Cavity Interface Research Articles

High-Q cavity interface for color centers in thin film diamond

Quantum information technology offers the potential to realize unprecedented computational resources via secure channels distributing entanglement between quantum computers. Diamond, as a host to optically-accessible spin qubits, is a leading platform to realize quantum memory nodes needed to extend such quantum links. Photonic crystal (PhC) cavities enhance light-matter interaction and are essential for an efficient interface between spins and photons that are used to store and communicate quantum information respectively. Here, we demonstrate one- and two-dimensional PhC cavities fabricated in thin-film diamonds, featuring quality factors (Q) of 1.8 × 105 and 1.6 × 105, respectively, the highest Qs for visible PhC cavities realized in any material. Importantly, our fabrication process is simple and high-yield, based on conventional planar fabrication techniques, in contrast to the previous with complex undercut processes. We also demonstrate fiber-coupled 1D PhC cavities with high photon extraction efficiency, and optical coupling between a single SiV center and such a cavity at 4 K achieving a Purcell factor of 18. The demonstrated photonic platform may fundamentally improve the performance and scalability of quantum nodes and expedite the development of related technologies.

Performance assessment of Si based dual metal double gate vertical TFET biosensor

This piece of work highlights the application of dual-metal double-gate VTFET as label free biosensor having enhanced switching ratio, current driving capability and sub-threshold swing and consequently high sensitivity. The use of dual-material namely tunneling gate and auxiliary gate in this device leads to high switching ratio (ION/IOFF) and low sub-threshold swing (SS). In order to observe outcome of this suggested biosensor, various biomolecules dielectric constant have been considered and examined with respect to electric field, energy band diagram, drain current characteristics and sub-threshold potential profile. Neutral biomolecules with a higher dielectric constant exhibits greater drain current sensitivity against biomolecules having lower dielectric constant. Here effect of cavity interface charge on the sensitivity performance of the proposed biosensor device is also verified. This fabrication feasible homo vertical TFET based biosensor gives best sensitivity performance for K = 12, both for the current (5.44 × 105) and transconductance (3.14 × 105) with the minimal sub-threshold swing of 9.9 mV/decade. Silvaco, a commercially accessible TCAD tool is used to investigate the proposed structure.

On the interfacial instabilities of a ventilation cavity induced by gaseous injection into liquid crossflow

This study gives insights into the interfacial instabilities of a ventilation cavity by injecting gas vertically into the horizontal liquid crossflow through both numerical and experimental investigations. We identified four distinct regimes of the ventilation cavity based on their topological characteristics: (I) discrete bubble, (II) continuous cavity, (III) bifurcated cavity, and (IV) bubble plume. The boundaries for these regimes are delineated within the parameter space of crossflow velocity and jet speed. A comprehensive analysis of the flow characteristics associated with each regime is presented, encompassing the phase mixing properties, the dominant frequency of pulsation, and the time-averaged profile of the cavity. This study conducted a detailed investigation of the periodic pulsation at the leading-edge interface of the cavity, also known as the ‘puffing phenomenon’. The results of local spectral analysis and dynamic mode decomposition indicate that the high-frequency instability in the near-field region exhibits the most significant growth rate. In contrast, the low-frequency mode with the largest amplitude spans a broader region from the orifice to the cavity branches. A conceptual model has been proposed to elucidate the mechanism behind the pulsation phenomenon observed along the cavity interface: the pulsation results from the alternate intrusion of the crossflow and the cavity recovery at the leading edge, being governed mainly by the periodic oscillating imbalance between the static pressure of gas near the orifice and the stagnation pressure of crossflow at the leading edge.

On-Chip Topological Photonic Crystal Nanobeam Filters.

