2D Behavior Research Articles

Asymptotic behavior of 2D stably stratified fluids with a damping term in the velocity equation

This article deals with the asymptotic behavior of the two-dimensional inviscid Boussinesq equations with a damping term in the velocity equation. Precisely, we provide the time-decay rates of the smooth solutions to that system. The key ingredient is a careful analysis of the Green kernel of the linearized problem in Fourier space, combined with bilinear estimates and interpolation inequalities for handling the nonlinearity.

Magnetoresistance investigation in the mixed state of a high temperature superconductor

In this work, we analyze the behavior of the magnetoresistance R (H, T) of a high temperature superconductor YBa 2 Cu 3 O 7−δ thin film optimally doped. Measurements of the magnetoresistance were carried out in the mixed state for a magnetic field up to 14 T applied parallel to c − axis then parallel to ab − plane with a dc transport current of 100 and 500 nA, 0.1 and 0.3 mA perpendicular to the magnetic field direction in both cases. The obtained results show that the magnetoresistance is in a good agreement with the thermally assisted flux creep. However, the magnetoresistance in the flux flow regime cannot be described by the Barden-Stephen model which conjectures another origin of these results. In this sense, the quantum fluctuations of the order parameter is a good alternative to understanding the shape of the magnetoresistance. The comparison of the magnetoresistance of the two directions shows that [see formula in PDF] is larger than [see formula in PDF] with anisotropy factor [see formula in PDF] depending on temperature and magnetic field. The irreversibility line H irr (T) as well as H C2 (T) are determined and the first one is fitted with the phenomenological model H irr (T) = H irr (0) (1 − T/T o ) α where H irr (0), T o and α are parameters obtained from the fit. The investigation of the scaling law allows us to prove that a crossover from 3D to 2D behavior is a feature of our sample which justifies the existence of the decoherence effect.

Cell and extracellular matrix interaction models in benign mesothelial and malignant pleural mesothelioma cells in 2D and 3D in-vitro.

Malignant pleural mesothelioma (MPM) is an aggressive tumour that grows in the pleural cavity. MPM spheroids released in the pleural fluid can form new tumour foci. Cell-cell, cell-extracellular matrix (ECM) interactions in 2D and 3D impact malignant cell behaviour during cell adhesion, migration, proliferation and epithelial-mesenchymal transition (EMT). In this study, epithelioid, biphasic and sarcomatoid MPM cell types as well as benign mesothelial cells were tested with regards to the above phenotypes. Fibronectin (FN) and homologous cell-derived extracellular matrix (hcd-ECM) treated substratum differentially affected the above phenotypes. 3D MPM spheroid invasion was higher in FN-collagen matrices in the epithelioid and biphasic cells, while 3D cell cultures of epithelioid and sarcomatoid MPM cells in FN-collagen showed a higher contractility compared to hcd-ECM-collagen. Cell aggregates demonstrated invasive behaviour in hcd-ECM matrices alone. Our results suggest that ECM and the dimensionality affect malignant cell behaviour during cell culture studies.

Influence of Erodible Beds on Shallow Water Hydrodynamics during Flood Events

Flooding has become the most common environmental hazard, causing casualties and severe economic losses. Mathematical models are a useful tool for flood control, and current computational resources let us simulate flood events with two-dimensional (2D) approaches. An open question is whether bed erosion must be accounted for when it comes to simulating flood events. In this paper we answer this question through numerical simulations using the 2D depth-averaged shallow-water equations. We analyze the effect of mobile beds on the flow patterns during flood events. We focus on channel confluences where water flow and sediment mobilization have a marked 2D behavior. We validate our numerical simulations with laboratory experiments of erodible beds with satisfactory results. Moreover, our sensitivity analysis indicates that the bed roughness model has a great influence on the simulated erosion and deposition patterns. We simulate the sediment transport and its influence on the water flow in a real river confluence during flood events. Our simulations show that the erosion and deposition processes play an important role on the water depth and flow velocity patterns. Accounting for the mobile bed leads to smoother water depth and velocity fields, as abrupt fields for the non-erodible model emerge from the irregular bed topography. Our study highlights the importance of accounting for erosion in the simulation of flood events, and the impact on the water depth and velocity fields.

