Circular Posts Research Articles

Hybrid integrated GaSb/Si3N4 narrow linewidth (<50 kHz) distributed Bragg reflector laser

A narrow linewidth hybrid integrated distributed Bragg reflector (DBR) laser platform operating at 2 μm wavelength region is demonstrated. The laser architecture comprises AlGaInAsSb/GaSb type-I quantum well reflective semiconductor optical amplifiers butt-coupled to a Si3N4 photonic integrated circuit (PIC), incorporating a narrow-band DBR. The DBR is realized with a long spiral-shaped waveguide structure with periodic circular posts placed adjacent to the waveguide. At room temperature operating conditions, the laser exhibits a maximum continuous wave output power of more than 17 mW for emission near 2 μm. Linewidth properties are analyzed with a heterodyne measurement technique, involving the mixing of the laser signal with a frequency comb phase-locked to an ultra-stable laser. The hybrid laser exhibits a narrow linewidth of ∼8 kHz in 1 ms timescale and ∼50 kHz in 10 ms timescale.

Oscillating flow around a circular cylindrical post confined between two parallel plates

This work is motivated by the interest in determining the effect of the micro-anatomy of the spinal subarachnoid space (SSAS) on the cerebrospinal fluid flow. To that aim, we model the nerve roots in the SSAS by circular posts of radius a, confined between two parallel plates separated by a distance 2h and subjected to an oscillatory flow of angular frequency ω. First, we analyze the asymptotic limit of small values of the dimensionless stroke length of the oscillatory flow, for a harmonic waveform, varying the aspect ratio of the post λ=h/a and the Womersley number Wo=(a2ω/ν)1/2. For low values of Wo, the time-averaged steady flow exhibits symmetric recirculating vortices attached to the wall of the post whose size decreases as Wo increases. However, for values of Wo larger than a critical one, Woc(λ), which depends on λ, a second, outer vortex is also formed. The dependence of Woc(λ) has been quantified in the range 0.5<λ<∞, showing a decrease in Woc with λ. The analysis has been corroborated experimentally for λ = 2, and varying Wo, the stroke length as well as the wave form of the oscillating flow. Imposing an anharmonic oscillating flow shows that the fort-and-aft symmetry of the steady flow is broken, with the formation of two vortices of different size when Wo<Woc and only one outer vortex in the systolic direction when Wo>Woc. Finally, the study is experimentally extended considering an array of equally spaced posts, separated a semi-distance d=2a aligned with the flow. Qualitatively, the steady flow patterns induced for ℓ=d/a=2 are similar to those for ℓ→∞, although the presence of the nearby posts confines the recirculating vortices and delays the flow transition, increasing Woc(λ).

Social media on the route to circular economy transition from a dialogic perspective: evidence from the agri-food industry

PurposeThis paper investigates circular economy communications and stakeholder dialogic engagement with circular economy posts published by European agri-food companies on Twitter from the spread of the COVID-19 pandemic. It explores the use of social media as a dialogic tool to activate circular economy engagement in order to involve all supply-chain actors on the route to a circular transition.Design/methodology/approachA coding framework based on the reclassification of the Glossary of Circular Economy, according to a 4-R paradigm (reduce, reuse, recycle and recover), was developed for the analysis. All tweets published by a sample of European agri-food companies, starting from the start of the COVID-19 pandemic until data extraction, were collected, purified and analysed.FindingsAgri-food companies showed a higher level of engagement through social media, even if mainly focused on “recycling” and “general circular economy” issues. In general, awareness among social network users of the need to be part of the circular economy transition emerged. Moreover, the highest percentage of posts published by the companies' Twitter accounts was informative rather than interactive. In addition, starting with the COVID-19 pandemic crisis, the circular economy has arisen as a central topic of debate and a driver for the rethinking process of the agri-food business community.Originality/valueTo the best of the authors' knowledge, this research represents the first study focused on circular economy engagement through social media from the company perspective in the agri-food industry.

Multicellular Cell Seeding on a Chip: New Design and Optimization towards Commercialization.

