Two-dimensional Gap Research Articles

Two-dimensional GaP monolayer with tunable electrical and optical properties

Two-dimensional GaP monolayer with tunable electrical and optical properties

Two-dimensional GaP monolayer with tunable electrical and optical properties

The optical characteristics of two-dimensional (2D) monolayer formations in GaP. According to the predicted binding energies, the GaP monolayers are in constant contact. GaP monolayer was revealed to be semiconducting, with gaps of 2.080 eV. Furthermore, the predicted optical properties indicate that the GaP monolayer will absorb light at wavelengths ranging from infrared to ultraviolet. As a result, GaP monolayer should be appealing for visible-light communication and photocatalytic devices. It is possible to determine that this layer is kinematically stable by studying the form of the phonon, as all frequencies have positive values and there are no negative values for frequency. It is also worth noting that the frequency values exceed 1150 cm-1. Finally, the unexpectedly good properties of GaP monolayer are expected to be used in a variety of combinations in solar cells, field-effect transistors, catalysts, and optical devices.

Two-Dimensional Gap Solitons in Parity-Time Symmetry Moiré Optical Lattices with Rydberg–Rydberg Interaction

Realizing single light solitons that are stable in high dimensions is a long-standing goal in research of nonlinear optical physics. Here, we address a scheme to generate stable two-dimensional solitons in a cold Rydberg atomic system with a parity-time (PT) symmetric moiré optical lattice. We uncover the formation, properties, and their dynamics of fundamental and two-pole gap solitons as well as vortical ones. The PT symmetry, lattice strength, and the degrees of local and nonlocal nonlinearity are tunable and can be used to control solitons. The stability regions of these solitons are evaluated in two numerical ways: linear-stability analysis and time evolutions with perturbations. Our results provide an insightful understanding of solitons physics in combined versatile platforms of PT-symmetric systems and Rydberg–Rydberg interaction in cold gases.

Primary cementing of vertical wells: displacement and dispersion effects in narrow eccentric annuli

Laminar miscible displacement flows in narrow, vertical, eccentric annuli show a wide range of interesting physical phenomena, e.g. static layers and channels, dispersive spikes/fronts and various instabilities. These are of relevance to the primary cementing of wells, where gas leakage and greenhouse gas emissions can result from ineffective cementing. The current popular way to model this process is via a Hele-Shaw approach, reducing the Navier–Stokes equations via scaling arguments and then averaging across the annular gap: the two-dimensional (2-D) gap averaged (2DGA) model. This leads to a reduced model that is computationally efficient and represents some important features of cementing flows, but is also deficient in capturing the effects of dispersion. While three-dimensional (3-D) simulations are able to capture dispersion and most other physical phenomena, they suffer from excessive computational times due to the extreme aspect ratios of cementing geometries and non-Newtonian properties of the fluids. Here we extend the 2DGA approach by modelling the high Péclet number limit of miscible duct displacement flows, to take into account the leading-order effects of dispersion. Our modified dispersive 2DGA model is well able to approximate dispersive effects that are observed by gap-averaging the results of 3-D computations, including geometric effects of eccentricity and instabilities. This represents a marked improvement over the 2DGA approach, while keeping the computational advantages of a 2-D model.

Retracted: “Motion Model of Free-Standing Racks Considering Two-Dimensional Gap Flow” [ASME Journal of Pressure Vessel Technology, 2022, 144(4), p. 041402; DOI: 10.1115/1.4052567

Abstract The spent fuel pool of a nuclear power plant is a huge water tank with a vertical and horizontal depth of more than a dozen meters, and multiple box-shaped spent fuel racks in which spent nuclear fuel is stored are lined up in the pool. A free-standing (FS) rack is considered one of the means to improve the earthquake resistance of the spent fuel pool. The rack is not fixed to the floor so that it can move in the pool. Therefore, the inertial force due to an earthquake can be reduced by the frictional force with the floor and the fluid force from the surrounding water, and improvement in earthquake resistance can be expected. In this study, to evaluate the fluid force more precisely, the flow between the racks and the one between the racks and pool wall is treated as a two-dimensional gap flow, and the pressure loss coefficient at the flow path junction and the top of the flow path was estimated based on the steady computational fluid dynamics (CFD) calculation and incorporated into the motion model.

Confined flow effects

Nanofluidics Most memory resistor (“memristor”) systems use electrons as the charge carrier, but it may also be possible to use ionic carriers, similar to the way that neurons work. Robin et al. studied an aqueous electrolyte confined into a pseudo two-dimensional gap between two graphite layers (see the Perspective by Hou and Hou). The authors observed a current–voltage relation that exhibits hysteresis, and the conductance depends on the history of the system, also known as the memresistor effect. Using simulations of their system, they can model the emission of voltage spikes characteristic of neuromorphic activity. Science , abf7923, this issue p. [687][1]; see also abj0437, p. [628][2] [1]: /lookup/doi/10.1126/science.abf7923 [2]: /lookup/doi/10.1126/science.abj0437

Modeling of emergent memory and voltage spiking in ionic transport through angstrom-scale slits.

