Ultra-low Aspect Ratio Research Articles

A magnetic diagnostic suite for the Pegasus-III experiment.

Pegasus-III is an ultralow aspect ratio spherical tokamak providing a dedicated US experiment for comparative solenoid-free startup studies. A new magnetic diagnostic suite for equilibrium and low frequency (<200kHz) magnetohydrodynamic mode analysis has been installed. These new diagnostics address the significant challenges of measuring magnetic field in a high noise environment with the majority constrained to fit in an 8mm diagnostic gap on the high field side. Electrostatic switching noise generated by the 16 independent current feedback-controlled power supplies produces dVcm/dt ∼ 1kV/μs and volt level common mode noise on the magnetics. Immunity to this switching noise is accomplished through differential signal runs and signal processing, along with end-to-end electromagnetic interference shielding. The magnetic measurements are simultaneously digitized at 1MHz and conditioned by precision 8 pole Butterworth filters with a corner frequency of 200kHz to prevent aliasing down to the 16-bit level over the full passband. Ex-vessel calibrations of the Bp coils were completed with a typical uncertainty of <0.5%. Stray toroidal field pickup from coil misalignment or positioning errors is corrected using a physics-based model. Comparisons of the corrected measurements to modeling agree to within 1.3% on average. This is within the 1.5% measurement uncertainty that a sensitivity analysis determined is needed for accurate fast boundary and equilibrium reconstruction.

Flow-Rate-Insensitive Plasma Extraction by the Stabilization and Acceleration of Secondary Flow in the Ultralow Aspect Ratio Spiral Channel.

Although microfluidic devices have made remarkable strides in blood cell separation, there is still a need for further development and improvement in this area. Herein, we present a novel ultralow aspect ratio (H/W = 1:36) spiral channel microfluidic device with ordered micro-obstacles for sheathless and flow-rate-insensitive blood cell separation. By introducing ordered micro-obstacles into the spiral microchannels, reduced magnitude fluctuations in secondary flow across different loops can be obtained through geometric confinement. As a result, the unique Dean-like secondary flow can effectively enhance the separation efficiency of particles in different sizes ranging from 3 to 15 μm. Compared to most existing microfluidic devices, our system offers several advantages of easy manufacturing, convenient operation, long-term stability, highly efficient performance (up to 99.70% rejection efficiency, including platelets), and most importantly, insensitivity to cell sizes as well as flow rates (allowing for efficient separation of different-sized blood cells in a wide flow rate from 1.00 to 2.50 mL/min). The unique characteristics, such as ultralow aspect ratio, sequential micro-obstacles, and controlled secondary flow, make our device a promising solution for practical plasma extraction in biomedical research and clinical applications.

Fabricating and Laminating Films with Through-Holes and Engraved/Protruding Structures for 3D Micro/Nanofluidic Platforms.

Micro/nanofluidic devices have become popular for delicately processing biological, material, and chemical samples. However, their reliance on 2D fabrication schemes has hindered further innovation. Here, a 3D manufacturing method is proposed through the innovation of laminated object manufacturing (LOM), which involves the selection of building materials as well as the development of molding and lamination techniques. Fabrication of interlayer films is demonstrated with both multi-layered micro-/nanostructures and through-holes, using an injection molding approach and establishing strategic principles of film design. Utilization of the multi-layered through-hole films in LOM allows reducing the number of alignments and laminations by at least two times compared to conventional LOM. Using a dual-curing resin for film fabrication, a surface-treatment-free and collapse-free lamination technique is shown for constructing 3D multiscale micro/nanofluidic devices with ultralow aspect ratio nanochannels. The 3D manufacturing method enables the development of a nanochannel-based attoliter droplet generator capable of 3D parallelization for mass production, which implies the remarkable potential to extend numerous existing 2D micro/nanofluidic platforms into a 3D framework.

