Narrow Slits Research Articles

Effect of temperature and loading mode on flexural properties and failure mechanisms of fine weave punctured C/C composites over 2000 °C

Fine weave punctured C/C composites are extensively utilized in aerospace applications owing to their superior mechanical properties. The effects of temperature over 2000 °C and loading mode on the flexural properties and failure mechanism were reported. It was found that the load-displacement curves of Y-direction flexure showed linear characteristics, but those of Z-direction flexure showed nonlinear characteristics because of interlayer failure. The flexural performances in the Z-direction were significantly higher than in the Y-direction. Both Y- and Z-directions flexural strengths increased dramatically, but flexural moduli initially climbed and subsequently declined with increasing temperature. In contrast with room temperature, the Y- and Z-direction flexural strengths increased by 55.6 % and 188.5 % at 2000 °C, while their corresponding flexural moduli increased by 14.3 % and 40.4 % at 1200 °C. Flexural failure in the Y direction was primarily distributed along the rows of Z-yarns. Due to narrower slits and tighter composite connections, failure gradually spreads over the Z-yarns at higher temperatures. While, the failure cracks of Z-direction flexural specimens were mainly distributed in the interlayer. As the temperature rose, the carbon fiber monofilaments of the pulled Z-direction yarns became harder linked, with neater breaks.

The dynamics of red blood cells traversing slits of mechanical heart valves under high shear

Hemolysis, including subclinical hemolysis, is a potentially severe complications of mechanical heart valves (MHVs), which leads to shortened red blood cell (RBC) lifespan and hemolytic anemia. Serious hemolysis is usually associated with structural deterioration and regurgitation. However, the shear stress in MHVs’ narrow leakage slits is much lower than the shear stress threshold causing hemolysis and the mechanisms in this context remain largely unclear. This study investigated the hemolysis mechanism of RBCs in cell-size slits under high shear rates by establishing in vitro microfluidic devices and a coarse-grained molecular dynamics (CGMD) model, considering both fluid and structural effects simultaneously. Microfluidic experiments and computational simulation revealed six distinct dynamic states of RBC traversal through MHVs' microscale slits under various shear rates and slit sizes. It elucidated that RBC dynamic states were influenced by not only by fluid forces but significantly by the compressive force of slit walls. The variation of the potential energy of the cell membrane indicated its stretching, deformation, and rupture during traversal, corresponding to the six dynamic states. The maximum forces exerted on membrane by water particles and slit walls directly determined membrane rupture, serving as a critical determinant. This analysis helps in understanding the contribution of the slit walls to membrane rupture and identifying the threshold force that leads to membrane rupture. The hemolysis mechanism of traversing microscale slits is revealed to effectively explain the occurrences of hemolysis and subclinical hemolysis.

A Novel Small Form-Factor Handheld Optical Coherence Tomography Probe for Oral Soft Tissue Imaging.

Tissue imaging is crucial in oral cancer diagnostics. Imaging techniques such as X-ray imaging, magnetic resonance imaging, optical coherence tomography (OCT) and computed tomography (CT) enable the visualization and analysis of tissues, aiding in the detection and diagnosis of cancers. A significant amount of research has been conducted on designing OCT probes for tissue imaging, but most probes are either heavy, bulky and require external mounting or are lightweight but straight. This study addresses these challenges, resulting in a curved lightweight, low-voltage and compact handheld imaging probe for oral soft tissue examination. To the best of our knowledge, this is the first curved handheld OCT probe with its shape optimized for oral applications. This probe features highly compact all-fiber optics with a diameter of 125 μm and utilizes innovative central deflection magnetic actuation for controlled beam scanning. To ensure vertical stability while scanning oral soft tissues, the fiber was secured through multiple narrow slits at the probe's distal end. This apparatus was encased in a 3D-printed angular cylinder tube (15 mm outer diameter, 12 mm inner diameter and 160 mm in length, weighing < 20 g). An angle of 115° makes the probe easy to hold and suitable for scanning in space-limited locations. To validate the feasibility of this probe, we conducted assessments on a multi-layered imaging phantom and human tissues, visualizing microstructural features with high contrast.