Recent advances in nanofluidics have enabled the confinement of water down to a single molecular layer. Such monolayer electrolytes show promise in achieving bioinspired functionalities through molecular control of ion transport. However, the understanding of ion dynamics in these systems is still scarce. Here, we develop an analytical theory, backed up by molecular dynamics simulations, that predicts strongly nonlinear effects in ion transport across quasi-two-dimensional slits. We show that under an electric field, ions assemble into elongated clusters, whose slow dynamics result in hysteretic conduction. This phenomenon, known as the memristor effect, can be harnessed to build an elementary neuron. As a proof of concept, we carry out molecular simulations of two nanofluidic slits that reproduce the Hodgkin-Huxley model and observe spontaneous emission of voltage spikes characteristic of neuromorphic activity.

Applying the Quality Function Deployment Method to Tourism’s Industry Analysis

Tourism has become a leading modern service industry. Unfortunately, there are few studies focusing on consumers' perception and acceptance as well as the impact of service quality on tourism consulting. Besides, there has been no investigation of this industry service using two-dimensional gaps, along with importance and performance analysis along with quality function. This study applied the PZB service quality gap model to extend SERVQUAL to design a questionnaire. Through service quality gap analysis and IPA model presentation, it was found there are five projects in the fourth aspect, and priority should be given to the improving "travel planning", "agent's responsibility", "agent's executive ability", "unique style" and "professional travel host". In the hierarchical analysis, the weights of "agent's responsibility" and "unique style" were 0.34 and 0.3, respectively. In the quality house section, interviewers explored the correlation between quality technology execution projects and customers' needs, and obtained absolute weights. They found that "skill knowledge" and "creative idea" were above 4.0, while the "original knowledge" had the lowest absolute weight. Finally, this study provides implementation methods for assessing resource utilization and improving service quality, to enhance the competitiveness of tourism agent entrepreneurs.

Motion model of spent fuel rack considering two-dimensional gap flow

Motion model of spent fuel rack considering two-dimensional gap flow

Motions and safety of a floating liquefied natural gas and shuttle tanker during side-by-side offloading operations

In recent years, the use of natural gas has remarkably increased due to growth in energy demands and concerns about the environment. Generally, pipelines are used for liquefied natural gas transportation; however, there are technical problems and cost increases in constructing liquefied natural gas pipelines in the deep sea. For this reason, floating liquefied natural gas system has attracted the attention of the industries, governments and academia. One of the major issues to be overcome in realisation of floating liquefied natural gas is the motion prediction of close-proximity floating bodies including the gap resonance between the two bodies. In this article, three steps were carried out in order to understand the ship motions and the gap resonance and their effects to the side-by-side offloading operations. First, the two-dimensional gap resonance between the two bodies was investigated using a viscous flow numerical method. Second, the three-dimensional gap resonance and the floating body motions were studied using a potential flow method and validated by the experimental model test. Finally, the limits of environmental conditions for the side-by-side offloading operations were examined by the results of numerical calculation.

One- and two-dimensional gap solitons in spin-orbit-coupled systems with Zeeman splitting

We elaborate a mechanism for the formation of stable solitons of the semi-vortex type (with vorticities 0 and 1 in their two components), populating a finite bandgap in the spectrum of the spin-orbit-coupled binary Bose-Einstein condensate with the Zeeman splitting, in the two-dimensional free space, under conditions which make the kinetic-energy terms in the respective coupled Gross-Pitaevskii equations negligible. Unlike a recent work which used long-range dipole-dipole interactions to construct stable gap solitons in a similar setting, we here demonstrate that stable solitons are supported by generic local interactions of both attractive and repulsive signs, provided that the relative strength of the cross/self interaction in the two-component system does not exceed a critical value ~ 0.77. A boundary between stable and unstable fundamental 2D gap solitons is precisely predicted by the Vakhitov-Kolokolov criterion, while all excited states of the 2D solitons, with vorticities (m, 1 + m) in the two components, m = 1, 2, ..., are unstable. The analysis of the one-dimensional (1D) reduction of the system produces an exact analytical solution for the family of gap solitons which populate the entire bandgap, the family being fully stable. Motion of the 1D solitons in the trapping potential is considered too, showing that their effective mass is positive or negative if the cubic nonlinearity is attractive or repulsive, respectively.