This paper shows both experimental and in-depth theoretical studies (including simulations and analytical solutions) on a microfluidic platform to optimize its design and use for 3D multicellular co-culture applications, e.g., creating a tissue-on-chip model for investigating diseases such as pulmonary arterial hypertension (PAH). A tissue microfluidic chip usually has more than two channels to seed cells and supply media. These channels are often separated by barriers made of micro-posts. The optimization for the structures of these micro-posts and their spacing distances is not considered previously, especially for the aspects of rapid and cost-efficient fabrication toward scaling up and commercialization. Our experimental and theoretical (COMSOL simulations and analytical solutions) results showed the followings: (i) The cell seeding was performed successfully for this platform when the pressure drops across the two posts were significantly larger than those across the channel width. The circular posts can be used in the position of hexagonal or other shapes. (ii) In this work, circular posts are fabricated and used for the first time. They offer an excellent barrier effect, i.e., prevent the liquid and gel from migrating from one channel to another. (iii) As for rapid and cost-efficient production, our computer-aided manufacturing (CAM) simulation confirms that circular-post fabrication is much easier and more rapid than hexagonal posts when utilizing micro-machining techniques, e.g., micro-milling for creating the master mold, i.e., the shim for polymer injection molding. The findings open up a possibility for rapid, cost-efficient, large-scale fabrication of the tissue chips using micro-milling instead of expensive clean-room (soft) lithography techniques, hence enhancing the production of biochips via thermoplastic polymer injection molding and realizing commercialization.

Theoretical analysis of close-contact melting on superhydrophobic surfaces

The present study deals with close-contact melting of a vertical cylinder on a horizontal isothermal superhydrophobic surface with an array of circular posts. A new numerical model for this phenomenon is formulated under several simplifying assumptions. For the limiting case of perfect slip and thermal contact, based on the model assumptions, it is demonstrated that superhydrophobic surfaces can enhance the melting time by no more than 30 %. Numerical solution of the new model reveals that the effect of superhydrophobic hydrodynamic slip can decrease the molten layer thickness. However, due to the dominant effect of thermal slip, the heat transfer rate can be decreased significantly, and the melting time can be roughly doubled. An approximate analytical model is developed for understanding the problem dynamics better. The analytical model predictions are compared extensively against the numerical model results. For sufficiently low surface volume fractions, the analytical model provides excellent estimations of the numerical model predictions. Dimensional analysis reveals that according to the analytical model, the ratio between the melting times for superhydrophobic and regular surfaces is governed by a single dimensionless group. Moreover, according to the analytical model, the melting time on a superhydrophobic surface is always longer than on a regular surface, which agrees qualitatively with the numerical model results. Based on this analysis, a dimensionless condition for the analytical model range of validity is formulated. Finally, a conservative criterion for the liquid–gas interface stability under a close-contact melting process is established.

Comparison of the Bond Strength of Circular and Oval-Shaped Fiber-Reinforced Composite Posts in Oval Shaped Canals

Background: Fiber reinforced composite resin (FRC) posts are used to restore endodontically treated teeth. Many factors affect the bond strength of posts; however, there is a concern regarding the mismatch between the posts and oval root canals and its effect on posts retention. Aim: To compare the bond strength of circular and oval-shaped fiber-reinforced composite posts in oval shaped canals. Materials and Methods: Forty Five extracted single rooted human premolars with single oval-shaped root canals were decorated, endodontically treated and prepared to receive quartz reinforced composite resin posts, then they were randomly assigned to three groups, the posts in the first group (control) (n=15) were parallel with circular cross section (Match post, RTD, France), the posts in the second group (n=15) were taper with circular cross section (DtLight Illusion post, RTD, France), The posts in the third group were oval shaped (Macro lock oval post, RTD, France). The posts in the three groups were cemented with dual cure resin cement (Permflo DC Composite Luting, Ultra dent, USA). All samples were then stored in 100% relative humidityat at room temperature for 24 hours then pull-out test was performed and data were analyzed using one-way analysis of variance (ANOVA) followed by Bonferonni's post hoc test (a = 0.05). Results: Oval shaped posts showed higher bond strength values than circular posts, whether the circular posts were conical(taper)or parallel (control) (p<0.05).Conclusions: The bond strength of fiber reinforced composite resin posts in oval root canals increased when the posts were oval-shaped.

