chain that applies an Ising model formalism to such release channel clusters and probable open channel configurations and demonstrated that spark activation is described as a system transition from a metastable to an absorbing state, analogous to the pressure required to overcome surface tension in bubble formation...

When it comes to simulate or calculate an optoelectronic tweezer (OET) response for a microparticle suspended in a given medium, a precise electrical conductivity (later referred to as conductivity) value for the microparticle is critical. However, there are not well-established measurements or well-referenced values for microparticle conductivities in the OET realm. Thus, we report a method based on measuring the escape velocity of a microparticle with a standard OET system to calculate its conductivity. A widely used 6  μ m polystyrene bead (PSB) is used for the study...

To maximize the capabilities of minimally invasive implantable bioelectronic devices, we must deliver large amounts of power to small implants; however, as devices are made smaller, it becomes more difficult to transfer large amounts of power without a wired connection. Indeed, recent work has explored creative wireless power transfer (WPT) approaches to maximize power density [the amount of power transferred divided by receiver footprint area (length × width)]. Here, we analyzed a model for WPT using magnetoelectric (ME) materials that convert an alternating magnetic field into an alternating voltage...

2'-Deoxy-ATP (dATP), a naturally occurring near analog of ATP, is a well-documented myosin activator that has been shown to increase contractile force, improve pump function, and enhance lusitropy in the heart. Calcium transients in cardiomyocytes with elevated levels of dATP show faster calcium decay compared with cardiomyocytes with basal levels of dATP, but the mechanisms behind this are unknown. Here, we design and utilize a multiscale computational modeling framework to test the hypothesis that dATP acts on the sarcoendoplasmic reticulum calcium-ATPase (SERCA) pump to accelerate calcium re-uptake into the sarcoplasmic reticulum during cardiac relaxation...

Arterial wall active mechanics are driven by resident smooth muscle cells, which respond to biological, chemical, and mechanical stimuli and activate their cytoskeletal machinery to generate contractile stresses. The cellular mechanoresponse is sensitive to environmental perturbations, often leading to maladaptation and disease progression. When investigated at the single cell scale, however, these perturbations do not consistently result in phenotypes observed at the tissue scale. Here, a multiscale model is introduced that translates microscale contractility signaling into a macroscale, tissue-level response...

Understanding defect creation is central to efforts to comprehend gate dielectric breakdown in metal-oxide-semiconductor-field-effect-transistors (MOSFETs). While gate dielectrics other than SiO2 are now popular, models develop for SiO2 breakdown are used for these dielectrics too. Considering that the Si-O bond is very strong, modeling efforts have focused in ways to weaken it so that defect creation (bond-breaking) is commensurate with experimental observations. So far, bond-breaking models rely on defect-precursors to make the energetics manageable...

A theoretical method is described to analytically calculate a pair of surface current densities, which produce a desired static magnetic field in one region of the space and zero magnetic field in another. The analysis is based on the known relationship between a surface current density and a stream function, the equivalence of stream functions and surface magnetic dipole density, and the scalar potential representation of the associated magnetic field in free space. From these relations, we formulate the magnetostatic problem, which is often treated as a vector field problem, as a scalar field problem in which a two-dimensional scalar field (stream function) is related to a three-dimensional one (magnetic scalar potential) via the differentiation of the electrostatic Green's function 1/|r-rs |...

We investigate the use of Raman spectroscopy to measure carrier concentrations in <mml:math xmlns:mml="https://www.w3.org/1998/Math/MathML"><mml:mi>n</mml:mi><mml:mo>-</mml:mo><mml:mtext>type</mml:mtext></mml:math> GaSb epilayers to aid in the development of this technique for the nondestructive characterization of transport properties in doped semiconductors. The carrier concentration is quantified by modeling the measured coupled optical phonon-free carrier plasmon mode spectra...

Heating magnetic nanoparticles (MNPs) with alternating magnetic fields (AMFs) have applications in biomedical research and cancer therapy. Accurate measurement of the heating efficiency or specific loss power (SLP) generated by the MNPs is essential to assess response(s) in biological systems. Efforts to develop standardized equipment and to harmonize results obtained from various MNP samples and AMF systems have met with little success. Without a standardized magnetic nanoparticle or calorimeter device, objective comparisons of estimated thermal output among laboratories remain a challenge...

A series of monofilamentary powder-in-tube MgB2 wires were fabricated with 2 mol. % C doping and co-additions of 0-3 wt. % Dy2 O3 . Irreversibility fields ( μ 0 Hirr ), upper critical fields ( μ 0 Hc 2 ), and transport critical currents were measured, and from these quantities, anisotropies <mml:math xmlns:mml="https://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:mi>γ</mml:mi> <mml:mo>)</mml:mo></mml:math> and electronic diffusivities <mml:math xmlns:mml="https://www...