We present an on-chip filter with a broad tailorable working wavelength and a single-mode operation. This is realized through the application of topological photonic crystal nanobeam filters employing synthesis parameter dimensions. By introducing the translation of air holes as a new synthetic parameter dimension, we obtained nanobeams with tunable Zak phases. Leveraging the bulk-edge correspondence, we identify the existence of topological cavity modes and establish a correlation between the cavity's interface morphology and working wavelength. Through experiments, we demonstrate filters with adjustable filtering wavelengths ranging from 1301 to 1570 nm. Our work illustrates the use of the synthetic translation dimension in the design of on-chip filters, and it holds potential for applications in other devices such as microcavities.

Mollow triplets under few-photon excitation

Resonant excitation is an essential tool in the development of semiconductor quantum dots (QDs) for quantum information processing. One central challenge is to enable transparent access to the QD signal without post-selection information loss. A viable path is through cavity enhancement, which has successfully lifted the resonantly scattered field strength over the laser background under weak excitation. Here, we extend this success to the saturation regime using a QD-micropillar device with a Purcell factor of 10.9 and ultra-low background cavity reflectivity of just 0.0089±0.0001. We achieve a signal to background ratio of 55 and overall system responsivity of 3.01±0.08%, i.e., we detect on average 0.03 resonantly scattered single photons for every incident laser photon. Raising the excitation to the few-photon level, the QD response is brought into saturation where we observe Mollow triplets as well as the associated cascaded single photon emissions, without resorting to any laser background rejection technique. Our work offers a perspective on a QD cavity interface that is not restricted by the laser background.

Development of a Cavitation Model Tracking the Sheet Cavity Interface and Investigation of its Impact on the Quantitative Accuracy of Hydrofoil Performance

Development of a Cavitation Model Tracking the Sheet Cavity Interface and Investigation of its Impact on the Quantitative Accuracy of Hydrofoil Performance

Growth and microanatomy of the paranasal sinuses in two species of New World monkeys

Paranasal sinuses of living apes and humans grow with positive allometry, suggesting a novel mechanism for bone enlargement. Here, we examine the paranasal sinuses of the owl monkey (Aotus spp.) and a tamarin (Saguinus midas) across postnatal development. The prediction that paranasal sinuses grow disproportionately faster than the main nasal chamber is tested. We used diffusible iodine-based contrast-enhanced computed tomography and histology to study sinuses in eight Aotus and three tamarins ranging from newborn to adult ages. Sinuses were segmented at the mucosa-air cavity interface and measured in volume. All sinuses were lined by a ciliated respiratory epithelium, except for the ethmoid air cells in Aotus, which are lined in part by olfactory epithelium. An age comparison indicates that only the maxillary sinus and ethmoid air cells are present in newborns, and two additional sinuses (invading the orbitosphenoid and the frontal bone), do not appear until late infancy or later. Comparing newborns and adults, the main nasal airway is 10 times larger in the adult Aotus and ~ 6.5 times larger in adult Saguinus. In contrast, the maxillary sinus far exceeds this magnitude of difference: 24 times larger in the adult Aotus and 46 times larger in adult Saguinus. The frontal sinuses add significantly to total paranasal space volume in both species, but this growth is likely delayed until juvenile age. Results suggest ethmoid air cells expand the least. These results support our prediction that most paranasal sinuses have a distinctly higher growth rate compared to the main nasal chamber.

On ventilated supercavities moving horizontally near free surface

By means of open source CFD tool OpenFOAM platform, a multiphase solver capable to deal with two phases flows is used to investigate ventilated supercavities. The VOF (volume of fraction) method is employed in order to capture cavity interface and the free surface. The main objective of this work is to investigate ventilated supercavity generated after a disk-cavitator which moves horizontally near a free surface. Most of the work in this research has been focused on the shape of supercavity and its asymmetry. Furthermore, two distinct cavity closure types, i.e. the re-entrant jet (RJ) and the twin vortex (TV) and are discussed separately to compare their gas leakage mechanisms at different submergence ratio. Numerical results indicate that the air-water free surface will have a significant influence on the cavity surface curvature and gas shedding process. Under the influence of free surface, the length diameter ratio of ventilated cavitation increases with H‾ decrease with decrease. The influence of free boundary on the upper surface of cavitation interface is greater than that on the lower surface. When Fr number and ventilation volume are constant, when approaching the free surface, the interface curvature of ventilation cavitation will increase. The deflection of cavitation axis is mainly affected by gravity and free surface. When the Fr number is small, the cavitation axis will be slightly disturbed. When the Fr number is large, the cavitation axis deflects reversely. These may give meaningful references for the design of surface vehicles.