Deterministic Lateral Displacement Using Hexagonally Arranged, Bottom-Up-Inspired Micropost Arrays.

Size-based separation of particles in microfluidic devices can be achieved using arrays of micro- or nanoscale posts using a technique known as deterministic lateral displacement (DLD). To date, DLD arrays have been limited to parallelogram or rotated-square arrangements of posts, with various post shapes having been explored in these two principal arrangements. This work examines a new DLD geometry based on patterning obtainable through self-assembly of single-layer nanospheres, which we call hexagonally arranged triangle (HAT) geometry. Finite element simulations are used to characterize the DLD separation properties of the HAT geometry. The relationship between the array angle, the gap spacing, and the critical diameter for separation is derived for the HAT geometry and expressed in a similar mathematical form as conventional parallelogram and rotated-square DLD arrays. At array angles <7°, HAT structures demonstrate smaller particle sorting capability (smaller critical diameter-to-gap spacing ratio) compared to published experimental results for parallelogram-type DLD arrays with circular posts. Experimental validation of DLD separation confirms the separation ability of the HAT array geometry. It is envisioned that this work will provide the first step toward future implementation of nanoscale DLD arrays fabricated by low-cost, bottom-up self-assembly approaches.

Design and analysis of an optimized microfluidic channel for isolation of circulating tumor cells using deterministic lateral displacement technique

Circulating tumor cells (CTCs) are extremely scarce cells which cut off from a primary tumor and percolate into the circulation of blood flow and are, thus, critical for precise cancer detection and treatment. Deterministic lateral displacement (DLD) which exploits asymmetric splitting of laminar flow around the implanted microposts has displayed trustworthy capabilities in separating cells of varying sizes. In this research work, a microfluidic channel consisting of three symmetrically aligned inlets and outlets and embedded circular posts has been proposed which effectively separates the CTCs from lymphocytes utilizing the concept of DLD. Using a commercial software COMSOL Multiphysics 5.4, the design of the proposed microchannel has been simulated and analyzed considering an injected blood sample containing massive CTCs and slim WBCs of radii 13.5 µm and 6 µm, respectively. The proposed model of microchannel isolates the CTCs from WBCs at a comparatively higher sample mass flow rate of 4 × 10–6 kg/s and Reynolds number of 8.9 thereby operating efficiently at higher throughput, and offers excellent linearity in terms of velocity magnitude, pressure, shear rate and Reynolds number. The computational analysis of the proposed microchannel reveals that it can isolate CTCs from WBCs with better separation ratio, offers higher throughput, reduces possibilities of clogging and maintains better uniformity of pressure distribution and other flow parameters when compared with existing microchannel designs. The maximum separation ratio for CTCs and WBCs has been obtained as 84% and 96%, respectively.

A Post-Loaded Rectangular Reentrant Cavity for Broadband Multiple-Beam Klystron

In an effort to enhance the bandwidth of a multiple-beam klystron having rectangular double reentrant cavity with circular cylindrical ferrule, reduction of the unloaded quality factor of the cavity was proposed by placing circular cylindrical posts extending from one of the cavity side-walls to the opposite wall in an orientation perpendicular to the electric field. A typical cavity was analyzed using 3D electromagnetic field solver CST Studio and the post-loading was found to reduce the unloaded quality factor by around 90% compared to that for no-post-loading. The proposed method was found to be the only method other than the use of passive loss to achieve this order of reduction in the quality factor with a minor increase in the cavity transverse dimensions. Post made of highly resistive material was found to have pronounced effect in reducing the quality factor. The 3D electromagnetic analysis was validated against measurements on a typical S-band cavity.

Deformation and dynamics of erythrocytes govern their traversal through microfluidic devices with a deterministic lateral displacement architecture.