Circumferential slots based decoupled wideband MIMO antenna for 5G and sub-6 GHz applications

This paper investigates a small size 2 × 2 wideband multiple input multiple output (MIMO) antenna covering frequency band of 2.61 to 5.52 GHz. The antenna structure consists of elliptical ring patch with multiple circumferential slots. The edge-to-edge separation between the patches are kept 3.6 mm with volumetric dimensions of 30 × 46 × 1.6 mm3. The narrow slits are etched in the tapered ground plane to obtain the wideband characteristics. The electromagnetic coupling is improved more than 16 dB by employing the neutralization technique. The measured average gain and radiation efficiency of the proposed antenna are above 2.61dBi and 83.54%, respectively across the operating band. In addition to that, the important MIMO diversity parameters are investigated. The group delay and signal analysis in different orientations are also studied to ensure the quality performance of the antenna. The proposed MIMO antenna is simulated using CST microwave studio and further validated with the measurements. In addition to that, the parallel and orthogonal configuration of 4 × 4 MIMO antennas are analyzed by extending the proposed 2 × 2 MIMO design. The 4-port MIMO antennas exhibit the operating frequency bands varying from 2.80 to 5.58 GHz and 3.4 to 5.52 GHz, respectively for parallel and orthogonal MIMO configurations. The diversity parameters of 4-port MIMO antennas are calculated and compared with the measured results to verify its practical applications. Finaly, the SAR analysis of the antenna is presented at 3.08 and 5.20 GHz for 1/10 g tissues and are found 0.111/0.106 and 0.079/0.063 W K−1g−1, respectively. The proposed MIMO antenna designs are suitable for modern high-speed communication for 5G and sub-6 GHz frequency bands.

Spout geometry of fine particle conical spouted beds equipped with internal devices

The size and geometry of the spout are crucial parameters for the design and scaling-up of spouted beds because they condition heat and mass transfer rates. It is well-established in the literature that spouted beds without draft tube show axisymmetric spout shape, but this does not occur with open-sided draft tubes. Particle velocity has been measured at several bed heights and angular coordinates, under different geometric parameters and operating conditions, to determine the location of the spout-annulus interface in beds provided with open-sided draft tubes. Narrow draft tube wall slits and low air velocities lead to spouts of small size and triangular shape. The greatest spout expansion (high air velocities and wide draft tube wall slits) leads to a Reuleaux triangle shape, in which the spout swallows the tube. The results allow a better understanding of fine particle hydrodynamics in conical spouted beds, which is essential information for their scaling-up.

Interiority, Metamorphosis, and Simone Leigh’s Hybrid Cowries

By way of an analysis of Simone Leigh’s You Don’t Know Where Her Mouth Has Been (2017), this essay argues that by hybridizing the cowrie and watermelon, Leigh creates her own natural history of these biological forms that disorders the rigid taxonomic classification on which systems of discrimination rely. The resulting hybrid cowrie not only defies classification, it also forms a folded architecture that facilitates a Deleuzian reading. The hybrid cowries, by way of their capacious construction and narrow slits, evoke an interiority that enables metamorphosis. By way of the analysis of the works of Cupboard (2014) and Cowrie (Pannier) (2015), the essay further investigates architectural forms. It considers the intricate interactions between the hybrid architecture of natural forms, such as cowries and watermelons, and human-fabricated forms, such as teleuks and crinolines.