Broadband Spectrum Light-Driven PANI/Au/Beta-Cyclodextrin Nanocomposite and Its Light-Triggered Interfacial Carrier Transfer

Polyaniline/Au nanocomposites were synthesized by a novel method. Aniline monomers were loaded in the hydrophobic cavities of beta-cyclodextrin, and a polymerization reaction occurred at the interface of the beta-cyclodextrin cavities and the liquid phase of chloroauric acid. UV-vis absorbance indicated that the nanocomposite covered the range of visible light and NIR (near infrared). The photo-excitation experiment was carried out with typical wavelengths in the visible light (405 nm, 532 nm, and 650 nm) and NIR (780 nm, 808 nm, 980 nm, and 1064 nm) regions (10–200 mW) based on Au inter-digital electrodes on flexible polymer substrates casting a thick film. The nanocomposites exhibited photo-current switching behavior in visible light and NIR. The ratio of on/off was enormously dependent on the power and wavelength of incident light. The robust interface coupling between Au and PANi of the nanocomposite promoted the separation and transfer of electron/hole. The mechanism of carrier generation, separation, and transfer at interfaces of Au/conjugated polymer/non-conjugated small organic molecules by light inducement was discussed at the electron level. The results illustrate that the nanocomposites quickly produced free electrons and holes by low-power incident light, could prevent the recombination of electron/hole pairs to a certain extent, and could overcome the interface barriers between metal, conjugated polymer, and small organic molecules for transfer. This provides a simple and practical approach for developing multi-functional nanocomposites that have the potential act as intelligent nano-carriers, photo-current switches, NIR detectors, and for information storage.

Vortex and cavity dynamics for the tip-leakage cavitation over a hydrofoil

Large eddy simulations were used to investigate unsteady tip-leakage cavitating flow over a National Advisory Committee for Aeronautics 0009 hydrofoil. The proper orthogonal decomposition (POD) was combined with fast Fourier transforms to help better understand the deformation dynamics of the vortex and cavity. The results show three typical vortices, i.e., the tip-leakage vortex (TLV), tip-separation vortex (TSV), and shedding–trailing vortex (STV) with their own helical core lines in the averaged cavitating flows. Upstream of x/C = 1.8, the mean TLV core carries the breathing mode waves through the vortex dilatation effect, while the TSV core generates the dilatation, shrinkage, and bending distortions near the cavity interface by vortex stretching and deflection effects. Further downstream, the TLV starts to intertwine with the TSV, and the STV gradually diffuses. The TLV wandering encourages large cavity deformations dominated by the breathing and bending modes. However, in the lower-order POD modes, the contribution of bending modes to the cavity fluctuation energy is greatly weakened due to the variation of the relative cavity radius, r*, which indicates that the breathing mode and the double helix mode play major roles in the cavity interfacial waves. The results also show that the cavity interfacial oscillations are highly correlated with the surrounding velocity fluctuations. Moreover, a modified theoretical dispersion equation can well reproduce the quantitative relation between the vibration frequencies and the axial wavenumbers of the TLV cavity, especially for the wave dynamics of the breathing modes and the double helix modes.