Nonlinear dielectric properties of random paraelectric-dielectric composites

The challenge of designing new tunable nonlinear dielectric materials with tailored properties has attracted an increasing amount of interest recently. Herein, we study the effective nonlinear dielectric response of a stochastic paraelectric-dielectric composite consisting of equilibrium distributions of circular and partially penetrable disks (or parallel, infinitely long, identical, partially penetrable, circular cylinders) of a dielectric phase randomly dispersed in a continuous matrix of a paraelectric phase. The random microstructures were generated using the Metropolis Monte Carlo algorithm. The evaluation of the effective permittivity and tunability were carried out by employing either a Landau thermodynamic model or its Johnson’s approximation to describe the field-dependent permittivity of the paraelectric phase and solving continuum-electrostatics equations using finite element calculations. We reveal that the percolation threshold in this composite governs the critical behavior of the effective permittivity and tunability. For microstructures below the percolation threshold, our simulations demonstrate a strong nonlinear behaviour of the field-dependent effective permittivity and very high tunability that increases as a function of dielectric phase concentration. Above the percolation threshold, the effective permittivity shows the tendency to linearization and the tunability dramatically drops down. The highly reduced permittivity and extraordinarily high tunability are obtained for the composites with dielectric impenetrable disks at high concentrations, in which the triggering of the percolation transition is avoided. The reported results cast light on distinct nonlinear behaviour of 2D and 3D stochastic composites and can guide the design of novel composites with the controlled morphology and tailored permittivity and tunability.

Keratocyte mechanobiology

In vivo, corneal keratocytes reside within a complex 3D extracellular matrix (ECM) consisting of highly aligned collagen lamellae, growth factors, and other extracellular matrix components, and are subjected to various mechanical stimuli during developmental morphogenesis, fluctuations in intraocular pressure, and wound healing. The process by which keratocytes convert changes in mechanical stimuli (e.g. local topography, applied force, ECM stiffness) into biochemical signaling is known as mechanotransduction. Activation of the various mechanotransductive pathways can produce changes in cell migration, proliferation, and differentiation. Here we review how corneal keratocytes respond to and integrate different biochemical and biophysical factors. We first highlight how growth factors and other cytokines regulate the activity of Rho GTPases, cytoskeletal remodeling, and ultimately the mechanical phenotype of keratocytes. We then discuss how changes in the mechanical properties of the ECM have been shown to regulate keratocyte behavior in sophisticated 2D and 3D experimental models of the corneal microenvironment. Finally, we discuss how ECM topography and protein composition can modulate cell phenotypes, and review the different methods of fabricating in vitro mimics of corneal ECM topography, novel approaches for examining topographical effects in vivo, and the impact of different ECM glycoproteins and proteoglycans on keratocyte behavior.

Investigation of dimensionality in superconducting NbN thin film samples with different thicknesses and NbTiN meander nanowire samples by measuring the upper critical field**Project supported by the Chinese Academy of Sciences (Grant No. XDB25000000).

We study superconducting properties of NbN thin film samples with different thicknesses and an ultra-thin NbTiN meander nanowire sample. For the ultra-thin samples, we found that the temperature dependence of upper critical field (Hc2) in parallel to surface orientation shows bending curvature close to critical temperature Tc, suggesting a two-dimensional (2D) nature of the samples. The 2D behavior is further supported by the angular dependence measurements of Hc2 for the thinnest samples. The temperature dependence of parallel upper critical field for the thick films could be described by a model based on the anisotropic Ginzburg–Landau theory. Interestingly, the results measured in the field perpendicular to the film surface orientation show a similar bending curvature but in a much narrow temperature region close to Tc for the ultra-thin samples. We suggest that this feature could be due to suppression of pair-breaking caused by local in-homogeneity. We further propose the temperature dependence of perpendicular Hc2 as a measure of uniformity of superconducting ultra-thin films. For the thick samples, we find that Hc2 shows maxima for both parallel and perpendicular orientations. The Hc2 peak for the perpendicular orientation is believed to be due to the columnar structure formed during the growth of the thick films. The presence of columnar structure is confirmed by transmission electron microscopy (TEM). In addition, we have measured the angular dependence of magneto-resistance, and the results are consistent with the Hc2 data.

