Small Confinement Research Articles

Interplay of surface interaction and magnetic torque in single-cell motion of magnetotactic bacteria in microfluidic confinement.

Swimming microorganisms often experience complex environments in their natural habitat. The same is true for microswimmers in envisioned biomedical applications. The simple aqueous conditions typically studied in the lab differ strongly from those found in these environments and often exclude the effects of small volume confinement or the influence that external fields have on their motion. In this work, we investigate magnetically steerable microswimmers, specifically magnetotactic bacteria, in strong spatial confinement and under the influence of an external magnetic field. We trap single cells in micrometer-sized microfluidic chambers and track and analyze their motion, which shows a variety of different trajectories, depending on the chamber size and the strength of the magnetic field. Combining these experimental observations with simulations using a variant of an active Brownian particle model, we explain the variety of trajectories by the interplay between the wall interactions and the magnetic torque. We also analyze the pronounced cell-to-cell heterogeneity, which makes single-cell tracking essential for an understanding of the motility patterns. In this way, our work establishes a basis for the analysis and prediction of microswimmer motility in more complex environments.

Malleable Patterns from the Evaporation of a Colloidal Liquid Bridge: Coffee Ring to the Scallop Shell.

The present article highlights an approach to generating contrasting patterns from drying colloidal droplets in a liquid bridge configuration, different from well-known coffee rings. Reduction of the confinement distance (the gap between the solid surfaces) leads to systematized nanoparticle agglomeration yielding spoke-like patterns similar to those found on scallop shells instead of circumferential edge deposition. Alteration of the confinement distance modulates the curvature that entails variations in the evaporation flux across the liquid-vapor interface. Consequently, flow inside different liquid bridges (LBs) varies significantly for different confinement distance. Small confinement distance results in the stick-slip motion of squeezed liquid bridges. On the contrary, the stretched LBs exhibit pinned contact lines. The confinement distance determines the characteristic length scales of the thin film formed near the contact line, and its theoretical estimations are validated against the experimental observations using reflection interferometry, further exhibiting good agreement (in order of magnitude). We decipher a proposition that a drying liquid thin film (height ∼ O(10-7)m) present during dewetting near the three-phase contact line is responsible for the aligned deposition of particles. The coupled interplay of contact line dynamics, evaporation induced advection, and dewetting of the thin film at a three-phase interface contributes to the differences in deposition patterns.

Peritonsillar Abscess Simulator: A Low-Cost, High-Fidelity Trainer.

Peritonsillar Abscess Simulator: A Low-Cost, High-Fidelity Trainer.

New H-mode regimes with small ELMs and high thermal confinement in the Joint European Torus

New H-mode regimes with high confinement, low core impurity accumulation, and small edge-localized mode perturbations have been obtained in magnetically confined plasmas at the Joint European Torus tokamak. Such regimes are achieved by means of optimized particle fueling conditions at high input power, current, and magnetic field, which lead to a self-organized state with a strong increase in rotation and ion temperature and a decrease in the edge density. An interplay between core and edge plasma regions leads to reduced turbulence levels and outward impurity convection. These results pave the way to an attractive alternative to the standard plasmas considered for fusion energy generation in a tokamak with a metallic wall environment such as the ones expected in ITER.

Quantum theory of two-dimensional materials coupled to electromagnetic resonators

We present a microscopic quantum theory of light-matter interaction in pristine sheets of two-dimensional semiconductors coupled to localized electromagnetic resonators such as optical nanocavities or plasmonic particles. The light-matter interaction breaks the translation symmetry of excitons in the two-dimensional lattice, and we find that this symmetry-breaking interaction leads to the formation of a localized exciton state, which mimics the spatial distribution of the electromagnetic field of the resonator. The localized exciton state is in turn coupled to an environment of residual exciton states. We quantify the influence of the environment and find that it is most pronounced for small lateral confinement length scales of the electromagnetic field in the resonator, and that environmental effects can be neglected if this length scale is sufficiently large. The microscopic theory provides a physically appealing derivation of the coupled-oscillator models widely used to model experiments on these types of systems, in which all observable quantities are directly derived from the material parameters and the properties of the resonant electromagnetic field. As a consistency check, we show that the theory recovers the results of semiclassical electromagnetic calculations and experimental measurements of the excitonic dielectric response in the linear excitation limit. The theory, however, is not limited to linear response, and in general describes nonlinear exciton-exciton interactions in the localized exciton state, thereby providing a powerful means of investigating the nonlinear optical response of such systems.

