Weak Confinement Research Articles

The propagation characteristics of a detonation wave in uniformly premixed gases within a semi-confined channel

Based on the OpenFOAM platform, a numerical study was conducted to investigate the propagation characteristics of a detonation wave in uniformly premixed gases within a semi-confined channel, specifically examining the changes in wave's structure and analyzing the detonation reinitiation-extinguishment process. The results indicate that, due to the weak confinement, the detonation wave experiences lateral expansion, with transverse waves on the detonation wave front penetrating into the inert gas and forming segmented protrusions on the oblique shock wave. During the propagation process, the number of transverse waves decreases gradually, and the reflected waves formed by the interaction between transverse waves and the inert gas are weak, collectively leading to a gradual decay in the strength of the detonation wave and a reduction in the frequency of pressure oscillation on the detonation wave front. Furthermore, when transverse waves interact with the inert gas and undergo Mach reflection, the reflected waves would detach the inert gas and form new transverse waves promoted by upward-moving old transverse waves and disturbances on the flame front, thereby extending the duration distance of the detonation wave. Subsequently, after the detonation wave decouples, a transverse wave reflected from the inert gas interface interacts with the lower wall, triggering local detonation reinitiation, which generates a higher-intensity longitudinal wave that couples with the leading shock wave, temporarily restoring the detonation wave and forming lateral detonation in the decoupled region. However, the detonation wave will ultimately extinguish due to the attenuation of transverse waves' intensity and decreasing number of these waves.

Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates

The first part of this work evaluates Al-doped ZnO (AZO) as an optically transparent top-gate material for studies on semiconductor quantum dots. In comparison with conventional Ti gates, samples with AZO gates demonstrate a more than three times higher intensity in the quantum dot emission under comparable excitation conditions. On the other hand, charges inside a process-induced oxide layer at the interface to the semiconductor cause artifacts at gate voltages above U≈ 1 V. The second part describes an optical and simulation study of a vertical electric-field (F)-induced switching from a strong to an asymmetric strong–weak confinement in GaAs cone-shell quantum dots (CSQDs), where the charge carrier probability densities are localized on the surface of a cone. These experiments are performed at low U and show no indications of an influence of interface charges. For a large F, the measured radiative lifetimes are substantially shorter compared with simulation results. We attribute this discrepancy to an F-induced transformation of the shape of the hole probability density. In detail, an increasing F pushes the hole into the wing part of a CSQD, where it forms a quantum ring. Accordingly, the confinement of the hole is changed from strong, which is assumed in the simulations, to weak, where the local radius is larger than the bulk exciton Bohr radius. In contrast to the hole, an increasing F pushes the electron into the CSQD tip, where it remains in a strong confinement. This means the radiative lifetime for large F is given by an asymmetric confinement with a strongly confined electron and a hole in a weak confinement. To our knowledge, this asymmetric strong–weak confinement represents a novel kind of quantum mechanical confinement and has not been observed so far. Furthermore, the observed weak confinement for the hole represents a confirmation of the theoretically predicted transformation of the hole probability density from a quantum dot into a quantum ring. For such quantum rings, application as storage for photo-excited charge carriers is predicted, which can be interesting for future quantum photonic integrated circuits.

Sustenance of hydrogen–oxygen cellular detonation with ozone additions in confined space

The sustenance of cellular detonation under weak confinement is studied through two-dimensional (2D) numerical simulations of hydrogen–oxygen mixtures surrounded by inert gas. The results show that in the weakly confined space, the cellular detonation with Chapman-Jouguet velocity can survive by increasing the width of the reactant layer and enhancing the reactivity of reactants, which ensures enough triple points and high reactivity in the reactant layer for detonation sustenance since transverse shocks cannot be regenerated and reinforced by boundary reflection. By adding ozone into the system and changing the width of the reactant layer, the relationship between induction length and detonation sustenance is established. It is found that the sustenance of cellular detonation in the weakly confined space is related to the ratio of the reactant layer width to the induction length. Ozone reactions can reduce the induction length and enhance reactivity, thereby promoting the generation of new transverse shocks and significantly improving the sustenance of cellular detonation in weakly confined space.