Triboelectric ‘electrostatic tweezers’ for manipulating droplets on lubricated slippery surfaces prepared by femtosecond laser processing

The use of ‘Electrostatic tweezers’ is a promising tool for droplet manipulation, but it faces many limitations in manipulating droplets on superhydrophobic surfaces. Here, we achieve noncontact and multifunctional droplet manipulation on Nepenthes-inspired lubricated slippery surfaces via triboelectric electrostatic tweezers (TETs). The TET manipulation of droplets on a slippery surface has many advantages over electrostatic droplet manipulation on a superhydrophobic surface. The electrostatic field induces the redistribution of the charges inside the neutral droplet, which causes the triboelectric charged rod to drive the droplet to move forward under the electrostatic force. Positively or negatively charged droplets can also be driven by TET based on electrostatic attraction and repulsion. TET enables us to manipulate droplets under diverse conditions, including anti-gravity climb, suspended droplets, corrosive liquids, low-surface-tension liquids (e.g. ethanol with a surface tension of 22.3 mN·m−1), different droplet volumes (from 100 nl to 0.5 ml), passing through narrow slits, sliding over damaged areas, on various solid substrates, and even droplets in an enclosed system. Various droplet-related applications, such as motion guidance, motion switching, droplet-based microreactions, surface cleaning, surface defogging, liquid sorting, and cell labeling, can be easily achieved with TETs.

Aerodynamic drag improvements on a circular cylinder using passive Venturi actuators

Scale-adaptive simulations (SAS) of three-dimensional flow around a circular cylinder fitted with a passive version of a novel flow control method (passive Venturi actuator, PVA) are performed at a diameter-based Reynolds number of Re = 28 000. The PVA consists of one or more narrow slits located at the top and/or bottom sides of the cylinder that connected to the throat of the axial Venturi slit in this cylinder. The main purpose of the study is to investigate the influence of divergence angle and narrow slit location relative to the axial Venturi slit on the aerodynamic performance of the cylinder. To this end, four models were designed with various PVAs. Additional models, a plain cylinder (unmodified model) and a cylinder fitted with an axial Venturi slit (model without a narrow slit), were also used for quantitative comparison. SAS predicts that an additional 5% reduction in the time-averaged drag coefficient, ⟨CD⟩, was observed when two narrow slits located on the surface at an angle of ±80° from the front stagnation line were fitted to the cylinder with an axial Venturi slit. Reducing the divergence angle of the PVA leads to improvements in ⟨CD⟩ and root mean square of fluctuating force coefficients, CD−rms and CL−rms. It is found that a cylinder with a PVA that has two narrow slits and a divergence angle of 6° can produce a 28.6% reduction in ⟨CD⟩, a 58.5% reduction in CD−rms, and an 81.2% reduction in CL−rms, when compared to the plain cylinder.

Tenfold sensitivity increase in streak camera detection by propagation synchronous integration without compromising time resolution.

For many applications that involve measuring ultrafast optical phenomena, the streak camera is the device of choice because of its excellent time resolution, its high sensitivity, the possibility to simultaneously measure lifetimes and spectra, and because it can capture the temporal dynamics in a single shot. Nevertheless, to obtain a good time resolution, often narrow slits have to be employed that restrict the image source area and, therefore, limit the light collection efficiency in the experiment. For some applications, it is therefore challenging to find an acceptable balance between the time resolution and signal-to-noise ratio. To overcome this limitation, we have devised the propagation synchronous integration principle for the streak camera, in which an effective spatio-dependent time-shift in the excitation of a sample is introduced and counteracted by the streak sweep, thereby effectively allowing for an increased image source area while maintaining the optimal time resolution. Using the Optronis streak camera with tunable streak sweep and large (1mm) photocathode width, we could achieve a sevenfold increase in light collection efficiency without affecting the time resolution. Furthermore, we were also able to achieve an 11-fold increase in light collection at the cost of a 26% decrease in the time resolution.

Modeling of Subwavelength Gratings: Near-Field Behavior

Subwavelength gratings have received considerable attention in the fields of photonics, optoelectronics, and image sensing. This paper presents simple analytical expressions for the near-field intensity distribution of radiation scattered by these gratings. Our proposed methodology employs a 2D point dipole model and a specialized version of perturbation theory. By validating our models via numerical techniques including boundary and finite element methods, we demonstrate their effectiveness, even for narrow slits.