Dispersion and nonlinearity properties of small solid-core photonic fibers with As2Se3 substrate

Characteristics of As2Se3 photonic crystal fibers (PCFs) with a solid-core and small-core diameter are numerically investigated in the long-wavelength range (from 2 to 10 μm). A full modal analysis and optical properties of designed photonic crystal fibers with lattice constant Λ and filling factor d/Λ are presented in terms of chromatic dispersion, effective refractive index, nonlinear coefficients, and confinement loss. The simulation results show that a high nonlinear coefficient of 4410.303 W–1·km–1 and a low confinement loss of 10−20 dB·km–1 can simultaneously be achieved in the proposed PCFs at a 4.5 μm wavelength. Chromatic dispersions are flat. The values of dispersion increase with increasing filling factor d/Λ and decrease with the increase in lattice constant Λ. In particular, some chromatic dispersion curves also cut the zero-dispersion line at two points. The flat dispersion feature, high nonlinearity, and small confinement loss of the proposed photonic crystal fiber structure make it suitable for supercontinuum.

The ordinary negative changing refractive index for estimation of optical confinement factor

Abstract The electro-optic effect is considered very important in optical communication systems. The small optical confinement factor is attributed to the weak overlap between the electric field and optical wave and hence the optical signal is not efficiently modulated. In this paper, the problem of the small optical confinement factor in the Mach–Zehnder modulator based on lithium niobate (LN) which is deeply studied. The data were analyzed through a proposed mathematical model to explain the relationship between the change in the ordinary negative refractive index and the confinement factor. The system is improved using a small length of the modulator arm as only 3 to 8 µm, low driving power of about 4 V/µm, a large change in the negative ordinary refractive index of about—0.2 × 10−7, and a compact optical modulator. This can reflect a strong optical confinement factor when the electric field is applied to the electrodes of the optical modulator.

Study on Lubrication Characteristics of C4-Alkane and Nanoparticle during Boundary Friction by Molecular Dynamics Simulation

Lubricant has been widely applied to reduce wear and friction between the contact surfaces when they are in relative motion. In the current study, a nonequilibrium molecular dynamics (NEMD) simulation was specifically established to conduct a comprehensive investigation on the dynamic contact between two iron surfaces in a boundary friction system considering the mixed C4-alkane and nanoparticles as lubricant. The main research objective was to explore the effects of fluid and nanoparticles addition on the surface contact and friction force. It was found that nanoparticles acted like ball bearings between the contact surfaces, leading to a change of sliding friction mode to rolling friction mode. Under normal loads, plastic deformation occurred at the top surface because nanoparticles were mainly supporting the normal load. By increasing the number of C4-alkane molecules between two contact surfaces, the contact condition has been changed from partial to full lubrication. In addition, an attractive force from the solid–liquid LJ interaction between C4-alkane and surfaces was observed at the early stage of sliding, due to the large space formed by wall surfaces and nanoparticles. The findings in this paper would be beneficial for understanding the frictional behavior of a simple lubricant with or without nanoparticles addition in a small confinement.

Effects of Packaging History on the Ejection of a Polymer Chain from a Small Confinement

Effects of Packaging History on the Ejection of a Polymer Chain from a Small Confinement

Circular anti-resonance fibre supporting orbital angular momentum modes with flat dispersion, high purity and low confinement loss

A novel ring anti-resonance fibre (ARF) is designed and demonstrated for the transmission of orbital angular momentum (OAM) modes. The fibre consists of two layers of negative curvature tubes arranged orderly inside and outside the ring region and OAM modes can be transmitted in the ring region. The properties of the fibre are investigated by the finite element method based on the COMSOL multiphysics software and a manufacturing method is proposed. The fibre shows stable transmission of 30 OAMs in the 1.5–1.6 μm band, low and flat dispersion (5.98 ps/(km nm)), extremely small nonlinear coefficient (0.539 km−1 W−1 at 1.55 μm) and confinement loss (10−9–10−11 dB/m), as well as high OAM purity (larger than 98.295%). Therefore, the structure has immense potential in optical communication.

