Concave Cavity Research Articles

Improved optical coupling based on a concave cavity lens fabricated by optical fiber facet etching

We report a low-fabrication-complexity and wideband fiber lens, which is formed by fiber facet etching and filling high refractive index UV adhesive. The optical field can be significantly shrunk by the facet lens so as to obtain improved optical coupling. Numerical simulations were carried out for different coupling conditions, on both fundamental mode and high-order mode, for a nine-mode fiber. The fundamental mode area can be reduced from 152.17 to 12.57 µm 2, and the coupling loss between the fiber lens and a photonic waveguide can be reduced to −2.9 dB with over 1000 nm 3 dB bandwidth.

Reconstructive options following orbital exenteration.

The purpose of this review is to examine current trends in reconstruction following orbital exenteration. Defects ranging from isolated exenteration to more complex midface resections are explored. Goals of reconstruction include separating the sino-orbital cavities and creating a safe, stable wound that can withstand adjuvant radiation. When planning for orbital rehabilitation, it is important to create a concave cavity that can accommodate a prosthesis. This is primarily achieved through secondary granulation or split-thickness skin grafts. Recently, the use of dermal allografts has been investigated and shown good success with epithelization of the orbital cavity. For complex orbitomaxillectomy defects, musculocutaneous free tissue flaps remain the mainstay for reconstruction. Reconstructive options following orbital exenteration are based on extent of the defect, need for postoperative radiation, and plans for orbital rehabilitation with prosthesis.

Progressive Folding and Adaptive Multivalent Recognition of Alkyl Amines and Amino Acids in p‐Sulfonatocalix[4]arene Hosts: Solid‐State and Solution Studies

The Front Cover shows the molecular recognition of folded 1,ω-amino-acid guests within p-sulfonatocalix[4]arene host anions stabilized with alternating hydrated cations and water molecules. The picture displays the burial of an alkyl chain of the amino acid of the guest within confined space offered by the concave cavity p-sulfonatocalix[4]arene host. Thus, under confinement folding is induced with three or two gauche conformations of the alkyl chain, so that hydrogen bonding is intramolecularly established between the ammonium and carboxyl groups of the folding guest. More information can be found in the Full Paper by M. Barboiu and co-workers (DOI: 10.1002/cplu.202000232).

Molecular dynamics simulation of heterogeneous nucleation from concave cavity at surface of grain refiner

Grain refiners are often used in practical production processes of metallic materials to promote and control nucleation. Although morphology of the grain refiner strongly affects nucleation behaviour, it is not well understood how unevenness of surface of the grain refiner affects nucleation from atomistic viewpoint. In this study, effect of concave cavity at surface of the grain refiner on heterogeneous nucleation is investigated by molecular dynamics (MD) simulation. HCP-Ti cube with a concave cavity is employed in the MD simulation as a grain refiner of the solidification of undercooled Al melt as a model study. HCP-Al solid is firstly formed at the tip or on the side wall of cavity and FCC-Al growth is followed on the exposed (0001) surface of HCP-Al for most of the cavities, whereas FCC-Al solid is directly formed on HCP(0001) terraces at the side wall of the cavity with large-obtuse apex angle.

Convex vs concave surface nano-curvature of Ta2O5 thin films for tailoring the osteoblast adhesion

In certain medical interventions, temporally introduced bone implants are required to exhibit high biocompatibility, yet combined with low osseointegration, to allow for their easy removal afterwards. In this work, Ta2O5 surfaces are developed with good biocompatibility and with the osteoblast adhesion regulated by the nano-topography. The surfaces with convex nano-curvature are produced by applying reactive magnetron sputtering of tantalum over sub-monolayers of hydrocarbon plasma polymer particles. Subsequent ultrasonication leads to the removal of the particles from the coatings and results in the formation of the surfaces with concave nano-curvature. Primary human osteoblasts are found to sustain the viability and the mineralization ability on all kinds of these surfaces; however, Ta2O5 with the concave topography shows restrained adhesion of the cells. The limited cell adhesion is associated with a closed nature of the concave cavities which poses additional potential barriers for protein-mediated cell-surface interactions.