Effect of nanopore network connectivity on the phase behavior of confined associating fluids

We investigate the phase behavior of associating fluids inside heterogeneous slit pores. Two distinct phase transitions are observed for connected pores of two slit widths for both hard and attractive walls. In the case of the hard wall, the wider pore undergoes the vapor-liquid transition earlier than the narrower pore due to its weaker confinement and increased fluid interactions. In the case of an attractive pore surface, the narrower pore undergoes the vapor-liquid transition earlier than the wider pore. This can be attributed to the enhanced surface interactions in the narrower pore, which promote the condensation of the fluid phase. The x-density profile of the systems reveals that the interfacial fluid molecules play an essential role in early/delayed phase transition in the respective pores of the heterogeneous systems.

Axial compressive performance of CFRP-steel composite tube confined seawater sea-sand concrete intermediate slender columns

To alleviate the scarcity of river sand resources and fully utilize the advantages of Carbon Fiber Reinforced Polymer (CFRP), a new type of CFRP-steel composite tube was developed to confine seawater-sea sand concrete (FCTSSC) column structures. This study conducted experimental research on FCTSSC intermediate slender columns for the first time, analyzing their failure modes and working mechanisms. The investigation explored the effects of outer CFRP layers and slenderness ratios on the mechanical performance. The results indicate that the FCTSSC intermediate slender column specimens exhibited global buckling accompanied by local bulging of steel tubes as their failure mode. The load-displacement curves can be divided into strong confinement and weak confinement models. Specimens confined by CFRP exhibited a 12.51–31 % increase in ultimate bearing capacity. The ultimate bearing capacity and its enhancement rate were positively correlated with the outer CFRP layers and negatively correlated with the slenderness ratio. Peak lateral displacements were positively correlated with both parameters. Finally, the model for calculating the axial compression ultimate bearing capacity of FCTSSC intermediate slender columns was proposed, providing a reference for future practical applications in offshore engineering.

Numerical simulation of dynamics behavior of pulsed-DC helium plasma jet confined by parallel magnetic field at atmospheric pressure

A two-dimensional axisymmetric fluid model is used to simulate the dynamics behavior of an atmospheric-pressure helium plasma jet in the presence of a parallel magnetic field. The plasma jet is generated in a coaxial dielectric barrier discharge (DBD) driven by pulsed direct-current voltage. Comparative analysis of the plasma jet with and without the parallel magnetic field indicates that a slightly thinner plasma sheath inside the tube is present with the parallel magnetic field as a result of the decreased accumulated electrons on the inner surface of dielectric tube. After the streamer propagates outside the tube, a little more concentrated electron distribution in the annular wall is observed by applying the magnetic field because of the reduced electron diffusion in the radial direction and the confinement effect of the magnetic field on the electrons in the avalanche heads. The tiny reduction in the length of plasma jet is attributed to the E × B drift of charged particles. These results demonstrate that the parallel magnetic field has no apparent effect on the propagation of the plasma jet, and it contributes little to the performance improvement of the coaxial DBD, which agrees well with the previous experimental observations. This little impact of the parallel magnetic field on the coaxial DBD plasma jet may result from negligible contribution of the memory effect to the sole discharge pulse as well as the weak confinement effect of the applied magnetic field on the surface electrons that moves along the magnetic field lines under electrostatic repulsion. Published by the American Physical Society 2024

Performance of Particle Swarm Optimization in Predicting the Orientation of π-Conjugated Molecules Inside Carbon Nanotubes Compared with Density Functional Theory Calculations.