Development Of A Turbulent Boundary Layer Over An Air Cavity

The turbulent boundary layer development over an air cavity is studied experimentally using planar Particle Image Velocimetry. An identification technique based on the gradient of correlation values was employed to detect the cavity interface which revealed a well-defined, asymmetric bump-like geometry at the spanwise-uniform region of the cavity. No separation was observed at the leeward side of the cavity, owing largely to the high boundary layer thickness to maximum cavity thickness ratio (δ/tmax ≈ 11.8). The shape of the cavity was found to dictate the turbulent boundary development by subjecting it to alternating streamwise pressure gradients: from an adverse to a favourable and back to an adverse, moving downstream along the cavity. Profiles o f mean s treamwise velocity and turbulent stresses show the alternate pressure gradients and air injection to be the dominant perturbations to the flow, with streamline curvature only having a minor influence, also based on previous observations.

Santalol Isomers Inhibit Transthyretin Amyloidogenesis and Associated Pathologies in Caenorhabditis elegans.

Transthyretin (TTR) is a homotetrameric protein found in human serum and is implicated in fatal inherited amyloidoses. Destabilization of native TTR confirmation resulting from mutation, environmental changes, and aging causes polymerization and amyloid fibril formation. Although several small molecules have been reported to stabilize the native state and inhibit TTR aggregation, prolonged use can cause serious side effects. Therefore, pharmacologically enhancing the degradation of TTR aggregates and kinetically stabilizing the native tetrameric structure with bioactive molecule(s) could be a viable therapeutic strategy to hinder the advancement of TTR amyloidoses. In this context, here we demonstrated α- and β-santalol, natural sesquiterpenes from sandalwood, as a potent TTR aggregation inhibitor and native state stabilizer using combined in vitro, in silico, and in vivo experiments. We found that α- and β-santalol synergize to reduce wild-type (WT) and Val30Met (V30M) mutant TTR aggregates in novel C. elegans strains expressing TTR fragments fused with a green fluorescent protein in body wall muscle cells. α- and β-Santalol extend the lifespan and healthspan of C. elegans strains carrying TTRWT::EGFP and TTRV30M::EGFP transgene by activating the SKN-1/Nrf2, autophagy, and proteasome. Moreover, α- and β-santalol directly interacted with TTR and reduced the flexibility of the thyroxine-binding cavity and homotetramer interface, which in turn increases stability and prevents the dissociation of the TTR tetramer. These data indicate that α- and β-santalol are the strong natural therapeutic intervention against TTR-associated amyloid diseases.

Numerical investigation of pulsating energy evolution in ventilated cavitation around the NACA0015 hydrofoil

The pulsation characteristics of the ventilated cavitation are investigated in this paper with the Large Eddy Simulation method. As the ventilation rate increases, the air entrainment effect aggravates the instability of vapor cavity, and the re-entrant jet further accelerates the separation of attached vapor cavity from the suction surface. The suppression of cloud vapor cavity and the formation of stable ventilated supercavity can significantly reduce the time-averaged pulsation level of pressure and velocity. The pulsating energy of cavitating flows essentially comes from the time-averaged flow in natural cavitation and ventilated cavitation. The gradient diffusion effect tends to transfer the turbulent kinetic energy carried by cavities to the mainstream region, while the redistribution of pulsating enstrophy through the gas-liquid interface can be significantly suppressed by the injected air. The viscous dissipation term cannot be ignored because it does perform some fluctuating strip-like structures near the interface of large-scale vortex in ventilated cavitation. Two fluctuation stages and mechanisms of the ventilated cavity interface on a hydrofoil are revealed, moreover, the transportation of pulsating enstrophy on the surface of ventilated cavity located above the suction surface is clarified as an important mechanism to maintain the interface fluctuating state.

The factorization method for inverse scattering by a two-layered cavity with conductive boundary condition

Abstract In this paper we consider the inverse scattering problem of determining the shape of a two-layered cavity with conductive boundary condition from sources and measurements placed on a curve inside the cavity. First, we show the well-posedness of the direct scattering problem by using the boundary integral equation method. Then, we prove that the factorization method can be applied to reconstruct the interface of the two-layered cavity from near-field data. Some numerical experiments are also presented to demonstrate the feasibility and effectiveness of the factorization method.