A hybrid structured PCF for fuel adulteration detection in terahertz regime

An elliptical core based hybrid structured photonic crystal fiber (PCF) is proposed and analyzed in order to identify the fuel adulteration level using the terahertz spectrum. The performance of the proposed sensor is assessed by COMSOL software which uses the finite element method as a solver. At 2.8 THz, the proposed sensor shows an extremely high relative sensitivity of 102% with a very small confinement loss of 3.46× 10−11 cm−1 and a high numerical aperture of 0.45. Moreover, the proposed sensor also shows a large effective area of 1.715× 10−8 m2 with a low effective material loss of 0.0105 cm−1 at optimum structural conditions. Except for one elliptical air hole in cladding, the optical sensor contains circular air holes which ensure less complexity during fabrication. The sensor's excellent sensing and guiding properties will make it a competitive candidate in chemical sensing applications.

A review of robotic surgical training: establishing a curriculum and credentialing process in ophthalmology.

Ophthalmic surgery requires a highly dexterous and precise surgical approach to work within the small confines of the eye, and the use of robotics offers numerous potential advantages to current surgical techniques. However, there is a lag in the development of a comprehensive training and credentialing system for robotic eye surgery, and certification of robotic skills proficiency relies heavily on industry leadership. We conducted a literature review on the curricular elements of established robotics training programs as well as privileging guidelines from various institutions to outline key components in training and credentialing robotic surgeons for ophthalmic surgeries. Based on our literature review and informal discussions between the authors and other robotic ophthalmic experts, we recommend that the overall training framework for robotic ophthalmic trainees proceeds in a stepwise, competency-based manner from didactic learning, to simulation exercises, to finally operative experiences. Nontechnical skills such as device troubleshooting and interprofessional teamwork should also be formally taught and evaluated. In addition, we have developed an assessment tool based on validated global rating scales for surgical skills that may be used to monitor the progress of trainees. Finally, we propose a graduating model for granting privileges to robotic surgeons. Further work will need to be undertaken to assess the feasibility, efficacy and integrity of the training curriculum and credentialing practices for robotic ophthalmic surgery.

Volume-constrained deformation of a thin sheet as a route to harvest elastic energy.

Thin sheets exhibit rich morphological structures when subjected to external constraints. These structures store elastic energy that can be released on demand when one of the constraints is suddenly removed. Therefore, when adequately controlled, shape changes in thin bodies can be utilized to harvest elastic energy. In this paper, we propose a mechanical setup that converts the deformation of the thin body into a hydrodynamic pressure that potentially can induce a flow. We consider a closed chamber that is filled with an incompressible fluid and is partitioned symmetrically by a long and thin sheet. Then, we allow the fluid to exchange freely between the two parts of the chamber, such that its total volume is conserved. We characterize the slow, quasistatic, evolution of the sheet under this exchange of fluid, and derive an analytical model that predicts the subsequent pressure drop in the chamber. We show that this evolution is governed by two different branches of solutions. In the limit of a small lateral confinement we obtain approximated solutions for the two branches and characterize the transition between them. Notably, the transition occurs when the pressure drop in the chamber is maximized. Furthermore, we solve our model numerically and show that this maximum pressure behaves nonmonotonically as a function of the lateral compression.