Compact contactless conductometric, ultraviolet photometric and dual-detection cells for capillary electrophoresis via additive manufacturing

The growing demand for tailored detectors in capillary electrophoresis (CE), addressing tasks like field deployment or dual-detection analysis, emphasizes the necessity for compact detection cells. In this work, we propose cost-effective and user-friendly additive manufacturing (3D-printing) approaches to produce such miniaturized detection cells suitable for a range of CE applications. Firstly, capacitively-coupled contactless conductivity detection (C4D) cells of different sizes are fabricated by casting low-melting-point alloy into 3D-printed molds. Various designs of Faraday shields are integrated within the cells and compared. A mini-C4D cell (9.5×7.0×7.5 mm3) is produced, with limits of detection for alkaline cations ranging from 8-12 μM in a short–capillary based CE application. Secondly, ultraviolet photometric (UV-PD) detection cells are fabricated using 3D printing. These cells feature two narrow slits with a width of 60 μm, which are positioned along the path of incident and transmission light to facilitate collimation. A deep UV-LED (235 nm or 255 nm) is employed as the light source, and black resin is determined to be the optimal material for 3D printing the UV-PD cell, owing to its superior UV light absorption capabilities. The UV-PD cell is connected to the LED and photodetector through two optical fibers, making it easy to switch the light source and detector. The effective pathlength and stray light percentage for detecting on a 75 μm id capillary are 74 μm and 0.5 %, respectively. Thirdly, a dual-detection cell that combined C4D and UV-PD at a single detection point is proposed. The performance of direct detection by C4D and indirect detection by UV-PD is compared for detecting organic acids. The strategies for developing cost-effective compact detection cells facilitate the versatile integration of multiple detection methods in CE analysis.

Numerical study of the behavior of rectangular acoustic black holes for sound absorption in air

In this work, the behavior of acoustic black holes (ABHs) serving as an anechoic termination of air-filled waveguides with a rectangular cross-section is numerically studied. These ABHs consist of a set of rigid ribs separated by narrow slits, whose height smoothly varies along the structure and whose aim is to slow-down the impinging acoustic wave and cause its absorption. For the purpose of this study, a 2D mathematical model based on linearized Navier–Stokes equations and employing the finite element method has been proposed, which allows for an accurate capturing the thermoviscous losses in the acoustic boundary layer adjacent to the solid–fluid interfaces, as well as the effects connected with geometrical details of the ABHs’ inner structure. The numerical results show that in rectangular ABHs with a fine internal structure, the acoustic wave slow-down plays a significant role and that absorption properties are strongly dependent on their inner structure details. Simplified 1D mathematical models of rectangular ABHs based on the Riccati equation or transfer matrix method have also been proposed. These simplified models are computationally highly efficient, as it has been demonstrated, they provide accurate results, especially in the case of ABHs with a fine internal structure, which feature superior acoustic energy absorbing properties.

Aging and temporal integration in the visual perception of object shape

It has been known for more than 160 years that highly occluded objects that would normally be visually unrecognizable can be successfully identified when they move. This anorthoscopic perception relies on the visual system’s ability to integrate information over time to complete the perception of an entire object’s shape. In this experiment, 16 younger and older adults (mean ages were 20.5 and 74.6 years, respectively) were familiarized with the (unoccluded) shapes of five naturally-shaped objects (bell peppers, Capsicum annuum) until they could be easily identified (i.e., with accuracies of at least 90 percent correct). All observers then viewed the stimulus objects anorthoscopically as they moved behind narrow slits; only small object fragments could be seen at any given time, because the objects were almost totally occluded from view. Even though the object identification performance for all observers was equivalent when whole object shapes were visible, a large age-related deficit in object identification emerged during anorthoscopic viewing such that the younger adults’ identification performance was 45.4 percent higher than that of the older adults. This first ever study of aging and anorthoscopic perception demonstrates that there is an age-related deficit in performing the temporal integration needed for successful object recognition.