A high-order nodal discontinuous Galerkin method for simulation of three-dimensional non-cavitating/cavitating flows

In this study, the nodal discontinuous Galerkin method is formulated in three-dimensions and applied to simulate three-dimensional non-cavitating/cavitating flows. For this aim, the three-dimensional preconditioned Navier-Stokes equations based on the artificial compressibility approach considering appropriate source terms to model cavitating phenomena are used. The spatial derivative terms in the resulting equations are discretized by utilizing the nodal discontinuous Galerkin method on tetrahedral elements and the derivative of the solution vector with respect to the artificial time is discretized by applying an explicit time integration method. An artificial viscosity method is formulated in three-dimensions and applied to properly capture the discontinuities in the cavitating flow-field. Here, different non-cavitating/cavitating flow problems including non-cavitating flow in a 3:1:1 driven cavity, non-cavitating flow between two concentric rotating spheres, cavitating flow over a sphere and cavitating flow over a wavy cylinder are solved to examine the accuracy and robustness of the proposed solution method. These flow problems are selected to properly assess the numerical method in the presence of straight and curved boundaries and for different Reynolds and cavitation numbers. From linear to cubic polynomial degrees are used in the simulations and the numerical results are compared with the available analytical and numerical results. Indications are that the present numerical method based on the NDGM formulated in three-dimensions can accurately simulate the three-dimensional non-cavitating/cavitating flows. • Formulating a nodal discontinuous Galerkin method (NDGM) in 3D to simulate noncavitating/cavitating flows. • Implementing an artificial viscosity approach in 3D for capturing the steep discontinuities in the cavity interface. • Examining the accuracy and robustness of the solution method by computing different 3D noncavitating/cavitating flow problems. • Considering the 3D NDGM proposed to assess other solution methods for computing noncavitating/cavitating flows.

Experimental and Numerical Research on the Formation Conditions and Entrainment Characteristics of Supercavity by Rear Jet Reflux

Aiming at better controlling the ventilated supercavity flow for drag reduction, the experimental and numerical researches of supercavity by rear gas reflux are proposed in this paper. Several experiments with different test bodies have been carried out to study the formation and collapse conditions of jet-reflux supercavity. An open-circulation water tunnel for ultra-high-speed jet experiment and air jet system is employed to form jet-reflux supercavity around the bodies installed in the forward strut. The experiment results show that the supercavity can be maintained by the reflux of tail jet flow when an initial supercavity covering the jet outlet is formed. However, the supercavity will be destroyed when the jet intensity is further enhanced. Under the same jet coefficient, the scale of jet-reflux supercavity extends as the increase of the body length, while the critical jet coefficient for the collapse of the supercavity decreases as the increase of the body length. The multiphase flow model coupling the VOF model and the level-set method is applied to capture the air-water interface. Then, the flow field characteristics of the jet-reflux supercavity are analyzed and compared with the ventilated supercavity. The streamline inside the cavity presents considerable three-dimensional asymmetry inflating flow characteristics. The variation of the gas reflux coefficient along the axial direction is obtained, which indicates that a handful of reflux gas are required to sustain the head cavity. Therefore, the jet-reflux supercavity can be formed within a certain range of the tail jet intensity. Although jet intensities are not equal to each other, the scale of cavity head is roughly maintained under the same reflux coefficient. When the supercavity gets closed to the nozzle outlet, the maximum scale of cavity is decreased, which leads to a weaker reflux at the outlet. The cavity interface will be impinged by the high-speed gas and mixture liquid, which obviously causes deformation and final collapse. In order to improve the stability of the jet-reflux supercavity, it is necessary to use the gas re-directed structure to control the reflux.

