Enhancement Phenomenon Research Articles

Investigation of slow magnetic relaxation in a series of 1D polymeric cyclobutane-1,1-dicarboxylates based on LnIIIVIV2 units (LnIII = Tb, Dy, Ho, Er, Tm, Yb): rare examples of VIV-4f single-molecule magnets.

The reactions of VOSO4·3H2O with Na2(cbdc) (cbdc2- - dianion of cyclobutane-1,1-dicarboxylic acid) and lanthanide(III) nitrates taken in a molar ratio of 1 : 2 : 1 were found to yield a series of isostructural heterometallic compounds [NaLn(VO)2(cbdc)4(H2O)10]n (1Ln, Ln = Tb, Dy, Ho, Er, Tm, Yb). These compounds are constructed from trinuclear anionic units [Ln(VO)2(cbdc)4(H2O)8]- ({LnV2}-) linked by Na+ ions into 1D polymeric chains. The crystal structures of 1Dy and 1Er were determined by single-crystal X-ray diffraction (XRD), and their isostructurality with 1Tb, 1Ho, 1Tm, and 1Yb was proved by powder X-ray diffraction (PXRD). According to alternating current (ac) magnetic susceptibility measurements, 1Dy, 1Er, and 1Yb exhibited field-induced slow relaxation of magnetization. Compound 1Er is the first representative of ErIII-VIV single-molecule magnets. Measuring the temperature dependences of the phase memory time (Tm) for 1Dy and 1Yb using pulsed EPR spectroscopy allowed us to observe the phenomenon of phase relaxation enhancement (PRE) at temperatures below 30 K. In future, this phenomenon may contribute to the evaluation of relaxation times of the lanthanide ions.

Fluorescence enhancement upon magnesium hydroxide micro/nanoparticles in the detection of ferulic acid

We found an exciting fluorescence enhancement phenomenon of ferulic acid (FA) and magnesium ions in strong alkaline medium. In KCl/NaOH buffer solution with pH = 12.30, Mg2+ ions could coordinate with FA to generate Mg-FA complex ions and also combined with hydroxide ions to form Mg(OH)2 nanosheets, and then the nanosheets further aggregated into Mg(OH)2-micro/nanoparticles (Mg(OH)2-MNPs). The Mg(OH)2-MNPs acted as potential matrix materials for surface-enhanced fluorescence (SEF). In this work, the fluorescence quantum yield and the fluorescence intensity of FA were significantly increased by about 50 times and hundreds of times by freshly formed Mg(OH)2-MNPs, respectively. Then, a highly sensitive method was developed for quantitative detection of FA. The fluorescence intensity at 440 nm under 370 nm light irradiation showed a good linearity with FA concentration in the range of 9.0 × 10−10 to 1.0 × 10–6 M (R2 = 0.9984), and the limit of detection (at S/N = 3) was 2.7 × 10−10 M. And then a convenient method for FA detection by smartphone assisted was also proposed. These methods were applied for detecting FA in real samples, and the recovery rates were range from 98.3 % to 103.1 %. This work provided an effective way for improving FA analytical sensitivity.

Latitudinal Characteristics of the Post‐Sunset Enhancements in Ionospheric Electron Density During the Geomagnetic Quiet Period in May 2021 Over East‐Asian Region

AbstractThis study investigated the latitudinal variations of post‐sunset enhancements in the ionospheric electron density during the geomagnetic quiet period in May 2021 with a combination of high‐precision ionospheric parameters obtained from four ionosondes, Beidou geostationary satellite (BD‐GEO) receiver network and Sanya incoherent scatter radar (SYISR). We identified four categories of post‐sunset enhancement phenomena (Types 1–4), each with unique spatial and temporal evolutions, yet uniformly accompanied by a decrease in hmF2. Measurements of plasma drift vector velocities from SYISR and hmF2 gradients across various latitudes provided pivotal insights, confirming that the ionospheric post‐sunset enhancements can result from downward plasma motion due to westward electric field, downward field‐aligned drift, or a combination of both. For Type 1, dominated by field‐aligned drift, plasma density enhancements not only intensify at low latitudes but may also extend to mid‐latitudes, exhibiting a distinct temporal delay with increasing latitude. In contrast, Type 4, primarily driven by the westward electric field, is characterized by modest increases in plasma density confined to localized low‐latitude regions, with no observable latitudinal time delay in the peak of enhancements. Types 2 and 3, which are subject to the combined influence of the westward electric field and field‐aligned drift, exhibit plasma density increases at certain low‐latitude areas, with Type 2 presenting a delayed pattern and Type 3 showing none with rising latitude. Meanwhile, neutral winds can partially account for the observed post‐sunset enhancement from low to middle latitudes. These findings offer new insights into the factors influencing ionospheric behavior after sunset.