Particle swarm optimization (PSO) was employed to obtain the global minimum of host-guest structures consisting of a triiodobenzene molecule (BzI3) inside an armchair (m,m) nanotube (BzI3@(m,m)), whose host-guest interactions are approximated by Lennard-Jones (LJ) potentials. The host-guest structures obtained using the PSO-LJ method were then compared with those obtained through dispersion-corrected density functional theory (DFT) calculations to evaluate the performance of the PSO-LJ approach in predicting the guest orientation inside a tube. When the inner space of the host tube is limited for guest encapsulation, the PSO-LJ method can reproduce the DFT results of BzI3@(m,m) in terms of the guest orientation. Conversely, in nanotubes with a sufficiently large space to allow a guest to freely move, corresponding to weak tube confinement, the PSO-LJ method yields guest orientations that are different from those obtained through DFT calculations; however, both methods obtain energetically close guest orientations. Accordingly, PSO-LJ method-assisted DFT calculations can quickly provide energetically stable guest orientations in BzI3@(m,m) in weak tube confinement, which can be ignored in DFT calculations, where a single initial geometry is typically used.

Surface-Originated Weak Confinement in Tetrahedral Indium Arsenide Quantum Dots.

While the shape-dependent quantum confinement (QC) effect in anisotropic semiconductor nanocrystals has been extensively studied, the QC in facet-specified polyhedral quantum dots (QDs) remains underexplored. Recently, tetrahedral nanocrystals have gained prominence in III-V nanocrystal synthesis. In our study, we successfully synthesized well-faceted tetrahedral InAs QDs with a first excitonic absorption extending up to 1700 nm. We observed an unconventional sizing curve, indicating weaker confinement than for equivalently volumed spherical QDs. The (111) surface states of InAs QDs persist at the conduction band minimum state even after ligand passivation with a significantly reduced band gap, which places tetrahedral QDs at lower energies in the sizing curve. Consequently, films composed of tetrahedral QDs demonstrate an extended photoresponse into the short-wave infrared region, compared to isovolume spherical QD films.

Thermalization of long range Ising model in different dynamical regimes: A full counting statistics approach

We study the thermalization of the transverse field Ising chain with a power law decaying interaction \sim 1/r^{\alpha}∼1/rα following a global quantum quench of the transverse field in two different dynamical regimes. The thermalization behavior is quantified by comparing the full probability distribution function (PDF) of the evolving states with the corresponding thermal state given by the canonical Gibbs ensemble (CGE). To this end, we used the matrix product state (MPS)-based Time Dependent Variational Principle (TDVP) algorithm to simulate both real time evolution following a global quantum quench and the finite temperature density operator. We observe that thermalization is strongly suppressed in the region with strong confinement for all interaction strengths \alphaα, whereas thermalization occurs in the region with weak confinement.

Insights into support effects of Ag/SiO2 catalysts for dimethyl glycolate semi-hydrogenation to methyl glycolate

Support materials play vital roles in heterogenous catalysis via the so-called support effects, and understanding on the support effects is beneficial for the design of high-performance catalysts. Herein, we represent detailed investigations on the support effects of Ag catalysts for dimethyl glycolate (DMO) semi-hydrogenation to methyl glycolate (MG), where G6 silica with amorphous mesopores, SBA-15 with parallel mesopores and silica nanospheres (MSNS) with center-radial ones were employed as the supports. The hydrogenation activity decreases in the order of Ag/MSNS > Ag/SBA-15 > Ag/G6 while the MG selectivity in the order of Ag/G6 > Ag/MSNS > Ag/SBA-15 at the same reaction conditions, indicating remarkable support effects on both activity and selectivity. Structural characterizations, temperature programmed experiments and in-situ FTIR of DMO adsorption experiments demonstrate that the weak confinement effect of G6 leads to the larger sized Ag nanoparticles and weakened activation of DMO and H2, which contributes to low hydrogenation activity. In contrast, the ordered mesoporous SBA-15 and MSNS deliver well confinement effects for Ag nanoparticles and the activation of DMO and H2, but the distinct pore structures result in different activation and diffusion behaviors. Finally, DMO conversion and MG yield are well correlated with the competitive adsorption of H2 versus DMO on Ag catalysts, indicating such competitivity as a descriptor for DMO semi-hydrogenation over Ag catalysts.