Member and structural fragility of reinforced concrete structure under fire

Purpose Despite recognizing the significance of risk-based frameworks in fire safety engineering, the usual approach in structural fire design is largely member/component level, wherein effect of uncertainties influencing the fire resistance of structures are not explicitly considered. In this context, a probabilistic framework is presented to investigate the vulnerability of a reinforced concrete (RC) members and structure under fire loading scenario. Design/methodology/approach The RC structures exposed to fire are modeled in a finite element (FE) platform incorporating material and geometric nonlinearity, in which the transient thermo-mechanical analysis is carried out by suitably incorporating the temperature variation of thermal and mechanical properties of both concrete and steel rebar. The stochasticity in the system is considered in structural resistance, thermal and fire model parameters, and the subsequent fragility curves are developed considering threshold limit state of deflection. Findings The fire resistance of RC structure is reported to be significantly lower in comparison to the RC members, thereby illustrating the current prescriptive design approaches based on studies of structural member behavior to be crucial from a safety and reliability point of view. Practical implications The framework developed for the vulnerability assessment of RC structures under fire hazard through FE analysis can be effectively used to estimate the structural fire resistance for other similar structure to enhance safety and reliability of structures under such extreme threats. Originality/value The paper proposes a novel methodology for vulnerability assessment of three-dimensional RC structures under fire hazard through FE analysis and provides comparison of the structural fragility with fragility developed for structural members. Moreover, the research emphasizes to assume 3D behavior of the structure rather than the approximate 2D behavior.

Experimental demonstration of the suppression of optical phonon splitting in 2D materials by Raman spectroscopy

Raman spectroscopy is one of the most extended experimental techniques to investigate thin-layered 2D materials. For a complete understanding and modeling of the Raman spectrum of a novel 2D material, it is often necessary to combine the experimental investigation to density functional theory calculations. We provide the experimental proof of the fundamentally different behavior of polar 2D vs 3D systems regarding the effect of the dipole − dipole interactions, which in 2D systems ultimately lead to the absence of optical phonons splitting, otherwise present in 3D materials. We demonstrate that non-analytical corrections (NACs) should not be applied to properly model the Raman spectra of few-layered 2D materials, such as WSe2 and h-BN, corroborating recent theoretical predictions (Sohier et al 2017 Nano Lett. 17 3758–63). Our findings are supported by measurements performed on tilted samples that allow increasing the component of photon momenta in the plane of the flake, thus unambiguously setting the direction of an eventual NAC. We also investigate the influence of the parity of the number of layers and of the type of layer-by-layer stacking on the effect of NACs on the Raman spectra.

A live cell reporter of exosome secretion and uptake reveals pathfinding behavior of migrating cells

Small extracellular vesicles called exosomes affect multiple autocrine and paracrine cellular phenotypes. Understanding the function of exosomes requires a variety of tools, including live imaging. Our previous live-cell reporter, pHluorin-CD63, allows dynamic subcellular monitoring of exosome secretion in migrating and spreading cells. However, dim fluorescence and the inability to make stably-expressing cell lines limit its use. We incorporated a stabilizing mutation in the pHluorin moiety, M153R, which now exhibits higher, stable expression in cells and superior monitoring of exosome secretion. Using this improved construct, we visualize secreted exosomes in 3D culture and in vivo and identify a role for exosomes in promoting leader–follower behavior in 2D and 3D migration. Incorporating an additional non-pH-sensitive red fluorescent tag allows visualization of the exosome lifecycle, including multivesicular body (MVB) trafficking, MVB fusion, exosome uptake and endosome acidification. This reporter will be a useful tool for understanding both autocrine and paracrine roles of exosomes.