Modelling the mechanisms of antibody mixtures in viral infections: the cases of sequential homologous and heterologous dengue infections.

Antibodies play an essential role in the immune response to viral infections, vaccination or antibody therapy. Nevertheless, they can be either protective or harmful during the immune response. Moreover, competition or cooperation between mixed antibodies can enhance or reduce this protective or harmful effect. Using the laws of chemical reactions, we propose a new approach to modelling the antigen-antibody complex activity. The resulting expression covers not only purely competitive or purely independent binding but also synergistic binding which, depending on the antibodies, can promote either neutralization or enhancement of viral activity. We then integrate this expression of viral activity in a within-host model and investigate the existence of steady-states and their asymptotic stability. We complete our study with numerical simulations to illustrate different scenarios: firstly, where both antibodies are neutralizing and secondly, where one antibody is neutralizing and the other enhancing. The results indicate that efficient viral neutralization is associated with purely independent antibody binding, whereas strong viral activity enhancement is expected in the case of purely competitive antibody binding. Finally, data collected during a secondary dengue infection were used to validate the model. The dataset includes sequential measurements of virus and antibody titres during viremia in patients. Data fitting shows that the two antibodies are in strong competition, as the synergistic binding is low. This contributes to the high levels of virus titres and may explain the antibody-dependent enhancement phenomenon. Besides, the mortality of infected cells is almost twice as high as that of susceptible cells, and the heterogeneity of viral kinetics in patients is associated with variability in antibody responses between individuals. Other applications of the model may be considered, such as the efficacy of vaccines and antibody-based therapies.

Quantum Calculation of the Vibrational Excitation of Nitrogen Molecules by Fast Ions: Can It Contribute to STEVE Formation?

AbstractThe vibrational‐translational (VT) excitation of nitrogen molecules led by collisions with fast ions in subauroral ion drifts (SAID) has been conceived as a potential underlying mechanism contributing to the formation of the Strong Thermal Emission Velocity Enhancement (STEVE) phenomenon (Harding et al., 2020, https://doi.org/10.1029/2020gl087102). In this study, we perform quantum calculations of the VT excitation rates of N2 led by fast‐drifting ions, and evaluate the resulting vibrational distribution of N2 with ionospheric/thermospheric parameters expected under intense SAID condition. We conclude that, while the VT energy transfer led by SAID plays a distinguishable role in the vibrational excitation of N2, it is incapable of populating the high vibrational levels to the required concentration (Harding et al., 2020, https://doi.org/10.1029/2020gl087102) to produce adequate nitric oxide density, and in turn the nitrogen‐dioxide continuum intensity, to account for the STEVE brightness.

Polariton-polariton interaction induced by the hopping effect between two monolayers

Investigating the quantum many-body interaction in microcavity semiconductor systems is a significant objective in current research. Hence, in this study, Green’s function was employed to investigate the hopping effect between two monolayers denoted as L and R. The interaction between excitons in L monolayer and R monolayer, characterized by spin-like properties, leads to the generation of Josephson currents and emergence of two quasiparticle branches, known as LP+ and LP− polaritons (i.e., two low polariton states). And compared with other papers, such as reference 5, the research shows that presence of hopping interaction and many-body interaction between monolayers causes significant enhancement phenomenon of residue Z, which will further reduce the effective mass. This is more conducive to Bose–Einstein condensates (BEC). Furthermore, we investigated the Parity-Time symmetry (PT symmetry) of the system. The PT broken phase transition point will appear when the condition of PT symmetry is satisfied.