Shock wave interactions within concave cavities

The interaction of a plane shock wave in air with concave profiles has been used in the past mainly to understand the nature of shock wave focusing. The current study examines the complex two-dimensional flow field resulting from the interaction of a plane shock wave entering a symmetrical cavity with curved walls. Of particular interest are the development of reflection patterns of the incident shock wave at the profile wall and the process of gas dynamic focus. These principal flow features are examined across a wide range of different reflector shapes. This includes a review of previously studied profiles such as cylindrical and parabolic, and also of a number of additional profiles, including compound profiles, where an inlet profile merging with that of the main cavity is shown to have major effects on the focusing mechanism and pressures. The various reflector shapes were specified by varying the shape of the profile and the depth-to-aperture ratio. The strength of the incident plane shock wave was limited between Mach numbers of 1.04 and 1.45. The principal flow features were established and examined experimentally using a variety of qualitative and quantitative flow visualization techniques, supplemented with numerical results. Time-resolved high-speed imaging was used to capture the interaction providing the unique ability to track the various transient flow features over the course of the interaction. The three primary factors that influence the maximum pressure amplification at focus, and the focus mechanism, are the incident shock strength, the depth-to-aperture ratio of the profile and an inlet profile leading into the main cavity, if present. An inlet profile results in higher-pressure amplifications for corresponding shock strengths and depth-to-aperture ratios. Increases in the depth-to-aperture ratio increase the maximum pressure amplification observed at focus. This occurs due to a combination of factors including: the strengthening of the individual shock waves involved in focus; the duration of focus; and the strengthening of a compressive flow field that develops adjacent to the shock system during focus. The compressive flow field adjacent to the shock system at focus is shown to be of great importance to the focus process.

Electron Microscopy-Based Comparison and Investigation of the Morphology of Exosomes Derived from Hepatocellular Carcinoma Cells Isolated at Different Centrifugal Speeds.

Exosomes derived from hepatocellular carcinoma (HCC) cells are nanovesicles and are involved in the occurrence and development of HCC, they also serve as important carriers and drug targets of nanodrug delivery systems. The external shape and internal structure of exosomes are important indexes of identification, and isolated intact morphology is crucial to biological function integrity. However, given their susceptibility to various influencing factors, the external shape and internal structure of exosomes derived from HCC cells remain incompletely studied. In this study, exosomes purified from HCC cells were isolated at different centrifugation speeds and examined via multiple electron microscopy (EM) techniques. The results demonstrate that exosomes possess a nearly spherical shape and bilipid membranous vesicle with a concave cavity structure containing electron-dense and coated vesicles, suggesting the possible existence of subpopulations of exosomes with specific functions. The exosomes isolated at ultracentrifugation (UC) speed (≥110,000×g) presented irregular and diverse external morphologies, indicating the effect on the integrity of the exosomes. Transforming growth factor signaling bioactive substances (TGF-β1, S100A8, and S100A9) can be found in exosomes by performing Western blotting, showing that the internal content is associated with metastasis of HCC. These findings show that EMelectron microscopy and UC speed can affect exosome characteristics, including external shape, internal structure, and content of bioactive substances. The electron-dense and coated vesicles that had been discovered in exosomes might become new additional morphological features, which could help to improve the interpretation of experimental results and widen our understanding of exosome morphology.

Investigation of the anode shaping process in counter-rotating electrochemical machining of a convex array

This paper presents the formation processes of convex arrays on revolving parts by using synchronous and differential counter-rotating electrochemical machining (CRECM) methods, in which cylindrical cathode tools with concave cavities rotate relatively to the anode workpiece at same and multifold rotational speeds. The anode shaping processes are numerically simulated on basis of a mathematical model. The profiles of the convex structures at rotating ratios of 1:1 and 5:1 are compared, and the shape evolution process at different feed depths of cathode tool is analyzed. The simulation results indicate that differential CRECM can achieve an approximate machining performance of a convex array with synchronous CRECM by using suitable diameter of the cathode tool. The profile of the convex structure changes from a tapered shape to an inverted cone shape with the increase of the feed depth of cathode tool. Experiments are conducted to verify the numerical analysis. An equal-size cathode tool with five concave cavities at the same rotation speed and a small cathode tool with a single concave cavity at a rotating ratio of 5:1 are used, respectively. It is seen that five array distributed convex structures are machined successfully on the anode surface by using both synchronous and differential CRECM methods. Furthermore, convex structures with tapered, straight and inverted conical sidewalls can be obtained by changing the depths of cathode tool in differential CRECM.