Flow-rate and particle-size insensitive inertial focusing in dimension-confined ultra-low aspect ratio spiral microchannel

Inertial microfluidics have shown its particular capability to manipulate micro-scale particles in a simple, high-throughput, and passive manner. Up till now, inertial focusing approaches remain challenging in the quest to achieve both flow-rate and particle-size insensitive focusing with simple design and robust operation. In this research, we develop a dimension-confined ultra-low aspect ratio spiral microchannel to realize flow-rate and particle-size insensitive inertial focusing. Equally distributing microstructures in the spiral microchannel, the secondary flow enhancement is explored by the computational fluid dynamics simulation. Utilizing the accelerated secondary flow, 15.5 µm polystyrene fluorescent particles are efficiently focused (>99%) in the similar position of microchannel within a wide range of flow rates (0.5–3.5 mL/min) during a long operation duration (0–60 min). Further, different sized particles (7.3, 9.9 and 15.5 µm) are all well focused (>90%) near the inner wall when different flow rates (1–3 mL/min) are applied. Similarly, three types of tumor cells (K562, HeLa and MCF-7) are successfully focused in the same position of the microchannel under high flow rates (1.5–2.5 mL/min). The enhanced secondary flow in our channel enables the flow-rate and particle-size insensitive inertial focusing in a sheath-less, high-throughput, and easy-to-fabricate manner, which is promising for development of portable inertial microfluidic device for flow cytometry, online sample processing, and so on.

Inkjet‐Patterned Microdroplets as Individual Microenvironments for Adherent Single Cell Culture (Small 19/2022)

Single Cell Culture In article number 2107992, Jin-Ming Lin and co-workers culture adherent single cells in their individual microenvironments patterned by inkjet printing. Adhesion strength is confirmed by the in-situ microfluidic probe assay. Altered morphology among single cells features ultra-low aspect ratio and shows a distinct behavior caused by “singleness.”

Flow-Rate and Particle-Size Insensitive Inertial Focusing in Dimension-Confined Ultra-Low Aspect Ratio Spiral Microchannel

Flow-Rate and Particle-Size Insensitive Inertial Focusing in Dimension-Confined Ultra-Low Aspect Ratio Spiral Microchannel

Multi-Vortex Regulation for Efficient Fluid and Particle Manipulation in Ultra-Low Aspect Ratio Curved Microchannels.

Inertial microfluidics enables fluid and particle manipulation for biomedical and clinical applications. Herein, we developed a simple semicircular microchannel with an ultra-low aspect ratio to interrogate the unique formations of the helical vortex and Dean vortex by introducing order micro-obstacles. The purposeful and powerful regulation of dimensional confinement in the microchannel achieved significantly improved fluid mixing effects and fluid and particle manipulation in a high-throughput, highly efficient and easy-to-use way. Together, the results offer insights into the geometry-induced multi-vortex mechanism, which may contribute to simple, passive, continuous operations for biochemical and clinical applications, such as the detection and isolation of circulating tumor cells for cancer diagnostics.

A passive Stokes flow rectifier for Newtonian fluids

Non-linear effects of the Navier–Stokes equations disappear under the Stokes regime of Newtonian fluid flows disallowing a flow rectification behavior. Here we show that passive flow rectification of Newtonian fluids is obtainable under the Stokes regime of both compressible and incompressible flows by introducing nonlinearity into the otherwise linear Stokes equations. Asymmetric flow resistances arise in shallow nozzle/diffuser microchannels with deformable ceiling, in which the fluid flow is governed by a non-linear coupled fluid–solid mechanics equation. The proposed model captures the unequal deflection profile of the deformable ceiling depending on the flow direction under the identical applied pressure, permitting a larger flow rate in the nozzle configuration. Ultra-low aspect ratio microchannels sealed by a flexible membrane have been fabricated to demonstrate passive flow rectification for low-Reynolds-number flows (0.001 < Re < 10) of common Newtonian fluids such as water, methanol, and isopropyl alcohol. The proposed rectification mechanism is also extended to compressible flows, leading to the first demonstration of rectifying equilibrium gas flows under the Stokes flow regime. While the maximum rectification ratio experimentally obtained in this work is limited to 1.41, a higher value up to 1.76 can be achieved by optimizing the width profile of the asymmetric microchannels.

Numerical Study of Multivortex Regulation in Curved Microchannels with Ultra-Low-Aspect-Ratio.