Aggregation induced emission enhancement of [Ag3Cu8] clusters protected by alkyne and phosphane ligands

In this work, three isostructural clusters of [Ag3Cu8(R-Ph-CC)6(N-triphos)2(Ph2PO2)3](NO3)2 (R = 4-H (1), 4-CH3 (2), 4-F (3)) were successfully synthesized and structurally determined by single crystal X-ray diffraction. At room temperature, they show weak photoluminescence in CH2Cl2 solution at ∼715 nm but with a 20-fold increase of quantum yields in their aggregation. Crystallographic and Hirshfeld surface analysis reveals a plentiful of intermolecular interactions (C−H…N, C−H…O, C−H…π, π…π) exist in their solid states, which can inhibit the intra-/inter-molecular motions (vibration and rotation) and thus generate the aggregation induced emission enhancement phenomenon. Moreover, their solid luminescent intensities at 100 K are much higher than those at room temperature. Comparisons of their luminescence show that the substituents on the para-positions of phenylethynes not only have a charge effect on emission, but also have steric effect on the molecular stacking and supramolecular interactions in the aggregated and crystalline states, and then on the aggregation-induced emission. The density functional theory (DFT) calculations show that the possible luminescence mechanism of these clusters is ligand-to-metal−metal charge transfer (LMMCT).

Piezofluorochromism in Covalent Organic Frameworks: Pressure-Induced Emission Enhancement and Blue-Shifted Emission.

Achieving enhanced or blue-shifted emission from piezochromic materials remains a major challenge. Covalent organic frameworks (COFs) are promising candidates for the development of piezochromic materials owing to their dynamic structures and adjustable optical properties, where the emission behaviors are not solely determined by the functional groups, but are also greatly influenced by the specific geometric arrangement. Nevertheless, this area remains relatively understudied. In this study, a successful synthesis of a series of bicarbazole-based COFs with varying topologies, dimensions, and linkages was conducted, followed by an investigation of their structural and emission properties under hydrostatic pressure generated by a diamond anvil cell. Consequently, these COFs exhibited distinct piezochromic behaviors, particularly a remarkable pressure-induced emission enhancement (PIEE) phenomenon with a 16-fold increase in fluorescence intensity from three-dimensional COFs, surpassing the performance of CPMs and most organic small molecules with PIEE behavior. On the contrary, three two-dimensional COFs with flexible structures exhibited rare blue-shifted emission, whereas the variants with rigid and conjugated structures showed common red-shifted and reduced emission. Mechanism research further revealed that these different piezochromic behaviors were primarily determined by interlayer distance and interaction. This study represents the first systematic exploration of the structures and emission properties of COFs through pressure-treated engineering and provides a new perspective on the design of piezochromic materials.

Piezofluorochromism in Covalent Organic Frameworks: Pressure‐Induced Emission Enhancement and Blue‐Shifted Emission

AbstractAchieving enhanced or blue‐shifted emission from piezochromic materials remains a major challenge. Covalent organic frameworks (COFs) are promising candidates for the development of piezochromic materials owing to their dynamic structures and adjustable optical properties, where the emission behaviors are not solely determined by the functional groups, but are also greatly influenced by the specific geometric arrangement. Nevertheless, this area remains relatively understudied. In this study, a successful synthesis of a series of bicarbazole‐based COFs with varying topologies, dimensions, and linkages was conducted, followed by an investigation of their structural and emission properties under hydrostatic pressure generated by a diamond anvil cell. Consequently, these COFs exhibited distinct piezochromic behaviors, particularly a remarkable pressure‐induced emission enhancement (PIEE) phenomenon with a 16‐fold increase in fluorescence intensity from three‐dimensional COFs, surpassing the performance of CPMs and most organic small molecules with PIEE behavior. On the contrary, three two‐dimensional COFs with flexible structures exhibited rare blue‐shifted emission, whereas the variants with rigid and conjugated structures showed common red‐shifted and reduced emission. Mechanism research further revealed that these different piezochromic behaviors were primarily determined by interlayer distance and interaction. This study represents the first systematic exploration of the structures and emission properties of COFs through pressure‐treated engineering and provides a new perspective on the design of piezochromic materials.