Flame Transfer Functions and Dynamics of a Closely Confined Premixed Bluff Body Stabilized Flame With Swirl

Abstract The flame transfer function (FTF) and flame dynamics of a highly swirled, closely confined, premixed flame is studied over a wide range of equivalence ratios and bulk velocities at a fixed perturbation level at the dump plane. The operating conditions are varied to examine the ratio of flame height to velocity in scaling the FTF. The enclosure geometry is kept constant, resulting in strong flame-wall interactions for some operating conditions due to varying flame height. The resulting effect on the FTF due to changes in the “effective flame confinement” can therefore be studied. For sufficiently high equivalence ratio, and the resulting sufficiently small effective confinement, modulations of the FTF are observed due to interference of the perturbations created at the swirler and at the dump plane. The small length scales and high velocities result in modulations centered at high frequencies and spanning a wide range of frequencies compared to previous studies of similar phenomena. A critical point was reached for increasing effective confinement, where the modulations are suppressed. This is linked to a temporal shift in the heat release rate where the flame impinges on the combustion chamber walls. The shift reduced the expected level of interference, demonstrating effective confinement is important for the FTF response. Additionally, a distributed time lag (DTL) model with two time lags is successfully applied to the FTFs, providing a simple method to capture the two dominant time scales in the problem, recreate the FTF, and examine the effect of effective confinement.

Integer topological defects of cell monolayers: Mechanics and flows.

Monolayers of anisotropic cells exhibit long-ranged orientational order and topological defects. During the development of organisms, orientational order often influences morphogenetic events. However, the linkage between the mechanics of cell monolayers and topological defects remains largely unexplored. This holds specifically at the timescales relevant for tissue morphogenesis. Here, we build on the physics of liquid crystals to determine material parameters of cell monolayers. In particular, we use a hydrodynamical description of an active polar fluid to study the steady-state mechanical patterns at integer topological defects. Our description includes three distinct sources of activity: traction forces accounting for cell-substrate interactions as well as anisotropic and isotropic active nematic stresses accounting for cell-cell interactions. We apply our approach to C2C12 cell monolayers in small circular confinements, which form isolated aster or spiral topological defects. By analyzing the velocity and orientational order fields in spirals as well as the forces and cell number density fields in asters, we determine mechanical parameters of C2C12 cell monolayers. Our work shows how topological defects can be used to fully characterize the mechanical properties of biological active matter.

Quantifying Material Properties of Cell Monolayers by Analyzing Integer Topological Defects.

In developing organisms, internal cellular processes generate mechanical stresses at the tissue scale. The resulting deformations depend on the material properties of the tissue, which can exhibit long-ranged orientational order and topological defects. It remains a challenge to determine these properties on the time scales relevant for developmental processes. Here, we build on the physics of liquid crystals to determine material parameters of cell monolayers. Specifically, we use a hydrodynamic description to characterize the stationary states of compressible active polar fluids around defects. We illustrate our approach by analyzing monolayers of C2C12 cells in small circular confinements, where they form a single topological defect with integer charge. We find that such monolayers exert compressive stresses at the defect centers, where localized cell differentiation and formation of three-dimensional shapes is observed.

Dynamic permeability of fluids in rectangular and square microchannels: Shift and coupling of viscoelastic bidimensional resonances

Pulsatile dynamics of Newtonian and Maxwellian fluids is exactly solved by theoretical analytical means when confined within rectangular microchannels subject to oscillatory driving forces. The analytical solution exhibits a complex behavior caused by the fluid dynamics along the smallest and the secondary confinement dimensions. For Newtonian fluids, the maximum and average flow velocities within the microchannel differ considerably from the ones predicted by simplified one-dimensional models when fluids are subject to moderate and high driving force frequencies. This is caused by the stagnation of flow velocity in the vicinity of the channel walls at the secondary confinement dimension. For Maxwellian fluids, the secondary confinement incorporates flow resonances that are coupled to the ones caused by the smallest confinement, leading to a shift of the main resonance and the arising of resonances when bidimensional vibration modes are excited. These effects depend on the aspect ratio between channel width and height and on the magnitude of the driving force frequency, compared to the characteristic viscous frequency of the microchannel. The theoretical results are compared with recent experimental results in the literature in pulsatile microfluidics for hyaluronic acid solutions with viscoelastic properties, as well as for water. In both cases, an agreement is found between theoretical and experimental results.

Instagranimal: Animal Welfare and Animal Ethics Challenges of Animal-Based Tourism.