Behavioral features fusion for ethological CNN classification of open field test videos

In both ethological and pharmacological experiments, open field test (OFT) is a classic experiment for measuring mouse general activity and exploratory behaviors. The OFT manual analysis is usually a time consuming and costly process. In this paper, we propose a convolutional neural network (CNN) based classification, which can automatically sort out two groups of mice with different behaviors. We first extract the multi-modality features from both spatial and time domain of the OFT video. Then, all extracted features are regularized and fused to a 2D behavior feature map. Finally, we train a CNN network to distinguish mice with different behaviors. On real OFT datasets experiments, the proposed classification significantly outperforms other methods.

Abrupt Transition between Three-Dimensional and Two-Dimensional Quantum Turbulence.

We present numerical evidence of a critical-like transition in an out-of-equilibrium mean-field description of a quantum system. By numerically solving the Gross-Pitaevskii equation we show that quantum turbulence displays an abrupt change between three-dimensional (3D) and two-dimensional (2D) behavior. The transition is observed both in quasi-2D flows in cubic domains (controlled by the amplitude of a 3D perturbation to the flow), as well as in flows in thin domains (controlled by the domain aspect ratio) in a configuration that mimics systems realized in laboratory experiments. In one regime the system displays a transfer of the energy towards smaller scales, while in the other the system displays a transfer of the energy towards larger scales and a coherent self-organization of the quantized vortices.

Charge Carrier Recombination Dynamics of Two-Dimensional Lead Halide Perovskites.

Two-dimensional (2D) lead halide perovskites with better chemical stability and tunable dimensionality offer new opportunities to design optoelectronic devices. We have probed the transient absorption behavior of 2D lead halide (bromide and iodide) perovskites of different dimensionality, prepared by varying the ratio of methylammonium:phenylethylammonium cation. With decreasing dimensionality (n = ∞ → 1), we observe a blue shift in transient absorption bleach in agreement with the trend observed with the shift in the excitonic peak. The lifetime of the charge carriers decreased with decreasing layer thickness. The dependence of charge carrier lifetime on the 2D layers as well as the halide ion composition shows the dominance of excitonic binding energy on the charge carrier recombination in 2D perovskites. The excited-state behavior of 2D perovskites discussed in this study shows the need to modulate the layer dimensionality to obtain desired optoelectronic properties.

Finite Element Modelling and Design of Underground Metro Station

Underground metro stations are influenced by critical external loads such as earth pressure, hydrostatic pressure, bedding spring stiffness and backfill soil cover. Optimization, constructability and sustainability is a need, which demands thorough critical analysis and design. The variation in design parameters like ground water level (GWT), bedding spring stiffness (ks) and earth pressure coefficient (ko) needs to be covered through the analysis. Accordingly, design demands the upper bound and lower bound parameters considerations for finite element analysis. This paper presents, best practices for finite element modelling approach such as mesh configuration, loading, geometry, support arrangement; analysis approach such as analysis parameters, solvers and design idealization of critical forces such as bending moment, shear force and axial force at wall slab junction and slab column junction based on the international codes such as Euro-code and Indian codes. Also paper compares the behavior of 2D and 3D finite element modelling of underground metro station.

A coupled micro–meso-scale study on the damage mechanism of 2D SiC/SiC ceramic matrix composites

A coupled micro–meso-scale modeling strategy is proposed to investigate the damage mechanism of 2D SiC/SiC ceramic matrix composites. The multi-scale modeling begins with microstructure construction using the representative volume elements (RVE). The effective properties of the SiC/SiC yarn are computed using the micro-scale RVE model. At meso-scale, the Tsai-Wu and Mohr’s failure criteria are used to describe the different failure modes of yarn and matrix. A satisfied agreement with experimental results obtained by uniaxial tension tests validates the proposed multi-scale modeling strategy. The damage behavior of 2D SiC/SiC composites under in-plane shear loading is further investigated.