Does Nasal Septal Deviation and Concha Bullosa Have Effect on Maxillary Sinus Volume and Maxillary Sinusitis?: A Retrospective Study.

PurposeThis study aimed to determine whether nasal septal deviation and concha bullosa affect the maxillary sinus volume, and whether this effect is associated with the prevalence of chronic sinusitis.Materials and MethodsThis study retrospectively reviewed 209 paranasal sinus CT (PNS CT) images of patients with sinonasal symptoms from January 2017 to December 2018. The maxillary sinus volume was measured twice by a radiologist, and statistical analysis was performed using SAS 9.4.ResultsIntersex comparison of the maxillary sinus volume (on left and right sides) revealed that the volume was significantly larger on both the sides (p < 0.0001) in men compared with that in women. Concha bullosa was found to occur mainly in the concave cavity of the septal deviation (p < 0.0001). No significant association was found between nasal septal deviation and maxillary sinusitis (p = 0.8756) as well as between concha bullosa and maxillary sinusitis prevalence (p = 0.3401) or maxillary sinus volume (both: p = 0.6289, Rt.: p = 0.9522, Lt.: p = 0.9201).ConclusionAlthough nasal septal deviation and the location of concha bullosa may affect each other, maxillary sinus volume and maxillary sinusitis were neither associated with nasal septal deviation nor concha bullosa.

Optimizing combustion performance in a solid rocket scramjet engine

To enhance combustion efficiency of a boron-based propellant solid rocket scramjet (SRS) engine, this study attempted a new organization scheme combining cavity and pneumatic slope. To optimize the proposed system, a series of numerical simulations were performed, and through orthogonal design and single factor analysis, the key factors were determined. The developed two-phase flow simulation has been verified by the full-scale ground test, given an error within 10%. The results show that for both combustion efficiency and total pressure recovery, the influence of gas injection mode is much greater than the ratio of the length to depth of the concave cavity as well as the cavity depth. And the combustion performance has proved to be optimized via the enlarged low speed area near the cavity and the strengthened particles reflux.

End-pump high efficiency 355 nm laser with a convex–concave cavity and optically-uncoated Brewster angle-cut LiB3O5 crystal

We demonstrate a 3.65 W, 40 kHz, 17.5 ns end-pumped YVO4/Nd:YVO4 ultraviolet (UV) laser at 355 nm with a beam propagation factor of 1.32 and 1.14. The frequency doubling and tripling are obtained by employing a parallel surfaces LBO crystal and a Brewster angle-cut uncoated LBO crystal in a convex–concave cavity. The arrangement allows the use of optically-uncoated third harmonic generation LBO crystal surfaces while providing wavelength separation. It is proved that the optically-uncoated THG-LBO crystal has a higher damage threshold. Pump-UV conversion efficiency of 15.5% is obtained and it is higher compared with other intra-cavity-wavelength-separation UV nanosecond lasers. By designing a convex–concave cavity structure, four advantages are showed, (1) to compensate for astigmatism caused by the Brewster angle-cut uncoated LBO crystal; (2) to offset the thermal lens effect of the gain medium; (3) to obtain a fundamental light spot size which matches with pump light spot size in the center of gain medium; (4) to obtain a small spot size in the center of the frequency conversion crystals. By employing these designs, UV beam quality Mx2 = 1.32 and My2 = 1.14 at 3.65 W are obtained.