We present high-resolution magnetic resonance imaging (MRI) at ultra-low field (ULF) with a proton Larmor frequency of around 120 kHz. The key element is a specially designed high-sensitivity sensing coil in the shape of a solenoid with a few millimeter gap between windings to decrease the proximity effect and, hence, increase the coil's quality ( <mml:math xmlns:mml="https://www.w3.org/1998/Math/MathML"><mml:mi>Q</mml:mi></mml:math> ) factor and sensitivity. External noise is strongly suppressed by enclosing the sensing coil in a copper cylindrical shield, large enough not to negatively affect the coil's <mml:math xmlns:mml="https://www...

Integrating miniature pumps within microfluidic devices is crucial for advancing point-of-care diagnostics. Understanding the emergence of flow from novel integrated pumping systems is the first step in their successful implementation. A Purcell-like elasto-magnetic integrated microfluidic pump has been simulated in COMSOL Multiphysics and its performance has been investigated and evaluated. An elastic, cilia-like element contains an embedded magnet, which allows for actuation via a weak, uniaxial, sinusoidally oscillating, external magnetic field...

Photoacoustic imaging is a hybrid imaging approach that combines the advantages of optical and ultrasonic imaging in one modality. However, for comprehensive tissue characterization, optical contrast alone is not always sufficient. In this study, we combined photoacoustic imaging with high-resolution ultrasound and shear wave elastography. The multi-modal system can calculate optical absorption, acoustic reflection, and stiffness volumetrically. We constructed a multi-modal phantom with contrast for each imaging modality to test the system's performance...

In recent years, interesting materials have emerged which are only available as μm-scale flakes, and whose novel physics might be better understood through broadband microwave spectroscopy; examples include twisted bilayer graphene [Y. Cao S. Fang, K. Watanabe, T. Taniguchi, E. Kaxiras and P. Jarillo-Herrero Nature 556 , 43 (2018).], 2D materials in which many-body phases are observed [S. Chen R. Ribeiro-Palau, K. Yang, T. Taniguchi, J. Hone, M. O. Goerbig and C. R. Dean Physical Review Letters 122 ¸ 026802 (2019)], and artificial lattices for analog quantum simulations [J...

The thick gate oxide breakdown mechanism has become an important topic again due to the rising demand for power electronics. The failure of the percolation model in explaining the observed Weibull shape factor, β , seriously hampers the establishment of thick gate oxide breakdown models and the ability to project reliability from measurement data. In this work, lifetime shortening by oxide defects are simulated to produce degraded breakdown distributions that match experimentally observed β s. The result shows that even a low density of defects with the right energy is enough to greatly degrade β for thick oxides...

Progress in computing architectures is approaching a paradigm shift: traditional computing based on digital complementary metal-oxide semiconductor technology is nearing physical limits in terms of miniaturization, speed, and, especially, power consumption. Consequently, alternative approaches are under investigation. One of the most promising is based on a "brain-like" or neuromorphic computation scheme. Another approach is quantum computing using photons. Both of these approaches can be realized using silicon photonics, and at the heart of both technologies is an efficient, ultra-low power broad band optical modulator...

We present a device that can achieve controlled transport of colloidal microparticles using an array of micro-electrodes. By exciting the micro-electrodes in regular sequence with an AC voltage, a time-varying moving dielectrophoretic force-field is created. This force propels colloidal microparticles along the electrode array. Using this method, we demonstrate bidirectional transport of polystyrene micro-spheres. Electromagnetic simulation of the device is performed, and the dielectrophoretic force profile around the electrode array is mapped...

All living cells constantly experience and respond to mechanical stresses. The molecular networks that activate in cells in response to mechanical stimuli are yet not well-understood. Our limited knowledge stems partially from the lack of available tools that are capable of exerting controlled mechanical stress to individual cells and at the same time observing their responses at subcellular to molecular resolution. Several tools such as rheology setups, micropipetes, and magnetic tweezers have been used in the past...

Gate-defined quantum dots (QD) benefit from the use of small grain size metals for gate materials because it aids in shrinking the device dimensions. However, it is not clear what differences arise with respect to process-induced defect densities and inhomogeneous strain. Here, we present measurements of fixed charge, Q f , interface trap density, D it , the intrinsic film stress, σ , and the coefficient of thermal expansion, α as a function of forming gas anneal temperature for Al, Ti/Pd, and Ti/Pt gates...