The field of inertial microfluidics has been significantly advanced in terms of application to fluid manipulation for biological analysis, materials synthesis, and chemical process control. Because of their superior benefits such as high-throughput, simplicity, and accurate manipulation, inertial microfluidics designs incorporating channel geometries generating Dean vortexes and helical vortexes have been studied extensively. However, existing technologies have not been studied by designing low-aspect-ratio microchannels to produce multi-vortexes. In this study, an inertial microfluidic device was developed, allowing the generation and regulation of the Dean vortex and helical vortex through the introduction of micro-obstacles in a semicircular microchannel with ultra-low aspect ratio. Multi-vortex formations in the vertical and horizontal planes of four dimension-confined curved channels were analyzed at different flow rates. Moreover, the regulation mechanisms of the multi-vortex were studied systematically by altering the micro-obstacle length and channel height. Through numerical simulation, the regulation of dimensional confinement in the microchannel is verified to induce the Dean vortex and helical vortex with different magnitudes and distributions. The results provide insights into the geometry-induced secondary flow mechanism, which can inspire simple and easily built planar 2D microchannel systems with low-aspect-ratio design with application in fluid manipulations for chemical engineering and bioengineering.

New Insight Into Aspect Ratio's Effect on Secondary Losses of Turbine Blades

Abstract In view of improving the understanding of the loss mechanisms existing on a compact turbine driving a cryogenic engine turbo-pump for a satellite delivering rocket, a new perspective on how the aspect ratio of turbine blades affects the secondary and profile losses is presented. This perspective, originally based on published experimental data, is further developed by a series of back-to-back highly resolved computational fluid dynamics (CFD) numerical simulations, with the aim of acquiring further insight into the dynamics of the secondary vortices, and the intermediate boundary layer flow for varying blade heights. The main outcome redefines the extreme cases and the partition of losses between secondary and profile, and establishes a new critical ultra-low aspect ratio of 0.35 as a threshold distinguishing two different behaviors. The final venue of this new perspective is the possibility to further improve existing off-design turbine loss models, like those presented by Craig–Cox and Ainley–Mathieson.

Ultralow-aspect-ratio micropore sensor for a particle translocation: Critical role of the access region

In this paper, we analyze particle translocation through micropores with low aspect ratios. Micropores with diameters of 11.6 μm and various lengths (1000 nm, 500 nm, 100 nm, and 50 nm) are fabricated on a silicon nitride membrane via laser machining at a low aspect ratio. After measuring the translocation signals of a 5.4- μm particle, we find that the effects of the access region become more significant than those of the pore region for detecting signals at low aspect ratios. To clarify this mechanism, finite element method simulation and mathematical analysis are performed and we describe the relationship between an inhomogeneous electric field and the critical role of the access region. Additionally, we detect the translocation signal of a double particle. As a result, we achieve a decrease in translocation speed and improve signal detection at an ultralow aspect ratio, demonstrating the potential to detect the shapes of small particles directly.

Ultra-low aspect ratio spiral microchannel with ordered micro-bars for flow-rate insensitive blood plasma extraction

The ability to regulate secondary flow is significant for efficient particle/cell focusing. Microfluidic technologies have accomplished impressive progress in particle/cell manipulation with the help of the Dean effect. Herein, we explored blood cell focusing with the ultra-low aspect ratio inertial microfluidic system which uses the geometric confinement to enhance the secondary flows to different degrees. Introducing a series of micro-bars in the spiral microchannels accelerates the secondary flow, which can greatly enhance highly-efficient particle/cell focusing under various flow rates. Further, plasma extraction can be successfully achieved from 15× diluted whole blood in an easy-to-use (without the assistance of sheath fluid and complex manufacturing of multi-layer structure), high and wide flow rates (1–5 mL/min, exhibiting no parallel construction design), long-term (at least 60 min), stable (processing at least 300 mL blood samples with consistent efficiency), and highly-efficient (99.99% blood cell rejection ratio) manner. Compared with previously-reported technologies, the engineering strategy of secondary flow in our designed dimension-confined spiral channel provides a balanced overall performance for plasma separation pointing to ease-to-fabrication, insensitive to flow-rate, high throughput and operation efficiency.

Electrochemical Impedance Spectroscopy for Real-Time Detection of Lipid Membrane Damage Based on a Porous Self-Assembly Monolayer Support.