Three-Dimensional Observations of an Aperiodic Oscillatory Gliding Behavior in Myxococcus xanthus Using Confocal Interference Reflection Microscopy.

The deltaproteobacterium Myxococcus xanthus is a model for bacterial motility and has provided unprecedented insights into bacterial swarming behaviors. Fluorescence microscopy techniques have been invaluable in defining the mechanisms that are involved in gliding motility, but these have almost entirely been limited to two-dimensional (2D) studies, and there is currently no understanding of gliding motility in a three-dimensional (3D) context. We present here the first use of confocal interference reflection microscopy (IRM) to study gliding bacteria, revealing aperiodic oscillatory behavior with changes in the position of the basal membrane relative to the substrate on the order of 90 nm in vitro First, we use a model planoconvex lens specimen to show how topological information can be obtained from the wavelength-dependent interference pattern in IRM. We then use IRM to observe gliding M. xanthus bacteria and show that cells undergo previously unobserved changes in their adhesion profile as they glide. We compare the wild type with mutants that have reduced motility, which also exhibit the same changes in the adhesion profile during gliding. We find that the general gliding behavior is independent of the proton motive force-generating complex AglRQS and suggest that the novel behavior that we present here may be a result of recoil and force transmission along the length of the cell body following firing of the type IV pili.IMPORTANCE 3D imaging of live bacteria with optical microscopy techniques is a challenge due to the small size of bacterial cells, meaning that previous studies have been limited to observing motility behavior in 2D. We introduce the application of confocal multiwavelength interference reflection microscopy to bacteria, which enables visualization of 3D motility behaviors in a single 2D image. Using the model organism Myxococcus xanthus, we identified novel motility behaviors that are not explained by current motility models, where gliding bacteria exhibit aperiodic changes in their adhesion to an underlying solid surface. We concluded that the 3D behavior was not linked to canonical motility mechanisms and that IRM could be applied to study a range of microbiological specimens with minimal adaptation to a commercial microscope.

Study of Structural and Magnetotransport Properties of Fe(Te, Se) Single Crystals

Single‐crystalline samples of nominal compositions FeTe0.88 and FeTe1−xSex are synthesized using the self‐flux method. The activation energy of the flux flow is estimated using the Arrhenius relation as well as by the modified thermally activated flux flow (TAFF) model. The field dependence of U0 shows transition from single to collective vortex pinning at a magnetic field of ≈2 T. The analysis of field‐dependent U0 data reveals the planar and the point defect magnetic field regions for both the models. The modified TAFF model is used to study the 2D and 3D behavior of the vortex state for all the superconducting samples. The single‐crystalline FeTe0.80Se0.20 and FeTe0.60Se0.40 samples show 3D behavior, whereas the FeTe0.40Se0.60 crystal shows 2D behavior. The vortex phase diagrams of all the superconducting samples are obtained by analyzing the magnetotransport data. The vortex phase diagrams reveal transitions from the unpinned to pinned vortex liquid state and the vortex liquid to vortex glass state. Below T*, the critical exponent s is in good agreement with q values for 2D/3D behavior of vortex states of all the superconducting samples.

Experimental investigation on response and failure modes of 2D and 3D woven composites under low velocity impact

In this study, the behavior of 2D and 3D woven composites is compared under low velocity impact. Several 2D and 3D specimens were tested using a drop-weight tower, and their performance was compared using extracted data such as damage threshold load, damage initiation time, absorbed energy and maximum deflection. Besides, their damage modes and delamination areas were examined by stereomicroscope and C-scan technique, respectively. The results showed that the 3D woven composites absorbed more impact energy than 2D ones while their maximum deflection was lower. Moreover, the delamination and damage areas were much smaller in the 3D composites than the 2D ones of similar thickness. A new parameter is presented for comparing damage severity of the 2D and 3D composites. Unlike conventional parameters, the presented one shows potential for being applicable to laminated composites, regardless of their areal densities, layer numbers and weave structures.