Deterministic lateral displacement (DLD) microfluidic devices promise versatile and precise processing of biological samples. However, this prospect has been realized so far only for rigid spherical particles and remains limited for biological cells due to the complexity of cell dynamics and deformation in microfluidic flow. We employ mesoscopic hydrodynamics simulations of red blood cells (RBCs) in DLD devices with circular posts to better understand the interplay between cell behavior in complex microfluidic flow and sorting capabilities of such devices. We construct a mode diagram of RBC behavior (e.g., displacement, zig-zagging, and intermediate modes) and identify several regimes of RBC dynamics (e.g., tumbling, tank-treading, and trilobe motion). Furthermore, we link the complex interaction dynamics of RBCs with the post to their effective cell size and discuss relevant physical mechanisms governing the dynamic cell states. In conclusion, sorting of RBCs in DLD devices based on their shear elasticity is, in general, possible but requires fine-tuning of flow conditions to targeted mechanical properties of the RBCs.

Numerical study of insulation structure characteristics and arrangement effects on cell trapping using alternative current insulating based dielectrophoresis

Insulator-based dielectrophoresis is a recently developed technique in which insulating posts are used to produce non-uniformity in the electric field in a microchannel. This study presents the effects of insulating posts geometry and arrangement on the trapping efficiency of red blood cells in an alternating current- Insulator-based dielectrophoresis system. Microchannels containing square, circular and diamond-shaped posts with particles under the influence of positive dielectrophoresis force and fluid flow were considered. Finite element method was used to compute the velocity of the flow and electric field. The numerical method was verified by comparing the numerical results with experimental data. Two distinct criteria for examining particle trapping for distinct shapes and arrangements of insulating posts were introduced. Particle tracing simulation was implemented to observe particle trapping and compare the trapping performance of systems with distinct posts. As shown in the results for the system with circular and square posts, insulators should be narrowed to improve particle trapping, while diamond post should be widened to increase the trapping efficiency. In addition, the particle tracing results showed that microchannel with square posts is more efficient in particle trapping.

Effects of the geometric shape and placing length of a fiber post on the stress distribution in a mandibular premolar tooth: A finite element analysis study

Aim: The aim of this study was to evaluate the effects of two geometrically different fiber post systems and two different placing lengths on the stress distribution of endodontically treated teeth.&#x0D; Methodology: Four different mandibular premolar tooth models were created. These models were restored using oval or circular fiber posts with two different placing lengths. An oblique force of 300 N was applied to the top of the tooth, and von Mises stress evaluations were carried out on the dentin tissue, luting cement, and fiber posts.&#x0D; Results: The maximum von Mises stresses were observed in the 10-mm long circular fiber post model, while the minimum stresses were seen in the 5-mm long oval fiber post model. In general, the oval fiber post models presented more homogeneous stresses than the circular fiber post models. Moreover, the 10-mm long fiber post models generated greater von Mises stresses than the 5-mm long fiber post models in the dentin tissue and luting cement.&#x0D; Conclusion: According to the study findings, the use of oval fiber posts at both placing lengths is suggested for oval shaped root canals due to the lower stress concentrations.

Influence of micro-structured superhydrophobic surfaces on nucleation and natural convection in a heated pool

This work experimentally explores sub-boiling pool nucleation on micro-structured superhydrophobic surfaces. All surfaces tested were submerged in a 20 mm deep pool of water and heated from below to maintain a constant surface temperature, while the side walls of the pool were insulated, and the top was covered. Three thermocouples positioned in the pool obtain the average pool temperature. A heat flux sensor is placed directly beneath the surface to measure the heat flux supplied to the pool. Free convection heat transfer coefficients are obtained for the sub-boiling temperature range of 40–90 °C. Six surface types are studied: smooth hydrophilic, smooth hydrophobic, superhydrophobic with rib/cavity structures, superhydrophobic with rib/cavity structures and additional sparsely spaced ribs to close off the cavities, circular posts, and circular holes. It is found that structured superhydrophobic surfaces provide cavities for nucleation to occur. More dissolved air effervesces from the water as the surface temperature increases due to an increased level of supersaturation and convection. The nucleation leads to large air bubble formations that reduce the overall convection coefficient when compared to the smooth surfaces. For the rib/cavity structured surfaces, the bubbles form in an anisotropic manner and are aligned with the surface structure. More bubbles are observed on the superhydrophobic surfaces where the cavities are bounded. Since water’s ability to dissolve air is dependent on temperature, heat and mass transfer cannot be treated independently on any of the superhydrophobic surfaces studied here.