Numerical Research on the Toroidal Shock Wave Focusing Detonation Initiation

Abstract Pressure gain combustion (PGC) is considered to be a potential technology to increase the cycle efficiency of gas turbine. As one viable candidate for PGC, rotating detonation engine (RDE) draws more attention due to its significant advances in continuous mode of operation. In practical, one of the basic challenges for RDE application is to reliably initiate detonation wave. For this purpose, both detonation initiation mechanism and enhancement approach are urgently needed to be understood. In this work, a toroidal shock wave focusing detonation initiator is presented. On this basis, the two-dimensional numerical simulations are carried out to investigate the detonation initiation characteristics by using the toroidal shock wave focusing. All of the flame acceleration, shock wave focusing, detonation wave forming, and propagation are analyzed in detail. The numerical results show that the toroidal shock wave focusing initiator developed in this study can rapidly realize the detonation initiation over a short distance and performs significantly better than the traditional smooth or obstructed tube based imitators under different operating conditions. Under the same operating condition, the novel developed initiator decreases time of 59.2% and distance of 84.7% for the smooth tube based initiator, and time of 52% and distance of 78.9% for the obstructed one. Besides, the multifield analysis indicates that both the local explosion induced by shock wave focusing in concave cavity and the entrainment vortex generated by shock wave and jet flame in front of diaphragm are important mechanisms to initiate detonation wave. This study is expected to enhance the understanding of the physical mechanism of shock wave focusing detonation initiation and contribute to the development of detonation propulsion technology.

Resorcinol-formaldehyde nanobowls modified thin film nanocomposite membrane with enhanced nanofiltration performance

The performance of thin film nanocomposite (TFN) membranes is substantively determined by the structure, composition and size of the incorporated nanofillers. In this work, an asymmetric organic nanofiller, resorcinol-formaldehyde nanobowls (RFB), was firstly designed via a modified Stöber approach and introduced into the polyamide selective layer of the TFN membrane via an interfacial polymerization process. Thanks to the asymmetric structure, concave cavity and chemical groups of the incorporated RFB, enhanced nanofiltration performance of the prepared TFN membrane was achieved. The optimized TFN membranes exhibited higher water fluxes and well maintained salt rejections. The water fluxes of the TFN-B0.12 membrane were 119.74 ± 4.28 for the Na2SO4 solution and 141.46 ± 5.92 L/(m2·h) for the MgCl2 solution, which are 1.5 times higher than that of the control thin film composite (TFC) membrane, with comparable rejection (95.76 ± 0.29%) for Na2SO4 and 4.63% higher (25.98 ± 0.45%) rejection for MgCl2, respectively. Meanwhile, the basic resistance of the RFB modified TFN membrane was reinforced simultaneously as compared with that of the control TFC membrane. The results demonstrate the incorporation of the RFB significantly strengthened the nanofiltration performance of the TFN membrane.

The valuation of concave-side thoracoplasty on the treatment of extremely severe scoliosis with severe pulmonary dysfunction on the base of halo-pelvic traction.

Extremely severe scoliosis patients, especially main thoracic Cobb’ s angle >150°, often have severe thoracic deformity and pulmonary dysfunction, even the scoliosis is reduced by halo-pelvic traction, the improvement of pulmonary function is not satisfactory, the risk of spinal osteotomy in the next stage is still very high and left with obvious thoracic deformity. How to further improve the pulmonary function and appearance of these patients is a difficult problem to be solved.Twenty extremely severe scoliosis patients with severe pulmonary dysfunction who underwent concave-side thoracoplasty in our hospital from September 2014 to September 2017 were included, data of thoracic volume and pulmonary function were collected before and after operation. The pulmonary function value reported was predicted forced vital capacity (FVC%), T-test was used to analyze the changes of the data by the statistical software SPSS21.0.The 20 patient's averaged Cobb's angle of main thoracic was 163° ± 8° at admission and all of them with severe pulmonary dysfunction before concave-side thracoplasty. After operation, the thoracic volume of patients increased by 500.9 ± 222.9 mL, FVC% increased by 8.9% ± 7.5%. Both the difference has statistical significance (P < .01).Concave-side thoracoplasty based on the halo-pelvic traction cannot only enlarge the volume of the concave thoracic cavity, lighten the compression of lung and further improve the pulmonary function of extremely severe scoliosis, but also can strengthen the correction of scoliosis and spinal rotation. Therefore, it is a safe and effective surgical approach.