Specific Heat Study of 1D and 2D Excitations in the Layered Frustrated Quantum Antiferromagnets Cs_{2}CuCl_{4-x}Br_{x}.

We report an experimental and theoretical study of the low-temperature specific heat C and magnetic susceptibility χ of the layered anisotropic triangular-lattice spin-1/2 Heisenberg antiferromagnets Cs_{2}CuCl_{4-x}Br_{x} with x=0, 1, 2, and 4. We find that the ratio J^{'}/J of the exchange couplings ranges from 0.32 to ≈0.78, implying a change (crossover or quantum phase transition) in the materials' magnetic properties from one-dimensional (1D) behavior for J^{'}/J<0.6 to two-dimensional (2D) behavior for J^{'}/J≈0.78. For J^{'}/J<0.6, realized for x=0, 1, and 4, we find a magnetic contribution to the low-temperature specific heat, C_{m}∝T, consistent with spinon excitations in 1D spin-1/2 Heisenberg antiferromagnets. Remarkably, for x=2, where J^{'}/J≈0.78 implies a 2D magnetic character, we also observe C_{m}∝T. This finding, which contrasts the prediction of C_{m}∝T^{2} made by standard spin-wave theories, shows that Fermi-like statistics also plays a significant role for the magnetic excitations in spin-1/2 frustrated 2D antiferromagnets.

(Invited) Non-Volatile Resistance Switching Phenomenon in Monolayer h-BN

Over the last decade, two-dimensional (2D) materials have drawn much attention for the next-generation electron devices, optoelectronics and bioelectronics [1, 2]. Recently, non-volatile resistance switching (NVRS) behavior has been observed in various 2D materials, including graphene oxide, functionalized MoS2 and partially degraded black phosphorus, etc. [3-5], where the resistance can be modulated between a high-resistance state (HRS) and a low-resistance state (LRS) [6]. In addition, there are several reports about NVRS in multi-layer hexagonal boron-nitride (h-BN) [7]. Although 2D materials are widely regarded as promising candidates to overcome vertical scaling obstacle in NVRS based on conventional metal-insulator-metal (MIM) structure [3], few researchers believe that single-layer 2D material can produce NVRS [8] due to excessive leakage current. Sangwan et al. discovered that grain boundaries in single-layer MoS2 can produce NVRS based on planar (horizontal) structure [9]. However, the planar structure without 3D stacking ability has the limitation of low integration density. Recently, we reported the discovery that NVRS phenomenon is accessible in a variety of single-layer transition metal dichalcogenides (TMDs) in vertical MIM structure [10, 11]. Herein, we report another 2D insulating material, single-layer h-BN, also shows stable and desirable NVRS behavior. Compared with monolayer TMDs with three atomic layers, monolayer h-BN has only one atomic layer and ~0.33 nm in thickness, which is the thinnest active layer in non-volatile resistance memory. These devices can be labelled as “atomristor”, which means the memristor effect in atomically thin nanomaterials.[12] The h-BN atomristors have been studied using a crossbar structure (Au/h-BN/Au) [See Figure a]. Figure b shows a representative I-V curve of h-BN atomristor, demonstrating forming-free switching with large on/off ratio (up to >106) and low switching voltage (down to <1V). In addition, pulse operation proves its fast switching speed (<15 ns), which is comparable to the state-of-the-art in 2D memory. Ab-initio simulation reveals that the metal ion substitution in sulfur vacancies may be related to the switching from HRS to LRS, and area scaling test result is also consistent with this conductive-bridge-like mechanism. The results of this work indicate a potential universal resistive switching behavior in 2D insulating monolayers, which is applicable to memory technology, neuromorphic computing, RF switch and flexible electronics.