N2/CO ratio in comets insensitive to orbital evolution

ABSTRACT Comets are seen as depleted in nitrogen compared to the protosolar value, but a small number exhibit significantly higher than typical N2/CO ratios: C/1908 R1 (Morehouse), C/1940 R2 (Cunningham), C/1947 S1 (Bester), C/1956 R1 (Arend–Roland), C/1957 P1 (Mrkos), C/1961 R1 (Humason), C/1969 Y1 (Bennett), C/1973 E1 (Kohoutek), C/1975 V1-A (West), C/1986 P1 (Wilson), C/1987 P1 (Bradfield), C/2001 Q4 (NEAT), C/2002 VQ94 (LINEAR), C/2016 R2 (PanSTARRS), and periodic comets 1P/Halley, 29P/Schwassmann–Wachmann 1, and 67P/Churyumov–Gerasimenko. This study examines the composition and dynamical histories of these N2-‘rich’ comets to unearth insights into their formation processes. Using updated N2 fluorescence factors, we re-estimate the N2/CO ratios of this sample and find that they are consistent with the expected values for comets based on estimations of the protosolar nebula. These also often display larger nucleus sizes and show rapid tail morphology variations due to their ionic nature. Numerical simulations reveal no common dynamical history, suggesting that the N2/CO ratio is independent of the number of inner Solar System passages and that N2 is homogeneously distributed within these comets. These volatile-rich comets share an Oort Cloud origin which is consistent with their survival over the past 4.5 Gyr. Our study also suggests that there may be a bias using modern high-resolution spectrometers with narrow slits, which could potentially overlook the ion tail of comets. We advocate for the use of long-slit spectroscopy to potentially detect a wider range of N2-rich comets, thereby enriching our understanding of comet compositions and origins.

Shapes and dynamic regimes of a polar active fluid droplet under confinement

Active droplets are artificial microswimmers built from a liquid dispersion by microfluidic tools and showing self-propelled motion. These systems hold particular interest for mimicking biological phenomena, such as some aspects of cell locomotion and collective behaviors of bacterial colonies, as well as for the design of droplet-based biologically inspired materials, such as engineered tissues. Growing evidence suggests that geometrical confinement crucially affects their morphology and motility, but the driving physical mechanisms are still poorly understood. Here, we study the effect of activity on a droplet containing a contractile polar fluid confined within microfluidic channels of various sizes. We find a surprising wealth of shapes and dynamic regimes, whose mechanics is regulated by a subtle interplay between contractile stress, droplet elasticity, and microchannel width. They range from worm-like and cell-like shaped droplets displaying an oscillating behavior within wider channels to bullet-shaped droplets exhibiting rectilinear motion in narrower slits. Our findings support the view that geometrical confinement can provide a viable strategy to control and predict the propulsion direction of active droplets. It would be of interest to look for analogs of these motility modes in biological cells or in synthetic active matter.

A Multicompressed-High-Order Modes Dipole Antenna With Wide-Beam and High-Gain Radiations in Two Different Bands

In this letter, a multi-compressed-high-order mode dipole antenna with wide-beam coverage and high-gain radiations in two respective sub-6 GHz bands is proposed. The capacitors and inductors are loaded at the current distribution nulls of the fifth-order mode of the dipole arms. The loading brings the resonant frequencies of the third- and the seventh-order modes closer to the fifth-order mode, and thus achieves wide bandwidth. In addition, the loadings change the current distribution of the third- and the seventh-order modes, and achieve radiation patterns with wide coverage in the lower band and high gain in the higher band. To facilitate fabrication, the capacitors and inductors are replaced by narrow slits and bending lines separately. A prototype of this design is fabricated and measured. The measurement and simulation results are in good agreement. The proposed antenna achieves a wideband of 3.30 to 5.35 GHz (VSWR < 2) with an omnidirectional radiation pattern in the horizontal plane. In addition, it achieves a ±57° coverage angle over 0 dBi in the lower band and 6.41 dBi peak gain in the higher band in the vertical plane, which can be applied for 5G wireless communication.