Simple SummaryAnimals of countless species, wild as well as tame, can now entertain tourists on their holidays. The popularity, however, of animal-based tourism comes with significant risks for the welfare of these animals. Many animals are kept in small confinements, are broken down to interact obediently with tourists, or are made to perform, entertain, transport or even give their lives for human leisure. In this paper, the challenges of animal-based tourism are presented from the perspectives of interdisciplinary researchers. The challenges are discussed based on a two-day symposium with workshop sessions. We bring attention to the problem of cultural relativism and the difficulty of imposing universal standards of animal welfare. We conclude that reforms and individual travel decisions as a result of biosecurity concerns will impact animal welfare. In addition to this, we observe that technology has a dual role to play in enhancing edutainment but also potentially inviting new challenges. In the end, we declare some possibilities for compassionate animal based tourism.By animal-based tourism, a host of activities offering passive viewing or active interaction with wild, semi-wild or captive animals is included. The multibillion dollar industry is on the rise globally today, offering modes of engagement with animals that trade on increasingly embodied close encounters with non-human animals. As new modes of animal-based tourism proliferate, such as sloth selfies, visiting cat cafes, swimming with sharks and agri-tourism petting zoos, animal welfare standards risk deteriorating. In the following paper, we collate concerns over animal welfare into a discussion on the challenges facing animal-based tourism. Our synthesis is the first to consider the full spectrum of such animal-based tourism: across agri-, hunting, zoo and safari tourism, to name a few, and crossing consumptive and non-consumptive boundaries. A literature review is first provided. Findings are then presented thematically following workshops at an international interdisciplinary symposium of leading tourism, animal welfare, ethics and leisure sciences scholars together with practitioners of the industry. It discusses macrolevel drivers to animal-based tourism as an industry, the problem of cultural relativism and the role of technology in enhancing or promoting the experience. We indicate ways forward toward implementing a compassionate animal-based tourism.

Theoretical analysis of large negative dispersion photonic crystal fiber with small confinement loss.

Solid core circular and octagonal photonic crystal fibers (CPCF and OPCF) are proposed for analyzing different guiding properties such as dispersion, effective mode area, nonlinearity, and confinement loss from 0.8 to 2.6 µm wavelength. The proposed structures use three different types of background materials: SF10, BK7, and silica. Moreover, the fill fraction is varied by changing the diameter of the air hole where the lattice pitch is unchanged. The proposed PCFs show a high negative dispersion with low confinement loss and small effective mode area. In the proposed design, the finite element method with a perfectly matched layer absorbing boundary condition is used. At 1.8 µm wavelength with 0.6 fill fraction, the maximum negative dispersion of -922.5ps/(nm.km) is observed for CPCF when the background material is SF10. In addition, at this particular wavelength, the confinement loss is observed to be very small. Moreover, -560.12ps/(nm.km) dispersion is found for the similar condition at 1.55 µm wavelength. On the other hand, using BK7 as the background material, -706.77ps/(nm.km) dispersion is found at 1.55 µm wavelength for CPCF. Results also imply that CPCF shows better performance than OPCF for a wide wavelength range. Furthermore, at 1.55 µm wavelength, silica-based glass exhibits maximum dispersion, whereas increasing wavelength flint type glass shows the similar result. Analyzing different guiding properties of PCFs has significant impact on broadband dispersion compensation applications, especially using SF10.

Investigation of the effect of impact load on concrete-filled steel tube columns under fire

Concrete-filled steel tube (CFST) columns are increasingly used in the construction of high-rise buildings which require high strength and large working space especially at lower stories. As compared to reinforced concrete columns, existence of the exterior steel tube not only bears a portion of axial load but also most importantly provides confinement to the infill concrete.with the confinement provided by the steel tube, axial strength of the infill concrete can be largely enhanced.this paper presents the investigation effect of impact load on concrete-filled steel tube columns under fire by numerical simulations using ABAQUS software.the results indicate that the CFST sections with larger confinement factor ξ=1.23 behaved in a very ductile manner under lateral impact. And the sections with smaller confinement factor ξ=0.44 generally behaved in a brittle mechanism.