The interior inverse scattering problem for a two-layered cavity using the Bayesian method

<p style='text-indent:20px;'>In this paper, the Bayesian method is proposed for the interior inverse scattering problem to reconstruct the interface of a two-layered cavity. The scattered field is measured by the point sources located on a closed curve inside the interior interface. The well-posedness of the posterior distribution in the Bayesian framework is proved. The Markov Chain Monte Carlo algorithm is employed to explore the posterior density. Some numerical experiments are presented to demonstrate the effectiveness of the proposed method.</p>

The Use of GPR and Microwave Tomography for the Assessment of the Internal Structure of Hollow Trees

Internal decays in trees can rapidly escalate into a full decomposition of the inner structural layer, i.e., the “heartwood” layer, due to the action of aggressive diseases and fungal infections. This process leads to the formation of big cavities and hollows, which remain surrounded by the sapwood layer only. Estimating the thickness of the sapwood layer with a high degree of accuracy is therefore crucial for correct assessment of the structural integrity of hollow trees, as well as an extremely challenging task. In this context, ground-penetrating radar (GPR) has proven effective in providing details of the internal structure of trees. Nevertheless, the existing GPR processing methods still offer limited information on their internal configuration. This study investigates the effectiveness of GPR enhanced by a microwave tomography inversion approach in the assessment of hollow trees. To this aim, a living hollow tree was investigated by performing a set of pseudocircular scans along the bark perimeter with a hand-held common-offset GPR system. The tree was then felled, and sections were cut for testing purposes. A dedicated data processing framework was developed and tested through numerical simulations of hollow tree sections. The internal structure of the real trunk was therefore reconstructed via a tomographic imaging approach and the outcomes were quantitatively analyzed by way of comparison with the real sections’ main geometric features. The tomographic approach has proven very accurate in locating the sapwood–cavity interface and in the evaluation of the sapwood layer thickness, with a centimeter prediction accuracy.

Light-Harvesting in Biophotonic Optofluidic Microcavities via Whispering-Gallery Modes.

Phycobiliproteins are a class of light-harvesting fluorescent proteins existing in cyanobacteria and microalgae, which harvest light and convert it into electricity. Owing to recent demands on environmental-friendly and renewable apparatuses, phycobiliproteins have attracted substantial interest in bioenergy and sustainable devices. However, converting energy from biological materials remains challenging to date. Herein, we report a novel scheme to enhance biological light-harvesting through light-matter interactions at the biointerface of whispering-gallery modes (WGMs), where phycobiliproteins were employed as the active gain material. By exploiting microdroplets as a carrier for light-harvesting biomaterials, strong local electric field enhancement and photon confinement at the cavity interface resulted in significantly enhanced bio-photoelectricity. A threshold-like behavior was discovered in photocurrent enhancement and the WGM modulated fluorescence. Systematic studies of biologically produced photoelectricity and optical mode resonance were carried out to illustrate the impact of the cavity quality factor, structural geometry, and refractive indices. Finally, a biomimetic system was investigated by exploiting cascade energy transfer in phycobiliprotein assembly composed of three light-harvesting proteins. The key findings not only highlight the critical role of optical cavity in light-harvesting but also offer deep insights into light energy coupling in biomaterials.

Experimental study on unsteady characteristics of the transient cavitation flow

The characteristics of unsteady cavitation flow under different cavitation numbers are investigated experimentally. An optical test rig is designed to visualize the cavitation flow and the cavity length is defined based on high-speed camera technology. The development of cavitation flow can be divided into inception and fusion region, expansion region and collapse region. Due to the interaction between the re-entrant jet and the cavity interface, the cavitation bubbles near the solid wall collapse earlier than them in the downstream. The cavitation number is also the important factor determining the cavity length pulsation. Further analysis shows that the smaller the cavitation number, the smaller the frequency of cavity length fluctuations and the larger the mean cavity length. The cavitation intensity is stronger at lower cavitation number. Meanwhile, the cycle collapsing frequency of cavitation is around 220–320 Hz. With the decrease of cavitation number, the amplitude of cavitation pulsation increases while the corresponding collapsing frequency decreases.