Research on counter-rotating electrochemical machining of convex structures with different heights

Counter-rotating electrochemical machining (CRECM) is an alternative method for the manufacture of aero-engine casing parts with complex convex structures. In previous studies, the revolving part with hollow windows was used as the cathode tool. However, only convex structures with the same height could be machined. In practice, there are usually differences in height between different convex structures on the surface of most casing parts. To machine convex structures of different heights by using CRECM, a specific cathode with concave cavities has been designed. The bottom surfaces of concave cavities are conductive, and the depths of concave cavities are changed according to the height of convex structures. The material of the workpiece in this study is Inconel 718. Forming processes of convex structures with the cathode are simulated by using the finite element method. Results show that during the processing, the top surface of the convex structure is gradually changed from stray corrosion at low current density to normal dissolution at high current density. The height of the convex structure increases and then approximately keeps constant with increasing amount of feed, and it also can be controlled by changing the depth of the concave cavity. Finally, convex structures of different heights on the cylindrical workpiece are machined experimentally, verifying the feasibility of the method.

Synthesis and structures of N-(4-picolyl)azacalix[4]arene and its bridged derivatives

Azacalixarenes have side arms (N-substituents) on the nitrogen atoms in their macrocyclic ring systems; thus, a variety of molecular designs are possible by modifying these side arms. This is a special feature of azacalixarene system which is not available in calix[n]arenes. In this paper, we used azacalix[3.1.3.1] and [3.1.1.1]arenes because these compounds have concave cavities. The cavity size of the azacalix[3.1.1.1] structure is small like the calix[4]arenes, but, supramolecular systems can be designed in which two or three azacalix units are connected by covalent or coordination bonds. Previously reported compounds, N-(4-picolyl)-[3.1.3.1] or [3.1.1.1]arenes, can be applied for this purpose. The 4-picolyl group can form covalent bonds with alkylation and form coordination bonds with a variety of transition metal ions. By using these bonds, we extend the cavity size of the azacalixarenes and construct newly designed supramolecular structures. We expected that these molecules would form larger molecular cavities upon side arm modification, and inclusion abilities of these cavities can be extended compared to the azacalixarenes of small cavity sizes. However, most of these molecular structures could not be determined, and none showed inclusion phenomena contrary to our expectations. Only the molecular structure of a p-xylylene-bridged molecule was confirmed, which possessed a self-inclusion structure in which the bridging unit (p-xylylene) was encapsulated by two azacalixarene cavities. Additionally, it was found that p-methyl-N-(4-picolyl)azacalix[3.1.1.1]arene 1 formed two molecular packing modes depending on the recrystallizing solvents. One is stacked structure by π–π interactions, and another is capsule type structure in which two solvent molecules were encapsulated. A self-inclusion type cage molecule was obtained by connecting N-(4-picolyl)azacalix[3.1.1.1]arene with a p-xylylene unit.

Wheat wounding-responsive HD-Zip IV transcription factor GL7 is predominantly expressed in grain and activates genes encoding defensins.

Several classes of transcription factors are involved in the activation of defensins. A new type of the transcription factor responsible for the regulation of wheat grain specific defensins was characterised in this work. HD-Zip class IV transcription factors constitute a family of multidomain proteins. A full-length cDNA of HD-Zip IV, designated TaGL7 was isolated from the developing grain of bread wheat, using a specific DNA sequence as bait in the Y1H screen. 3D models of TaGL7 HD complexed with DNA cis-elements rationalised differences that underlined accommodations of binding and non-binding DNA, while the START-like domain model predicted binding of lipidic molecules inside a concave hydrophobic cavity. The 3'-untranslated region of TaGL7 was used as a probe to isolate the genomic clone of TdGL7 from a BAC library prepared from durum wheat. The spatial and temporal activity of the TdGL7 promoter was tested in transgenic wheat, barley and rice. TdGL7 was expressed mostly in ovary at fertilisation and its promoter was active in a liquid endosperm during cellularisation and later in the endosperm transfer cells, aleurone, and starchy endosperm. The pattern of TdGL7 expression resembled that of genes that encode grain-specific lipid transfer proteins, particularly defensins. In addition, GL7 expression was upregulated by mechanical wounding, similarly to defensin genes. Co-bombardment of cultured wheat cells with TdGL7 driven by constitutive promoter and seven grain or root specific defensin promoters fused to GUS gene, revealed activation of four promoters. The data confirmed the previously proposed role of HD-Zip IV transcription factors in the regulation of genes that encode lipid transfer proteins involved in lipid transport and defence. The TdGL7 promoter could be used to engineer cereal grains with enhanced resistance to insects and fungal infections.