Evolution of structural and electronic properties standardized description in rhenium disulfide at the bulk-monolayer transition

The structural and electronic properties of ReS2 different forms — three-dimensional bulk and two-dimensional monolayer — were studied within density functional theory and pseudopotentials. A method for standardizing the description of bulk unit cells and "artificial" slab unit cells for DFT research has been proposed. The preference of this method for studying zone dispersion has been shown. The influence of the vacuum layer thickness on specified special high-symmetry points is discussed. Electron band dispersion in both classical 3D Brillouin zones and transition to 2D Brillouin zones in the proposed two-dimensional approach using the Niggli form of the unit cell was compared. The proposed two-dimensional approach is preferable for low-symmetry layered crystals such as ReS2. It was established that the bulk ReS2 is a direct gap semiconductor (band gap of 1.20 eV), with the direct transition lying in the X point of the first Brillouin zone, and it is in good agreement with published experimental data. The reduction in material dimension from bulk to monolayer was conducted with an increasing band gap up to 1.45 eV, with a moving direct transition towards the Brillouin zone center. The monolayer of ReS2 is a direct-gap semiconductor in a wide range of temperatures, excluding only a narrow range at low temperatures, where it comes as a quasi-direct gap semiconductor. The transition, situated directly in the Γ-point, lies 3.3 meV below the first direct transition located near this point. The electronic density of states of ReS2 in the bulk and monolayer cases of ReS2 were analyzed. The molecular orbitals were built for both types of ReS2 structures as well as the electron difference density maps. For all types of ReS2 structures, an analysis of populations according to Mulliken and Voronoi was carried out. All calculated data is discussed in the context of weak quantum confinement in the 2D case.

A tight-binding model for illustrating exciton confinement in semiconductor nanocrystals.

The Brus equation describes the relation between the lowest energy of an electron-hole pair and the size of a semiconductor crystallite. However, taking the strong confinement regime as a starting point, the equation does not cover the transition from weak to strong confinement, the accompanying phenomenon of charge-carrier delocalization, or the change in the transition dipole moment of the electron-hole pair state. Here, we use a one-dimensional, two-particle Hubbard model for interacting electron-hole pairs that extends the well-known tight-binding approach through a point-like electron-hole interaction. On infinite chains, the resulting exciton states exhibit the known relation between the Bohr radius, the exciton binding energy, and the effective mass of the charge carriers. Moreover, by introducing infinite-well boundary conditions, the model enables the transition of the exciton states from weak to strong confinement to be tracked, while straightforward adaptations provide insights into the relation between defects, exciton localization, and confinement. In addition, by introducing the dipole operator, the variation of the transition dipole moment can be mapped when shifting from electron-hole pairs in strong confinement to delocalized and localized excitons in weak confinement. The proposed model system can be readily implemented and extended to different multi-carrier states, thus providing researchers a tool for exploring, understanding, and teaching confinement effects in semiconductor nanocrystals under different conditions.

Amphoteric Chelating Ultrasmall Colloids for FAPbI3 Nanodomains Enable Efficient Near-Infrared Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) are the next promising display technologies because of their high color purity and wide color gamut, while two classical emitter forms, i.e., polycrystalline domains and quantum dots, are encountering bottlenecks. Weak carrier confinement of large polycrystalline domains leads to inadequate radiative recombination, and surface ligands on quantum dots are the main annihilation sites for injected carriers. Here, pinpointing these issues, we screened out an amphoteric agent, namely, 2-(2-aminobenzoyl)benzoic acid (2-BA), to precisely control the in situ growth of FAPbI3 (FA: formamidine) nanodomains with enhanced space confinement, preferred crystal orientation, and passivated trap states on the transport-layer substrate. The amphoteric 2-BA performs bidentate chelating functions on the formation of ultrasmall perovskite colloids (<1 nm) in the precursor, resulting in a smoother FAPbI3 emitting layer. Based on monodispersed and homogeneous nanodomain films, a near-infrared PeLED device with a champion efficiency of >22% plus enhanced T80 operational stability was achieved. The proposed perovskite nanodomain film tends to be a mainstream emitter toward the performance breakthrough of PeLED devices covering visible wavelengths beyond infrared.