Investigation of heat transfer enhancement and thermal stratification phenomenon on supercritical hydrogen fuel flow

Thermal stratification is one of the major issues in rectangular regenerative cooling channels because of the asymmetric heating and limited turbulent diffusion of thermal energy of the fuel. As a result, the heat transfer performance is decreased. This paper uses Ansys fluent software to construct a novel cooling structure that combines wavy wall surfaces with cylindrical fins. In addition to this new configuration, this study also examined three other configurations (straight-smooth, cylindrical-ribs, and wavy-smooth) and compared them with each other. This structure aims to efficiently enhance hydrogen coolant flow and heat transfer characteristics while reducing the extent of the non-uniform distribution issue. The results show that the new structure’s Nusselt number and maximum wall temperature are enhanced by 46.89% and 22.71%, respectively, compared to the straight-smooth structure; in contrast, the friction factor increased only by 3.64% over the smooth channel. The novel design has the best thermal performance factor compared to the other three designs, which is improved by 43.33% over the smooth channel. Among all configurations, the new structure is the best fluid temperature distribution configuration, which shows an optimal distribution of the coolant temperatures between layers; thus, the stratification phenomena decreased significantly.

Fluorescent Enhancement of [AgS4] Microplates by Mechanical Force Induced Crystallinity Breaking.

Mechanofluorochromic materials are a type of "smart" material because of their adjustable fluorescent properties under external mechanical force, making them significant members of the materials family. However, as the fluorescent characteristics of these materials highly depend on their microstructures, the still insufficiently in-depth research linking molecular structures to light emission motivates researchers to explore the fluorescent properties of these materials under external stimuli. In this work, based on synthetic [AgS4] microplates, we explore a fascinating mechanical-induced photoluminescent enhancement phenomenon. By applying mechanical force to solid-state [AgS4] to damage the surface morphology, a significant enhancement in photoluminescence is observed. Moreover, the emitted intensity increases with the extent of damage, which can be attributed to alterations in crystallinity. This work provides valuable insights into the relationship among photoluminescence, crystallinity, and mechanical force, offering new strategies for designing luminescent devices.

High‐Efficiency Luminescent Solar Concentrators Based on Carbon Dots with Simultaneously Ultrabright Solid‐State and Liquid‐State Luminescence

AbstractCarbon dots (CDs) are ideal fluorophores for optoelectronic devices. However, it is still a great challenge to obtain CDs with high solid‐state photoluminescence quantum yields (PLQYs). In this work, it is first reported that the barium‐doped CDs (Ba‐CDs), which can be simply synthesized on a large scale via a direct one‐step heating approach using an open vessel. The as‐synthesized Ba‐CDs exhibit ultrabright luminescence both in liquid and solid states. The as‐synthesized Ba‐CDs with a scale of 8.6 g per batch show a Stokes shift of ≈0.68 eV and high PLQYs of 80.8% and 66.8% in liquid and solid state, respectively. Interestingly, an efficient fluorescence enhancement phenomenon occurs when Ba‐CDs are mixed with polyvinylpyrrolidone (PVP), which reveals the critical issue of compatibility between CDs and polymer matrix can be well resolved. As a proof‐of‐concept, the Ba‐CDs are employed as fluorophores for high‐efficiency luminescent solar concentrator (LSC) fabrication. The Ba‐CDs@PVP‐based LSC has a PLQY of 88.78%, showing a breakthrough optical conversion efficiency of 7.16% and power conversion efficiency of 6.87% under natural light irradiation (40 mW cm−2). The results demonstrate the potential application of the ultrabright Ba‐CDs in efficient photovoltaic devices.

The effect of micro-nanostructural changes on the absorption and emission characteristics of InGaAsP photocathodes

In this paper, three structures (cylinder, square column, and hexagonal prism) of InGaAsP nanowire arrays are designed based on the excellent light trapping effect of nanostructures. The effects of nanowire aperture, array period, and nanowire height on the light absorption properties are simulated and analyzed using the finite-domain time-difference (FDTD) method. The photoelectron emission capacity of the nanowire arrays was also calculated using MATLAB. The results show that the cylindrical nanowire array has phenomenon of resonance enhancement (absorption peak) in the near-infrared band of 820–1000[Formula: see text]nm, and the shift of absorption peaks can be achieved by adjusting the geometric parameters. Meanwhile, the quantum efficiency is taken to 9.98%. These simulation results provide some reference for the photocathode design of InGaAsP in the near-infrared band.