A Triple-Mode Bandpass Filter With Controllable Bandwidth Using QMSIW Cavity

A compact triple-mode bandpass filter using a modified quarter-mode substrate integrated waveguide (QMSIW) cavity is presented. It is realized by exploiting the first three resonant modes of the QMSIW cavity. Specifically, the dominant mode (TE101) is shifted toward the second resonant mode (TE202) through the perturbation induced by the metallized via-holes array. The resonant frequency of the third resonant mode (TE303) is lowered toward the TE202 mode owing to the capacitive loading effect of the loaded circular conductive posts array. In this way, by adjusting the via-holes array and the conductive posts array, the resonant frequencies of the first and third resonant modes can be independently tuned while the second resonant mode remains unchanged. As a result, the bandwidth of the resulting filter can be flexibly controlled at a preassigned center frequency. Moreover, to suppress the spurious frequencies generated by the higher order modes, three cascaded defected ground structures were introduced below the feedline to distinctly widen the stopband and increase the out-of-band rejection.

Vortex interaction with a rough wall formed by a hexagonal lattice of posts

An experimental study is reported which investigates the head-on collision of a laminar vortex ring of diameter D (ReΓ= 3000) on a fakir-like surface composed of slender circular posts protruding out of a planar layer. Lattices of the posts in hexagonal and random distribution (average porosity of ϵ = 0.94 in the layer) are compared to each other with respect to the plain wall. Prior to impact, the vortex ring develops the early state of natural azimuthal instabilities of different mode numbers N = 5-7 competing with each other. While impacting with the wall, the hexagonal lattice causes the rapid growth of secondary vortex structures in a regular mode number N = 6 arrangement at the outer edge of the primary ring in the form of six lobes which are aligned with the orientations of preferential “pathways” in the lattice. At the outer tip of the lobes, radial wall-jets are generated. Rotating the layer with the hexagonal lattice results in the same rotation of the secondary flow pattern with the jets’ orientation lock-in with the orientation of the lattice. The layer with random distribution of the posts at the same number density is not able to repeat this observation and no regular secondary flow pattern is seen. The results show that a tailored arrangement of such posts can be used for near-wall flow control such as in impacting jet flows or in boundary layer flows when instability modes in the flow lock-in with the wall pattern consisting of preferred pathways in the posts’ layer.

An efficient finite element method for simulation of droplet spreading on a topologically rough surface

We study numerically the dynamics of a three-dimensional droplet spreading on a rough solid surface using a phase-field model consisting of the coupled Cahn–Hilliard and Navier–Stokes equations with a generalized Navier boundary condition (GNBC). An efficient finite element method on unstructured meshes is introduced to cope with the complex geometry of the solid surfaces. We extend the GNBC to surfaces with complex geometry by including its weak form along different normal and tangential directions in the finite element formulation. The semi-implicit time discretization scheme results in a decoupled system for the phase function, the velocity, and the pressure. In addition, a mass compensation algorithm is introduced to preserve the mass of the droplet. To efficiently solve the decoupled systems, we present a highly parallel solution strategy based on domain decomposition techniques. We validate the newly developed solution method through extensive numerical experiments, particularly for those phenomena that can not be achieved by two-dimensional simulations. On a surface with circular posts, we study how wettability of the rough surface depends on the geometry of the posts. The contact line motion for a droplet spreading over some periodic rough surfaces are also efficiently computed. Moreover, we study the spreading process of an impacting droplet on a microstructured surface, a qualitative agreement is achieved between the numerical and experimental results. The parallel performance suggests that the proposed solution algorithm is scalable with over 4,000 processors cores with tens of millions of unknowns.