Layer-by-layer dissolution and permeable pore formation are two typical membrane damage pathways, which induce membrane function disorder and result in serious disease, such as Alzheimer's disease, Keshan disease, Sickle-cell disease, and so on. To effectively distinguish and sensitively monitor these two typical membrane damage pathways, a facile electrochemical impedance strategy was developed on a porous self-assembly monolayer (pSAM) supported bilayer lipid membrane (BLM). The pSAM was prepared by selectively electrochemical reductive desorption of the mercaptopropionic acid in a mixed mercaptopropionic acid/11-mercaptoundecanoic acid self-assembled monolayer, which created plenty of nanopores with tens of nanometers in diameter and several nanometers in height (defined as inner-pores). The ultralow aspect ratio of the inner-pores was advantageous to the mass transfer of electrochemical probe [Fe(CN)6]3-/4-, simplifying the equivalent electric circuit for electrochemical impedance spectroscopy analysis at the electrode/membrane interface. [Fe(CN)6]3-/4- transferring from the bulk solution into the inner-pore induce significant changes of the interfacial impedance properties, improving the detection sensitivity. Based on these, the different membrane damage pathways were effectively distinguished and sensitively monitored with the normalized resistance-capacitance changes of inner-pore-related parameters including the electrolyte resistance within the pore length ( Rpore) and the metal/inner-pore interfacial capacitance ( Cpore) and the charge-transfer resistance ( Rct-in) at the metal/inner-pore interface.

Chromatographic Properties of Minimal Aspect Ratio Monolithic Silica Columns.

We report on a study wherein we synthesized TMOS-based silica monolithic skeletons in capillaries with an i.d. of 5 and 10 μm to produce skeleton structures with very low capillary-to-domain size aspect-ratios. These structures include the absolute minimal aspect-ratio case of a monolithic structure whose cross-section only contains a single node point. With domain-sized based reduced plate heights running as low as hmin = 1.3-1.5 for retained coumarin dyes providing a retention factor of k = 0.6-1.0, the study confirms the classic observation that ultralow aspect ratio columns generate a markedly lower dispersion than columns with a larger aspect ratio made in the past by Knox, Jorgenson, and Kennedy for the packed bed of spheres, but now for silica monoliths. The course of the reduced van Deemter curves, and more specifically the ratio of A-term versus C-term band broadening, could be interpreted in terms of the width and persistence length of the velocity bias zones in the columns. Considering the overall kinetic performance, it is found that the two best performing structures are also the structures with the lowest number of domains or node points, that is, with the lowest capillary-to-domain size aspect-ratio and, hence, resembling closest to the open-tubular format, which remains confirmed as the column format with the best kinetic performance. This is quantified by the fact that the minimal impedance values (order of Emin = 100) of the best performing ultralow aspect ratio monolithic columns are still significantly larger than the Emin values for the reference open-tubular columns (order of Emin = 15-20).

Noninductively Driven Tokamak Plasmas at Near-Unity Toroidal Beta.

Access to and characterization of sustained, toroidally confined plasmas with a very high plasma-to-magnetic pressure ratio (β_{t}), low internal inductance, high elongation, and nonsolenoidal current drive is a central goal of present tokamak plasma research. Stable access to this desirable parameter space is demonstrated in plasmas with ultralow aspect ratio and high elongation. Local helicity injection provides nonsolenoidal sustainment, low internal inductance, and ion heating. Equilibrium analyses indicate β_{t} up to ∼100% with a minimum |B| well spanning up to ∼50% of the plasma volume.

Aerodynamic Performance of an Ultra-Low Aspect Ratio Centripetal Turbine Stator

An extensive measurement campaign was carried out at the von Karman Institute for Fluid Dynamics to assess the aerodynamic performance of an ultra-low aspect ratio centripetal turbine stator. The test section consisted of 18 periodic sectors of two blade passages each, tested at transonic conditions in a blow-down facility. Particle image velocimetry (2D-PIV) measurements were performed in the trailing edge area at blade mid-height. Further downstream, 16 micro virtual 3-hole pressure probes were used to measure the aerodynamic performance at about 44% of the radial chord, downstream of the trailing edge. Results describe a highly swirling flow-field characterized by a very large tangential velocity component increasing at smaller radii. The radial component decreased instead to compensate for an opening of the test section closer to its center, therefore enhancing the tangential nature of the generated flow field. Adjacent blades showed asymmetric wakes as an effect of the particular design of the nozzle. The performance analysis exhibited very high loss coefficients (always higher than 12%) which have to be related to the extremely small aspect ratio of the cascade.