Microscopy of terahertz spoof surface plasmons propagating on planar metamaterial waveguides

Surface plasmon polaritons (SPPs) are electromagnetic waves that have attracted significant interest owing to their subwavelength confinement and the strong field enhancement that they provide. Yet in the terahertz (THz) frequency region of the spectrum, which is well below the plasma frequency of metals, these surface waves are characterized by extremely weak confinement that has severely limited their exploitation for information processing and sensing. One means to circumvent this limitation is through subwavelength structuring of a metallic surface, which can thereby be engineered to support the propagation of spoof surface plasmon polaritons (SSPPs) that closely mimic the properties of SPPs. In this work, we report the design and experimental characterization of an ultra-thin metamaterial planar waveguide that supports SSPPs at THz frequencies. Finite-element method simulations are shown to predict the excitation of SSPPs on the surface of our devices under free-space illumination at 3.45 THz. We investigate these structures experimentally using THz scattering-type scanning near-field microscopy (THz-s-SNOM) to map directly the out-of-plane electric field associated with the propagation of SSPPs on the surface of the waveguides. Our work paves the way for the future development of plasmonic integrated circuit technologies and components operating in the THz frequency band.

Effects of composition on the explosive properties of potassium chlorate and oils

Abstract Potassium chlorate has long been utilized as an excellent oxidizing agent in pyrotechnics and explosives. As mixtures of potassium chlorate and any type of combustible material can be explosive, there is a potential risk of misuse in homemade explosives. Unlike commercial explosives, homemade chlorate and oil mixtures do not have a constant composition, which limits their understanding. This study reports the effects of two types of oil (motor oil and cooking oil) and their ratios (ranging from 2.5% to 40.0% (w/w)) on the explosive properties of such mixtures. The impact sensitivity was highest at a motor oil ratio of 5%. The friction sensitivity increased with an increasing oil ratio, reaching a maximum at an oil ratio of around 22.5%, and was close to those of primary explosives. The motor oil mixtures exhibited higher sensitivity than the cooking oil mixtures at oil ratios of 25% or less. A 10% oil mixture, which was close to the ratio of oxygen balance equal to zero, detonated in weak confinement, such as a paper cylinder. The highest detonation velocities in a polypropylene tube were around 2300 and 2550 m/s at a 10% ratio of motor oil and cooking oil, respectively. The velocities of the metal case wall, measured by photonic Doppler velocimetry, reached about 1100 m/s near the end of acceleration. These results show that homemade chlorate and oil mixtures are capable of detonation and quite sensitive over a wide range of oil ratios, with sufficient power to cause damage in the vicinity.

Soliton confinement in the double sine-Gordon model

The double sine-Gordon field theory in the weak confinement regime is studied. It represents the small non-integrable deformation of the standard sine-Gordon model caused by the cosine perturbation with the frequency reduced by the factor of 2. This perturbation leads to the confinement of the sine-Gordon solitons, which become coupled into the ‘meson’ bound states. We classify the meson states in the weak confinement regime, and obtain three asymptotic expansions for their masses, which can be used in different regions of the model parameters. It is shown, that the sine-Gordon breathers, slightly deformed by the perturbation term, transform into the mesons upon increase of the sine-Gordon coupling constant.

Capillary imbibition of confined monodisperse emulsions in microfluidic channels.

We study imbibition of a monodisperse emulsion into high-aspect ratio microfluidic channels with the height h comparable to the droplet diameter d. Two distinct regimes are identified in the imbibition dynamics. In a strongly confined system (the confinement ratio d/h = 1.2 in our experiments), the droplets are flattened between the channel walls and move more slowly compared to the average suspension velocity. As a result, a droplet-free region forms behind the meniscus (separated from the suspension region by a sharp concentration front) and the suspension exhibits strong droplet-density and velocity fluctuations. In a weaker confinement, d/h = 0.65, approximately spherical droplets move faster than the average suspension flow, causing development of a dynamically unstable high-concentration region near the meniscus. This instability results in the formation of dense droplet clusters, which migrate downstream relative to the average suspension flow, thus affecting the entire suspension dynamics. We explain the observed phenomena using linear transport equations for the particle-phase and suspension fluxes driven by the local pressure gradient. We also use a dipolar particle interaction model to numerically simulate the imbibition dynamics. The observed large velocity fluctuations in strongly confined systems are elucidated in terms of migration of self-assembled particle chains with highly anisotropic mobility.