Microfluidically Reconfigurable Rectangular Waveguide Filter Using Liquid Metal Posts

In this letter, the integration of microfluidically controlled liquid metal with WR42 rectangular waveguide to implement reconfigurable band-reject/band-pass filter is introduced. Here, microfluidic channels carrying liquid metal are used to realize off-centered adjustable partial/full-height circular posts at the dominant ${TE}_{10}$ mode. First, a liquid metal post is partially inserted into the waveguide to create a tunable transmission zero over a 2.9 GHz rejection tuning range (18.20 GHz to 21.10 GHz). Next, the band-reject element (partial-height post) is used in conjunction with another microfluidic metal post to design a reconfigurable 1-pole band-pass filter with a transmission zero in the stop-band. The filter is configured for two states. The measured insertion loss of the filter at $f_{0}$ is 2.3 dB and 2.8 dB while the return loss is better than 20 dB and 30 dB for State 1 and State 2 respectively.

Push-out bond strength of oval versus circular fiber posts irradiated by erbium-doped yttrium aluminum garnet laser

Statement of problemFiber posts in conjunction with resin cements are widely used to provide retention in endodontically treated teeth. The bond strength of restorative materials to root canal dentin is an important issue for the long-term success of restorative procedures. The push-out test is widely used to measure the bonding between the post and radicular dentin. PurposeThe purpose of this in vitro study was to evaluate the effect of erbium-doped yttrium aluminum garnet (Er-YAG) laser treatment of dentinal walls on the bond strength of circular and oval fiber posts luted in oval root canals. Material and methodsForty mandibular premolar teeth were endodontically treated and restored with 2 different intracanal post systems. Push-out tests were performed and data were analyzed by using 2-way analysis of variance and post hoc Bonferroni tests. ResultsLaser pretreatment of dentinal walls resulted in higher push-out bond strength than that of the nonlasered groups (P<.05). Oval fiber posts showed significantly higher push-out bond strength values than those of circular fiber posts in the coronal region (P<.05). In the apical region, no statistically significant difference was noted among the groups regarding push-out bond strength (P>.05). ConclusionsThe laser pretreatment with an oval ultrasonic tip of an oval fiber post system improved bonding to root canal dentin when compared with a circular post system with conventional preparation.

Radio‐frequency performance comparison of several H ‐plane rectangular waveguide filters loaded with circular dielectric posts

The study presents a radio-frequency performance comparison between several H-plane geometry filters based on rectangular waveguide technology. The basic all-metal filter of resonant cavities is compared with filters loaded with circular dielectric resonators, either in propagative or evanescent mode. The use of these resonators is claimed to reduce the length of the filter, increase the rejection band until the first spurious frequency and to improve the voltage magnification factor (VMF), at the cost of increasing the losses. Therefore, in order to properly assess and quantify the possible advantages of these filters, an accurate analysis of six of them has been developed. All the filters have been designed to have the same electrical response, and the length, losses, rejection band, VMF, and fabrication cost for all the filters are compared.

Topographical pathways guide chemical microswimmers.

Achieving control over the directionality of active colloids is essential for their use in practical applications such as cargo carriers in microfluidic devices. So far, guidance of spherical Janus colloids was mainly realized using specially engineered magnetic multilayer coatings combined with external magnetic fields. Here we demonstrate that step-like submicrometre topographical features can be used as reliable docking and guiding platforms for chemically active spherical Janus colloids. For various topographic features (stripes, squares or circular posts), docking of the colloid at the feature edge is robust and reliable. Furthermore, the colloids move along the edges for significantly long times, which systematically increase with fuel concentration. The observed phenomenology is qualitatively captured by a simple continuum model of self-diffusiophoresis near confining boundaries, indicating that the chemical activity and associated hydrodynamic interactions with the nearby topography are the main physical ingredients behind the observed behaviour.