Engineering topological phases with a three-dimensional nodal-loop semimetal

A three-dimensional (3D) nodal-loop semimetal phase is exploited to engineer a number of intriguing phases featuring different peculiar topological surface states. In particular, by introducing various two-dimensional gap terms to a 3D tight-binding model of a nodal-loop semimetal, we obtain a rich variety of topological phases of great interest to ongoing theoretical and experimental studies, including chiral insulator, degenerate-surface-loop insulator, second-order topological insulator, as well as Weyl semimetal with tunable Fermi arc profiles. The unique concept underlying our approach is to engineer topological surface states that inherit their dispersion relations from a gap term. The results provide one rather unified principle for the creation of novel topological phases and can guide the search for new topological materials. Two-terminal transport studies are also carried out to distinguish the engineered topological phases.

Numerical investigation of viscous effects on the gap resonance between side-by-side barges

This paper presents a numerical study of the gap resonance between two side-by-side barges by using a multiphase Navier-Stokes equations model. In order to verify the multiphase flow model, it is firstly applied to simulate a two-dimensional gap resonance problem for two fixed boxes under various wave conditions. A comparison of the free surface elevations obtained on successively refined grids confirms the mesh convergence of numerical solutions. The calculated wave elevation response amplitude operators (RAOs) in the gap compare well with the experimental measurements. The multiphase flow model is further extended to calculate a three-dimensional gap resonance problem for two adjacent rectangular barges. The computed free surface RAOs in the gap also agree well with the experimental results. A close examination of the flow velocity and vorticity in the gap region at the piston resonant mode reveals that large amount of vortices are generated by the sharp corners of the two barges and shed downwards, which provide an effective mechanism to dissipate the flow kinematic energy and to reduce the wave elevation in the gap. On the contrary, rounded corners are not able to induce the same level amount of vortices to dampen the gap resonance. The effects of incident wave steepness on the viscous damping associated with the twin-barge system are highlighted.

One- and two-dimensional gap solitons and dynamics in the [formula omitted]-symmetric lattice potential and spatially-periodic momentum modulation

The influence of spatially-periodic momentum modulation on beam dynamics in parity-time (PT) symmetric optical lattice is systematically investigated in the one- and two-dimensional nonlinear Schrödinger equations. In the linear regime, we demonstrate that the momentum modulation can alter the first and second PT thresholds of the classical lattice, periodically or regularly change the shapes of the band structure, rotate and split the diffraction patterns of beams leading to multiple refraction and emissions. In the Kerr-nonlinear regime for one-dimension (1D) case, a large family of fundamental solitons within the semi-infinite gap can be found to be stable, even beyond the second PT threshold; it is shown that the momentum modulation can shrink the existing range of fundamental solitons and not change their stability. For two-dimension (2D) case, most solitons with higher intensities are relatively unstable in their existing regions which are narrower than those in 1D case, but we also find stable fundamental solitons corroborated by linear stability analysis and direct beam propagation. More importantly, the momentum modulation can also utterly change the direction of the transverse power flow and control the energy exchange among gain or loss regions.

Ultracompact Slow Surface Plasmon Polaritons Superlattice with Broad Bandwidth and Super-High Normalized Delay-Bandwidth Product

In this paper, we propose an ultracompact low-loss plasmonic superlattice for slow surface plasmon polaritons. The superlattice consists of a two-dimensional metal gap waveguide (Ag-SiO2-Ag) inserted with thin metal films working as coupled reflectors. Theoretical calculations indicate that the device is working on a broad bandwidth of 37 THz including the two telecom wavelengths of 1,310 and 1,550 nm and with mean group refractive index of 3.5 and mean transmission of 60 %. As the total geometric thickness is only 1.6 μm, the normalized delay-bandwidth product of the superlattice is as high as 0.44. All the theoretical prediction based upon the transfer matrix method is validated by the finite-difference time-domain numerical simulation on surface plasmon polaritons propagating in the superlattice.

Computational design of a test article to investigate 2-D surface excrescences on a swept laminar-flow wing

The construction of a spanwise-invariant swept-wing test article designed to facilitate the inclusion of a range of two-dimensional (2-D) step and gap excrescences in flight via an internal articulation mechanism has been completed. Using a finite-element Navier-Stokes solution and a spectrally accurate boundary-layer solver, coupled with stability analyses, the model has been designed to be subcritical to all instabilities except the crossflow instability. The model can be safely flown in a flight experiment, and be mounted in the Klebanoff-Saric Wind Tunnel at Texas A&M University. The model can be tested at multiple angles of attack (pressure gradients), as well as multiple Reynolds numbers, including unit Reynolds numbers typical of transports. Stability behaviour of the test article was designed to be conducive to a thorough examination of the interaction between an inherent crossflow instability and the shear layer created by the step and gap excrescences. The computations and experiments will together provide data and correlations complementing the previous studies of 2-D excrescences on an unswept flat plate and wedges subject to favourable pressure gradients by The Northrop Grumman Corporation. The current paper focuses on the design and stability analyses of the smooth-wing test article, that is, without excrescences present, as a baseline configuration.