Effect of electric field, mass flow rate, and subcooling degree on subcooled flow boiling in a micro-slit channel

This study investigated the design and cooling performance of a micro-slit-channel heat sink for electrical device cooling. The subcooled flow-boiling performance of a dielectric liquid, HFE-7000, was experimentally characterized. A flat electrode made from stainless steel with 10 narrow slits, each 1 mm width and 17 mm long, was placed at 600 μm above the heated surface to generate a high electric field. The flow boiling heat transfer performance of an electroplated diamond surface was evaluated. Four electric field intensities from 0 to −5 kV/mm, three mass flow rates from 1.83 to 4.8 g/s, and four inlet subcooling from 5 to 25 K were tested at an atmospheric system pressure. Four flow boiling patterns were categorized using a high-speed camera: single-phase flow, subcooled nucleate boiling, saturated nucleate boiling, and local dry out boiling. The maximum critical heat flux (CHF) and heat transfer coefficient were 95 W/cm2 and 30 kW/m2K, respectively, for mass flow rate of 4.83 g/s, electric field of −5 kV/mm, subcooling degree of 9 K, and mass flow rate of 4.83 g/s. A semi-empirical prediction of the CHF exhibited good agreement with the experimental results within ±18 %.

A notch-mask and dual-prism system for snapshot spectral imaging

In this paper, we present a notch-mask and dual-prism based system for snapshot spectral imaging. Different from traditional spectrometers that utilize band-pass filters or narrow slits to prevent spectral overlap, losing most of the light emitted from the scene, the main idea of our system is to design a spatial notch mask that only occludes the light of sparsely distributed spectral samplings, and introduce a dual-prism architecture to form a non-dispersive RGB measurement on the detector, resulting in the system’s superiority of high light efficiency and high spatial resolution within the snapshot. Then, we develop a model-based algorithm to reconstruct a high-resolution spectral image from the captured RGB measurement, which is of high tolerance to calibration noise since the spectral information can be directly calculated by a minus operation. Simulated experiments have been conducted to verify the effectiveness of the proposed method, and we also build up a prototype system to further demonstrate the practical application and feasibility of our scheme.

Evaluation of coplanar line type thin film magnetic field sensor with narrow slits

We have proposed coplanar line type thin-film magnetic field sensor with narrow slits. The slit is employed to flow more carrier current on the signal line by improving the impedance matching. Several sensors having 6, 10, 26, 36, and 50 μm slit widths were fabricated and evaluated from the phase and the amplitude of the transmission coefficient (S21) and reflection coefficient (S11) measured by the network analyzer. The amplitude of S21 with slit was improved about five times larger than the sensor without one at around 2 GHz. The appropriate slit width was evaluated as around 10 μm for the coplanar line type thin film magnetic field sensor and the sensitivity will enhance more than 10 times higher than the sensor without slits.

Molecular dynamics simulations of the monomer density profiles of knotted ring polymer chains confined in a slit of two parallel walls with one attractive and another repulsive surface.

We have used Molecular Dynamics simulations to obtain the monomer density profiles for real linear and ring polymer chains of 360 monomers length with different topological structures such as simple knots: 31, 61, 91, 10124, complex knots 313151 and twisted knots with n = 10 and n = 20 in a slit geometry of two parallel walls with one attractive and another repulsive surface. We have used Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software to perform simulations with the Verlet integration algorithm. The interactions between monomers were simulated as Lennard-Jones 12-6 potential, for bonds we have used Finitely Extensible Nonlinear Elastic (FENE) potential and the interaction with the walls was taken into account via Lennard-Jones 9-3 potential. We observed that topologically complex polymers have lower monomer density profiles near the attractive wall, but at some distance in the direction to the repulsive wall this tendency changes to the opposite. We showed that most complex twisted knots have two maxima in narrow slits. In the wide slits we do not observe such relation for twisted knots at higher temperatures. These results are important for better understanding the nature of the depletion forces which arise in a slit geometry of two parallel walls with one attractive and one repulsive wall.