Optical mapping of single-molecule human DNA in disposable, mass-produced all-polymer devices

We demonstrate all-polymer injection molded devices for optical mapping of denaturation–renaturation (DR) patterns on long, single DNA-molecules from the human genome. The devices have channels with ultra-low aspect ratio, only 110 nm deep while 20 μm wide, and are superior to the silica devices used previously in the field. With these polymer devices, we demonstrate on-chip recording of DR images of DNA-molecules stretched to more than 95% of their contour length. The stretching is done by opposing flows Marie et al (2013 Proc. Natl Acad. Sci. USA 110 4893–8). The performance is validated by mapping 20 out of 24 Mbp-long DNA fragments to the human reference genome. We optimized fabrication of the devices to a yield exceeding 95%. This permits a substantial economies-of-scale driven cost-reduction, leading to device costs as low as 3 USD per device, about a factor 70 lower than the cost of silica devices. This lowers the barrier to a wide use of DR mapping of native, megabase-size DNA molecules, which has a huge potential as a complementary method to next-generation sequencing.

The Relationship of Ultra-Low Permeability Sandstone Aspect Ratio With Porosity, Permeability

The ultra-low permeability sandstone reservoir has large aspect ratio which significantly influences the multi-phase percolation characteristic. The ratio could be accurately measured by rate-controlled mercury porosimetry, but the testing technology is expensive, time-consuming and core-contaminating. There is not a simple effective method to describe the aspect ratio. The pores of the ultra-low permeability sandstone are mainly connected by the very long narrow throats, which could be advantageously simulated by the compound capillary bundles model. The analytical expressions of porosity and permeability about major pore structure parameters are established based on the model for the tight porous media. After solving the two expressions, the relationship between aspect ratio and parameter combination of porosity, permeability is obtained for the ultra-low permeable sandstone. Then the relation is fitted in this article using many previous published rate-controlled mercury data on compact sandstone and the relevance is strong, which proves that aspect ratio of tight rock is able to be calculated with its porosity and permeability. Key words : Ultra-low permeability sandstone; Aspect ratio; Pore; Throat; Porosity; Permeability

Fabrication of Centimeter Long, Ultra-Low Aspect Ratio Nanochannel Networks in Borosilicate Glass Substrates

Nanofluidic devices have a broad range of applications resulting from the dominance of surface-fluid interactions. Examples include molecular gating, sample preconcentration, and sample injection. Manipulation of small fluid samples is ideal for micro total analysis systems or lab on chip devices which perform multiple unit operations on a single chip. In this paper, fabrication procedures for two different ultra-low aspect ratio (ULAR) channel network designs are presented. The ULAR provides increased throughput compared to higher aspect ratio features with the same critical dimensions. Channel network designs allow for integration between microscale and nanoscale fluidic networks. A modified calcium assisted glass–glass bonding procedure was developed to fabricate chemically uniform, all glass nanochannels. A polydimethylsiloxane (PDMS)-glass adhesive bonding procedure was also developed as adhesive bonding allows for more robust fabrication with lower sensitivity to surface defects. The fabrication schemes presented allow for a broad array of available parameters for facile selection of device fabrication techniques depending on desired applications for lab on chip devices.

Tokamak startup using outboard current injection on the Pegasus Toroidal Experiment

Localized current injection near the outboard midplane is used to form 0.1 MA plasma discharges with no induction supplied from a central solenoid in the ultra-low aspect ratio Pegasus Toroidal Experiment. The discharges are initiated by driving open-field-line currents that perturb the vacuum magnetic field such that the magnetic topology transitions to a tokamak-like configuration. The plasma is subsequently driven via helicity injection from the edge current sources and poloidal field induction. Intermittent n = 1 MHD activity is observed during periods of strong edge current drive and each event leads to a rapid inward expansion of the plasma volume and a drop in the plasma inductance. The plasmas are sufficiently turbulent such that the equilibrium approaches the lowest energy state described by Taylor relaxation theory. In agreement with that theory, the maximum Ip scales with (ITFIinj/w)1/2, where ITF is the toroidal field rod current, Iinj is the injected edge current and w is the radial width of the average poloidal magnetic flux in the driven open flux region.