230-fold Enhancement of second-harmonic generation by coupled double resonances in a dolmen-type gold metasurface

Optical metasurfaces, artificial planar nanostructures composed of subwavelength meta-atoms, have attracted significant attention due to their ability to tailor optical nanoscale properties, making them a versatile platform for shaping light in both linear and nonlinear regimes. This paper reports on the realization of second harmonic generation (SHG) enhancement based on a dolmen-type gold metasurface containing two resonances. Nonlinear scattering theory is employed to numerically investigate the SHG enhancement phenomenon in the resonant metasurface. The periodic dolmen-type gold metasurface introduces a diffraction coupling effect between Fano resonance and surface lattice resonance (SLR), providing strong local-field enhancement and significantly enhancing the nonlinear effect. We analyze the influence of the coupling between Fano resonance and SLR on the SHG intensity and achieve a 230-fold enhancement in SHG intensity compared to the single resonance case by adjusting the periodicity of the metasurface. The SHG-enhanced gold metasurface may find applications in sensing, imaging, optical computing, and integrated nonlinear optics.

Topological Exciton Polaritons in Compact Perovskite Junction Metasurfaces

AbstractExciton polaritons are hybrid light‐matter quasi‐particles that hold exceptional opportunities for future optoelectronic devices. Taking the synergic advantages of room‐temperature perovskite excitons and topological photonic structures, topological exciton‐polaritons are experimentally demonstrated in organic–inorganic hybrid perovskite thin films. Topological junction structures based on perovskite gratings are realized using a momentum‐space analog of the 1D Dirac system. Desired enhancement phenomena are observed including narrow‐beam polariton emission from a tightly localized junction region, polaritonic nonlinearity boost, and enhanced luminescence. These remarkable features are obtained from highly compact devices with footprint widths on the order of a few micrometers and are efficiently tailorable with simple unit‐cell geometry control. Therefore, the proposed approach can be a powerful platform for room‐temperature topological exciton‐polaritons and concomitant device applications.

Theoretical and experimental investigation on magnetorheological shear thickening polishing force using multi-pole coupling magnetic field

The magnetorheological shear thickening polishing method, with its dual-stimulus response of shear thickening and magnetization enhancement, has emerged as a promising magnetic field-assisted polishing technology. However, in existing theories and experimental studies on polishing forces, the phenomenon of magnetization enhancement was mainly considered. The shear thickening effect has not yet to be incorporated into. Furthermore, there have been few systematic investigations on the polishing mechanism considering variations of force characteristics. The study aims to fill in these research gaps by developing theoretical models for both normal and tangential forces, and revealing the microscopic polishing mechanism during the magnetorheological shear thickening polishing process. Both normal and tangential polishing force models were established through taking the rheological properties of polishing media under magnetic field and plastic indentation theory into account. Polishing force measurement experiments under a multi-pole coupling magnetic field were conducted to reveal the variations of the polishing forces with different polishing parameters and to validate the established models. Furthermore, the microstructural evolutions of the polishing media components and the surface morphologies after polishing were combined with in-depth analysis to elucidate the polishing mechanism. The polished surface quality was significantly improved without visible scratches. The surface roughness of 48 nm was achieved from the initial value of 245 nm under the normal force of 3.36 N and the tangential force of 2.42 N. The study provides deep insights into the polishing forces characteristics and the polishing mechanism, which contributes to a theoretical guidance for optimizing polishing parameters and improving polishing quality.

Vortex beam induced spatial modulation of quantum-optical effects in a coherent atomic medium

We have studied two-dimensional absorption, gain, and corresponding refractive index profiles in a ladder-type three-level atomic system interacting with three coherent fields. One is a weak probe field considered as a plane wave, while the other two are the control fields taken as two Laguerre–Gaussian doughnut beams. Position dependence of two vortex beams induces the spatially modulated coherence at the condition of resonance, which enables us to obtain space-dependent absorption, transparency, gain without inversion (GWI), and refractive index enhancement in the present scheme. The azimuthal modulation of coherence effects is attributed to the presence of optical angular momentum of the vortex beams. Under the influence of an additional travelling wave field with the presence of two vortex beams, the present model leads us to obtain an ultra-large enhancement of refractive index at the resonant detuning of the fields. This phenomenon makes the atom-field system to play the equivalent role of a high-refractive-index prism. The role of near dipole–dipole (NDD) interaction on the modulation of position-dependent coherence effects has also been investigated. It has been shown that, without any inclusion of the travelling wave field in the system, the phenomenon of resonant enhancement of refractive index may also occur in the presence of NDD effect. The new way of generating spatially controlled GWI and nonlinear refractive index enhancement is specific to the present model. This work seems to be useful for finding its applications in spatially modulated coherence controlled electromagnetically induced transparency-based quantum devices like quantum optical memory, switches, and quantum logic gates, where the refractive index switching phenomenon is a prerequisite.

