Hydrodynamically induced helical particle drift due to patterned surfaces.

Advances in microfabrication enable the tailoring of surfaces to achieve optimal sorting, mixing, and focusing of complex particulate suspensions in microfluidic devices. Corrugated surfaces have proved to be a powerful tool to manipulate particle motion for a variety of applications, yet the fundamental physical mechanism underlying the hydrodynamic coupling of the suspended particles and surface topography has remained elusive. Here, we study the hydrodynamic interactions between sedimenting spherical particles and nearby corrugated surfaces, whose corrugations are tilted with respect to gravity. Our experiments show three-dimensional, helical particle trajectories with an overall drift along the corrugations, which agree quantitatively with our analytical perturbation theory. The theoretical predictions reveal that the interaction of the disturbance flows, induced by the particle motion, with the corrugations generates locally a transverse anisotropy of the pressure field, which explains the helical dynamics and particle drift. We demonstrate that this dynamical behavior is generic for various surface shapes, including rectangular, sinusoidal, and triangular corrugations, and we identify surface characteristics that produce an optimal particle drift. Our findings reveal a universal feature inherent to particle transport near patterned surfaces and provide fundamental insights for future microfluidic applications that aim to enhance the focusing or sorting of particulate suspensions.

Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages.

Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 ± 0.3 [Formula: see text] to 215 ± 90.2 [Formula: see text]) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.

Relationship between Standalone Performance Validity Test Failure and Emotionality among Youth/student Athletes Experiencing Prolonged Recovery following Sports-related Concussion.

This study documented the rate of Performance Validity Testing (PVT) failure in 81 youth athletes, aged 10-21 years, experiencing prolonged recovery following sports-related concussion, and the relationship between PVT and emotional symptoms. Neuropsychological assessments were conducted across three test sessions with a stand-alone PVT at each session. Results showed that 48% (39/81) of individuals failed at least one PVT, with an overall PVT failure rate of 26% (64/243). Those failing at least one PVT scored significantly higher on anxiety but not depression or somatization. Results illustrate the importance of including measures of emotional and behavioral functioning in testing following SRC.

The stability of engagement over comprehensive neuropsychological assessment in student athletes diagnosed with sports related concussion.

We documented effort stability during neuropsychological (NP) testing examining failure rates on three Performance Validity Tests (PVTs). 65 student athletes, ages 8-21, were evaluated in an outpatient practice, following sports-related concussion over three sessions within 18 months of injury (mean=6 months). 7.7% of student athletes failed PVTs at all three test sessions, 7.7% failed PVTs at two test sessions, and 12.3% failed PVTs at one session; 28% of this sample was sub-optimally engaged for at least one test session, producing invalid neuropsychological data at the time of testing and 72% produced valid neuropsychological data across the comprehensive evaluation.

Development of an advanced microfluidic micropipette aspiration device for single cell mechanics studies.

Various micro-engineered tools or platforms have been developed recently for cell mechanics studies based on acoustic, magnetic, and optical actuations. Compared with other techniques for single cell manipulations, microfluidics has the advantages with simple working principles and device implementations. In this work, we develop a multi-layer microfluidic pipette aspiration device integrated with pneumatically actuated microfluidic control valves. This configuration enables decoupling of cell trapping and aspiration, and hence causes less mechanical perturbation on trapped single cells before aspiration. A high trapping efficiency is achieved by the microfluidic channel design based on fluid resistance model and deterministic microfluidics. Compared to conventional micropipette aspiration, the suction pressure applied on the aspirating cells is highly stable due to the viscous nature of low Reynolds number flow. As a proof-of-concept of this novel microfluidic technology, we built a microfluidic pipette aspiration device with 2 × 13 trapping arrays and used this device to measure the stiffness of a human breast cancer cell line, MDA-MB-231, through the observation of cell deformations during aspiration. As a comparison, we studied the effect of Taxol, a FDA-approved anticancer drug on single cancer cell stiffness. We found that cancer cells treated with Taxol were less deformable with a higher Young's modulus. The multi-layer microfluidic pipette aspiration device is a scalable technology for single cell mechanophenotyping studies and drug discovery applications.