Control effect of micro vortex generators on attached cavitation instability

The control effect of micro-vortex generators (VGs) on the instability of attached cavitation was investigated in a series of experiments. The micro-VGs, located at the leading edge of a NACA0015 hydrofoil, were used to alter the near-wall flow and control the attached cavitation dynamics. The effect of the nondimensional height of micro-VGs on the nondimensional cavity length was quantitatively evaluated by regression equations through response surface methodology. The micro-VGs increased the nondimensional cavity length. The counter-rotating streamwise vortices induced by micro-VGs had a rectifying effect on the near-wall flow and withstood the flow disturbance in the spanwise direction. Additionally, the micro-VGs partially suppressed Rayleigh–Taylor instability and Kelvin–Helmholtz instability arising from reverse flow underneath the cavity. Under a partial cavity oscillation (PCO) condition, the growth of sheet cavitation was highly two-dimensional in the spanwise direction, and the cloud cavity shedding had a strict periodicity with a smaller Strouhal number (St) than for the smooth hydrofoil. The shedding cloud cavity was captured in a single spanwise vortex core, which was advected toward the trailing edge of the hydrofoil. The transition from PCO to transitional cavity oscillation (TCO) occurred when the cavity length was larger than 0.8 of chord length. Under the TCO condition, the concave cavity closure line of sheet cavitation on the hydrofoil showed perfect symmetry and the St was nearly constant. As a result of our investigation, the micro-VGs have high potential to manipulate and control the attached cavitation dynamics.

Placing Metal in the Bowl: Does Rim Alkylation Matter?

In-depth theoretical analysis of the consequences of methylation of the rim sites of corannulene is completed. The full set of derivatives ranging from parent C20H10 to fully substituted C20(CH3)10 has been evaluated, revealing consistent trends along the series. The controlled one-electron chemical reduction of selected methylated corannulenes, such as monomethyl- (C20H9(CH3)), sym-pentamethyl- (1,3,5,7,9-C20H5(CH3)5), and decamethylcorannulene (C20(CH3)10) has also been investigated. Cesium metal was used as a reducing agent to access endo complexes having cesium ion placed inside the concave cavity of the monoreduced bowls. Two products, [{Cs+(18-crown-6)}{C20H9(CH3)−}] (1) and [{Cs+(18-crown-6)}{C20H5(CH3)5–}] (2), have been crystallized in the presence of 18-crown-6 ether and crystallographically characterized to confirm the concave cesium ion coordination. The direct structural comparison of 1 and 2 with the complex of unsubstituted corannulene, [{Cs+(18-crown-6)}{C20H10–}] (3), has been conducted. ...

Metasurface for Constructing a Stable High‐Q Plano‐Planar Open Cavity

AbstractTraditional open cavities are constructed by planar or concave mirrors. A Fabry–Pérot (FP) cavity is convenient to integrate and fabricate, but highly sensitive to the parallelism of the end mirrors. In contrast, a concave cavity is more stable and possesses a lower leaky rate, but the curved geometry brings inconvenience. Here, it is suggested that a planar meta‐cavity can simultaneously possess the advantages of both of the above open cavities by using a metasurface to create a planar meta‐mirror that mimics the behavior of a concave mirror. For demonstration, a microwave meta‐cavity is constructed, whose meta‐mirror consists of subwavelength ceramic blocks on a metal substrate. Compared to an FP cavity, the meta‐cavity is more robust against the alignment error of the end mirrors, and 15‐fold enhancement of the quality factor is observed numerically. Experimental results are in good agreement with the simulated results. The suggested method may be extended to work in high frequency ranges. This work would support the planarization and miniaturization of an open cavity and may also increase the functionality.