In biased and soft-walled channels: Insights into transport phenomena and damped modulation.

The motion of a particle along a channel of finite width is known to be affected by either the presence of energy barriers or changes in the bias forces along the channel direction. By using the lateral equilibrium hypothesis, we have successfully derived the effective diffusion coefficient for soft-walled channels, and the diffusion is found to be influenced by the curvature profile of the potential. A typical phenomenon of diffusion enhancement is observed under the appropriate parameter conditions. We first discovered an anomalous phenomenon of quasi-periodic enhancement of oscillations, which cannot be captured by the one-dimensional effective potential, under the combination of sub-Ohmic damping with two-dimensional restricted channels. We innovatively develop the effective potential and the formation mechanism of velocity variance under super-Ohmic and ballistic damping, and meanwhile, ergodicity is of concern. The theoretical framework of a ballistic system can be reinterpreted through the folding acceleration theory. This comprehensive analysis significantly enhances our understanding of diffusion processes in constrained geometries.

Adaptive maleimide-fused macrocyclic clamps: Synthesis, structures, and complexations with polycyclic aromatic hydrocarbons

The photoactive macrocyclic molecules attract attention because of their important roles in supramolecular chemistry as well as photoelectronic applications. Herein, two D-A conjugated macrocycles containing two maleimide nodes have been successfully obtained via an one-pot cascade reaction of Perkin and imidization condensations. Owing to the incorporation of two bulky 1,4-dimethoxybenzene moieties at the narrow maleimide corners, the obtained conjugated macrocycles have been equipped with two adaptive clamps, which can adjust to the guest sizes to capture the guest molecules. Interestingly, the co-crystallization with larger-sized polycyclic aromatic hydrocarbons (PAHs) leads to the 1:1 host-guest complexes, while with smaller-sized solvents results in the 1:2 complexes. Furthermore, the rotatable 1,4-dimethoxybenzene moieties endowed such macrocyclic fluorophores with pronounced solvatochromic and aggregation-induced emission enhancement (AIEE) phenomena.

Effects of Eccentric Speed during Front Squat Conditioning Activity on Post-activation Performance Enhancement of Hip and Thigh Muscles.

The phenomenon of post-activation performance enhancement plays an unidentified role in movement eccentric speed and individual muscle group responses. Therefore, this study aimed to determine whether the loaded front squat (FSq) speed of the eccentric phase would influence the post-activation performance enhancement effect and whether the FSq would elicit similar performance enhancement of knee flexion, knee extension, hip flexion, and hip extension muscles. Twenty resistance-trained handball players performed the FSq under maximum eccentric-concentric speed and 2-s eccentric speed (only the eccentric phase performed), while pre- and post-front squat countermovement jump, knee, and hip isokinetic flexion/extension performance were tested. The FSq conditioning activity was performed in a single set of three repetitions with either 90% (maximum eccentric-concentric speed) or 120% (2-s eccentric speed) of one repetition maximum, and post-performance was measured 4-12 min after the FSq. Athletes randomly changed the FSq eccentric speed and tested the hip or knee isokinetic flexion/extension strength at 180°/s. ANOVA showed that the rate of force development during the jump increased (Cohen d = 0.59-0.77) with no differences between 2-s eccentric and maximum speed eccentric protocols. Isokinetic strength increased after the 2-s eccentric FSq in hip extension (d = 0.76-0.86), knee flexion (d = 0.74-0.88), and hip flexion (d = 0.82), with no differences in knee extension strength. After maximum eccentric-concentric speed, isokinetic strength increased in hip extension (d = 1.25). In conclusion, the FSq conditioning activity enhances hip extensors' performance more than knee extensors' performance. Different eccentric types of muscle action during a conditioning activity alter the level of local muscle enhancement.