Stability of two-dimensional gap solitons in periodic potentials: Beyond the fundamental modes

Gross-Pitaevskii or nonlinear-Schrödinger equations with a sinusoidal potential is commonly used to describe nonlinear periodic media, such as photonic lattices in optics and Bose-Einstein condensates (BECs) loaded into optical lattices (OLs). Previous studies have shown that the 2D version of this equation, with the self-focusing (SF) nonlinearity, supports stable solitons in the semi-infinite gap. It is known, too, that under both the self-defocusing (SDF) and SF nonlinearities, several families of gap solitons (GSs) exist in finite bandgaps. Here, we investigate the stability of 2D dipole-mode GS families, via the computation of their linear-stability eigenvalues and direct simulations of the perturbed evolution. We demonstrate that, under the SF nonlinearity, one species of dipole GSs is stable in a part of the first finite bandgap, provided that the OL depth exceeds a threshold value, while other dipole and multipole modes are unstable in that case. Bidipole bound states (vertical, horizontal, and diagonal), as well as square- and rhombic-shaped vortices and quadrupoles, built of stable fundamental dipoles, are stable too. Under the SDF nonlinearity, the family of dipole solitons is shown to be stable in a part of the second finite bandgap. Transformations of unstable dipole GSs are studied by means of direct simulations. Direct simulations are also performed to investigate the stability of other GS families, in the first and second bandgaps, under both types of the nonlinearity. In particular, "tripole" solitons, sustained in the second bandgap under the action of the SF nonlinearity, demonstrate stable behavior in the course of long propagation, in a certain region within the bandgap.

Coupling surface plasmon waves across gaps in a dielectric/metal interface by transformation optics

On the basis of transformation optics, we propose an approach to couple surface plasmon waves across gaps in a dielectric/metal interface. The coupler employs a slab of complementary medium with negative refraction index to virtually bridge the gap by optically compensating the rest air region in the gap. Several design examples through transformation optics have been demonstrated which could enable plasmonic waves to propagate through two-dimensional gaps in metal surfaces with transversal offset, vertical offset or tilt geometry. The functionality of the proposed couplers has been validated through finite-element method-based full-wave simulations.

Mechanical pre-treatment (MPT) – revitalised by MBR process

Since the mid-nineties membrane bioreactor (MBR) technology has been introduced to municipal wastewater treatment in Europe. The first MBR plants went into operation performing a conventional mechanical pre-treatment (MPT) without any advanced treatment units. After a short operation period, clogging caused by fibrous substances and hence module sludging was observed. Thus, MPT was upgraded introducing sieves. Several investigations had been carried out to determine the removal efficiency of different sieve units and entire MPT systems. Meanwhile experiences from long-term operation at different MBR sites indicate dependencies between different MPT units, especially between the aerated grit chamber/grease trap and the subsequent sieve unit. Usually the sieve is the final MPT unit and its performance depends on the performance of the upstream MPT units. This report describes and discusses results from a research project at MBR Kaarst-Nordkanal in Germany conducted in 2008 to 2010 by the Water Board of River Erft and the Department of Sanitary and Environmental Engineering. Main focus is addressed for the parameters SS (settable solids) and grease. One major experience is the confirmation of relevant interactions between the grit chamber and the downstream sieve unit. Stable operation of the grit chamber and grease trap is essential to achieve a constantly high removal performance of the sieve unit and therefore the entire MPT stage. In turn, negative impacts on the grit chamber performance from the return flow concept have to be avoided. Finally, it is shown that the appropriate two-dimensional sieve gap size should not go beyond 1 mm when operating hollow fibre membranes.

数值模拟二维间隙表面等离子波导传输特性

Two-dimensional gap plasmonic waveguide employing surface plasmon polaritons is proposed.Transmission characters of 90 degrees sharp bend waveguide,T-shaped splitter and switch based on gap plasmonic waveguide are numerical simulated with finite-difference time-domain method.It is shown that the energy loss of 90 degrees sharp bend waveguide is ohmic losses which are different to radiation losses of dielectric optical waveguide.When the gap width is larger than 40 nm,the transmission of bend waveguide is larger than straight waveguide with the same length.In the T-shaped splitter,when the gap width ratio of two output waveguides is larger than 0.6,the output energy is mainly assigned to the output waveguide which effective index is smaller.The result is different from dielectric optical splitter.The T-shaped switch is off with two input light out of phase and is on with two input light in phase.The plasmonic modes in the above devices beyond the diffraction limit and can be employed in super-large-scale optical integrated circuit.