Giant optical absorption of a PtSe2-on-silicon waveguide in mid-infrared wavelengths.

Low-dimensional platinum diselenide (PtSe2) is a promising candidate for high-performance optoelectronics in the short-wavelength mid-infrared band due to its high carrier mobility, excellent stability, and tunable bandgap. However, light usually interacts moderately with low-dimensional PtSe2, limiting the optoelectronic responses of PtSe2-based devices. Here we demonstrated a giant optical absorption of a PtSe2-on-silicon waveguide by integrating a ten-layer PtSe2 film on an ultra-thin silicon waveguide. The weak mode confinement in the ultra-thin waveguide dramatically increases the waveguide mode overlap with the PtSe2 film. Our experimental results show that the absorption coefficient of the PtSe2-on-silicon waveguide is in the range of 0.0648 dB μm-1 to 0.0704 dB μm-1 in a spectral region of 2200 nm to 2300 nm wavelengths. Furthermore, we also studied the optical absorption in an ultra-thin silicon microring resonator. Our study provides a promising approach to developing PtSe2-on-silicon hybrid optoelectronic integrated circuits.

Strong anapole-plasmon coupling in dielectric-metallic hybrid nanostructures.

The nanoscale ampification of light-matter interactions exhibits profound potential in multiple scientific fields, such as physics, chemistry, surface science, materials science, and nanophotonics. Nonetheless, achieving robust optical mode coupling within cavities faces significant hurdles due to modal dispersion and weak optical field confinement. In this theoretical investigation, we demonstrate the viability of strong coupling between the anapole mode of a slotted silicon nanodisk and the plasmonic modes of an Ag nanodisk dimer at visible light frequencies. By introducing anapole modes, we successfully confine light to subwavelength volumes, suppressing radiative losses and achieving a remarkable Rabi splitting of 468 meV. This substantial coupling is facilitated by the large spatial overlap of intense optical fields. Capitalizing on this strong mode coupling, we generate novel hybrid energy states with significant electromagnetic field enhancement. Our study serves as a valuable blueprint for designing platforms based on strong anapole mode coupling at visible frequencies and paves the way for deeper explorations into nanoscale light-matter interactions.

Numerical analysis of high-strength centrifugal precast RC hollow pipe columns using grouted corrugated duct connection: Confinement effect and ductility evaluation

High-strength centrifugal precast (HSCP) reinforced concrete (RC) hollow pipe columns using grouted corrugated duct connection (GCDC) is a novel structure form in accelerated bridge construction (ABC). Nevertheless, the confinement effect of the HSCP hollow column core concrete provided by single-layer transverse rebar and its impact on ductility is not clear. Therefore, in this paper, the confinement effect and the ductility of hollow columns is studied using finite element analysis (FEA) method. A modified model is established to evaluate the constitutive relation of the core concrete confined by single layer transverse rebar. Based on the modified model, a simplified fiber model for predicting the hysteric response of HSCP hollow pipe column using GCDC, which considers bond-slip effect in GCDC joint was developed. The results indicate that the confinement effect of HSCP hollow pipe column is sensitive to the wall thickness ratio. When the wall thickness ratio decreases, the ultimate strain of the core concrete significantly decreases, while the effect on strength is not significant. The simplified model which considers confinement effect is more accurate in predicting the ductility of HSCP hollow columns. It proves that the weak confinement effects can lead to early cracking of the inner wall of hollow columns, which leads a significant impact on the ductility of HSCP hollow columns. Based on the parametric analysis, the peak load of the hollow column increases by 16.7% when the wall thickness ratio rises from 0.1 to 0.2, but only slightly changes when the wall thickness ratio is increased beyond 0.2. The wall thickness ratio of HSCP hollow pipe columns should be set above 0.2 to ensure the strength and ductility. In addition, a ductility evaluation method and a design example were developed to guide preliminary ductile design of HSCP hollow columns.